Simulation study to improve the performance of a whole-body PbF2 Cherenkov TOF-PET scanner.

Using Cherenkov radiation in positron emission tomography (PET) has the potential to improve the time of flight (TOF) resolution and reduce the cost of detectors. In previous studies promising TOF results were achieved when lead fluoride (PbF2) crystals were used instead of a scintillator. In this work, a whole-body PbF2 Cherenkov TOF-PET scanner was simulated and optimized. Different configurations of the PbF2 crystals and their surface treatment were considered. Also evaluated was the influence of the crystal-photodetector coupling and of the detection efficiency of the photodetectors. Of special interest is a whole-body PbF2 Cherenkov TOF-PET scanner with a multi-layer detector, which improves the time resolution and reduces the parallax error, without compromising the detection efficiency. Images of a phantom were reconstructed for different configurations of the simulated whole-body PbF2 Cherenkov TOF-PET scanner and the quality of images was compared to that of a whole-body TOF-PET scanner with standard LSO scintillators. The TOF resolution of the whole-body PbF2 Cherenkov TOF-PET scanner with a multi-layer detector was 143 ps FWHM, out of which the fundamental limitation due to light production and transportation was only 22 ps FWHM.

Stress-rest myocardial perfusion scintigraphy and adverse cardiac events in heart failure patients.

INTRODUCTION: Heart failure, primarily in the elderly, is a growing epidemic in today's world. It leads to high rates of disability and mortality, as well as significant health care expenditures, making it important to assess possible predictors of adverse cardiac events. In Cuba, heart failure mortality is 19.1/100,000 population. OBJECTIVES: Assess the value of stress-rest protocol gated-SPECT for identifying patients with symptomatic heart failure likely to suffer adverse cardiac events. METHODS: A study was conducted of 52 patients (mean age 59 years, SD 9; 62% women) with functional capacity II/III (New York Heart Association scale) and left ventricular ejection fraction <40%. Patients were divided into two groups based on coronary heart disease diagnosis: those with coronary heart disease (41), labeled ischemic; and those without (11), labeled nonischemic. All underwent gated SPECT myocardial perfusion scintigraphy with technetium-99m-labeled methoxyisobutyl isonitrile, using a two-day stress-rest protocol, including evaluation of intraventricular synchrony by phase analysis. Patients were followed over 36 months for adverse cardiac effects. RESULTS: No significant differences were observed between the two groups during the stress test with regard to exercise time, metabolic equivalents or percentage of maximal heart rate during maximal stress. Summed stress, rest and difference scores, however, were significantly different between the ischemic and nonischemic groups: 16.82 (SD 6.37) vs. 7.54 (SD 5.8), p <0.001; 14.43 (SD 6.28) vs. 6.45 (SD 3.77), p = 0.001; and 2.39 (SD 4.89) vs. 1.09 (SD 3.7), p = 0.034. No differences were found in ventricular function, although stress-minus-rest left ventricular ejection fraction was slightly lower in patients with ischemic heart disease (-1.29, SD 5.8) than in patients without ischemic heart disease (1.27, SD 4.31). Dyssynchrony was greater in patients with ischemic heart disease than in those without, primarily during stress (p <0.01). The only variable that showed a possible association with the occurrence of adverse events was <5 metabolic equivalents on the stress test (p = 0.03), while resting phase SD showed only a tendency toward association (p = 0.05). CONCLUSIONS: Information on myocardial perfusion, functional capacity and intraventricular synchrony obtained from stress-rest gated SPECT may help identify patients with symptomatic heart failure who are likely to develop adverse cardiac events, enabling better management of higher-risk cases and improved allocation of resources.