MP2RAGEME: T1 , T2* , and QSM mapping in one sequence at 7 tesla.

Matthan W A Caan,Gilles De Hollander,Wietske Van Der Zwaag,Serge O Dumoulin,Pierre‐Louis Bazin,José P Marques

doi:10.1002/hbm.24490

Abstract

Quantitative magnetic resonance imaging generates images of meaningful physical or chemical variables measured in physical units that allow quantitative comparisons between tissue regions and among subjects scanned at the same or different sites. Here, we show that we can acquire quantitative T1, T2 *, and quantitative susceptibility mapping (QSM) information in a single acquisition, using a multi‐echo (ME) extension of the second gradient‐echo image of the MP2RAGE sequence. This combination is called MP2RAGE ME, or MP2RAGEME. The simultaneous acquisition results in large time savings, perfectly coregistered data, and minimal image quality differences compared to separately acquired data. Following a correction for residual transmit B1 +‐sensitivity, quantitative T1, T2 *, and QSM values were in excellent agreement with those obtained from separately acquired, also B1 +‐corrected, MP2RAGE data and ME gradient echo data. The quantitative values from reference regions of interests were also in very good correspondence with literature values. From the MP2RAGEME data, we further derived a multiparametric cortical parcellation, as well as a combined arterial and venous map. In sum, our MP2RAGEME sequence has the benefit in large time savings, perfectly coregistered data and minor image quality differences.

Highlights

Quantitative magnetic resonance imaging (MRI) is becoming a popular tool in neuroimaging, in a large part due to the increasing availability of 7 T MR scanners, where the increased signal-to-noise ratio (SNR) accommodates more complex and generally longer acquisitions
With quantitative MRI, we depart from volumetric representations of the underlying tissues, and obtain a directly comparable measure of more tissuespecific MRI quantities that may not be captured by studying volume alone (Draganski et al, 2011)
For this 0.64 mm resolution protocol, MP2RAGEME offers a 40% time saving over separate scans (16 instead of 26 min) as the multiecho gradient echo (ME-GRE) is acquired in the empty time of the TRMP2RAGE

Summary

Introduction

Quantitative magnetic resonance imaging (MRI) is becoming a popular tool in neuroimaging, in a large part due to the increasing availability of 7 T MR scanners, where the increased signal-to-noise ratio (SNR) accommodates more complex and generally longer acquisitions (van der Zwaag, Schäfer, Marques, Turner, & Trampel, 2016). With quantitative MRI, we depart from volumetric representations of the underlying tissues, and obtain a directly comparable measure of more tissuespecific MRI quantities that may not be captured by studying volume alone (Draganski et al, 2011). In white matter (WM), the longitudinal relaxation rate R1 = 1/T1 has been shown to be linearly related to myelin concentration (Stüber et al, 2014) and axon diameter (Harkins et al, 2016) In gray matter, both R2* and quantitative susceptibility mapping (QSM) are linearly related to iron concentration (Deistung et al, 2013a). Cortical gray matter shows a spatial distribution of both myelin and iron, apparent in T1- and T2*-maps (Waehnert et al, 2016)

Methods

Results

Conclusion