T2 Mapping of Muscle Activity using Ultrafast Imaging

Abstract

Measuring exercise-induced muscle activity is essential in sports medicine. Previous studies proposed measuring transverse relaxation time (T 2 ) using muscle functional magnetic resonance imaging (mfMRI) to map muscle activity. However, mfMRI uses a spin-echo (SE) sequence that requires several minutes for acquisition. We evaluated the feasibility of T 2 mapping of muscle activity using ultrafast imaging, called fast-acquired mfMRI (fastmfMRI), to reduce image acquisition time. The current method uses 2 pulse sequences, spin-echo echo-planar imaging (SE-EPI) and true fast imaging with steady precession (TrueFISP). SE-EPI images are used to calculate T 2 , and TrueFISP images are used to obtain morphological information. The functional image is produced by subtracting the image of muscle activity obtained using T 2 at rest from that produced after exercise. Final fast-mfMRI images are produced by fusing the functional images with the morphologic images. Ten subjects repeated ankle plantar ‰exion 200 times. In the fused images, the areas of activated muscle in the fast-mfMRI and SE-EPI images were identical. The geometric location of the fast-mfMRI did not diŠer between the morphologic and functional images. Morphological and functional information from fast-mfMRI can be applied to the human trunk, which requires limited scan duration. The diŠerence obtained by subtracting T 2 at rest from T 2 after exercise can be used as a functional image of muscle activity.

Interrelations of muscle functional MRI, diffusion‐weighted MRI and 31P‐MRS in exercised lower back muscles

“…We observed load‐induced changes of T 2 of approximately 10% confirming recent findings , changes in high‐energy phosphate metabolism (PCr depletion of about 30% and Pi accumulation of approximately 130%), again in line with previous work , and increases in vascular tissue perfusion of up to 3 percentage points.…”

“…To this end, we applied dynamic 31 P-CSI, diffusion-weighted and T 2 -weighted MRI in the lower back muscles of a group of 14 healthy volunteers. We observed load-induced changes of T 2 of approximately 10% confirming recent findings (2,9,(49)(50)(51), changes in highenergy phosphate metabolism (PCr depletion of about 30% and Pi accumulation of approximately 130%), again in line with previous work (3,42,(52)(53)(54)(55), and increases in vascular tissue perfusion of up to 3 percentage points.…”

“…Muscle functional MRI (mfMRI) is an established non-invasive technique to investigate muscle activation (1) and is frequently used to determine spatial patterns of muscular involvement in exercising humans. Recently, it has been applied extensively to leg (2)(3)(4)(5)(6)(7)(8)(9)(10) and lower back muscles (11)(12)(13)(14)(15)(16). The technique is based on the acquisition of T 2 -weighted MR images and subsequent quantitation of spin-spin transverse relaxation times (T 2 ) before and after muscular loading.…”

Fast measurement of the quadriceps femoris muscle transverse relaxation time at high magnetic field using segmented echo-planar imaging

“…While this approach is less sensitive to B 1 and B 0 errors, it provides a low temporal resolution and is more sensitive to diffusion phenomenon as compared to MSME. The use of echo‐planar readout (EPI) can increase the temporal resolution, thereby allowing measurements of dynamic signal changes and/or T 2 values in exercising muscles . Given the high sensitivity of EPI to B 0 inhomogeneities, the latter studies were limited to low magnetic field ( i.e.…”

“…The use of echo-planar readout (EPI) can increase the temporal resolution, thereby allowing measurements of dynamic signal changes and/or T 2 values in exercising muscles. [23][24][25][26] Given the high sensitivity of EPI to B 0 inhomogeneities, the latter studies were limited to low magnetic field (i.e. B 0 5 1.5T) and to explorations with a small volume coverage.…”