A FEASIBILITY STUDY ON QUANTITATING MYOCARDIAL PERFUSION WITH ALBUNEX(R), AN ULTRASONIC CONTRAST AGENT

Quantitating regional myocardial perfusion has been the much sought-af ter but still elusive goal of many intensive investigations over the y ears. Videodensitometry of the variation of myocardial echogenicity in two-dimensional (2-D) echocardiograms as a function of time in conjun ction with the injection of a bolus of an ultrasound contrast agent ha s been used clinically as a tool for a direct assessment of regional m yocardial perfusion, despite that the precise relationship between tis sue echogenicity observed on an image and the echoes detected by the u ltrasonic probe is unknown. A study was undertaken to determine whethe r ultrasonic backscatter calculated from unprocessed radio frequency ( RF) echoes returned from myocardium could be used to quantitate region al myocardium perfusion. A real-time ultrasonic scanner has been modif ied and interfaced to a microcomputer to acquire RF data at a rate up to 10 frames per second. Preliminary experimental data were obtained f rom four open-chest dogs following intracoronary injection of a bolus of Albunex(R) and two dogs following intravenous injection with this m odified scanner. On one hand, these results indicate that the integrat ed backscatter measured from the region of myocardium perfused by the coronary artery where Albunex(R) is injected and selected for monitori ng initially increases, reaches a peak, and then decreases as the cont rast agent is washed out and that the magnitude of the peak is approxi mately linearly proportional to the volume concentration of Albunex(R) microspheres injected, clearly demonstrating the feasibility of this approach for quantitating region myocardial perfusion. On the other ha nd, intravenous injections did not result in any appreciable change in myocardial backscatter in the left ventricle although a response coul d be observed in the left ventricular blood pool.