Performance analysis of a high-sensitivity multi-pinhole cardiac SPECT system with hemi-ellipsoid detectors.
Performance analysis of a high-sensitivity multi-pinhole cardiac SPECT system with hemi-ellipsoid detectors.
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DOI：
10.1002/mp.13277
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发表时间：
2019-01
期刊：
影响因子：
3.8
通讯作者：
Pretorius PH
中科院分区：
文献类型：
--
作者：
Bhusal N;Dey J;Xu J;Kalluri K;Konik A;Mukherjee JM;Pretorius PH
单光子发射计算机断层扫描（SPECT）是一种无创成像方式，用于心肌灌注成像。大多数临床SPECT系统面临的挑战是灵敏度低，分辨率差，对患者的辐射剂量相对较高。新一代系统（GE Discovery， DSPECT）专门用于心脏成像，灵敏度提高了5-8倍。这种改进可用于减少采集时间和/或剂量。然而，在超低剂量（~3 mCi）注射的情况下，获取时间仍然很长，需要10-12分钟。这项工作的目的是研究一种新的伽玛相机设计，它有21个半椭球探测器，每个探测器都有一个针孔准直器，用于心脏SPECT，以进一步提高灵敏度和分辨率，减少患者暴露和成像时间。为了评估我们的半椭球体系统的分辨率，在点源、杆源和NCAT模型上进行了GATE蒙特卡罗模拟。对于与基平面探测器的平均全宽-半最大值（FWHM）等效，发现弯曲半椭球探测器的针孔直径为8.68 mm，名义上预计其工作针孔直径比目前最先进的系统高3倍。用21个探测器系统获得感兴趣区域内等间距的棒源，并使用我们的多小孔（MPH）迭代OSEM算法进行重建，并具有准直器分辨率恢复。结果与文献中可用的最先进系统（GE Discovery）的结果进行了比较。该系统还使用数学拟人化NCAT （NURBS-based Cardiac躯干；Segars等）进行评估。核科学进展。1999；46:503-506)幻影，全（临床）剂量获取（25 mCi） 2分钟，超低剂量获取3 mCi 5.44分钟。估计的左心室（LV）计数与最先进的系统（spect）上的可用文献进行比较。估计了准直器分辨率恢复后mph - osem重建图像上左室壁的FWHM。在获得的杆状源上，重建后的平均分辨率（FWHM）与整个感兴趣区域（ROI）的分辨率恢复相比平均为4.44 mm（±2.84），而GE Discovery报道的平均分辨率为6.9 mm（±1 mm） （Kennedy et al., J Nucl Cardiol. 2014: 21:43 - 452）。对于NCAT研究，提高的灵敏度允许全剂量（25 mCi） 2分钟采集（Ell8.68mmFD），产生3.79 M LV计数。与最先进的DSPECT临床全剂量在2分钟内获得的1.13 M LV计数相比，这是约3.35倍。增加的灵敏度还允许在5.44分钟内进行超低剂量获取方案（Ell8.68 mmULD）， 3 mCi（注射剂量减少的8倍）。这种超低剂量方案产生了~1.23 M LV计数，与DSPECT的全剂量2分钟获取相当。在Ell8.68mmFD和ell8.68 mmmuld中-短轴切片周围，经过12次OSEM重建后估计的左室壁NCAT平均FWHM分别为4.95和5.66 mm。我们的蒙特卡罗模拟研究和重建表明，使用（倒酒杯大小）带针孔准直器的半椭球探测器可以将灵敏度提高到新一代专用心脏SPECT系统的3.35倍，同时也提高了棒源的重建分辨率，在感兴趣区域平均为4.44 mm。额外的灵敏度可用于~5.44分钟的超低剂量成像（3 mCi），用于与最先进的系统相当的临床计数。关键词：弯曲检测器，高性能心脏SPECT，多针孔心脏SPECT
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 hemi-ellipsoid detectors each with a pinhole collimator for cardiac SPECT for further improvement in sensitivity and resolution and reduced patient exposures and imaging times. 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. 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 (±2.84), compared to 6.9 mm (±1 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 around the mid-short-axis slices for Ell8.68mmFD and Ell8.68mmULD, respectively. Our Monte-Carlo simulation studies and reconstruction suggest using (inverted wineglass sized) hemi-ellipsoid detectors with pinhole collimators can increase the sensitivity ~3.35 times over the new generation of dedicated cardiac SPECT systems, while also improving the reconstructed resolution for rod-sources with an average of 4.44 mm in region of interest. The extra sensitivity may be used for ultra-low dose imaging (3 mCi) at ~5.44 min for comparable clinical counts as state-of-the-art systems. Key words: curved detectors, high-performance cardiac SPECT, multi-pinhole cardiac SPECT
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