Performance of long rectangular semi‐monolithic scintillator PET detectors

Abstract

Purpose: High-sensitivity and high-resolution depth-encoding positron emission tomography (PET) detectors are required to simultaneously improve the sensitivity and spatial resolution of a PET scanner so that the quantitative accuracy of PET studies can be improved. The semi-monolithic scintillator PET detector has the advantage of measuring the depth of interaction with single-ended readout as compared to the traditional pixelated scintillator detector, and significantly reducing the edge effect that deteriorates the spatial resolution at edges of the detector as compared to the monolithic scintillator detector if a long rectangular semi-monolithic detector is used. In this work, depth-encoding PET detector modules were built by using long rectangular semi-monolithic scintillators and single-ended readout by silicon photomultiplier (SiPM) arrays. The performance of the detector modules was measured. Methods: The rectangular semi-monolithic scintillator detector has an outside dimension of 11.6 9 37.6 9 10 mm 3 and consists of 11 polished lutetium-yttrium oxyorthosilicate (LYSO) slices measuring 1 9 37.6 9 10 mm 3 . The enhanced specular reflector (ESR) was glued on both crosssectional surfaces of each crystal slice. For the face opposite to the SiPM array and the two end faces of the detectors, surface treatments with and without black paint were implemented for performance comparison. The bottom face of the semi-monolithic detector was coupled to a 4 9 12 SiPM array that was grouped along rows and columns separately into 16 signals. The four row signals were used to identify the slices, and the 12 column signals were used to estimate the y (monolithic direction) and z (depth direction) interaction positions. The detector was irradiated at multiple positions with a collimated 511 keV gamma beam. The collimated beam was obtained with electronic collimation by using a 22 Na point source and a reference detector. The estimated width of the gamma beam is around 0.5 mm. The flood histogram for crystal slices was measured by using the center of gravity (COG) method. The COG method and the squared COG method were used for y position estimation. The standard deviation of the column signals, the ratio of maximum to the sum of the column signals, and the sum of squared column signals were used for z position estimation. Results: All slices were clearly resolved from the measured flood histograms for both detectors with different crystal surface treatments. The estimated y positions roughly linearly change with the true positions at the middle of the detector until~5 mm from both ends of the detector. The y and z spatial resolutions of the detectors were estimated for all middle positions located more than 5 mm from both ends of the detector. The squared COG method provides better y position resolution than the COG method. The three z estimation methods provide similar depth of interaction (DOI) resolution. Surface treatment with black paint significantly improves both y and z position resolution but degrades the energy an...

Timing evaluation of a PET detector block based on semi‐monolithic LYSO crystals

“…6 In another work, a semi-monolithic block with 11 rectangular slabs of 1 × 37.6 × 10 mm 3 was studied with different surface treatments. 7 The detector exhibited 1.07 mm spatial resolution in the monolithic direction, 1.55 mm DOI resolution, 24.9% energy resolution (for one slab), and 788 ps timing resolution with black painting. The timing and energy resolutions were improved to 596 ps and 15.8%, respectively, with ESR treatment, but the spatial and DOI resolution worsen to 1.77 mm and 2.71 mm, respectively.…”

“…The LD in the monolithic direction can be characterized, and the DOI information recovered, preserving both the high sensitivity and good spatial resolution of monolithic detectors. 6,7 The effects on the resolvability of slabs with two different reflectors applied to the lateral walls and different light guide thicknesses have been tested elsewhere. 8 There it is shown that the use of light guides and enhanced specular reflector (ESR) improve the resolvability of the slabs.…”

“…This improves the SNR and, thus, the timing capabilities of the detector. The LD in the monolithic direction can be characterized, and the DOI information recovered, preserving both the high sensitivity and good spatial resolution of monolithic detectors 6,7 …”

“…A semi‐monolithic block consisting of 11 slabs of 1 × 11.6 × 10 mm 3 was tested, obtaining 1.15 mm for both spatial and DOI resolutions, a timing resolution of 575 ps, and an energy resolution of 14.9% for a single slab 6 . In another work, a semi‐monolithic block with 11 rectangular slabs of 1 × 37.6 × 10 mm 3 was studied with different surface treatments 7 . The detector exhibited 1.07 mm spatial resolution in the monolithic direction, 1.55 mm DOI resolution, 24.9% energy resolution (for one slab), and 788 ps timing resolution with black painting.…”

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

“…Multiple methods to collimate gamma photons have been used in literature: the most simple method is electronic collimation as no further instrumentation except PET components is needed [29], [30]. However, the beam profile depends on the accuracy the coincidence detector achieves.…”