our study population comprised 46 patients ( 35 men and 11 women ) with a mean age of 58.5 ( range , 52 - 72 ) years . seventy - three lesions were detected and included 30 hepatocellular carcinomas ( hcc ) in 20 patients , 12 metastases in six , 15 cysts in nine , 13 hemangiomas in eight , and three cholangiocarcinomas in three . in each subject , between one and four lesions were present . that of hcc was based on the findings of percutaneous biopsy ( n=7 ) , examination of a surgical specimen ( n=3 ) , or was on the basis of typical clinical and laboratory findings in combination with evidence of disease progression , as depicted at follow - up imaging ( n=10 ) . liver metastases were diagnosed on the basis of histological findings in the primary tumor and rapid progression of the lesion , as depicted at serial follow - up imaging ( n=2 ) or by examining percutaneous needle biopsy specimens ( n=4 ) . liver metastases were related to the following histologically proven primary tumors : carcinoma of the colon ( n=3 ) , stomach ( n=2 ) , and lung ( n=1 ) . confirmation of cholangiocarcinomas was based on the histological findings ( n=3 ) , while hemangiomas were diagnosed on the basis of their typical appearance at triple - phase helical computed tomography and dynamic mr imaging performed sequentially over a five - minute period following the injection of iodinated contrast medium or gadolinium chelates , and the absence of growth during a follow - up period of at least six months ( 15 - 18 ) . for liver cysts , diagnosis was based on established criteria , as observed at contrast - enhanced ct , ultrasound and unenhanced mr imaging , and during a clinical follow - up period of at least six months ( 15 , 16 ) . images were obtained with a 1.5 t scanner ( symphony ; siemens medical systems , erlangen , germany ) using a body phased - array coil . , u.s.a.)-enhanced mr imaging using the following sequences : respiratory - triggered , t2-weighted turbo spin - echo ( tse ) ; breath - hold t2 * -weighted gradient - recalled echo ( gre ) ; breath - hold t2-weighted tse ; and breath - hold t1-weighted double - echo gre images ( te 4.2/ 2.1 msec ) . for respiratory - triggered t2-weighted tse imaging , the following parameters were used : a tr range / effective te of 3500 - 5600/80 , an echo - train length of 15 , three signal averages , and a matrix of 192256 . those for breath - hold t2-weighted tse included a tr / te of 2500/100 , a flip angle of 150 , and a matrix of 132256 , while for breath - hold t2 * -weighted gradient - echo imaging , a tr / te of 180/12 , a flip angle of 30 , and a matrix of 132256 were used . breath - hold t1-weighted double - echo gre images were obtained with a tr / te 150/4.2 and 2.1 , a 70 flip angle , one signal average , and a matrix of 256132 . for all sequences , imaging was performed in the axial plane with a section thickness of 7 mm , an intersection gap of 3 mm , and a rectangular field of view of 24 - 2830 - 34 cm . ferumoxides was administered at 15 mol of iron per kilogram of body weight ; the suspension was diluted in 100 ml of 5% glucose solution and administered intravenously at a rate of approximately 4 ml / min for 25 minutes . postcontrast t1-weighted mr images were obtained not more than 10 minutes later ( distributional phase ) , and postcontrast t2-weighted and t2 * -weighted images were obtained 10 - 30 minutes after the end of contrast administration ( accumulation phase ) . two radiologists experienced in abdominal mr imaging assessed the enhancement pattern of both precontrast and postcontrast ( ferumoxides - enhanced ) mr images . they had no knowledge of patient history or diagnosis , and reached their conclusion by consensus . for each lesion , signal intensity relative to hepatic parenchyma was recorded as hypo- , iso- or hyperintense . for hyperintense lesions showing enhancement at ferumoxides - enhanced t1-weighted imaging , the readers were asked to state whether or not the enhancement patterns were ring - shaped . to assess the reliability of ferumoxides - enhanced t1-weighted imaging for the characterization of focal liver lesions , two radiologists who interpret mr images of the liver as part of their daily clinical and research practice , and who were blinded to the diagnosis and clinical history , reviewed two sets of images : a ) postcontrast accumulation - phase t2-weighted and t2 * -weighted ( reading set a ) ; and b ) combined distributional - phase t1-weighted in- and opposed - phase and accumulation phase ( reading set b ) . the images were randomized and presented at two sessions , with patient data masked . to minimize learning bias , the review sessions were held at two - week intervals . at each , the readers were asked to provide a diagnosis according to previously published established criteria , and a consensus was then reached ( 8 - 12 , 14 - 16 ) . lesions showing no enhancement at postcontrast t1- and t2-weighted imaging were considered to be cysts ; those showing positive enhancement similar to that of the intrahepatic vessels at t1-weighted and negative enhancement at t2-weighted imaging were classified as hemangiomas . lesions in which ring enhancement was apparent at postcontrast - t1 weighted imaging were considered to be metastases , while those showing slight enhancement at t1-weighted and no enhancement at t2-weighted imaging were classed as hccs . to assess the statistical significance of the differences between the reading sessions , the mcnemar test was used . the degree of enhancement of the liver , tumors , and the portal vein was calculated from signal intensity measurements before and after intravenous injection of ferumoxides . for a lesion and for normal liver parenchyma , operator - defined region - of - interest ( roi ) si measurements were obtained directly from the monitor . during the various imaging sequences , care was taken to place the roi for the liver or portal vein in the same area , and for lesions with necrotic areas , care was taken to measure si only in solid portions of the tumor . whenever possible , an roi of at least 35 mm was used ; similar regions of interest were used for unenhanced and ferumoxides - enhanced images . for each image , background noise was measured ventral to the liver outside the patient along the direction of the phase - encoding gradient and included any ghosting artifacts that might have been propagated over the images . for each sequence , signal - to - noise ratios ( snrs ) for lesions and liver were calculated using the following formula : snr = si / sd , where si is the signal intensity of the lesion or liver parenchyma and sd is the standard deviation of background noise . in addition , contrast - to - noise ratios ( cnrs ) for lesion - to - liver and portal vein - to - liver were computed for each sequence as follows : cnrlesion = ( si lesion - si liver ) / sd , and cnrpv = ( si portal vein - si liver ) / sd . one - way analysis of variance with pair - wise comparisons was used to determine the statistical significance of the differences between the ferumoxides - enhanced cnrs of each type of tumor , as seen at t1-weighted flash imaging . the post hoc tukey test was used to determine which differences were statistically significant , indicated by a p value of less than 0.05 . our study population comprised 46 patients ( 35 men and 11 women ) with a mean age of 58.5 ( range , 52 - 72 ) years . seventy - three lesions were detected and included 30 hepatocellular carcinomas ( hcc ) in 20 patients , 12 metastases in six , 15 cysts in nine , 13 hemangiomas in eight , and three cholangiocarcinomas in three . in each subject , between one and four lesions were present . that of hcc was based on the findings of percutaneous biopsy ( n=7 ) , examination of a surgical specimen ( n=3 ) , or was on the basis of typical clinical and laboratory findings in combination with evidence of disease progression , as depicted at follow - up imaging ( n=10 ) . liver metastases were diagnosed on the basis of histological findings in the primary tumor and rapid progression of the lesion , as depicted at serial follow - up imaging ( n=2 ) or by examining percutaneous needle biopsy specimens ( n=4 ) . liver metastases were related to the following histologically proven primary tumors : carcinoma of the colon ( n=3 ) , stomach ( n=2 ) , and lung ( n=1 ) . confirmation of cholangiocarcinomas was based on the histological findings ( n=3 ) , while hemangiomas were diagnosed on the basis of their typical appearance at triple - phase helical computed tomography and dynamic mr imaging performed sequentially over a five - minute period following the injection of iodinated contrast medium or gadolinium chelates , and the absence of growth during a follow - up period of at least six months ( 15 - 18 ) . for liver cysts , diagnosis was based on established criteria , as observed at contrast - enhanced ct , ultrasound and unenhanced mr imaging , and during a clinical follow - up period of at least six months ( 15 , 16 ) . images were obtained with a 1.5 t scanner ( symphony ; siemens medical systems , erlangen , germany ) using a body phased - array coil . u.s.a.)