Tc-99m Myocardial Perfusion Research Articles

Comparison of the Kit Performance of Three 99mTc Myocardial Perfusion Agents

In this study we report a comparison of the three 99mTc myocardial perfusion imaging agents: Cardiolite®, Myoview® and Technescan® Q12. The three agents were compared for ease of preparation, quality control (QC) analysis and shelf life after reconstitution under a variety of 99mTc activity levels. Myoview® was the easiest agent to prepare, the QC method for Cardiolite® was the most straightforward and Technescan® Q12 showed the greatest stability over time. All three agents gave >90% radiochemical purity within the manufacturers’ specifications for use.

Tc-99m Myocardial Perfusion SPECT Findings of Angina Patients Showing Normal Coronary Angiography

Background:Tc-99m myocardial perfusion imaging agents have recently found wide spread use as detecting agents of coronary diseases. Unfortunately, false positive results are not infrequent. Methods:We analyzed Tc-99m myocardial perfusion SPECT(Tc-SPECT findings in angina patients showing normal coronary angiography. Seventy patients who underwent myocardial SPECT wihin one month of coronary angiography which revealed no significant stenosis were studied. Results:Forty six(65.7% patients showed perfusion defects on Tc-SPECT. Eighteen were due to soft tissue attenuation, thirteen were due to technical problems such as low count rate, six were associated with intraventricular conduction abnormalities, four with coronary spasms, three with old infarctions, and one with slow coronary flow. Conclusion:Photon attenuation and inadequate count rates were the main causes of false positive results on myocardial SPECT imaging with Tc-99m agents. However, pathological conditions such as conduction disturbance, coronary spasm or slow coronary flow were also associated with positive SPECT findings in patients with normal coronary angiograms.

Evaluation of coronary artery disease in women.

Diagnostic techniques have been refined to improve the accuracy of coronary artery disease detection in women compared to that achieved by clinical assessment and stress electrocardiography alone. Noninvasive cardiac imaging with 99mTc myocardial perfusion agents improves the specificity of coronary artery disease diagnosis over that achieved with 201Tl imaging, particularly when this technique is combined with ECG-gated image analysis. Improvements in diagnostic accuracy should enhance physician confidence in the use of noninvasive diagnostic testing in women. Combined clinical and noninvase imaging assessment can define those women at very high and very low risk for future cardiac events, permitting physicians to direct appropriate patients to aggressive treatment (ie, coronary revascularization) to improve outcomes. The reduction in unneccessary coronary cardiac catheterization accomplished by improved specificity, and the accurate determination of cardiac risk, provides for the most cost-efficient use of medical resources in the female population with known or suspected coronary artery disease.

Generalized matrix inverse reconstruction for SPECT using a weighted singular value spectrum

A method of weighting the singular value spectrum for SPECT image reconstruction with generalized matrix inverses (GMIs) has been developed, for the purpose of obtaining more localized source activity estimates than can be obtained with the use of a truncated spectrum. At each source voxel, spectral weights are computed to minimize the misfit of the resolution kernel with an ideal unit response (discretized delta function), subject to a constraint on the variance of the reconstructed source activity. This method was applied to a Monte Carlo simulated Tc-99m myocardial perfusion study and a Tc-99m myocardial perfusion phantom study acquired on a clinical scanner. GMI reconstructions using weighted and truncated spectra were compared. Resolution kernels for a weighted spectrum are narrower and have smaller sidelobes than kernels for a truncated spectrum. As a result, with the use of a weighted spectrum the resolution of reconstructed SPECT images is improved, the simulated myocardial wall thickness is better estimated and reconstructed activity is smoother in regions of uniform activity. The use of a weighted singular value spectrum is an important tool for obtaining more localized source activity estimates with GMI reconstruction.

Comparison of SPECT using technetium-99m agents and thallium-201 and PET for the assessment of myocardial perfusion and viability

This report reviews the applications of tomographic imaging with current and new tracers in assessing myocardial perfusion and viability. Multiple studies with thallium-201 (Tl-201) single photon emission computed tomography (SPECT) imaging for the detection of coronary artery disease (CAD) have demonstrated high sensitivity, high rates of normalcy and high reproducibility. In assessing viability, fixed defects are frequently detected in viable zones in 4-hour studies with Tl-201 imaging. Redistribution imaging performed 18 to 72 hours after injection or reinjection of Tl-201 before 4-hour redistribution imaging has been shown to improve accuracy of viability assessment. Tl-201 SPECT studies are limited by the suboptimal physical properties of Tl-201, which result in variable image quality. The 2 new technetium-99m (Tc-99m) — labeled myocardial perfusion tracers offer the ability to inject much higher amounts of radioactivity, making it possible to assess ventricular function as well as myocardial perfusion from the same injection of radiotracer. Tc-99m sestamibi has very slow myocardial clearance, which allows for prolonged imaging time and results in image quality superior to that obtained with Tl-201 and Tc-99m teboroxime. The combination of minimal redistribution of Tc-99m sestamibi and high count rates makes gated SPECT imaging feasible, and also permits assessment of patients with acute ischemic syndromes by uncoupling the time of injection from the time of imaging. The combination of high image quality and firstpass exercise capabilities may lead to a choice of this agent over Tl-201 for assessment of chronic CAD. Tc-99m teboroxime is efficiently extracted by the myocardium in proportion to myocardial perfusion even at extremely high flow rates; however, this tracer demonstrates rapid myocardial washout, necessitating the completion of images very quickly after injection and generally resulting in suboptimal image quality. Positron emission tomography (PET) has been applied with both rest and stress myocardial perfusion studies using rubidium-82, which has recently become commercially available, or nitrogen-13 ammonia. Although PET is clearly established as highly accurate for noninvasive detection of CAD, there are still divergent views as to whether PET is more accurate than Tl-201 SPECT for these studies. No direct comparisons have been made with attenuation-corrected Tl-201 SPECT or with the newer Tc-99m myocardial perfusion imaging agents. With respect to myocardial viability, studies using PET with fluorine-18 fluorodeoxyglucose remain the “gold standard.” The principal limitations of this approach are the high costs of equipment and radiopharmaceuticals. The availability of multiple excellent agents for the scintigraphic assessment of myocardial perfusion is likely to greatly expand the use of nuclear cardiology techniques and to result in the ability to choose a particular agent to fit a given clinical situation.