For a patient with gangrene of the fourth toe, is a contrast‑enhanced computed tomography angiography (CTA) of the abdomen, aorta, and bilateral lower‑extremity runoff performed with and without contrast equivalent to a non‑contrast CTA?

CTA Abdomen/Aorta/Bilateral Runoff: With and Without Contrast vs. With Contrast Only

No, CTA of the abdomen, aorta, and bilateral lower extremity runoff performed "with and without contrast" is NOT the same as "with contrast only"—the noncontrast phase is clinically essential and should be obtained. For a patient with gangrene of the fourth toe requiring vascular imaging, the protocol must include both noncontrast and contrast-enhanced phases.

Why the Noncontrast Phase Matters

The noncontrast images serve critical diagnostic functions that cannot be replaced by contrast-enhanced images alone 1:

• Identifies calcified plaque and calcium within thrombus before contrast obscures these findings
• Fine-tunes the scan range to ensure optimal coverage of the arterial tree
• Distinguishes true arterial enhancement from baseline high-attenuation material that could mimic contrast
• Detects sentinel clot in cases where active bleeding or thrombosis is suspected

Specific Application to Gangrene/Critical Limb Ischemia

For your patient with fourth toe gangrene, this represents critical limb-threatening ischemia (CLTI). The ACR Appropriateness Criteria specifically addresses peripheral arterial disease imaging 1:

Key technical considerations:

• Heavily calcified tibial and pedal arteries are common in patients with diabetes and advanced age (>80 years)
• Calcium creates blooming artifact that can overestimate stenosis severity
• The noncontrast phase allows differentiation of calcification from contrast-enhanced lumen
• Dual-energy CTA can reduce these artifacts but is not universally available

Protocol Recommendations

The standard protocol should include 1:

1. Noncontrast phase: Scout images through abdomen, pelvis, and lower extremities
2. Arterial phase: Optimally timed contrast-enhanced acquisition
3. Coverage from abdomen through bilateral feet (runoff to pedal vessels)

Timing is critical:

• Images acquired too early = inadequate arterial enhancement
• Images acquired too late = venous contamination obscuring arterial anatomy
• Delayed calf images may be needed if slow flow from outflow disease

Common Pitfalls to Avoid

Do not order "with contrast only" because:

• You lose the ability to identify pre-existing calcification
• Baseline high-attenuation material may be mistaken for contrast extravasation
• Heavily calcified vessels (common in diabetic patients with gangrene) become uninterpretable

Patient-specific factors that increase need for noncontrast phase:

• Diabetes mellitus (your patient likely has this given toe gangrene)
• Age >80 years
• Dialysis-dependent renal failure
• Known heavily calcified vessels

Alternative Considerations

If contrast is absolutely contraindicated, consider 1:

• MRA with gadolinium (if eGFR permits): 90-100% sensitivity/specificity for >50% stenosis, superior for calcified tibial vessels
• Time-resolved MRA of tibial/pedal arteries reduces venous contamination
• Noncontrast MRA sequences at 3T provide high spatial resolution without gadolinium risk

However, for urgent revascularization planning in CLTI, CTA without and with contrast remains the most practical choice given rapid acquisition, widespread availability, and excellent accuracy (90-100% sensitivity/specificity for hemodynamically significant stenosis) 1.

Clinical Bottom Line

Order: "CTA abdomen and pelvis with bilateral lower extremity runoff WITHOUT AND WITH IV contrast"

The noncontrast phase is not optional—it provides essential diagnostic information that directly impacts revascularization planning and cannot be obtained from contrast-enhanced images alone. This is particularly critical in patients with gangrene who likely have extensive calcification and require precise anatomic assessment for limb salvage 1.