-enhanced mr imaging using the following sequences : respiratory - triggered , t2-weighted turbo spin - echo ( tse ) ; breath - hold t2 * -weighted gradient - recalled echo ( gre ) ; breath - hold t2-weighted tse ; and breath - hold t1-weighted double - echo gre images ( te 4.2/ 2.1 msec ) . for respiratory - triggered t2-weighted tse imaging , the following parameters were used : a tr range / effective te of 3500 - 5600/80 , an echo - train length of 15 , three signal averages , and a matrix of 192256 . those for breath - hold t2-weighted tse included a tr / te of 2500/100 , a flip angle of 150 , and a matrix of 132256 , while for breath - hold t2 * -weighted gradient - echo imaging , a tr / te of 180/12 , a flip angle of 30 , and a matrix of 132256 were used . breath - hold t1-weighted double - echo gre images were obtained with a tr / te 150/4.2 and 2.1 , a 70 flip angle , one signal average , and a matrix of 256132 . for all sequences , imaging was performed in the axial plane with a section thickness of 7 mm , an intersection gap of 3 mm , and a rectangular field of view of 24 - 2830 - 34 cm . ferumoxides was administered at 15 mol of iron per kilogram of body weight ; the suspension was diluted in 100 ml of 5% glucose solution and administered intravenously at a rate of approximately 4 ml / min for 25 minutes . postcontrast t1-weighted mr images were obtained not more than 10 minutes later ( distributional phase ) , and postcontrast t2-weighted and t2 * -weighted images were obtained 10 - 30 minutes after the end of contrast administration ( accumulation phase ) . two radiologists experienced in abdominal mr imaging assessed the enhancement pattern of both precontrast and postcontrast ( ferumoxides - enhanced ) mr images . they had no knowledge of patient history or diagnosis , and reached their conclusion by consensus . for each lesion , signal intensity relative to hepatic parenchyma was recorded as hypo- , iso- or hyperintense . for hyperintense lesions showing enhancement at ferumoxides - enhanced t1-weighted imaging , the readers were asked to state whether or not the enhancement patterns were ring - shaped . to assess the reliability of ferumoxides - enhanced t1-weighted imaging for the characterization of focal liver lesions , two radiologists who interpret mr images of the liver as part of their daily clinical and research practice , and who were blinded to the diagnosis and clinical history , reviewed two sets of images : a ) postcontrast accumulation - phase t2-weighted and t2 * -weighted ( reading set a ) ; and b ) combined distributional - phase t1-weighted in- and opposed - phase and accumulation phase ( reading set b ) . the images were randomized and presented at two sessions , with patient data masked . to minimize learning bias , the review sessions were held at two - week intervals . at each , the readers were asked to provide a diagnosis according to previously published established criteria , and a consensus was then reached ( 8 - 12 , 14 - 16 ) . lesions showing no enhancement at postcontrast t1- and t2-weighted imaging were considered to be cysts ; those showing positive enhancement similar to that of the intrahepatic vessels at t1-weighted and negative enhancement at t2-weighted imaging were classified as hemangiomas . lesions in which ring enhancement was apparent at postcontrast - t1 weighted imaging were considered to be metastases , while those showing slight enhancement at t1-weighted and no enhancement at t2-weighted imaging were classed as hccs . to assess the statistical significance of the differences between the reading sessions , the mcnemar test was used . the degree of enhancement of the liver , tumors , and the portal vein was calculated from signal intensity measurements before and after intravenous injection of ferumoxides . for a lesion and for normal liver parenchyma , operator - defined region - of - interest ( roi ) si measurements