ISMRM 23rd Annual Meeting & Exhibition • 30 May - 05 June 2015 • Toronto, Ontario, Canada

Power Pitch Session
Microstructure in CNS
Power Pitch Theatre, Exhibition Hall, 10:45 - 11:45
Plasma Screens, Exhibition Hall, 11:45 - 12:45
Moderators: Shannon Kolind, Ph.D., Robert V. Mulkern, Jr., Ph.D.
Monday 1 June 2015

Click this video icon to view the introductory session:

Note: The videos below are only the slides from each presentation. They do not have audio.

Plasma #

Program #

1 0004.
Whole-brain in-vivo measurements of the axonal g-ratio in a group of 19 healthy volunteers
Siawoosh Mohammadi1, Daniel Carey2, Fred Dick3, Joern Diedrichsen4, Martina F. Callaghan5, Marty Sereno2, Marco Reisert6, and Nikolaus Weiskopf5
1Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Hamburg, Germany, 2Birkbeck/UCL Centre for NeuroImaging, London, London, United Kingdom, 3Birkbeck/UCL Centre for NeuroImaging, London, United Kingdom, 4UCL Institute of Cognitive Neurology, London, United Kingdom,5Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, London, United Kingdom, 6University of Freiburg Medical Center, Freiburg, Germany

Quantitative MRI aims to generate measures that are specific to particular aspects of tissue microstructure. The g-ratio, quantifying the ratio between the inner and outer diameters of a fibre, has been shown to be related to the conductance velocity and exhibit plasticity in functional stimulation experiments. Here we present in vivo g-ratio measures and population statistics from 19 volunteers. The g-ratio was calculated by combining magnetisation saturation maps and high angular resolution diffusion imaging (HARDI) data. The MRI-based in vivo g-ratio measures are in good agreement with histological findings and have the potential to become an important neuroimaging biomarker.

2 0005.
In vivo mapping of myelin g-ratio in the human spinal cord
T. Duval1, S. Lévy1, N. Stikov1,2, A. Mezer3, T. Witzel4, B. Keil4, V. Smith4, L. L. Wald4, E. Klawiter4, and J. Cohen-Adad1,5
1Institute of Biomedical Engineering, Polytechnique Montréal, Montréal, Québec, Canada, 2Montreal Neuronal Institute, McGill University, Montréal, Québec, Canada,3Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University, Jerusalem, Israel, 4A.A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, United States, 5Functional Neuroimaging Unit, CRIUGM, Université de Montréal, Montréal, Québec, Canada

The myelin g-ratio is the ratio of the inner to the outer diameter of the myelin sheath. As such, it provides a measure of the myelin thickness that complements axon morphology, with high specificity towards demyelination. We demonstrate for the first time in vivo mapping of myelin g-ratio in the human spinal cord using 300 mT/m gradient system. Average g-ratio was 0.74, which is consistent with the reported optimal g-ratio of 0.70 in from histology work. The proposed method is feasible in a clinically-acceptable time and could be useful for assessing demyelination in multiple sclerosis.

3 0006.
Physiological noise compensation in gradient echo based myelin water imaging
Yoonho Nam1 and Jongho Lee1
1Department of Electrical and Computer Engineering, Seoul National University, Seoul, Seoul, Korea

Recently, a few studies investigated the signal decay characteristics of multi-echo GRE data in white matter. They showed that the signal is composed of two or three components which have different decay rates and frequency offsets. Based on this finding, complex signal models were suggested and they generated more reliable myelin water images (MWI). However, the resulting myelin water fraction (MWF) maps still suffer from artifacts which may originate from physiological sources (e.g. respiration and cardiac). In this work, we explored the contribution of respiration- and cardiac-induced noises in GRE-MWI and proposed an approach to compensate for the noises.

4 0007. Comparison of ViSTa myelin water imaging with DTI and MT
Han Jang1, Yoonho Nam1, Yangsoo Ryu1, and Jongho Lee1
1Department of Electrical and Computer Engineering, Seoul National University, Seoul, Seoul, Korea

A new myelin water imaging (ViSTa) was compared with DTI and MT.

5 0008. The role of myelin geometry on magnetic susceptibility-driven frequency shifts: toward realistic geometries
Tianyou Xu1, Sean Foxley1, Michiel Kleinnijenhuis1, and Karla Miller1
1Oxford Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, Oxfordshire, United Kingdom

This work investigates the role that the geometry of myelin has on susceptibility driven frequency shifts in white matter. Packed axons, representative of axon bundles, capture important aspects of tissue microstructure. Here we demonstrate via simulation that axonal shape has a nontrivial effect on the underlying distribution of proton frequencies and on the free induction decay signal magnitude and phase. To bridge simulation with physical reality, we derive a structural template from electron microscopy in excised white matter, which is then used to forward calculate the frequency distribution and signal.

