Division of Medical Imaging Physics, Department of Radiology, Johns Hopkins Medical Institutions, Baltimore, MD 21287, USA.
Phys Med Biol. 2010 Sep 21;55(18):5483-97. doi: 10.1088/0031-9155/55/18/014. Epub 2010 Aug 27.
In targeted radionuclide therapy (TRT), dose estimation is essential for treatment planning and tumor dose response studies. Dose estimates are typically based on a time series of whole-body conjugate view planar or SPECT scans of the patient acquired after administration of a planning dose. Quantifying the activity in the organs from these studies is an essential part of dose estimation. The quantitative planar (QPlanar) processing method involves accurate compensation for image degrading factors and correction for organ and background overlap via the combination of computational models of the image formation process and 3D volumes of interest defining the organs to be quantified. When the organ VOIs are accurately defined, the method intrinsically compensates for attenuation, scatter and partial volume effects, as well as overlap with other organs and the background. However, alignment between the 3D organ volume of interest (VOIs) used in QPlanar processing and the true organ projections in the planar images is required. The aim of this research was to study the effects of VOI misregistration on the accuracy and precision of organ activity estimates obtained using the QPlanar method. In this work, we modeled the degree of residual misregistration that would be expected after an automated registration procedure by randomly misaligning 3D SPECT/CT images, from which the VOI information was derived, and planar images. Mutual information-based image registration was used to align the realistic simulated 3D SPECT images with the 2D planar images. The residual image misregistration was used to simulate realistic levels of misregistration and allow investigation of the effects of misregistration on the accuracy and precision of the QPlanar method. We observed that accurate registration is especially important for small organs or ones with low activity concentrations compared to neighboring organs. In addition, residual misregistration gave rise to a loss of precision in the activity estimates that was on the order of the loss of precision due to Poisson noise in the projection data. These results serve as a lower bound on the effects of misregistration on the accuracy and precision of QPlanar activity estimate and demonstrate that misregistration errors must be taken into account when assessing the overall precision of organ dose estimates.
在靶向放射性核素治疗（TRT）中，剂量估计对于治疗计划和肿瘤剂量反应研究至关重要。剂量估计通常基于患者接受计划剂量后采集的全身共轭视图平面或 SPECT 扫描的时间序列。从这些研究中量化器官中的活性是剂量估计的重要组成部分。定量平面（QPlanar）处理方法涉及对图像降级因素进行准确补偿，并通过图像形成过程的计算模型和定义要量化的器官的 3D 感兴趣区域（ROI）的组合来校正器官和背景重叠。当器官 ROI 准确定义时，该方法本质上补偿了衰减、散射和部分容积效应，以及与其他器官和背景的重叠。然而，需要在 QPlanar 处理中使用的 3D 器官 ROI 与平面图像中的真实器官投影之间进行对齐。本研究的目的是研究 ROI 配准不良对 QPlanar 方法获得的器官活性估计的准确性和精密度的影响。在这项工作中，我们通过随机错位源自用于衍生 ROI 信息的 3D SPECT/CT 图像和平面图像，模拟自动配准程序后预期的残留配准程度。基于互信息的图像配准用于将逼真的模拟 3D SPECT 图像与 2D 平面图像对齐。残余图像配准用于模拟真实水平的配准，并允许研究配准对 QPlanar 方法的准确性和精密度的影响。我们观察到，对于与相邻器官相比体积较小或活性浓度较低的器官，准确的配准尤为重要。此外，残留配准导致活性估计的精密度损失与投影数据中泊松噪声引起的精密度损失相当。这些结果是 ROI 配准对 QPlanar 活性估计准确性和精密度影响的下限，并表明在评估器官剂量估计的整体精密度时，必须考虑配准误差。
