Urography

Urography is a radiologic technique used for evaluation of the genitourinary system—specifically, the kidneys, ureters, and bladder. Although it was originally performed using plain radiographic techniques, advanced imaging modalities have been progressively refined such that computed tomography (CT) and/or magnetic resonance imaging (MRI) have largely replaced excretory urography (EU) as the optimal way to image the genitourinary system.[1, 2, 3, 4, 5, 6]

Despite advances in radiologic techniques, there is no particular gold standard for noninvasive imaging evaluation of the urinary collecting system; each modality has its own set of pitfalls that preclude optimal visualization of the entire urinary system. This article outlines indications for urography, discusses advantages and disadvantages of each technique, and presents key points in performing urography using the different modalities.

Indications

Excretory urography

Following are accepted indications for excretory urography (EU), as delineated by the American College of Radiology (ACR)[7] :

• To evaluate the presence or continuing presence of suspected or known ureteral obstruction.

• To assess the integrity of urinary tract status post trauma (including iatrogenic interventions), particularly in situations in which cross-sectional imaging is unavailable or inappropriate.

• To assess the urinary tract for suspected congenital anomalies, particularly in situations in which cross-sectional imaging is unavailable or inappropriate.

• To assess the urinary tract for lesions that may explain hematuria or infection. In particular, EU may be used to evaluate for an underlying parenchymal mass or for a lesion of the urothelial tract in settings in which cross-sectional imaging is unavailable or inappropriate.

Excretory urography (EU) historically was the most frequently performed imaging modality for uroradiology. With advances in ultrasonography and development of cross-sectional urography with CT and MRI, EU is now seldom performed. Consequently, there has been a decline in expertise for this technique. However, EU offers multiple advantages such as its dynamic nature, easy availability, and low cost and radiation burden. These render it potentially highly valuable in specific indications such as congenital anomalies, urothelial lesions, and urinary leaks.[8]

Computed tomographic urography

Computed tomography (CT) urography is currently the imaging modality of choice for assessment of the whole urinary tract, providing the possibility of detecting and characterizing benign and malignant conditions. In particular, CT urography offers improved visualization of the urinary collecting system through acquisition of delayed scans obtained after excretion of intravenous contrast medium from the kidneys. Remaining scans are of great help for identification, characterization, and staging of urologic tumors.[9]

The indications for CT urography are similar to those for EU. CT urography is most often used for evaluation of the urinary collecting system in the setting of hematuria. Multidetector CT (MDCT) has been shown to be more sensitive than EU in detection of transitional cell carcinoma of the upper tracts, with sensitivity of 95.8% vs 75%.[2, 3, 10, 11, 12, 13, 14]

Other clinical situations in which CT urography may be useful include trauma with suspected ureteral injury, as well as recurrent and/or complex urinary infections to exclude an underlying obstructive etiology or formation of an abscess. CT urography is also used to detect renal stones and may be used in preoperative planning for percutaneous nephrolithotomy (PCNL).[15] CT urography has been used in the postoperative setting to evaluate the urinary collecting system following cystectomy.[16]

Anatomic variations in the urogenital tract have generally been diagnosed through intravenous (IV) urography as the modality of choice. CT urography has replaced traditional IV imaging of the genitourinary tract. Hematuria, tumoral mass, obstructive uropathy, and congenital collecting system abnormalities are indications for CT imaging.[17]

With continued confirmation of the accuracy and advantages of MDCT urography, MDCT has essentially replaced conventional EU. More specifically, the advantages offered by MDCT urography include high spatial and contrast resolution, with ability to obtain isotropic volume data in as thin as 0.5-mm acquisitions, which may be reformatted in multiple planes or reconstructed in 3D. Evaluation of enhancement characteristics through measurement of attenuation values allows characterization of renal lesions.

In a study by Abuhasanein et al to determine the diagnostic accuracy of CT urography to rule out urinary bladder cancer and possibly eliminate the need for cystoscopy, CT urography with corticomedullary phase was found to successfully exclude urinary bladder cancer with high accuracy. In cases of negative findings on CT urography, the authors suggested it might be reasonable to omit cystoscopy. Negative predictive value was 99%, false negative rate was 7%, and false positive rate was 1%. [18]

The French Society of Genitourinary Imaging provided the following guidelines for CT urography[19] :

• Intravenous injection of 20 mg of furosemide before iodinated contrast medium injection was judged mandatory.
• Improving the quality of excretory phase imaging through oral or intravenous hydration of the patient or through the use of an abdominal compression device was not deemed necessary.
• The patient should be imaged in the supine position and placed in the prone position only at the radiologist's request.
• The choice between single-bolus and split-bolus protocols depends on the context, but split-bolus protocols should be favored whenever possible to decrease patient irradiation.
• Repeated single-slice test acquisitions should not be performed to decide the timing of excretory phase imaging; instead, excretory phase imaging should be performed 7 min after the injection of the contrast medium.

