In various neurological conditions, urinary continence is impaired. Only a few studies evaluated by imaging brain areas involved in the volunteer control of micturition¹. In this work, we compared two fMRI paradigms to assess the volunteer pelvic floor muscles contraction.

MR acquisitions were performed on a 3T Philips Achieva dStream scanner (Philips medical systems). 11 healthy participants were enrolled (ages 22-31 years) and underwent anatomical 3D T1 acquisition (TR/TR = 9/4ms, flip angle 8°, FOV = 256x256mm² in 384x384 matrices, slice thickness=0.9mm) followed by T2 weighted EPI sequences (TR/TR = 3000/35ms, flip angle 90°, FOV = 260x260mm² in 160x160 matrices, slice thickness=4mm). Cerebral activation sequences were performed with two different paradigms: "continuous" and "pulsed". Instructions were given in the form of simple vocal order. Paradigms suited the block-design method and the action phases consisted in contraction of the pelvic floor muscles (continuously in "Continuous" paradigm and repeated in "pulsed" paradigm) and rest phases were complete relaxation. Each paradigm was constituted with four rest blocks alternating with four action blocks (each of which lasting 30s – 10 volumes acquired). For the “pulsed” paradigm, 10 contractions were performed per block.

Activation maps were first generated with FSL FEAT2 software. Activation maps were generated with a Z-score threshold> 3.5 and registered onto MNI template to locate the five largest areas as well as the 5 most intense areas (Highest Z-max) for each participant. A t test was performed to compare the distribution of the cluster size and the Z-max obtained with each paradigm.

The two paradigms have isolated the same areas of interest, i.e. the primary motor cortex (Brodmann area 4) and secondary (Brodmann area 6). Other regions involved in control voiding were also detected less frequently (Insula, GCA, Pons). For each subject, paradigms have isolated at least five areas with a Z score > 3.5. There was no significant difference in cluster size between "continuous" and "pulsed" paradigms (p = 0.28). However, Z-max was significantly higher in the “pulsed” paradigm than in the “continuous” one (p <0.001).Our study is the first to compare two different paradigms to assess volunteer pelvic floor muscles contraction. Our main result showed a significantly increased the Z score (p <0.001) in the “pulsed” paradigm meaning that repetitive contractions of striated urethral sphincter yield a more intense cerebral activation than a single sustained contraction. This innovative study intended to extend the functional MRI technique to clinical applications, particularly in the pathophysiology of bladder and sphincter disorders and idiopathic neurological origins.