Impact of the spatial normalization template and realignment procedure on the SPM analysis of [11C]Raclopride PET studies

Background/Objectives: In this paper, we address the issue of how the preprocessing steps of a typical neuroreceptor PET study may influence the outcome of a statistical parametric mapping (SPM) analysis examining intercondition differences. Two preprocessing steps and their possible interaction were investigated: 1) the realignment of dynamic images to correct for patient´s motion and 2) the effect of the template in the spatial normalization step required by SPM. Methods : The impact of different realignment methods was tested by performing the SPM analysis on a six patient-two conditions ¹¹C-raclopride (RAC) study where the dynamic images of each subject were re-aligned with four methods. Once realigned, the images were spatially normalized to the standard cerebral blood flow (CBF) template, available in SPM, and to a RAC template. The SPM pattern showing the intercondition differences obtained in each case was compared with the expected one. The accuracy of the four realignment methods used was further tested using a set of motion-free RAC studies. Results/Conclusion: We found that: 1) different realignment methods may create different intercondition difference patterns; 2) such differences in the results may be due to a failure in accuracy of some realignment methods; and 3) the use of a template that closely matches the spatial distribution of the tracer under investigation can minimize these problems.