Estimating myocardial attenuation from M-mode ultrasonic backscatter

The objective of this investigation was to determine whether measurements of myocardial attenuation can be obtained from analyses of M-mode images. We exploited the inherent anisotropy of myocardial properties as a means of systematically varying the attenuation to evaluate this M-mode image-based method for myocardial tissue characterization. A commercially available ultrasonic imaging system was used to acquire M-mode images of 24 excised cylindrical specimens from six formalin-fixed sheep hearts that were analyzed using video signal analysis. Data were compensated for the presence of bright intramural myocardial echoes, a potentially significant contributor to uncertainty in measurements of attenuation from backscattered ultrasound. The estimated attenuation coefficient in dB/cm at an effective center frequency of 2.75 MHz as a function of angle of insonification for measurements obtained from analyses of M-mode images is presented. Given a linear frequency-dependence of attenuation in myocardial tissue over frequencies ranging from 1.5 MHz to 8 MHz, as has been previously reported, M-mode image-based analyses were used to estimate the slope of attenuation. Results showed slopes of attenuation (over a −10 dB transmit bandwidth of 1.875 MHz to 3.75 MHz) ranging from 1.00 ± 0.07 to 1.81 ± 0.08 dB/(cm · MHz) for perpendicular and parallel insonification, respectively. These values were in good agreement with contemporaneously measured values (0.99 ± 0.02 to 1.77 ± 0.04 dB/(cm · MHz)) obtained over a frequency bandwidth of 4 MHz to 7 MHz using a through-transmission radio-frequency-based approach. These data suggest that robust measurements of myocardial attenuation can be obtained from analyses of M-mode images and that this method may be diagnostically feasible in the clinical setting. (E-mail: jgm@wuphys.wustl.edu)