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 1mm 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 set-up. In the latter configuration, the fraction of gammas in the beam region on a $50\times 50$ mm2 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. This demonstrates that our collimator produces a very defined and clean beam and provides optimal conditions for calibration.
Highlights
P OSITRON emission tomography (PET) is a tracer-based functional imaging technique which has found broad applications in research and clinical praxis [1], [2]
We presented an adjustable fan-beam collimator for fast calibration of monolithic scintillation detectors used for PET
The collimator was characterized by Geant4 simulations to evaluate the beam profile and energy spectrum
Summary
P OSITRON emission tomography (PET) is a tracer-based functional imaging technique which has found broad applications in research and clinical praxis [1], [2]. Radiation detectors based on monolithic scintillation crystals are an attractive alternative to segmented detector concepts. Monolithic crystals provide good spatial, energy, and timing resolution [6]–[12]. These detectors have intrinsic depth-of-interaction (DOI) capabilities [13]–[16]. While preclinical scanners based on DOI-capable monolithic detectors are already available [19], [20], most current wholebody scanner employ segmented detector designs without DOI [21]. One of the main challenges to widely translate monolithic scintillators to both preclinical and clinical application are efficient calibration routines and positioning algorithms
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