Definition:
- Having higher signal intensity, not attributable solely to T2 shine-through, than liver on diffusion-weighted (DW) images.
Usage
- Applies to observations that unequivocally:
- Are hyperintense relative to liver on DW images acquired with at least moderate diffusion weighting (e.g., b ≥ 400 s/mm2) AND
- If ADC map is generated, have low apparent diffusion coefficient (ADC) – i.e., similar to or lower than that of liver by visual estimation.
- Restricted diffusion is an ancillary feature favoring malignancy.
If unsure about feature:
Synonyms:
- Synonyms: Impeded diffusion, Diffusion restriction
- Preferred terms: Restricted diffusion
- Rationale for preferred terms: Most commonly used term in the literature
Background:
- Observations demonstrating restricted diffusion can aid in differentiating HCC from benign nodules.
- Studies have shown improved accuracy in HCC diagnosis when combined with contrast enhanced MRI.
- There is a general trend towards higher histologic grade with increasing restricted diffusion.
- Sensitivity and specificity for HCC diagnosis are not high enough to warrant inclusion as a major feature at this time given the present, most widely available technology.
- Not currently used as a feature in UNOS/OPTN
Potential pitfalls and challenges
- Relative lack of increased cellularity in HCCs (as opposed to metastases) may lead to decreased sensitivity on DW imaging.
- Intra-lesional fat can hamper the diagnosis of HCC on DW imaging.
- Cirrhosis may also negatively affect the diagnosis of HCC.
- Different MR vendors with variable DW sequence acquisitions (multi- or dual b-values) can potentially result in different acquisition times and ADC values.
- As DW imaging is signal dependent, it is highly sensitive to artifacts (susceptibility, motion artifacts, etc.)
- Artifacts can be greatest in the left lobe (cardiac and diaphragm motion, air in the stomach, upper and lower GI tract)
- Techniques to lessen these artifacts may include (but are not limited to): respiratory gating, prone imaging, oral contrast administration.
References:
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