Clinical fMRI: evidence for a 7T benefit over 3T

Abstract

Despite there being an increasing number of installations of ultra high field MR systems (>3T) in clinical environments, no functional patient investigations have yet examined possible benefits for functional diagnostics. Here we performed presurgical localization of the primary motor hand area on 3T and 7T Siemens scanners with identical investigational procedures and comparable system specific sequence optimizations. Results from 17 patients showed significantly higher functional sensitivity of the 7T system measured via percent signal change, mean t-values, number of suprathreshold voxels and contrast to noise ratio. On the other hand, 7T data suffered from a significant increase of artifacts (ghosting, head motion). We conclude that ultra high field systems provide a clinically relevant increase of functional sensitivity for patient investigations.

Fig. 1

Patient P6. A: Functional EPI slices covering central parts of the primary motor hand area at 3 T and 7 T. B: Same as A with neuroanatomical ROIs depicting the primary motor hand area (light green). C: Same as B with depiction of all suprathreshold voxels (p < = 0.05, FWE — corrected) within the neuroanatomical ROIs. Only these voxels entered statistical analysis and formed the functional ROI. Color bar indicates t-values of active voxels (3 T maximum = 22.3, 7 T maximum = 25.3).

Fig. 2

Patient P13. Same es Fig. 1. 3 T t-value maximum = 11.8, 7 T t-value maximum = 15.2).

Fig. 3

Position of ROIs for quantification of ghosting artifacts (P6, 3 T data). Blue: ROIs for detection of ghosting signals, Green: central reference ROI. The relation between the mean absolute signals within the ghosting ROIs to the reference ROIs was calculated.

Fig. 4

Signal time course differences averaged over all peak CNR voxels of all patients.

Fig. 5

Quantification of head motion. Translational head movements between two consecutively recorded brain volumes are larger with the 7 T system. Data show mean and standard deviation of the patient specific motion indicators.

Fig. 6

Quantification of ghosting signals. The ghost to signal ratio is significantly larger with the 7 T system. Data show mean and standard deviation of the patient specific ghost to signal ratios.