Task-free presurgical mapping using functional magnetic resonance imaging intrinsic activity

Abstract

Object: Low-frequency components of the spontaneous functional MR imaging signal provide information about the intrinsic functional and anatomical organization of the brain. The ability to use such methods in individual patients may provide a powerful tool for presurgical planning. The authors explore the feasibility of presurgical motor function mapping in which a task-free paradigm is used.

Methods: Six surgical candidates with tumors or epileptic foci near the motor cortex participated in this study. The investigators directly compared task-elicited activation of the motor system to activation obtained from intrinsic activity correlations. The motor network within the unhealthy hemisphere was identified based on intrinsic activity correlations, allowing distortions of functional anatomy caused by the tumor and epilepsy to be directly visualized. The precision of the motor function mapping was further explored in 1 participant by using direct cortical stimulation.

Results: The motor regions localized based on the spontaneous activity correlations were quite similar to the regions defined by actual movement tasks and cortical stimulation. Using intrinsic activity correlations, it was possible to map the motor cortex in presurgical patients.

Conclusions: This task-free paradigm may provide a powerful approach to map functional anatomy in patients without task compliance and allow multiple brain systems to be determined in a single scanning session.

Fig. 1

Task and fcMR imaging–based mapping localizing similar regions. Hand motor regions defined by actual motor task movements (left column) and task-free fcMR imaging (center column) are plotted on sagittal sections for each patient (overlaid on their structural image). Colors represent Z values, with the threshold set to Z = 0.4–0.5. The overlap of the two techniques is shown in red (right column). Each row displays a different patient, with the sex (M or F) and age (in years) indicated in the rightmost panel. Brain lesions are indicated by the white triangles for the patients in Cases 1, 2, and 4; the patient in Case 3 has no visible lesion.

Fig. 2

Functional mapping based on fcMR imaging is anatomically specific. These studies are comparisons of hand and tongue motor regions defined by actual motor task movements (left columns) and task-free fcMR imaging (center columns). The overlap of the two techniques is shown in red (right columns). The upper panels show data from the patient in Case 2, and the lower panels from the patient in Case 4. The right hemisphere is displayed on the right side of the panel. Note the systematic shift of the location of the hand and tongue regions in each patient, which is present for the fcMR analysis. The fcMR analysis of the hand region in the patient in Case 2 is less stable than other measures, possibly due to the location of the seizure activity (see text).

Fig. 3

Functional mapping based on fcMR imaging is robust across different image resolutions. These studies are comparisons of hand and tongue motor regions defined by actual motor task movements (left column) and task-free fcMR imaging (center column), similar to those in Fig. 2. The resting-state images were acquired using 3-mm isotropic voxels and 2-second TR, as in the task scans.

Fig. 4

Comparison of results of direct cortical stimulation and fcMR imaging. The intraoperative photograph in the upper panel shows the grid placement for the patient in Case 2 and the locations of the electrodes that disrupted hand (14, 22) and tongue (40, 47, 48) movements. The fcMR analysis results are displayed in the lower panels; the hand motor region (left column) and the tongue motor region (right column) are displayed. Activation maps show the results of fcMR imaging analysis from Fig. 2. Filled green circles show the locations of cortical stimulation electrodes that selectively disrupted hand and tongue movements. The hand and tongue regions defined by fcMR imaging correlate with the estimates of the regions based on stimulation.