Imaging Tests of the Urinary Tract
There are a variety of tests that can be used in the evaluation of a suspected kidney or urinary tract disorder. (See also Overview of the Urinary Tract.)
X-rays are usually not helpful in evaluating urinary tract disorders. Sometimes x-rays can help detect certain types of kidney stones and monitor their position and growth. Some types of kidney stones do not show up on plain x-rays.
Ultrasonography is a useful imaging technique because it
Ultrasonography is commonly used to obtain images of urinary tract stones and swellings and masses (lumps) in the urinary tract, such as in the kidneys, bladder, scrotum and testes, penis, and urethra. Ultrasonography can also be used to look for blockages in the kidneys or bladder, determine whether the bladder retains urine after a person urinates, determine the size of the prostate gland, and provide images that help guide where to obtain samples for biopsies of the prostate or kidney. Doppler ultrasonography forms images by analyzing reflected sound waves. Doppler ultrasonography provides information on blood flow, which helps doctors determine the cause of erectile dysfunction and testicular disorders, such as testicular torsion and epididymitis.
Computed tomography (CT) provides images of the urinary tract and structures that surround it. CT angiography, a less invasive alternative to conventional angiography, is useful for evaluating many urinary tract conditions. A radiopaque contrast agent is sometimes given by vein (intravenously). After the contrast agent is given, images are taken immediately to provide more detail about the kidneys and sometimes 10 minutes later to provide more detail about the muscular tubes that carry urine from the kidneys to the bladder (ureters). Disadvantages of CT include exposure to significant amounts of ionizing radiation and, when a radiopaque contrast agent is given, risk of kidney damage and allergic-type reactions.
Magnetic resonance imaging (MRI), like CT, provides images of the urinary tract and surrounding structures. Unlike CT, MRI does not involve exposure to ionizing radiation. MRI can be used to provide images of blood vessels (called magnetic resonance angiography, or MRA). For some disorders, MRI provides more detail than CT. However, MRI does not provide much useful information about stones in the urinary tract. Use of paramagnetic contrast agents given by vein makes MRI images clearer. This contrast agent is very different from the agent used in CT scans. However, paramagnetic contrast often cannot be used in people with poor kidney function because in those people the contrast agent rarely causes a serious and irreversible disorder called nephrogenic systemic fibrosis, which affects the skin and other organs.
In retrograde urography, a radiopaque contrast agent is introduced directly into the ureters or the collecting tubules of the kidney through the bladder. This procedure is usually done during cystoscopy or another routine urologic procedure such as ureteroscopy (insertion of a catheter into the ureters) or placement of a stent in the ureter or kidney. The urinary tract can be examined, including the parts of the kidney through which urine drains. Retrograde urography can be done to diagnose scarring, tumors, or abnormal connections between parts of the urinary tract and other structures (fistulas). Retrograde urography can be done if a radiopaque contrast agent cannot be given (for example, if kidney function is poor).
In percutaneous antegrade urography, a radiopaque contrast agent is introduced directly into the parts of the kidney through which urine drains through an opening in the back (called a nephrostomy opening). This test may be done if retrograde urography cannot be done (for example, if the instrument's insertion path is blocked) or if a person already has a nephrostomy tube used to treat a disorder such as a tumor or stone that blocks the urinary tract.
Cystography is any test that provides bladder images after a radiopaque contrast agent is introduced into the bladder (for example, through a cystoscope or a catheter in the urethra). Cystography is used most commonly to detect a hole in the bladder, which may occur after an injury or surgery.
In cystourethrography (sometimes called retrograde cystourethrography), a radiopaque contrast agent is injected through the urethra into the bladder. This procedure is used to identify abnormalities in the urethra, such as scarring or tearing as a result of injury. When x-ray films of the bladder and urethra are taken during and immediately after urination, the study is called voiding cystourethrography. This variation of cystourethrography is used to evaluate whether the valves that prevent urine from flowing backward from the bladder into the ureters during urination work properly and to detect abnormalities, such as narrowing, that affect the back part of the urethra (the part nearest the bladder).
In retrograde urethrography, a radiopaque contrast agent is introduced directly into the end of the urethra using either a syringe with a special adapter or a urethral catheter placed only a few centimeters into the urethra with the balloon partially inflated so that it fits snugly. The radiopaque contrast agent is injected into the urethra and fills the entire urethra to visualize any injury or strictures. This test is typically used in people who have experienced trauma that may have injured the urethra. Physicians do retrograde urethrography to make sure that placing a urethral catheter into the bladder is safe and will not injure the urethra.
Radionuclide scanning of the kidneys is an imaging technique that relies on the detection of small amounts of radiation by a special gamma camera after the injection of a radioactive chemical. This procedure is most commonly used to assess kidney blood flow and urine production.
Angiography (sometimes called conventional angiography to differentiate it from CT angiography and magnetic resonance angiography) involves injecting a radiopaque contrast agent directly into an artery. In people who have urinary tract disorders, this test is used because it can be combined with treatments that repair blood vessels affected by certain disorders, such as severe bleeding or abnormal connections between blood vessels (vascular fistulas). Complications of angiography may include injury to the injected arteries and neighboring organs, bleeding, and reactions to radiopaque contrast agents.