Design study of fully wearable high-performance brain PETs for neuroimaging in free movement

Abstract

A practical wearable brain PET scanner capable of dynamic neuroimaging during free bodily movement will enable potential breakthrough basic neuroscience studies and help develop imaging-based neurological diagnoses and treatments. Weight, brain coverage, and sensitivity are three fundamental technical obstacles in the development of Fully Wearable High-Performance (FWHP) brain PET scanners. The purpose of this study is to investigate the feasibility of building a FWHP brain PET using a limited volume of lutetium-yttrium oxyorthosilicate (LYSO) scintillator crystals. Six scanners, consisted of the same volume (2.66 kg) of LYSO scintillators with combinations of 2 different crystal pitches (3 mm and 1.5 mm) and 3 different crystal lengths (20 mm, 10 mm, and 5 mm), were simulated. The performances of the six scanners were assessed and compared with Siemen's HRRT brain PET and mCT whole-body PET, in terms of aperture, axial field of views (AFOV), sensitivity, spatial resolution, count rates, and image noise property. The time-of-flight (TOF) information was included in the image reconstruction to improve the effective sensitivity. The effects of the TOF was assessed by scanning a Jaszczak phantom and reconstructing images with the maximum likelihood expectation maximization (MLEM) algorithm with different timing settings (non-TOF, 500 ps, 200 ps, 100 ps and 50 ps Coincidence Time Resolution, CTR). The signal-noise ratio (SNR) of the images were assessed and compared with those of the HRRT scanner and mCT scanner. The results show that it is possible to construct a FWHP brain PET with better spatial resolution than the dedicated HRRT brain PET, comparable effective sensitivity (with 50 ~100 ps CTR), and whole-brain coverage (23.7 cm inner diameter and 13.4 cm axial field of view) using 2.66 kg of LYSO.

Real-time motion-enabling positron emission tomography of the brain of upright ambulatory humans

“…Our team has previously published results that modeled the number and placement of (and angular coverage by) detectors as well as different crystal thicknesses, time-of-flight (TOF) parameters, and the tradeoffs that occur therein 57 . Ours and other simulations indicate that the advantages of greater volume coverage exceed the advantages of locally thicker crystal 38 due to PET-specific capture physics. Extended angular coverage would also facilitate non-invasive carotid arterial sampling to enable quantitative dynamic imaging in place of arterial blood draws 62,63 .…”

“…In terms of upgrade suggestions for expanding FOV, based on simulation studies, brain coverage could be increased considerably, and the imager could still remain lightweight with a wider field-of-view (FOV), using thinner scintillators as a potential trade-off 38 . The thickness of the crystal affects the stopping power of the annihilation photons, and thus the number of coincident events detected, which is an important factor in the overall sensitivity of the device.…”

“…We further envision support systems incorporating robotics that would allow for substantially heavier imagers, affording very high sensitivity and/or whole-brain FOV 64 , although safety and accommodating momentum would require careful planning and testing. Alternatively, in order to take advantage of freedom from any tethers, one could utilize a backpack support 65,66 , although the heaviness of such a system currently being developed, likened to wearing a large motorcycle helmet and backpack, may restrict researchers to relatively strong participants 38 .…”

“…Bolus-infusion F 18 -FDG studies in humans using traditional PET scanners have demonstrated task appropriate activity for visual and auditory task paradigms, with a same-session baseline control, and with ON/OFF task period cycles as short as one to two minutes [30][31][32][33] . In terms of physical device changes, the massive heavy detectors that limited PETs motion tolerance can be replaced with lightweight detectors due to advances in detector materials, such as solid-state Silicon Photomultiplier (SiPM) technology 34,35 , which have been used in headdedicated brain scanners 36,37 , although these so far are fixed and do not tolerate head motion 38 . One of the first SiPM PET imagers that was constructed to allow for large natural movements was the RatCap, designed for small animals 28,39 .…”