Genitourinary Imaging Tests

Abdominal x-rays without radiopaque contrast agents may be done to check for positioning of ureteral stents or to monitor position and growth of kidney stones. However, for initial diagnosis of urolithiasis Urinary Calculi Urinary calculi are solid particles in the urinary system. They may cause pain, nausea, vomiting, hematuria, and, possibly, chills and fever due to secondary infection. Diagnosis is based on... read more , plain x-rays are less sensitive and less specific than CT and lack anatomic detail, so they are not the study of choice.

Images taken after administration of water-soluble contrast agents highlight the kidneys and urinary collecting system. Nonionic iso-osmolal agents (eg, iohexol, iopamidol) are now widely used; they have fewer adverse effects than older hyperosmolal agents but still pose a risk of acute kidney injury (contrast nephropathy Contrast nephropathy Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based. Iodinated... read more ).

In urography, an x-ray is taken after IV, percutaneous antegrade or retrograde, or cystoscopic retrograde administration of a radiopaque contrast agent Radiographic Contrast Agents and Contrast Reactions Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based. Iodinated... read more . Primary contraindications for all patients are iodine allergy and risk factors for contrast nephropathy.

Ultrasonography can provide useful images of many genitourinary structures without exposing patients to ionizing radiation. Images are interpreted as they are acquired, so the technician can focus on concerning areas and obtain additional information if necessary. Its main disadvantages are the need for a skilled operator and the time required. A full bladder helps provide better images of certain structures but no other preparation is needed.

Structures that can be imaged and common indications include the following:

Computed tomography provides a broad view of the urinary tract and surrounding structures. Conventional or helical scanners are used for most purposes with or without IV contrast agents Radiographic Contrast Agents and Contrast Reactions Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based. Iodinated... read more . Use of contrast agents with either technique resembles IV urography (IVU) but provides additional detail. Previously, in trauma patients, there was concern that use of contrast would make it difficult to distinguish abdominal hemorrhage from urinary tract disruption, but with modern imaging techniques and protocols, this distinction can be made. Helical CT without a contrast agent is the study of choice for imaging of calculi; dual-energy scanners may provide additional information that can help determine stone composition.

The main disadvantage of CT is that it exposes patients to a relatively large dose of ionizing radiation. CT angiography CT angiography CT shows a focal area of osteolysis (arrows) involving the right acetabulum that is consistent with particle disease. In CT, an x-ray source and x-ray detector housed in a doughnut-shaped assembly... read more is a less invasive alternative to conventional angiography.

Compared with CT, MRI is safer for patients at risk of contrast nephropathy Contrast Nephropathy Contrast nephropathy is worsening of renal function after IV administration of radiocontrast and is usually temporary. Diagnosis is based on a progressive rise in serum creatinine 24 to 48 hours... read more , does not expose patients to ionizing radiation, and provides superior soft-tissue detail (but images bones and calculi poorly). Magnetic resonance imaging is contraindicated in patients with ferromagnetic metal (ie, containing iron) implants and magnetically activated or electronically controlled devices (eg, cardiac pacemakers). See also the MRI safety web site.

Also, due to the risk of nephrogenic systemic fibrosis, MRI with gadolinium contrast is contraindicated in patients with glomerular filtration rate (GFR) < 30 mL/min.

Urologic application of MRI includes the evaluation of renal cysts and small renal masses. MRI is also helpful in imaging blood vessels (eg, for renal artery stenosis Renal Artery Stenosis and Occlusion Renal artery stenosis is a decrease in blood flow through one or both of the main renal arteries or their branches. Renal artery occlusion is a complete blockage of blood flow through one or... read more and renal vein thrombosis Renal Vein Thrombosis Renal vein thrombosis is thrombotic occlusion of one or both main renal veins, resulting in acute kidney injury or chronic kidney disease. Common causes include nephrotic syndrome, primary hypercoagulability... read more ), and its use is increasing as MRI becomes more widely available.

Multiparametric MRI is now the imaging study of choice for staging prostate cancer Prostate Cancer Prostate cancer is usually adenocarcinoma. Symptoms are typically absent until tumor growth causes hematuria and/or obstruction with pain. Diagnosis is suggested by digital rectal examination... read more and for serial imaging of patients with prostate cancer on active surveillance. A multiparametric MRI examination includes paramagnetic contrast and consists of 3 separate imaging techniques (parameters): T2-weighted imaging, diffusion-weighted imaging, and dynamic contrast-enhanced imaging. A technique known as MRI fusion biopsy is sometimes used during a prostate biopsy Prostate biopsy Biopsy of the urinary tract requires a trained specialist (nephrologist, urologist, or interventional radiologist). Indications for diagnostic biopsy include unexplained nephritic or nephrotic... read more . An MRI of the prostate is obtained prior to ultrasound-guided prostate biopsy, during which the MRI image is digitally combined (fused) with the ultrasound image to better identify lesions that need to be biopsied.

Cortical tracers that bind to proximal tubular cells (eg, technetium-99m dimercaptosuccinic acid [^99mTc DMSA]) are used to image the renal parenchyma. Excretory tracers that are rapidly filtered and excreted into urine (eg, iodine-125 iothalmate, ^99mTc diethylenetriamine pentaacetic acid [DTPA], ^99mTc mercaptoacetyltriglycine-3 [MAG3]) are used to assess glomerular filtration rate (GFR) and overall renal perfusion. Radionuclide scanning can be used to evaluate renal function. It also has the benefit of not requiring IV contrast and may be used safely in patients at risk for contrast nephropathy Contrast Nephropathy Contrast nephropathy is worsening of renal function after IV administration of radiocontrast and is usually temporary. Diagnosis is based on a progressive rise in serum creatinine 24 to 48 hours... read more . Radionuclide scanning also provides more information than does IV urography or cross-sectional imaging about the following:

^99mTc pertechnetate can be used to image blood flow to the testes and to distinguish torsion Testicular Torsion Testicular torsion is an emergency condition due to rotation of the testis and consequent strangulation of its blood supply. Symptoms are acute scrotal pain and swelling, nausea, and vomiting... read more from epididymitis Epididymitis Epididymitis is inflammation of the epididymis, occasionally accompanied by inflammation of the testis (epididymo-orchitis). Scrotal pain and swelling usually occur unilaterally. Diagnosis is... read more in patients with acute testicular pain, although Doppler ultrasonography is used more commonly because it is quicker. No patient preparation is necessary for radionuclide scanning, but patients should be asked about known allergies to the tracer.

Newly available nuclear positron emission tomographic (PET) agents can detect metastatic prostate cancer. Routine FDG PET scans are not very useful for most cases of prostate cancer but can be useful for other genitourinary tumors such as kidney or testicular cancer. Newer PET imaging includes targeting PSMA (prostate-specific membrane antigen) on the surface of prostate cancer cells.