Intravenous urography is a radiographic study of the urinary system using an intravenous contrast agent (dye).
Of the many ways to obtain images of the urinary system, the intravenous injection of a contrast agent has been traditionally considered the best, although other modalities, such as computed tomography (CT) or ultrasound, are better for some disease processes. The kidneys excrete the contrast into the urine, which becomes visible when x rayed (radiopaque), creating images of the urinary collection system.
The procedure has several variations and many names, including:
- Intravenous pyelography (IVP).
- Intravenous urography (IVU).
- Antegrade pyelography differentiates this procedure from retrograde pyelography, which injects the contrast agent directly into the lower end of the system. The contrast agent flows backward, hence the name "retrograde." Retrograde pyelography is used to better define problems in the lower ureters and is the only way to get x rays if the kidneys are non-functional.
- Nephrotomography, or tomographic slices of the kidneys, is taken by a moving x-ray source emitting x rays onto a film moving in the opposite direction. Images above and below the level of the kidneys are blurred, allowing a more detailed image of the kidneys with no overlying material, such as gas or fecal material.
There are numerous exams available for detecting kidney abnormalities, with varying risks and costs.
- Nuclear renal scans rely on the radiation given off by certain atoms (isotopes), which are injected into the bloodstream. They reach the kidneys, where images are constructed by measuring the radiation emitted. The radiation is no more dangerous than standard x rays. This exam has limited applications, including the evaluation of reflux, chronic obstruction, and renal function. It is also used to evaluate high blood pressure that is refractory to treatment, and is commonly used to evaluate the kidney of a renal transplant patient for early rejection where renal artery stenosis is suspected as the cause.
- Ultrasound is a quick, safe, simple, and inexpensive way to obtain views of internal organs. Renal size can be measured as well as the visualization of hydronephrosis, cysts, tumors, and renal calculi. Small stones in the ureters are not as well visualized and the function of the kidneys can not be determined.
- Retrograde pyelography is better able to define problems in the lower part of the ureters, and is the only way to completely opacify the ureters in patients with reduced kidney function. This exam is performed in an operating room by a urologist. A cystoscope is placed into the bladder and a catheter is placed into each ureter to inject the contrast agent. The advantage of this method is that small stones can be removed immediately by the urologist.
- Computed tomography scans (CT or CAT scans) use a fine beam of x rays creating images at precise levels in the body. The information is processed by a computer and imaged onto film with a laser printer. Three-dimensional images can be constructed from this method of imaging. An injection of a contrast agent is necessary to visualize the kidneys in detail. The CT scan is done without IV contrast to look for stones (calculi). In some centers, this modality has replaced IVPs and ultrasound for this application. Special equipment is necessary and the exam can be costly.
- Magnetic resonance imaging (MRI) uses magnetic fields and radio frequency signals instead of ionizing radiation to create computerized images. This form of energy is entirely safe as long as the patient has no metal in his or her body. It has limited applications and usually is not done for common problems, such as pain and hematuria (blood in the urine). MRI usually is done if other tests are inconclusive. MRA (magnetic resonance angiography) may be done to evaluate the renal arteries, particularly is renal artery stenosis is suspected as a cause of hypertension that is refractory to treatment. MRI requires special apparatus and installation and is a very costly exam.
An intravenous urogram is ordered to demonstrate the structure and function of the kidneys, ureters, and bladder. Patients complaining of abdominal pain radiating to the back may require this exam to rule out kidney stones. Hematuria may also be an indication of kidney stones, infection, or tumors. Patients with high blood pressure (hypertension) and recurrent bladder infections may also require an intravenous urogram (but hypertension usually is imaged with MRA or nuclear medicine imagery and this exam is done when renal artery stenosis is the suspected cause of refractory hypertension). Sometimes the exam is ordered to evaluate the function of the kidney in a renal transplant patient. The transplanted kidney is located in the iliac fossa, so special films of the pelvis area are done instead of the normal routine views. The radiographic technologist may also be required to take x rays in the operating room when a retrograde pyelogram is ordered by a urologist during a C and P (cystoscopy and pyelography).
A serious complication of an intravenous urogram is an allergic reaction to the iodine-containing contrast agent. Severe reactions are rare, but can be dramatic and even lethal. For this reason all radiology departments performing this exam are equipped with emergency drugs and oxygen in the x-ray room itself.
The patient will be required to change into a hospital gown and empty his or her bladder. The x-ray technologist will verify that the patient has followed the bowel preparation and complete a detailed questionnaire on the current medical history of the patient. This includes previous contrast reactions, known allergies,
The patient will be instructed to lie supine (face-up) on the x-ray table and a preliminary KUB will be done. This is an abdominal view of the kidneys, ureter, and bladder used to verify patient preparation, centering, and the radiographic technique needed to demonstrate all the required structures.
Kidney stones may or may not be visualized on the preliminary film. The x-ray technologist prepares the required amount of contrast to be used depending on the weight of the patient (1 ml per pound). This is normally 50–75 cc of contrast for an average-sized patient. The contrast will be injected all at once (bolus injection) or in some cases, through an intravenous drip. Some radiologists prefer to start an intravenous drip with saline as a precautionary measure while others inject with a small butterfly needle. The needle usually remains in place for 10–15 minutes, in case more contrast is needed or in case drugs need to be administered because of an allergic reaction. Most reactions occur immediately but some can take place 10 or 15 minutes after the injection.
