Performance Evaluation of the Small-Animal nanoScan PET/MRI System

Abstract

nanoScan is a high-resolution integrated system for consecutive PET and MR imaging of small laboratory animals. We evaluated the performance of the system, using the NEMA NU 4-2008 protocol for the PET component and the NEMA MS 1-2007, MS 2-2008, and MS 3-2007 standards for the MR imaging component. Methods:The imaging system uses magnetically shielded position-sensitive photomultiplier tubes and a compact 1-T permanent-magnet MR imaging platform. Spatial resolution, sensitivity, counting rate capabilities, and image quality parameters were evaluated in accordance with the aforementioned NEMA standards. Further in vivo evaluation experiments complement the physical validation results. Results: The spatial resolution of the PET system enabled the 0.8-mm rods of a Derenzo phantom to be resolved. With point source and 2-dimensional filtered backprojection reconstruction, the resolution varied from 1.50 to 2.01 mm in full width at half maximum in the radial direction and from 1.32 to 1.65 mm in the tangential direction within the radius of 25 mm. Peak absolute sensitivity was 8.41%. Scatter fraction was 17.3% and 34.0%, and maximum noise-equivalent counting rate was 406 and 119 kcps in the mouselike and ratlike phantom, respectively. The image quality test found a nonuniformity of 3.52% and a spillover ratio of 6.2% and 5.8% in water and air, respectively. In testing of the MR imaging component, artifact-free images with high signal-to-noise ratio were recorded. Geometric distortion was below 5%, and image uniformity was at least 94.5% and 96.6% for the 60-and 35-mm radiofrequency coils, respectively. Conclusion: The nanoScan integrated small-animal PET/MR imaging system has excellent spatial resolution and sensitivity. The performance characteristics of the PET and the MR imaging components are not compromised as a result of their integration onto a single platform. Because of its combination of features and performance parameters, the system provides crucial advantages for preclinical imaging studies over existing PET/CT systems, especially in neurologic and oncologic research.Key Words: preclinical PET; PET/MR imaging; small-animal imaging; performance evaluation; multimodality imaging The unique advantages of molecular imaging with PET in various fields of biomedical research have clearly been shown during the past few decades. PET can play a significant role in the development of therapeutic drugs and molecular imaging biomarkers, in the exploration of physiologic and biochemical processes, and in the in vivo mapping of receptor transmitters and enzymes (1,2). Because of the increasing availability of animal disease models, there is growing interest in using PET for studies on small animals (3,4). In vivo anatomic and biochemical studies on rodents require dedicated scanners with high resolution and sensitivity.PET can localize picomolar concentrations of a labeled molecule (5) but does not provide the anatomic context of the tracer. Resolving brain morphology is of unique importance in dedicated central nervo...

Neurokinin-3 Receptor Binding in Guinea Pig, Monkey, and Human Brain: In Vitro and in Vivo Imaging Using the Novel Radioligand, [18F]Lu AF10628

“…into the 2 guinea pigs. Radioactivity was measured for 123 minutes according to a preprogrammed series of 35 frames, using the small-animal nanoScan PET/CT and PET/MRI systems (Mediso Ltd.; Szanda et al, 2011; Nagy et al, 2013) at Karolinska Experimental Research Imaging Center.…”

Combined PET/MR: A Technology Becomes Mature

“…They combine a 1-T permanent magnet-based small-animal MR system with a high-resolution PET system based on cerium-doped lutetium yttrium orthosilicate and position-sensitive PMT sensors (11). Such a system clearly shows that PET/MR is on the verge of taking over the coveted place once held by PET/CT systems in the preclinical field by joining highsensitivity molecular information provided by PET with the high resolution and superb soft-tissue contrast of MR imaging.…”

Principles of PET/MR Imaging

“…A third clinical system has recently been presented but has not been introduced commercially (11). The first commercially available combined system for preclinical research offers sequential imaging with PMT-based PET detectors, and the gantry is attached to a permanent 1-T MR magnet (12). In the following sections, the different technologies used in PET/MR are discussed in more detail.…”