Investigation of depth-of-interaction by pulse shape discrimination in multicrystal detectors read out by avalanche photodiodes

Abstract

The measurement of depth of interaction (DOI) within detectors is necessary to improve resolution uniformity across the FOV of small diameter PET scanners. DO1 encoding by pulse shape discrimination (PSD) has definite advantages as it requires only one readout per pixel and it allows DO1 measurement of photoelectric and Compton events. The PSD time characteristics of various scintillators were studied with avalanche photodiodes (APD) and the identification capability was tested in multi-crystal assemblies with up to four scintillators. In the PSD time spectrum of an APD-GSO/LSO/ BGO/CsI(Tl) assembly, four distinct time peaks at 45, 26, 88 and 150 ns relative to a fast test pulse, having resolution of 10.6, 5.2, 20 and 27 ns, can be easily separated. Whereas the number and position of scintillators in the multi-crystal assemblies affect detector performance, the ability to identify crystals is not compromised. Compton events have a significant effect on PSD accuracy, suggesting that photopeak energy gating should be used for better crystal identification. However, more sophisticated PSD techniques using parametric time-energy histograms can also improve crystal identification in cases where PSD time or energy discrimination alone is inadequate. These results c o n f i i the feasibility of PSD DO1 encoding with APD-based detectors for PET.

Advances in clinical molecular imaging instrumentation

“…Various ways of doing this have been proposed, mainly based on solid-state detectors for scintillation light read-out. The most straightforward approach is to use multiple layers of crystals that can be identified based on differences in the pulse shape for light emitted from different types of crystals [20,21]. Another possibility is to utilise a depth-dependent light-sharing between two crystals [22].…”

Advanced radiation measurement techniques in diagnostic radiology and molecular imaging

“…In this case, some LORs (especially those having a high geometrical inclination) are subjected to a potentially significant depth-of-interaction (DOI) error. A number of techniques for designing detectors with DOI capability have been proposed, based either on the direct measurement of the DOI within the crystal (18) or by segmenting the crystal into two layers, so that the photodetection system is able to discriminate events occurring in one layer from the other (19,20) . Nowadays, a detector based on a matrix of high Z, fast, scintillating crystals (e.g.…”

A novel method for the line-of-response and time-of-flight reconstruction in TOF-PET detectors based on a library of synchronized model signals

“…Although detectors used in Positron Emission Tomography are presently at the highly advanced stage of development there is still a large room for improvement, and there is ongoing research especially aiming at (i) refinement of time resolution by search and adaptation of new inorganic crystals [7][8][9][10][11], (ii) reduction of parallax errors due to the unknown depth of interaction (DOI) e.g. by application of new geometrical configurations of crystals and APD and photomultipliers [12][13][14][15][16], (iii) finding cost-effective solutions which would allow for construction of large detectors enabling single-bed whole-body PET imaging as e.g. straw tubes drift chambers [17,18] or large area Resistive Plate Chambers (RPC) [19,20], and (iv) adaptation of PET detectors for their simultaneous usage together with MRI and CT modalities [12,[21][22][23][24][25][26].…”