Genes for familial hemeplegic migraine (FHM), episodic ataxia type-2 (EA-2), common forms of migraine, and other episodic neurological disorders, such as epilepsy, have been mapped to chromosome 19p13. A brain-specific P/Q type calcium channel subunit gene, covering 300 kb with 47 exons is provided. The exons and their surroundings reveal polymorphic variations and deleterious mutations that are linked to various types of cation channel dysfunctions causing episodic neurological disorders in man or animals.

Migraine is a frequent paroxysmal neuro-vascular disorder, characterized by recurrent attacks of disabling headache, vomiting, photo/phonophobia, malaise, and other general symptoms (migraine without aura). Up to 20% of patients may, in addition, experience transient neurological (aura) symptoms during attacks (migraine with aura) (HCC, 1988). Up to 24% of females and 12% of males in the general population are affected, however with variable attack frequency, duration and severity (Russell et al., 1995). Knowledge about the mechanisms of the final common pathway of migraine attacks has increased substantially the last five years, resulting in improved, though still only symptomatic (and sub-optimal) acute treatment for the attack. There is, however, still very little knowledge about the etiology of migraine attacks, i.e. why and how attacks begin and recur. Accordingly, prophylactic treatment for migraine is non-specific and has only limited efficacy.
Family, twin and population-based studies suggest that genetic factors are involved In migraine, most likely as part of a multifactorial mechanism (reviewed by Haan et al., 1996). The complex genetics has hampered identification of candidate genes for migraine. Familial Hemiplegic Migraine (FHM) is a rare, autosomal dominant, subtype of migraine with aura, associated with ictal hemiparesis and, in some families cerebellar atrophy (HCC, 1988). Otherwise, the symptoms of the headache and aura phase of FHM and xe2x80x9cnormalxe2x80x9d migraine attacks are very similar and both types of attacks may alternate within subject and co-occur within families. FHM is thus part of the migraine spectrum and can be used as a model to study the complex genetics of the more common-forms of migraine (Haan et al., 1996). A gene for FHM has been assigned to chromosome 19p13 in about half of the families tested (Joutel et al., 1993; Ophoff et al., 1994; Joutel et al., 1995). Remarkably, cerebellar atrophy was found only in families with FHM linked to chromosome 19p13, but not in unlinked families. Recently, we showed the 19p13 FHM locus to be also involved in xe2x80x9cnormalxe2x80x9d migraine (May et al., 1995).
Episodic ataxia type 2 (EA-2) is another, autosomal dominant, paroxysmal neurological disorder, characterized by acetazolamide-responsive attacks of cerebellar ataxia and migraine-like symptoms, and interictal nystagmus and cerebellar atrophy. Recently, a gene for EA-2 was assigned to chromosome 19p13, within the same interval as for FHM (Kramer et al., 1995). This finding, as well as the clinical similarities, raise the possibility of EA-2 and FHM being allelic disorders.
Since other hereditary episodic neurological disorders responding to acetazolamide (such as hypokalaemic and hyperkalaemic periodic paralysis), as well as EA type-1 A (which, in contrast to EA-2, is associated with continuous myokymia and non-responsive to acetazolamide) have all been associated with mutations in genes encoding for ion channels (Ptacek et al., 1991; Ptacek et al., 1994; Brown et al., 1994), we specifically looked for similar genes within the FHM and EA-2 candidate region.
In view of the above, the FHM/EA-2 locus can, since FHM is part of the migraine spectrum, thus be used to study the genetic factors and biological mechanisms that are related to various episodic neurological disorders such as FHM, EA-2, common migraine and others such as epilepsy.
Calcium channels are multisubunit complexes composed of at least an xcex11, an xcex12xcex4, and a xcex2 subunit. The central xcex11 subunit is functionally the most important component, acting as a voltage sensor and forming the ion-conducting pore. The other subunits have auxiliary regulatory roles. The membrane topology of the xcex11 subunit consist of four hydrophobic motifs (I to IV), each containing six transmembrane xcex1-helices (S1-S6) and one hairpin (P) between S5-S6 that spans only the outer part of the transmembrane region.
The present invention provides an isolated and/or recombinant nucleic acid, or fragments thereof, encoding a Ca2+-channel xcex11 subunit related to familial hemiplegic migraine and/or episodic ataxia type-2, derived from a gene present on chromosome 19p13.1-19p13.2; a gene encoding the xcex11 (ion-conducting) subunit of a P/Q-type voltage gated calcium channel. The present invention also provides access to and methods to study the genetic background and identify other subunits of the calcium channel subunit complexes and the proteins related therewith that are associated with the genetic factors and biological mechanisms that are related to various episodic neurological disorders such as FHM, EA-2, common migraine and others such as epilepsy which are related to cation channel dysfunction.
The sequence of the cDNA of the gene is highly related (xe2x89xa790%) to a brain-specific rabbit and rat voltage gated P/Q-type calcium channel al subunit (Mori et al., 1991; Starr et al., 1991), and the open reading frame consists of 2261 amino acid residues. Northern blot analysis showed a brain-specific expression, especially in the cerebellum. Primary study of a cosmid contig harbouring the gene already indicated an exon distribution over at least 300 kb of genomic DNA. Recently, a neuronal Ca2+ xcex11A subunit gene was localized to chromosome 19p13.1-p13.2 by FISH analysis (Diriong et al, 1995). The gene symbol is CACNL1A4 and the al subunit is classified as a P/Q-type. No sequence data for the CACNL1A4 gene have been provided by Diriong or others, but the same localization (chromosome 19p13.1) and the identical classification (P/Q-type) suggests that the Ca2+ channel xcex11 subunit we have identified is very similar to CACNL1A4. No relation with migraine has been disclosed for CACNL1A4. The genomic structures of three other human Ca2+ channel xcex11 subunit genes (CACNL1A1, CACNL1A2 and CACNL1A3) have been published to date (Hogan et al, 1994; Soldatov, 1994; Yamada et al, 1995). Both CACNL1A1 and CACNL1A2 span about 150 kb and consist of 50 and 49 exons, respectively. The smaller CACNL1A3 gene is composed of 44 exons, distributed over 90 kb.
The present invention also provides an isolated and/or recombinant nucleic acid comprising alleles of the invented gene which contain mutations relevant to the occurence of migraine and other neurological disorders which are related to cation channel dysfunction. Such mutations are for example a mutation at codon 192 resulting in the replacement of arginine by glutamine (R192Q), and/or a mutation at codon 666 resulting in the replacement of threonine by methionine, and/or a mutation at codon 714 resulting in a replacement of valine by alanine and/or a mutation at codon 1811 resulting in a replacement of isoleucine by leucine, but also other mutations of alleles of said gene which bear relationships with cation channnel dysfunction.
The present invention also provides isolated and/or recombinant nucleic acid comprising alleles of said gene which contain a polymorphic CA-repeat sequence specific for various alleles of said gene. The present invention also provides isolated and/or recombinant nucleic acids comprising alleles of said gene which contain a CAG repeat.
The present invention also provides methods and tests (such as PCR, but also other tests to detect or amplify nucleic acids are known in the art) to detect, identify and localize or distinguish genes and alleles of such genes, or fragments thereof, encoding for proteins or xcex1, xcex2 or "khgr" sub-units of specific cerebral cation channels, more specifically the invented gene and its various alleles encoding the xcex11 subunit of a P/Q-type voltage gated calcium channel and the gene encoding the xcex22 sub-unit, which are involved in the primary pathogenesis of neurological disorders such as FHM, migraine, EA-2 and SCA6. With such methods and tests one can study abnormalities of said gene.
The invention also provides recombinant expression vectors comprising isolated and/or recombinant nucleic acid comprising alleles of said genes or fragments therof, and provides host cells or animals that comprise such vectors or that are otherwise transformed with an isolated and/or recombinant nucleic acid according to the invention.
The invention thus also provides a rationale and methods for the testing and the development of specific prophylactic medication for migraine and other episodic neurological, in particular brain, disorders, such as epilepsy, associated with cation channel dysfunction.
The invention for example provides cells or animals that comprise recombinant vectors that comprise variants of said genes or cells or animals that are transformed with said variants. Also, the invention provides means to identify naturally occuring variants of experimental animals with changes in said gene related to FHM, EA-2, SCA7, migraine or other neurological disorders associated with cation channel dysfunction. An example of such an animal is the tottering mouse, and its variants called leaner and rolling, described in the experimental part of the invention. The invention also provides cells or animals in which changes such as deletions or mutations in said gene have been introduced by recombinant nucleic acid techniques. All such cells or animals provided by the invention can be used to study the pathophysiology of FHM, EA-2, migraine or other neurological disorders associated with cation channel dysfunction, for example to test or develop specific medication for the treatment of said disorders.
The invention also provides proteins or peptides encoded by said genes, or fragments thereof, related with cation channel dysfunction, and detection of such proteins or peptides by antibodies directed against said proteins or peptides. Such antibodies can be of natural or synthetic origin, and can be produced by methods known in the art. Such proteins and antibodies and detection methods can be used to further in vitro or in vivo studies towards the pathophysiology of FHM, EA-2, migraine or other neurological disorders associated with cation channel dysfunction, in addition such proteins, antibodies and detection methods can also be used to diagnose or identify such disorders in patients or in experimental animals.