Magnetic resonance urography

To date, magnetic resonance (MR) urography has been used in patients with urinary tract dilation or urinary obstruction who cannot receive iodinated contrast material or for whom imaging using ionizing radiation is undesirable.[20] As such, patient populations for which this modality has been most widely used include children and pregnant patients.[20] Note that MR urography is relatively insensitive for detection of renal and ureteral calculi when compared with CT scanning.[3, 5, 6, 20, 21, 22, 23, 24]

Additionally, MR urography may be indicated in the diagnosis and staging of cancers involving the kidney, bladder, and prostate. This is due, in part, to the fact that MR imaging offers superior soft tissue contrast resolution and better detection of contrast enhancement.[25]

Congenital abnormalities of the kidney and urinary tract include a wide range of malformations ranging from asymptomatic to life-threatening conditions. MR urography plays a fundamental role in classifying and managing congenital abnormalities of the kidney and urinary tract. This technique provides an overview of different clinical pictures through its panoramic views and high anatomic detail. Deep knowledge of the complexities of embryogenesis and of possible phenotypic patterns enables correct interpretation of MR urography images.[26]

In children, MR urography can be used for preoperative anatomic assessment of vascular anatomy; for evaluation of duplicated collecting systems, renal dysplasia, ectopic ureter, retrocaval ureter, and primary megaureter; and for differentiating hydronephrosis from cystic renal disease.[4, 20, 27] Furthermore, MR urography can be used to obtain physiologic information about the collecting systems such as renal transit time, differential renal function, and estimated glomerular filtration rate (eGFR), obviating the need for nuclear scintigraphy and consequently avoiding associated radiation exposure.[28, 29]

The most common indications for MR urography in children are evaluation of congenital anomalies of the kidney and urinary tract, including hydronephrosis and renal malformations, and identification of ectopic ureters in children with incontinence.[30]  MR urography is a preferred method in the diagnostic algorithm for megaureter, providing both anatomic and functional information. Research suggests that MR urography is superior to ultrasonography and scintigraphy in diagnosing urinary tract anomalies with megaureter.[31]

In pregnant patients, MR urography is generally used to distinguish physiologic dilatation of the ureters from an underlying obstructive uropathy.[32]

Advances in MR imaging techniques, including parallel imaging, free-breathing motion compensation techniques, and compressed sensing may dramatically shorten examination times and may improve image quality and patient tolerance.[33]  

Contraindications

Excretory urography

The technique used in performing a complete EU examination is discussed in detail later; however, the basic premise involves obtaining plain radiographic images of the abdomen at various time points after administration of intravenous iodinated contrast material. A compression device is often used for optimal visualization of the collecting system. Thus, contraindications to EU pertain to use of iodinated contrast material and use of the compression paddle. A positive pregnancy test is an additional absolute contraindication to this procedure.

Risk factors pertaining to use of iodinated contrast material include the following[34] :

• Allergy: A history of a prior allergic-like reaction to contrast media is associated with an up to 5-fold increase in the likelihood of experiencing a subsequent reaction. ^[35] In addition, any patient with a predilection to allergic reactions may be predisposed to a reaction after administration of contrast media. Given the increased risk of severe life-threatening anaphylaxis related to administration of contrast media in the setting of a history of atopy, risk vs benefit should be discussed before this procedure is begun. A premedication regimen may be used to reduce the risk of anaphylaxis.
• Asthma: A history of asthma may be indicative of a greater likelihood of developing a contrast reaction. ^[35]
• Cardiac status: Attention must focus on patients with significant cardiac disease (congestive heart failure, aortic stenosis, severe cardiomyopathy, and/or pulmonary hypertension), as higher volumes and osmolality of contrast material may result in increased risk for a contrast reaction.
• Renal insufficiency: Contrast nephrotoxicity is defined as rapid deterioration in renal function after administration of contrast media, when no other etiology can be determined from the clinical records. ^[28] Major predisposing risk factors include preexisting renal insufficiency (defined as serum creatinine level >1.5 mg/dL) and diabetes. ^[36] Other risk factors include dehydration, cardiovascular disease, use of diuretics, advanced age (>70 yr), hypertension, and hyperuricemia. ^[37]  Performing multiple contrast-enhanced studies within a 24-hour period is thought to increase the risk for contrast-induced nephrotoxicity. ^[38]
• Miscellaneous: Relative contraindications to the use of high-osmolality iodinated contrast media (HOCM) in patients with pheochromocytoma, sickle cell disease, and multiple myeloma have been reported. Although administration of low-osmolality or iso-osmotic contrast media may be beneficial for patients with pheochromocytoma and sickle cell disease, little evidence suggests that these agents mitigate the risks associated with multiple myeloma. ^[34]

