What is the procedure for performing computed tomography (CT) venography?

CT Venography Procedure

CT venography is performed by administering intravenous iodinated contrast through a peripheral or contralateral arm vein, followed by delayed imaging at 120-180 seconds to capture optimal venous opacification, with multiplanar reconstructions and 3D renderings produced for comprehensive evaluation. 1

Contrast Administration Protocol

Injection technique and timing:

• Iodinated contrast agent is injected intravenously, typically through a peripheral vein 1
• For upper extremity or thoracic outlet evaluation, contrast should be administered via the contralateral arm or alternative location to avoid artifact in the symptomatic side 1
• Standard contrast volume is approximately 2.0 mL/kg body weight using 300-370 mgI/mL concentration 2
• Typical total volume ranges from 100-150 mL depending on protocol 2, 3, 4
• Injection rate is generally 3.0 mL/s for adequate venous filling 3

Critical timing consideration:

• The scan delay is 120-180 seconds after contrast injection initiation to achieve venous phase opacification 1, 3
• This delayed timing distinguishes CT venography from CT angiography (which uses 15-20 second arterial phase timing) 1

Image Acquisition

Scanning parameters:

• Images are obtained from the region of interest (e.g., ankle to pelvis for lower extremity, elbow to aortic arch for upper extremity) 1
• Scanning direction is typically caudal-to-cranial (starting distally and moving proximally) 3
• Thin-section volumetric acquisition is performed to allow detailed reconstructions 1
• Lower tube voltage settings (100 kVp or 80 kVp) can enhance venous opacification and reduce radiation dose compared to standard 120 kVp 2, 4

Positional imaging (when indicated):

• For thoracic outlet syndrome evaluation, images are obtained in both "neutral" (arms adducted) and "stressed" (arms abducted) positions 1
• This dynamic positioning helps identify positional venous compression 1

Image Post-Processing

Essential reconstruction elements:

• Multiplanar reformations are produced to evaluate the thoracic space and assess true axial compression of vessels 1
• Center-line and volume-rendered 3D images are created to aid visualization and comprehensive assessment 1
• These 3D renderings are a required element that distinguishes CT venography from standard contrast-enhanced CT 1
• Primary transverse reconstructions serve as the foundation for interpretation 1

Clinical Applications and Anatomic Coverage

Lower extremity and pelvic venography:

• Provides direct imaging of the inferior vena cava, pelvic veins, and lower extremity veins 1, 5
• Can be performed immediately after CT pulmonary angiography without additional contrast, adding only minutes to the examination 1
• Particularly valuable for detecting proximal DVT extending into iliac veins or IVC that ultrasound cannot adequately visualize 1, 5

Upper extremity and central venography:

• Evaluates brachiocephalic veins, subclavian veins, axillary veins, and superior vena cava 1
• Essential for diagnosing malignant superior vena cava syndrome and catheter-related thrombosis 1, 6
• CT is the preferred modality over MRI due to superior lung parenchyma discrimination 1

Important Technical Considerations

Contrast-related factors:

• Requires relatively high concentrations of contrast agent, which may be problematic in patients with renal insufficiency 5
• Venous enhancement correlates moderately with iodine dose per body weight (correlation coefficient 0.41-0.62), though body weight alone is not a perfect predictor 3
• Lower kVp settings (80-100 kVp) can maintain adequate venous attenuation while reducing iodine load 2, 4

Radiation exposure:

• CT venography adds radiation exposure that must be weighed against diagnostic benefits, particularly in younger patients 5, 6
• Modern techniques using model-based iterative reconstruction can significantly reduce radiation dose while maintaining image quality 4

Artifact avoidance:

• Some centers place the contralateral arm in abduction (with symptomatic arm neutral) to minimize streak artifact during upper extremity evaluation 1
• Venous contrast mixing artifacts can occur and must be distinguished from true pathology, particularly in renal vein assessment 1

Diagnostic Capabilities

Thrombus detection:

• Thrombus appears as a filling defect, abrupt cutoff of opacification, or complete absence of venous filling 1
• Average attenuation of thrombus is approximately 48 HU, compared to enhanced veins at 110-145 HU 2, 3
• Can detect perivascular inflammatory changes around acute thrombi 1

Additional pathology identification:

• Visualizes external processes causing vascular compression or invasion (neoplasms, lymphadenopathy) 1
• Identifies collateral venous pathways indicating chronic obstruction 1, 6
• Evaluates fixed venous stenoses and anatomic variants 1