Sixteen FHM patients were selected, including eight individuals from four unrelated chromosome 19-linked FHM families (NL-A, UK-B, USA-C (Ophoff et al, 1994), and USA-P (Elliot et al., 1995), two affected individuals from two small FHM families from Italy (Italy I and II) and six individuals with sporadic hemiplegic migraine (i.e. no other family member was shown to suffer from attacks of hemiplegic migraine). In families NL-A and USA-P cerebellar ataxia and/or nystagmus is associated with FHM. An additional set of four subjects from four unrelated EA-2 families linked to chromosome 19, was also included (CAN-25, -45, -191, -197. Fifty randomly collected individuals from the Dutch population (Smith et al., 1988) were used as a control to determine the allele frequencies of polymorphic sites.
Patients with migraine with or without aura were diagnosed according to the international Headache-Society (IHS) classification criteria. Patients attending the neurology outpatient clinic of Leiden University Medical Center, The Netherlands, and patients responding to calls in local newspapers or in the periodical of the Dutch Migraine Patients Association, were screened for a positive family history of migraine. Only families with migraine in at least two generations were asked to participate. Probands (n=36) and relatives (n=492) were personally examined and interviewed using semi-structured questionnaires. The questionnaire included questions about age at onset, frequency and duration of attacks, aura symptoms, premonitory signs and symptoms, triggers for attacks, medication, and additional headaches. When family members were not available for a personal interview, information on their migraine was collected by interviewing their relatives. Because of the low validity of diagnosing migraine auras through relatives, we only assessed the presence or absence of migraine headaches. Whenever possible, medical records were examined.
Ten different cosmids from the contig extending the invented gene, were subcloned separately in either M13 or pBlueScript KS vector. From each cosmid library at least 3xc3x9796 random clones with an average insert size of about 2 kb, were picked. Positive clones were identified by hybridization techniques and subsequently sequenced with vector-specific primers; intron-exon boundary sequences were completed using cDNA-based primers.
Genomic DNA was used as template to generate polymerase chain reaction (PCR) products for single-strand conformational polymorphism (SSCP) analysis and denaturing high-performance liquid chromatography (DHPLC). Amplifications were performed in standard conditions with primer pairs as listed in Table 1 or listed below. Except for the 5xe2x80x2 side of exon 6, primers were chosen to produce fragments that contained a single exon and at least 35 basepairs (including primer) of each flanking intron sequence. Amplification of exons 1 and 20 was performed producing two overlapping fragments and exon 19 was amplified into three overlapping fragments. In addition, the following markers;
D10S191 Primer sequence 1 (SEQ ID NO: 141) CTT TAA TTG CCC TGT CTT C
Primer sequence 2 (SEQ ID NO: 142) TTA ATT CGA CCA CTT CCC
D10S245 Primer sequence 1 (SEQ ID NO: 143) AGT GAG ACT CGT CTC TAA TG
Primer sequence 2 (SEO ID NO: 144) ACC TAC CTG AAT TCC TGA CC
DIOS89 Primer sequence 1 (SEQ ID NO: 145) AAC ACT AGT GAC ATT ATT TTC A
Primer sequence 2 (SEQ ID NO: 146) AGC TAG GCC TGA AGG CTT CT
DHPLC (Oefner et al., 1995; Hayward et al., 1996) was carried out on automated HPLC instrumentation. Crude PCR products, which had been subjected to an additional 3-minute 95xc2x0 C. denaturing step followed by gradual reannealing from 95-65xc2x0 C. over a period of 30 minutes prior to analysis, were eluted with a linear acetonitrile (9017-03, J. T. Baker, Phillipsburg, N.J., USA) gradient of 1.8% per minute at a flow-rate of 0.9 ml/min. The start- and end-points of the gradient were adjusted according to the size of the PCR products (Huber et al., 1995). The temperature required for successful resolution of heteroduplex molecules was determined empirically by injecting one PCR product of each exon at increasing mobile phase temperatures until a significant decrease in retention was observed.
For SSCP analysis, primary PCR products were labeled by incorporation of [xcex1-32P]dCTP in a second round of PCR. Samples were diluted and denatured in formamide buffer before electrophoresis. SSCP was carried out according to published protocols (Orita et al., 1989; Glavac et al., 1994). Digestion of several exons to yield products suitable for SSCP analysis.
Sequencing of PCR products was performed with an ABI 377 automated sequencing apparatus with cycle sequencing according to the manufacturer. Furthermore, PCR products were cloned in the TA vector (Invitrogen) and subjected to manual dideoxy sequence analysis (T7 Sequencing kit, Pharmacia Biotech.).
A total of 481 blood samples were collected from patients with migraine. Genomic DNA was isolated as described by Miller et al., 1988. The analyses of the highly informative microsatellite markers D19S391, D19S394, D19S221 and D19S226, D10S191, D10S248 and D10S89 were performed by PCR; primer sequences related to these markers are available through the human Genome Data Base (GDB).
The relative frequencies of marker alleles were estimated on the entire family material, with the relevant correction for genetic relationships between individuals (Boehnke, M, 1991) with the ILINK option of the I-INKAGE package, version 5.03 (Lathrop et al., 1985). The following marker order and recombination frequencies were used in the multipoint sib-pair analysis: D19S391-5%-D19S394-3%-D19S221-5%-D19S226. Affected-sib-pair analysis was performed using the MAPMAKER/SIBS software package, simultaneously including marker information for all four DNA markers (Kruglyak, 1995). Separate analyses were performed for migraine with aura, migraine without aura, and a combination of both. Allowance was made for dominance variance. When more than two affected sibs occurred in a single sibship, weighted scores were computed according to Suarez and Hodge (1979).
In a sib-pair analysis, the occurrence of parental marker alleles is compared among sibs. Normally, 25% of sib pairs share their marker alleles from both parents, 50% share one marker allele from one of their parents, while the remaining 25% share no parental allele. Deviations from this pattern towards increased sharing, and consistent with the constraints of Holmans""s (1993) possible triangle, are explained as linkage (expressed as the maximum lod score MLS). Increased sharing of marker alleles thus indicate that the marker is located closely near a genetic risk factor. The relative-risk ratio for a sib (xcexR), defined as the ratio of the prevalence of a disease in sibs of affected individuals, divided by the prevalence of a disease in the population, can be calcutated (May et al., 1995). In other words:       λ    p    =            Affected                    xe2x80x83                  risk                    xe2x80x83                  for                    xe2x80x83                  sib                    xe2x80x83                  of                    xe2x80x83                  a                    xe2x80x83                  proband              Affection                    xe2x80x83                  risk                    xe2x80x83                  for                    xe2x80x83                  an                    xe2x80x83                  individual                    xe2x80x83                  in                    xe2x80x83                  the                    xe2x80x83                  general                    xe2x80x83                  population
The combination of hybridization and PCR strategies resulted in a rapid assembly of the complete coding sequence of the human cDNA, with an open reading frame of 6783 nucleotides encoding 2261 amino acid residues (FIG. 4). The spatial distribution of the human Ca2+ channel expression was assayed in rhesus monkey tissues. Total RNA was isolated from several tissues, including various brain structures, and probed with a human cDNA fragment. The probe detected a major transcript of approximately 9.8 kb in cerebellum, cerebral cortex, thalamus and hypothalamus, whereas no transcript was detected in heart, kidney, liver or muscle. There was also no hybridization signal found in RNA preparations from mouse skin tissue or from human peripheral lymphocytes. In addition, an attempt to amplify parts of the cDNA from human peripheral lymphocytes failed.
Complete alignment between the cDNA and individual exon sequences was achieved, allowing the establishment of the exon-incron structure (Table 1). The reconstruction of the exon-intron structure of the CACNL1A4 gene revealed 47 exons ranging in size from 36 bp (exon 44) to 810 bp (exon 19). The exons are distributed over about 300 kb at genomic DNA level. The result shows that the first 10 exons are located in a region of about 150 kb covered by the first 5 cosmids of the contig indicating relatively large introns at 5xe2x80x2 side of the gene. Sequences (FIG. 1) were obtained of all exons including approximately 100 bp of flanking introns, except for intron 5 adjacent to exon 6. The forward primer of exon 6 harbours the splice junction and 3 bp of exon 6. Splice sites around all exons are compatible with consensus sequence with the exception of splice donor and acceptor of the first intron.
The cosmid conzig that yielded the initial Ca2+ channel gene exons was extended to cover more than 300 kb. Hybridization experiments showed that the first and last cosmids of the contig were positive for 3xe2x80x2- and 5xe2x80x2-end cDNA sequences, respectively, indicating a genomic distribution of the gene over at least 300 kb (FIG. 2). The cosmid contig has been placed into the LLNL physical map of chromosome 19 at band p13.1, between the markers D19S221 and D19S226 (FIG. 2). We identified a new polymorphic CA-repeat sequence (D19S1150) on the cosmid contig. Oligonucleotide primers (Table 1) flanking the repeat were synthesized and amplification was performed by PCR as described. Analysis of D19S1150 in 45 random individuals from the Dutch population revealed nine alleles with an observed heterozygosity of 0.82. This highly polymorphic marker is located within the gene and is therefore very useful in genetic analysis.
Exons and flanking intron sequences, containing the complete coding region of CACNL1A4 and part of untranslated sequences, were screened for the presence of mutations by SSCP and DHPLC analysis in 20 individuals with either FHM or EA-2. Several synonymous nucleotide substitutions and polymorphisms were identified including a highly polymorphic (CAG)n-repeat in the 3xe2x80x2 untranslated region of exon 47 (Table 2). Of all polymorphisms only one was identified predicting an amino acid change, an alanine to threonine substitution at codon 454 (A454T).
