Ultrasound characterization of coronary artery wall in vitro using temperature-dependent wave speed
Temperature dependence of the speed of sound, /spl part/c//spl part/T, is examined as a parameter to characterize tissue-equivalent phantoms and coronary artery tissue in vitro. The experimental system comprises an ultrasound biomicroscope, operating at center frequency of 50 MHz, and a temperature controlled micropositioning sample cell. Radio frequency (RF) backscattered signals were recorded, with a digital oscilloscope, from 64 independent positions and at 5 temperatures starting at 31/spl deg/C (phantom) and 36/spl deg/C (tissue) in steps of one degree. Time shift per degree Celsius (/spl part/t//spl part/T) was obtained with a correlation technique applied between gated sections of two RF-signals collected with one degree temperature difference from the same location in the sample. The average , calculated for every position of the gated sections along the propagation axis of the ultrasound beam, has the slope proportional to the difference between the linear coefficient of thermal expansion and the thermal sensitivity of the speed of sound. Calibration measurements of /spl part/c//spl part/T, made with single- and three-layer tissue equivalent phantoms, correlated well (r/spl ges/0.91) with those measured by the time-of-flight substitution method. The /spl part/c//spl part/T was estimated for the three layers on the wall of eight samples of human coronary arteries, obtained at autopsy from four individuals. The /spl part/c//spl part/T for the intima layers decreases as the disease progresses from mild intimal thickening to a more advanced atherosclerosis.