Performance of a PET Insert for High-Resolution Small-Animal PET/MRI at 7 Tesla

Abstract

We characterize a compact MR-compatible PET insert for simultaneous preclinical PET/MRI. Although specifically designed with the strict size constraint to fit inside the 114-mm inner diameter of the BGA-12S gradient coil used in the BioSpec 70/20 and 94/20 series of small-animal MRI systems, the insert can easily be installed in any appropriate MRI scanner or used as a stand-alone PET system. The insert consists of a ring of 16 detector-blocks each made from depth-of-interaction-capable dual-layer-offset arrays of cerium-doped lutetium-yttrium oxyorthosilicate crystals read out by silicon photomultiplier arrays. Scintillator crystal arrays are made from 22 × 10 and 21 × 9 crystals in the bottom and top layers, respectively, with respective layer thicknesses of 6 and 4 mm, arranged with a 1.27-mm pitch, resulting in a useable field of view 28 mm long and about 55 mm wide. Spatial resolution ranged from 1.17 to 1.86 mm full width at half maximum in the radial direction from a radial offset of 0-15 mm. With a 300- to 800-keV energy window, peak sensitivity was 2.2% and noise-equivalent count rate from a mouse-sized phantom at 3.7 MBq was 11.1 kcps and peaked at 20.8 kcps at 14.5 MBq. Phantom imaging showed that features as small as 0.7 mm could be resolved. F-FDG PET/MR images of mouse and rat brains showed no signs of intermodality interference and could excellently resolve substructures within the brain. Because of excellent spatial resolvability and lack of intermodality interference, this PET insert will serve as a useful tool for preclinical PET/MR.

Preliminary Results that Assess Metformin Treatment in a Preclinical Model of Pancreatic Cancer Using Simultaneous [18F]FDG PET and acidoCEST MRI

“…This result agreed with previous PET assessments of this technology [23]. The SNR of spin-echo and gradient echo MR images with the NuPET™ insert were within 97–101 % of the SNR without the insert, with a standard deviation of 2.3–3.4 % among the seven measurements made with each MR imaging protocol.…”

NEMA NU‐4 2008 performance evaluation of Xtrim‐PET: A prototype SiPM‐based preclinical scanner

“…In spite of the fact that there are many factors influencing the counting rate performance of the scanners but generally higher sensitivity leads to higher NECR values at lower activity concentrations. The peak NECR for Xtrim‐PET (113.8 kcps, peak absolute sensitivity of 2.99%) is comparable to respective values for systems with approximately similar peak detection sensitivity including ClearPET (72 kcps, 3.03%), Argus (117 kcps, 4.32%), VrPET (74 kcps, 2.36%), and exceeds the reported values for current generation of PET inserts such as MADPET4 (29 kcps, 0.76%), PET insert by Ko et al (42.2 kcps, 3.36%), PET insert by Stortz et al (20.8 kcps, 2.2%), Lee et al (21.1 kcps,1.5%), Albira (16.5 kcps, 2.5%) and MRS‐PET (61.9 kcps, 4.7%) …”

“…To ensure a fair comparison between different scanners and objectively optimize data acquisition and reconstruction protocols for a variety of applications, the National Electrical Manufacturers Association (NEMA) provided a specific standard (NEMA NU‐4) for the evaluation and performance characterization of preclinical PET scanners in terms of spatial resolution, sensitivity, scatter fraction, count rate characteristics and overall imaging performance . Subsequently, the majority of commercial small‐animal PET scanners and prototype models have been characterized according to the NEMA NU‐4 standards …”

Imaging Modalities Used in Preclinical Studies

“…(6,39). Yüksek rezolüsyon avantajından faydalanabilmek amacıyla PET dedektörü eklenebilen, silikon PMT'lerin kullanıldığı SiPM-MRG/PET (hyperion-IID-a digital-SiPM-based MRG-compatible PET insert) sitemi de hem anatomik hem fonksiyonel bilginin daha detaylı elde edilmesi amacıyla geliştirilen bir modalitedir (40).…”