The first film is taken immediately after the injection to see a detail of the renal outline (nephrogram). Films are usually taken at five-minute intervals depending on the routine of the radiologist. Compression may be applied to the lower abdomen with a wide band to keep the contrast material in the kidneys longer. This creates a more detailed image of the renal collecting system. When the compression is released after approximately 10 minutes the contrast material drains quickly and a detailed, filled image of the ureters is obtained. Films done in the upright or prone (face-down) position may also be ordered to better visualize the lower ureters. Some departments require routine renal tomographic images to be done as well when the kidneys are well visualized. This allows the kidneys to be seen free of gas or fecal shadows. Sometimes the radiologist requires oblique views of the kidneys or bladder to determine the exact location of calculi (stones). At approximately 20 minutes after the injection a film centered on the bladder may be required. The x-ray tube is angled slightly caudad (towards the feet) so that there is no superimposition of the pubic area of the pelvis over the bladder. The films are shown to the radiologist and if no further films are necessary the patient will be asked to void (urinate) and a post-void film will be taken. The exam can take from 30 minutes to one hour depending on the number of films required. If the kidney is obstructed, delayed films may be required to complete the exam.
In order to obtain the best visualization of the kidneys, ureters, and bladder, the intestines must be free of gas and fecal material. Every radiology department has their own specific requirements. Most include a laxative such as X-Prep or Dulcolax tablets taken around 4 p.m. the day preceeding the exam. This is followed with a light fat-free dinner which includes lean meats, noodles, white rice, bread with no butter, and tea or black coffee. Fluids are permitted until midnight, after which no food or liquid is allowed until after the intravenous urogram is completed. Patients who are diabetic are sometimes done early in the morning to avoid any complications. Patients who have had a previous reaction to a contrast material can be given a series of steroids and antihistamines the day before the exam as well as the morning of the exam. The patient must consult with their physician before this is administered. In patients with known or suspected renal failure, lab tests, including BUN and creatinine, may be ordered prior to the IVP.
An allergic reaction to the contrast agent is the primary risk, although kidney damage is also a potential complication. Patients with a possible iodine allergy or a previous reaction to a radiographic contrast agent should inform the x-ray technologist. A detailed history of known allergies, risk of pregnancy, and current medications is required before an intravenous urogram. All radiology departments have consent forms that must be signed by the patient before starting the exam. Emergency equipment and specific drugs such as antihistamines (Benadryl), adrenaline, and atropine are kept in the x-ray room. All radiography technologists must have specific training and education on the various signs and symptoms of an allergic reaction. A mild reaction consists of a skin rash or hives, whereas a more serious reaction includes swelling of the larynx, difficulties in breathing, asthmatic attacks, and a severe drop in blood pressure (hypotension).
Since x-rays are involved during this procedure, there is a minimal risk due to radiation. This exam is not
done on pregnant women or women who think they may be pregnant.
A normal intravenous urogram indicates no visible abnormality in the structure or function of the urinary system. The radiologist looks for a smooth non-lobulated outline of each kidney, no clubbing or other abnormality of the renal calyces (collecting system), and no abnormal fluid collection in the kidneys that could suggest obstruction. The ureters must contain no filling defects (stones) or deviations due to an adjacent tumor. The bladder must have a smooth outline and empty normally as visualized on the post-void film.
Abnormal results include hydronephrosis (distension of the renal pelvis and calices due to obstruction) as a result of tumors or calculi (stones). Cysts or abscesses may also be present in the urinary system. A delay in renal function can also indicate renal disease. An abnormal amount of urine in the bladder after voiding may indicate prostate or bladder problems.
Intravenous urograms are often done on children to rule out a rapid developing tumor in the kidneys, called a Wilm's tumor. Children are also prone to infections of the bladder and kidneys due to urinary reflux (return back-flow of urine).
Health care team roles
The x-ray technologist must work in conjunction with the doctors and nurses in making sure the patient has not had a previous allergic reaction to a contrast agent. All hospitals have an emergency team ready to react in such a situation, so the technologist must be aware of the procedure to follow when assistance is necessary due to a severe reaction. Details of patient preparation must also be communicated to the hospital wards. In some hospitals the radiologic technologists are trained to give injections, but if this is not the case nurses may be asked to install an intravenous drip before the patient is brought to the radiology department.
The x-ray technologist must explain the risks of an allergic reaction to each patient even though severe reactions are extremely rare due to the advances made in the preparation of contrast agents. The x-ray technologist explains to the patient that a warm, flushed feeling or a metallic taste in the mouth are normal reactions in some patients. Breathing instructions are also important since the kidneys change position depending on the phase of respiration and to prevent motion artifacts. Sometimes an emergency patient with renal colic (acute abdominal pain) is asked to urinate through a special filter used to trap small stones. All radiographic technologists must be certified and registered with the American Society of Radiologic Technologists or an equivalent organization. Continued education credits are mandatory to remain registered.
Contrast agent—A radiopaque substance used in radiology to permit visualization of body structures.
Intravenous—Into a vein.
Ballinger, Frank, et al.. Merrill's Atlas of Radiographic Positioning. 9th ed. St. Louis, MO: Mosby, 1999.
Schull, Patricia, ed. Illustrated Guide to Diagnostic Tests. 2nd ed. Springhouse, PA: Springhouse Corporation, 1998.
Lorraine K. Ehresman