How this calculator works
Use region-of-interest attenuation from the same lesion and a dedicated CT protocol. Absolute washout requires unenhanced, enhanced and delayed values; relative washout omits the unenhanced scan. Delay timing changes interpretation. This tool reports arithmetic and does not declare a lesion benign or exclude malignancy or phaeochromocytoma. The result is an estimate for information only and is not medical advice.
Formula
Absolute washout = (enhanced - delayed) / (enhanced - unenhanced). Relative washout = (enhanced - delayed) / enhanced. Multiply each fraction by 100 for percent. Rearrange the selected equation to recover a missing attenuation.
Worked example
Unenhanced 20 HU, enhanced 100 HU and delayed 40 HU give 60/80 = 75% absolute and 60/100 = 60% relative washout. With 10, 90 and 50 HU, the results are 50% and 44.4444%.
Advertisement
Frequently asked questions
Can I calculate without an unenhanced scan?
Choose relative washout. Absolute washout cannot be obtained without that baseline value.
Can washout be negative or above 100%?
Yes mathematically. Continued enhancement or delayed attenuation below the baseline can produce those values; check the images and protocol.
Does reaching a published cutoff prove an adenoma?
No. There is overlap with other lesions, and imaging findings must be considered with hormonal testing and clinical context.