Fig. 1

a Photograph of the adapted commercial coil. The four medial openings have been merged into two larger ones, the cut edges sealed and reinforced by rigid polymer frames produced on a 3D printer. b Setup of the patient positioned in the prone position on the MRI table, with the flexible coil placed on the lower back. A small silicone marker (arrow) is placed on the skin entry point inside the coil opening before acquisition of confirmatory images. The coil is attached by fastening straps. c, d Intraprocedural proton density (PD) original (not reconstructed) sagittal oblique and axial images, showing the needle in its final position behind an exiting L5 nerve root, within the neural foramen, more clearly seen on the image inset encircled by white (d) freehand region of interest (ROI). The needle tip location is confirmed behind an exiting L5 nerve root, within the neural foramen; e Heavily T2-weighted fat-saturated (FS) axial image acquired after the injection of a small quantity of sterile saline solution, seen as a signal hyperintensity surrounding the nerve root, encircled by red freehand ROI in image inset