Kim H J, Zeeberg B R, Reba R C
Department of Radiology, George Washington University, Washington, DC.
J Nucl Med. 1992 Jun;33(6):1225-34.
The use of SPECT to diagnose physiological alterations in disease states depends on the potential of SPECT to provide a quantitatively accurate reconstructed image. However, the reconstructed values depend upon the shape and size of the brain region as strongly as they depend upon true radioactivity concentration. We report here the results of applying an iterative reconstruction algorithm (IRA) to compensate for shape- and size-dependence, as well as for attenuation and scatter. The IRA is designed only for the reconstruction of images for which the true radioactivity in the white matter within the actual brain is negligible compared with the true radioactivity in the grey matter within the actual brain. The IRA incorporates an accurate three-dimensional model of detector response and utilizes an MRI image which defines the anatomical features of the brain being imaged by segmenting the grey, white and ventricular regions. It is the assumption of radioactivity localization exclusively in the grey matter which permits the efficient incorporation of the MRI image. The IRA was validated by simulation studies that utilized a slice through the basal ganglia in the realistic Hoffman three-dimensional mathematical brain model. FBP images deviate significantly from true radioactivity distribution, whereas IRA images are nearly identical to true radioactivity distribution, except for random fluctuations due to the presence of statistical noise. These results indicate that the application of the IRA will permit SPECT to distinguish deficits due to true physiological changes from apparent deficits due to imaging/reconstruction artifacts.
利用单光子发射计算机断层扫描（SPECT）诊断疾病状态下的生理改变取决于SPECT提供定量准确重建图像的潜力。然而，重建值对脑区形状和大小的依赖程度与对真实放射性浓度的依赖程度一样强烈。我们在此报告应用迭代重建算法（IRA）来补偿形状和大小依赖性以及衰减和散射的结果。IRA仅设计用于重建这样的图像：在实际脑内，白质中的真实放射性与实际脑内灰质中的真实放射性相比可忽略不计。IRA纳入了准确的探测器响应三维模型，并利用通过分割灰质、白质和脑室区域来定义所成像脑部解剖特征的磁共振成像（MRI）图像。正是放射性仅定位于灰质这一假设使得能够有效地纳入MRI图像。IRA通过模拟研究得到验证，这些模拟研究利用了现实的霍夫曼三维数学脑模型中穿过基底神经节的一个切片。傅里叶反投影（FBP）图像显著偏离真实放射性分布，而IRA图像除了由于存在统计噪声导致的随机波动外，几乎与真实放射性分布相同。这些结果表明，应用IRA将使SPECT能够区分由真实生理变化引起的缺陷与由成像/重建伪影导致的明显缺陷。
