CT Urography Protocol
A CT urogram protocol involves unenhanced images followed by intravenous contrast-enhanced images with nephrographic and excretory phases (acquired at least 5 minutes after contrast injection), using thin-slice acquisition and 3D reconstructions to optimize visualization of the entire urinary tract. 1
Standard Protocol Components
Image Acquisition Phases
- Unenhanced (non-contrast) phase: Initial baseline images
- Contrast-enhanced nephrographic phase: Typically 90-100 seconds after contrast injection
- Excretory phase: Acquired at least 5 minutes after contrast injection 1
Technical Parameters
- Thin-slice acquisition (typically 1-3mm)
- 3D reconstructions using:
Contrast Administration
- Intravenous iodinated contrast (e.g., iohexol)
- Standard or split-bolus technique options:
Optimization Techniques
Improving Urinary Tract Distension
- Oral hydration before the examination
- IV saline hydration
- Compression bands (selectively used)
- Low-dose furosemide (10mg) administration 3-5 minutes before contrast injection 1, 4
Radiation Dose Reduction
- Automatic exposure control
- Iterative reconstruction algorithms
- Higher noise tolerance in specific phases
- Split-bolus technique to reduce number of acquisitions 5
Clinical Applications
Primary Indications
- Evaluation of hematuria (especially gross hematuria or microhematuria with risk factors) 1, 6, 7
- Suspected urinary tract malignancy 1
- Urolithiasis evaluation 1
- Upper tract urothelial carcinoma staging and surveillance 1, 2
- Evaluation of complex renal and urinary tract abnormalities 5
Advantages Over Standard CT
- Superior visualization of both upper and lower urinary tracts
- Better detection of small urothelial lesions
- Improved characterization of filling defects
- Higher sensitivity for detecting urinary tract malignancies (sensitivity 96%, specificity 99%) 2
- Detection of CT-radiolucent stones 5
Important Considerations
Contraindications and Cautions
- Impaired renal function (risk of contrast-induced nephropathy)
- Dehydration (increases risk of renal injury) 3
- Allergy to iodinated contrast media
- Pregnancy (consider MR urography as alternative) 8
- Thyroid dysfunction risk in pediatric patients 0-3 years 3
Common Pitfalls
- Inadequate contrast excretion in patients with poor renal function
- Insufficient delay time for excretory phase (minimum 5 minutes needed)
- Overlapping bowel loops on MIP reconstructions
- Misinterpretation of normal anatomic variants
- Missing small lesions due to inadequate urinary tract distension 4
CT urography has largely replaced conventional intravenous urography for comprehensive evaluation of the urinary tract due to its superior diagnostic capabilities and ability to detect both urinary tract and non-urinary tract pathology in a single examination 8, 7.