Abstract
Positron Emission Mammography (PEM) with 18F-Fluorodeoxyglucose (18F-FDG) is a functional imaging technique for breast cancer detection. The development of dedicated imaging systems with high sensitivity and spatial resolution are crucial for early breast cancer diagnosis and an efficient therapy. Clear-PEM is a dual planar scanner designed for high-resolution breast cancer imaging under development by the Portuguese PET Mammography consortium within the Crystal Clear Collaboration. It brings together a favorable combination of high-density scintillator crystals coupled to compact photodetectors, arranged in a double readout scheme capable of providing depth-of-interaction information.A Monte Carlo study of the Clear-PEM system counting rates is presented in this paper. Hypothetical breast exam scenarios were simulated to estimate the single event rates, true and random coincidence rates. A realistic description of the patient and detector geometry, radiation environment, physics and instrumentation factors was adopted in this work. Special attention was given to the 18F-FDG accumulation in the patient torso organs which, for the Clear-PEM scanner, represent significant activity outside the field-of-view (FOV) contributing to an increase of singles, randoms and scattered coincidences affecting the overall system performance. The potential benefits of patient shielding to minimize the influence of the out-of-field background was explored. The influence of LYSO:Ce crystal intrinsic natural activity due to the presence of the 176Lu isotope on the counting rate performance of the proposed scanner, was also investigated.
Highlights
(b) the detectors at different separation distances, while allowing to apply lateral compression of the breast during the exam — figure 1(a)
One module is an array of 4×8 LYSO:Ce crystal pixels with dimensions of 2 × 2 × 20 mm3
Realistic imaging conditions were simulated taking into account the influence of out-of-field activity due to 18F-FDG uptake in the organs of an anthropomorphic patient model, a detailed description of the detector geometry and the modeling of data acquisition and trigger system response
Summary
In the adopted simulation methodology, efforts have been made in order to reproduce the radiation environment, physics and instrumentation factors as realistically as possible, which guarantees that results are of practical value for the scanner development phase. That requires an anthropomorphic patient phantom to simulate the background activity, besides the detailed description of the detector geometry and an effective modeling of the data acquisition and trigger systems. These components were integrated in a dedicated Monte Carlo simulation framework specially developed for the Clear-PEM scanner, based on the Geant toolkit [11, 12].
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