The route of contrast injection in MCU is by inserting a catheter into bladder either via urethra or if the patient has suprapubic cystostomy, then by that route. The purpose is basically to fill the bladder with contrast and then ask the patient to micturate , during which X ray is taken. In contrast, in urethrography, only urethra is opacified passively ie by contrast injection into urethra.
