PCr/ATP ratio mapping of the human head by simultaneously imaging of multiple spectral peaks with interleaved excitations and flexible twisted projection imaging readout trajectories at 9.4 T

Abstract

Quantitative 31P MR imaging of the whole human brain is often time-consuming even at low spatial resolution due to the low concentrations, long T1 relaxation times and low detection sensitivity of phosphorus metabolites. We report herein the results of combining the increased detection sensitivity of an ultra-high field 9.4 Tesla scanner designed for human imaging with a new pulse sequence termed Simultaneously Imaging of Multiple Spectral Peaks with InterLeaved Excitations and flexible Twisted Projection Imaging Readout Trajectories (SIMPLE-TPI) to rapidly sample multiple resonances in the 31P spectrum. The PCr and γ-ATP images, obtained simultaneously from the entire human head, are demonstrated at 1.5 cm isotropic nominal resolution in a total acquisition time of 33 minutes. The PCr/γ-ATP ratio calculated for brain parenchyma (1 to 2) and the superficial temporalis muscle (3 to 5) are in agreement with literature values.

Electrodynamics and radiofrequency antenna concepts for human magnetic resonance at 23.5 T (1 GHz) and beyond

“…Some of the benefits are already clear: we have already seen progress in remotely probing local concentrations of fluorine, sodium, potassium and chlorine in human tissues (9)(10)(11)(12)(13)(14), in assessing bioenergetic conditions (15)(16)(17) and oxygen consumption (18) in vivo along with the advances in 9.4 T human MR (15,(19)(20)(21)(22)(23)(24). Pioneering reports on MR physics, radiofrequency (RF) power deposition considerations and novel RF antenna designs (25,26) spurred the installation of a 10.5 T whole-body MR system at the Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, USA (27).…”

Toward 20 T magnetic resonance for human brain studies: opportunities for discovery and neuroscience rationale

“…We have collected 31 P spectra at 9.4 and 16.4 T from cat brains that prove we can measure relative concentrations of all the important phosphorylated species at ultrahigh fields. Human brain studies at 9.4 T have shown the ability to map the distribution of the major components of ATP kinetics [69]. The frequency of 31 P at 11–21 T (190–360 MHz) is on par with 1 H frequencies at 4.5–8.5 T.…”

Iterative reconstruction of radially-sampled 31 P bSSFP data using prior information from 1 H MRI

“…Also the feasibility of direct 31 P mapping has been demonstrated although the spatial resolution was limited. To overcome the low in vivo SNR per unit time, several approaches were proposed including turbo spin echo (TSE) [15][16][17][18], fast low angle shot (FLASH) [19,20], or balanced steady-state free precession (bSSFP) [21,22] sequences.…”