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

Abstract

Aims: Integrated backscatter (IB) and its cyclic variation (CV) derived from radio-frequency (RF) data have been used as parameters to attempt myocardial tissue characterization. Prior imaging systems used to measure IB and its CV typically acquired data at frame rates of 20-30 Hz and at a resolution of 6-8 bits. If changes in IB levels are in part related to specific short-lived events, occurring within the cardiac cycle, this frame rate and resolution could have been too low to resolve adequately what might be a more complex data set. Methods and Results:To investigate this possibility, we acquired real time two-dimensional (2D) myocardial IQ data (the 'in-phase quadrature' sampled RF data) at high frame rate (>100 Hz), high dynamic resolution (theoretical 19-bit) and a sector angle of 20 . Several consecutive heart cycles of myocardial data were acquired from individual cardiac walls in five closed chest dogs and 10 healthy, young volunteers at normal heart rates. On the reconstructed RF data regions of interest were indicated, and IB and its CV were calculated.The extracted high frame rate curves showed that the CV of IB is not a smooth sinusoidal-like curve, but is made up of multiple reproducible peaks and troughs with local minima and maxima which are temporally related to active or passive mechanical events, i.e. systolic contraction, early ventricular relaxation and ventricular filling due to atrial contraction. Conclusions:This study shows that increasing the rate of real-time RF data acquisition results in a more complex, reproducible IB curve. The resolved maxima and minima in IB levels are related to specific phases of the myocardial contraction. Furthermore, spectral analysis showed that IB curves acquired at normal heart rates contain information up to 40 Hz. Hence, cardiac imaging data sets used to analyse regional myocardial function obtained at frequencies lower than 80 frames per second can contain aliased information.

Measurements of the anisotropy of ultrasonic attenuation in freshly excised myocardium

“…For example, by accounting for myocardial attenuation, the well-known phenomenon of drop out in the lateral and septal walls in parasternal short-axis echocardiographic views of the heart can be mitigated in studies of wall motion and estimates of ventricular volume ͑Aygen and Popp, 1987;Holland et al, 1998;Melton and Skorton, 1983;Perez et al, 1992;Recchia et al, 1993͒. In addition, quantitative characterization of cardiac tissue through analyses of the apparent backscatter are influenced by attenuation. The cyclic variation of myocardial backscatter has shown promise as a diagnostic tool ͑Barzilai et Castaldo et al, 2000;Ciliberto et al, 1996;Colonna et al, 1999;D'Hooge et al, 2000;Di Bello et al, 2001;Finch-Johnston et al, 2000;Goens et al, 1996;Hancock et al, 2002;Holland et al, 2004;Kovacs et al, 2004;Mottley et al, 1984;Naito et al, 1994;Ohara et al, 2005;Pasquet et al, 1998;Pislaru et al, 2001;Rijsterborgh et al, 1993;Sagar et al, 1990;van der Steen et al, 1997;Vandenberg et al, 1991;Vered et al, 1989;Wickline et al, 1986;Yuda et al, 2002͒. However, measurements of the cyclic variation of "apparent" integrated backscatter ͑uncompen-sated for the effects of attenuation͒ are influenced by both the attenuation of overlying tissue as well as that occurring in the region-of-interest. Recent steps have been taken with excised, formalin-fixed tissue toward the goal of measurement of myocardial attenuation in vivo using two-dimensional B-mode images ͑Baldwin et Sosnovik et al, 2001a;Sosnovik et al, 2001b͒ andM-mode ͑Baldwin et al, 2005;Baldwin et al, 2004͒.…”

Assessment of Fetal Myocardial Deformation Using Speckle Tracking Techniques

“…At least 60–110 frames per second are recommended when imaging the adult heart [13,39,40], and even higher rates are desirable to provide enough frames per heart beat in the fetus [12]. The frame rate is optimized by using the narrowest possible ultrasound field and avoiding multiple focal zones during image acquisition.…”

Echocardiographic integrated backscatter for detecting progression and regression of aortic valve calcifications in rats

“…Aortic valve calcification is rather regarded as a categorical variable with the current qualitative methodology [19]. However, by analyzing backscatter reflections generated by the interaction of ultrasound with small tissue structures, it is possible to quantitatively extract information related to the valve’s composition [12,20,21]. IB has previously been extensively validated in the myocardium as a surrogate marker of fibrosis and for the differentiation of atherosclerotic lesions [22,23].…”