Characterization and Simulation of an Adaptable Fan-Beam Collimator for Fast Calibration of Radiation Detectors for PET

Abstract

Monolithic scintillators for positron emission tomography systems perform best when calibrated individually. We present a fan-beam collimator with which a crystal can be calibrated within less than 1 h when suitable positioning algorithms are applied. The collimator is manufactured from lead, features an easily adaptable slit to tune the beam width and can be operated together with a coincidence detector to select a clean sample of 511-keV annihilation photons. We evaluated the performance of the collimator with a Geant4 simulation for slit widths of 0.25 mm, 0.4 mm, and 1 mm and validated the shape of the beam profile experimentally by step-wisely moving a detector into the beam. This shows a clear narrow and box-shaped beam profile even if the collimator is operated without the coincidence setup. In the latter configuration, the fraction of gammas in the beam region on a 50×50 mm 2 large detector is between 48% and 79% which is improved significantly to more than 94% by using only coincidence events. Analyzing the energy distribution shows that the fraction of 511-keV photons is increased from less than 50% to more than 96% by selecting coincidences.

High-Throughput FPGA-Based Inference of Gradient Tree Boosting Models for Position Estimation in PET Detectors

“…II-B). This data as well as test data for evaluation were acquired in a benchtop coincidence calibration setup [42]. The sensor tile was placed on a translation stage and the scintillator array was irradiated in both planar directions with a fan-beam collimator by a gamma photon beam created by a slit of 0.4 mm width with two 22 Na sources, each with an activity of 5.5 MBq.…”

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

“…The setup consists of two 22 Na sources and an electrically driven translation stage (LIMES 90,Owis) to irradiate the detector under calibration at known positions by moving through a fan beam. 34 At both sides of the collimator setup, the beam width can be changed independently by adjusting the corresponding slit width. The slit width for the coincidence detector was chosen to be bigger, compared to the calibration detector slit to avoid losing coincidences due to geometrical aspects.…”

“…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.…”

“…In most presented routines, every individual detector is calibrated with an external reference for positioning estimation, which takes days up to weeks using parallel hole collimators illuminating single points. 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 24,30,33–35 . For position estimation, a wide range of algorithms have been proposed, for example, k ‐nearest neighbors, 25,36–38 maximum likelihood, 31,39 Voronoi diagrams, 40 or neural networks 29,41–43 .…”

Modelling of A New X-Ray Backscatter Imaging System: Simulation Investigation

“…X-ray backscatter imaging (XBI) technology has attracted a lot of attention during the turn of the century and it has been applied for vehicle surveillance, IED detections and for detection of buried objects such as land mines. Unlike conventional transmission X-ray, which is more sensitive for detecting high atomic number material [1][2][3], BAXI relies on the Compton scattering of the X-ray with the core electrons [1,2,4,5], and is more sensitive to low atomic number materials like explosives [2,6]. Furthermore, BAXI is more attractive in operations as both the X-ray source and detector are mounted in the same housing; thereby, it can scan large objects [7].…”