Department of Nuclear Medicine, Imaging Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
Phys Med Biol. 2010 Sep 21;55(18):5363-81. doi: 10.1088/0031-9155/55/18/007. Epub 2010 Aug 24.
The lesion detection performance of SPECT and PET scanners is most commonly evaluated with a phantom containing hollow spheres in a background chamber at a specified radionuclide contrast ratio. However, there are limitations associated with a miniature version of a hollow sphere phantom for small-animal SPECT and PET scanners. One issue is that the 'wall effect' associated with zero activity in the sphere wall and fill port causes significant errors for small diameter spheres. Another issue is that there are practical difficulties in fabricating and in filling very small spheres (<3 mm diameter). The need for lesion detection performance assessment of small-animal scanners has motivated our development of a micro-hollow sphere phantom that utilizes the principle of superposition. The phantom is fabricated by stereolithography and has interchangeable sectors containing hollow spheres with volumes ranging from 1 to 14 microL (diameters ranging from 1.25 to 3.0 mm). A simple 60 degrees internal rotation switches the positions of three such sectors with their corresponding background regions. Raw data from scans of each rotated configuration are combined and reconstructed to yield superposition images. Since the sphere counts and background counts are acquired separately, the wall effect is eliminated. The raw data are subsampled randomly prior to summation and reconstruction to specify the desired sphere-to-background contrast ratio of the superposition image. A set of images with multiple contrast ratios is generated for visual assessment of lesion detection thresholds. To demonstrate the utility of the phantom, data were acquired with a multi-pinhole SPECT/CT scanner. Micro-liter syringes were successful in filling the small hollow spheres, and the accuracy of the dispensed volume was validated through repeated filling and weighing of the spheres. The phantom's internal rotation and the data analysis process were successful in producing the expected superposition images. Visual inspection of the multi-contrast images provided simple determination of lesion detection thresholds for this scanner (4:1 ratio for 1.5 mm spheres and 3:1 ratio for 2.0 mm spheres) at a specified cumulated background concentration (30 kBq-min microL(-1)). In summary, the micro-hollow sphere phantom demonstrated its practical utility for lesion detection evaluation and is well suited for comparing the task-based performance of small-animal SPECT and PET scanners.
SPECT 和 PET 扫描仪的病灶检测性能通常使用在指定放射性核素对比比的背景腔中包含空心球体的体模进行评估。然而，对于小动物 SPECT 和 PET 扫描仪的微型空心球体体模存在一些局限性。一个问题是，球体壁和填充端口中零活性相关的“壁效应”会导致小直径球体产生显著误差。另一个问题是，制造和填充非常小的球体（<3 毫米直径）存在实际困难。对小动物扫描仪的病灶检测性能评估的需求促使我们开发了一种利用叠加原理的微空心球体体模。该体模通过立体光刻制造，具有可互换的扇形区域，其中包含体积为 1 至 14 微升（直径为 1.25 至 3.0 毫米）的空心球体。简单的 60 度内部旋转可切换三个具有相应背景区域的扇形区域的位置。从每个旋转配置的扫描中获取原始数据，并将其组合并重建以生成叠加图像。由于球体计数和背景计数是分别获取的，因此消除了壁效应。在求和和重建之前，原始数据随机进行子采样以指定叠加图像的期望球体与背景的对比度。生成一组具有多个对比度比的图像，用于视觉评估病灶检测阈值。为了证明体模的实用性，使用多针孔 SPECT/CT 扫描仪获取了数据。微升注射器成功地填充了小的空心球体，并且通过对球体进行重复填充和称重验证了分配体积的准确性。体模的内部旋转和数据分析过程成功地产生了预期的叠加图像。多对比度图像的目视检查为该扫描仪提供了简单的病灶检测阈值确定（对于 1.5 毫米球体为 4:1 比，对于 2.0 毫米球体为 3:1 比），在指定的累积背景浓度（30 kBq-min 微升-1）下。总之，微空心球体体模证明了其在病灶检测评估中的实际应用价值，非常适合比较小动物 SPECT 和 PET 扫描仪的基于任务的性能。
