[Quantitative integrated backscatter characteristics in the normal and infarcted canine myocardium].

Abstract

To develop ultrasonic cardiac tissue characterization, serial changes in intensity of backscattered ultrasound from the normal and infarcted myocardium were studied in vitro, with frequency-domain analysis. As an index of backscattered signal intensity, quantitative integrated backscatter [(10 X log-S2/S1)] (dB), S1 and S2 = areas of power spectra of digitized (sample rate = 100 MHz, 8 bits) ultrasonic signals from a perfect reflector and good specimens) were calculated for 60 regions of the myocardium (N = 20, MI = 40) excised from 10 dogs 3 days, 1, 2, and 4 weeks after coronary artery ligation in 2, 3, 3, and 2 dogs, respectively. The myocardial specimens and a stainless steel reflector were mounted at the focal distance of a newly-developed wide-band transducer having a center frequency of 4.0 MHz, in a water bath filled with degassed physiological saline. Tissue concentrations of hydroxyproline (HP) were also established using a HPLC (Hitachi amino acid analyzer model 835). The results obtained were as follows: 1. No significant changes in the integrated backscatter of the normal myocardium were observed throughout the experimental period (3 days = -52.5 +/- 0.7, one week = -53.6 +/- 1.8, two weeks = -51.6 +/- 0.8, four weeks = -52.8 +/- 1.4 (dB) (mean +/- SE). 2. Integrated backscatter of the infarcted myocardium [3 days = -47.3 +/- 0.6, one week = -49.2 +/- 1.3, two weeks = -40.7 +/- 1.3, four weeks = -39.6 +/- 2.0 (dB)] was significantly increased compared with the integrated backscatter of the normal myocardium in the early stage of myocardial infarction, before tissue concentrations of hydroxyproline increased, as well as in the chronic stage of myocardial infarction. 3. Results of histological examinations suggest that minute changes in structure, such as interstitial edema or neovascular proliferations, may be the cause of an early increase in integrated backscatter. The results suggest that quantitative integrated backscatter is a sensitive parameter for detecting both early and old myocardial infarction by cardiac tissue characterization.