CT Urography Protocol for Suspected Urinary Tract Abnormalities
CT urography should include unenhanced, nephrographic phase, and excretory phase images, with the latter providing detailed anatomic depiction of the kidneys, intrarenal collecting systems, ureters, and bladder. 1
Standard CT Urography Protocol Components
Required Phases:
- Unenhanced phase: Essential for detection of calculi and baseline tissue density
- Nephrographic phase: For evaluation of renal parenchyma (70-80 seconds after contrast)
- Excretory phase: Critical for evaluation of the collecting system, ureters, and bladder (5-minute delay) 1
Technical Considerations:
- Contrast administration: Intravenous contrast is essential for comprehensive evaluation
- Diuretic administration: Consider prior to excretory phase to augment urinary tract distention and opacification 1
- Radiation dose reduction: Employ automatic exposure control, iterative reconstruction algorithms, and higher noise tolerance when possible 2
Clinical Indications and Protocol Modifications
For Hematuria Evaluation:
- Complete three-phase protocol is recommended for patients with:
- For patients <30 years without risk factors, consider starting with ultrasound or non-contrast CT 1
For Suspected Urinary Tract Injuries:
- Add CT cystography when bladder injury is suspected
- CT with delayed phase is less sensitive than retrograde cystography for bladder injuries 4
- For suspected ureteral injury, intravenous contrast-enhanced CT with delayed phase is recommended 1
For Recurrent UTIs:
- CTU is the primary test for evaluation of recurrent complicated UTIs
- Useful for detecting congenital anomalies or obstruction of the urinary tract 1
Advantages of CT Urography
- Excellent sensitivity and specificity for identification of renal and urothelial lesions 1
- Superior to conventional imaging for detecting:
- Urinary tract malignancies
- Renal papillary and medullary abnormalities
- CT radiolucent stones
- Congenital abnormalities
- Chronic inflammatory conditions
- Perinephric collections 2
Common Pitfalls and Limitations
- Incomplete evaluation without all three phases, particularly missing the excretory phase
- Inadequate distention of the collecting system (can be improved with diuretic)
- Higher radiation exposure compared to single-phase studies
- Limited evaluation in patients with renal insufficiency or contrast allergies 5
CT urography has largely replaced intravenous urography (IVU) at most institutions for comprehensive urinary tract evaluation 1. The excretory phase is particularly crucial as many abnormalities would be difficult or impossible to diagnose without this delayed imaging 2.