774-3 Influences of Acoustic Power, TGC and Location of Region of Interest on the Measurement of Integrated Back Scatter Signal Using Acoustic Densitometry In Vivo

Abstract

To test the hypothesis that differences in transducer frequency (FR), acoustic power (AP), time gain control (TGC), and the location of myocardial region of interest (ROI) examined would influence the measurement of cyclic variation of integrated backscatter (CV/IBS) olthe heart, measurement of CV/BS were performed in vivo in the left ventricular (LV) mid-papillary short axis view of 10 open chest swine. On-line measurement of IBS was obtained using the acoustic densitometry package on the Hewlett-Packard Sonos 1500, with FR between 2.0 and 5.0 MHz, varying AP between 0 and 40 dB, TGC between o and 60 dB and with ROI placed at the anterior (ANT), inferior (INF) and posterior (POST) walls of the LV CV/\BS (dB) AP ANT INF POST TGC ANT INF POST 5 2.0 ± 0.9 1.7 ± 1.3 1.8 ± 1.0 10 17 ± 1.3 0.6 ± 0.2 0.9 ± 0.2 15 4.3 ± 1.2 2.4 ± 1.5 4.2 ± 1.5 20 3.4 ± 0.8 1.3 ± 0.6 2.9 ± 1.2 20 5.7 ± 1.4 3.2 ± 2.1 6.9 ± 1.9 ** 30 4.7 ± 12 2.6 ± 1.4 6.5 ± 1.0 ** 30 4.5 ± 1.5 5.5 ± 2.5 * 7.2 ± 1.6 * 40 4.8 ± 1.4 5.5 ± 2.3 * 7.9 ± 1.6 ** 35 3.2 ± 0.9 5.5 ± 2.1 * 7.4 ± 1.3 * 50 3.0 ± 1.3 4.2 ± 1.6 * 7.0 ± 2.0 ** 40 4.1 ± 2.1 6.4 ± 2.7 * 6.8 ± 26 60 1.9 ± 1.6 3.3 ± 0.8 4.2 ± 1.9 * p < 0.01 ** p < 0.005 vs. AP 15 dB or TGC 20 dB For varying FR between 2.0 and 5.0 MHz, CV/IBS was consistently higher for FR greater than 2.0 MHz for all ROI at fixed AP and TGC (for 2.0 MHz CV did not differ because of saturation of IBS). For varying Ap, CV/IBS was consistently higher between 20–35 dB in the POST ROI only. For varying TGC, CV/IBS also was consistently higher for 30–50 dB in the POST ROI only. AP less than 20 dB and TGC less than 30 dB produced minimal CV. AP greater than 35 dB and TGC greater than 50 dB caused image saturation. These data indicate that proper transducer selection and setting of AP and TGC, as well as an understanding of ROI, are necessary and critical for interpretation of the analysis of CWIBC in vivo .