Assessment of reliability in functional imaging studies

To investigate the reliability of functional magnetic resonance imaging (fMRI), an approach for mapping and quantifying reliably activated voxels was developed.First, a SPM99 analysis was performed, and the resulting statistical maps were taken as the basis for subsequent analyses of reliability. Several approaches were demonstrated using 1). a voxel-wise intraclass correlation coefficient (ICC); 2). an analysis of scatter plots, calculating the correlation of contrast t-values for pairs of activation maps; and 3). the ratio of overlapping volumes as suggested in the literature. The methods were applied to an fMRI study in which subjects were asked to vary their attentional effort during watching a flickering checkerboard pattern with varying letters in the center. The subjects had to ignore or attend to the presentation, or they had to detect a target letter within the checkerboard.The imaging data showed good reliability in terms of ICC for regions of visual processing, as well as for frontal areas, especially in the letter detection task. Furthermore, the size of reliable clusters depended on the presumed attentional effort of the subjects.Application of the method demonstrated that the activation due to visual stimulation could also be detected very consistently during a no-attend condition, but the reliability of the activations were best during the attended tasks