X-Ray Films and Other Imaging Modalities - Renal and Urinary Tract Function

X-RAY FILMS AND OTHER IMAGING MODALITIES

Kidney, Ureter, and Bladder Studies

An x-ray study of the abdomen or kidney, ureters, and bladder (KUB) may be performed to delineate the size, shape, and posi-tion of the kidneys and to reveal any abnormalities, such as calculi (stones) in the kidneys or urinary tract, hydronephrosis (distention of the pelvis of the kidney), cysts, tumors, or kidney displacement by abnormalities in surrounding tissues.

General Ultrasonography

Ultrasonography is a noninvasive procedure that uses sound waves passed into the body through a transducer to detect abnormalities of internal tissues and organs. Structures of the urinary system cre-ate characteristic ultrasonographic images. Abnormalities such as fluid accumulation, masses, congenital malformations, changes in organ size, or obstructions can be identified. During the test, the lower abdomen and genitalia may need to be exposed. Ultra-sonography requires a full bladder; therefore, fluid intake should be encouraged before the procedure. Because of its sensitivity, ultra sonography has replaced many other tests as the initial diagnostic procedure.

Bladder Ultrasonography

Bladder ultrasonography is a noninvasive method of measuring urine volume in the bladder. It may be indicated for urinary fre-quency, inability to void after removal of an indwelling urinary catheter, measurement of postvoiding residual urine volume, in-ability to void postoperatively, or assessment of the need for catheterization during the initial stages of an intermittent catheter-ization training program. Portable, battery-operated devices are available for bedside use. The scan head is placed on the patient’s abdomen and directed toward the bladder. The device automat-ically calculates and displays urine volume.

Computed Tomography and Magnetic Resonance Imaging

Computed tomography (CT) and magnetic resonance imaging (MRI) are noninvasive techniques that provide excellent cross-sectional views of the kidney and urinary tract. They are used in evaluating genitourinary masses, nephrolithiasis, chronic renal infections, renal or urinary tract trauma, metastatic disease, and soft tissue abnormalities. The nurse should explain to the patient that a sedative may be prescribed. Claustrophobia is often a problem, especially with MRI. Patient preparation for the MRI includes removal of any metallic objects, such as jewelry or cloth-ing with metallic clasps. Credit cards should be kept away from the MRI area because of their magnetic strips. MRI is con-traindicated in patients with pacemakers, surgical clips, or any metallic objects anywhere in the body. Occasionally, an oral or intravenous radiopaque contrast material is used in CT scanning to enhance visualization. Nursing care guidelines for patient preparation and test precautions for any imaging procedure re-quiring a contrast agent (also called contrast medium) are ex-plained in Chart 43-3.

Nuclear Scans

Nuclear scans require injection of a radioisotope (technetium-99m–labeled compound or iodine-131 hippurate) into the cir-culatory system; the isotope is then monitored as it moves through the blood vessels of the kidneys. A scintillation camera is placed behind the kidney with the patient in a supine, prone, or seated position. Hypersensitivity to the radioisotope is rare. The technetium scan provides information about kidney perfusion; the hippurate scan provides information about kidney function.

Nuclear scans are used to evaluate acute and chronic renal fail-ure, renal masses, and blood flow before and after kidney trans-plantation. The radioisotope is injected at a specified time before the study to achieve the proper concentration in the kidneys. After the procedure is completed, the patient is encouraged to drink flu-ids to promote excretion of the radioisotope by the kidneys.

Intravenous Urography

Intravenous urography includes various tests such as excretory urog-raphy, intravenous pyelography (IVP), and infusion drip pyelogra-phy. A radiopaque contrast agent is administered intravenously. An IVP, or intravenous urogram, shows the kidneys, ureter, and blad-der via x-ray imaging as dye moves through the upper and then lower urinary system. A nephrotomogram may be carried out as part of the study to visualize different layers of the kidney and the diffuse structures within each layer and to differentiate solid masses or lesions from cysts in the kidneys or urinary tract.

Intravenous urography may be used as the initial assessment of any suspected urologic problem, especially lesions in the kid-neys and ureters. It also provides a rough estimate of renal func-tion. After the contrast agent (sodium diatrizoate or meglumine diatrizoate) is administered intravenously, multiple x-rays are ob-tained to visualize drainage structures.

Infusion drip pyelography requires an intravenous infusion of a large volume of a dilute contrast agent to opacify the renal parenchyma and fill the urinary tract. This examination method is useful when prolonged opacification of the drainage structures is desired so that tomograms (body-section radiography) can be made. Images are obtained at specified intervals after the start of the infusion. These images show the filled and distended collect-ing system. The patient preparation is the same as for excretory urography, except that fluids are not restricted.

Retrograde Pyelography

In retrograde pyelography, catheters are advanced through the ureters into the renal pelvis by means of cystoscopy. A contrast agent is then injected. Retrograde pyelography is usually per-formed if intravenous urography provides inadequate visual-ization of the collecting systems. It may also be used before extracorporeal shock-wave lithotripsy or in patients with urologic cancer who need follow-up and are allergic to intravenous contrast agents. Possible complications include infection, hematuria, and perforation of the ureter. Retrograde pyelography is used infre-quently because of improved techniques in excretory urography.

Cystography

Cystography aids in evaluating vesicoureteral reflux (backflow of urine from the bladder into one or both ureters) and assessing the patient for bladder injury. A catheter is inserted into the bladder, and a contrast agent is instilled to outline the bladder wall. The con-trast agent may leak through a small bladder perforation stem-ming from bladder injury, but such leakage is usually harmless. Cystography can also be performed with simultaneous pressure recordings inside the bladder.

Voiding Cystourethrography

Voiding cystourethrography uses fluoroscopy to visualize the lower urinary tract and assess urine storage in the bladder. It is commonly used as a diagnostic tool to identify vesicoureteral reflux (between bladder and ureter). A urethral catheter is inserted, and a contrast agent is instilled into the bladder. When the bladder is full and the patient feels the urge to void, the catheter is removed, and the pa-tient voids. Retrograde urethrography, in which a contrast agent is injected retrograde into the urethra, is always performed before ure-thral catheterization if urethral trauma is suspected.

Renal Angiography

A renal angiogram, or renal arteriogram, provides an image of the renal arteries. The femoral (or axillary) artery is pierced with a needle, and a catheter is threaded up through the femoral and iliac arteries into the aorta or renal artery. A contrast agent is in-jected to opacify the renal arterial supply. Angiography is used toevaluate renal blood flow in suspected renal trauma, to differen-tiate renal cysts from tumors, and to evaluate hypertension. It is used preoperatively for renal transplantation. Before the proce-dure, a laxative may be prescribed to evacuate the colon so that unobstructed x-rays can be obtained. Injection sites (groin for femoral approach or axilla for axillary approach) may be shaved. The peripheral pulse sites (radial, femoral, and dorsalis pedis) are marked for easy access during postprocedural assessment. The pa-tient is informed that there may be a brief sensation of heat along the course of the vessel when the contrast agent is injected.

After the procedure, vital signs are monitored until stable. If the axillary artery was the injection site, blood pressure measurements are taken on the opposite arm. The injection site is examined for swelling and hematoma. Peripheral pulses are palpated, and the color and temperature of the involved extremity are noted and com-pared with those of the uninvolved extremity. Cold compresses may be applied to the injection site to decrease edema and pain. Possible complications include hematoma formation, arterial thrombosis or dissection, false aneurysm formation, and altered renal function.