Ultrasonic tissue characterization: detection of acute myocardial ischemia in dogs.

Abstract

Ultrasonic tissue characterization is a new area of investigation in the field of cardiac ultrasound. The amplitude and frequency of the ultrasound signal are normally altered as the signal penetrates through tissue. It is assumed that the amplitude distribution and frequency shift of diseased or edematous tissue are different than those of normal tissue. A statistical approach to the analysis of the unprocessed radiofrequency signal in the amplitude domain was used to study the effect of acute myocardial ischemia on the parameter mean amplitude/standard deviation of the amplitude (MSR). Ten dogs were anesthetized and underwent left lateral thoracotomy. Baseline mean MSR from the interventricular septum was 1.99 + 0.05, but increased by 30 min after coronary artery occlusion and started to plateau at 1 hr (mean 2.24 + 0.06). Reproducibility in noninfarcted myocardium (left ventricular inferoposterior wall) was good, with a mean MSR of 2.00 + 0.05 at baseline and 1.98 0.04 3 to 4 hr later. There was no difference in mean MSR when data were obtained through chest wall and when they were obtained directly from the surface of the heart. We conclude that statistical analysis in the amplitude domain of the unprocessed radiofrequency signal can detect acute myocardial ischemia within 30 min after coronary artery occlusion, provides reproducible measurements, and is unaffected by chest wall filtering. Circulation 72, No. 1, 193-199, 1985. DETECTION OF early acute myocardial ischemia in man is currently suboptimal. The electrocardiogram may not always reveal acute ischemia because it may demonstrate only nonspecific changes. The technetium pyrophosphate scintigram usually requires a delay of 24 hr before it can be interpreted as positive for myocardial injury. The information obtained from serum creatine kinase-MB levels is also delayed. A history of angina pectoris may be the only evidence of ongoing myocardial infarction in these patients. It would be highly desirable to have a noninvasive tool available for diagnosis and localization of early acute myocardial injury.Echocardiography has traditionally been used as an imaging device. Recent work by several investigators suggests that interactions between the ultrasound energy and tissue can be analyzed to characterize the histologic state of tissue, both in vitro1' 2 and in vivo.36

Fundamental correlation lengths of coherent speckle in medical ultrasonic images

“…This would derive from a temporal PSF whose square is given by (23) WAGNER et al Page 11 The Fourier transform of this function is a triangle and its square is the parabolic shape whose right half is given in Fig. 7.…”

“…From the preceding discussion it would appear that either the speckle contrast (or its inverse, SNR o -see, e.g., [23]), or the speckle cell size, would serve as a tissue signature corresponding to the value of the specular to diffuse scattering ratio r. This is only true, however, when there are very many diffuse scatterers per resolution cell. We now consider the case where this number decreases toward zero.…”

“…When this component is peeled away, leaving the steady or average level of the specular component, the techniques of the previous section and the calibration described above in this section may be applied rigorously. (Without this step the results are open to ambiguous interpretations, as in [19], [23]). When this calibration is measured, it will be possible to obtain measures of the specular/diffuse scattering ratio and the density of diffuse scatterers from the analysis of the statistics of the speckle texture described here.…”

<b>Dipyridamole Stress Echocardiography and Ultrasonic Myocardial Tissue Characterization in Predicting Myocardial Ischemia, in Comparison With Dipyridamole Stress Tc-99m MIBI SPECT Myocardial Imaging</b>

“…CVIBS is blunted promptly by ischemia and is augmented after reperfusion in animals and humans. 25,[29][30][31] Lin, et al 32) found that the cut-off value was 2.0 db in predicting reversible myocardial dyssynergy after revascularization. Vitale, et al 33) showed that the maximum-minimum difference of the integrated backscatter (CVIBS) was reduced significantly by stress in the septum (4.6 ± 0.9 versus 2.7 ± 0.8) (difference, 1.9 db).…”

High Frame Rate Myocardial Integrated Backscatter. Does this Change our Understanding of this Acoustic Parameter?

“…This implies that IB is a measure of the mean reflected ultrasonic energy from a particular region of tissue [4] . The aspect of myocardial tissue characterization which has aroused most interest has been the potential predictive value of the cyclic variation (CV) of IB for determining myocardial viability, initially described in vivo in animal models [5][6][7][8][9] . This work has also been reproduced in the clinical setting [10][11][12] .…”