What this calculator does
Calculates the two commonly used CT washout formulas for an adrenal lesion.
Enter unenhanced, enhanced, and delayed attenuation in HU. The tool returns absolute and relative washout.
Clinical scope
Use the formulas to characterize an enhancing adrenal mass on a dedicated CT protocol that includes unenhanced, enhanced, and delayed attenuation measurements from comparable regions of interest.
Applicability and exclusions
- Do not calculate washout when the required phases are absent, measurements are not comparable, or a denominator is zero.
- Hemorrhage, calcification, necrosis, marked heterogeneity, and protocol timing can invalidate or limit threshold interpretation.
Method and calculation logic
Absolute washout uses all three phases; relative washout uses enhanced and delayed attenuation. Negative values indicate delayed enhancement rather than washout. Published thresholds depend on acquisition timing and population.
Absolute washout = (enhanced HU - delayed HU) / (enhanced HU - unenhanced HU) × 100Relative washout = (enhanced HU - delayed HU) / enhanced HU × 100Interpretation table
| 15-minute result | Traditional interpretation |
|---|---|
| Absolute washout ≥60% | Supports an adenoma in the appropriate protocol |
| Relative washout ≥40% | Supports an adenoma in the appropriate protocol |
| Below threshold or negative | Indeterminate; not diagnostic of malignancy |
Worked example
Case: Fictional example: unenhanced 30 HU, enhanced 100 HU, and 15-minute delayed 50 HU.
Calculation: Absolute: (100-50)/(100-30) × 100 = 71.4%. Relative: (100-50)/100 × 100 = 50%.
Interpretation: Both values exceed traditional 15-minute thresholds, but morphology, protocol quality, prior imaging, and the complete adrenal workup remain decisive.
How to use this calculator
- Complete the visible imaging and measurement fields. Required inputs are marked in the workbench.
- Review the calculated category, score, measurements, and any recommendation or warning.
- Copy the report-ready text only after checking the result against the complete examination and source guideline.
Calculator-specific questions
What happens if a denominator is zero?
That formula is undefined and must not be reported as a percentage.
Does sub-threshold washout diagnose malignancy?
No. It is indeterminate and must be interpreted with morphology, history, other imaging, and appropriate biochemical evaluation.
Are patient measurements sent to RadPhrases?
No. Calculator inputs and results are processed in the browser and are not submitted by this page.