Dixon-based MRI for assessment of muscle-fat content in phantoms, healthy volunteers and patients with achillodynia: comparison to visual assessment of calf muscle quality
Fischer MA, Pfirrmann CW, Espinosa N, Raptis DA, Buck FM.
Eur Radiol. 2014 Mar 7.
• 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.
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.
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).
In vivo measurement of fat-fractions derived from 2-point Dixon gradient-echo MRI (FFDIXON) and MR-spectroscopy (FFMRS) in a 77-year-old male patient with achillodynia. FFDIXON (15 %) were calculated by placing an ROI in the gastrocnemius muscle on both the fat- (a) and water- (b) only image corresponding to the spectroscopic voxel (d). FFMRS (16 %) integrated the water (from 3.6 to 5.8 ppm) and lipid (methylene and methyl signals of α-CH2, (CH2)n-2, and CH3 from 0 to 3.6 ppm) signals of the spectral analysis (d). In comparison, T1-weighted images (c) were evaluated semi-quantitatively for fatty infiltration according to Goutallier (grade 2)
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.