Use the free Adrenal Washout Calculator on ToolVexa to work out absolute and relative washout from CT numbers. Enter the three HU values, press Calculate, and both percentages appear straight away.
How to Use
Enter the unenhanced value, the portal venous value and the delayed value, all in Hounsfield units, then press Calculate. The result box shows absolute washout and relative washout as percentages.
Formula in Plain Words
Absolute washout is portal minus delayed, divided by portal minus unenhanced, times 100. Relative washout is portal minus delayed, divided by portal, times 100. Both measure how much contrast has washed out by the delayed phase.
Worked Example
For unenhanced 10, portal venous 80 and delayed 30 HU, absolute washout is 80 minus 30, which is 50, divided by 80 minus 10, which is 70, times 100, which is about 71.4%. Relative washout is 50 divided by 80, times 100, which is 62.5%.
FAQs
Is this a diagnosis?
No. Washout values are one part of imaging assessment. Only a clinician or radiologist who sees the full scan and history can interpret them.
What is the difference between absolute and relative washout?
Absolute washout uses the unenhanced value as a baseline, while relative washout does not need it. Relative washout is used when no unenhanced scan is available.
What if portal and unenhanced values are equal?
Then absolute washout cannot be calculated, because its denominator would be zero. Check the numbers and use relative washout in that case.