Fig. 3

Flowchart of the inclusion process of participants and data for analyses. Seventeen participants were scanned, whereof 12 completed all three study days. The remaining participants completed 1–2 study days. One subject completed only the placebo day due to loss to follow up. One subject withdrew after scan 1 on the first study day (placebo) due to claustrophobia, thus scan 2 data are missing. One subject completed the sildenafil and CGRP day, but thalamus data were excluded from the sildenafil day as the subject fell asleep during the thalamus baseline scan. One subject did not complete the CGRP day due to loss to follow up. One subject only participated on the sildenafil day due to finalization of the study. Data were further missing due to technical issues: scan 1 data (brainstem and thalamus) after placebo from one subject, and scan 1 brainstem data after CGRP from another subject. Brainstem data were excluded from one subject for all three study days due to poor spectral quality. n: Number