Four different missense mutations were found in FHM patients of which one mutation was observed in two unrelated FHM affected individuals (Table 3). The mutations were shown to segregate with the disease within the families, and were not present in about 100 control chromosomes. A G-to-A transition was identified in family Italy-II at codon 192, resulting in a substitution of arginine to glutamine (R192Q) within the first voltage sensor domain (IS4). A second missense mutation occurs at codon 666, within the P-segment of the second repeat replacing a threonine residue for methione (T666M) in family USA-P. Two other mutations are located in the 6th transmembrane spanning segment of respectively repeat II and IV. The IIS6 mutation is a T-to-C transition at codon 714, resulting in a substitution of valine to alanine (V714A), identified in FHM family UK-B. The mutation in domain IVS6 is an A-to-C transversion at codon 1811 resulting in a substitution of isoleucine to leucine (I1811L). This I1811L mutation is found in family NL-A and family USA-C, two unrelated FHM families. Comparison of haplotypes in this region, including intragenic markers, did not reveal any evidence for a common founder of family NL-A and USA-C (data not shown). No mutation was found in FHM family Italy-I nor in the six sporadic hemiplegic migraine patients. In addition to missense mutations in FHM families, we also identified mutations in two out of four EA-2 families (Table 3). In EA-2 family CAN-191, a basepair deletion occurs in exxon 22 at nucleotide position 4073 causing a frameshift and a premature stop. The second EA-2 mutation is a transition of G-to-A of the first nucleotide of intron 24, predicted to leading to an aberrant splicing in family CAN-26. The invented gene also contains a CAG repeat, of which expansions have been found in patients with autosomal dominant cerebellar ataxia (SCA6). Hence FHM, EA-2 and SCA6 are alielic ion channel disorders and different mutations are associated with different clinical symptomatologies.
Our study patients with common migraine (with or without aura) included 36 independent multigenerational Dutch families. At least some data were available on 937 family members and 212 persons who xe2x80x9cmarried-inxe2x80x9d (spouses). Of these, 442 family members (247 affected) and 86 spouses (7 affected) were personally interviewed. The distribution of the different types of migraine among the 247 affected family members are as follows: 132 family members showed migraine without aura, 93 showed migraine with aura and 22 showed months-migraine, not fulfilling all critera by IHS. Among the 7 affected spouses these figures were 4, 1 and 2, respectively. We scored the parental transmission of migraine in the 36 families (Tabel 4) to investigate if an additional X-linked dominant or mitachondrial aene was involved. An approximately 2.5:1 preponderance of females among the migraine sufferers was noted, which remained in the affected offspring. Affected fathers were found to transmit migraine to their sons in 21 cases, making X-linked dominant or mitochondrial inheritance highly unlikely.
The genetic analysis included 204 potentially affected sib pairs; after correction for more than one sib pair in a single sibship the total number of sib pairs was 108. Affected-sib-pair analysis was performed for sib pairs who were both affected with any form of migraine and, in separate analyses, for sib pairs who where both suffering from either migraine with aura or migraine without aura. The informativeness of the region between the markers D19S391, D19S394, D19S221 and D19S226 varied between 82% and 96%. The combined analysis of migraine with and without aura resulted in a maximum multipoint lod score of 1.69 (p≈0.005) with marker D19S226. For migraine with aura the maximum multipoint lod score was 1.29 corresponding with p≈0.013 with marker D19S394. The maximum lod score for migraine without aura was not significant (MLS  less than 0.25)(data not shown). The relative risk ratio for a sib to suffer from migraine with aura (xcexp), defined as the increase in risk of the trait attributable to the 19p13 locus, varied between xcexR=1.5 (for marker D19S394) and xcexR=2.4 (for marker D19S226). When combining migraine with and without aura, xcexR was 1.25. In a selected portion of 36 Dutch families with migraine with aura and without aura, affected sib-pair analysis was performed for sib pairs who were affected with any form of migraine. The following markers, flanking the xcex22(CACNB2) calcium channel subunit gene on chromosome 10p12, were tested: D108191, D1OS246 and D10S89. For the combined phenotype (migraine with and without aura) a maximum pultipoint iod score of 0,95 (p less than 0,01) was obtained with marker; D10S191. This result gives independent evidence for a role of the P/Q type Ca2+ channel in migraine and other neurological disorders.
The genomic structure of the exemplified invented gene revealed 47 exons distributed over about 300 kb (Table 1; FIG. 1). A comparison of the gene structure to already known Ca2+ channel al subunit genes (CACNL1A1, CACNL1A2, and CACNL1A3) (Soldatov, 1994; Yamada et al., 1995; Hogan et al., 1995), reveals a similar number of exons (50, 49, and 44 respectively) but a larger genomic span (300 kb vs 90-150 kb). Remarkebly, all splice sites are according to consensus sequence except for intron 1. Splice donor as well as splice acceptor of the first intron do not contain the expected gt . . . ag intron sequence. An incorrect CDNA sequence is unlikely because the cDNA sequence containing the junction of the first two exons is identical to rabbit and rat sequence. Sequences corresponding to splice donor and acceptor are present in exon 1 and 2, suggesting an additional (yet unidentified) exon in the first intron encompassing part of sequences of exon 1 and exon 2.
To test the possible involvement of the invented gene relating to the CA2+-channel sub-unit in migraine FHM, SCA6 and EA-2, we performed a mutation analysis by DHPLC and SSCP and found several alterations (For example Table 2 and 3). Only one missense variation was observed also present in 2% of the normal controls (Table 2). This polymorphism is a alanine to threonine substitution at codon 454 (A454T), located in the intracellular loop between IS6 and IIS1 (FIG. 2). This region contains a conserved alpha interaction domain (AID) that binds subunits (De Waard et al., 1996). However, A454T is located outside the AID consensus sequence and is not likely to be involved.
The identification of two mutations that disrupt the predicted translation product of the invented gene in two unrelated EA-2 patients and the segregation of these mutations with the episodic ataxia phenotype in their families provide strong evidence that the invented gene is the EA-2 gene. A basepair deletion leads to a frame-shift in the putative translation product and encounters a stop codon in the next exon. The frame-shift in this EA-2 family is predicted to yield a calcium channel al subunit polypeptide consisting of repeat I and II, and a small portion of repeat III (IIIS1). The G-to-A transition of the first nucleotide of intron 24 is affecting the nearly invariant GT dinucleotide of the intronic 5xe2x80x2 splice junction. The brain-specific expression of the exemplified invented gene makes it extremely difficult to test the hypothesis that this mutation produces aberrantly spliced RNAs by retaining the intron or utilizing other cryptic 5xe2x80x2 splice sites.
The frameshift and splice site mutations in EA-2 may suggest a dominant negative effect of the truncated proteins by overruling the (corresponding) intact al subunits.
No mutations were found in the remaining EA-2 families (CAN-25 and -197). The use of two independent techniques for mutation screening (DHPLC and SSCP) makes it unlikely that we missed a heterozygote PCR product. Mutations in the promoter region or in intron sequences, resulting in aberrant splicing, may have been the cause of EA-2 in these families. We could also have missed a mutation around the splice acceptor site of intron 5, covered by the forward primer of exon 6. However, larger deletions of e.g. complete exons with flanking intron sequence will disturb the predicted translation product, like the xcex94C4073 and splice site mutation do, but this is not detectable by a PCR-based screening method but can be seen Southern blot analysis instead.
Four different missense mutations were identified in five unrelated FHM families. These mutations all segregate with FHM within a family and are not observed in over 100 normal chromosomes. The first missense mutation that we describe in the exemplified invented gene occurs in the IS4 domain of the al subunit (Table 3; FIG. 3). The S4 domains are postulated to be voltage sensors because they have an unusual pattern of positively charged residues at every third or fourth position separated by hydrophobic residues (Tanabe et al., 1987). In calcium channels the positively charged amino acid is an arginine residue (Stea et al., 1995). The mutation in FHM family Italy-II predicts a substitution of the first arginine in the IS4 segment with a neutral, non-polar alutamine (R192Q). The change of the net positive charge of this conserved region of the protein may influence correct functioning of the voltage sensor.
The second missense mutation in FHM family USA-P occurs in the P-segment of the second transmembrane repeat. A C-to-T transition predicts substitution of a threonine residue with methionine at codon 666 (T666M). Various observations have shown that P-segments, the hairpin between S5 and S6 that spans only the outer part of the transmembrane region, form the ion-selectivity filter of the pore and binding sites for toxins (Guy and Durell (1996). Alignment of protein sequence of different P-segments indicating that some residues occur in many different channel genes (Guy and Durell, 1996). The T666M substitution alters one of the conserved residues in the P-segment. It is conceivable that an alteration of a P-segment affects the ion-selectivity or toxin binding of a channel gene.
The remaining two missense mutations identified in FHM families alter the S6 segment of the second and the fourth repeat. A valine to alanine substitution in FHM family UK-B is found in domain IIS6 at codon 714 (V714A). Domain IVS6 is mutated in two unrelated FHM families (NL-A and USA-C), predicting a isoleucine to leucine substitution at codon 1811 (I1811L). The V714A and I1811L missense mutations do not really change the neutral-polar nature of the amino acid residues. However, both S6 mutations are located nearly at the same residue at the intracellular site of the segment and are conserved in all calcium channel al subunit genes. In addition, the A-to-C transversion leading the I1811L substitution occurred in two unrelated FHM families on different haplotypes indicating recurrent mutations rather than a founder effect. Although the exact function of the S6 domains are not known, these data strongly suggest that mutations in IIS6 and IVS6 result in FHM.
The I1811L mutation is present in two FHM families of which one (NL-A) also displays a cerebellar atrophy in (some) affected family members. The presence of cerebellar atrophy in FHM families has been reported in about 40% of chromosome 19-linked FHM families, whereas none of the unlinked families was found to have cerebellar atrophy (Terwindt et al., 1996).
