Design and performance simulation studies of a breast PET insert integrable into a clinical whole-body PET/MRI scanner

Abstract

Objective: Three different breast PET insert geometries are proposed for integration into an existing MRI breast coil (Breast Biopsy Coil, NORAS MRI products) to be used inside a whole-body PET/MRI scanner (Biograph mMR, Siemens Healthineers) to enhance the sensitivity and spatial resolution of imaging inside the breast. Approach: Monte Carlo simulations were performed to predict and compare the performance characteristics of the three geometries in terms of the sensitivity, spatial resolution, scatter fraction, and noise equivalent count rate (NECR). In addition, the background single count rate due to organ uptake in a clinical scan scenario was predicted using a realistic anthropomorphic phantom. Main results: In the center of the field of view (cFOV), absolute sensitivities of 3.1 %, 2.7 %, and 2.2 % were found for Geometry A (detectors arranged in two cylinders), Geometry B (detectors arranged in two partial cylinders), and Geometry C (detectors arranged in two half cylinders combined with two plates), respectively. The full width at half maximum (FWHM) spatial resolution was determined to be 1.7 mm (Geometry A), 1.8 mm (Geometry B) and 2.0 mm (Geometry C) at 5 mm from the cFOV. Designs with multiple scintillation-crystal layers capable of determining the depth of interaction (DOI) strongly improved the spatial resolution at larger distances from the transaxial cFOV. The system scatter fractions were 33.1 % (Geometries A and B) and 32.3 % (Geometry C). The peak NECRs occurred at source activities of 300 MBq (Geometry A), 310 MBq (Geometry B) and 340 MBq (Geometry C). The background single-event count rates were 17.1×106 cps (Geometry A), 15.3×106 cps (Geometry B) and 14.8×106 cps (Geometry C). Geometry A in the three-layer DOI variant exhibited the best PET performance characteristics but could be challenging to manufacture. Geometry C had the lowest impact on the spatial resolution and the lowest sensitivity among the investigated geometries. Significance: Geometry B in the two-layer DOI variant represented an effective compromise between the PET performance and manufacturing difficulty and was found to be a promising candidate for the future breast PET insert.

New GATE Digitizer Unit for versions post v9.3

“…To illustrate good agreement of the results between previous and new versions, the simulation studies of the expected performance of an under-development breast PET insert, originally performed with the old GDU and GATE v9.1 [9], were reconducted to compare the results. The macro files of the simulations were translated into GATE v9.3 compatible macros using the gt_digi_mac_converter conversion tool.…”

“…The simulated axial sensitivity profile for one of the three breast PET insert geometries introduced by [9] (geometry C) is shown in Figure 3. The old and new GDUs produced consistent axial sensitivity profiles with a mean relative difference of 0.7% and the largest relative difference of 3.4% at the source position with an offset of 50 mm.…”

“…The aim of this test was to check the speedup due to architecture simplifications and the influence of the Digitizer Manager introduction, i.e., speed of the Simulated sensitivity of the future breast PET insert (geometry C) obtained using GATE v9.1 (old GDU) and GATE v9.3 (new GDU). The GATE v9.1 data were taken from [9]. Simulated count rates obtained using GATE v9.1 (old GDU) and GATE v9.3 (new GDU).…”

“…Simulated noise equivalent count rates (NECRs) obtained using GATE v9.1 (old GDU) and GATE v9.3 (new GDU). The GATE v9.1 data were taken from [9].…”

Evaluation of the MRI compatibility of PET detectors modules for organ‐specific inserts in a 3T and 7T MRI scanner

“…In particular, we aim to develop a PET insert dedicated to breast imaging in combination with the whole‐body 3T PET/MRI scanner Biograph mMR 12 as well as a brain PET insert for the 7T MRI scanner MAGNETOM Terra (Siemens Healthineers, Erlangen, Germany).…”