Multipinhole collimator with 20 apertures for a brain SPECT application

Abstract

Purpose: Several new technologies for single photon emission computed tomography (SPECT) instrumentation with parallel-hole collimation have been proposed to improve detector sensitivity and signal collection efficiency. Benefits from improved signal efficiency include shorter acquisition times and lower dose requirements. In this paper, the authors show a possibility of over an order of magnitude enhancement in photon detection efficiency (from 7.6 × 10(-5) to 1.6 × 10(-3)) for dopamine transporter (DaT) imaging of the striatum over the conventional SPECT parallel-hole collimators by use of custom-designed 20 multipinhole (20-MPH) collimators with apertures of 0.75 cm diameter.

Methods: Quantifying specific binding ratio (SBR) of (123)I-ioflupane or (123)I-iometopane's signal at the striatal region is a common brain imaging method to confirm the diagnosis of the Parkinson's disease. The authors performed imaging of a striatal phantom filled with aqueous solution of I-123 and compared camera recovery ratios of SBR acquired between low-energy high-resolution (LEHR) parallel-hole collimators and 20-MPH collimators.

Results: With only two-thirds of total acquisition time (20 min against 30 min), a comparable camera recovery ratio of SBR was achieved using 20-MPH collimators in comparison to that from the LEHR collimator study.

Conclusions: Their systematic analyses showed that the 20-MPH collimator could be a promising alternative for the DaT SPECT imaging for brain over the traditional LEHR collimator, which could give both shorter scan time and improved diagnostic accuracy.

FIG. 1.

(a) Tungsten 20-pinhole aperture plate. (b) Assembled with collimator mount for use with a dual-head clinical SPECT scanner (GE Infinia Hawkeye 4).

FIG. 2.

Illustration of the process by which the SBR and SNR are calculated for the 20-MPH. (a) Original image. (b) The striatal VOIs were chosen to cover both striata. (c) The image is smoothed to remove statistical variation and all voxels brighter than M_ns in the VOI replaced with M_ns. (d) The image is heavily filtered to generate a smooth contour. (e) A threshold boundary is generated with 0.5M_ns to remove partial volume effects associated with the outside of the head. (f) The final image used to estimate the nonspecific binding in all regions of the head. (g) The threshold boundary and the striatal VOIs are used as a mask in (a) to create the region for the calculation of the noise in the SNR of Eq. (5).

FIG. 3.

Reconstructed striatal phantom I-123 images with 14.4:1 (L) and 9:1 (R) SBR setting. (a) Acquired with conventional LEHR collimator for 30 min and 120 total views and reconstructed with OSEM (10 subset, 2 iterations). Acquired with 0.75 cm aperture 20-MPH collimator for 20 min and 8 total views, (b) reconstructed with 240-iterative MLEM, (c) 8 subsets, 30 iterations POSEM, and (d) 16 subsets, 15 iterations POSEM. (e) CT image of the striatal phantom with arrows indicating radionuclide concentration distribution. The two small circles are vinyl screws.

FIG. 4.

Reconstructed prefiltered striatal phantom I-123 images with 14.4:1 (L) and 9:1 (R) SBR setting. Acquired with 0.75 cm aperture 20-MPH collimator for 20 min and 8 total views, (a) reconstructed with 240-iterative MLEM, (b) 8 subsets, 30 iterations POSEM. Images constructed from noisy projections with (c) 240-iterative MLEM, (d) 8 subsets, 30 iterations POSEM.