An assembly of portable, battery-powered devices designed for the extracorporeal ultrasound measurement of the male or female urinary bladder volume. It typically consists of an electronic measuring and imaging display unit with a connected ultrasound transducer which together reproduce digitized data of the bladder, typically bladder volume and post-void residual (PVR), and images. It will generate ultrasound pulses, direct them to a the target area, detect the ultrasound echoes, and process the resulting information to produce and display static or dynamic three-dimensional (3-D) data/images. It is used in the diagnosis of urinary retention and postoperative urinary retention (POUR).