On an attenuation correction using gamma ray TCT for quantitative SPECT imaging

本研究是通过校正伽马射线的衰减和散射来获得定量的SPECT图像。在衰减校正中，我们使用Chang的方法与伽马射线扇束透射CT （FTCT）测量的线性衰减系数的精确图。FTCT扫描使用市售伽玛相机系统（东芝GCA-9300A）和风扇束准直器进行。作为FTCT的外部源，我们在每个风扇束准直器的焦点处使用了Tc-99m线源。通过消除每个平面图像的散射光子计数进行散射校正。所采用的方法是三重能量窗口（TEW）法，该方法通过三个窗口在每个像素处获取计数数据：一个以光峰能量为中心的主窗口和主窗口两侧的两个子窗口。将包含在主窗口中的散射光子估计为由子窗口计数和主窗口宽度形成的梯形区域，并从主窗口计数中减去。这些衰减和散射校正方法通过蒙特卡罗方法的模拟以及包括幻影研究和初步临床研究在内的实验进行了评估。这些模拟和实验的结果表明，在临床情况下，可以实现对物体活动的定量测量。

This study was carried out to obtain quantitative SPECT images by correcting attenuation and scattering of gamma rays.In the attenuation correction, we used Chang's method with an accurate map of linear attenuation coefficients measured by gamma ray fanbeam transmission CT (FTCT).FTCT scanning was performed using a commercially available gamma camera system (Toshiba GCA-9300A) with fanbeam collimators.As an external source for FTCT,we used a Tc-99m line source positioned at the focal point of each fanbeam collimator.Scatter correction was performed by eliminating the counts of scattered photons from each planar image.The method used was the triple energy window (TEW) method, in which the count data were acquired at each pixel using three windows : amain window centered at photopeak energy and two subwindows on both sides of the main window.The scattered photons included in the main window were estimated as a trapezoidal region shaped by the counts of the subwindows and the width of the main window, and were subtracted from the count of the main window.These attenuation and scatter correction methods were evaluated by simulations using a Monte Carlo method and by experiments including phantom studies and preliminary clinical studies.The results of these simulations and experiments showed that quantitative measurement of activity in an object was realized in clinical situations.