G.P.123: NMR imaging of short T2-components in skeletal muscle tissue

Abstract

Excessive accumulation of fibrous connective tissue in the SKM extracellular matrix is one of the main long term consequences of the chronic inflammatory/necrotic/degenerative insults in muscle disorders. Quantitation and distribution of intramuscular connective tissue (IMCT) will constitute an important and new biomarker of disease progression and of response to treatments. Although UTE sequences were shown to be able to image and characterize connective tissue structures such as tendons and cartilage no parametric image of the short T2 component has ever been reported in the SKM. Our goal was to develop an ultra-short TE (UTE)-based NMR tool for imaging short T2 components (∼1ms) in the skeletal muscle (SKM) tissue, expected to reveal IMCT content. Fat-fraction- and T2 ∗ -maps were extracted from six 2D-UTE image series of the same axial slice acquired in the calf of 8 healthy volunteers at echo-times (TE) of 2.5,3,4,6,12.5 and 26.5ms. A short T2-fraction-map, Sf, was calculated by the equation Sf=(∣ S (t0)∣e t0/T2∗ −∣ S (t1)∣e t1/T2∗ − F ∣ S (t0)∣(f0−f1))/( S (t0) e t0/T2∗ ) S (ti) is the signal of the image acquired at TE=ti, t0/t1=0.2/2.5ms, F is the relative signal contribution from lipids and flΞ∣ ∑ k pke iwk·tl ∣; pk and wk are the relative fraction and frequency of each peak in the frequency spectrum of lipids. A significant relative fraction of signal from water protons with short T2 was systematically observed in all muscles. The highest values were found within fascia. No short T2 was observed in the subcutaneous fat and spongy bone, confirming that there were no contributions from lipids. The average short T2 fraction observed in SKM was 4.2(0.7)%. Very short T2 components were imaged for the first time in SKM tissue. Although the characterization of a short T2 component in SKM has been previously reported, suggesting that it might represent IMCT, healthy and diseased tissues must be further investigated in order to ensure the origin of this fast relaxing signal.