Semi-LASER localized dynamic³¹P magnetic resonance spectroscopy in exercising muscle at ultra-high magnetic field

Abstract

Magnetic resonance spectroscopy (MRS) can benefit from increased signal-to-noise ratio (SNR) of high magnetic fields. In this work, the SNR gain of dynamic 31P MRS at 7 T was invested in temporal and spatial resolution. Using conventional slice selective excitation combined with localization by adiabatic selective refocusing (semi-LASER) with short echo time (TE = 23 ms), phosphocreatine quantification in a 38 mL voxel inside a single exercising muscle becomes possible from single acquisitions, with SNR = 42 ± 4 in resting human medial gastrocnemius.The method was used to quantify the phosphocreatine time course during 5 min of plantar flexion exercise and recovery with a temporal resolution of 6 s (the chosen repetition time for moderate T1 saturation). Quantification of inorganic phosphate and pH required accumulation of consecutively acquired spectra when (resting) Pi concentrations were low. The localization performance was excellent while keeping the chemical shift displacement acceptably small. The SNR and spectral line widths with and without localization were compared between 3 T and 7 T systems in phantoms and in vivo.The results demonstrate that increased sensitivity of ultra-high field can be used to dynamically acquire metabolic information from a clearly defined region in a single exercising muscle while reaching a temporal resolution previously available with MRS in non-localizing studies only. The method may improve the interpretation of dynamic muscle MRS data. Magn Reson Med, 2011. © 2011 Wiley-Liss, Inc.

Dynamic 31P–MRSI using spiral spectroscopic imaging can map mitochondrial capacity in muscles of the human calf during plantar flexion exercise at 7 T

“…Thus, several 31 P–MR localization methods attempting to improve spatial specificity have recently emerged. On one hand, this includes 31 P–MRS techniques, focused on single muscles 24, 25, 45. On the other hand, 31 P–MRI techniques aim to map oxidative metabolism over the whole FOV simultaneously 28, 29, 30, 31, 47…”

“…An interleaved technique providing information from two voxels within one dynamic experiment was suggested recently,23 but this still lacks the high spatial resolution of our MRSI approach. Furthermore, accurate spatial selection of SVS at 7 T requires relatively long T E , thus reducing sensitivity for important 31 P metabolites such as ATP 25. The proposed MRSI approach is FID based, and therefore does not require such long T E .…”

Localized Metabolic and T2 Changes Induced by Voluntary and Evoked Contractions

“…Considering the low values of voxel contamination (i.e., approximately 10%), it seems unlikely that the sampling of both activated and nonactivated muscles can have significantly affected the Pi splitting we found in the present study. It should be pointed out that the use of even more accurate localized 3IP-MRS techniques (e.g., semi-LASER) at higher magnetic field (i.e., 7 T) (28,29), which are associated with negligible voxel contamination (i.e., approximately 1%), small voxel size (24-57 cm3), and high temporal resolution (i.e., 6 s), would definitively provide relevant information about the physiological mechanisms accounting for the higher occur rence of two peaks of Pi associated with NMES. Overall, our 3IP CSI investigation suggests that NMES can activate fast muscle fibers even at low force levels (i.e., <30% MVC).…”

A form‐fitted three channel 31P, two channel 1H transceiver coil array for calf muscle studies at 7 T

“…To demonstrate in vivo applicability of the coil, localized 31 P MR spectra were acquired using a slice selective excitation combined with localization by adiabatic selective refocusing (semi‐LASER) sequence with a T R of 6 s. The two volumes of interest (VOI) were located in the Gm (VOI ≈ 42 cm 3 ) and Sol muscles (VOI ≈ 50 cm 3 ). The respective sequence parameters were T E = 24 ms, refocusing pulse duration = 3.4 ms, 5 averages in the Gm muscle; and T E = 29 ms, refocusing pulse duration = 4.6 ms, 5 averages in the Sol muscle.…”