Title of Invention: Method of and apparatus for histological human tissue characterization using ultrasound
Abstract: A method and apparatus for determining important histological characteristics of tissue, including a determination of the tissue's health. Electrical pulses are converted into meaningful numerical representations through the use of Fourier Transforms. These numerical representations are then used to determine important histological characteristics of tissue. This novel invention does not require rectification and thus provides for detailed information from the ultrasonic scan.
Detailed Description: Part PAC: DETAILED DESCRIPTION OF THE INVENTION
Part PAR: Referring more particularly to the drawings, a well-damped 10 MHz transducer one-eighth inch (1/8") diameter crystal 12 is connected to a wide band pulser-receiver 14. The pulser-receiver 14 is a sonic generator and receiver for generating, sending and receiving waves. The wide-band (non-rectified) output of the pulser-receiver 14 is connected to a digital oscilloscope 16, which has a plotter 18 connected to it to record the data output. The oscilloscope 16 provides live visual reading of the output. The data-point plotter 18 gives a graphic reading of the output. The oscilloscope 16 also has Fast Fourier Transform capability.
Part PAR_2: The transducer 12 emits an ultrasonic pulse that travels through the body 20 into the subcutaneous tissue that is under examination. This tissue reflects a sequence of small amplitude echoes back to the transducer 12. The sequence of echoes from the tissue is received by the transducer 12, which converts the ultrasonic pulse sequence into a sequence of electrical pulses. The electrical pulse sequence is amplified by the wide-band amplifier in the pulser-receiver 14 and sent to the oscilloscope 16 for measurement. The oscilloscope 16, further processes the data, displays it on a visual monitor, and sends it to a plotter 18 for a hard-copy record. The oscilloscope 16 has the ability to perform Fast Fourier Transforms on the digitized pulses.
Part PAR_3: Specifically, the transforming equations used are as follows: ##EQU1## where G(f) is the Fourier Transform of h(t).
Part PAR_4: The following properties of this type of transform are used: ##EQU2## Consider the echo train from an alternating stacked sequence of tissues. The following relationships are used: EQU P.sub.2n-1 =P.sub.0 (T.sub.12 T.sub.21).sup.2(n-1) R.sub.12 exp(-2n.varies..sub.1 l.sub.1 -2(n-1).varies..sub.2 l.sub.2)(odd members)3(a) EQU P.sub.2n =-P.sub.0 (T.sub.12 T.sub.21).sup.2n-1 R.sub.12 exp(-2n[.varies..sub.1 l.sub.1 +.varies..sub.2 l.sub.2 ])(even members)3(b )
Part PAL: In examining the echos, each received echo is subscripted with an index to indicate the temporal order of reception ##EQU3## where t.sub.0 marks the reception of the first echo, and .DELTA.t.sub.j is the time interval between the jth received reflection and the first echo.
Part PAR_5: By allowing G.sub.j (f)=F[h.sub.j (t-t.sub.0)] and using (1a), (2a) and (3a) the following relationship is obtained ##EQU4## It is assumed that the later reflections are small and equation (6) is not greatly affected by letting m approach infinity, the equation is rewritten: ##EQU5## by substituting the sum for each series.
Part PAR_6: In general, any part of the transform may be used to express a relationship among the ultrasonic variables and, hence, give useful information about the significant tissue classifications. For purposes of illustration, the magnitude is used, although the real part, the imaginary part, the phase or any combination is just as instructive.
Part PAR_7: Next, the Fourier transform of the incident ultrasonic pulse, ##EQU6## is evaluated by substitution into equation 1(a) ##EQU7## which upon evaluation gives ##EQU8## Using standard algebraic techniques and trigonometric substitutions the magnitude is rewritten: ##EQU9## where f.sub.0 is the center frequency of the ultrasonic transducer, H.sub.0 is .alpha..sub.1 l.sub.1+ .alpha..sub.2 l.sub.2, H.sub.1 is .alpha..sub.1 l.sub.1, H.sub.2 is .alpha..sub.2 l.sub.2, T is (T.sub.12 T.sub.21), t.sub.2 is l.sub.2 /c.sub.2, t.sub.s is l.sub.1 /c.sub.1 +l.sub.2 /c.sub.2, .alpha..sub.1 is the attenuation coefficient of the type 1 material, and .alpha..sub.2 is the attenuation coefficient of the type 2 material.
Part PAR_8: An analysis of equation (10) shows the shape of .vertline.G(f&gt;0, t=0).vertline. is determined by two different undulations. The more rapid undulation occurs between much smaller frequency intervals, and is determined by the cosine function in the denominator of the radical. The cosine function, cos 4.pi.ft, causes this denominator to vary between the values EQU [1-(T.sup.2 exp(-2H.sub.0))].sup.2, and [1+(T.sup.2 exp(-2H.sub.0))].sup.2
Part PAL_2: both values are perfect squares. This occurs when cos 4.pi.ft.sub.s varies between +1 and -1, for which 4.pi.ft.sub.s =n.pi. or ##EQU10## where .DELTA.f.sub.s is the smaller frequency interval for the more rapid undulation. The numerator inside the radical also varies between EQU [1-(T exp(-2H.sub.2))].sup.2, and [1+(T exp(-2H.sub.2))].sup.2
Part PAL_3: but with a frequency of ##EQU11## where .DELTA.f.sub.s is the frequency of the slower undulation. Solving equations (11) and (12) for l.sub.1 and l.sub.2 respectively it is determined: ##EQU12## By measuring the frequency intervals, .DELTA.f.sub.s and .DELTA.f.sub.2, one can determine an average thickness of a ground substance, l.sub.2 and the cluster of substantive cells, l.sub.1.
