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Use of an analytical model for optimizing the design of a small-animal PET scanner with DOI capability - Size 7.4E-02 m Size 1.14E-01 m

The optimization of spatial resolution is a critical issue for small-animal PET scanners, and is often addressed by Monte-Carlo simulation. Analytical models, though less versatile are very fast and their simplicity allows a direct appreciation of the influence of different model parameters. The authors have developed an analytical model for multi-layer PET systems, which provides estimates of the radial and tangential resolution at different positions within the field of view. After a preliminary validation, this model was used to optimize the design of a small single-slice multi-layer PET scanner with depth of interaction capability. The authors found satisfactory agreement between the analytical model and Monte Carlo results for several scanner configurations. The dependence of the resolution on the crystal width, the number of layers, and the crystal layout was determined for a scanner with internal and external diameters at 74 mm and 114 mm respectively. Both simulation methods agreed perfectly on the influence of these parameters. In particular confirming the degree of resolution improvement obtained using multiple-layers of crystals. These results show that an analytical model can provide accurate estimates of the spatial resolution, and can be used to complement or cross-validate Monte Carlo simulations. (7 References)

An improved analytical detector response function model for multilayer small-diameter PET scanners

The optimization of spatial resolution is a critical consideration in the design of small-diameter positron emission tomography (PET) scanners for animal imaging, and is often addressed with Monte Carlo simulations. As a faster and simpler solution, we have developed a new analytical model of the PET detector response function, and implemented the model for a small single-slice, multilayer PET scanner. The accuracy of the model has been assessed by comparison with both Monte Carlo simulations and experimental measurements published in the literature. Results from the analytical model agreed well with the Monte Carlo method, being noise free and two to three orders of magnitude faster. The only major discrepancy was a slight underestimation of the width of the point spread function by the analytical method as inter-crystal scatter is neglected. We observed good agreement between the predictions of the model and experimental measurements. For two large-diameter scanners additional discrepancies were seen due to photon acollinearity, which is not considered in the model. We have shown that the simple and fast analytical detector response function model can provide accurate estimates of spatial resolution for small-diameter PET scanners, and could be a useful tool for several applications, complementing or cross-validating other simulation methods

PET and NMR dual acquisition (PANDA): Applications to isolated, perfused rat hearts

Positron emission tomography and nuclear magnetic resonance spectroscopy are non-invasive techniques that allow serial metabolic measurements to be obtained in a single subject, Significant advantages could be obtained if both types of scans could be acquired with a single machine, A small-scale PET scanner, designed to operate in a high magnetic field, was therefore constructed and inserted into the top half of a 7.3 cm bore, 9.4 T NMR magnet and its performance characterized. The magnetic field did not significantly affect either the sensitivity (similar to 3 kcps/MBq) or the spatial resolution (2.0 mm full width at half maximum, measured using a 0.25 mm diameter line source) of the scanner, However, the presence of the PET scanner resulted in a small decrease in field homogeneity, The first, simultaneous P-31 NMR spectra (200, 80 degrees pulses collected at 6 s intervals) and PET images (transverse, mid-ventricular slices at the level of the mitral value) from isolated, perfused rat hearts were acquired using a specially designed NR IR probe inserted into the bottom half of the magnet, The PET images were of excellent quality, enabling the left ventricular wall and interventricular septum to be clearly seen. In conclusion, we have demonstrated the simultaneous acquisition of PET and NMR data from perfused rat hearts; we believe that the combination of these two powerful techniques has tremendous potential in both the laboratory and the clinic, (C) 1997 John Wiley & Sons, Ltd

Development of a PET detector system compatible with MRI/NMR systems

We report the development of a prototype positron emission tomography (PET) scanner compatible with clinical magnetic resonance imaging (MRI) scanners and nuclear magnetic resonance (NMR) spectrometers. This single slice PET system consists of 72 2x2x5 mm lutetium oxyorthosilicate (LSO) crystals coupled by 2 mm diameter, 4 meter long double clad optical fibers to three multi-channel photomultiplier tubes (MC-PMT's) shielded inside an aluminum closure. The ring diameter is 54 mm and the slice thickness is similar to 1 mm FWHM. Measurements with a point source demonstrate that this PET system has a reconstructed resolution of 2.1 mm, a coincidence time resolution of 26 ns and a typical energy resolution of 45%. Simultaneously acquired PET and MR phantom images show no significant artifacts or distortions. We also obtained simultaneous NMR spectra and PET images from an isolated, perfused rat heart, demonstrating the power of obtaining temporally correlated PET and NMR information in biological systems. Again, no artifacts in the PET or NMR data were apparent, despite the high field strength of 9.4T. The challenge for the future is to scale up the design to develop a high resolution, high sensitivity device that can be used in simultaneous PET and MR studies of in vivo systems