Quantitative evaluation of local myocardial blood volume in contrast echocardiography

Abstract

Myocardial perfusion is usually assessed by Single Photon Emission Computed Tomography (SPECT) imaging. Information about myocardial perfusion is sometimes deduced from angiography or Computed Tomography (CT) angiography, which detect coronary artery stenosis. Contrast echocardiography can be used for that purpose as well. However, the currently available data acquisition and analysis methods are difficult to manage in the clinical environment. This paper presents a novel contrast echo data acquisition protocol and parameter extraction procedure, providing an automatic quantitative evaluation of the local myocardial blood volume for the entire left ventricular myocardium. This information is indicative of local perfusion. Our method evaluates the myocardial blood volume according to the local gray level intensity, as measured during a single heartbeat, when there is a distinct myocardial opacification (based on visual estimation). The echocardiographic image analysis is based on a new attenuation correction technique, which compensates for the ultrasonic signal attenuation in both the tissue and the contrast agent. In comparison, the existing contrast echo based methods utilize the long-term temporal variability of the gray level to extract information regarding the local myocardial blood flow velocity. Our technique has been tested on 17 cine-loops of 15 different patients. We have found a high correlation between abnormal segments, detected automatically by our technique, and segments that have been clinically diagnosed as ischemic (at rest) or infarcted. For that purpose, we have defined ischemic segments as segments fed by coronary arteries with severe stenosis, as determined by angiography, and infarcted segments as segments after Acute Myocardial Infarction, as detected by electrocardiography. Furthermore, we have found a high correlation between the automatically calculated myocardial blood volume levels and the clinical evaluation of segmental contractility, based on echocardiographic imaging.