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In vivo measurement of sound velocity in liver by pulse-echo techniques
ABSTRACTS.
These
tories niques topics will
ULTRASONIC
IMAGING
AND TISSUE
CHARACTERIZATION
SYMPOSIUM
will be presented. Possible differences due to the various will be emphasized. be opened for discussion by the panel members and audience. SESSION
1:
ULTRASONIC
tech-
PARAMETERS
IN LIVER BY PULSE-ECHO TECHNIQUFS, L. S. Wilson, --IN VIVO MEASUREMENT OF SOUND VELOCITY C. F. Chen and D. E. Robinson, Ultrasonics Institute, 5 Hickson Road, Millers Point, NSW 2000, Australia. The velocity of sound in tissue may be determined by measuring the amount --in vivo of misregistration between simultaneous pulse-echo images of the same target scanned from different directions. Because this technique does not require through transmission, it may be applied to any organ which may be imaged by pulse echo techniques [I]. The amount of shift between the two images is up to 3 mm, or 7 pixels in a 512 x 512 pixel reconstruction. This shift is measured by a cross-correlation technique, and requires a suitable target such as a bile duct or vessel in the liver. The accuracy of the technique is affected by refraction out of the nominal plane of the echogram as also occurs in ultrasound CT velocity imaging. In abdominal measurements, this is minimized by ensuring that the normal to the skin lies in the scan plane. Analysis has shown the maximum expected error to be small compared with the velocity changes associated with pathology. Normal and pathological livers have been examined using this technique. The average velocity in normal liver is 1582 + 9 m s-l. Cirrhotic livers show a reduced velocity (1530 m s-l), solid primary hepatic tumours have a slightly reduced velocity (1550 m s-l) while metastases show slightly increased velocity. As the clinical trial is continuing, further results will be presented at the meeting. [I] Robinson, D. E., Chen, F. and Wilson, L., Ultrasound Med. Biol. 8, 413-420 (1982). --A CROSSED BEAM METHOD FOR ULTRASONIC SPEED MEASUREMENT IN TISSUE, D. J. Haumschild and J. F. Greenleaf, Department of Physiology and Biophysics, Biodynamics Research Unit, Mayo Clinic, Rochester, MN 55905. Many studies have dealt with the characterization of tissues on the basis of attenuation measurements. Although these parameters are important, speed characterization has not been utilized to full potential. Traditionally, ultrasonic speed measurements in soft tissue have been constrained by the necessity of axial alignment of the trasmitter and receiver. This works well in the breast where there is ready access to specific tissue. Refraction, mostly by intervening bony structures, prevents or severely limits accurate velocity measurements elsewhere in the body. This study was designed to allow accurate acoustic speed measurement of --in viva specific tissue by use of planar, angularly-aligned transducer arrangements. As ultrasonic beam profiles exhibit a Gaussian-like configuration, it is proposed that tissue acoustic speeds can be predicted by calculating the center of gravity (time) of beams of a transmitter/ the energy scattered from the intersection of the crossed receiver pair of transducers. Distance is calculated using simple geometry. Initial modeling for precision and accuracy was conducted in a heated water bath (lo-50 "C) The center of gravity of the intersecusing circulating microbubbles as reflectors. In water, ting volume was calculated from the digitized scans of up to 5,000 pulses. measurements were carried out the SEM of the measurement was fO.O1 ns, 20 OC. Tissue To check the accuracy of the at 40 OC on 20 samples of fresh human liver specimens. samples of each liver were also examined using axiallycrossed beam measurements, The scattering profile in tissue was defined by rocking the two aligned transducers. intersecting beams such that reflectors within the tissue continually move through the A proposed system is discussed such that for --in vivo examiintersecting beam volume. the crossed beam transducer orientation may be used for specific tissue speed nations, regardless of overlying structures. characterization, This work was supported by WIH, grant no. HL-04664. COMPARISON OF TWO PHASE-INDEPENDENT TECHNIQUES FOR TRANSMISSION ATTENUATION IMAGING USING AN ARRAY RECEIVER, R. M. Schmitt, C. R. Meyer, P. L. Carson, T. L. Chenevert, and Peyton H. Bland, Department of Radiology, University of Michigan School of Medicine and Hospitals, Ann Arbor, MI 48109. attenuation ultrasonic computed The use of a receiving array for quantitative tomography of the female breast was evaluated. 2.25 MHz experimental array having a single element aperture Of 1.2 A 46 element, Digitized transspacing of 1.4 mm was employed. x 1.2 mm* and a center-to-center mission signals were collected from a refractive (4% and a non-refractive breast
