title: Comparing neural response to painful electrical stimulation with functional MRI at 3 and 7 T.
abstract: Progressing from 3T to 7 T functional MRI enables marked improvements of human brain imaging in vivo. Although direct comparisons demonstrated advantages concerning blood oxygen level dependent (BOLD) signal response and spatial specificity, these mostly focused on single brain regions with rather simple tasks. Considering that physiological noise also increases with higher field strength, it is not entirely clear whether the advantages of 7T translate equally to the entire brain during tasks which elicit more complex neuronal processing. Therefore, we investigated the difference between 3T and 7 T in response to transcutaneous electrical painful and non-painful stimulation in 22 healthy subjects. For painful stimuli vs. baseline, stronger activations were observed at 7 T in several brain regions including the insula and supplementary motor area, but not the secondary somatosensory cortex (p<0.05 FWE-corrected). Contrasting painful vs. non-painful stimulation limited the differences between the field strengths to the periaqueductal gray (PAG, p<0.001 uncorrected) due to a similar signal increase at 7 T for both the target and specific control condition in most brain regions. This regional specificity obtained for the PAG at higher field strengths was confirmed by an additional spatial normalization strategy optimized for the brainstem. Here, robust BOLD responses were obtained in the dorsal PAG at 7 T (p<0.05 FWE-corrected), whereas at 3T activation was completely missing for the contrast against non-painful stimuli. To summarize, our findings support previously reported benefits obtained at ultra-high field strengths also for complex activation patterns elicited by painful electrical stimulation. However, this advantage depends on the region and even more on the contrast of interest. The greatest gain at 7 T was observed within the small brainstem region of the PAG, where the increased field strength offered marked improvement for the localization of activation foci with high spatial specificity.
authors.affiliation: Department of Psychiatry and Psychotherapy, Medical University of Vienna, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hahn
authors.forename: Georg S
authors.initials: GS
authors.lastname: Kranz
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Seidel
authors.forename: Ronald
authors.initials: R
authors.lastname: Sladky
authors.forename: Christoph
authors.initials: C
authors.lastname: Kraus
authors.forename: Martin
authors.initials: M
authors.lastname: Küblböck
authors.forename: Daniela M
authors.initials: DM
authors.lastname: Pfabigan
authors.forename: Allan
authors.initials: A
authors.lastname: Hummer
authors.forename: Arvina
authors.initials: A
authors.lastname: Grahl
authors.forename: Sebastian
authors.initials: S
authors.lastname: Ganger
authors.forename: Christian
authors.initials: C
authors.lastname: Windischberger
authors.forename: Claus
authors.initials: C
authors.lastname: Lamm
authors.forename: Rupert
authors.initials: R
authors.lastname: Lanzenberger
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010146:Pain / Q000503:physiopathology*; D017288:Pain Threshold / Q000502:physiology; D055815:Young Adult
keywords: 3T; 7T; Pain stimulation; fMRI