High-resolution monolithic LYSO detector with 6-layer depth-of-interaction for clinical PET

Abstract

The system spatial resolution of whole-body positron emission tomography (PET) is limited to around 2 mm due to positron physics and the large diameter of the bore. To stay below this 'physics'limit a scintillation detector with an intrinsic spatial resolution of around 1.3 mm is needed. Currently used detector technology consists of arrays of 2.6-5 mm segmented scintillator pixels which are the dominant factor contributing to the system resolution. Pixelated detectors using smaller pixels exist but face major drawbacks in sensitivity, timing, energy resolution and cost. Monolithic continuous detectors, where the spatial resolution is determined by the shape of the light distribution on the photo detector array, are a promising alternative. Without having the drawbacks of pixelated detectors, monolithic ones can also provide depth-of-interaction (DOI) information. In this work we present a monolithic detector design aiming to serve high-resolution clinical PET systems while maintaining high sensitivity. A 50 x 50 x 16 mm 3 Lutetium-Yttrium oxyorthosilicate (LYSO) scintillation crystal with silicon photomultiplier (SiPM) back side readout is calibrated in singles mode by a collimated beam obtaining a reference dataset for the event positioning. A mean nearest neighbour (MNN) algorithm and an artificial neural network for positioning are compared. The targeted intrinsic detector resolution of 1.3 mm needed to reach a 2 mm resolution on system level was accomplished with both algorithms. The neural network achieved a mean spatial resolution of 1.14 mm FWHM for the whole detector and 1.02 mm in the centre (30 x 30 mm 2 ). The MNN algorithm performed slightly worse with 1.17 mm for the whole detector and 1.13 mm in the centre. The intrinsic DOI information will also result in uniform system spatial resolution over the full field of view.

A semi‐monolithic detector providing intrinsic DOI‐encoding and sub‐200 ps CRT TOF‐capabilities for clinical PET applications

“…More efficient calibration setups, for example, fan beam collimators, significantly reduce the calibration time down to hours or less, which seems more feasible for scanners with many detectors. 24,30,[33][34][35] For position estimation,a wide range of algorithms have been proposed, for example, k-nearest neighbors, 25,[36][37][38] maximum likelihood, 31,39 Voronoi diagrams, 40 or neural networks. 29,[41][42][43] In previous work, we have established a positioning method based on the supervised machine learning algorithm gradient tree boosting (GTB), enabling an easy tradeoff between positioning performance and computational requirements.…”

Recent advances in combined Positron Emission Tomography and Magnetic Resonance Imaging

“…In PET detectors, the scintillation crystals are usually pixellated to improve the spatial resolution of the photon interaction point. Some manufacturers have developed monolithic scintillators too [30][31][32].…”

Technical opportunities and challenges in developing total-body PET scanners for mice and rats

“…Different methods have been proposed to obtain the DOI resolution [11,157]. These include using monolithic scintillator [136,158], multilayer scintillator [105,[159][160][161][162][163], customized reflector designs [116,164,165], and the dual-ended readout method [22,22,56,166]. While current detectors based on scintillator arrays can have a resolution as good as 0.5 mm [52,53,156], it is still difficult to obtain the equivalent 0.5 mm DOI resolution without sacrificing other performance such as by reducing the thickness of the scintillator or significantly increasing the complexity of the detector.…”