The I1811L mutation excludes the possibility of allelic mutations in FHM and FHM with cerebellar atrophy. However, it is likely that FHM or FHM with cerebellar atrophy are the result of pleiotropic expression of a single defective gene.
No mutation was found in a small Italian FHM family (Italy-I). Apart from the possibilities discussed for EA-2, it should be noted that linkage to 19p13 was only suggested but never proved with significant lod scores (M. Ferrari, personal knowledge).
The four missense mutations identified indicate a mechanism for FHM in which both alleles of the xcex11 subunit are expressed, one harbouring an amino acid substitution which affects the function of this calcium channel xcex11 subunit by reducing or enhancing the electrical excitability. The relationship of FHM and other types of migraine makes it highly rewarding to investigate the involvement of the only missense variant observed (A454T) (Table 2), and to continue the search for other variants of the exemplified invented gene specific for common types of migraine.
The mutations in EA-2 and FHM demonstrate among others that the brain specific calcium channel gene CACNL1A4 is responsible for both EA-2 and FHM, and is also involved in the primary pathogenesis of the more common forms of migraine. We conducted the common migraine study in an independent sample of 36 extended Dutch families, with migraine with aura and migraine without aura. We found significant increased sharing of the marker alleles in sibs with migraine with aura (MLS=1.29 corresponding with p≈0.013). Although no such increased sharing was found for migraine without aura, a combined analysis for both migraine types resulted in an even more significant increased sharing (MLS=1.69 corresponding with p≈0.005). These results clearly indicate the involvement of the calcium cSIA-subunit gene region on 19p13 in both migraine with and without aura; the contribution to migraine with aura, however, seems strongest.
The positive findings in our study clearly demonstrate an involvement of the FHM locus region in non-hemiplegic familial migraine, notably in migraine with aura. The P/Q-type calcium channel xcex11A-subunit gene on chromosome 19p13 may be an xe2x80x9caura-genexe2x80x9d and is involved in both FHM and migraine with aura, but not in migraine without aura. This however, seems unlikely since an increased sharing of marker alleles was also found when we combined the results for migraine with and without aura. Furthermore, the increase in sharing was stronger than expected to be only due to the contribution of migraine with aura. An alternative explanation is that the gene is involved in both types of migraine, but in migraine without aura there is an additional strong effect of other, possibly environmental factors, thereby reducing the penetrance.
The latter view is also supported by the results obtained from calculating the relative risk ratios (xcexR) for sibs from affected individuals to also have migraine. The relative risk ratio for a sib to suffer from migraine with aura was xcexR=2.4. When combining migraine with and without aura, xcexR was 1.25. In a population-based study the relative risk for first degree relatives of probands with migraine with aura to also have migraine with aura was xcexR=3.8. Because of the female preponderance among migraine patients, X-linked dominant or mitochondrial inheritance has been suggested to be involved in familial migraine. Although a predominant maternal inheritance pattern was noted in our families, X-linked dominant or mitochondrial inheritance were found to be highly unlikely because affected fathers transmit migraine to their sons. Furthermore, the predominant maternal inheritance can be explained by the female preponderance among the migraine patients.
We conclude that the well-established genetic contribution to the etiology of migraine is partly, but not entirely, due to genetic factors located in the chromosomal region of the P/Q-type calcium channel xcex11A-subunit gene. Further analysis of the cerebral distribution and function of this calcium channel, as well as of the xe2x80x9cmutated channelsxe2x80x9d, will help to unravel the pathogenetic pathway of migraine. It may also contribute to a better understanding of the mechanisms involved in related disorders such as episodic ataxia type-2, autosomal dominant cerebellar ataxia (SCA6), cerebral atrophy, and epilepsy, which all have been found to be associated with mutations in this gene. Study of FHM, EA-2 mutants and variants such as the A454T variant expressed in vitro or in mouse or other experimental animal models will ultimately lead to better understanding of the diseases, their cellular mechanisms, and the clinical relationship between FHM, EA-2, migraine, and other episodic neurological disorders such as epilepsy, and will provide rationales for the development of prophylactic therapy.
Localization and identification of the mouse gene related to the neurological mouse mutations tottering, leaning and rolling.
The tottering (tg) mutation arose spontaneously in the DBA inbred strain, and has been back-crossed into a C57BL/6J (B6) inbred strain for at least 30 generations. The genome of the tg mouse therefore is of B6 origin except for a small region around the tg gene on chromosome 8. Interestingly, the chromosome 8 region in mouse has synteny with the human chromosome 19p13.1, in which the human calcium channel alphal subunit has been identified. We therefore consider the tg locus as a possible site of the mouse homologue of the human calcium channel gene.
To determine the exact localization of the mouse homologue, PCR was carried out with primers based on human cDNA sequence selected from FIG. 1 and mouse genomic DNA aE template. In human, primers were known to be located in different flanking exons. POR amplification on human DNA yielded a 1.5kb fragment.
Forward primer (SEQ ID NO: 45)5xe2x80x2-caa cat cat gct ttc ctg cc-3xe2x80x2
Reversed primer (SEQ ID NO: 46)5xe2x80x2-atg atg acg gcg aca aag ag-3xe2x80x2
Amplification on mouse DNA yielded a 750-bp fragment. The fragment mainly consists of intronic sequences. SSCP analysis revealed several polymorphisms in the different inbred strains (each strain a specific pattern). Analysis of amplified product of the tg/tg (homozygote) and tg/+(heterozygote) mice demonstrated a DBA specific signal in the tg/tg mouse, and a heterozygous pattern of DBA and B6 inbred strains in the heterozygous tg/+mouse. These results show that the mouse homologue of the human calcium channel alphal subunit is located within the mouse tottering interval on chromosome 8.
In conclusion: the phenotypic characteristics of the tg mouse (tg/tg and tg/+) suggest involvement of ion-channels in the tg-etiology. The localization of the mouse homologue of the human calcium gene within the tottering interval show that a tottering phenotype in mouse is caused by a mutation in the mouse homologue of the CACNL1A4 gene. With various variants of the tottering mouse (the Jackson Laboratory, Bar Habor, Me., USA), such as the leaner and rolling varieties, such mutations in the mouse homologue of the CACNL1A4 gene can be found, clearly demonstrating that the gene is related to a variety of episodic neurologic disorders and using this genetic information one can engage in a variety of pathofysiological studies, as for example indicated below.
The tg mutation arose spontaneously in the DBA/2 inbred strain. tg/tg homozygotes are characterized by a wobbly gait affecting the hindquarters in particular, which begins at about 3 to 4 weeks of age, and by intermittent spontaneous seizures which resemble human epileptic absence seizures. The central nervous system of the mice appears normal by light microscopy. There is no discernible cerebellar hypoplasia. In fluorescent histochemistry studies tg/tg mice show a marked increase in number of noradrenergic fibers in the terminal fields innervated by locus ceruleus axons, the hippocampus, cerebellum, and dorsal lateral geniculate. Treatment of neonatal tg/tg mice with 6-hydroxydopamine, which selectively causes degeneration of distal noradrenergic axons from the locus ceruleus, almost completely abolishes the ataxic and seizure symptoms.
The leaner mutation of the tottering mouse arose spontaneously in the AKR/J strain. Homozygotes are recognized at 8 to 10 days of age by ataxia, stiffness, and retarded motor activity. Adults are characterized by instability of the trunk, and hypertonia of trunk and limb muscles. The cerebellum is reduced in size, particularly in the anterior region, in tg less than la greater than /tg less than la greater than mice, as is the case with a certain number of FHM patients. There is loss of granule cells beginning at 10 days of age and loss of Purkinje and Golgi cells beginning after 1 month. Cell loss later slows but continues throughout life. Granule and Purkinje cells are more severely affected than Golgi cells and the anterior folia more severely affected than other parts of the cerebellum. The cerebellum of tg less than la greater than /tg mice shows shrinkage and degenerative changes of the Purkinje cells. The loss in cerebellar volume in tg less than la greater than /tg and in tg/tg mice is specific to the molecular layer, with no change in volume of the granule cell layer or the white matter layer. Allelism of aleaner with tottering was shown in complementation and linkage tests.
A third variety of the tottering mouse is (tg less than rol greater than ) called the rolling Nagoya. Found among descendants of a cross between the SIII and C57BL/6 strains, the tg less than rol greater than mutation apparently occurred in the SIII strain. Homozygotes show poor motor coordination of hindlimbs that may lead to falling and rolling, and sometimes show stiffness of the hindlimbs and tail. No seizures have been observed. Symptoms are recognizable at 10 to 14 days old. They appear a little earlier than those of tg/tg mice and are somewhat more severe. The cerebellum is grossly normal until 10 days of age, but after that grows more slowly than normal. The size of the anterior part of the central lobe of the cerebellum is reduced with reduction in the numbers of granule, basket, and stellate cells but normal numbers of Purkinje cells. There is a reduced concentration of glutamate and an increased concentration of glycine and taurine in the cerebellum and decreased activity of tyrosine hydroxylase in the cerebellum and other areas.


An electronic cash register comprises a keyboard including a data input key and a time zone setting key; a central processing unit coupled to the keyboard; a memory coupled to the central processing unit and having a plurality of memory places for storing accumulated sales amounts on a time zone basis; a time memory coupled to the central processing unit to store time zone defining time data by the operation of the time zone setting key; a timepiece coupled to the time memory to supply current time data; and a comparator coupled to the timepiece and to the time memory to compare current time data from the timepiece with the time data stored in the time memory. The central processing unit includes means for writing entry data in one memory place of the memory according to the time zone determined by the result of a comparison by the comparator when entry data from the keyboard is completed.

The present invention relates to an electronic cash register which includes a time counting function and automatically totalizes data such as the sale total, the item count and the like within a predetermined time.
