Lalush David S, DiMeo Andrew J
Department of Biomedical Engineering, University of North Carolina at Chapel Hill, USA.
J Nucl Med. 2002 Nov;43(11):1578-83.
Dual-plane circular-orbit cone-beam (DPCB) SPECT uses a pair of dissimilar cone-beam collimators to expand the axial field of view for brain SPECT. We applied observer study methodology to evaluate the improvement in detection of small defects in brain perfusion provided by DPCB SPECT, compared with conventional parallel-beam imaging. We also evaluated the effect of changing the radius of rotation on DPCB imaging.
Images were realistically simulated using a brain phantom. High-count Monte Carlo simulations were performed for 4 imaging configurations: low-energy high-resolution parallel-beam imaging at a radius of rotation of 18 cm and DPCB imaging (52-cm focal length) at radii of rotation of 20, 24, and 28 cm. These distances corresponded to those required for our camera to clear the shoulders of a patient in the 5th, 50th, and 95th percentiles of shoulder width. Perfusion defects of approximately 1.8-cm diameter were simulated at 4 locations in the brain. Poisson noise was simulated, and images were reconstructed to create a set of 200 images for each of the 4 configurations. All reconstructions used ordered-subset expectation maximization with attenuation modeling. Eight observers viewed images on which the possible location of the defect was marked. The observers were trained using 384 images, were tested using 416 images, and rated on a continuous scale their confidence about the presence of a defect.
Using a paired t test for the estimated areas under the receiver operating characteristic (ROC) curve for each observer, we found that all 3 DPCB configurations resulted in higher areas under the ROC curve than did the parallel-beam configuration. Further, area under the ROC curve for the DPCB configurations improved with decreasing radius of rotation. All comparisons were significant at P < 0.05, except for DPCB 20 cm to DPCB 24 cm (P = 0.089).
Use of a dual-plane cone beam is feasible for brain SPECT and better detects small perfusion defects than does a parallel beam, despite the possibility that the radius of rotation will need to be increased significantly to clear the patient's shoulders. A dual-plane cone beam should be used with the shortest radius of rotation possible to maximize the detectability of small perfusion defects.
双平面圆形轨道锥束（DPCB）单光子发射计算机断层扫描（SPECT）使用一对不同的锥束准直器来扩大脑SPECT的轴向视野。我们应用观察者研究方法来评估与传统平行束成像相比，DPCB SPECT在检测脑灌注小缺陷方面的改进。我们还评估了改变旋转半径对DPCB成像的影响。
使用脑部模型逼真地模拟图像。对4种成像配置进行了高计数蒙特卡罗模拟：在18 cm旋转半径下的低能高分辨率平行束成像以及在20、24和28 cm旋转半径下的DPCB成像（焦距52 cm）。这些距离对应于我们的相机在第5、第50和第95百分位肩宽的患者肩部处进行扫描所需的距离。在脑内4个位置模拟了直径约1.8 cm的灌注缺陷。模拟泊松噪声，并对图像进行重建，为4种配置中的每种创建一组200张图像。所有重建均使用带衰减建模的有序子集期望最大化算法。8名观察者查看标记了缺陷可能位置的图像。观察者使用384张图像进行训练，使用416张图像进行测试，并以连续量表对他们对缺陷存在的信心进行评分。
对每个观察者的接收器操作特征（ROC）曲线下估计面积使用配对t检验，我们发现所有3种DPCB配置的ROC曲线下面积均高于平行束配置。此外，DPCB配置的ROC曲线下面积随着旋转半径的减小而改善。除了DPCB 20 cm与DPCB 24 cm比较（P = 0.089）外，所有比较在P < 0.05时均具有显著性。
双平面锥束用于脑SPECT是可行的，并且与平行束相比能更好地检测小灌注缺陷，尽管可能需要显著增加旋转半径以避开患者肩部。应使用尽可能短旋转半径的双平面锥束以最大化小灌注缺陷的可检测性。
