gms | German Medical Science

Objective: Achieving a high test-retest reliability when mapping language regions by functional MRI (fMRI) is highly relevant for clinical applications like presurgical mappings. We, therefore, systematically tested the short- and long-term fMRI-reliability in a group of healthy subjects, using a picture naming task and a sparse-sampling fMRI-protocol, aiming at reduced speech-related movement artifacts.

Methods: 16 right-handed, healthy subjects (mean age: 29 years) participated in three fMRI-sessions separated by 2-6 days (short-term) and 21-34 days (long-term). In each session, subjects performed an overt picture naming task. Reliability was tested by means of: (i) Euclidean distances (ED) between local activation maxima and Centers of Gravity (CoGs), (ii) overlap volumes and (iii) voxel-wise intraclass correlation coefficients (ICCs). The following regions of interest (ROIs) were included in the analysis: primary motor cortex (M1), superior temporal gyrus (STG), inferior frontal gyrus (IFG).

Results: The activation centers were highly reliable with significantly smaller ED for local activation maxima (6.45±1.36 mm) as compared to CoGs (8.03±2.01 mm). In contrast, the extent of activation revealed rather low reliability values (overlap volumes: 24%-56%). Although mean ICCs ranged between poor and moderate reliability, highly reliable voxels (ICC>0.75) were found for all ROIs. Voxel-wise reliability of the different ROIs was influenced by the intersession interval.

Conclusion: There is a considerable ROI-dependent variation of the extent of activation over time. In contrast, highly reliable centers of activation can be identified using an overt picture naming paradigm independent of the time-interval between sessions.