168
These
tories niques topics will
ULTRASONIC
IMAGING
AND TISSUE
CHARACTERIZATION
SYMPOSIUM
will be presented. Possible differences due to the various will be emphasized. be opened for discussion by the panel members and audience. SESSION
1:
ULTRASONIC
tech-
PARAMETERS
IN LIVER BY PULSE-ECHO TECHNIQUFS, L. S. Wilson, --IN VIVO MEASUREMENT OF SOUND VELOCITY C. F. Chen and D. E. Robinson, Ultrasonics Institute, 5 Hickson Road, Millers Point, NSW 2000, Australia. The velocity of sound in tissue may be determined by measuring the amount --in vivo of misregistration between simultaneous pulse-echo images of the same target scanned from different directions. Because this technique does not require through transmission, it may be applied to any organ which may be imaged by pulse echo techniques [I]. The amount of shift between the two images is up to 3 mm, or 7 pixels in a 512 x 512 pixel reconstruction. This shift is measured by a cross-correlation technique, and requires a suitable target such as a bile duct or vessel in the liver. The accuracy of the technique is affected by refraction out of the nominal plane of the echogram as also occurs in ultrasound CT velocity imaging. In abdominal measurements, this is minimized by ensuring that the normal to the skin lies in the scan plane. Analysis has shown the maximum expected error to be small compared with the velocity changes associated with pathology. Normal and pathological livers have been examined using this technique. The average velocity in normal liver is 1582 + 9 m s-l. Cirrhotic livers show a reduced velocity (1530 m s-l), solid primary hepatic tumours have a slightly reduced velocity (1550 m s-l) while metastases show slightly increased velocity. As the clinical trial is continuing, further results will be presented at the meeting. [I] Robinson, D. E., Chen, F. and Wilson, L., Ultrasound Med. Biol. 8, 413-420 (1982). --A CROSSED BEAM METHOD FOR ULTRASONIC SPEED MEASUREMENT IN TISSUE, D. J. Haumschild and J. F. Greenleaf, Department of Physiology and Biophysics, Biodynamics Research Unit, Mayo Clinic, Rochester, MN 55905. Many studies have dealt with the characterization of tissues on the basis of attenuation measurements. Although these parameters are important, speed characterization has not been utilized to full potential. Traditionally, ultrasonic speed measurements in soft tissue have been constrained by the necessity of axial alignment of the trasmitter and receiver. This works well in the breast where there is ready access to specific tissue. Refraction, mostly by intervening bony structures, prevents or severely limits accurate velocity measurements elsewhere in the body. This study was designed to allow accurate acoustic speed measurement of --in viva specific tissue by use of planar, angularly-aligned transducer arrangements. As ultrasonic beam profiles exhibit a Gaussian-like configuration, it is proposed that tissue acoustic speeds can be predicted by calculating the center of gravity (time) of beams of a transmitter/ the energy scattered from the intersection of the crossed receiver pair of transducers. Distance is calculated using simple geometry. Initial modeling for precision and accuracy was conducted in a heated water bath (lo-50 "C) The center of gravity of the intersecusing circulating microbubbles as reflectors. In water, ting volume was calculated from the digitized scans of up to 5,000 pulses. measurements were carried out the SEM of the measurement was fO.O1 ns, 20 OC. Tissue To check the accuracy of the at 40 OC on 20 samples of fresh human liver specimens. samples of each liver were also examined using axiallycrossed beam measurements, The scattering profile in tissue was defined by rocking the two aligned transducers. intersecting beams such that reflectors within the tissue continually move through the A proposed system is discussed such that for --in vivo examiintersecting beam volume. the crossed beam transducer orientation may be used for specific tissue speed nations, regardless of overlying structures. characterization, This work was supported by WIH, grant no. HL-04664. COMPARISON OF TWO PHASE-INDEPENDENT TECHNIQUES FOR TRANSMISSION ATTENUATION IMAGING USING AN ARRAY RECEIVER, R. M. Schmitt, C. R. Meyer, P. L. Carson, T. L. Chenevert, and Peyton H. Bland, Department of Radiology, University of Michigan School of Medicine and Hospitals, Ann Arbor, MI 48109. attenuation ultrasonic computed The use of a receiving array for quantitative tomography of the female breast was evaluated. 2.25 MHz experimental array having a single element aperture Of 1.2 A 46 element, Digitized transspacing of 1.4 mm was employed. x 1.2 mm* and a center-to-center mission signals were collected from a refractive (4% and a non-refractive breast
168