Pourmoghaddas Amir, Wells R Glenn
Physics Department, Carleton University, Ottawa, Ontario K1S 5B6, Canada and Cardiology, The University of Ottawa Heart Institute, Ottawa, Ontario K1Y4W7, Canada.
Med Phys. 2016 Jan;43(1):44. doi: 10.1118/1.4937601.
Recently, there has been increased interest in dedicated cardiac single photon emission computed tomography (SPECT) scanners with pinhole collimation and improved detector technology due to their improved count sensitivity and resolution over traditional parallel-hole cameras. With traditional cameras, energy-based approaches are often used in the clinic for scatter compensation because they are fast and easily implemented. Some of the cardiac cameras use cadmium-zinc-telluride (CZT) detectors which can complicate the use of energy-based scatter correction (SC) due to the low-energy tail-an increased number of unscattered photons detected with reduced energy. Modified energy-based scatter correction methods can be implemented, but their level of accuracy is unclear. In this study, the authors validated by physical phantom experiments the quantitative accuracy and reproducibility of easily implemented correction techniques applied to (99m)Tc myocardial imaging with a CZT-detector-based gamma camera with multiple heads, each with a single-pinhole collimator.
Activity in the cardiac compartment of an Anthropomorphic Torso phantom (Data Spectrum Corporation) was measured through 15 (99m)Tc-SPECT acquisitions. The ratio of activity concentrations in organ compartments resembled a clinical (99m)Tc-sestamibi scan and was kept consistent across all experiments (1.2:1 heart to liver and 1.5:1 heart to lung). Two background activity levels were considered: no activity (cold) and an activity concentration 1/10th of the heart (hot). A plastic "lesion" was placed inside of the septal wall of the myocardial insert to simulate the presence of a region without tracer uptake and contrast in this lesion was calculated for all images. The true net activity in each compartment was measured with a dose calibrator (CRC-25R, Capintec, Inc.). A 10 min SPECT image was acquired using a dedicated cardiac camera with CZT detectors (Discovery NM530c, GE Healthcare), followed by a CT scan for attenuation correction (AC). For each experiment, separate images were created including reconstruction with no corrections (NC), with AC, with attenuation and dual-energy window (DEW) scatter correction (ACSC), with attenuation and partial volume correction (PVC) applied (ACPVC), and with attenuation, scatter, and PVC applied (ACSCPVC). The DEW SC method used was modified to account for the presence of the low-energy tail.
T-tests showed that the mean error in absolute activity measurement was reduced significantly for AC and ACSC compared to NC for both (hot and cold) datasets (p < 0.001) and that ACSC, ACPVC, and ACSCPVC show significant reductions in mean differences compared to AC (p ≤ 0.001) without increasing the uncertainty (p > 0.4). The effect of SC and PVC was significant in reducing errors over AC in both datasets (p < 0.001 and p < 0.01, respectively), resulting in a mean error of 5% ± 4%.
Quantitative measurements of cardiac (99m)Tc activity are achievable using attenuation and scatter corrections, with the authors' dedicated cardiac SPECT camera. Partial volume corrections offer improvements in measurement accuracy in AC images and ACSC images with elevated background activity; however, these improvements are not significant in ACSC images with low background activity.
最近，由于针孔准直和改进的探测器技术的专用心脏单光子发射计算机断层扫描（SPECT）扫描仪相较于传统平行孔相机具有更高的计数灵敏度和分辨率，人们对其兴趣日益增加。在临床上，对于传统相机，基于能量的方法常用于散射补偿，因为它们快速且易于实施。一些心脏相机使用碲锌镉（CZT）探测器，由于低能尾（检测到的未散射光子数量增加但能量降低），这可能会使基于能量的散射校正（SC）的使用变得复杂。可以实施改进的基于能量的散射校正方法，但其准确性尚不清楚。在本研究中，作者通过物理体模实验验证了应用于基于CZT探测器的多头γ相机进行（99m）Tc心肌成像的易于实施的校正技术的定量准确性和可重复性，每个相机都配备单针孔准直器。
通过15次（99m）Tc - SPECT采集测量了拟人化躯干体模（Data Spectrum Corporation）心脏区域的活性。器官区域活性浓度的比值类似于临床（99m）Tc - 司他比扫描，并在所有实验中保持一致（心脏与肝脏为1.2:1，心脏与肺为1.5:1）。考虑了两种背景活性水平：无活性（冷）和活性浓度为心脏的1/10（热）。在心肌插入物的间隔壁内放置一个塑料“病变”以模拟无示踪剂摄取区域的存在，并计算所有图像中该病变的对比度。使用剂量校准器（CRC - 25R，Capintec，Inc.）测量每个区域的真实净活性。使用配备CZT探测器的专用心脏相机（Discovery NM530c，GE Healthcare）采集10分钟的SPECT图像，随后进行CT扫描以进行衰减校正（AC）。对于每个实验，创建单独的图像，包括无校正（NC）重建、AC重建、应用衰减和双能窗（DEW）散射校正（ACSC）重建、应用衰减和部分容积校正（PVC）重建（ACPVC）以及应用衰减、散射和PVC重建（ACSCPVC）。所使用的DEW SC方法进行了修改以考虑低能尾的存在。
t检验表明，对于（热和冷）两个数据集，与NC相比，AC和ACSC在绝对活性测量中的平均误差均显著降低（p < 0.001），并且与AC相比，ACSC、ACPVC和ACSCPVC的平均差异显著降低（p≤0.001），同时未增加不确定性（p > 0.4）。在两个数据集中，SC和PVC在降低AC误差方面的效果均显著（分别为p < 0.001和p < 0.01），导致平均误差为5%±4%。
使用作者的专用心脏SPECT相机，通过衰减和散射校正可以实现心脏（99m）Tc活性的定量测量。部分容积校正可提高AC图像和背景活性升高的ACSC图像的测量准确性；然而，在背景活性低的ACSC图像中，这些改进并不显著。
