INFLUENCE OF ATTENUATION ON MEASUREMENTS OF ULTRASONIC MYOCARDIAL INTEGRATED BACKSCATTER DURING CARDIAC CYCLE (AN INVITRO STUDY)

The purpose of this study was to investigate the dependence of ultrasonic integrated backscatter (IB) and attenuation in myocardium on wall thickness in a state of acute ischemia. Therefore, an in vitro experiment was set up in which attenuation, IB and wall thickness of a piece of freshly excised myocardium could be measured almost simultaneously. The myocardium was taken from 11 Yorkshire pigs (25-30 kg) that were killed less than 45 min before the experiment. The myocardium was placed in the far field of an ultrasound transducer (3.2-7.2 MHz) and then compressed by a stainless steel sphere. Data were processed off-line. Backscatter and attenuation were also measured as a function of frequency at 100% and 75% wall thickness, respectively. Both attenuation and IB varied during compression. Attenuation had an initial value of 2.19 +/- 0.76 dB/cm and a slope of 0.015 +/- 0.017 dB/cm% wall thickness. IB had an initial value of -76.9 +/- 2.7 dB and a slope of -0.12 +/- 0.07 dB/% wall thickness. After subtracting the influence of the attenuation from the IB the initial value of IB was -74.0 +/- 2.7 dB and the slope -0.08 +/- 0.07 dB/% wall thickness. Attenuation appeared to have a linear dependency on frequency. Backscatter appeared not to increase with increasing frequency without correction of the spectrum for the frequency dependent insonified volume.