Rajeevan N, Zubal I G, Ramsby S Q, Zoghbi S S, Seibyl J, Innis R B
Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, USA.
J Nucl Med. 1998 Oct;39(10):1719-26.
The purposes of this study were to develop a method for nonuniform attenuation correction of 123I emission brain images based on transmission imaging with a longer-lived isotope (i.e., 57Co) and to evaluate the relative improvement in quantitative SPECT images achieved with nonuniform attenuation correction.
Emission and transmission SPECT scans were acquired on three different sets of studies: a heterogeneous brain phantom filled with 1231 to simulate the distribution of dopamine transporters labeled with 2beta-carbomethoxy-3beta-(4-123I-iodophenyl)tropane (123I-beta-CIT); nine healthy human control subjects who underwent transmission scanning using two separate line sources (57Co and 123I); and a set of eight patients with Parkinson's disease and five healthy control subjects who received both emission and transmission scans after injection of 123I-beta-CIT. Attenuation maps were reconstructed using a Bayesian transmission reconstruction algorithm, and attenuation correction was performed using Chang's postprocessing method. The spatial distribution of errors within the brain was obtained from attenuation correction factors computed from uniform and nonuniform attenuation maps and was visualized on a pixel-by-pixel basis as an error image.
For the heterogeneous brain phantom, the uniform attenuation correction had errors of 2%-6.5% for regions corresponding to striatum and background, whereas nonuniform attenuation correction was within 1%. Analysis of 123I transmission images of the nine healthy human control subjects showed differences between uniform and nonuniform attenuation correction to be in the range of 6.4%-16.0% for brain regions of interest (ROIs). The human control subjects who received transmission scans only were used to generate a curvilinear function to convert 57Co attenuation values into those for 123I, based on a pixel-by-pixel comparison of two coregistered transmission images for each subject. These values were applied to the group of patients and healthy control subjects who received transmission 57Co scans and emission 123I scans after injection of 123I-beta-CIT. In comparison to nonuniform attenuation correction as the gold standard, uniform attenuation with the ellipse drawn around the transmission image caused an approximately 5% error, whereas placement of the ellipse around the emission image caused a 15% error.
Nonuniform attenuation correction allowed a moderate improvement in the measurement of absolute activity in individual brain ROIs. When images were analyzed as target-to-background activity ratios, as is commonly performed with 123I-beta-CIT, these outcome measures showed only small differences when Parkinson's disease patients and healthy control subjects were compared using nonuniform, uniform or even no attenuation correction.
本研究的目的是开发一种基于使用寿命更长的同位素（即57Co）的透射成像对123I发射脑图像进行非均匀衰减校正的方法，并评估非均匀衰减校正所实现的定量SPECT图像的相对改善。
在三组不同的研究中进行发射和透射SPECT扫描：一个填充有123I的异质脑模型，以模拟用2β-甲氧基羰基-3β-（4-123I-碘苯基）托烷（123I-β-CIT）标记的多巴胺转运体的分布；九名健康人类对照受试者，他们使用两个单独的线源（57Co和123I）进行透射扫描；以及一组八名帕金森病患者和五名健康对照受试者，他们在注射123I-β-CIT后接受了发射和透射扫描。使用贝叶斯透射重建算法重建衰减图，并使用Chang的后处理方法进行衰减校正。从均匀和非均匀衰减图计算得到的衰减校正因子中获得脑内误差的空间分布，并逐像素可视化为误差图像。
对于异质脑模型，对应于纹状体和背景区域的均匀衰减校正误差为2%-6.5%，而非均匀衰减校正误差在1%以内。对九名健康人类对照受试者的123I透射图像分析表明，感兴趣脑区（ROI）的均匀和非均匀衰减校正之间的差异在6.4%-16.0%范围内。仅接受透射扫描的人类对照受试者用于生成曲线函数，以根据每个受试者的两个配准透射图像的逐像素比较将57Co衰减值转换为123I的衰减值。这些值应用于在注射123I-β-CIT后接受57Co透射扫描和123I发射扫描的患者组和健康对照受试者。与作为金标准的非均匀衰减校正相比，在透射图像周围绘制椭圆的均匀衰减导致约5%的误差，而在发射图像周围放置椭圆导致15%的误差。
非均匀衰减校正使个体脑ROI中绝对活性的测量有适度改善。当图像作为目标与背景活性比进行分析时，如通常对123I-β-CIT所做的那样，在比较帕金森病患者和健康对照受试者时，使用非均匀、均匀甚至不进行衰减校正，这些结果测量仅显示出微小差异。