Generally, in an electronic cash register, an amount of each goods is inputted by an entry key and then a department key of the department to which the goods sold belongs is operated. The inputted data is properly processed, assorted and accumulatively stored in memories allotted for totalizations of the sale amount and the item count for each department, the gross sale total of the day and the sale total for each clerk. At the end of the work day, the cash register is set to a reset mode to successively print out the various data stored in the corresponding memories and then these memories are cleared. These assorted sale data will be used for management materials. Therefore, it is preferable that the sale data are detailed and correct with brevity.
Since the conventional cash register is not provided with a clock function, it can totalize only one day's sales so that the data obtained is insufficient for such a purpose. If we know the sale condition at specific time zones of a day, for example, morning, afternoon, and evening, it would be effective and useful for management reference. Further, if the time counting function is extended to year, month, week and day, an operator can preset the time period for totalization, for example, a week, a month, every two days or the like. Accordingly, the totalization for longer periods than a day may be automatically made, resulting in remarkable improvement of the totalization function of the register.
In the conventional register, the operator must key the date data such as year, month and day at the beginning of the work day, for receipt issuing.
Accordingly, an object of the present invention is to provide an electronic cash register which can automatically totalize sales data within a given time zone, with proper time zones preset.

Electronic cash register for totalizing sales data on a time zone basis


A micromechanical resonator including a motion arresting mechanism to rapidly damp the vibration of a resonator beginning at any given moment in time to remove vibration caused by previous events. An electrostatic clamp uses a bias voltage between an electrode and the resonator to damp the resonator and return it to its equilibrium position. A mechanical clamp includes an actuator that forces the mechanical clamp to contact the resonator. These micromechanical resonators facilitate condition based monitoring of complex electromechanical machines and components by allowing signature analysis in multiple temporal and frequency domains.

The present invention relates generally to the field of signal analysis, and more particularly to a micromechanical resonator that allows signal detection in multiple time and frequency domains.
Future electro-mechanical machines and structures will increasingly participate in their own service and maintenance using embedded distributed self-diagnostics that are remotely accessible to monitor machine health, detect and isolate subtle performance degradation, and in some cases even reconfigure some machines to adapt to changing operating environments. Traditionally, corrective maintenance and preventative maintenance have been the only two service paradigms. More recently, predictive or condition-based maintenance using micromechanical resonators, enabled by Micro-Electro-Mechanical Systems (MEMS) technology is emerging as an alternative. Condition-based maintenance is just-in-time maintenance based on the actual health of the machine and its components. Since it avoids the cumulative cost of unnecessary service calls associated with preventative maintenance and the occurrence of machine failure and degradation associated with corrective maintenance, condition-based maintenance provides substantial cost savings.
Fault manifestation in electro-mechanical systems with multiple moving elements in complex operating regimes, however, is typically non-stationary in that the frequencies describing specific faults vary over time. The multiple actuating elements such as motors and solenoids produce rich mechanical excitation signals at multiple time and frequency domains. Traditional Fourier spectral analysis techniques, such as the Fourier transform, while useful for establishing the signal bandwidth, is unsuitable for analyzing the time-varying properties of the signal that are important for diagnosis purposes. Another problem is that failure modes of system components are difficult to identify and characterize using time-based or frequency-based analysis. Hence, signature analysis with a time-frequency representation, such as that provided by the short-time Fourier transform (STFT) is required for condition monitoring of these systems.
A conventional micromechanical resonator for signature analysis is an array of tuning forks. Each tuning fork of the array resonates at a particular frequency while being insensitive to other frequencies. Thus, the entire spectral content of a vibration signal can be covered using a large number of tuning forks with closely spaced resonant frequencies. As shown in FIG. 1, array 10 includes higher frequency tuning forks 12, mid frequency tuning forks 14, and lower frequency tuning forks 16. Conventional arrays typically use a gas to damp out resonant vibration of the tuning forks.
Conventional micromechanical resonators provide frequency information, but do not provide the ability to separate this information into specific time intervals or windows of constant length. These tuning fork arrays, however, suffer from two problems. First, the duration of the time interval is limited by the viscous properties of the damping gas. Since elements that move faster will damp out sooner, the duration of time intervals is frequency dependent and varies for different frequency tuning forks. Thus, the amount of damping that may be employed will be limited by the sensitivity of the high frequency components. This affects the ability of the low frequency tuning forks to distinguish new events from old events in situations in which the new event occurs before the old event has been damped out. Second, some condition-based maintenance algorithms, such as short-time Fourier transform, require all the tuning forks to be damped simultaneously while others, such as wavelet transformation, require a hierarchy of time intervals between damping. Conventional tuning fork arrays, however, do not provide this capability.
In light of the foregoing, there is a need for a method and a micromechanical resonator for arresting the motion of micromechanical resonators to allow detection of rich electromechanical excitation signals at multiple time and frequency domains.
Accordingly, the present invention is directed to an micromechanical resonator that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
In accordance with the purposes of the present invention, as embodied and broadly described, the invention provides a micromechanical resonator including at least one resonant mass having an equilibrium position, at least one anchor electrode that provides electrostatic damping of the resonant mass, and a substrate having a planar surface.
In another embodiment, the present invention provides a micromechanical resonator including at least one resonant mass having an equilibrium position, a clamp, wherein the clamp provides mechanical clamping of the resonant mass, and a actuator for applying the clamp.
In another embodiment, the present invention provides an array of micromechanical resonators including a plurality of resonant masses and a plurality of mechanisms to damp the resonant masses, wherein the damping mechanisms are simultaneously activated to allow the array to measure discrete time intervals.
In another embodiment, the invention provides an array of micromechanical resonators including a plurality of resonant masses and a plurality of mechanisms to clamp the resonant masses, wherein the clamping mechanisms are configured to allow the array to measure a hierarchy of time intervals.
In yet another embodiment, the invention provides a method of clamping and releasing a mechanical sensor including the steps of measuring the frequency of an event for an initial time interval using a resonant mass having an equilibrium position, clamping the resonant mass, and releasing the resonant mass in its equilibrium position to measure a second time interval.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description serve to explain the principles of the invention.

Micromechanical discrete time and frequency characterization of signals via resonator clamping and motion-arresting mechanisms


A reference object (24) is disposed in an image region (20) with a subject (22) to be examined. The reference object has known parameters such as relaxation time, spin density, dimensions, and position. Magnetic resonance signals in which the spatial position of resonating nuclei is encoded in the relative phase and frequency thereof are sampled and temporarily stored in a view memory (56). A Fourier transform (60) is performed to convert the stored signals view into a representation of at least the positions and spin density of the resonating magnetic dipoles of the subject and reference object. The parameters of the reference object measured from the image representation are compared or inverse transformed back to data space for comparison with actual parameters of the reference object or thresholds. Based on the comparison, the resonance signals or the image representation are adjusted. For example, the magnetic resonance signals are rotated (78) through a phase correction to correct for offsets in the phase encoding. As other examples, the spin density may be adjusted, low magnitude data discarded, spatially offset data shifted, or the like. Alternately, the reference object may be interconnected with the subject to undergo movement therewith. The position of the reference object is then utilized to select views in which the movement of the subject is within preselected ranges or to approximately correct for the motion. The image can be shifted to a selected location or interpolated.

The present invention relates to the magnetic resonance examination art. It finds particular application in conjunction with the reconstruction of images of examined regions of patients and will be described with particular reference thereto. However, it is to be appreciated that the invention may find further application in the imaging of other objects, in other types of magnetic resonance examinations, in other imaging modalities, and the like.
Heretofore, magnetic resonance imaging included positioning the patient in a strong, substantially uniform, longitudinal magnetic field. Magnetic dipoles were caused to precess generating magnetic resonance signals. Various known techniques were utilized to select a region of the patient to be imaged and to spatially encode the resonance signals therefrom. In one technique, the resonance excitation was limited to the region of interest. Othogonal magnetic field gradients were applied across the selected image region to provide a two dimensional spatial encoding, which encoding was carried by the frequency and phase of the resonance signal. The resonance signals were transformed from a frequency and phase domain to a spatial domain to produce an image representing the density of resonanting nuclei in each pixel or incremental area of the image region. The accuracy with which an image could be reconstructed was limited by the accuracy of the phase and frequency encoding.
The magnetic field gradients commonly altered the frequency of the magnetic resonance signal as a function of spatial position. More specifically, the read gradient altered the resonance frequency of at least three megahertz linearly by about 30 hertz for each millimeter in the selected direction. Thus, when utilizing one millimeter pixels, a random frequency fluctuation of merely one thousandth of one percent shifted the encoding by a full pixel, thus degrading the image. Variations in the strength of the magnetic field caused corresponding fluctuations in the frequency of the resonance signal. although, hardware solutions have been provided for improving the magnetic field uniformity and otherwise limiting frequency fluctuations, such hardware solutions commonly were only able to limit the frequency fluctuations to about 50 hertz over a five minute interval. Although a very small percentage variation, significant image degradation was caused.
The second spatial direction was commonly encoded with the phase of the magnetic resonance signal. The phase was encoded by the application of a second magnetic field gradient, commonly transverse to the first magnetic field gradient. Because the accuracy of the phase encoding again varied with the accuracy with which the magnetic field and resonance frequencies were maintained, analogous image degradation was caused by the inability to hold the phase encoding more precisely.
Commonly, the final magnetic resonance image was a compilation or sum of a plurality of views, each view having been taken with a different phase or frequency encoding. From time to time, one or more of the views which was combined to form the image include badly degraded or otherwise undesirable data. In the prior art, the effect of this bad data was lessened by averaging a large number of views. However, no technique was provided for removing or correcting individual bad views or bad points.
