Performance Evaluation of a High-Resolution Nonhuman Primate PET/CT System.

The LFER 150 PET/CT device (large-field-of-view extreme-resolution portable research imager) is a system for nonhuman primate (NHP) imaging. The objective of this study was to evaluate the performance of the system using the National Electrical Manufacturers Association NU 4-2008 standard protocol. As a preliminary in vivo evaluation of the system, a PET measurement in an NHP was also performed. Methods: Resolution, sensitivity, image quality, and noise-equivalent count rate (NECR) were measured. NECR measurement was performed with a ratlike phantom and a monkeylike phantom. A Derenzo phantom experiment was performed to test the resolution using 3-dimensional ordered-subset expectation maximization reconstruction. One cynomolgus monkey (4.5 kg, intravenous ketamine/xylazine anesthesia) was examined with the dopamine transporter radioligand 18F-FE-PE2I (94 MBq) to evaluate the in vivo performance of the system. List-mode PET data acquired for 93 min were reconstructed into 38 frames with the Tera-Tomo 3-dimensional engine. Binding potential for caudate nucleus, putamen, and substantia nigra was evaluated using the simplified reference tissue model. Results: Radial full-width half-maximum resolution using Fourier rebinning and a 2-dimensional filtered backprojection algorithm was less than 2.2 mm and less than 3.2 mm in the central 60-mm-diameter and 140-mm-diameter regions, respectively. Maximum sensitivity in the 400- to 600-keV and 250- to 750-keV energy windows was 30.03 cps/kBq (3.3%) and 49.11 cps/kBq (5.4%), respectively. The uniformity in the image-quality phantom was 3.3%, and the spillover ratio for air and water was 0.1. The peak of the NECR curve was 430 kcps (at 115 MBq) with the ratlike phantom and 78 kcps (at 139 MBq) with the monkeylike phantom. Rods of the Derenzo phantom with 1-mm diameter could be distinguished by eye. In the NHP experiment, binding potentials in the caudate, putamen, and substantia nigra (4.9, 4.9, and 1, respectively) were similar to those previously reported using the same radioligand and a high-resolution research tomograph. Conclusion: The results obtained from phantom experiments and 1 representative PET measurement in an NHP confirm that the LFER 150 is a high-resolution PET/CT system with suitable performance for brain imaging in NHPs.

Characterization of 176Lu background in LSO-based PET scanners.

LSO and LYSO are today the most common scintillators used in positron emission tomography. Lutetium contains traces of 176Lu, a radioactive isotope that decays ß - with a cascade of γ photons in coincidence. Therefore, Lutetium-based scintillators are characterized by a small natural radiation background. In this paper, we investigate and characterize the 176Lu radiation background via experiments performed on LSO-based PET scanners. LSO background was measured at different energy windows and different time coincidence windows, and by using shields to alter the original spectrum. The effect of radiation background in particularly count-starved applications, such as 90Y imaging, is analysed and discussed. Depending on the size of the PET scanner, between 500 and 1000 total random counts per second and between 3 and 5 total true coincidences per second were measured in standard coincidence mode. The LSO background counts in a Siemens mCT in the standard PET energy and time windows are in general negligible in terms of trues, and are comparable to that measured in a BGO scanner of similar size.

Distinct regional age effects on [11C]AZ10419369 binding to 5-HT1B receptors in the human brain.

PURPOSE: Age-related changes in the serotonin system have been described, and proposed to be associated with behavioral changes observed particularly in the elderly population. The 5-HT1B receptor is thought to have a regulatory role in a number of physiological functions, and has been implicated in several age-related diseases. The purpose of the present study was to examine if the availability of 5-HT1B receptors is decreasing with age in healthy subjects. METHODS: Data from five previous studies were reanalyzed and pooled, generating data from fifty-one healthy subjects, age 20 to 70, that had been examined with positron emission tomography (PET) and the 5-HT1B specific radioligand [11C]AZ10419369 at baseline conditions. The binding potential (BPND) in cortical and subcortical areas was calculated using the simplified reference tissue model (SRTM). After correction for partial volume effects (PVEc), the correlation between age and regional BPND was examined. RESULTS: A statistically significant negative correlation between age and BPND was obtained for neocortical regions and the ventral striatum (VST). The average reduction in BPND per decade was 8% in cortex and 4% in VST. The BPND in the caudate nucleus and the putamen was mainly unaffected by age. CONCLUSION: The 5-HT1B receptor availability decreases by age in cortical regions, whereas it remains stable in the caudate nucleus and putamen. By consequence, age-matching of control subjects will be necessary in future clinical studies.