Which diagnostic examination is used to examine the flow of urine from the bladder and through the urethra?

Voiding cystourethrography is the correct choice because it specifically involves taking X-ray images of the bladder and urethra while the patient is urinating. This diagnostic examination allows healthcare providers to visualize the flow of urine, assess the anatomy of the bladder and urethra, and identify any abnormalities such as obstructions, tumors, or issues related to bladder function.

This procedure is particularly useful for diagnosing conditions related to urinary tract issues, as it reveals how well urine flows and any potential complications during the voiding process. As a contrast agent is used, it makes the bladder and urethra visible in the X-ray images, providing essential information about the patient's urinary function.

In contrast, the other options serve different purposes and do not specifically focus on visualizing urine flow. An intravenous pyelogram, for example, examines the kidneys and urinary system with a contrast dye but does not focus on the flow through the urethra during urination. An ultrasound is typically used for imaging soft tissues and organs but does not provide real-time information about the flow of urine. Conventional X-rays are also not targeted at evaluating the urinary flow and are more general in their application.