6 0009. Understanding Signal Sources of MT Asymmetry and Inhomogeneous MT for Imaging Myelination - permission withheld
Jae-Woong Kim1, Seung Hong Choi2, and Sung-Hong Park1
1Korea Advanced Institute of Science and Technology, Daejeon, Korea, 2Seoul National University, Seoul, Korea

As methods for imaging myelination, we investigated signal sources of MT asymmetry (MTA) and inhomogeneous MT (IHMT), both of which utilize asymmetric aspects of MT spectrum. The phantom study showed similar specificity of MTA and IHMT to myelination. Under the same average power and total saturation duration, however, IHMT was independent of asymmetric shift in saturation offset frequencies but dependent on duration of each saturation RF pulse, whereas MTA showed characteristics opposite to IHMT. Although both IHMT and MTA may be useful for myelin imaging, further studies are necessary to understand the signal sources and sensitivity/specificity of MTA and IHMT.

7 0010. Fast absolute myelin water mapping without an external water standard
Thanh D Nguyen1, Sneha Pandya1, Pascal Spincemaille1, Susan A Gauthier1, and Yi Wang1
1Weill Cornell Medical College, New York, NY, United States

The objective of this study is to develop a fast absolute myelin water quantification method which does not require the use of an external water standard. Results in 6 volunteers show excellent agreement with the conventional method with a whole brain scan time of 7 min at 1.5T.

8 0011.
Frequency difference mapping for measurement of white matter microstructure
Benjamin Tendler1, Samuel Wharton1, and Richard Bowtell1
1Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

Frequency difference mapping (FDM) is a novel technique that takes advantage of the non-linear temporal evolution of the phase in gradient echo sequences to obtain images that carry information about white matter (WM) microstructure. In contrast to other phase-based approaches for probing WM properties such as QSM and STI, FDM can yield local contrast that is sensitive to microstructure without requiring sophisticated filtering of phase images. Here a straightforward implementation of FDM is presented. The application of this approach to the measurement of the variation of microstructure across the corpus callosum in a study of 10 subjects is also described.

9 0012. Modelling the effect of white matter microstructure on gradient echo signal evolution
Benjamin Tendler1, Samuel Wharton1, and Richard Bowtell1
1Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

The evolution of the magnitude and phase of gradient echo (GE) signals is sensitive to white matter (WM) microstructure. This effect has been characterised by using a three-pool model of WM, comprised of axonal, myelin and external compartments. This work compares the magnitude and phase signals produced using triple-exponential and geometric single/multiple-fibre models, showing that the triple-exponential model can be improved in the static dephasing regime by adding in terms which approximately account for frequency variation in the myelin and external compartments. We also demonstrate the effects of including a range of fibre sizes and diffusion in a multiple-fibre model.

10 0013.
Possible Contribution of the Extracellular Matrix to the MRI Contrast in the Brain
Riccardo Metere1, Markus Morawski2, Henrik Marschner1, Carsten Jäger2, Tobias Streubel1, Stefan Geyer1, Katja Reimann1, Andreas Schäfer1, and Harald E. Möller1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 2Paul-Flechsig-Institute for Brain Research, University of Leipzig, Leipzig, Germany

The tissue composition of the brain can be related to different contrast sources in quantitative MRI imaging. Particularly, myelin and iron are considered to be the major source of MRI contrast, with strong correlation to T1 and T2*, respectively. However, other components, and particularly the relatively abundant extracellular matrix, may play a role in the generation of MRI contrast. In this work we present preliminary experiments showing a contrast change in quantitative relaxation maps of a brain tissue sample before and after the digestion of the extracellular matrix, thus supporting the hypothesis that this componet contributes to MRI contrast.

11 0014. Signatures of microstructure in conventional gradient and spin echo signals
Pippa Storey1, Sohae Chung1, Noam Ben-Eliezer1, Gregory Lemberskiy1, Yvonne W. Lui1, and Dmitry S. Novikov1
1Radiology Department, New York University School of Medicine, New York, NY, United States

Diffusion imaging has long been the method of choice for probing tissue microstructure. We show that signatures of microstructure are also present in the signals from conventional gradient and spin echo sequences. Preliminary results from phantoms containing polystyrene beads of known diameter demonstrate that the logarithms of the signals from both multiple gradient echo and single spin echo sequences decrease nonlinearly with TE, in agreement with theory. Numerical fits provide estimates of bead diameter and magnetic susceptibility in rough agreement with expected values. This has implications for studies of tissue microstructure and for interpretation of gradient and spin echo signals.