Another problem encountered in the prior art resided in the standardization of the image. In particular, the resonance signals in each view tended to vary from each other. Thus, some views were unintentionally weighted more heavily than others during the summing, again causing image degradation.
Yet another problem resided in the accuracy with which the phase encoding could be maintained from view to view. Commonly, there was a phase shift error between views, which error again lead to image degradation.
Another source of image degradation was attributable to movement in the image region. For example, respiratory or cardiac movement of the patient caused severe image degradation in the resultant image. Respiratory and cardiac gating apparatae were used to limit the collection of the views substantially to the same portion of the respiratory or cardiac cycle. However, such cardiac and respiratory gating increased scan time and still suffered from motion artifacts, especially for multi-slice imaging.
The present invention provides a new and improved magnetic resonance imaging technique which overcomes the above referenced problems and others to provide magnetic resonance images of greater accuracy and with reduced artifacts.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a method of magnetic resonance imaging is provided. A subject to be imaged and a reference are both positioned in an image region. The reference has known values for at least one of a preselected set of parameters, such as relaxation time, spin density, dimensions, and position within the image region. Resonance is excited in magnetic dipoles of at least the portion of the subject and reference object which are disposed in the image region. Magnetic field gradients are caused across the uniform magnetic field in the image region for encoding the spatial positions of the resonating magnetic dipoles in the frequency and phase of the resonance signal. The magnetic resonance signal from each view is received and temporarily stored. The resonance signal is transformed from a spatial frequency and phase domain to a spatial domain to reconstruct a representation of an image of at least the reference. A value corresponding to one of the reference known values is measured from the image representation to produce a measured value. The corresponding measured value and known value are compared to determine a deviation therebetween.
In accordance with a more limited aspect of the present invention, at least one of the resonance signal and the image representation are altered in accordance with the deviation between the known and measured values in such a manner that the deviation is minimized. For example, the phase of the resonance signal may be rotated by an appropriate correction phase angle, the spatial position of each pixel may be shifted in accordance with a frequency variation, the spin density may be varied to standardize a plurality of views, or the like.
In accordance with another aspect of the present invention, the deviation between the measured and known values may be compared with a preselected maximum deviation. In response to the deviation exceeding the preselected maximum, the resonance signal may be discarded and the same view taken again or, to save time, data from adjacent views interpolated to create a replacement view.
In accordance with yet another aspect of the present invention, the reference is disposed to be moved with a moving part of the patient. For example, the reference object may be disposed to move with the patient's respiratory cycle. As another example, the reference object might be a portion of the patient's heart wall which moves in conjunction with the cardiac cycle. In this manner, the spatial position of the reference varies in accordance with the motion. The deviation between the measured position of the reference and a rest or other preselected position provides an indication of the relative movement for which correction may be made.
In one embodiment, the views are sorted in accordance with the deviation such that views of substantially the same degree of movement are combined together. In this manner, a series of images may be generated, each representing a different point in the patient's respiratory or cardiac cycle. Alternately, each view may be triggered, accepted, discarded, or the like in accordance with the degree of movement.
In accordance with another aspect of the present invention, a magnetic resonance imaging apparatus is provided. The apparatus includes means for supporting a subject and a reference object in an image region. The reference object has a plurality of parameters, such as relaxation time, spin density, dimensions, and position within the image region. A value of at least a preselected one of the parameters is known. Magnets create a substantially uniform main magnetic field through the image region. Resonance excitation means excite magnetic dipoles in at least the image region to precess, generating a magnetic resonance signal. Magnetic gradient means selectively cause magnetic field gradients across the image region to encode spatial position of the resonating dipoles in the frequency and phase of the resonance signal. A receiving means receives the resonance signal from the resonating nuclei and stores each resonance signal in a memory means. An image reconstruction means reconstructs a representation of at least the reference object from the resonance signal stored in the memory means and stores the representation in an intermediate memory means. A measuring means measures a value of the preselected parameter from the image representation in the intermediate image memory to obtain a measured parameter value. A comparing means compares the measured and known values to determine a deviation therebetween.
In accordance with a more limited aspect of the present invention, the apparatus further includes an altering means for altering at least one of the stored resonant signals and the image representation in the intermediate image memory in such a manner that the deviation between the known and measured parameter values is minimized.
In accordance with another more limited aspect of the present invention, the reference object is disposed to move with a moving portion of the subject in the image region. The magnetic resonance apparatus further includes a position determining means for determining the position of the referenced object from the image representation in the intermediate image memory.
A first advantage of the present invention resides in the correction of magnetic resonance data.
Another advantage of the present invention is that it enables patient motion to be monitored.
Another advantage is the more precise reconstruction of image representations.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be embodied in various parts and arrangements of parts or in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiment and are not to be construed as limiting the invention.
FIG. 1A and 1B taken together provide a diagrammatic illustration of a magnetic resonance imaging apparatus in accordance with the present invention; and,
FIG. 2A and 2B provide a diagrammatic illustration of a magnetic resonance imaging apparatus for monitoring patient motion in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIG. 1A and B, a main magnetic field generating means 10 generates a strong, generally uniform main magnetic field which extends generally longitudinally through an image region 20 in which a sample and reference are disposed. A resonance excitation means 30 selectively excites magnetic dipoles of nuclei in the image region to precess about the main magnetic field. Each precessing magnetic dipole generates a component of a resonance signal. A gradient field means 40 selectively causes gradients across the main magnetic field in the image region at selectable orientations. The gradient magnetic fields spatially encode the resonance signal components transmitted by resonating magnetic dipoles within the image region. Specific to the preferred embodiment, the frequency and relative phase of each component is encoded in accordance with the spatial location of the corresponding generating dipole.
A sampling means 50 discretely samples and stores an integral number of data points of each received resonance signal. A transform means 60 transforms or maps each resonance signal from data space or the phase/Frequency domain into a view or image representation in image space or the spatial domain.
After each view is sampled and reconstructed in image space, an image calibration means 70 measures a parameter of the reference from the reconstructed image representation and determines a deviation between a known and the measured parameter values. The parameters may include relaxation time, spin density, dimensions, position, and the like. In accordance with the comparison, at least one of the received resonance data and the image representation is altered so as to minimize the deviation. For example, the data may be shifted or interpolated to correct for motion. Alternately, the data may be discarded and resampled or approximated from adjoining views. The improved image may be displayed or stored on a tape, disc, or other memory for later retreival and processing.
The main magnetic field means 10 includes a plurality of annular superconducting or fluid cooled high power magnets 12 for generating the main magnetic field generally axially therethrough. A main magnetic field control circuit 14 controls and applies appropriate electric power to the annular magnets such that a substantially uniform constant magnetic field is generated longitudinally therethrough. However, small variations in the applied voltage commonly occur causing corresponding variations in the main magnetic field. Because the frequency of the generated resonance signal varies as a function of the magnetic field strength, variations in the voltage cause corresponding variations in the frequency of the resonance signal. Commonly, the main magnetic field generated by a high power magnet is only maintained with sufficient accuracy that the resonance signal, which has a frequency in the 1-200 megahertz range, tends to vary as much as 50 hertz over a period of five minutes. However, as discussed above, with each one millimeter pixel being defined by a 30 hertz frequency difference, a 50 hertz random variation among the views causes significant image degradation.
A subject 22 is supported in the image region 20 for examination. A first reference object 24 is disposed in the image region adjacent the subject but offset in the read direction. The read direction offset enables the subject signal to be deconvolved from the signal of the reference object. Preferably, a second reference object 26 is provided, with different dimensions from the first reference object. The objects are elongated along the axial direction of the magnets to accomodate the imaging of multiple slices. If the reconstructed view of one reference object is less precise than the other, view correction may be based on the more precisely imaged reference object. More particular to the preferred embodiment, the size of the reference object is selected such that the signal in the read direction is nearly flat near the echo and in the phase encoding direction rapidly changes near zero phase encoding. This condition is met when the read direction dimension of the reference object is an integral multiple of the field of view divided by the number of samples.
The excitation means 30 includes a coil 32 which is connected with a radio frequency transmitter 34 for broadcasting radio frequency excitation pulses. The radio frequency pulses are of the appropriate timing and duration, as is known in the art, to cause precession of the magnetic dipoles about the main magnetic field. In the illustrated embodiment, coil 32 functions between excitation pulses as an antenna for receiving radio frequency resonance signals. Optionally, a separate pick up coil assembly may be provided.
The gradient field means 40 includes gradient field coils 42 which surround the image region for selectively applying gradient magnetic fields transversely across the main magnetic field. A gradient magnetic field control circuit 44 controls the angular orientation with which the gradient fields are applied and the relative timing between the application of othogonal gradient pulses. More specific to the preferred embodiment, the gradient control circuit controls and selects phase and frequency encoding of the resonance signal components such that spatial position along one axis is encoded in the frequency and spatial position along an orthogonal axis is encoded in the phase. The exact sequence and timing between resonance excitation transmission and application of the gradient fields will vary in accordance with the imaging technique selected. Although the preferred embodiment is described in conjunction with spin-echo two dimensional Fourier transform imaging, it is to be appreciated that the apparatus is equally applicable to hybrid imaging, echo planar imaging, projection reconstruction imaging, inversion recovery, saturation recovery, and other imaging techniques.
