Which procedure is required to assess urine flow dynamics?

The correct choice is voiding cystourethrography, as this procedure specifically evaluates the flow dynamics of urine through the bladder and urethra. It involves taking X-ray images while the patient empties their bladder, allowing for the assessment of how effectively and efficiently urine is expelled. This technique helps identify issues such as urinary obstruction, urinary incontinence, or other functional abnormalities related to urination.

Other imaging techniques like ultrasound can be used to examine kidney structure or bladder volume, but they do not provide dynamic information about urine flow during voiding. Cystoscopy is primarily used for direct visualization of the inside of the bladder and urethra, making it more suited for diagnosing conditions like tumors or stones rather than assessing flow dynamics. Dialysis is a treatment for removing waste products from the blood when the kidneys are not functioning properly and does not pertain to urine flow assessment at all.