Contraindications to compression include the following[39] :

• Evidence of obstruction on the 5-minute image

• Abdominal aortic aneurysm or other abdominal mass

• Severe abdominal pain

• Recent abdominal surgery

• Suspected urinary tract trauma

• Presence of a urinary diversion

• Presence of a renal transplant

Computed tomographic urography

Safe use of iodinated contrast material and compression devices pertains to both CT urography and EU. Additionally, some studies have shown that applying abdominal compression did not improve distention or opacification of the ureters compared with giving the patient a saline bolus.[40, 41] Furthermore, CT urography should not be performed in a pregnant patient.

Another precaution involved in both techniques, but perhaps more pertinent with CT urography, involves the relatively high doses of ionizing radiation involved in imaging the genitourinary tract. The mean effective dose for patients undergoing MDCT urography has been reported at 14.8 mSv ± 3.1, which is about 1.5 times the exposure of EU.[42] Use of dose modulation with iterative reconstruction techniques is expected to bring further reductions in dose. This issue becomes of special importance in both children and pregnant patients, for whom MR urography may be the preferred imaging modality.

Magnetic resonance urography

One of the techniques used for MR urography requires use of a gadolinium-based contrast agent. Information is available on the risks of gadolinium-based contrast agents.

Relevant anatomy

The anatomy of the bladder (see the image below) forms an extraperitoneal muscular urine reservoir that lies behind the pubic symphysis in the pelvis. A normal bladder functions through complex coordination of musculoskeletal, neurologic, and psychological functions that allows filling and emptying of bladder contents. The prime influence on continence is seen in synergic relaxation of detrusor muscles and contraction of bladder neck and pelvic floor muscles.

Gross anatomy of the bladder.

Anesthesia

Anesthesia is generally not required for adult patients undergoing urographic examination, regardless of the modality. However, children undergoing MR urography often require sedation. Consequently, many institutions coordinate MR urographic examinations with staff in the anesthesia department.

Equipment

In excretory urography (EU), radiographs are performed with standard radiographic equipment to obtain multiple kidney, ureter, bladder (KUB) radiographs. Images may be obtained in a variety of projections, with oblique images providing helpful information in evaluating abnormal calcifications.[43]

Multidetector CT scanners have become increasingly commonplace, and CT urography using this equipment has been well studied. As mentioned earlier, multidetector arrays enable acquisition of isotropic volume information, which is routinely reformatted into axial, coronal, and sagittal image series. In addition, the data are amenable to multiplanar reformatting and 3D manipulation within the CT scanner work console, at standalone computer workstations, or within the PACS environment.

MR urography performed on 1.5 T machines has been well studied. Studies have reported the use of 3.0 T MR systems for MR urography. No clear difference has been shown between 1.5 and 3.0 T examinations, and 3.0 T examinations have been shown to have inherent problems, including prolonged T1 relaxation times and worsening of some artifacts.[44]

Compression, as has been mentioned, is considered by some to be an essential component of an effective urographic examination,[43] whereas others use alternative techniques to image the ureters.[40] Different types of compression devices exist, some of which are placed around the patient; others are attached to the examination table. For EU, patients may be placed in various positions, and positioning is limited only by the patient’s comfort level and the range of the radiographic equipment.

Positioning

In both CT and MR urographic studies, the patient is preferably placed with arms above the head while in the supine position. In the CT examination, this position limits the effect of beam hardening artifact; in the MR examination, this position limits the wrap-around artifact.