The sampling means 50 includes a receiver 52 which receives the analog resonance signal which includes a large multiplicity of superimposed resonance signal components. The frequency and relative phase of each component is indicative of the encoded spatial position of the corresponding generating dipole. A digital sampling circuit 54 discretely samples each received resonance signal to generate one view of digital data for storage in a view memory means 56. After each view of the resonance data is collected and stored in the view memory means 56, the gradient magnetic field control alters the applied gradients so as to alter at least one of the frequency and phase encoding and the angular orientation thereof. The view data is transformed or mapped by a fast Fourier transform or other appropriate transform or reconstructing means 60 from the frequency and phase domain into a two dimensional spatial domain image representation. The spatial domain image representation is stored in an intermediate image memory 62.
The image calibration means 70 includes a phase angle encoding correction or adjustment means 72. A phase angle reading or measuring means 74 reads or derives a value from the image representation which is indicative of phase. Specific to the preferred embodiment, the reading means reads or determines the position of a preselected element or elements of at least one reference object, such as an edge or the central region of the reference object in the read direction for all views. A phase angle comparing means 76 compares the phase of the preselected incremental element or elements as reconstructed in the intermediate image memory with the actual phase of a reference view as determined by actual measurement, or the like. The deviation between the reconstructed and references phases is cured by shifting the phase of the resonance data by a corresponding amount. To this end, a phase shift means 78 multiplies the received image data by a phase correction value, e.sup.i.phi.. The position of the preselected incremental element as reconstructed with the phase shifted data is read by the phase angle read means 74 and compared by the phase comparing means 76 to determine whether further phase adjustment is required. This process is repeated for each view. In this manner, the phase of the resonance data is rotated for each view until correspondence between the reconstructed and reference phases of the incremental element are optimized.
An unacceptable data rejecting means 80 reads the magnitude of a plurality of pixels of the reconstructed image representation in the intermediate image memory 62. A magnitude averaging means 84 averages the magnitudes to provide an indication of the strength or magnitude of the received signal. The average magnitude is compared by a magnitude comparing means 86 with a preselected minimum magnitude. If the magnitude fails to exceed the preselected minimum, indicating weak data signals of questionable relability, the magnitude comparing means causes the same view to be collected again. Optionally, data from adjacent views can be interpolated to replace the defective data.
An image standardization means 90 standardizes the images from view to view. In particular, the resultant spin density is adjusted such that the spin density of the reconstructed image representation is standardized in each view. In particular, the spin density is adjusted for both a deviation in the spin densities from view to view, a deviation in the longitudinal and transverse relaxation times, and deviations in other system constants which contribute to the spin density number. In the illustrated embodiment, a spin density reading means 92 reads the spin density at one or more preselected pixels disposed within the reference object. A spin density comparing means 94 compares each read spin density with a known spin density of a corresponding element of the reference object. A spin density adjusting means 96 adjusts the spin density of the data in all pixels of the intermediate image memory to create a spin density standardized image representation for storage in a second intermediate image memory means 98.
A frequency shift correcting means 100 corrects the reconstructed image data for spatial shifts in the frequency encoding direction. In particular, a read means 102 reads the location in the frequency encoding direction at which a preselected incremental element of the reference object, such as an edge, is disposed in the reconstructed image representation. A comparing means 104 compares the read reconstructed position with the actual position of the corresponding incremental element. A spatial shift means 106 adds a spatial offset to each pixel of the reconstructed image representation in the second intermediate image memory means. This shifts the spatial position of the reconstructed image to bring the reconstructed and the actual positions into coincidence. Further, this correction may be in the form of an interpolation via a model to correct for motion. That is, although the edge may have shifted, points inside the subject may be shifted by any different amounts. Hence, interpolation may be required. In this case, information from several points which do not overlap in the frequency encode direction would be desirable. Motion in any direction may be monitored.
The reconstructed image representation of each view is summed and stored in an image memory means 110 for display on a video monitor or other man-readable display 112, recording on tape or disc for later use or processing, or the like.
FIGS. 2A and B illustrates an alternate embodiment to the embodiment of FIGS. 1A and B which is particularly adapted for monitoring movement in the examined object. In the embodiment of FIGS. 2A and B, like elements with the embodiment of FIGS. 1A and B are denoted by the same reference numerals but followed by a prime ('). A main magnetic field means 10' causes a generally uniform and stationary magnetic field longitudinally through an image region 20'. An object to be examined 22' is disposed within the image region with a reference object 24' affixed thereto. The reference object is connected to the examined object such that it moves in coordination with the movement to be monitored or for which compensation is to be made. For example, the reference object may be attached to the patient's abdomen to monitor for respiratory movement. Alternately, the reference object may be a preselected portion of the examined object, such as an outer wall or diameterically opposed outer walls of the patient's heart. The reference object, whether a part of the examined object or a separate object, has one or more physical properties which enable its reconstructed image to be recognized and separated from the reconstruction of the other portions of the examined object.
A resonance excitation means 30' excites magnetic resonance in the examined and reference objects. A spatial position encoding means 40' encodes the spatial position of resonating nuclei. Preferrably, a frequency and phase encoding is employed, although other encoding techniques may be utilized. A receiving means 50' receives the encoded magnetic resonance signals which are transformed by a transforming means 60' into an image representation for storage in an image memory 110'. A calibration means 70' adjusts the data as described in conjunction with FIG. 1A and B to improve the quality thereof.
A motion determining means 120 monitors the spatial position of the reference object, hence, motion of the examined object. In particular, a spatial position reading means 122 reads the spatial position of the reference object represented in the stored image representation. In one embodiment, a scan gating means 124 causes scans to be gated in accordance with the movement of the reference object. Optionally, views taken during unacceptable movement are discarded and retaken.
As another option, a sorting means 130 sorts the views as a function of the monitored movement. Each view image representation is added with other views of the like reference object position in a corresponding memory 132. In this manner, data may be collected continuously and sorted by the relative phase of the cardiac cycle, the relative phase of the respiratory cycle, or the like. A selection means 134 selects the image of desired portion of the cardiac or respiratory cycle for display on a display means 134 selects the image of desired portion of the cardiac or respiratory cycle for display on a display means 112' or for storage on tape, disc, or the like. No monitoring hardware is required.
Although illustrated as separate components for simplicity of illustration, it is to be appreciated that the functions of the above discussed means may be performed by programs and sub-routines of an appropriately programmed computer or processor. To provide for more detailed understanding of the present invention and to assist in the programming of the appropriate algorithms when making and using the present invention, the following mathematical analysis and explanation is provided.
In the above discussed preferred embodiments, the phase and amplitude of the signal are monitored by introducing a reference object outside of the image in the frequency encoding direction. For a reference object which is A in height and B in width, i.e., along the phase encoding axis, and frequency encoding axis respectively, then the received magnetic resonance signal S is proportional to: EQU S(t,G.sub.pe)=.rho..sub.o AB sinc (.pi..gamma.t.sub.pe G.sub.pe A) sinc (.pi..gamma.tG.sub.r B). (1)
where .gamma. is measured in Hz/G, pe refers to phase encoding, r to read, and .rho..sub.o as the spin density of the reference object. This signal is superimposed on the other image data. However, due to the linearity and the placement of the strips outside of the main object in the read direction, the signal from the reference object can be isolated after performing an inverse Fourier transform in the x domain. The resultant signal is then expressed as: EQU S(x,G.sub.pe)=.rho..sub.o A sinc (.pi..gamma.t.sub.pe G.sub.pe A)(2)
In Equations (1) and (2), the reference object is centered at the origin. If the reference object is shifted from the origin to a position (x.sub.1, y.sub.1), then the expression for the shifted signal S becomes: EQU S.sub.s (t,G.sub.pe)=e.sup.-i2.pi..gamma.(t.sbsp.pe.sup.G.sbsp.pe.sup.y 1.sup. +tG.sbsp.r.sup.x.sbsp.1.sup.) S(t,G.sub.pe) (3)
and EQU S.sub.s (x,G.sub.pe)=e.sup.-i2.pi..gamma.t.sbsp.pe.sup.G.sbsp.pe.sup.y.sbsp.1 S(x-x.sub.1, G.sub.pe) (4)
Because the views are regularly and linearly encoded, the gradient in the phase encode direction for the kth view can be defined as: EQU G.sub.pe =k.DELTA.G (5)
The phase is then expressed as: EQU .phi..sub.k =-2.pi..gamma.t.sub.pe k.DELTA.Gy.sub.1 ( 6a) EQU .phi..sub.k =-2.pi.ky.sub.1 /L.sub.y, (6b)
which uses the Nyquist relation: ##EQU1## This then is the phase of the control data.
In order to extract any random phase errors, the phase of the actual data .phi..sub.k.sup.', can be monitored by subtracting .phi..sub.k. The difference: EQU .DELTA..phi..sub.k =.phi..sub.k -.phi..sub.k ' (8)
is ideally a constant or deviates from a constant at most a small, random number in nature. Thus, by rotating each view by .DELTA..phi..sub.k, the received data .phi..sub.k ' should be returned to the actual phase relationship .phi..sub.k. Thus, by using a reference object with known properties, it is possible to monitor and correct for phase rotations caused by field fluctuations or synthesizer problems.
Looking now in detail to the techniques for removing random phase rotations, the phase of the received signal attributable to the reference object after the Fourier transform by means 60 is expressed as: EQU .phi..sub.k =-2.pi.ky.sub.1 /L.sub.y ( 9)
If the actual data have a DC rotation of .phi..sub.o, a spurious phase rotation of .phi..sub.k ', and a random phase rotation of .phi..sub.k ", then the actual phase, .phi..sub.k, will be: EQU .phi..sub.k =.phi..sub.k +.phi..sub.o +.sub.k '+.phi..sub.k ".(10)
The correction in phase to be applied then is: EQU .phi..sub.kcor =.phi..sub.k -.phi..sub.k. (11)
Each view then is multiplied by exp(i.phi..sub.kcor), i.e., each view is rotated through .phi..sub.kcor radians. As long as the random phase rotation is small, its correction will enhance the image. If the phase of the reference object .phi..sub.k is not encoded in .phi..sub.kcor, then all phases are rotated to zero. This results in an image which is shifted such that the center of the reference object occurs at the center of the image in the phase encoding direction.
