Time-efficient relaxation measurements by ³¹P MR fingerprinting in human brain at 7T

Abstract

Purpose: The goal of the study is to develop 31P spectroscopic MR fingerprinting (MRF) at 7T to measure T1 and T2 relaxation times simultaneously and to compare time efficiency and test-retest reproducibility of MRF with conventional inversion recovery and multi-TE methods. Methods: A 31P MRF scheme was designed based on a balanced steady-state free precession type sequence. Dictionary was generated using the Bloch equations. B0 map was acquired experimentally and incorporated into the dictionary. Simulations were performed to evaluate estimation bias. 7 phantoms with different T1 and T2 relaxation times were prepared for MRF validation. 7 volunteers were scanned twice using both MRF and the conventional methods to evaluate the reproducibility. Results: In phantom measurements, T1 and T2 values between MRF and conventional methods demonstrated a good agreement with Pearson's correlation coefficients of 0.99 and 0.97, respectively. In in vivo experiments, estimated T1 by MRF were in good agreement with those measured by the inversion recovery and in literatures. On the other hand, estimated T2 values by MRF were shorter than those measured by the multi-TE method. 31P MRF method can reduce the acquisition time by 15 min providing less than 10% of mean CV for T1 estimations and less than 20% of mean CV for T2 estimations of metabolites. Conclusion: Our results shows the feasibility of simultaneous T1 and T2 measurements of 31P metabolites in human brain using the MRF technique at 7T. High reproducibility can be achieved especially for T1 measurement with 40% time reduction over conventional methods.

The future is 2D: spectral‐temporal fitting of dynamic MRS data provides exponential gains in precision over conventional approaches

“…Dynamic MRS refers to an experiment in which a series of 1D spectra are acquired sequentially, often while varying a sequence parameter or administering an external time‐dependent stimulus or manipulation. This encompasses a wide range of experimental designs, including observation of the dynamic incorporation of carbon‐13 and deuterium–labeled metabolites following the injection of a labeled compound 1 , 2 , 3 , 4 , 5 , 6 , 7 ; functional MRS designed to detect endogenous metabolic changes in glutamate, GABA, and lactate in response to an external visual, motor, or cognitive manipulation 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ; multiparametric MR spectroscopic experiments aimed at simultaneously and efficiently quantifying multiple spin parameters 21 , 22 , 23 , 24 , 25 , 26 ; diffusion MRS whereby the diffusion‐weighting gradients are varied to quantify the diffusion coefficient of different metabolites 27 , 28 , 29 , 30 , 31 , 32 ; and even simple relaxometry, where, for example, T 2 might be measured by measuring spectral data at different TEs (MTE). 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 …”

The Future is 2D: Spectral-Temporal Fitting of Dynamic Magnetic Resonance Spectroscopy Data Provides Exponential Gains in Precision Over Conventional Approaches

“…Dynamic Magnetic Resonance Spectroscopy refers to an experiment by which a series of one dimensional spectra are acquired sequentially, often while varying a sequence parameter or administering an external time-dependent stimulus or manipulation. This encompasses a wide range of experimental designs, including the observation of the dynamic incorporation of 13 C or 2 H-labeled metabolites following the injection of a labeled compound (1-7); Functional MRS, designed to detect endogenous metabolic changes in glutamate, GABA and lactate in response to an external visual, motor or cognitive manipulation (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20); Multiparametric magnetic resonance spectroscopic experiments, aimed at simultaneously and efficiently quantifying multiple spin parameters (21)(22)(23)(24)(25)(26); Diffusion MRS, whereby the diffusion-weighting gradients are varied to quantify the diffusion coefficient of different metabolites (27)(28)(29)(30)(31)(32); and even simple relaxometry, where, e.g., T 2 might be measured by measuring spectral data at different echo times (MTE) (33)(34)(35)(36)(37)(38)(39)(40)(41).…”