Part PAR_9: The plot of equation (10) reveals a series of maximum and minimum values. One can trace the envelopes of the relative maxima and minima by noting the occurrence when cos 4.pi.ft.sub.s =+1 and -1, respectively ##EQU13## For a given frequency, f.sub.1 (e.g. at a maximum for .vertline.G.sub.upper (f.sub.1, t=0).vertline.) the ratio, ##EQU14## Solving for T.sup.2 gives ##EQU15## where .epsilon. is the ratio of maximum envelope to minimum envelope. Using data measurements one can obtain the values of .epsilon. as a function of frequency and by curve fitting obtain values for T and H.sub.0.
Part PAR_10: In determining the collagen content in the ground substance, equation (17) is solved for and ##EQU16## is used to obtain ##EQU17## where Z.sub.1 is the acoustic impedance of the cluster of fat cells, which is assumed to be the same as the acoustic impedance of the lipids stored in the fat cell clusters. These lipids possess a measurable acoustic impedance. Combined with the experimental determination of e, Z.sub.1 and H.sub.0, Z.sub.2, the acoustic impedance of the ground substance, can be calculated. This analysis suggests a closer examination of the factors of the ground substance's acoustic impedance.
Part PAR_11: In determining the collagen and mass density [gms/cm] of tissues, the published values of the mass density of pure collagen varies from 1.16 to 1.33. However, collagen is only one of the many specialized molecular species found in tissues. Upon examination of the mass densities of the other constituents however it was discovered that a reasonable mass density model for ultrasonic applications is essentially a two-component mixture comprised of collagenous and other materials. Using the definition of mass density and further assuming that the collagen fiber diameters are smaller than the ultrasonic wavelength in the tissue it can be written ##EQU18## where C is the wet weight percent of collagen, .rho..sub.1 is the density of the non-collagenous material in the tissue and .rho..sub.2 is the density of the collagenous material.
Part PAR_12: The sound velocity in a mouse tail tendon fibers has been reported to be 1.733+0.056.times.10.sup.5 cm/sec (Goss and O'Brien, Journal of Acoustical Society of America, Vol. 65, pages 507-511; 1979). Tendon collagen is 30% wet weight. O'Brien (in "Proceedings Ultrasonic International 77", IPC Science and Technology Press, Guildford, England, pages 194-205; 1977) has empirically determined that the velocity of sound in tissue, c, depends upon the percent wet weight of collagen in the tissue's composition, C, according to the following relation EQU c=(1.588+0.032 log.sub.e C).times.10.sup.5 cm/sec (20)
Part PAR_13: The acoustic impedances are calculated to be ##EQU19## The measurement and analysis technique gives Z.sub.2. With equation (21) it is possible to determine the weight percent of collagen in the ground substance in-vivo if the density is known of the collagen fibers. But the density of collagen fibers depends in part on the health and nutrition of the patient. This makes the value of Z.sub.2 a potentially good indicator of tissue health with the larger values of Z.sub.2 indicating more and better grade collagen in the ground substance. By assuming a reasonable range of values for the collagen fiber density the determination gives a range of values for the weight percent of collagen in tissues in-vivo. The linkage is the degradation of the mechanical properties of these tissues is directly involved with the failure of the tissue's mechanical properties. That connection is the weight percent of collagen and the collagen's density (the higher the density, the better its structural properties) in the ground substance.
Part PAR_14: Using a curve fitting algorithm for the experimentally determined quantity ##EQU20## Both T.sub.2 and H.sub.0 can be determined by solving the equation ##EQU21## where H is .alpha..sub.1 l.sub.1 +.alpha..sub.2 l.sub.2. Since l.sub.1 and l.sub.2 are determined according to equations 13(a), 13(b) and .alpha..sub.1 can be estimated from scattering and absorption of ultrasonic waves by fat cells, one can determine .alpha..sub.2 ##EQU22## which can be measured as a function of frequency. This information can be used to assess the quality of collagen fibers and the areal density of the fiber network (weave) in the ground substance. A correlation with invasive measurements and to a lesser extent to in vitro measurements will permit the best estimates of these quantities.
Part PAR_15: In this manner, it is clear that more than a broad classification of healthy or unhealthy can be realized for smaller regions of interest. Most significantly, a diagnosis for the development of pressure ulcers can be facilitated through the use of this invention.
Part PAR_16: It is specifically intended that the present invention not be specifically limited to the embodiments and illustrations contained herein, but embrace all such modified forms thereof as come within the scope of the following claims.


{'bibliographic_information': "{'Patent Number': '060074892', 'Series Code': '9', 'Application Number': '0714526', 'Application Type': '1', 'Art unit': '377', 'Application Filing Date': '19980421', 'Title of Invention': 'Method of and apparatus for histological human tissue characterization using ultrasound', 'Issue Date': '19991228', 'Number of Claims': '14', 'Exemplary Claim Number(s)': '1', 'Primary Examiner': 'Jaworski; Francis J.', 'Number of Drawing Sheets': '5', 'Number of figures': '5'}", 'source_file': './grant/1999/pftaps19991228_wk52.txt', 'source_data': 'USPTO-Grant'}