Simulation study of spatial resolution and sensitivity for the tapered depth of interaction PET detectors for small animal imaging

Abstract

Improvements to current small animal PET scanners can be made by improving the sensitivity and the spatial resolution of the scanner. In the past, efforts have been made to minimize the crystal dimensions in the axial and transaxial directions to improve the spatial resolution and to increase the crystal length to improve the sensitivity of the scanner. We have designed tapered PET detectors with the purpose of reducing the gaps between detector modules and optimizing the sensitivity of a future generation small animal PET scanner. In this work, we investigate spatial resolution and sensitivity of a scanner based on tapered detector elements using Monte Carlo simulations. For tapered detector elements more scintillation material is used per detector resulting in a higher sensitivity of the scanner. However, since the detector elements are not uniform in size, degradation in spatial resolution is also expected. To investigate characteristics of tapered PET detectors the spatial resolution and sensitivity of a one-ring scanner were simulated for a system based on traditional cuboid detectors and a scanner based on tapered detectors. Additionally, the effect of depth of interaction (DOI) resolution on the spatial resolution for the traditional and tapered detectors was evaluated. All simulations were performed using the Monte Carlo simulation package GATE. Using the tapered arrays a 64 % improvement in the sensitivity across the field of view was found compared with traditional detectors for the same ring diameter. The level of DOI encoding was found to be the dominating factor in determining the radial spatial resolution and not the detector shape. For all levels of DOI encoding, no significant difference was found for the spatial resolution when comparing the tapered and the cuboid detectors. Detectors employing the tapered crystal design along with excellent DOI resolution will lead to PET scanners with higher sensitivity and uniform spatial resolution across the field of view.

A Monte Carlo investigation of the spatial resolution performance of a small-animal PET scanner designed for mouse brain imaging studies

“…Each detector has a 14 × 14 array of lutetium oxyorthosilicate (LSO) crystals separated by a 50 mm thick reflector; the crystal array has been designed with a tapered geometry to increase sensitivity [14]. At the entrance face of the detector the crystal elements have dimensions of 0.45 × 0.45 mm 2 with a pitch of 0.5 mm, while at the far end the crystals are 0.45 × 0.814 mm 2 with a pitch of 0.5 mm in the axial direction and 0.864 mm transaxially.…”

“…The experimental DOI encoding accuracy was simulated by following the procedure reported by St. James et al [14]. From the simulations, the energy-weighted (x, y, z ) position of interaction in the scintillator was extracted as well as the crystal element identification for every recorded coincidence event.…”

“…Our group has pursued detectors with good depth-encoding accuracy of ~2 mm [10,11] and small scintillation crystal cross-sections [2,12–14] suitable to build an animal PET scanner with a small ring diameter that can simultaneously obtain high spatial resolution and high sensitivity. The design of our detectors involves dual-ended readout of finely pixelated scintillator arrays with position-sensitive avalanche photodiodes (PSAPDs).…”

Efficient system modeling for a small animal PET scanner with tapered DOI detectors

“…The timing window was 20 ns, the energy resolution was 25% and the energy window was set to 250–750 keV. The parameters were selected based on our previous work (Yang et al 2008, James et al 2009, Rodríguez-Villafuerte et al 2014). To evaluate the effect on image quality, we simulated a Derenzo phantom with hot rods sizes of 0.75 mm, 0.6 mm, 0.5 mm, 0.45 mm, 0.4 mm and 0.35 mm.…”

A prototype detector for a novel high-resolution PET system: BazookaPET

“…In order to provide greater specificity and accuracy, a high-spatial-resolution PET scanner is required and various designs have been proposed to achieve this high spatial resolution [5]–[10]. Recent advances in CCD technology have allowed for high-spatial-resolution small-animal single-photon-emission-computed-tomography (SPECT) systems using CCD-based gamma cameras.…”