Liver steatosis calculator (CT) - Radiology calculators

Note: correct placement of the region of interest (ROI) and appropriate size is crucial to get reliable results. Avoid including vessels or bile ducts in the ROI, and do not place it immediately next to the liver/splenic margin in order to avoid spurious HU values due to partial volume effects.

Notes

On non-contrast CT moderate to severe steatosis can be confirmed by:
- Liver attenuation at least 10 HU lower than that of the spleen
  - ^{Hamer OW, Aguirre DA, Casola G, Lavine JE, Woenckhaus M, Sirlin CB. Fatty liver: imaging patterns and pitfalls. Radiographics. 2006 Nov-Dec;26(6):1637-53. doi: 10.1148/rg.266065004. PMID: 17102041.}
- Absolute liver attenuation lower than 40 HU
  - ^{Kodama Y, Ng CS, Wu TT, Ayers GD, Curley SA, Abdalla EK, Vauthey JN, Charnsangavej C. Comparison of CT methods for determining the fat content of the liver. AJR Am J Roentgenol. 2007 May;188(5):1307-12. doi: 10.2214/AJR.06.0992. PMID: 17449775.}
On contrast-enhanced CT consensus is less established, and various cutoffs for relative liver hypoattenuation have been reported. This calculator uses a relatively agressive threshold of relative liver hypoattenuation greater than 20 HU. This cutoff has been shown previously to be a reasonable trade-off between sensitivity (86%) and specificity (87%).
- ^{Jacobs JE, Birnbaum BA, Shapiro MA, Langlotz CP, Slosman F, Rubesin SE, Horii SC. Diagnostic criteria for fatty infiltration of the liver on contrast-enhanced helical CT. AJR Am J Roentgenol. 1998 Sep;171(3):659-64. doi: 10.2214/ajr.171.3.9725292. PMID: 9725292.}
ROI positioning is crucial. Ideally it should be sufficiently large, not involving bile ducts or larger vessels, and positioned not immediately next to the liver surface to avoid partial volume averaging. Also inhomogeneous areas, transient hepatic attenuation differences, areas of focal fatty changes should be avoided.
For ROI placement dedicated liver windows (e.g. width, 150 HU; level, 88 HU) may be used. Also it is prudent to use the average of multiple measurements.
If there is no non-enhanced phase the portal venous or late phase are better second options than the arterial phase, as in the arterial phase exam perfusion inhomogenities can make the above calculations unreliable.

For further informations and if unfamiliar with quantitative CT evaluation of liver steatosis please visit the relevant radiopaedia.org article.

Last updated: 2021-09-06

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