Initial PET performance evaluation of a preclinical insert for PET/MRI with digital SiPM technology

Abstract

Hyperion-IID is a positron emission tomography (PET) insert which allows simultaneous operation in a clinical magnetic resonance imaging (MRI) scanner. To read out the scintillation light of the employed lutetium yttrium orthosilicate crystal arrays with a pitch of 1 mm and 12 mm in height, digital silicon photomultipliers (DPC 3200-22, Philips Digital Photon Counting) (DPC) are used. The basic PET performance in terms of energy resolution, coincidence resolution time (CRT) and sensitivity as a function of the operating parameters, such as the operating temperature, the applied overvoltage, activity and configuration parameters of the DPCs, has been evaluated at system level. The measured energy resolution did not show a large dependency on the selected parameters and is in the range of 12.4%–12.9% for low activity, degrading to ~13.6% at an activity of ~100 MBq. The CRT strongly depends on the selected trigger scheme (trig) of the DPCs, and we measured approximately 260 ps, 440 ps, 550 ps and 1300 ps for trig 1–4, respectively. The trues sensitivity for a NEMA NU 4 mouse-sized scatter phantom with a 70 mm long tube of activity was dependent on the operating parameters and was determined to be 0.4%–1.4% at low activity. The random fraction stayed below 5% at activity up to 100 MBq and the scatter fraction was evaluated as ~6% for an energy window of 411 keV–561 keV and ~16% for 250 keV–625 keV. Furthermore, we performed imaging experiments using a mouse-sized hot-rod phantom and a large rabbit-sized phantom. In 2D slices of the reconstructed mouse-sized hot-rod phantom (∅ = 28 mm), the rods were distinguishable from each other down to a rod size of 0.8 mm. There was no benefit from the better CRT of trig 1 over trig 3, where in the larger rabbitsized phantom (∅ = 114 mm) we were able to show a clear improvement in image quality using the time-of-flight information. The findings will allow system architects—aiming at a similar detector design using DPCs—to make predictions about the design requirements and the performance that can be expected.

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

“…Compared with photomultiplier tubes, avalanche photodiodes result in poor timing resolution and low, temperature-sensitive gain (11). Silicon photomultipliers (SiPMs) have recently become an attractive alternative to avalanche photodiodes for PET/MR (12)(13)(14) because they offer gain and timing resolution comparable to photomultiplier tubes while also functioning in strong magnetic fields with little temperature dependence (11,15,16).…”

Maximum likelihood positioning algorithm for high‐resolution PET scanners

“…This effect is even more dominant for higher validation and lower trigger thresholds. 30 For high validation thresholds, the probability increases that DPCs of low-energy events are not validated. Lower trigger thresholds increase the number of noise-induced triggers and the dead time causes incomplete light distributions.…”

Development of a PET/OMRI combined system for simultaneous imaging of positron and free radical probes for small animals

“…[18][19][20] Recently silicon photomultipliers (Si-PMs) have been developed and used for PET/MRI systems. [21][22][23][24][25] Si-PM is also a candidate for semiconductor-based photosensors for PET/OMRI systems. Both advantages and disadvantages can be found among these two types of systems.…”