Excretory urography

Details pertaining to patient preparation are institution specific. At the authors' institution, patients are instructed to consume 1 bottle of magnesium citrate oral solution the evening before the examination. Magnesium citrate acts as a laxative, ensuring that subtle renal, ureteral, or bladder calcifications are not masked by abundant amounts of stool. In addition, the patient is instructed to not consume liquids or solids on the morning of the examination.

Recent laboratory values are screened prior to the procedure to ensure normal renal function, and a negative pregnancy test (as applicable) is obtained. A detailed list of medications and allergies is prepared by the technologist before the procedure is begun. The procedure is explained to the patient, and a consent form is signed. The patient is asked to void prior to the start of the study.

After the above information is reviewed and after it is determined that the procedure is not contraindicated, a preliminary KUB radiograph is obtained (see the image below). This radiograph is obtained on a standard 14x17-inch cassette centered at the iliac crest and taken in full inspiration. For larger patients, the radiograph is centered at the umbilicus. The preliminary radiograph is examined by the radiologist to ensure that the field of view is appropriate (the radiograph should encompass the suprarenal region to a level below the pubic symphysis). Additionally, the radiologist should note the presence of any calcifications. Additional oblique radiographs may be required to localize and delineate suspected calcifications seen on the KUB radiograph.

Excretory urography imaging sequence: A plain KUB radiograph is first obtained to detect the presence of any calcifications.

If satisfied with the preliminary radiograph(s), the radiologist places a peripheral intravenous line through which two 50-mL syringes of Omnipaque 300 are briskly injected. After injection of contrast, a cone-down radiograph focused on the kidneys is obtained during full expiration at the 1-minute mark (see the first image below). A subsequent full KUB of the abdomen is obtained at 3 minutes. At this juncture, if abdominal compression is not contraindicated, the patient is placed prone onto a compression paddle, with the top of the paddle situated just above the superior aspect of the iliac crests.

Excretory urography imaging sequence: At 1 minute, a cone down radiograph of the kidneys is obtained.

Excretory urography imaging sequence: At 3 minutes, a plain radiograph of the abdomen is obtained.

Abdominal compression allows better visualization of the renal collecting system, especially in situations in which low osmolar contrast is used. Once the compression device is placed, an additional anteroposterior cone-down radiograph of the kidneys and bilateral oblique radiographs are obtained (see the first 3 images below). The radiologist is shown the images, and if optimal opacification of the collecting systems is evident, the compression paddle is released, with a subsequent KUB obtained by the technologist (see the fourth image below). An additional cone-down post-void radiograph of the bladder may be requested in frontal and oblique projections (see final 3 images below).

Excretory urography imaging sequence: The patient is placed prone and a coned down image of the kidneys is obtained. A compression device is typically used unless it is contraindicated.

Excretory urography imaging sequence: Oblique radiographs of the abdomen are obtained with the patient in the prone position.

Excretory urography imaging sequence: Oblique radiographs of the abdomen are obtained with the patient in the prone position.

Excretory urography imaging sequence: A full KUB radiograph is obtained after release of the compression paddle with the patient in the prone position.

Excretory urography imaging sequence: A coned down radiograph of the bladder is obtained in the frontal projection.

Excretory urography imaging sequence: Oblique radiographs of the bladder are obtained.

Excretory urography imaging sequence: Oblique radiographs of the bladder are obtained.

A modification of the technique may be used in patients with suspected ureteropelvic junction (UPJ) obstruction. The patient is specifically asked if he/she has an allergy to Lasix (furosemide) before this portion of the procedure is begun. If no history of an allergic reaction is reported, 15-20 minutes after the initial contrast injection, 0.5 mg/kg of Lasix (up to 40 mg) is injected through the peripheral intravenous line. Subsequent KUB radiographs are obtained at 5, 10, and 15 minutes after administration of intravenous Lasix. UPJ pathology is suspected if the contrast fails to clear the collecting system at the 10-minute mark after Lasix is injected.

Excretory urography with Lasix: A plain radiograph of the abdomen is obtained prior to starting the procedure.

Excretory urography with Lasix: A 1-minute coned down radiograph of the kidneys is obtained. Note the relatively larger size of the left kidney.

Excretory urography with Lasix: An abdominal radiograph is obtained at the 3-minute mark. Note the relatively decreased nephrogram in the enlarged left kidney.

Excretory urography with Lasix: The patient is placed prone and an additional radiograph is obtained. The left renal pelvis is dilated with diffuse pelvocaliectasis.

