Performance analysis of a high‐sensitivity multi‐pinhole cardiac SPECT system with hemi‐ellipsoid detectors

Abstract

Purpose: Single-photon emission computed tomography (SPECT) is a noninvasive imaging modality, used in myocardial perfusion imaging. The challenges facing the majority of clinical SPECT systems are low sensitivity, poor resolution, and the relatively high radiation dose to the patient. New generation systems (GE Discovery, DSPECT) dedicated to cardiac imaging improve sensitivity by a factor of 5-8. This improvement can be used to decrease acquisition time and/or dose. However, in the case of ultra-low dose (~3 mCi) injections, acquisition times are still significantly long, taking 10-12 min. The purpose of this work is to investigate a new gamma camera design with 21 hemiellipsoid detectors each with a pinhole collimator for cardiac SPECT for further improvement in sensitivity and resolution and reduced patient exposures and imaging times. Methods: To evaluate the resolution of our hemi-ellipsoid system, GATE Monte-Carlo simulations were performed on point-sources, rod-sources, and NCAT phantoms. For average full-width-half-maximum (FWHM) equivalence with base flat-detector, the pinhole-diameter for the curved hemi-ellipsoid detector was found to be 8.68 mm, an operating pinhole-diameter nominally expected to be~3 times more sensitive than state-of-the-art systems. Rod-sources equally spaced within the region of interest were acquired with a 21-detector system and reconstructed with our multi-pinhole (MPH) iterative OSEM algorithm with collimator resolution recovery. The results were compared with the results of a state-of-the-art system (GE Discovery) available in the literature. The system was also evaluated using the mathematical anthropomorphic NCAT (NURBS-based Cardiac Torso; Segars et al. IEEE Trans Nucl Sci. 1999;46:503-506) phantom with a full (clinical)-dose acquisition (25 mCi) for 2 min and an ultra-low dose acquisition of 3 mCi for 5.44 min. The estimated left ventricle (LV) counts were compared with the available literature on a state-of-the-art system (DSPECT). FWHM of the LV wall on MPH-OSEM-reconstructed images with collimator resolution recovery was estimated. Results: On acquired rod-sources, the average resolution (FWHM) after reconstruction with resolution recovery in the entire region of interest (ROI) for cardiac imaging was on the average 4.44 mm (AE2.84), compared to 6.9 mm (AE1 mm) reported for GE Discovery (Kennedy et al., J Nucl Cardiol. 2014:21:443-452). For NCAT studies, improved sensitivity allowed a full-dose (25 mCi) 2-min acquisition (Ell8.68mmFD) which yielded 3.79 M LV counts. This is~3.35 times higher compared to 1.13 M LV counts acquired in 2 min for clinical full dose for state-of-the-art DSPECT. The increased sensitivity also allowed an ultra-low dose acquisition protocol (Ell8.68 mmULD), 3 mCi (eight times less injected dose) in 5.44 min. This ultra-low dose protocol yielded~1.23 M LV counts which was comparable to the full-dose 2-min acquisition for DSPECT. The estimated NCAT average FWHM at the LV wall after 12 iterations of the OSEM reconstruction was 4.95 and 5.66 mm...

The clinical utilities of multi-pinhole single photon emission computed tomography

“…Bhusal et al (95) investigated a novel cardiac SPECT system consisting of 21 pinhole collimators, each coupled to a hemi-ellipsoid detector. They performed GATE simulations with various phantoms to evaluate the system performance.…”

Review on Recent Developments in Collimators of Single Photon Emission Computed Tomography Imaging

“…Space limitation, spatial resolution and sensitivity are determinant in collimator selection for a particular imaging task [14,11]. An appropriate collimator needs to be selected for a specific imaging application, for instance a fan or cone beam collimator for brain imaging, a pin-hole collimator for thyroid, and parallel-hole collimator as generally used in SPECT and planar imaging [7,20,26].…”

Solid-State Detector SPECT Myocardial Perfusion Imaging

“…In a simulation, Zeng et al (70) demonstrated that multidivergent beam collimators could double the photon sensitivity of current SPECT camera systems without sacrificing spatial resolution. Simulations of multipinhole designs with paired curved paraboloid or hemi-ellipsoid detectors could improve photon sensitivity by up to 300% (71,72). In phantom studies, these designs have improved photon sensitivity and spatial resolution compared with published characteristics or commercially available solid-state camera systems (72).…”

“…Simulations of multipinhole designs with paired curved paraboloid or hemi-ellipsoid detectors could improve photon sensitivity by up to 300% (71,72). In phantom studies, these designs have improved photon sensitivity and spatial resolution compared with published characteristics or commercially available solid-state camera systems (72). Nevertheless, these published reports are still preclinical, and it remains to be seen if these designs will be cost-effective and adequate for clinical implementation.…”