Darwesh Reem M, Shin Evelyn, Morgan Paul S, Perkins Alan C
aRadiological and Imaging Sciences, School of Medicine, University of Nottingham bDepartment of Medical Physics and Clinical Engineering, Nottingham University Hospitals NHS Trust, Nottingham, UK cDepartment of Medical Physics, King Abdul-Aziz University, Jeddah, Saudi Arabia.
Nucl Med Commun. 2014 Feb;35(2):189-96. doi: 10.1097/MNM.0000000000000015.
Single-photon emission computed tomography ventilation/perfusion (SPECT V/Q) imaging is recommended both by the Society of Nuclear Medicine and by the European Association of Nuclear Medicine for the diagnosis of pulmonary embolism. However, respiratory motion produces image blurring and degradation of detail in the lungs. We have investigated respiratory gating of SPECT images, correcting for motion to reduce blur and improve image definition.
Wedge-shaped defects of different sizes ranging from 15 to 4 mm were fixed in the lung cavities of an anthropomorphic lung phantom to simulate perfusion defects. Gated and nongated SPECT images were obtained using a double-headed SPECT system. Three-dimensional movement was introduced using a purpose-built moving platform with two motion frequencies of 10 and 20 cycles/min. Motion was tracked with a respiratory-gating system. Gated SPECT data were acquired in 16 discrete data bins in synchronization with the breathing cycle. The images were reconstructed using ordered-subset expectation maximization algorithms and corrected for rigid motion. Contrast and contrast-to-noise ratios (CNRs) were measured to quantify any improvement in the gated motion-corrected images. Visualization of defects in the reconstructed images was performed by seven observers and analyzed using alternative free-response receiver operating characteristic analysis.
Assessment of gated and nongated SPECT phantom images demonstrated that motion adversely affected the detectability of defects. Quantification of data demonstrated that, in the controlled simulation, image quality, defect definition, observer confidence, contrast, and CNR were increased after applying motion correction. Improvement in CNRs was found to be significant using alternative free-response receiver operating characteristic analysis (P=0.0002).
Respiratory-gated motion-corrected SPECT images enhanced the visualization of defects compared with matched moving/nongated images in a realistic moving phantom. This approach may be particularly valuable for SPECT V/Q imaging and may improve the diagnosis of pulmonary embolism.
核医学协会和欧洲核医学协会均推荐采用单光子发射计算机断层扫描通气/灌注（SPECT V/Q）成像来诊断肺栓塞。然而，呼吸运动会导致肺部图像模糊且细节丢失。我们研究了SPECT图像的呼吸门控技术，通过校正运动来减少模糊并改善图像清晰度。
在一个仿真人体肺部模型的肺腔内固定不同大小（范围从15至4毫米）的楔形缺损，以模拟灌注缺损。使用双头SPECT系统获取门控和非门控SPECT图像。通过一个特制的移动平台引入三维运动，该平台具有10和20次/分钟两种运动频率。利用呼吸门控系统跟踪运动。与呼吸周期同步，在16个离散数据仓中采集门控SPECT数据。使用有序子集期望最大化算法重建图像，并对刚体运动进行校正。测量对比度和对比噪声比（CNR），以量化门控运动校正图像的任何改善情况。由7名观察者对重建图像中的缺损进行可视化评估，并使用交替自由响应接收器操作特性分析进行分析。
对门控和非门控SPECT模型图像的评估表明，运动对缺损的可检测性有不利影响。数据量化显示，在受控模拟中，应用运动校正后，图像质量、缺损清晰度、观察者信心、对比度和CNR均有所提高。使用交替自由响应接收器操作特性分析发现CNR的改善具有显著性（P = 0.0002）。
与在实际运动模型中匹配的移动/非门控图像相比，呼吸门控运动校正的SPECT图像增强了缺损的可视化。这种方法对于SPECT V/Q成像可能特别有价值，并可能改善肺栓塞的诊断。