This shifting can be taken advantage of by replacing y.sub.1 in Equation (9) with a selected shift, e.g. .DELTA.y.sub.s . This is useful for centering images. It can also be used for image interpolation. For example, the data is transformed with no shift for n points; the data with .DELTA.y.sub.s shifted for n points is transformed; and the two sets of n points are interleaved to get a 2n image. This is an advantageous interpolation and an alternative to zero padding the initial n points to 2n points and doing the larger transform. This can also be extended to allow oblique imaging of data in two or three dimensions.
Calculating the phase near zero amplitudes is a difficulty which can be overcome in two ways. First, the reference object height A=A.sub.min is chosen such that .pi.kA.sub.min /L.sub.y =.pi. for k=n. Because L.sub.y =2n.DELTA.y, A=2.DELTA.y as the largest value of A in which no zero crossing occurs in the phase encoding direction. As an alternative, a second reference object with a larger height A may be provided such that one reference has a zero crossing and the other does not.
Having a sufficient signal after the Fourier transform for accurately calculating the phase can be achieved by insurint that the spin density and relaxation time values, T.sub.1 and T.sub.2 , for the reference object are such that the largest signal per unit dimension in the object being imaged is roughly equal to that of the reference object. The peak signal in the object being imaged after the Fourier transform then is at most 2n times that in the reference object. For the value scaled up to 2.sup.16 , the signal from the strip will be 2.sup.8 for n=2.sup.7 .
Another way to enhance the signal is to increase the signal from the strip relative to the signal from the examined object by appropriately adjusting the spin density and relaxation times. The signal in the vicinity of the origin can be significantly improved by increasing the height of the reference object from A to mA. However, the signal has increasingly more zero crossings which renders only those regions away from the zero crossings useful. The ratio of the local maximum, l, away from the central peak as a function of m is just m/l for 1<l<m.
Another approach is to create Bm.sup.2 pixels across and then average over the m.sup.2 colums to reduce the noise by a factor of m and improve the phase determinations. Of course, if two strips are used, then the results from each can be averaged, provided the errors from each are on the same order. Otherwise, it is expedient not to average but to take the results of the reference object with the lowest noise level.
Local phase fluctuations .theta. (x, y) are another source of variation. Any x-dependent phases can be removed by taking the magnitude of this Fourier transformed signal from Fourier transformed means 60. The magnitude is used to detect a bad view, rather than to correct for phase. The average signal strength is defined by: ##EQU2## where x=x.sub.o and x.sub.o is the position of the center of the reference object. If the reference object is too thick, problems are encountered because the signal has different phase contributions at different y positions. The phase contributions from the different y positions can be resolved with a field map which is used to modify the signal. The modified signal is compared with the data after the first Fourier transform without taking the magnitude.
These local phase fluctuations are due to static, gradient, and local field inhomogeneities. For this region, a finite rather than point like reference object (where phase would be measured) is advantageous. For example, an improved signal to noise ratio is achieved. If RF inhomogeneities exist, then the pulses will deviate from .pi./2 or .pi. pulses. This spatially dependent variation will also modify the comparison of the actual data and the reference object data.
In the preferred embodiment, the amplitude of the signal from each reference object is monitored. If the monitored signal decreases below a threshold level for one of the reference objects, the phase correction obtained from the other reference object is used. If both amplitudes fall below the threshold, the phase is not corrected. Rather, the data is rejected and new data collected or other collected data is interpolated as a replacement therefor.
The signal which the reference object can be expected to produce can be expressed as: EQU S(x,G.sub.pe)=.rho..sub.o A sin c(.pi.kA/L.sub.y). (13)
By comparing the expected signal with the actual signal, S(x,G.sub.pe) , a decision to accept or correct the data can be made. In particular, the data is accepted if the difference between the actual and anticipated signals are less than a preselected maximum, .alpha. EQU .vertline..vertline.S(x,G.sub.pe).vertline.-.vertline.S(x,G.sub.pe).vertlin e..vertline.<.alpha. (14)
If the condition of Equation (14) is not met, then an average view is created by averaging the nearest good neighboring views.
Another option is to discard most of the image except the data from one reference object and do an inverse Fourier transform operation back to data space. The same thresholding procedure can be used for S(t,G.sub.pe) on a point-by-point basis to remove bad data points. In that case, points from surrounding good views could be used to average out those bad points. A difficulty arises if the reference objects are too narrow. Narrow reference objects may cause truncation of the signal caused by bad points which leads to a broadening of the bad points in the time domain. If the reference object is a single pixel thick, one bad point may lead to a whole view being deleted.
When the bad views are determined during data acquisition, the view may be repeated. This would avoid errors associated with interpolation and averaging.
As indicated above, one of the drawbacks to resistance type main magnetics resides in the frequency variations which are attributable to voltage fluctuations. In some instances, these frequency variations may be limited to as little as 30 hertz in a five minute interval, although variations up to 200 hertz in a five minute interval are not uncommon. In a conventional sequence in which the Nyquist frequency is 6.25 kHz, the frequency per pixel is about 50 hertz. Thus, ideal resolution will be achieved only if the frequency fluctuations can be held below 25 hertz. The present technique corrects for both random phase shifts associated with the frequency shift as well as correcting the frequency variations. Random phase fluctuations, on the order of 0.05 radians are associated with the frequency drift. It has been found that averaging over 10 views gives up to about 3% accuracy in phase determination, with a noise of 10% after the transformation by the Fourier transform means 60. To meet this standard, the minimum thickness of one strip should be about 3A.sub.min, with at least 10 useable pixels across.
With this physical configuration of the reference objects, two zero crossings occur before the outer views. This causes regions where the amplitude will lie below the noise threshold. To resolve this problem, a second reference object of thickness 4A.sub.min is provided which has its zero crossings staggered from those of the first reference object. The phase correction .phi..sub.kcor is adjusted for those views past the zero crossing because the vector has changed from positive to negative. Accordingly, an additional phase adjustment is added to the algorithm. EQU .phi..sub.kcor '=.phi..sub.kcor +l.pi. (15)
where l refers to the number of the last zero crossing passed. This addition of l.pi. makes knowledge of the exact thickness of the strip important.
To correct the frequency shift, a test for the boundary of the reference object on a view by view basis is made. When the noise is 10-20% of the signal in the worst case, a threshold can be set so that the first point above the threshold is the edge of the reference object. A test in both sides can serve to check on the number of pixels shifted. Once the shift is known, a whole view can simply be shifted back to the correct position by the appropriate amount and the processing continues. This significantly improves resolution on a system which drifts rapidly. Further, if expansion or shifting has occured, this can be corrected by interpolating and shifting back.
With the present invention, the value of the image of the reference object can be standardized. If the standardization is established such that a value for t.sub.rep approaches infinity, then any change in t.sub.rep could be accounted for in the final image appropriately normalized. For example, if the image of the reference object prior to adjustment gives a spin density level of .rho.', and the standard is set for .rho..sub.o , then the new value for the spin density will be: EQU .rho..sub.1 =.rho..sub.o (1-e.sup.-t rep.sup./T 1). (16)
where T.sub.1 is the longitudinal relaxation time of the reference object. The spin densities for the remainder of the image become ##EQU3## It should be pointed out that the longitudinal relaxation time is not a function of x in this normalization.
This equation can be further refined to account sequence variations with T.sub.1 and T.sub.2 and normalize the reference object data accordingly. If the predicted image varies with T.sub.1 and T.sub.2 , EQU .rho.'=.rho..sub.o f(T.sub.1, T.sub.2) (18)
then ##EQU4## By adjusting the window and level, the operator can produce an ideal image with specific .rho., T.sub.1, T.sub.2 normalization to .rho..sub.o . Other possible solutions could be listed out if other images to compute T.sub.1 and T.sub.2 are not available.
The accurate determination of .DELTA.G.sub.pe is important in reducing imaging noise levels. Commonly, a search coil and integrator are provided to determine the phase encode gradient values. One way to verify the measured values is to compare the actual data from the reference object with Equation (2). This technique is advantageous because it deals directly with a physical signal from an object and can be done accurately.
Moreover, the coverage of Fourier space from an oscillating wave form can be monitored using Equation (1). To do this using a search coil requires double integration to find all points. Minor variations in the coil angle and response to zero crossings can lead to inaccuracies in the physical measurement and in comparisons from system to system. From the reference object data one can determine whether a non-linear sampling would obtain the best linear coverage in data space.
By way of specific example, a reference object of 0.5 cm by 3 cm by 5 cm is filled with 1.95 liters of 4.4 mM Cu.sup.+2 and 100 milliliters of 0.256 mM Mn.sup.+2 . The T.sub.1 and T.sub.2 values for this reference object are about 600 and 250 ms respectively. The size of the reference object is chosen such that the signal in the read direction is nearly flat near the echo and in the phase encoding direction rapidly changing near zero phase encoding. This condition is met by kA/L=1, where k is the index away from the echo, A is the dimension of the reference object, and L is the field of view. For B/L=1/60, an essentially flat signal near the echo is obtained. For A/L=1/10, the signal drops to zero near the tenth view from the echo.
The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to those of ordinary skill in the art upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such alterations and modifications in so far as they come within the scope of the appended claims or the equivalents thereof.

Magnetic resonance reconstruction and scanning techniques using known information, constraints, and symmetry relations