were obtained directly from the monitor . during the various imaging sequences , care was taken to place the roi for the liver or portal vein in the same area , and for lesions with necrotic areas , care was taken to measure si only in solid portions of the tumor . whenever possible , an roi of at least 35 mm was used ; similar regions of interest were used for unenhanced and ferumoxides - enhanced images . for each image , background noise was measured ventral to the liver outside the patient along the direction of the phase - encoding gradient and included any ghosting artifacts that might have been propagated over the images . for each sequence , signal - to - noise ratios ( snrs ) for lesions and liver were calculated using the following formula : snr = si / sd , where si is the signal intensity of the lesion or liver parenchyma and sd is the standard deviation of background noise . in addition , contrast - to - noise ratios ( cnrs ) for lesion - to - liver and portal vein - to - liver were computed for each sequence as follows : cnrlesion = ( si lesion - si liver ) / sd , and cnrpv = ( si portal vein - si liver ) / sd . two radiologists experienced in abdominal mr imaging assessed the enhancement pattern of both precontrast and postcontrast ( ferumoxides - enhanced ) mr images . they had no knowledge of patient history or diagnosis , and reached their conclusion by consensus . for each lesion , signal intensity relative to hepatic parenchyma was recorded as hypo- , iso- or hyperintense . for hyperintense lesions showing enhancement at ferumoxides - enhanced t1-weighted imaging , the readers were asked to state whether or not the enhancement patterns were ring - shaped . to assess the reliability of ferumoxides - enhanced t1-weighted imaging for the characterization of focal liver lesions , two radiologists who interpret mr images of the liver as part of their daily clinical and research practice , and who were blinded to the diagnosis and clinical history , reviewed two sets of images : a ) postcontrast accumulation - phase t2-weighted and t2 * -weighted ( reading set a ) ; and b ) combined distributional - phase t1-weighted in- and opposed - phase and accumulation phase ( reading set b ) . the images were randomized and presented at two sessions , with patient data masked . to minimize learning bias , the review sessions were held at two - week intervals . at each , the readers were asked to provide a diagnosis according to previously published established criteria , and a consensus was then reached ( 8 - 12 , 14 - 16 ) . lesions showing no enhancement at postcontrast t1- and t2-weighted imaging were considered to be cysts ; those showing positive enhancement similar to that of the intrahepatic vessels at t1-weighted and negative enhancement at t2-weighted imaging were classified as hemangiomas . lesions in which ring enhancement was apparent at postcontrast - t1 weighted imaging were considered to be metastases , while those showing slight enhancement at t1-weighted and no enhancement at t2-weighted imaging were classed as hccs . to assess the statistical significance of the differences between the reading sessions , the mcnemar test was used . the degree of enhancement of the liver , tumors , and the portal vein was calculated from signal intensity measurements before and after intravenous injection of ferumoxides . for a lesion and for normal liver parenchyma , operator - defined region - of - interest ( roi ) si measurements were obtained directly from the monitor . during the various imaging sequences , care was taken to place the roi for the liver or portal vein in the same area , and for lesions with necrotic areas , care was taken to measure si only in solid portions of the tumor . whenever possible , an roi of at least 35 mm was used ; similar regions of interest were used for unenhanced and ferumoxides - enhanced images . for each image , background noise was measured ventral to the liver outside the patient along the direction of the phase - encoding gradient and included any ghosting artifacts that might have been propagated over the images . for each sequence , signal - to - noise ratios ( snrs ) for lesions and liver were calculated using the following formula : snr = si / sd , where si is the signal intensity of the lesion or liver parenchyma and sd is the standard deviation of background