Visualizing pain-processing networks with 7T resting-state functional MRI using pseudo-continuous arterial spin...

Arterial spin labeling (ASL) at ultra‑high field MRI at 7 T provides enhanced signal‑to‑noise ratio and spatial resolution, enabling more sensitive functional imaging. The objective of this study was to investigate regional perfusion changes and their relationship to perceived pain during sustained capsaicin‑induced nociception. Twenty‑seven healthy right‑handed volunteers (mean age 31.9 ± 4.1 years; 12 female) underwent two MRI sessions: at baseline and during capsaicin-induced tonic pain. Participants rated pain and were classified as responders or weak responders. MRI included T1‑weighted structural imaging, resting BOLD‑fMRI and 3D turbo‑FLASH pCASL. Images were segmented, normalized to MNI space, and CBF maps calculated. Mean CBF was extracted from gray matter and 10 predefined pain‑matrix regions. Voxel‑wise linear regression analyzed correlations between CBF and pain ratings, with false discovery rate correction. Group differences between responders and weak responders were assessed voxel‑wise. Global gray matter CBF was unchanged between baseline and capsaicin conditions and did not differ by responder status. However, CBF increased significantly with pain in a network including the contralateral insular cortex, primary and secondary somatosensory cortices, supplementary motor area, bilateral anterior cingulate cortex, right dorsolateral prefrontal cortex and contralateral thalamus. Average perfusion in these regions rose by 8-15% and correlated strongly with pain scores (r ≈ 0.66; p < 0.001). Weak responders showed higher CBF in right fusiform and bilateral primary visual cortices and lower CBF in bilateral superior frontal gyrus compared with responders. In conclusion, pCASL at 7 T enables quantitative mapping of brain perfusion during sustained pain. Sustained capsaicin stimulation increases regional CBF in a distributed cortico‑subcortical network, with perfusion changes closely tracking perceived pain intensity. These findings demonstrate that tonic nociception engages broader associative networks and highlight the utility of ultra‑high field ASL for studying chronic pain mechanisms.