New Insights on Human Skeletal Muscle Tissue Compartments Revealed by In Vivo T2 NMR Relaxometry

Abstract

The spin-spin (T2) relaxation of (1)H-NMR signals in human skeletal muscle has been previously hypothesized to reveal information about myowater compartmentation. Although experimental support has been provided, no consensus has yet emerged concerning the attribution of specific anatomical compartments to the observed T2 components. Potential application of a noninvasive tool that might offer such information urges the quest for a definitive answer to this question. The purpose of this work was to obtain new information that might help elucidate the mechanism of T2 distribution in muscle. To do so, in vivo T2 relaxation data was acquired from the soleus of eight healthy volunteers using a localized Carr-Purcell-Meiboom-Gill technique. Each acquisition contained 1000 echoes with an interecho spacing of 1 ms. Data were acquired from each subject under different vascular filling preparations expected to change exclusively the extracellular water fraction. Two exponential components were systematically observed: an intermediate component (T2 ~ 32 ms) and a long component (100 < T2 < 210 ms). The relative fraction and T2 value characterizing the long component systematically increased after progressive augmentation of extracellular water volume. Characteristic relaxation behavior for each vascular filling condition was analyzed with a two-site exchange model and a three-site two-exchange model. We show that a two-site exchange model can only predict the observations for small exchange rates, much more representative of transendothelial than transcytolemmal exchange regimes. The three-site two-exchange model representing the intracellular, interstitial, and vascular spaces was capable of precisely predicting the observations for realistic transcytolemmal and transendothelial exchange rates. The estimated intrinsic relative fractions of each of these compartments corroborate with estimations from previous works and strongly suggest that the T2 relaxation from water within the intracellular and interstitial spaces is described by the intermediate component, whereas the long component represents water within the vascular space.

Acute changes in extracellular volume fraction in skeletal muscle monitored by23Na NMR spectroscopy

“…Using a localized proton ISIS‐CPMG sequence and a three‐sites two‐exchange model, authors provided quantitative information about histological tissues compartmentation and water exchange rates (Araujo et al. 2014). However, such a proton approach can be hampered by the signal originating from lipids.…”

“…In addition, ${\mathrm{T}}_2^{\ast }$ spectra were obtained from the temporal decay of the FID by the deconvolution method presented in the study by Araujo et al. (2014). This allowed to determine a short ${\mathrm{T}}_2^{\ast }$ fraction as well as short and long ${\mathrm{T}}_2^{\ast }$ values for Na + .…”

In Vivo Measurements of T2 Relaxation Time of Mouse Lungs during Inspiration and Expiration

“…Tissue T2 generally increases slightly at higher field strengths. Assuming that the magnetic field dependence of degassed lung T2 is similar to that of muscle and not different for rat and mouse [28,29], then the intrinsic T2 is 25 ms for mouse lung at 4.7T. Other input data are echo-time 3.5 ms and the diffusion coefficient D = 1.26 10 −8 m 2 /s representing the apparent diffusion coefficient in highly vascularized tissue [30].…”

Application of texture analysis to muscle MRI: 1-What kind of information should be expected from texture analysis?

“…Furthermore, the speed of exchange between bound and free water determines if there is a mean relaxation time or two or more separately detectable relaxation times: in healthy muscle, it has been established that two spin-spin relaxation times can be separately identified expressing a slow exchange between different water phases [28,29]. Table 2 T1 and T2 frequency dependence of human skeletal muscle in-vivo measured on 13 MRI units after correction resulting from a preliminary quality assessment using Eurospin TO5 test object [26] NMR frequency 4.…”