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

本研究采用Chang的衰减校正方法，利用γ射线扇束透射CT（FTCT）测量的线性衰减系数图，利用市售γ射线照相机系统进行FTCT扫描，通过校正γ射线的衰减和散射，获得定量SPECT图像（Toshiba GCA-9300 A）。作为FTCT的外部源，我们用了Tc-在扇形束准直器的焦点上放置99 m的线源，通过消除每个平面图像中散射光子的计数来进行散射校正，所用的方法是三重能量窗口（TEW）方法，其中使用三个窗口在每个像素处采集计数数据：在主窗的两侧各设一个子窗，主窗内的散射光子被估计为一个由子窗数目和主窗宽度构成的梯形区域，这些衰减和散射校正方法通过使用Monte Carlo方法的模拟以及包括体模研究和初步临床研究的实验来评估。这些模拟和实验的结果表明，在临床上实现。

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.