Short Echo-Time fMRI using Magnetization Transfer Contrast

Poster No:

2005 

Submission Type:

Abstract Submission 

Authors:

Jenni Schulz1, Zahra Fazal1, Riccardo Metere1, José Marques1, David G. Norris1,2

Institutions:

1Donders Institute, Radboud University, Nijmegen, Netherlands, 2Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany

First Author:

Jenni Schulz  
Donders Institute, Radboud University
Nijmegen, Netherlands

Co-Author(s):

Zahra Fazal  
Donders Institute, Radboud University
Nijmegen, Netherlands
Riccardo Metere  
Donders Institute, Radboud University
Nijmegen, Netherlands
José Marques  
Donders Institute, Radboud University
Nijmegen, Netherlands
David G. Norris  
Donders Institute, Radboud University|Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen
Nijmegen, Netherlands|Essen, Germany

Introduction:

Magnetization Transfer (MT) [Wolff1989] is an MRI technique generating contrast in the presence of molecules with bound protons. While brain tissue is known to show an MT contrast (MTC), blood does not display such behavior [Balaban1991]. Hence, an MT-weighted signal may be sensitive to cerebral blood volume (CBV) changes, with a maximum at echo-time TE=0. By contrast, most fMRI studies rely on Blood-Oxygenated Level Dependent (BOLD) experiments, whose optimal sensitivity is obtained at TE~T2* (30ms at 3T). Changes in CBV during brain activation can be expected to occur mainly in the arterioles and capillaries [Kim2006], and may therefore be expected to have a better spatial localization than BOLD, which is dominated by the downstream vasculature. Previous investigations into enhancing BOLD with MT have used off-resonance MT combined with long TR [Zhou2005] or inversion recovery [Song1997] which preclude efficient fMRI studies. Here, it is shown that an acquisition using on-resonance MT preparation can be sensitive to the hemodynamics induced by brain activations at short TE, which maximizes the sensitivity to CBV and reduces BOLD contamination, without increasing acquisition time.

Methods:

To suppress the tissue signal, a net 0° on-resonance MT preparation block was added, before every excitation, to a standard single-shot 2D-EPI. Such a block combines 2 non-selective binomial pulses of opposite phases ±1/∓2/±1 (6ms), followed by a pseudo-random gradient spoiler scheme (3ms) in all directions.
The MT-EPI was evaluated with MT-ON/-OFF using the following parameters: 38 slices, res 3mm iso, 80x80 matrix, TE/TR/TA 7.5ms/2000ms/10min, Partial-Fourier 6/8, GRAPPA 3, Flip-Angle 50°, MT-Flip-Angle ±77°/∓154°/±77°, BW=2718 Hz/px, FatSat on. MT-FA was optimised to maximise signal difference between CSF and tissue. A standard BOLD EPI was acquired with identical parameters at TE=30ms and a MPRAGE at 1mm iso resolution, TE/TR/TA/T1 = 3ms/2.3s/5min/900ms.
Task fMRI data from 7 subjects (3M/5F 25±4yr) were acquired using Siemens 3T Prisma scanner.
A hemifield (R/L) checkerboard flickering at 4Hz was randomly distributed across trials with a block-design [10s on, 18-22s off].
MT-ON, MT-OFF and BOLD contrasts were analyzed using FSL 6.0.1 to find the activation in: (1) right visual cortex for left hemifield, (2) left visual cortex for right hemifield and (3) their combination for both hemifields. The group-level analysis was carried out using FSL's FLAME, with a one-sample t-test across parameter estimate for each contrast, family-wise error corrected (FWE, z>2.3). The difference between protocols was performed by paired t-test within FLAME.

