TITLE: Performance Evaluation of the GE eXplore VISTA DR Small Animal PET Scanner

 

AUTHORS: Yuchuan Wang, Jurgen Seidel, Benjamin M.W. Tsui, Juan J. Vaquero, and Martin G. Pomper

 

PURPOSE: We evaluated the performance characteristics of the GE Healthcare eXplore VISTA DR (dual ring) small animal positron emission tomography (PET) scanner, a stationary, ring-type "depth-of-interaction" (DOI) correcting system designed to simultaneously maximize sensitivity, resolution and resolution uniformity over a field-of-view sufficient to image rodent-sized animals.

 

METHODS AND MATERIALS: We measured the intrinsic spatial resolution response of the VISTA detector modules, spatial and volume resolution throughout a representative portion of the field of view and imaged several common resolution phantoms to provide a qualitative picture of resolution performance. We obtained an axial sensitivity profile and measured central point source sensitivity, scatter fractions and noise equivalent count (NEC) rates curves for rat and mouse sized objects using different energy windows, and count rate linearity. In addition, we measured energy and timing resolution of both crystal layers (GSO and LYSO) that give the VISTA machines a DOI compensation capability, and the effectiveness of this DOI compensation by comparing spatial resolution measurements with and without the DOIthis correction enabled. Finally, several animal studies provided by users of the VISTA machine at John Hopkins Medical Institutions (JHMI) are included to illustrate the system performance in the field, including image reconstructions with a 3D 3D-OSEM algorithm tailored to the VISTA scanner. ing geometry and available as an option from the manufacturer.

 

RESULTS: Spatial and volume resolutions averaged approximately 1.4 mm and 2.9 mm3 respectively (all 3D-FORE/2D-FBP image reconstructions, all 250-700 keV energy window) along the scanner central axis and spatial resolution was better than 1.7 mm and 2.1 mm at 1 and 2 cm off the central axis, respectively. Central point source sensitivityCPS measured approximately 4% with peak NEC rates of 126.8 kcps at 455 kBq/ml and 77.1 kcps at 141 kBq/ml for mouse and rat-sized uniform, cylindrical phantoms, respectively. Count rate does not depart significantly from true linearity for these objects of either size up to a prompt coincidence rate of approximately 250 k/sec (407 kBq/ml mouse, 133 kBq/ml rat, 250-700 keV window).  Intrinsic spatial resolution of the VISTA detector modules averaged 1.3 mm (FWHM) and energy resolution averaged 27% (LYSO) and 32% (GSO) over the 6084 crystals in each layer.  Ninety-five percent of scintillation events were assigned to the correct scintillator-of-interactioncrystal by the DOI algorithm.  Radial spatial resolution 2.8-cm off-axis with DOI compensation was 2.5 mm but degraded (by 56%) to 3.9 mm without DOI compensation (as would be the case with a geometrically identical scanner without DOI capability).

 

CONCLUSIONS: These results indicate that the VISTA small animal PET scanner is exceptionally well suited to imaging rodent-sized animals. The combination of high spatial resolution, resolution uniformity, sensitivity and count rate performance, made possible in part by the novel use of phoswich detector modules, confer significant technical advantages over machines of similar geometry but without DOI correction capability.

 

FUNDING SOURCES: NIH grant no. CA92871.