Development of a dual fanbeam gamma ray TCT system for quantitative myocardial SPECT

为了重建定量SPECT图像，需要校正γ射线在体内的衰减，因此，期望获得由γ射线透射CT测量的真实衰减图。已经提出了许多γ射线透射数据采集系统的方法和几何结构，然而，在闪烁体的尺寸上存在限制，并且这在胸部的重建图像中引起严重的伪影。我们提出了一种新的几何形状，以获取伽马射线透射CT数据使用扇束准直器。在所提出的数据采集系统中，我们使用两个探测器采集伽马射线透射数据。配备有相同焦距的扇形束准直器的两个探测器一起围绕患者身体旋转。位于扇束准直器焦点处的外部伽马射线线源与探测器的旋转同时旋转。从两个探测器获得的两个平面图像中，我们得到了一个具有大视场的理想透射数据。理想视场的大小可以通过扇束准直器的焦距来控制。如果探测器长度为40 cm，焦距从50 cm变化到60 cm，则使用单个探测器时有效视场的半径从13.5 cm增加到14.4 cm。另一方面，如果我们使用所提出的数据采集几何结构，则半径分别从19.2cm增加到23.5cm。从基本结果出发，通过改变焦距和探测器尺寸进行了仿真，验证了该方法的有效性。总之，该方法可以使用小尺寸的普通闪烁体显著地扩大视场，并且很好地消除了投影数据的截断。

In order to reconstruct the quantitative SPECT images, it is necessary to correct attenuation of the gamma rays in the body, therefore, it is desired to obtain a true atenuation map measured by gamma-ray transmission CT.Many methods and geometries of the gamma-ray transmission data acquisition system have been proposed, however, there is a limitation in the size of the scintillator and this causes a serious artifact in reconstructed images of thorax. We propose a new geometry to acquire gamma-ray transmission CT data using fanbeam collimators. In the proposed data acquisition system, we use two detectors for the acquisition of gamma-ray transmission data. The two detectors equipped with the fanbeam collimator of the same focal length rotate together around the patient body. An external gamma-ray line source located at the focal point of the fanbeam collimators rotates simultaneously as the rotation of the detectors. From the two planar images acquired by two detectors, we make an ideal transmission data having large field of view. The size of the ideal field of view can be controlled by the focal length of the fanbeam collimators. If the detector length is 40cm and the focal length changes from 50cm to 60cm, the radius of the effective field of view increases from 13.5cm to 14.4cm using a single detector. On the other hand, if we use the proposed data acquisition geometry, the radius increases from 19.2cm to 23.5cm, respectively. From the basic results, we made some simulations by changing the focal length and the detector size, and confirmed the effectivity of the proposed method. In summary, the proposed method could enlarge the field of view using an ordinary scintillator with smal size significantly, and the truncation of projection data was eliminated perfectly.