noise . in addition , contrast - to - noise ratios ( cnrs ) for lesion - to - liver and portal vein - to - liver were computed for each sequence as follows : cnrlesion = ( si lesion - si liver ) / sd , and cnrpv = ( si portal vein - si liver ) / sd . one - way analysis of variance with pair - wise comparisons was used to determine the statistical significance of the differences between the ferumoxides - enhanced cnrs of each type of tumor , as seen at t1-weighted flash imaging . the post hoc tukey test was used to determine which differences were statistically significant , indicated by a p value of less than 0.05 . before ferumoxides administration , t1-weighted flash imaging showed that 61 of 70 lesions were hypointense relative to the liver . for each type of lesion , ferumoxides - enhanced t1-weighted double - echo gre images obtained during the distributional phase demonstrated some degree of characteristic enhancement . all 13 hemangiomas showed positive enhancement at t1-weighted in- and out - of - phase gre imaging ( fig . intrahepatic vessels were also hyperintense to the liver , with a degree of intensity similar to that demonstrated by hemangiomas . in all of these , a slight degree of signal intensity drop was noted , though for metastatic tumors , hccs and cysts , this was not the case . ferumoxides - enhanced t1-weighted double - echo imaging revealed no enhancement of cystic lesions , though at distributional - phase t1-weighted in- and out - of - phase imaging , peripheral rim enhancement was seen in nine metastases ( 75% ) and two of three cholangiocarcinomas ( 67% ) ( figs . 2 , 3 ) . in addition , t1-weighted dual - echo imaging of hccs revealed slight enhancement in 24 lesions ( 80% ) , ring enhancement in two ( 6.7% ) , and no noticeable enhancement in four ( 13.3% ) . in terms of the relative signal intensity of focal liver lesions observed at t1-weighted double - echo gre imaging , out - of - phase images obtained using minimum echo time better differentiated hemangiomas from other tumors than did in - phase images ( table 1 ) . distributional - phase t1-weighted out - of - phase imaging showed that no hemangioma was hypointense , but 11 of 12 metastatic lesions ( 92% ) and three cholangiocarcinomas ( 100% ) were ( table 1 ) . this same modality showed that 19 of 30 hccs ( 63% ) were hypointense , but nine hccs seen as hyperintense at precontrast t1-weighted imaging were also seen as hyperintense on all ferumoxides - enhanced t1-weighted out - of - phase images because liver parenchyma showed a signal decrease after the infusion of ferumoxides ( fig . a summary of the mean signal - to - noise ratios of liver lesions , liver parenchyma , and the portal vein , as seen at t1-weighted imaging before and after ferumoxides enhancement , is shown in table 2 . the enhancement of hemangiomas was most marked , followed by that of hccs , cholangiocarcinomas , and metastases . the degree of enhancement of hccs or adenocarcinomas revealed by t1-weighted postcontrast imaging was considerably lower than that of hemangiomas ( p < .05 ) . at t2-weighted postcontrast imaging , figure 5 and table 3 show cnrs for various tumors at t1-weighted sequences before and after ferumoxides administration . at distributional - phase t1-weighted imaging , hemangiomas exhibited the greatest cnrs relative to surrounding liver , and also the greatest lesion - to - portal vein cnrs ( table 4 ) . a statistically significant difference was noted between the cnrs of hemangiomas and metastases ( p < .05 ) and between those of hemangiomas and hccs ( p < .05 ) . set b ( combined distributional phase and accumulation phase imaging ) shows that all hemangiomas and cysts were correctly diagnosed . the characterization of focal liver lesions as benign or malignant was better evaluated by set b ( overall accuracy=88% ) than set a ( overall accuracy=75% ) ( p = .07 ) . when a specific diagnosis was requested , the accuracy of set b decreased to 82% , but was still better than that of set a ( p < .05 ) . the additional information provided by ferumoxides - enhanced t1-weighted images obtained during the distributional phase has been shown to be useful for further characterization of focal liver lesions . before ferumoxides administration , t1-weighted flash imaging showed that 61 of 70 lesions were hypointense relative to the liver . for each