Measurement of postvoid residual urine in conscious mice using high-frequency transrectal ultrasound

The aim of this study was to develop a novel technique for a minimally invasive ultrasound measurement of postvoid residual urine (PVR) in conscious mice using a miniature ultrasound probe and a transrectal approach. The PVR was determined by the ellipsoid formula in the maximum sectional image of the bladder visualized with a 20-MHz ultrasound probe (2 mm in diameter) inserted into the rectum. The accuracy, including the intra- and interobserver reproducibilities, of the ultrasonic PVR measurements (in 10 5- to 50-week-old mice) was evaluated, which revealed excellent internal consistency. In M(3) muscarinic acetylcholine receptor knockout male mice, a chronological evaluation of the PVR identified abnormal urinary retention present at infancy and exacerbated with aging, suggesting significant voiding dysfunction. Our technique for the measurement of PVR in conscious mice was accurate and useful for identifying the voiding dysfunction in mice.