Excretory urography with Lasix: A 5-minute post-Lasix radiograph is obtained. Contrast has almost cleared from the right collecting system but remains pooled within the pelvis and calyces of the left kidney.

Excretory urography with Lasix: A 10-minute post-Lasix radiograph demonstrates persistent but decreased dilatation of the left renal pelvis.

Excretory urography with Lasix: A 15-minute radiograph demonstrates persistent dilatation of the left renal pelvis. These findings are compatible with known history of left ureteropelvic obstruction.

Computed tomographic urography

Patients are encouraged to maintain good hydration prior to the CT examination to reduce the risk of contrast-induced nephropathy. After studying 176 patients, Weatherspoon et al concluded that oral hydration is more cost-effective and produced ureteral distention and opacification similar to IV techniques.[45]

As with EU, patients answer a questionnaire prior to the examination, highlighting their medications and history of allergic reactions. All metal is removed from the area of interest (to reduce beam hardening artifact from metallic objects). Peripheral intravenous access is ensured prior to commencement of the examination. The patient is placed supine on the table with arms raised over the head.

A digital scout radiograph is obtained to ensure coverage from the diaphragm to the iliac crests. A non-contrast CT scan is obtained (see image below), scanning from the top of the kidneys through to the pubic symphysis using the following parameters:

Table 1. Noncontrast CT Parameters (Open Table in a new window)

CT urogram: Non-contrast axial computed tomographic (CT) scan of the abdomen and pelvis is routinely obtained as part of a CT urogram to look for underlying calculi.

The mA is alternated as the gantry rotates around the patient according to shape and attenuation characteristics of the patient obtained from the scout radiograph (ie, dose modulation) to decrease the radiation dose. In addition, the noise index is increased at the level of the iliac crest to minimize the radiation dose to the gonads. The trade-off, inevitably, is poorer-quality images; however, the authors feel this is a reasonable compromise because the non-contrast scan is used to look for stones, which are still visible on higher noise index images.

The authors subsequently inject 120 mL of intravenous contrast (or 85 mL if there is only one functioning kidney) via a peripheral IV line at a rate of 2-3 mL/sec and image through only the kidneys after a 100-second delay (from the start of the bolus injection) to obtain a nephrographic phase of renal enhancement (see the image below). No oral contrast is administered. The parameters used are shown below.

Table 2. IV Contrast With 100-Second Delay CT Parameters (Open Table in a new window)

CT urogram: Nephrographic phase image of the kidney at 70 seconds post contrast administration.

After this acquisition, a bolus of 200 mL of saline is administered. The patient is then asked to sit up for approximately 8 minutes (counting from initial bolus injection of contrast), after which the patient is instructed to lie supine on the CT table with arms over the head. A second digital scout radiograph spanning the diaphragm through to the pelvis is now obtained. The patient is then scanned from above the kidneys through the pubic symphysis to obtain a 10-minute delayed excretory image to opacify ureters and bladder. Sagittal and coronal reformats are obtained from axial imaging data, and 3D volumetric images are generated by the radiologist at a separate, dedicated 3D workstation (see the images below). The parameters used are shown below.

Table 3. IV Contrast With 10-Minute Delay CT Parameters (Open Table in a new window)

CT urogram: Excretory phase obtained 7 minutes following contrast administration. This phase is used to look for filling defects in the urinary collecting system.

CT urogram utilizing a split dose technique: Axial image through the kidneys and collecting systems demonstrates both nephrographic and excretory phases of enhancement in the same imaging sequence.

CT urogram utilizing a split dose technique: Axial images displayed with wider window settings are suitable for display of the opacified collecting systems and urinary tract calculi.

Example of 3D postprocessing work performed by the radiologist after the acquisition of the imaging data.

3D post-processing image created by the radiologist after the acquisition of the imaging data. The image has been obliqued to optimally visualize the left distal ureter and left ureterovesicular junction.

3D post-processing image created by the radiologist after the acquisition of the imaging data. The image has been obliqued in order to optimally visualize the right distal ureter and right ureterovesicular junction.

Note that the noise index is increased to compensate from the increased dose brought on by using the thinner slices needed to accurately evaluate the collecting systems for subtle filling defects.

An alternative technique that is typically used in patients younger than 40 years is referred to as the "split dose" technique. The premise of this technique is to administer a divided dose of iodinated contrast, with subsequent CT acquisition timed so that a single contrast-enhanced scan contains both nephrographic and excretory phases of renal enhancement.