type of lesion , ferumoxides - enhanced t1-weighted double - echo gre images obtained during the distributional phase demonstrated some degree of characteristic enhancement . all 13 hemangiomas showed positive enhancement at t1-weighted in- and out - of - phase gre imaging ( fig . intrahepatic vessels were also hyperintense to the liver , with a degree of intensity similar to that demonstrated by hemangiomas . in all of these , a slight degree of signal intensity drop was noted , though for metastatic tumors , hccs and cysts , this was not the case . ferumoxides - enhanced t1-weighted double - echo imaging revealed no enhancement of cystic lesions , though at distributional - phase t1-weighted in- and out - of - phase imaging , peripheral rim enhancement was seen in nine metastases ( 75% ) and two of three cholangiocarcinomas ( 67% ) ( figs . 2 , 3 ) . in addition , t1-weighted dual - echo imaging of hccs revealed slight enhancement in 24 lesions ( 80% ) , ring enhancement in two ( 6.7% ) , and no noticeable enhancement in four ( 13.3% ) . in terms of the relative signal intensity of focal liver lesions observed at t1-weighted double - echo gre imaging , out - of - phase images obtained using minimum echo time better differentiated hemangiomas from other tumors than did in - phase images ( table 1 ) . distributional - phase t1-weighted out - of - phase imaging showed that no hemangioma was hypointense , but 11 of 12 metastatic lesions ( 92% ) and three cholangiocarcinomas ( 100% ) were ( table 1 ) . this same modality showed that 19 of 30 hccs ( 63% ) were hypointense , but nine hccs seen as hyperintense at precontrast t1-weighted imaging were also seen as hyperintense on all ferumoxides - enhanced t1-weighted out - of - phase images because liver parenchyma showed a signal decrease after the infusion of ferumoxides ( fig . a summary of the mean signal - to - noise ratios of liver lesions , liver parenchyma , and the portal vein , as seen at t1-weighted imaging before and after ferumoxides enhancement , is shown in table 2 . the enhancement of hemangiomas was most marked , followed by that of hccs , cholangiocarcinomas , and metastases . the degree of enhancement of hccs or adenocarcinomas revealed by t1-weighted postcontrast imaging was considerably lower than that of hemangiomas ( p < .05 ) . at t2-weighted postcontrast imaging , figure 5 and table 3 show cnrs for various tumors at t1-weighted sequences before and after ferumoxides administration . at distributional - phase t1-weighted imaging , hemangiomas exhibited the greatest cnrs relative to surrounding liver , and also the greatest lesion - to - portal vein cnrs ( table 4 ) . a statistically significant difference was noted between the cnrs of hemangiomas and metastases ( p < .05 ) and between those of hemangiomas and hccs ( p < .05 ) . set b ( combined distributional phase and accumulation phase imaging ) shows that all hemangiomas and cysts were correctly diagnosed . the characterization of focal liver lesions as benign or malignant was better evaluated by set b ( overall accuracy=88% ) than set a ( overall accuracy=75% ) ( p = .07 ) . when a specific diagnosis was requested , the accuracy of set b decreased to 82% , but was still better than that of set a ( p < .05 ) . the additional information provided by ferumoxides - enhanced t1-weighted images obtained during the distributional phase has been shown to be useful for further characterization of focal liver lesions . the use of ferumoxides in mr imaging of the liver has been the focus of many investigations , and it is now widely accepted that ferumoxides increase the detection rate of focal liver lesions at t2-weighted imaging ( 4 - 6 ) . several authors , however , have encountered difficulties in differentiating benign from malignant lesions at ferumoxides - enhanced mr imaging ( 11 , 19 ) , and until recently , only a small number of reports focused on lesion characterization under this circumstance ( 8 - 13 ) . furthermore , in most previous studies , investigators employed a t2-weighted sequence to characterize focal liver lesions , using the signal loss related to iron particle uptake of kupffer cells located in benign liver lesions such as focal nodular hyperplasia , adenoma and hemangioma ( 8 - 11 ) . however , in a clinical setting , the signal change of focal liver lesions makes it difficult