In a study involving 10 different sites, independent results of measurements of ultrasonic properties on equivalent tissue-mimicking samples are reported and compared. The properties measured were propagation speed, attenuation coefficients, and backscatter coefficients. Reasonably good agreement exists for attenuation coefficients, but less satisfactory results were found for propagation speeds. As anticipated, agreement was not impressive in the case of backscatter coefficients. Results for four sites agreed rather well in both absolute values and frequency dependence, and results from other sites were lower by as much as an order of magnitude. The study is valuable for laboratories doing quantitative studies. KEY WORDS: Measurements; Speed; Attenuation; Backscatter; Interlaboratory comparison. n 1986 an article was published to compare measurements made of ultrasonic attenuation coefficients and propagation speeds in TM phantom materials produced at the University of Wisconsin and sent to participating laboratories. 1 To assess stability of ultrasonic properties during the study, measurements were done on those phantoms at the University of Wisconsin laboratories before and after the measurements were made at other laboratories. The same type of study, involving 10 labo-

To determine whether contraction and relaxation influence quantitative myocardial ultrasonic backscatter we measured systolic and diastolic integrated backscatter separately in 10 pentobarbital-anesthetized dogs with defined, paced heart rates, before and after coronary occlusion. Data were acquired from intramural sites by coupling a broadband 5-MHz transducer to the left ventricular epicardium. Integrated backscatter was obtained from seven sequential ECG gated intervals throughout the cardiac cycle over the frequencies of 2.5-7.5 MHz and referenced to values obtained with a steel reflector. Before coronary occlusion myocardium in all dogs exhibited a decrease in integrated backscatter from end diastole to end systole (P less than 0.05) in control zones and in zones destined to become ischemic (P less than 0.05). Thirty minutes after occlusion integrated backscatter did not change in control zones but was elevated in ischemic zones with blunting of the diastolic-to-systolic variation. Thus myocardium undergoing contraction exhibits a decrease in integrated backscatter, and measurement of integrated backscatter at end systole differentiates ischemic from normal myocardium.

To determine the feasibility of quantitative ultrasonic techniques to define the composition of atherosclerotic plaques, samples of freshly excised human aortas were sewn to a sample holder and immersed in a saline bath for ultrasonic interrogation. Integrated backscatter of a 2-microsecond portion of the backscattered radiofrequency signal was measured with a 10 MHz focused transducer. A noninvasive, quantitative method is needed for ultimate application to longitudinal assess-L ment of the temporal evolution of atherosclerosis and the efficacy of therapy designed to retard or reverse atherogenesis. Although conventional ultrasonic methods are suitable for characterization of flow patterns and dimensions of vessels (pulsed and continuous Doppler and B-mode ultrasound), 1 -2 they do not characterize structural alterations of the vessel wall such as fibrosis, calcification, or deposition of lipid. Furthermore, quantification of present B-mode ultrasonic images lacks standardization and is hampered by subjectivity with which gain and energy settings are selected by the operator.We have shown that selected quantitative ultrasonic indexes can identify structural features of tissue manifesting diverse pathophysiological processes.3 For example, integrated backscatter, a measure of the energy efficiency of acoustic backscatter from a tissue sample, readily differentiated acutely ischemic. from normal myocardium. 4 In addition, backscatter analysis identified focal scarring and calcification in myocardium from cardiomyopathic Syrian hamsters.5 Thus, integrated backscatter provides a sensitive index of altered tissue structure.Because it entails reflected rather than transmitted ultrasound, integrated backscatter can be utilized to evaluate the physical properties of arterial walls in a

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The purpose of this investigation was to determine the angular dependence of the backscatter from canine myocardial tissue in vivo and to compare it with the variation of backscatter over the cardiac cycle that has been recognized and reported previously. The backscatter was measured from regions of left ventricular wall in canine hearts in which the fibers of the muscle lay parallel to the surface of the heart and were oriented predominantly in a circumferential fashion. Because of technical considerations, the angle of insonification was varied systematically through two cycles in which the angle relative to the muscle fiber axes ranged from 60 degrees-120 degrees. Backscatter was maximum at angles of interrogation perpendicular to the myocardial fibers and minimum at those most acute (60 degrees) relative to the orientation of the fibers. The previously observed variation of integrated backscatter over the heart cycle was evident at each angle of interrogation. At end systole, the average maximum-to-minimum angular variation of integrated backscatter as 5.0 +/- 0.4 dB. At end diastole, the average maximum-to-minimum angular variation was 3.2 +/- 0.4 dB. Thus, even though angular dependence of the backscatter from tissues with directionally oriented structures is substantial, the anisotropy does not account for cardiac-cycle-dependent variation of backscatter. Accordingly, the angular dependence should be incorporated in approaches to quantitative tissue characterization with ultrasound.