Rapid and accurate dictionary-based T 2 mapping from multi-echo turbo spin echo data at 7 Tesla

Julian Emmerich, Sebastian Flassbeck, Simon Schmidt, Peter Bachert, Mark E. Ladd, Sina Straub

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Background: Using lower refocusing flip angles in multi-echo turbo spin echo (ME-TSE) sequences at ultra-high magnetic field leads to non-monoexponential signal decay and overestimation of T 2 values due to stimulated and secondary echoes. Purpose: To investigate the feasibility of a fast and accurate reconstruction of quantitative T 2 values using an ME-TSE sequence with reduced refocusing flip angles at 7 Tesla, a dictionary-based reconstruction method was developed and is presented in this work. Study Type: Prospective. Subjects: Phantom measurements with relaxation phantom, four healthy volunteers. Field Strength/Sequence: 7 Tesla MRI, multi-echo turbo spin echo (ME-TSE), spin echo (SE), and B 1 mapping. Assessment: Based on Bloch simulations and the extended phase graph model, signal decay curves were calculated to account for nonrectangular slice profile, B 1 inhomogeneity, and reduced refocusing flip angles and stored in a dictionary. Data obtained with an ME-TSE sequence at 7 Tesla were matched to this dictionary to obtain T 2 values. To compare the proposed method to reference T 2 values, a spin echo sequence with different echo times was used. Statistical Tests: Welch's t-test was used to compare T 2 values in phantom measurements. Results: T 2 values obtained with the proposed ME-TSE method coincided with the T 2 values from the spin echo experiment in phantom measurements (P = 0.89 for 120° flip angle, P = 0.75 for 180° flip angle). Only for very low B 1 transmit fields, a slight overestimation of T 2 values was observed. In vivo measurements showed lower T 2 values in gray matter (55 ± 2 millisecond) and white matter (39 ± 5 millisecond) compared with literature values of 3 Tesla data. Data Conclusions: The proposed dictionary-based ME-TSE approach provided accurate T 2 values in short measurement time at 7 Tesla with low specific absorption rate burden due to the reduction of refocusing flip angles. Therefore, it can provide new opportunities in clinical high-field MRI to further improve radiographic diagnosis by using quantitative imaging. Level of Evidence: 1. Technical Efficacy: Stage 1. J. Magn. Reson. Imaging 2019;49:1253–1262.

Original languageEnglish (US)
Pages (from-to)1253-1262
Number of pages10
JournalJournal of Magnetic Resonance Imaging
Volume49
Issue number5
DOIs
StatePublished - May 2019
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2018 International Society for Magnetic Resonance in Medicine

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