A Prototype High-Resolution Small-Animal PET Scanner Dedicated to Mouse Brain Imaging

Abstract

A prototype small-animal PET scanner was developed based on depth-encoding detectors using dual-ended readout of very small scintillator elements to produce high and uniform spatial resolution suitable for imaging the mouse brain. Methods The scanner consists of 16 tapered dual-ended readout detectors arranged in a ring of diameter 61 mm. The axial field of view is 7 mm and the transaxial field of view is 30 mm. The scintillator arrays consist of 14×14 lutetium oxyorthosilicate (LSO) elements, with a crystal size of 0.43×0.43 mm2 at the front end and 0.80×0.43 mm2 at the back end, and the crystal elements are 13 mm long. The arrays are read out by 8×8 mm2 and a 13×8 mm2 position-sensitive avalanche photodiodes (PSAPDs) placed at opposite ends of the array. Standard nuclear instrumentation module (NIM) electronics and a custom designed multiplexer are used for signal processing. Results The detector performance was measured and all except the very edge crystals could be clearly resolved. The average detector intrinsic spatial resolution in the axial direction was 0.61 mm. A depth of interaction resolution of 1.7 mm was achieved. The sensitivity of the scanner at center of the field of view was 1.02% for a lower energy threshold of 150 keV and 0.68% for a lower energy threshold of 250 keV. The spatial resolution within a field of view that can accommodate the entire mouse brain was ~0.6 mm using a 3D Maximum Likelihood-Expectation Maximization (ML-EM) reconstruction algorithm. Images of a micro hot-rod phantom showed that rods with diameter down to 0.5 mm could be resolved. First in vivo studies were obtained using 18F-fluoride and confirmed that 0.6 mm resolution can be achieved in the mouse head in vivo. Brain imaging studies with 18F-fluorodeoxyglucose were also acquired. Conclusion A prototype PET scanner achieving a spatial resolution approaching the physical limits for a small-bore PET scanner set by positron range and acolinearity was developed. Future plans are to add more detector rings to extend the axial field of view of the scanner and increase sensitivity.

Development of depth encoding small animal PET detectors using dual‐ended readout of pixelated scintillator arrays with SiPMs

“…The gaps between detector modules will also bring image artifacts if analytical image reconstruction such as filter back projection is used. There is no problem for iterative image reconstruction which can accurately model the system geometry . The advantage of dual‐ended readout detector is that small crystals can be resolved, a good DOI resolution can be obtained, long crystal of 20 mm or more can be used and the timing resolution may be also better than single‐ended readout detector .…”

“…There is no problem for iterative image reconstruction which can accurately model the system geometry. 18 The advantage of dual-ended readout detector is that small crystals can be resolved, a good DOI resolution can be obtained, long crystal of 20 mm or more can be used 19,20 and the timing resolution may be also better than single-ended readout detector. 21 Among all the depth encoding PET detector techniques, dual-ended readout detector has the greatest potential to be used to build small animal PET scanners that simultaneously achieve high spatial resolution and high sensitivity.…”

“…16,17,23,24 Prototype small animal PET scanners were also built and it was demonstrated that uniform high spatial resolution can be achieved using dual-ended readout detector. 18,24 Silicon photomultiplier (SiPM) is a new type of photodetector which has a few properties similar to APD such as compact size and low sensitivity to magnet field. It can be used in dual-ended readout PET detectors and MRI compatible PET scanners.…”

Hybrid Pixel-Waveform (HPWF) Enabled CdTe Detectors for Small Animal Gamma-Ray Imaging Applications

“…While there has been substantial efforts for using finely pixelated scintillation detectors with 500 um wide crystal elements for achieving an ultrahigh PET imaging resolution by Cherry's group [7], physical difficulties still exist. Such challenges as finely segmenting the crystal elements, the inevitable loss in detection efficiency with size, finding photon detectors with sufficient spatial resolution and the resulting increase in cost begin to pose a challenge when a very high intrinsic spatial resolution is desired with compact geometries.…”

Imaging neuronal pathways with 52Mn PET: Toxicity evaluation in rats

“…Moreover, intense work aiming at improving the spatial resolution of PET scanners is taking place and simulation results of new designs, as well as first experimental data, show that resolution of 0.5-0.6 mm full width at half maximum (FWHM) may be achieved (Park et al, 2007, Yang et al, 2016. With scanners of the improved spatial resolution, some investigations at the sub-regional level may become feasible, at least in rats.…”