Dennis Kirch

Comparison of Simultaneous Dual-Isotope Multipinhole SPECT with Rotational SPECT in a Group of Patients with Coronary Artery Disease

A triple-detector, multipinhole SPECT system was optimally configured to perform simultaneous 201Tl (stress)/99mTc (rest) myocardial perfusion imaging (MPI) using a protocol that permitted direct diagnostic comparison of this multipinhole SPECT system with conventional rotational SPECT. Methods: Both the rotational and the multipinhole SPECT systems used the same model γ-detectors. The 2 systems were applied in tandem to study 26 patients with documented coronary status. Visual image evaluation of the MPI together with quantitative analysis using circumferential profile curves (CPC) were used for interpretation of stress/rest myocardial flow differences. A dual-peak attenuation compensation (DPAC) technique was applied to the stress 201Tl multipinhole SPECT images by weighted combination of the images from the upper and lower peaks. Results: Detection of myocardial infarction by location and extent correlated closely, and correlation of differential flow changes between stress and rest indicated similar accuracy in terms of location and extent of myocardial blood flow differences as well. In addition, the application of DPAC clarified the multipinhole stress 201Tl images through reduced background and increased statistics and also improved the relative superposition of the normalized CPC, especially for the inferior and more basal reconstructed regions. Conclusion: The prototype 3-detector multipinhole SPECT system achieved diagnostic results comparable to those for rotational SPECT and required only a single image-acquisition session to generate stress/rest MPI and 16-segment poststress gated studies. This reduction in acquisition time significantly improves productivity without compromising diagnostic accuracy. In addition, DPAC is a useful adjunct to the multipinhole SPECT modality because it improves both the visual clarity of the stress images and the stress/rest quantitative comparability.

Measurement of left heart ejection fraction and end-diastolic volume by a computerized, scintigraphic technique using a wedged pulmonary arterial catheter☆

Abstract A technique is described for visualizing the left heart chambers with a bolus injection of radionuclide tracer using a wedged pulmonary arterial catheter. Technetium-99m as pertechnetate is injected and the heart imaged with an Anger scintillation camera interfaced to a digital computer. Time-activity curves are extracted from areas of interest coincident with the cardiac chambers and corrected for background. These curves are analyzed in two ways: high-frequency data (beat by beat ejection fraction) and low frequency data (exponential fitting to the chamber washout curve). Left ventricular ejection fraction and end-diastolic volume determined by this technique correlated with these measurements obtained from left cineventriculography. Correlation was good between the two methods of data analysis, ejection fraction and exponential curve fitting. This technique is an accurate method for measuring left heart function without performing left heart catheterization.

Quantitation of valvular insufficiency by computerized radionuclide angiocardiography

Abstract Linear differential equation techniques for modeling tracer dynamics that assume constant flow rates and fixed chamber volumes are not totally suitable for describing the pulsatile conditions of cardiac tracer dynamics. In this paper, z-transformation methods for solving finite difference equations have resulted in a set of solutions for a pulsatile flow model of the atrial-ventricular-arterial system that accurately describes the cardiac dynamics associated with valvular insufficiency. This model can be applied to data extracted from radionuclide angiocardiographic studies on patients with mitral or aortic insufficiency as well as tricuspid or pulmonary insufficiency. Application of the model requires that the proximal atrium be labeled by a discrete bolus injection of radionuclide. Rapid sequential scintigraphic images are then recorded by an Anger camera-computer system, and the time-activity curves extracted from the resulting dynamic data are representative of the activity in the atrium and ventricle as functions of time. Determination of at most four parameters from this pair of curves then permits quantitation of total, forward and regurgitant ejection fractions and regurgitant fractions. In addition, end-diastolic and end-systolic cardiac chamber volumes can be computed from forward stroke volume. These quantities, determined by radionuclide angiocardiographic methods in 12 patients with mitral or aortic insufficiency, are compared with results from conventional contrast angiographic studies.

A new method for the correction of gamma camera nonuniformity due to spatial distortion

A methodology for correcting scintillation camera nonuniformity resulting from spatial linearity distortion is described. The method simultaneously corrects for both variations in count density and distortions in spatial linearity without altering the intrinsic sensitivity or resolution of the imaging system. This approach to linearity correction requires only a single flood image from which the spatial shift vectors are derived. The algorithm has been implemented on a PC-based, EISA bus microcomputer, and reduces the measurement of integral uniformity for 201Tl from 25% to 5%. Combined with regional correction for photopeak pulse-heights shifts (i.e. energy correction), the algorithm represents a novel technique for implementing uniformity correction completely within software.

Simulation and Validation of Point Spread Functions in Pinhole SPECT Imaging

Modeling and assessment of point spread functions (PSFs) of pinhole collimators is essential for the design of small animal single photon emission computed tomography (SPECT) imaging systems, and are gaining increasing importance with the advent of multipinhole imaging techniques. PSFs also can be used in resolution recovery methods implemented in reconstruction algorithms. Therefore, we have developed and validated a ray-tracing approach to calculate PSFs and absolute detection efficiency of pinhole collimators in radionuclide imaging. The PSFs were calculated for user defined pinhole and source geometries with multiple rays to account for collimator penetration. For validation we compared our simulations to analytical models, Monte Carlo simulations from literature, and experiments with 99 mTc sources using a variety of pinhole geometries including knife and keel edges. We find that shape and magnitude of the simulated PSFs are in very good agreement with analytical and experimental results. Importantly, our simulations show that the absolute detection efficiency of pinhole systems can be computed with an accuracy error of less than 10% using the ray-tracing approach. In contrast to Monte Carlo simulations ray-tracing simulations are computational very efficient and therefore very fast. In conclusion, we developed a ray-tracing method that calculates PSFs and detection efficiencies for different pinhole and source geometries quickly and reliably

Effect of exercise on left ventricular ejection fraction in men with coronary artery disease.

