Monitoring of myocardial edema with quantitative ultrasonic parametric imaging

Myocardial edema is associated with impaired ventricular compliance and diastolic dysfunction. To determine the sensitivity of high-frequency ultrasound to myocardial edema, we employed a model in which edema was induced by immersion of heart tissue in isotonic saline. Formation of edema after rapid-freezing and thawing of myocardium was also evaluated. Rat hearts were arrested at end-diastole and insonified fresh within 15 minutes of excision (n=5) or after being frozen for 24 hours and thawed (n=4). A high-frequency, acoustic microscope was employed to perform ultrasonic measurements of attenuation, backscatter, speed of sound, and tissue thickness at baseline and hourly for 4 hours while immersed in solution. Parametric images of these ultrasonic indices were constructed to monitor changes in microscopic material properties due to edema and to allow identification of localized regions of interest. Fresh tissue demonstrated a greater propensity for the development of edema than frozen tissue. Integrated backscatter increased in both tissues while the magnitude and slope of attenuation decreased as edema evolved. We conclude that high-frequency ultrasound sensitively detects myocardial edema and may prove useful for monitoring and treatment of cardiac edematous disease states.