Stability and sensitivity of water T₂ obtained with IDEAL‐CPMG in healthy and fat‐infiltrated skeletal muscle

Abstract

Quantifying muscle water T 2 (T 2‐water) independently of intramuscular fat content is essential in establishing T 2‐water as an outcome measure for imminent new therapy trials in neuromuscular diseases. IDEAL‐CPMG combines chemical shift fat–water separation with T 2 relaxometry to obtain such a measure. Here we evaluate the reproducibility and B 1 sensitivity of IDEAL‐CPMG T 2‐water and fat fraction (f.f.) values in healthy subjects, and demonstrate the potential of the method to quantify T 2‐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 T 2‐water and the fat signal amplitude muscle regions manually segmented.Overall mean calf‐level muscle T 2‐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 T 2‐water and 41.1% and 15.4% for f.f. Bland–Altman mean bias and ±95% coefficients of repeatability were for T 2‐water (0.15, −2.65, 2.95) ms and f.f. (−0.02, −1.99, 2.03)%. There was no relationship between T 2‐water (ρ = 0.16, p = 0.07) or f.f. (ρ = 0.03, p = 0.7761) and B 1 error or any correlation between T 2‐water and f.f. in the healthy subjects (ρ = 0.07, p = 0.40). In HypoPP there was a measurable relationship between T 2‐water and f.f. (ρ = 0.59, p < 0.001).IDEAL‐CPMG provides a feasible way to quantify T 2‐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 T 2‐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.

Decreased water T2 in fatty infiltrated skeletal muscles of patients with neuromuscular diseases

“…Previous imaging studies have attempted to suppress or separate the effect of fat in order to measure T 2w instead of global T 2 in the context of NMD imaging . Many of these studies have investigated the relationship between T 2w and PDFF, aiming at a result where T 2w is not related to PDFF in order to validate the performance of the proposed methods in suppressing the effect of fat on the T 2w measurement.…”

“…Several approaches have been proposed to suppress the fat signal or separate the water from the fat signal via the chemical shift difference between water and fat. Existing techniques include the acquisition of 2D multi‐echo spin‐echo (MESE) combined with Dixon water‐fat separation and the processing of 2D‐MESE data using a multi‐exponential T 2 decay model without and with the extended phase graph (EPG) formalism to additionally remove the effects of B1‐inhomogeneities. Water‐fat separation has also been combined with a 2D radial gradient and spin echo (GRASE) sequence to acquire T 2w maps in regions affected by motion …”

Towards defining muscular regions of interest from axial magnetic resonance imaging with anatomical cross-reference: part II - cervical spine musculature

“…A number of conventional MRI applications (T1, T2, proton-density, Gradient Echo) are available and have been used to qualitatively and quantitatively measure the water and fat species of healthy and diseased soft-aqueous skeletal muscle tissue [ 1 , 3 , 41 , 43 – 49 ]. Technological advancements have also produced alternatives that can be used to image muscle, such as dual acquisition methods, where frequency is selectively excited to produce a water image [ 50 ] and a standard image of fat and water.…”

Quantifying fat replacement of muscle by quantitative MRI in muscular dystrophy

“…IDEAL fat–water separation has also been combined with a CPMG spin-echo train in the so-called IDEAL-CPMG sequence [ 23 ]. Although IDEAL-CPMG is thus far not widely available, this approach enables independent measurements of the T2-relaxation times of the separated fat and water components in skeletal muscle, an important capability in conditions where water- and fat-based pathologies may exist simultaneously [ 24 , 25 ].…”

“…Finally, some studies on neuromuscular disease have been performed to investigate new MR methods in these patients, but contain valuable information about patient cohorts (Table 4 ). These include quality assurance and reproducibility studies [ 25 , 38 ], work to accelerate image acquisition [ 43 , 45 ], and correlations between MRI and MRS methods [ 38 , 46 ].…”