Initial imaging parameters are the same for the 2 techniques: A scout radiograph and a non-contrast CT scan are obtained (using dose modulation and increasing the noise index at the iliac crests to decrease the dose to the gonads). Subsequently, 75 mL of intravenous noniodonated contrast is injected via a peripheral line at 2-3 mL/sec; this is followed by a 150-mL bolus of saline.

Typically, the authors wait 8 minutes after injection of contrast and then administer an additional 75 mL of noniodonated contrast at 2-3 mL/sec, followed by a 50-mL bolus of saline. No oral contrast is administered. After a 100-second delay, a CT scan is obtained from the top of the kidneys through to the pubic symphysis using the parameters shown below.

Table 4. IV Contrast Combined Nephrographic/Excretory CT Parameters (Open Table in a new window)

Volume data, consisting of 0.625 mm slices, as well as reformatted 3.75 mm slices, are provided by the technologist to the radiology console for interpretation. 3D volumetric images are subsequently generated by the radiologist at a separate, dedicated 3D workstation.

In a study by Morrison et al, single-bolus CT urography was found to result in significantly fewer repeat excretory phases (28.6% vs 46.3%) and faster scan time (678s vs 978s), with only slightly higher radiation dose, in patients 50 years and older.[46]

Magnetic resonance urography

Magnetic resonance (MR) urography has evolved into a comprehensive evaluation of the urinary tract that combines anatomic imaging with functional evaluation in a single test without ionizing radiation. Quantitative functional MR imaging is based on dynamic contrast-enhanced MR acquisitions that provide progressive, visible enhancement of the renal parenchyma and urinary tract. Functional evaluation with MRI has continued to improve as a result of both significant technical advances allowing for faster image acquisition and new tracer kinetic models of renal function.[30]

The challenge of MR urography is to obtain diagnostic quality images of the kidneys, ureters, and bladder within a reasonable time frame, while taking into account the effects of respiratory motion, ureteral peristalsis, and flowing urine.[25]

Magnetic resonance urography requires patient preparation in the form of pre-examination IV hydration, placement of a urinary catheter, and administration of diuretics at the time of the exam. The imaging protocol is based on T2-weighted images for anatomic assessment and dynamic post-contrast images for functional evaluation. These images are then used to generate quantitative and graphic results, including contrast transit and excretion time, and to calculate differential renal function.[47]

Early MR urography relied on T2-weighted techniques to take advantage of the high signal intensity of urine in the collecting systems, ureters, and bladder. Obvious advantages of this technique are that images can be obtained in any plane and images can be obtained relatively quickly. However, this technique is limited to use in patients with distended urinary collecting systems. Additional interventions such as intravenous hydration, ureteral compression, and intravenous diuretics may be introduced to optimize the examination.

Excretory MR urography, on the other hand, is similar to CT urography and conventional EU. A gadolinium-based contrast agent is administered intravenously, and collecting systems are then imaged during the excretory phase. Generally, to avoid T2 effects of concentrated contrast in the urine, low-dose gadolinium-based contrast is administered.[48] Again, IV diuretics may be administered to optimize the examination.[20] The primary imaging sequence is a 3D gradient-echo, generally with fat suppression. Motion suppression is best achieved with breath-hold acquistions, as opposed to respiratory triggering.[49]

Ultimately, most modern MR urographic studies combine T1- and T2-weighted sequences in axial and coronal planes. Contrast administration should not occur until after the T2-weighted sequences are obtained, because the gadolinium-based contrast agent causes decreased signal on T2-weighted sequences. At our institution, the initial set of T2-weighted images are reviewed by the radiologist to evaluate for an underlying obstruction. If no obstruction is noted, intravenous Lasix (furosemide) is administered to optimize excretion. Comprehensive examinations may take 30-60 minutes, with more tailored examinations taking 15-30 minutes. The authors routinely obtain our post-contrast images at 3 minutes and at 7-10 minutes. Images at 3 minutes are obtained in both axial and coronal planes; remaining contrast-enhanced images are obtained in the coronal plane (see the images below). A radiologist is present to monitor the case for quality assurance.

