Design and performance evaluation of a 20-aperture multipinhole collimator for myocardial perfusion imaging applications

Abstract

Single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) remains a critical tool in the diagnosis of coronary artery disease (CAD). However, after more than three decades of use, photon detection efficiency remains poor and unchanged. This is due to the continued reliance on parallel-hole collimators first introduced in 1964. These collimators possess poor geometric efficiency. Here we present the performance evaluation results of a newly designed multipinhole collimator with 20 pinhole apertures (PH20) for commercial SPECT systems. Computer simulations and numerical observer studies were used to assess the noise, bias and diagnostic imaging performance of a PH20 collimator in comparison with those of a low energy high resolution (LEHR) parallel-hole collimator. Ray-driven projector/backprojector pairs were used to model SPECT imaging acquisitions, including simulation of noiseless projection data and performing MLEM/OSEM image reconstructions. Poisson noise was added to noiseless projections for realistic projection data. Noise and bias performance were investigated for five mathematical cardiac and torso (MCAT) phantom anatomies imaged at two gantry orbit positions (19.5 cm and 25.0 cm). PH20 and LEHR images were reconstructed with 300 MLEM iterations and 30 OSEM iterations (10 subsets), respectively. Diagnostic imaging performance was assessed by a receiver operating characteristic (ROC) analysis performed on a single MCAT phantom; however, in this case PH20 images were reconstructed with 75 pixel-based OSEM iterations (4 subsets). Four PH20 projection views from two positions of a dual-head camera acquisition and sixty LEHR projections were simulated for all studies. At uniformly-imposed resolution of 12.5 mm, significant improvements in SNR and diagnostic sensitivity (represented by the area under the ROC curve, or AUC) were realized when PH20 collimators are substituted for LEHR parallel- hole collimators. SNR improves by factors of 1.94-2.34 for the five patient anatomies and two orbital positions studied. For the ROC analysis the PH20 AUC is larger than the LEHR AUC with a p-value of 0.0067. Bias performance, however, decreases with the use of PH20 collimators. Systematic analyses showed PH20 collimators present improved diagnostic imaging performance over LEHR collimators, requiring only collimator exchange on existing SPECT cameras for their use.

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

“…The pin-hole collimation has been introduced to compensate the low photon detection efficiency of parallel-hole systems and to improve the image contrast [11,17]. The collimator consists of a single hole drilled into a lead sheet [6,20].…”

“…There has been much improvement in collimator geometry and also reconstruction algorithms [7,8,[10][11][12]. Parallel hole collimator is routinely used to planar and SPECT imaging [13][14][15][16][17]. An array of holes separated by thin walls (septa), which are fabricated by employing heavy elements, e.g.…”

Multipinhole collimator with 20 apertures for a brain SPECT application

“…The effects of scatter and parallax were not included in the system matrix. 29 Finally, all reconstructed images were postprocessed with a low-pass order 10 Butterworth filter with 0.7 cycles per pixel (pixel size of 0.368 cm) as previously suggested 9,10 and to match the postfiltering used in the vendor provided software for LEHR OSEM reconstruction of the brain. This postfilter helps to remove high frequency noise that may be a result of the acquisition or reconstruction.…”

“…In our recent study inspired by an earlier work by Funk, 28 we reported the performance test of the multipinhole collimation and showed that the new 20-pinhole collimator improves the SNR of myocardial perfusion imaging (MPI) by a factor greater than 2 over that of using LEHR collimators with a fixed resolution of 12.5 mm. 29 The purpose of this study was to investigate the performance of a new 20 multipinhole (20-MPH) collimator over the conventional LEHR technology for brain SPECT imaging and to perform physical experimental measurements with the 20-MPH. Our working hypothesis was that a substantial improvement in counting statistics (signal-to-noise, efficiency, etc.)…”

Segmented slant hole collimator for stationary cardiac SPECT: Monte Carlo simulations

“…11 However, for human cardiac studies, the multipinhole system operates in minification mode, that is, the object is placed away from the pinhole and the images on the detector are smaller than the object [ Fig. 1(b)], e.g., UC San Francisco and Western Cardiology Associate's stationary multipinhole system 7,8,12 and Discovery NM 530c (GE Healthcare, Haifa, Israel). 9,10 The detection sensitivity is proportional to the image magnification factor.…”