RGU is a special X-Ray procedure done to study the urethra, i.e., the terminal part of your urinary passage, to look for any abnormalities like stricture (narrowing) etc. It is usually done in males. A Micturating Cysto-Urethrogram (or MCU) is a study using X-rays and x-ray dye to show the bladder and urethra while passing urine. The test is performed to determine if the urine goes from the bladder back up to the kidneys instead of out through the urethra.