Stability and sensitivity of water T2obtained with IDEAL-CPMG in healthy and fat-infiltrated skeletal muscle.
Quantifying muscle water T2(T2-water) independently of intramuscular fat content is essential in establishing T2-water as an outcome measure for imminent new therapy trials in neuromuscular diseases. IDEAL-CPMG combines chemical shift fat-water separation with T2relaxometry to obtain such a measure. Here we evaluate the reproducibility and B1sensitivity of IDEAL-CPMG T2-water and fat fraction (f.f.) values in healthy subjects, and demonstrate the potential of the method to quantify T2-water variation in diseased muscle displaying varying degrees of fatty infiltration. The calf muscles of 11 healthy individuals (40.5 ± 10.2 years) were scanned twice at 3 T with an inter-scan interval of 4 weeks using IDEAL-CPMG, and 12 patients with hypokalemic periodic paralysis (HypoPP) (42.3 ± 11.5 years) were also imaged. An exponential was fitted to the signal decay of the separated water and fat components to determine T2-water and the fat signal amplitude muscle regions manually segmented. Overall mean calf-level muscle T2-water in healthy subjects was 31.2 ± 2.0 ms, without significant inter-muscle differences (p = 0.37). Inter-subject and inter-scan coefficients of variation were 5.7% and 3.2% respectively for T2-water and 41.1% and 15.4% for f.f. Bland-Altman mean bias and ±95% coefficients of repeatability were for T2-water (0.15, -2.65, 2.95) ms and f.f. (-0.02, -1.99, 2.03)%. There was no relationship between T2-water (ρ = 0.16, p = 0.07) or f.f. (ρ = 0.03, p = 0.7761) and B1error or any correlation between T2-water and f.f. in the healthy subjects (ρ = 0.07, p = 0.40). In HypoPP there was a measurable relationship between T2-water and f.f. (ρ = 0.59, p < 0.001). IDEAL-CPMG provides a feasible way to quantify T2-water in muscle that is reproducible and sensitive to meaningful physiological changes without post hoc modeling of the fat contribution. In patients, IDEAL-CPMG measured elevations in T2-water and f.f. while showing a weak relationship between these parameters, thus showing promise as a practical means of quantifying muscle water in patient populations.
UCL Institute of Neurology, MRC Centre for Neuromuscular Diseases, London, WC1N 3BG, UK.|UCL Institute of Neurology, Neuroradiological Academic Unit, London, WC1N 3BG, UK.
Christopher D J
CD
Sinclair
UCL Institute of Neurology, MRC Centre for Neuromuscular Diseases, London, WC1N 3BG, UK.
Jasper M
JM
Morrow
GlaxoSmithKline, Uxbridge, UK.
Robert L
RL
Janiczek
UCL Institute of Neurology, MRC Centre for Neuromuscular Diseases, London, WC1N 3BG, UK.
Matthew R B
MR
Evans
UCL Institute of Neurology, Neuroradiological Academic Unit, London, WC1N 3BG, UK.
Elham
E
Rawah
UCL Institute of Neurology, Neuroradiological Academic Unit, London, WC1N 3BG, UK.
Sachit
S
Shah
UCL Institute of Neurology, MRC Centre for Neuromuscular Diseases, London, WC1N 3BG, UK.
Michael G
MG
Hanna
UCL Institute of Neurology, MRC Centre for Neuromuscular Diseases, London, WC1N 3BG, UK.
Mary M
MM
Reilly
UCL Institute of Neurology, MRC Centre for Neuromuscular Diseases, London, WC1N 3BG, UK.|UCL Institute of Neurology, Neuroradiological Academic Unit, London, WC1N 3BG, UK.
Tarek A
TA
Yousry
UCL Institute of Neurology, MRC Centre for Neuromuscular Diseases, London, WC1N 3BG, UK.|UCL Institute of Neurology, Neuroradiological Academic Unit, London, WC1N 3BG, UK.
John S
JS
Thornton
D000273:Adipose Tissue / Q000000981:diagnostic imaging*; D000328:Adult; D000465:Algorithms; D001834:Body Water / Q000000981:diagnostic imaging*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018908:Muscle Weakness / Q000000981:diagnostic imaging*; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted
HypoPP; IDEAL-CPMG; Magnetic resonance imaging; Muscle; Musculoskeletal; Neuromuscular diseases; Relaxometry; Water fat imaging