Inversion recovery zero echo time (IR-ZTE) imaging for direct myelin detection in human brain: a feasibility study

Abstract

Background: Myelin alteration is closely associated with neurological diseases such as multiple sclerosis (MS). Unfortunately, due to myelin's extremely short T2* (~0.3 ms or shorter at 3T), it cannot be directly imaged with conventional MR imaging techniques. Recently, ultrashort echo time (UTE) imaging-based methods have been proposed for direct imaging of myelin. In this study, we explore the feasibility and efficacy of inversion recovery prepared zero echo time (IR-ZTE) imaging for direct volumetric imaging of myelin in white matter of the brain in vivo.Methods: In the proposed method, an adiabatic IR preparation pulse is used to suppress long T2 white matter signal, followed by dual echo ZTE imaging where the remaining long T2 components, including gray matter, are suppressed by dual echo subtraction. In the implementation of ZTE, the sampling strategy introduced in Water-and Fat-Suppressed Proton Projection MRI (WASPI) was incorporated to acquire the k-space data missing due to the radiofrequency (RF) transmit/receiver switching time. The IR-ZTE sequence was implemented on a 3T clinical MR system and evaluated using a myelin phantom composed of six different myelin concentrations (0% to 20%), a cadaveric human brain, four healthy volunteers, and seven MS patients.Results: In the myelin phantom experiment, the ZTE signal intensity showed high linearity to the myelin concentrations (R 2 =0.98). In the ex vivo and in vivo experiments, the IR-ZTE sequence provided high contrast volumetric imaging of myelin in human brains. The IR-ZTE sequence was able to detect demyelinated foci lesions in all MS patients.Conclusions: Adiabatic IR prepared dual echo ZTE imaging allows for direct, volumetric imaging of myelin in white matter of the brain in vivo.

Myelin Imaging Using Dual-echo 3D Ultra-short Echo Time MRI with Rosette k-Space Pattern

“…Overall, the results of uT 2 components quantification, acquired by the dual-echo 3D rosette sequence, agree with previous publications with 3D radial or 3D cones trajectories (7,42). Firstly, little or no contrast at short TEs (i.e., below 100 ‫)ݏߤ‬ was achieved without IR suppression.…”

“…Overall, the reconstructed images with different TEs and the uT 2 fraction maps agree with previous publications (7,38). The contrast between WM and GM was higher at longer TEs, and the uT 2 components were mainly distributed in WM voxels.…”

“…The contrast between WM and GM was higher at longer TEs, and the uT 2 components were mainly distributed in WM voxels. Previous publications were using the IR suppression (7,38) approach, which caused WM signal loss creating contrast between WM and GM at short TEs. In this study, little or no contrast at short TEs was achieved without IR suppression.…”

“…The contrast between WM and GM was higher at longer TEs, and the uT 2 components were mainly distributed in WM voxels. Previous publications were using the IR suppression (7,38) approach, which caused WM signal (which was not certified by peer review) is the author/funder. All rights reserved.…”

Feasibility of an Inversion Recovery-Prepared Fat-Saturated Zero Echo Time Sequence for High Contrast Imaging of the Osteochondral Junction

“…Unfortunately, ZTE encoding inevitably leaves a hole of missing data in the encoded central k-space due to the RF coil deadtime (a blind time during RF transmit/receive mode switching). In this study, the hole was filled with additional encoding with a reduced readout gradient amplitude, similar to the strategy used in Water-And Fat-Suppressed Proton Projection MRI (WASPI) (38,39), as indicated with blue dots in Figure 1D. A WASPI factor, defined as the ratio between the gradient amplitude of ZTE and WASPI encoding, was introduced to control the size of the central k-space data to be acquired in the second acquisition.…”