Soroosh Firoozan

Quantification of Myocardial Blood Flow With Ultrasound-Induced Destruction of Microbubbles Administered as a Constant Venous Infusion

BACKGROUND Ultrasound can cause microbubble destruction. If microbubbles are administered as a continuous infusion, then their destruction within the myocardium and measurement of their myocardial reappearance rate at steady state will provide a measure of mean myocardial microbubble velocity. Conversely, measurement of their myocardial concentration at steady state will provide an assessment of microvascular cross-sectional area. Myocardial blood flow (MBF) can then be calculated from the product of the two. METHODS AND RESULTS Ex vivo and in vitro experiments were performed in which either flow was held constant and pulsing interval (interval between microbubble destruction and replenishment) was altered, or vice versa. In vivo experiments were performed in 21 dogs. In group 1 dogs (n=7), MBF was mechanically altered in a model in which coronary blood volume was constant. In group 2 dogs (n=5), MBF was altered by direct coronary infusions of vasodilators. In group 3 dogs (n=9), non-flow-limiting coronary stenoses were created, and MBF was measured before and after the venous administration of a coronary vasodilator. In all experiments, microbubbles were delivered as a constant infusion, and myocardial contrast echocardiography was performed using different pulsing intervals. The myocardial video intensity versus pulsing interval plots were fitted to an exponential function: y=A(1-e[-betat]), where A is the plateau video intensity reflecting the microvascular cross-sectional area, and beta reflects the rate of rise of video intensity and, hence, microbubble velocity. Excellent correlations were found between flow and beta, as well as flow and the product of A and beta. CONCLUSIONS MBF can be quantified with myocardial contrast echocardiography during a venous infusion of microbubbles. This novel approach has potential for measuring tissue perfusion in any organ accessible to ultrasound.

Basis for detection of stenosis using venous administration of microbubbles during myocardial contrast echocardiography: bolus or continuous infusion?

OBJECTIVES This study sought to determine the basis of detection of stenosis by myocardial contrast echocardiography using venous administration of microbubbles and to define the relative merits of bolus injection versus continuous infusion. BACKGROUND The degree of video intensity (VI) disparity in myocardial beds supplied by stenosed and normal coronary arteries can be used to quantify stenosis severity after venous administration of microbubbles. However, the comparative merits of administering microbubbles as a bolus injection or continuous infusion has not been studied. METHODS Coronary stenoses of varying severity were created in either the left anterior descending or the left circumflex coronary artery in 18 dogs. Imagent US (AF0150) was given as a bolus injection in 10 dogs (Group I) and as both a bolus injection and a continuous infusion in 8 dogs (Group II). For bolus injections, peak VI was derived from time-intensity plots. During continuous infusion, microbubble velocity and microvascular cross-sectional area were derived from pulsing interval versus VI plots. Myocardial blood flow (MBF) was determined using radiolabeled microspheres. RESULTS During hyperemia, VI ratios from the stenosed versus normal beds correlated with radiolabeled microsphere-derived MBF ratios from those beds for both bolus injections (r = 0.81) and continuous infusion (r = 0.79). The basis for detection of stenosis common to both techniques was the decrease in myocardial blood volume distal to the stenosis during hyperemia. The advantage of continuous infusion over bolus injection was the abolition of posterior wall attenuation and the ability to quantify MBF. CONCLUSIONS Both bolus injection and continuous infusion provide quantitative assessment of relative stenosis severity. Compared with bolus injection, continuous infusion also allows quantification of MBF and data acquisition without attenuation of any myocardial bed.

Three-dimensional myocardial contrast echocardiography : Validation of in vivo risk and infarct volumes

OBJECTIVES The aim of this study was to determine whether three-dimensional (3D) myocardial contrast echocardiography (MCE) could provide an accurate in vivo assessment of risk and infarct volumes. BACKGROUND MCE has been shown to accurately define risk area and infarct size in single tomographic slices. The ability of this technique to measure risk and infarct volumes by using three-dimensional echocardiography (3DE) has not been determined. METHODS Fifteen open chest dogs underwent variable durations of coronary artery occlusion followed by reperfusion. At each stage, MCE was performed by using left atrial injection of AIP201, a deposit microbubble with a mean diameter of 10 +/- 4 microm and a mean concentration of 1.5 x 10(7) x ml(-1). Images were obtained over a 180 degree arc with use of an automated rotational device and were stored in computer as a 3D data set. Postmortem risk area and infarct size were measured in six to eight left ventricular short-axis slices of equal thickness using technetium-99m autoradiography and tissue staining, respectively. MCE images corresponding to these planes were reconstructed off-line. RESULTS A close linear relation was noted between the volume of myocardium not showing contrast enhancement on 3D MCE during coronary occlusion and postmortem risk volume (y = 1.2x - 3.0, r = 0.83, SEE = 5.1, n = 15). The volume of myocardium not showing contrast enhancement on 3D MCE after reperfusion also closely correlated with postmortem infarct volume (y = 1.1x - 3.9, r = 0.88, SEE = 4.8, n = 11). No changes in systemic hemodynamic variables were noted with injections of AIP201. CONCLUSIONS When combined with AIP201, a deposit microbubble, 3D MCE can be used to accurately determine both risk and infarct volumes in vivo. This method could be used to assess the effects of interventions that attempt to alter the infarct/risk volume ratio.

Incremental value of cardiac imaging in patients presenting to the emergency department with chest pain and without ST-segment elevation: A multicenter study

BACKGROUND We hypothesized that imaging of regional myocardial function (RF) and perfusion (PER) will add incremental value for both diagnosis and short-term prognosis to routine demographic, clinical, and electrocardiographic findings in patients presenting to the emergency department (ED) with chest pain and without ST-segment elevation on the electrocardiogram. METHODS We compared contrast echocardiography (CE) with gated single-photon emission computed tomography (SPECT) for this purpose. Both CE and SPECT readings included separate and composite assessments of both RF and PER. Adverse events in the first 48 hours after ED presentation included acute myocardial infarction, emergent revascularization, and cardiac-related death. RESULTS Concordance between CE and SPECT was 77% (73% to 82%) for all territories, with a higher concordance for the anterior wall of 84% (78% to 89%). Of the 203 patients recruited for the study, 38 (19%) had a cardiac event within 48 hours of ED presentation: 21 had acute myocardial infarction, 16 underwent an urgent revascularization procedure, and 1 died. In multivariate logistic regression models, the number of abnormal segments on CE and SPECT were significant predictors (P <.05) of cardiac events. The composite scores on CE provided 17% incremental information (P =.009, n = 203) and gated SPECT provided 23.5% additional information (P =.020, n = 163) for predicting cardiac events compared with routine demographic, clinical, and electrocardiographic variables. RF and composite evaluation was superior on SPECT compared with CE, whereas PER alone was not. CONCLUSIONS Cardiac imaging of RF and PER at the time of ED presentation offers substantially greater diagnostic and prognostic information for early cardiac events in patients presenting to the ED with chest pain and no ST elevation than does the routine demographic, clinical, and electrocardiographic assessment.