Format

Send to

Choose Destination
Magn Reson Med. 2018 May;79(5):2607-2619. doi: 10.1002/mrm.26907. Epub 2017 Sep 23.

Whole brain inhomogeneous magnetization transfer (ihMT) imaging: Sensitivity enhancement within a steady-state gradient echo sequence.

Author information

1
Aix Marseille Univ, CNRS, CRMBM UMR 7339, Marseille, France.
2
Radiology, Division of MR Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA.
3
Aix Marseille Univ, APHM, Hôpital de La Timone, Pôle d'Imagerie Médicale, CEMEREM, Marseille, France.
4
Aix Marseille Univ, APHM, Hôpital de La Timone, Pôle de Neurosciences Cliniques, Service de Neurologie, Marseille, France.

Abstract

PURPOSE:

To implement, characterize, and optimize an interleaved inhomogeneous magnetization transfer (ihMT) gradient echo sequence allowing for whole-brain imaging within a clinically compatible scan time.

THEORY AND METHODS:

A general framework for ihMT modelling was developed based on the Provotorov theory of radiofrequency saturation, which accounts for the dipolar order underpinning the ihMT effect. Experimental studies and numerical simulations were performed to characterize and optimize the ihMT-gradient echo dependency with sequence timings, saturation power, and offset frequency. The protocol was optimized in terms of maximum signal intensity and the reproducibility assessed for a nominal resolution of 1.5 mm isotropic. All experiments were performed on healthy volunteers at 1.5T.

RESULTS:

An important mechanism driving signal optimization and leading to strong ihMT signal enhancement that relies on the dynamics of radiofrequency energy deposition has been identified. By taking advantage of the delay allowed for readout between ihMT pulse bursts, it was possible to boost the ihMT signal by almost 2-fold compared to previous implementation. Reproducibility of the optimal protocol was very good, with an intra-individual error < 2%.

CONCLUSION:

The proposed sensitivity-boosted and time-efficient steady-state ihMT-gradient echo sequence, implemented and optimized at 1.5T, allowed robust high-resolution 3D ihMT imaging of the whole brain within a clinically compatible scan time. Magn Reson Med 79:2607-2619, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

KEYWORDS:

Provotorov theory of radiofrequency saturation; dipolar order; dual frequency RF saturation; ihMT; inhomogeneous magnetization transfer; magnetization transfer model; myelin

PMID:
28940355
DOI:
10.1002/mrm.26907

Supplemental Content

Full text links

Icon for Wiley
Loading ...
Support Center