Left ventricular ejection fraction (LVEF) was measured at rest and during supine bicycle exercise in 31 men with arteriographically defined coronary disease and in 15 normal men. LVEF was calculated from a left ventricular time vs activity curve (collimated scintillation probe, 99m Technetium) as the fracitonal fall in count-rate divided by the background-corrected left ventricular end-diastolic count-rate. In normal men LVEF at rest averaged .59 +/- .06 (+/-SD) and during exercise was .72 +/- .08. LVEF did not increase with exercise in men with coronary disease (.55 +/- .03 to .57 +/- .03; N = 31; AVE +/-SEM; NS). In 17 men with coronary disease who had ST segment depression with exercise, LVEF either decreased or was unaltered in all (55 +/- .04 to .49 +/- .03; P less than 0.05); whereas in 14 without ST depression, LVEF increased in 10 (71 per cent) and was unaltered in 4 (29 per cent) (.54 +/- .04 to .66 +/- .04; P less than 0.01). Results suggest that LVEF during exercise normally increases, but in men with coronary disease LVEF either fails to increase or actually decreases. In addition there appears to be a relationship between ST segment changes during exercise and ejection fraction.

Application of a Computerized Image-Intensifier Radionuclide Imaging System to the Study of Regional Left Ventricular Dysfunction

A light-sensitive, self-scanning, silicon diode array has been used to interface an image-intensifier gamma camera to a digital computer for performing high resolution dynamic radionuclide angiocardiography. The spatial resolution of this image-intensifier camera (IIC) system, which does not perform pulse-height analysis, is somewhat worse than that of the Anger camera (AC) at count-rates below 50 K cps. Between 50 K and 250 K cps the IIC demonstrates linear countrate performance without the distortion and resolution loss associated with the AC. The ability of the IIC to maintain resolution at extremely high count-rates is of particular value for performing first transit, radionuclide bolus washout studies of cardiac dynamics. The high contrast and increased information density achieved by this approach provides accurate measurement of left ventricular volume and its first derivative with respect to time as verified by direct comparison with left cine ventriculography (cine). For the study of regional left ventricular wall motion, radionuclide images corresponding to end-diastole and end-systole have been used to compute functional images which accurately describe abnormally contracting segments of the left ventricular wall. The ability to study left ventricular volume and segmental wall motion without left heart catheterization is of significant diagnostic and investigative value.

The Square Left Ventricle: an Angiographic and Radionuclide Sign of Left Ventricular Thrombus

The association of mural thrombus with left ventricular aneurysm is well documented, though angiographic documentation of left ventricular thrombus can be difficult. The authors describe the unique appearance of the left ventricular cavity in 5 patients. In all cases, ventriculograms obtained in the right anterior oblique position showed a squared apex. In 2 patients this phenomenon was also demonstrated by radionuclide angiocardiography. All 5 patients were found to have left ventricular thrombus at operation or autopsy.

Advantages of list-mode acquisition of high resolution dynamic cardiac data

Frame-mode acquisition of MUGA studies is an imprecise means to study cardiac dynamics. List-mode acquisition offers significant advantages in temporal and spatial resolution as well as allowing flexibility in selecting those beats included in the final image sequence. Using list-mode, spatial coordinates (x and y), energy value (e), and an encoded physiologic/timing signal (p/t) are stored on an event-by-event basis as byte integer values. The four integers associated with each detected event (x,y,e, and p/t) are streamed onto a hard disk storage device allowing even stress gated blood pool studies to be recorded. Among the advantages we have been able to demonstrate are: Using the stored multispectral energy information to perform scatter correction on the dynamic images; measuring and correcting respirational displacement of the ventricle to minimize motion blurring; applying a variable zoom window after the fact to keep the ventricles centered for analysis; allowing formation of gated sequences representing only a specific aberrancy for detection of ectopic ventricular foci; and improving temporal precision necessary to analyze complex ventricular dynamics associated with aberrant neural conduction affecting the synchrony of muscle contraction. To demonstrate the improved resolution of the list-mode methodology, a dynamic phantom was used to simulate blurring due to respiration and segmental wall motion defects.

Sustained release nitroglycerin improves myocardial thallium-201 images in men with coronary artery disease

Ten men with coronary disease and angina-limited exercise participated in a study of the effects of sustained release nitroglycerin capsules on exercise performance and myocardial thallium images. Dose titration to ascertain the maximally tolerated dose, 6.5 to 26 mg orally four times a day, followed by double-blind, placebo-controlled cross-over treatment was undertaken. Following the administration of sustained release nitroglycerin exercise performance and exercise thallium images improved and appeared to remain so for four hours.