Liver Elastography Protocol: Probe Positioning, Number of Measurements, and Quality Criteria (IQR/M)
Probe Positioning and Region of Interest (ROI)
According to ACR/SRU (2024), when placing the region of interest (ROI), large blood vessels, bile ducts, and focal lesions should be avoided. The depth for ROI placement [clarification needed: specific depth value ≥10 mm is not provided in the fragments].
Number of Measurements
For point shear wave elastography (pSWE), 10 measurements from 10 independent images in the same location should be obtained using the median value (ACR/SRU, 2024). For 2D-SWE, at least five measurements may suffice if a quality assessment parameter is used.
Quality Criteria (IQR/M)
The interquartile range to median ratio (IQR/M) is used as a quality measure. According to ACR/SRU (2024), a data set is considered accurate if:
| Unit of Measurement | IQR/M Threshold |
|---|---|
| kPa | ≤30% |
| m/s | ≤15% |
According to EFSUMB (2019), a study is considered reliable when the IQR is less than 30% of the median. SWE values vary between different devices and are not interchangeable.
Factors Overestimating Stiffness
According to ACR/SRU (2024), liver fibrosis may be overestimated in the presence of transaminitis, biliary obstruction, acute hepatitis, infiltrative liver disease, or congestive hepatopathy at the time of the study.
Report Formatting
Recommended wording (ACR/SRU, 2024): the IQR/M value and its interpretation (adequate or low-quality data set) should be indicated, as well as the median liver stiffness with interpretation according to the "rule of 4" or "rule of 5" when using transient elastography.
Frequently asked questions
How many measurements are needed for pSWE?
10 measurements from 10 independent images in one location using the median value (ACR/SRU, 2024).
Are 5 measurements sufficient for 2D-SWE?
Yes, at least five measurements may suffice for 2D-SWE if a quality assessment parameter is used (ACR/SRU, 2024).
What is the acceptable IQR/M threshold?
IQR/M ≤30% for kPa and ≤15% for m/s indicates an accurate data set (ACR/SRU, 2024). According to EFSUMB (2019), IQR less than 30% of the median.
What can overestimate liver stiffness?
Transaminitis, biliary obstruction, acute hepatitis, infiltrative liver disease, and congestive hepatopathy (ACR/SRU, 2024).
Are SWE values interchangeable between devices?
No. SWE values vary between different devices and are not interchangeable (EFSUMB, 2019).