Difference Between CTA Runoff and CT Angiography of Lower Extremity
CTA runoff refers to a comprehensive imaging protocol that examines the arterial system from the abdominal aorta through the lower extremities to the feet, while CT angiography of the lower extremity typically focuses only on the arterial system of the legs without including the abdominal and pelvic vessels.
Key Differences
Anatomical Coverage
CTA Runoff:
- Examines the entire arterial system from the abdominal aorta through the iliac arteries and down to the feet
- Typically labeled as "CTA Abdomen and Pelvis with Bilateral Lower Extremity Runoff" 1
- Provides complete visualization of inflow and outflow vessels
CT Angiography Lower Extremity:
- Focuses specifically on the arterial system of the legs
- May not include the abdominal aorta and iliac arteries
- Limited to evaluating the arterial system from the femoral arteries distally 1
Clinical Applications
CTA Runoff:
- Preferred when comprehensive evaluation of the entire arterial tree is needed
- Essential when aortoiliac disease is suspected or needs to be ruled out 1
- Valuable for planning endovascular interventions that may involve the aorta or iliac arteries
- Used when the source of claudication could be proximal (aortoiliac) or distal (femoropopliteal or tibial) 2
CT Angiography Lower Extremity:
- Appropriate when disease is known to be limited to the lower extremity vessels
- Useful for focused evaluation of known peripheral arterial disease (PAD) below the inguinal ligament
- May be preferred when radiation dose and contrast volume need to be minimized
Technical Considerations
Both examinations use similar imaging techniques but differ in:
- Contrast Timing: CTA runoff requires precise timing to capture the arterial phase from the aorta to the feet, which is technically more challenging 1
- Radiation Exposure: CTA runoff involves greater radiation exposure due to the larger field of view
- Contrast Volume: CTA runoff typically requires more contrast medium to opacify the entire arterial tree 1
- Acquisition Time: CTA runoff takes longer to acquire due to the larger anatomical coverage
Clinical Decision Making
When deciding between these studies, consider:
Suspected Location of Disease:
- If aortoiliac disease is suspected or needs to be ruled out → Choose CTA runoff
- If disease is known to be limited to below the inguinal ligament → CT angiography lower extremity may suffice
Planning for Intervention:
- For comprehensive revascularization planning → CTA runoff provides complete arterial mapping 1
- For focused intervention on known lower extremity lesions → CT angiography lower extremity
Patient Factors:
- Renal function (contrast volume considerations)
- Radiation exposure concerns
- Prior imaging results
Diagnostic Performance
Both examinations have excellent diagnostic performance:
Common Limitations
- Heavily calcified vessels: Both examinations struggle with accurate stenosis assessment in heavily calcified arteries, particularly in the tibial vessels 1
- Timing challenges: Both require precise timing of contrast bolus, but this is more challenging with CTA runoff due to the larger coverage area 1
- Metal artifacts: Stents and other metallic implants can create artifacts in both examinations 1
Recent Advances
Dual-energy CTA techniques have improved visualization of vessels with heavy calcification or stents by reducing blooming artifacts in both types of examinations 1.
Remember that structured reporting of these examinations significantly improves clarity, completeness, and clinical relevance for referring physicians 4.