Ru-Ling Chou

Quantification of Myocardial Perfusion in Human Subjects Using 82Rb and Wavelet-Based Noise Reduction

UNLABELLED Quantification of myocardial perfusion with 82Rb has been difficult to achieve because of the low signal-to-noise ratio of the dynamic data curves. This study evaluated the accuracy of flow estimates after the application of a novel multidimensional wavelet-based noise-reduction protocol. METHODS Myocardial perfusion was estimated using 82Rb and a two-compartment model from dynamic PET scans on 11 healthy volunteers at rest and after hyperemic stress with dipyridamole. Midventricular planes were divided into eight regions of interest, and a wavelet transform protocol was applied to images and time-activity curves. Flow estimates without and with the wavelet approach were compared with those obtained using H2(15)O. RESULTS Over a wide flow range (0.45-2.75 mL/g/min), flow achieved with the wavelet approach correlated extremely closely with values obtained with H2(15)O (y = 1.03 x -0.12; n = 23 studies, r = 0.94, P < 0.001). If the wavelet noise-reduction technique was not used, the correlation was less strong (y = 1.11 x + 0.24; n = 23 studies, r = 0.79, P < 0.001). In addition, the wavelet approach reduced the regional variation from 75% to 12% and from 62% to 11% (P < 0.001 for each comparison) for resting and stress studies, respectively. CONCLUSION The use of a wavelet protocol allows near-optimal noise reduction, markedly enhances the physiologic flow signal within the PET images, and enables accurate measurement of myocardial perfusion with 82Rb in human subjects over a wide range of flows.

Absolute quantitation of coronary steal induced by intravenous dipyridamole

OBJECTIVE The study was done to determine whether coronary steal (defined as an absolute decrease in perfusion from resting blood flow) is induced by intravenous (IV) dipyridamole in patients with severe coronary artery disease (CAD). BACKGROUND Myocardial ischemia during coronary vasodilation is usually attributed to coronary steal. However, there is limited data on the absolute magnitude of coronary steal in humans. METHODS Eighteen patients with multivessel CAD underwent dynamic positron emission tomography (PET) imaging with 13NH3 at rest and after infusion of IV dipyridamole. Eight myocardial sectors were analyzed per short axis slice and myocardial blood flow calculated with a two-compartment model in absolute terms. RESULTS Coronary steal occurred in 8 of the 18 patients. In the 8 patients with coronary steal, myocardial blood flow decreased from 90 +/- 18 ml/100 g/min at rest to 68 +/- 27 ml/100 g/min following dipyridamole in the segments with steal, and increased from 87 +/- 19 to 138 +/- 16 ml/100 g/min following dipyridamole in the segments without steal. Significant clinical correlates of coronary steal were either ST elevation or the combination of ST depression and angina. CONCLUSIONS Coronary vasodilation with IV dipyridamole is associated with significant reductions in blood flow to collateral-dependent myocardium consistent with coronary steal in about 45% of patients with severe CAD.

Assessment of cardiac wall motion and ejection fraction with gated PET using N-13 ammonia

Background: Cardiac gating is not routinely used in cardiac positron emission tomography (PET). The aim of this study was to determine the feasibility of assessing regional wall motion, ejection fraction (EF), cardiac volumes, and mass with nitrogen-13 ammonia (N-13 ammonia) at the time of PET myocardial perfusion imaging. Methods: We studied 12 healthy volunteers (mean age, 28 ± 8 years) and 53 patients with documented coronary artery disease (CAD) (mean age, 59 ± 11 years). All subjects received a single administration of approximately 600 MBq (16 mCi) of N-13 ammonia intravenously. A 6-minute dynamic scan was performed for quantitative assessment of myocardial perfusion at rest, followed by a separate, 13-minute static scan acquired in the gated mode (8 equal bins). Gated data was imported into the Emory Toolbox. Wall motion was evaluated by dividing the myocardium into 9 anatomic regions graded semiquantitatively. Results: Healthy volunteers had a normal EF (61 ± 6), end systolic volume (ESV) (37 ± 15 mL), end diastolic volume (EDV) (89 ± 25 mL), and cardiac mass (116 ± 18 g). In contrast, patients with CAD showed reduced EF (32 ± 13%) and increased ESV (129 ± 56 mL), EDV (188 ± 68 mL), and cardiac mass (173 ± 45g) (P < 0.001 for each). In patients with CAD, EF measured by gated PET correlated significantly to independent measurements of EF (P < 0.001). Conclusions: Gating of cardiac perfusion images obtained after administration of N-13 ammonia is feasible and appears to be an accurate means of evaluating regional and global cardiac function. Gating can provide important additional diagnostic and prognostic information.

Positron emission tomography, echo-doppler, and exercise studies of functional capacity in hypertensive heart disease ☆

BACKGROUND This study examines the relationship between functional capacity, left ventricular diastolic function, and myocardial perfusion reserve (MPR) in patients with left ventricular hypertrophy (LVH). METHODS We studied 16 patients with LVH and 10 controls. Functional capacity was assessed by cardiopulmonary exercise, MPR by positron emission tomography, and left ventricular diastolic function by echo-Doppler. RESULTS Functional capacity and MPR were significantly lower in the patients. Functional capacity correlated positively with MPR and left ventricular diastolic function. CONCLUSIONS Diminished functional capacity in patients with hypertension-induced LVH is related to the impairment in MPR and left ventricular diastolic function.

Correlates of myocardial oxygen demand measured by positron emission tomography in the hypertrophied left ventricle

BACKGROUND The aim of this study was to identify the best correlate of myocardial oxygen demand (MVO(2)) in patients with hypertension induced left ventricular hypertrophy (LVH), and to examine whether relationships between these surrogates and MVO(2) differed between patients with LVH and control subjects. METHODS We measured MVO(2) by positron emission tomography using carbon-11 acetate in 20 patients and 10 normotensive control subjects, and compared the relationships between commonly used surrogates and MVO(2). RESULTS With the exception of diastolic blood pressure, the same variables correlated with resting MVO(2) in the patients and control subjects. CONCLUSIONS The best correlate of resting MVO(2) in the patients with hypertension induced LVH was the stress-mass-heart rate product.