Assessment of the axial resolution of a compact gamma camera with coded aperture collimator

• Published in: EJNMMI physics Vol. 11; no. 1; pp. 30 - 21
• Main Authors: Meißner, Tobias, Cerbone, Laura Antonia, Russo, Paolo, Nahm, Werner, Hesser, Jürgen
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 21.03.2024; Springer Nature B.V; SpringerOpen
• Subjects: Algorithms; Aperture; Apertures; Applied and Technical Physics; Axial resolution; Cameras; Coded aperture; Collimators; Compact gamma camera; Computational Mathematics and Numerical Analysis; Diameters; Engineering; Image reconstruction; Imaging; Intraoperative imaging; Maximum likelihood decoding; Medicine; Medicine & Public Health; Nuclear Medicine; Original Research; Radioguided surgery; Radiology; Coded aperture; Timepix3; Axial resolution; Radioguided surgery; Intraoperative imaging; Compact gamma camera; Image reconstruction
• DOI: 10.1186/s40658-024-00631-5
• ISSN: 2197-7364

Purpose Handheld gamma cameras with coded aperture collimators are under investigation for intraoperative imaging in nuclear medicine. Coded apertures are a promising collimation technique for applications such as lymph node localization due to their high sensitivity and the possibility of 3D imaging. We evaluated the axial resolution and computational performance of two reconstruction methods. Methods An experimental gamma camera was set up consisting of the pixelated semiconductor detector Timepix3 and MURA mask of rank 31 with round holes of 0.08 mm in diameter in a 0.11 mm thick Tungsten sheet. A set of measurements was taken where a point-like gamma source was placed centrally at 21 different positions within the range of 12–100 mm. For each source position, the detector image was reconstructed in 0.5 mm steps around the true source position, resulting in an image stack. The axial resolution was assessed by the full width at half maximum (FWHM) of the contrast-to-noise ratio (CNR) profile along the z-axis of the stack. Two reconstruction methods were compared: MURA Decoding and a 3D maximum likelihood expectation maximization algorithm (3D-MLEM). Results While taking 4400 times longer in computation, 3D-MLEM yielded a smaller axial FWHM and a higher CNR. The axial resolution degraded from 5.3 mm and 1.8 mm at 12 mm to 42.2 mm and 13.5 mm at 100 mm for MURA Decoding and 3D-MLEM respectively. Conclusion Our results show that the coded aperture enables the depth estimation of single point-like sources in the near field. Here, 3D-MLEM offered a better axial resolution but was computationally much slower than MURA Decoding, whose reconstruction time is compatible with real-time imaging.