Pediatric MR urography can be performed at 1.5 or 3 Tesla (T) in children. The 3 T magnets can provide superior spatial resolution, which can be particularly helpful in younger children and provide  improved visualization of small urinary tract structures. The 1.5 T magnets, however, generally allow for more homogeneous fat saturation and are less susceptible to artifacts, such as dielectric effect, T2* effects of excreted gadolinium, and any artifacts from surgical material. Imaging is performed with multi-element phased-array surface coils. Generally, children who are younger than 10 years or those with developmental delay will require the use of anesthesia or sedation to prevent motion artifacts.[50]

CT urogram: Axial image obtained in the excretory phase demonstrates a small filling defect in the distal right ureter in this patient with hematuria. Biopsy confirmed the presence of right ureteral transitional cell carcinoma.

CT urogram: Coronal reconstruction demonstrates an elongated filling defect in the distal right ureter. Biopsy revealed the presence of a transitional cell carcinoma.

Retrograde ureterogram: Fluoroscopic spot image obtained during ureteral biopsy demonstrates an elongated stricture of the distal right ureter corresponding to the filling defect on the CT urogram. Biopsy confirmed a transitional cell carcinoma.

Medullary sponge kidney: CT urogram in the excretory phase demonstrates thin linear striations of contrast outlining the papillae of the upper right kidney, compatible with a history of medullary sponge kidney.

Medullary sponge kidney: CT urogram in the excretory phase demonstrates thin linear striations of accumulated contrast within the papillae of both kidneys, more prominent on the right.

MR urogram: Coronal T2 weighted image of the abdomen demonstrates right-sided hydronephrosis. Note the atrophic upper pole of the right kidney.

MR urogram: Coronal T1 fat saturation (FS) post contrast image of the abdomen at 3 minutes after contrast administration demonstrates prompt enhancement of the kidneys except for the upper pole of the right kidney which is atrophic and nonfunctioning secondary to long-standing reflux.

MR urogram: 3D maximum intensity projection image in the coronal plane demonstrates a duplicated left collecting system with normal excretion in the bladder. Hydronephrosis is noted in the lower pole moiety of a right-sided duplicated system, while the upper pole demonstrates no excretion secondary to chronic reflux nephropathy. A round intraluminal filling defect in the right side of bladder is compatible with a ureterocele from the distal ureter of the right upper pole moiety.

MR urogram: 3D maximum intensity projection image in the coronal plane demonstrates a duplicated left collecting system with normal excretion into the bladder. Hydroureteronephrosis is noted within the lower pole moiety of a right-sided duplicated system, while the upper pole demonstrates no excretion secondary to chronic reflux nephropathy. The lower pole moiety of the right kidney is obstructed by an ureterocele of the upper pole moiety's distal ureter.

Complications

Complications revolve around contrast administration and use of compression.

Infiltration of the intravenous access site may occur. Small amounts of extravasated iodinated iso-osmolar contrast are unlikely to cause serious complications; this event may be treated with warm soaks or ice packs, massage, and/or elevation until the fluid is resorbed, which generally occurs over 2-4 hours. During this time, the patient remains under observation in the imaging department.

The patient should be given specific discharge instructions by the radiologist and should be followed up in the next 24 hours to confirm that there are no further symptoms or signs that might indicate development of blistering, skin sloughing, cellulitis, or thrombophlebitis. Larger volumes of contrast extravasation may be associated with compartment syndrome, and referral to the ED with a plastic surgery consultation for infiltrations greater than 30 mL is advisable.

Iodinated contrast may cause nephrotoxicity in patients with impaired renal function; thus, it is important to obtain laboratory work on patients prior to administration of IV iodinated contrast. Similarly, impaired renal function may result in severe adverse effects if gadolinium-based contrast is administered—namely, nephrogenic systemic fibrosis.

Complications from the use of compression paddles range from patient discomfort to severe, life-threatening emergencies if used in a patient with an abdominal aortic aneurysm. Additionally, patients with a transplanted kidney should be approached carefully, if at all, with compression devices.

Furosemide (Lasix)

Furosemide works to increase excretion of water by interfering with the chloride-binding co-transport system, which in turn inhibits sodium and chloride reabsorption in the ascending limb of the loop of Henle and in the distal renal tubule. Bumetanide does not appear to act in the distal renal tubule. For the purpose of EU, our institution administers Lasix as follows: 0.5 mg/kg of Lasix is injected through a peripheral intravenous line up to a maximum dose of 40 mg.

Gadolinium-based contrast agents

Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). This disease has occurred in patients with moderate to end-stage renal disease after they were given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography (MRA) scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. Great caution should therefore be exercised in evaluating patients with renal insufficiency.