OBJECTIVES: To quantify the muscle fat-content (MFC) in phantoms, volunteers and patients with achillodynia using two-point Dixon-based magnetic resonance imaging (2pt-MRIDIXON) in comparison to MR spectroscopy (MRS) and visual assessment of MFC.
METHODS: Two-point Dixon-based MRI was used to measure the MFC of 15 phantoms containing 0-100 % fat-content and calf muscles in 30 patients (13 women; 57 ± 15 years) with achillodynia and in 20 volunteers (10 women; 30 ± 14 years) at 1.5 T. The accuracy of 2pt-MRIDIXON in quantification of MFC was assessed in vitro using phantoms and in vivo using MRS as the standard of reference. Fat-fractions derived from 2pt-MRIDIXON (FFDIXON) and MRS (FFMRS) were related to visual assessment of MFC (Goutallier grades 0-4) and Achilles-tendon quality (grade 0-4).
RESULTS: Excellent linear correlation was demonstrated for FFDIXON with phantoms and with FFMRS in patients (p c = 0.997/0.995; p < 0.001). FFDIXON of the gastrocnemius muscle was significantly higher (p = 0.002) in patients (7.0 % ± 4.7 %) compared with volunteers (3.6 % ± 0.7 %), whereas visual-grading showed no difference between both groups (p > 0.05). FFMRS and FFDIXON were significantly higher in subjects with (>grade 1) structural damage of the Achilles-tendon (p = 0.01).
CONCLUSIONS: Two-point Dixon-based MRI allows for accurate quantification of MFC, outperforming visual assessment of calf muscle fat. Structural damage of the Achilles tendon is associated with a significantly higher MFC.
KEY POINTS: Two-point Dixon-based MRI allows accurate quantification of muscular fat content (MFC). Quantitative analysis outperforms visual analysis in the detection of elevated MFC. Achillodynia results in an increased MFC of the gastrocnemius muscles. Structural damage of the Achilles tendon further increases the MFC.