Results:

The MT preparation leads to an average tissue signal reduction of 43±6%. The average SAR for the MT-ON experiment is 47±8% while 5.2±0.9% for MT-OFF.
Fig.1 shows (A) an example of the images for each acquisition, (B) the activation maps from adding the contrasts for the L and R regressors at the group level for MT-ON and BOLD, and (C) the activation difference between MT on/off and BOLD/ MT-ON.
As expected, (1) the signal drop-out is reduced at short TE; (2) MT-OFF only showed sub-threshold activation (not shown); (3) both MT-ON and BOLD show significant activation in early visual areas.
The group-level contrast MT-ON>MT-OFF comparison shows significant results that are similar, but not identical, to MT-ON, while no significantly activated voxels were found for the MT-OFF>MT-ON comparison. The group-level contrast from BOLD>MT-ON shows differences only in voxels distal to early visual cortex. No significantly activated voxels were found for MT-ON>BOLD.
Supporting Image: ohbm2020_fig1.png
   ·Figure1: Comparison of MT-ON, MT-OFF and BOLD task fMRI
 

Conclusions:

The MT-enhanced fMRI experiment is robustly sensitive to brain activation although the intrinsic signal change is lower than for standard BOLD. The use of MT-preparation offers the potential to both improve the intrinsic spatial resolution of brain activation studies, and also to improve image quality by measuring at short TE.

Modeling and Analysis Methods:

Activation (eg. BOLD task-fMRI) 2
Exploratory Modeling and Artifact Removal
Methods Development

Novel Imaging Acquisition Methods:

Non-BOLD fMRI 1

Keywords:

fMRI CONTRAST MECHANISMS
Other - Magnetization Transfer (MT)

1|2Indicates the priority used for review

My abstract is being submitted as a Software Demonstration.

No

Please indicate below if your study was a "resting state" or "task-activation” study.

Task-activation

Healthy subjects only or patients (note that patient studies may also involve healthy subjects):

Healthy subjects

Was any human subjects research approved by the relevant Institutional Review Board or ethics panel? NOTE: Any human subjects studies without IRB approval will be automatically rejected.

Yes

Was any animal research approved by the relevant IACUC or other animal research panel? NOTE: Any animal studies without IACUC approval will be automatically rejected.

Not applicable

Please indicate which methods were used in your research:

Functional MRI

For human MRI, what field strength scanner do you use?

3.0T

Which processing packages did you use for your study?

FSL

Provide references using author date format

[b][Balaban1991][/b] Balaban, R S, S Chesnick, K Hedges, F Samaha, and F W Heineman. “Magnetization Transfer Contrast in MR Imaging of the Heart.” Radiology 180, no. 3 (September 1, 1991): 671–75. https://doi.org/10.1148/radiology.180.3.1871277.
[Kim2006] Kim, Tae, Kristy S. Hendrich, Kazuto Masamoto, and Seong-Gi Kim. “Arterial versus Total Blood Volume Changes during Neural Activity-Induced Cerebral Blood Flow Change: Implication for BOLD FMRI:” Journal of Cerebral Blood Flow & Metabolism, December 20, 2006. https://doi.org/10.1038/sj.jcbfm.9600429.
[Song1997] Song, Allen W., Steven D. Wolff, Robert S. Balaban, and Peter Jezzard. “The Effect of Off-Resonance Radio Frequency Pulse Saturation on FMRI Contrast.” NMR in Biomedicine 10, no. 4–5 (1997): 208–15. https://doi.org/10.1002/(SICI)1099-1492(199706/08)10:4/5<208::AID-NBM467>3.0.CO;2-S.
[Wolff1989] Wolff, Steven D., and Robert S. Balaban. “Magnetization Transfer Contrast (MTC) and Tissue Water Proton Relaxation in Vivo.” Magnetic Resonance in Medicine 10, no. 1 (April 1, 1989): 135–44. https://doi.org/10.1002/mrm.1910100113.
[Zhou2005] Zhou, Jinyuan, Jean-Francois Payen, and Peter C. M. van Zijl. “The Interaction between Magnetization Transfer and Blood-Oxygen-Level-Dependent Effects.” Magnetic Resonance in Medicine 53, no. 2 (2005): 356–66. https://doi.org/10.1002/mrm.20348.