What is the name of the CT abdomen protocol used to assess contrast washout effect?

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Adrenal Protocol CT

The CT abdomen protocol used to assess contrast washout effect is called "Adrenal Protocol CT" (also known as "Dedicated Adrenal Protocol CT"). 1

Protocol Components

This specialized imaging protocol consists of three distinct phases 1:

  1. Noncontrast phase - baseline imaging without IV contrast
  2. Contrast-enhanced venous phase - obtained at 60-70 seconds post-intravenous contrast administration
  3. Delayed phase - typically acquired after 15 minutes

Clinical Application

The washout analysis from this protocol allows calculation of relative and absolute washout percentages, which are critical for distinguishing benign adenomas from malignant adrenal lesions 1:

  • Relative washout >40% suggests adenoma
  • Absolute washout >60% suggests adenoma

The physiologic basis is that adenomas demonstrate marked early enhancement with rapid contrast loss (washout), while malignant lesions show slower washout due to abnormal vasculature 1.

Important Caveats

Recent evidence suggests adrenal protocol CT performance may be less accurate than previously reported 1. Specific pitfalls include:

  • Pheochromocytomas (up to 35% of cases) can mimic adenoma washout characteristics 1
  • Certain metastases (renal cell carcinoma, hepatocellular carcinoma) may also show similar washout patterns 1
  • Heterogeneous lesions are poorly characterized by this protocol 1

Routine single-phase abdominal CT protocols are NOT recommended for characterization of known adrenal lesions - the dedicated three-phase protocol is required 1.

Recent endocrine guidelines now generally recommend MRI over contrast-enhanced CT when additional imaging beyond noncontrast CT is needed, given these limitations 1.

References

1
Guideline

imaging of adrenal masses.

Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologist, 2025

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