to distinguish metastases from hemangioma on t2-weighted images because metastatic lesions are hyperintense . this can be a more serious problem when small lesions of less than two centimeters are being imaged . several authors have recently described t1-weighted gre images obtained 30 minutes to 1 hour after the administration of ferumoxides , noting that they were valuable for characterizing focal liver lesions observed at spio - enhanced mr imaging ( 8 - 10 , 12 , 13 ) . in this study , t1-weighted imaging began within ten minutes of the end of contrast infusion , a rationale based on the results of previous reports regarding the plasma half - life of ferumoxides ( 19 , 20 ) . the most noticeable findings observed in this study were that t1-weighted out - of - phase imaging using minimum echo - time best differentiated hemangiomas from other tumors . as in the findings of previous studies regarding lesion characterization with ferumoxides - enhanced mr imaging ( 9 , 10 ) , hemangiomas showed the highest degree of signal enhancement at t1-weighted imaging . during the distributional phase , only hemangiomas showed a positive mean lesion - to - liver cnr ; for other lesions this was negative . only hccs showing hyperintensity at precontrast t1-weighted imaging demonstrated hyperintensity at postcontrast t1-weighted out - of - phase imaging using 2.1 ms echo time , but due to the t1 effects of circulating iron particles , the degree of hyperintensity was much lower than that of the portal vein . these results suggest that to improve the efficacy of ferumoxides - enhanced mr imaging for the differentiation of hepatic hemangiomas and malignant liver lesions , t1-weighted gre imaging using minimum echo - time and performed during the distributional phase , thus demonstrating the t1-effect of circulating iron particles in the blood , should be added to t2-weighted and t2 * -weighted imaging . quantitative analysis performed in this study showed that the lesion - to - liver cnrs of lesions seen at postcontrast t1-weighted gre imaging were relatively lower than those observed in the previous studies of nakayama et al . this is because during the distributional phase , the contrast uptake of kupffer cells was small and the liver parenchyma signal therefore decreased only slightly . however , the lesion - to - liver cnrs of lesions seen at t2 * -weighted gre imaging during the accumulation phase of our study were similar to those observed in previous studies ( figs . 3 , 4 ) . given that t1-weighted spio - enhanced mr imaging is useful for lesion characterization , not lesion detection , obtaining t1-weighted images during the distributional phase may , because of the presence of circulating iron particles , be better for observing positive enhancement of focal liver lesions . owing to the differences demonstrated by the hepatic tumor enhancement profiles , most tumors ( 82% ) could be correctly characterized during the distributional phase of t1- and t2-weighted imaging . hemangiomas became hyperintense at postcontrast t1-weighted imaging , with a characteristic drop in si at postcontrast t2-weighted imaging ( 8 , 9 ) . the enhancement pattern of hemangiomas seen at ferumoxides - enhanced imaging is probably due to the high volume of ferumoxide - laden blood present in the enlarged vascular spaces of the lesion . although hccs showed some enhancement at ferumoxides - enhanced t1-weighted imaging , the degree of this was significantly lower than for hemangiomas ( p < .05 ) . all hypovascular tumors , including metastases ( n=12 ) and cholangiocarcinomas ( n=3 ) , showed only slight enhancement ( n=4 ) or peripheral ring enhancement ( n=11 ) at ferumoxides - enhanced t1-weighted imaging , but cysts showed no enhancement . these differences in the characteristics of t1-weighted enhancement , combined with the characteristic drop in si for hemangiomas at t2-weighted postcontrast imaging , may be of some value in the characterization of these lesions . it has been suggested that the presence of ring enhancement following the administration of ferumoxides can help characterize focal hepatic lesions ( 21 ) and also differentiate benign from malignant liver lesions . in our study , most hypovascular malignant tumors , such as metastases and cholangiocarcinomas ( 11/15 , 73.3% ) , and a small number of hccs ( 3/30 , 10% ) demonstrated