Assessment of the Axial Resolution of a Compact Gamma Camera With Coded Aperture Collimator

The dataset contains 21 images of a point-like gamma source, taken with a compact gamma camera that was equipped with a coded aperture collimator. The pixel intensity represents the accumulated energy deposited by the captured gamma photons. This dataset was acquired as part of the following paper, to which the reader is referred for an in-depth explanation.

Note: Although the TIFF files may appear as all black or all transparent images, they will be displayed correctly when opened with an image processing tool such as ImageJ or a Python script.

Assessment of the Axial Resolution of a Compact Gamma Camera With Coded Aperture Collimator

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 0.08mm in diameter in a 0.11mm 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 to 100mm. For each source position, the detector image was reconstructed in 0.5mm 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 4,400 times longer in computation, 3D-MLEM yielded a smaller axial FWHM and a higher CNR. The axial resolution degraded from 5.3mm and 1.8mm at 12mm to 42.2mm and 13.5mm at 100mm 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.