Practical video demonstration of the technique to identify the posterior superior insula orthogonal scalp projection without neuronavigation: the Fast-PSI

BACKGROUND: The posterior-superior insula (PSI) has emerged as a potential target for non-invasive brain stimulation (NIBS) in the treatment of peripheral neuropathic pain. However, current methods for identifying the PSI require expensive and time-consuming brain imaging and neuronavigation. Here, we propose the Fast-PSI method, a novel approach based on craniometry and intracranial Euclidean distances proportions comparisons between scalp landmarks, to swiftly and accurately locate the PSI projection on the scalp. METHODS: Eleven healthy participants underwent identification of the PSI and cranial landmarks (CL) MNI152 coordinates using neuronavigation. Euclidean distances between nasion and PSI (N-sPSI), nasion and inion (N-I), vertex and PSI (Cz-sPSI), and vertex and tragus (Cz-T) were calculated. Craniometric-based Euclidean distances between PSI and CL were also measured. Correction factors were developed based on the proportionality of distances. RESULTS: Mean distances’ proportions were consistent between stereotactic-based and craniometric-based measurements. Correction factors were determined as 0.67 for N-sPSI and 0.75 for Cz-sPSI. The Fast-PSI formula was established using these factors to swiftly locate the PSI projection on the scalp. Test-retest, intra- and inter-rater reliability coefficients were high, with no statistical difference compared to neuronavigated coordinates. The mean time for Fast-PSI determination was significantly shorter than traditional neuronavigation. CONCLUSION: The Fast-PSI method demonstrates high precision and reliability in identifying the PSI projection for NIBS in neuropathic pain treatment. Its rapid execution and accuracy make it a promising alternative to current techniques, potentially reducing time and resource burdens associated with neuronavigation. Further validation in clinical trials and everyday practice is warranted to assess its utility in clinical settings.