ring enhancement ; hemangiomas or cysts , on the other hand , did not . we thus assume that this sign also helps to differentiate hypovascular malignant tumor lesions from other tumors seen at ferumoxides - enhanced t1-weighted imaging . in ferumoxides - enhanced mr imaging , the fact that the infusion time of the contrast medium is long has given rise to controversy as to whether , for this reason , precontrast imaging is needed . kim et al . ( 13 ) have demonstrated that at t1-weighted minimum - te gre imaging , all fnhs and hemangiomas , but no hccs and only 3% of metastases , were hyperintense , results which suggest that from a clinical standpoint , the need to obtain precontrast images is not great . in our study , however , the signal intensity of hccs at unenhanced t1-weighted imaging varied : approximately 37% were hyper- or iso - intense compared to the liver at postcontrast t1-weighted out - of - phase gre imaging . the observed reduction in the signal intensity of liver parenchyma after the infusion of ferumoxides is almost always greater than that of hccs ; a lesion which is hyperintense at precontrast t1-weighted imaging can become more hyperintense and harder to differentiate from hemangioma . furthermore , although it may save time , the elimination of unenhanced imaging can be detrimental to the characterization of hepatocellular tumors such as fnh , adenoma , and well - differentiated hcc , for which si relationships with normal unenhanced liver are routinely examined in lesion characterization . for this reason , it would seem prudent to retain the use of unenhanced scanning , though to clarify this issue , further studies may be necessary . first , although the study group was large , the relative number of benign lesions was small , thereby reflecting the prevalence of some less common lesions . instead , typical clinical and laboratory findings in combination with typical imaging findings of other imaging modalities were used as the diagnostic criteria . last , cases of neither focal nodular hyperplasia nor adenoma , which can cause difficulties in differentiating focal liver lesions , were included in this study . in conclusion , the use of t1-weighted double - echo flash imaging , performed soon after the infusion of ferumoxides , improved the differentiation of hepatic hemangiomas from malignant liver lesions and may help increase the accuracy with which malignant lesions are detected .
objectiveto determine the potential value of distributional - phase t1-weighted ferumoxides - enhanced magnetic resonance ( mr ) imaging for tissue characterization of focal liver lesions.materials and methodsferumoxides - enhanced mr imaging was performed using a 1.5-t system in 46 patients referred for evaluation of known or suspected hepatic malignancies . 
 seventy - three focal liver lesions ( 30 hepatocellular carcinomas [ hcc ] , 12 metastases , 15 cysts , 13 hemangiomas , and three cholangiocarcinomas ) were evaluated . 
 mr imaging included t1-weighted double - echo gradient - echo ( tr / te : 150/4.2 and 2.1 msec ) , t2 * -weighted gradient - echo ( tr / te : 180/12 msec ) , and t2-weighted turbo spin - echo mr imaging at 1.5 t before and after intravenous administration of ferumoxides ( 15 mmol / kg body weight ) . 
 postcontrast t1-weighted imaging was performed within eight minutes of infusion of the contrast medium ( distributional phase ) . 
 both qualitative and quantitative analysis was performed.resultsduring the distributional phase after infusion of ferumoxides , unique enhancement patterns of focal liver lesions were observed for hemangiomas , metastases , and hepatocellular carcinomas . on t1-weighted gre images obtained during the distributional phase , hemangiomas showed a typical positive enhancement pattern of increased signal ; metastases showed ring enhancement ; and hepatocellar carcinomas showed slight enhancement . 
 quantitatively , the signal - to - noise ratio of hemangiomas was much higher than that of other tumors ( p < .05 ) and was similar to that of intrahepatic vessels . 
 this finding permitted more effective differentiation between hemangiomas and other malignant tumors.conclusiont1-weighted double - echo flash images obtained soon after the infusion of ferumoxides , show characteristic enhancement patterns and improved the differentiation of focal liver lesions .