Motivation: Intramuscular fat is associated with muscle degeneration. Chemical shift-encoded MRI quantifies proton density fat fraction (PDFF), but multi-site, multi-vendor reproducibility for intramuscular assessment is scarcely reported. Goal(s): To evaluate the reproducibility of a vendor-independent thigh muscle PDFF quantification approach using multi-site, multi-vendor data and then assess PDFF in patients 10 years post-anterior cruciate ligament reconstruction (ACLR). Approach: Phantoms, traveling controls, and ACLR patients were scanned using five scanners (three sites, two vendors). A correction was developed to address image scaling variations. Results: Average absolute PDFF standard deviation was below 1% after correction. The ACLR patient cohort had elevated PDFF in operated leg hamstrings. Impact: Harmonized acquisition and vendor-independent processing with the proposed image scaling correction can provide reproducible thigh intramuscular proton density fat fraction across sites and vendors. This approach may characterize within-patient muscle changes, such as bilateral differences or potentially longitudinal assessment.

Reproducible Intramuscular Fat Quantification using Vendor-Independent Processing in a Multi-Site, Multi-Vendor Setting