Soonawala Darius, Amin Tania, Ebmeier Klaus P, Steele J Douglas, Dougall Nadine J, Best Jonathan, Migneco Octave, Nobili Flavio, Scheidhauer Klemens
Department of Psychiatry, University of Edinburgh, Kennedy Tower, Royal Edinburgh Hospital, Morningside Park, Edinburgh EH10 5HF, United Kingdom.
Neuroimage. 2002 Nov;17(3):1193-202. doi: 10.1006/nimg.2002.1259.
For a quantitative comparison of images obtained during (99m)Tc-hexamethylpropylene amine oxime (HMPAO) single-photon emission computed tomography (SPECT), brain activity values are usually normalized to a reference region. In studies of Alzheimer-type dementia (ATD), the cerebellum is often used as a reference region, assuming that it is spared any major pathological involvement. Statistical parametric mapping (SPM) may enhance the evaluation of SPECT scans in ATD patients. However, current SPM software only allows scaling to average whole brain activity (i.e., global normalization). The aim of this study was to develop an easily applied, objective, and reproducible method for determining average cerebellar tracer uptake so that images can be scaled specifically to cerebellar activity prior to the performance of SPM analysis. We also investigated whether cerebellar normalization increases the sensitivity and specificity of SPM analysis of ATD patients compared with global normalization.
Image files were taken from a parallel study investigating the use of SPECT as a diagnostic tool for early onset of ATD. Two methods for determining cerebellar activity were developed: one manually, using templates, the other automated, using specified coordinates entered into a Matlab routine. Group comparison of ATD patients versus controls (= healthy volunteers and depressed patients) was performed on a voxel-by-voxel basis using SPM 96 on Windows 95. Receiver operator characteristics (ROC) were computed for 20 student raters examining patient and control scans with and without single-subject SPMs.
The reduction of cerebral blood flow in the group of ATD patients appeared 1.7 times greater in spatial extent when the tracer uptake was normalized to cerebellum rather than to average whole brain activity. Computing the reverse contrast (reductions in the control group compared with ATD patients) produced clusters of significance in globally normalized images which were not manifest after normalizing to cerebellum. This is consistent with the notion that the cerebellum is spared in ATD. Analysis of the area under the ROC curve showed that cerebellar-normalized SPM produced significantly improved accuracy over perfusion scans alone.
An easily applied, objective, reproducible method was developed for normalizing images to cerebellum prior to the performance of SPM analysis. Cerebellar normalization produced more extensive abnormalities in SPM analyses of ATD patients than global normalization. Furthermore, cerebellar normalization produced marginally more accurate diagnostic results in single-scan SPM analysis of ATD patients than did global normalization.
为了对锝-99m六甲基丙烯胺肟（HMPAO）单光子发射计算机断层扫描（SPECT）过程中获取的图像进行定量比较，脑活动值通常会被归一化到一个参考区域。在阿尔茨海默型痴呆（ATD）的研究中，小脑常被用作参考区域，假定它未受任何重大病理累及。统计参数映射（SPM）可能会增强对ATD患者SPECT扫描的评估。然而，当前的SPM软件仅允许按平均全脑活动进行缩放（即全局归一化）。本研究的目的是开发一种易于应用、客观且可重复的方法来确定小脑示踪剂摄取量，以便在进行SPM分析之前能将图像按小脑活动进行特异性缩放。我们还研究了与全局归一化相比，小脑归一化是否能提高ATD患者SPM分析的敏感性和特异性。
图像文件取自一项平行研究，该研究调查了SPECT作为ATD早期发病诊断工具的应用情况。开发了两种确定小脑活动的方法：一种是手动方法，使用模板；另一种是自动方法，使用输入到Matlab程序中的指定坐标。在Windows 95系统上使用SPM 96逐体素地对ATD患者与对照组（=健康志愿者和抑郁症患者）进行组间比较。计算了20名学生评分者在有和没有单受试者SPM的情况下检查患者和对照扫描图像的受试者操作特征（ROC）。
当示踪剂摄取量归一化到小脑而非平均全脑活动时，ATD患者组脑血流量减少的空间范围增大了1.7倍。计算反向对比（对照组与ATD患者相比的减少情况）在全局归一化图像中产生了显著簇，而在归一化到小脑后这些簇并不明显。这与小脑在ATD中未受影响的观点一致。对ROC曲线下面积的分析表明，小脑归一化的SPM比单独的灌注扫描产生了显著提高的准确性。
开发了一种易于应用、客观且可重复的方法，用于在进行SPM分析之前将图像归一化到小脑。在ATD患者的SPM分析中，小脑归一化比全局归一化产生了更广泛的异常。此外，在ATD患者的单扫描SPM分析中，小脑归一化比全局归一化产生的诊断结果略更准确。
