Habraken J B, de Bruin K, Shehata M, Booij J, Bennink R, van Eck Smit B L, Busemann Sokole E
Department of Nuclear Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
J Nucl Med. 2001 Dec;42(12):1863-9.
Ex vivo measurements in animals are used frequently in the field of nuclear medicine for the characterization of newly developed radioligands and for drug development. In vivo SPECT would replace these ex vivo measurements in a relatively large number of cases if one were able to adequately image small organs. The pinhole collimator has been used extensively to obtain greater detail in planar imaging. However, using a pinhole collimator for SPECT is difficult because it requires a heavy collimated detector to rotate around a small object with a constant radius of rotation.
We have developed a mechanism in which the gantry and collimator are fixed and the animal rotates. Hollow cylinders of different sizes were made to enable imaging of small animals of different sizes: mice, hamsters, and rats. The cylinder is mounted on a stepping motor-driven system and positioned exactly above the pinhole collimator of an ARC3000 camera with a 1-mm pinhole insert. The stepping motor is controlled by the Hermes acquisition/processing system. After imaging each projection, a signal is given to rotate the stepping motor with the desired number of angular degrees. Filtered backprojection, adapted to pinhole SPECT, was used for reconstruction. The system allows adjustments of the radius of rotation and along the axis of the cylinder to select the field of view. Calibration experiments were performed to ensure that the axis of rotation was exactly in the middle of the cylinder. Phantom experiments were performed to assess sensitivity, spatial resolution, and uniformity of the system and to test the system for distortion artifacts. In addition, a brain dopamine transporter rat study and a hamster myocardial study were performed to test the clinical feasibility of the entire system.
In the line source experiment, the spatial resolution obtained in air was 1.3 mm full width at half maximum, with a radius of rotation of 33 mm. Furthermore, the system has good uniformity and is capable of detecting cold spots of 2-mm diameter. The animal studies showed that it was feasible to image receptors or transporters and organs with sufficient detail in a practical setup.
A rotating cylinder mechanism for pinhole SPECT is feasible and shows the same characteristics as conventional pinhole SPECT with a rotating camera head, without distortion artifacts. This mechanism permits pinhole SPECT to replace many ex vivo animal experiments.
动物离体测量在核医学领域常用于新开发放射性配体的表征及药物研发。如果能够对小器官进行充分成像，那么在相当多的情况下，体内单光子发射计算机断层扫描（SPECT）将取代这些离体测量。针孔准直器已被广泛用于在平面成像中获取更多细节。然而，将针孔准直器用于SPECT很困难，因为它需要一个沉重的准直探测器围绕一个小物体以恒定的旋转半径旋转。
我们开发了一种龙门架和准直器固定而动物旋转的机制。制作了不同尺寸的空心圆柱体，以便对不同大小的小动物（小鼠、仓鼠和大鼠）进行成像。圆柱体安装在步进电机驱动系统上，并精确地定位在带有1毫米针孔插件的ARC3000相机的针孔准直器上方。步进电机由Hermes采集/处理系统控制。在对每个投影进行成像后，会发出一个信号，使步进电机以所需的角度旋转。适用于针孔SPECT的滤波反投影用于重建。该系统允许调整旋转半径和沿圆柱体轴线的位置以选择视野。进行了校准实验以确保旋转轴正好位于圆柱体的中间。进行了体模实验以评估系统的灵敏度、空间分辨率和均匀性，并测试系统是否存在畸变伪影。此外，进行了一项脑多巴胺转运体大鼠研究和一项仓鼠心肌研究，以测试整个系统的临床可行性。
在线源实验中，在空气中获得的空间分辨率为半高宽1.3毫米，旋转半径为33毫米。此外，该系统具有良好的均匀性，能够检测到直径为2毫米的冷区。动物研究表明，在实际设置中对受体、转运体和器官进行足够详细的成像具有可行性。
用于针孔SPECT的旋转圆柱体机制是可行的，并且显示出与具有旋转摄像头的传统针孔SPECT相同的特性，且无畸变伪影。这种机制使针孔SPECT能够取代许多动物离体实验。
