Clinical fMRI at 3 Tesla with reproducible and standardised tactile stimulation

Objective: Standardized tactile stimulation of fingers and lips in order to localize the primary (SI) and secondary (SII) somatosensory cortex can be used for various purposes, such as presurgical identification of these important brain areas in patients with cerebral tumors as well as in clinical studies with patients with different diseases and healthy volunteers. Standardized and reproducible stimulation and an optimized block design paradigm are important prerequisites for robust localization of SI and SII in clinical context. Methods: We used a 3 Tesla Siemens Trio MR scanner to perform fMRI measurements in an previously described optimized block design (Stippich et al. 2004, 2005) in 16 healthy, right handed volunteers (8 male, 8 female, aged 21 to 52 years). All volunteers received measurements with separated tactile stimulation of lips and fingers. For the lips we developed a new device which allows standardized tactile stimulation. It is a mask (fig. 1) with four embedded pneumatically driven membranes (4D Neuroimaging, Aachen, Germany), that can be applied with a well defined reproducible mean surface pressure of 110 mN/cm 2 . The mask is placed over upper and lower lips and can easily be fixed by a hook and loop fastener. For the fingers we used commercially available finger clips with membranes (4D Neuroimaging). All data was analyzed with a general linear model approach in Brain Voyager QX (BrainInnovation, Maastricht, The Netherlands). Results: Primary somatosensory activations were detected in 92% of cases after stimulation of the lips and in 100% after finger stimulation. The detection rate for ipsi- and contralateral SII in individual subjects was between 83% and 100%. Fig. 2 and 3 show the statistical means and standard deviations of magnitude (dS) and correlation (r) of the BOLD signal. Conclusion: Our results show high detections rates, relatively low standard deviations and stable magnitudes of BOLD signals. For this we can postulate, that the used devices lead to reproducible and robust activations. This allows reliable usage for clinical applications in patients where these qualities are coercively necessary.