A novel single-ended readout depth-of-interaction PET detector fabricated using sub-surface laser engraving

Abstract

We propose a novel scintillation detector design for positron emission tomography (PET), which has depth of interaction (DOI) capability and uses a single-ended readout scheme. The DOI detector contains a pair of crystal bars segmented using sub-surface laser engraving (SSLE). The two crystal bars are optically coupled to each other at their top segments and are coupled to two photo-sensors at their bottom segments. Initially, we evaluated the performance of different designs of single crystal bars coupled to photomultiplier tubes at both ends. We found that segmentation by SSLE results in superior performance compared to the conventional method. As the next step, we constructed a crystal unit composed of a 3 × 3 × 20 mm crystal bar pair, with each bar containing four layers segmented using the SSLE. We measured the DOI performance by changing the optical conditions for the crystal unit. Based on the experimental results, we then assessed the detector performance in terms of the DOI capability by evaluating the position error, energy resolution, and light collection efficiency for various crystal unit designs with different bar sizes and a different number of layers (four to seven layers). DOI encoding with small position error was achieved for crystal units composed of a 3 × 3 × 20 mm LYSO bar pair having up to seven layers, and with those composed of a 2 × 2 × 20 mm LYSO bar pair having up to six layers. The energy resolution of the segment in the seven-layer 3 × 3 × 20 mm crystal bar pair was 9.3%-15.5% for 662 keV gamma-rays, where the segments closer to the photo-sensors provided better energy resolution. SSLE provides high geometrical accuracy at low production cost due to the simplicity of the crystal assembly. Therefore, the proposed DOI detector is expected to be an attractive choice for practical small-bore PET systems dedicated to imaging of the brain, breast, and small animals.

Performance of long rectangular semi‐monolithic scintillator PET detectors

“…For the phoswich detector, crystals with different decay time are used, and specialized electronics is used to analyze the pulse shape to obtain the DOI information, so the cost of both crystals and electronics increases . For multilayer detectors based on either different reflector arrangements or half crystal shift, the cost of crystal array manufacture increases, and the flood histogram degrades as the number of crystal layers increases . The latter two kinds of the detectors also only provide limited DOI resolution depending on the number of crystal layers used.…”

Innovations in Instrumentation for Positron Emission Tomography

“…Another common DOI encoding scheme is to stack layers of scintillators. The scintillator layers can vary in their temporal emission properties such as decay time [33, 174], or can be configured such that interactions in each layer produces a unique spatial distribution of scintillation light incident on the photodetectors [143, 175–177]. However, one of the major limitations for these methods is the loss of scintillation light at each crystal interface resulting in generally poor timing resolution and energy resolution, however this can be minimized with novel fabrication techniques [178–181].…”

Sub‐2 mm depth of interaction localization in PET detectors with prismatoid light guide arrays and single‐ended readout using convolutional neural networks

“…Regardless of the chosen readout method, most studies use standard DOI estimation approaches that rely on measuring the ratio between multiple readout signals [6,11,14]. Maximum-likelihood estimation algorithms have been explored [15,16], along with methods based on look-up tables [17,18] and supervised learning algorithms such as gradient tree boosting, neural networks and support vector machines [18][19][20][21][22].…”