Speaker
Description
γ-cameras with coded apertures have been proved to be an efficient method to identify weak γ-radioactive sources in three-dimensional space, providing planar images with sufficient spatial resolution and signal-to-noise ratio [1]. In this work, we attempted a single-photon-emission computerized tomography with the filtered-back-projection method, exploiting planar images derived by a fast-simulation code. The field of view (FOV) comprised by the system is specifically designed for human-centric applications, focusing on the accurate three-dimensional localization of radioactive tracers within the human body for clinical diagnostics. The evaluation of the method has been done via the appropriate figures of merit like the source-location-accuracy, the signal-to-noise ratio (SNR) and the full width at half maximum (FWHM) of the point-spread function.
Planar images of the simulated radioactive sources are captured by rotating the mask-detector system around the origin of coordinates, with motion constrained to the x-z plane. Coded aperture comprised by arranging lead spheres on a transparent plate in a Modified Uniformly Redundant Array (MURA) mask configuration [2]. The system is evaluated in a near-field geometry —a configuration essential for medical settings where source-to-detector distances are limited— with the detector and the mask positioned 860 mm and 820 mm from the center of rotation, respectively. The radioactive sources placed in the whole range of FOV even at the edge, i.e. (230, 230, 230) mm, demonstrating high-fidelity tomographic images.
The reconstruction process is based on 3D back-projection, while a Ram-Lak filter is incorporated to mitigate the ambiguity and artifacts introduced by simple back-projection. Both point and extended radioactive sources are examined, with the latter being geometrically approximated as rectangular parallelepipeds to simulate distributions of radioactivity in human tissues. The quantitative results demonstrate the system's ability to accurately reconstruct radioactivity distributions and distinguish between various source configurations, providing a robust computational foundation for high-resolution 3D medical diagnostic imaging with modified uniformly redundant array (MURA) coded apertures []. For tomographic images, a point source at the center of rotation yields an SNR of 18 and a FWHM of 50 mm, whereas at the eccentric position (230, 230, 230) mm the SNR is 17.5 with a FWHM of 54 mm, indicating that the 3D back-projection method maintains adequate reconstruction fidelity even at off-center source locations approaching the edge of the field of view.
[1] I. Kaissas et al 2020 JINST 15 C01012
[2] Stephen R. Gottesman and E. E. Fenimore, Appl. Opt. 28, 4344-4352 (1989)