What is CT (Computed Tomography) urography?

What is CT Urography?

CT urography (CTU) is a specialized, multi-phase computed tomography examination specifically designed to comprehensively evaluate the entire urinary tract—kidneys, renal collecting systems, ureters, and bladder—in a single imaging session. 1

Technical Protocol

CTU differs fundamentally from standard CT abdomen/pelvis imaging through its specific acquisition phases 1:

• Unenhanced (non-contrast) phase: Initial images obtained without contrast to identify calculi and characterize baseline tissue density 1
• Nephrographic phase: Images acquired during peak renal parenchymal enhancement after intravenous contrast administration 1
• Excretory (delayed) phase: Critical images obtained at least 5 minutes post-contrast injection to visualize contrast-opacified urine filling the collecting systems, ureters, and bladder 1

Alternative techniques include split-bolus protocols, which use an initial contrast loading dose followed by a second dose, allowing combined nephrographic-excretory phase imaging to reduce radiation exposure 1. Some protocols incorporate arterial phase imaging for specific indications 1.

Image Acquisition and Reconstruction

CTU requires thin-slice acquisition with multiplanar reconstruction capabilities 1:

• Maximum intensity projection (MIP) reconstructions enhance visualization of contrast-filled structures 1
• 3-D volume rendering provides comprehensive anatomic display 1
• Low-dose techniques using reduced milliampere-seconds and kilovoltage peak minimize radiation exposure while maintaining diagnostic quality 1
• Dual-energy CT enables stone composition characterization and generation of virtual unenhanced images 1

Clinical Advantages Over Traditional Imaging

CTU has essentially replaced intravenous urography (IVU) for evaluating the renal collecting systems and ureters 1. The American College of Radiology guidelines emphasize several critical advantages 1:

• Direct visualization of small masses that may be obscured by contrast material or overlying bowel gas on excretory urography 1
• Identification of focal wall thickening not visible on conventional studies 1
• Differentiation of enhancing tumors from non-enhancing calculi or blood clots, which appear as nonspecific filling defects on IVU 1
• Assessment of non-functioning or obstructed kidneys that would not excrete contrast medium required for excretory urography 1

Primary Clinical Indications

CTU demonstrates exceptional diagnostic accuracy with reported sensitivity of 96% and specificity of 99% for detecting urothelial carcinomas 1, 2. The American College of Radiology recommends CTU as the primary imaging modality for 1, 2, 3:

• Evaluation of hematuria in patients at high risk for urinary tract malignancy, particularly those over 50 years of age with risk factors 1, 3
• Detection and staging of upper tract urothelial carcinoma (UTUC), where CTU is considered the most accurate and preferred modality 1
• Comprehensive evaluation of recurrent complicated urinary tract infections requiring detailed anatomic assessment 1
• Detection of synchronous disease in patients with known bladder cancer, as 2-4% will develop upper-tract disease 1

Key Distinction from Standard CT

A critical pitfall is confusing CTU with standard "CT abdomen and pelvis without and with IV contrast" 1. Standard CT protocols are not specifically tailored for urinary tract evaluation and lack both the pre-contrast phase (essential for stone detection) and the delayed excretory phase (essential for visualizing the urothelium) 1. This distinction matters clinically because standard CT may miss urothelial lesions that CTU would detect 1.

Limitations

CTU involves significant radiation exposure, which limits its use for repeated examinations, particularly in younger patients 2. The examination requires intravenous contrast administration, which may be contraindicated in patients with renal insufficiency or contrast allergies 2. While excellent for detecting masses and structural abnormalities, CTU has limited accuracy in differentiating non-muscle invasive from muscle-invasive bladder cancer, where MRI provides superior soft tissue contrast resolution 1, 4.