12 0015. Dependance of the apparent T1 on Magetization Transfer
Peter van Gelderen1, Xu Jiang1, and Jeff H Duyn1
1AMRI, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States

In human brain, T1-contrast is strongly affected by bound protons in myelin, whose rapid T1-relaxation influences the more mobile water protons through magnetization transfer. MT also affects the apparent, instantaneous T1-relaxation in inversion recovery (IR) experiments due to magnetization differences between bound and mobile protons generated by the inversion pulse. The amplitude and timescale of this effect was investigated comparing the IR following inversions at different B1-levels, which differentially saturate the bound proton magnetization. The white-matter IR resembled a two- exponential decay, with the more rapid decay having a 90ms time constant and a B1-dependent amplitude ranging from 12-19%.

13 0016.
Towards an Optimized and Standardized Amide Proton Transfer (APT) MRI Sequence and Protocol for Clinical Applications
Hye-Young Heo1, Yi Zhang1, Jochen Keupp2, Yansong Zhao3, Michael Schar1, Dong-Hoon Lee1, Peter C.M van Zijl1,4, and Jinyuan Zhou1,4
1Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, United States, 2Philips Research, Hamburg, Germany, 3Philips Healthcare, Cleveland, Ohio, United States, 4F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, United States

APT-weighted imaging is a novel chemical exchange saturation transfer (CEST)-based MRI modality that gives contrast due to endogenous cytosolic protein and peptide content, as well as tissue pH, in vivo. In this abstract, several APTw-MRI sequences that are feasible for clinical applications were compared on phantoms, healthy subjects, and a patient with glioblastoma. Time-interleaved pTX sequences, particularly using the TSE acquisition, can maximize SNRs and APT-MRI effects on clinical scanners by avoiding RF amplifier limitations to the saturation pulses.

14 0017. Can Nuclear Overhauser Enhancement Mediated Chemical Exchange Saturation Transfer (NOE-CEST) Offer a New Insight in Acute Stroke Diagnosis?
Yee Kai Tee1, George WJ Harston2, Nicholas Blockley3, Robert Frost3, Thomas W Okell3, Sivarajan Thandeswaran2, Fintan Sheerin4, Peter Jezzard3, James Kennedy2, Stephen Payne5, and Michael Chappell5
1Department of Mechatronics and BioMedical Engineering, Universiti Tunku Abdul Rahman, KL, KL, Malaysia, 2Acute Stroke Programme, Radcliffe Department of Medicine, Oxford University, Oxfordshire, United Kingdom, 3Oxford Centre of Functional MRI of the Brain, Nuffield Department of Clinical Neurosciences, Oxford University, Oxfordshire, United Kingdom, 4Department of Neuroradiology, Oxford University Hospitals NHS Trust, Oxfordshire, United Kingdom, 5Department of Engineering Science, Institute of Biomedical Engineering, Oxford University, Oxfordshire, United Kingdom

Chemical exchange saturation transfer (CEST) data in acute stroke patients (within 6 hours of onset) were acquired to compare nuclear Overhauser enhancement mediated CEST (NOE-CEST) with apparent diffusion coefficient (ADC) and pH-weighted imaging using amide proton transfer (APT). This work is the first demonstration of NOE-CEST in acute human stroke. NOE-CEST provides a unique contrast compared to ADC and pH-weighted imaging in tissue that progresses to infarction, suggesting that NOE-CEST may offer a new insight in acute stroke management.

15 0018. GluCEST imaging in a primate model of Alzheimer’s disease - permission withheld
Julien Flament1,2, Charlotte Gary2,3, James Koch2,4, Fabien Pifferi5, Emmanuel Comoy6, Jean-Luc Picq7, Julien Valette2,3, and Marc Dhenain2,3
1INSERM US27, CRC-MIRCen, Fontenay-aux-Roses, France, 2CEA/DSV/I2BM/MIRCen, Fontenay-aux-Roses, France, 3CNRS URA 2210, Fontenay-aux-Roses, France,4Department of Psychology, University of Wisconsin, Oshkosh, WI, United States, 5CNRS-MNHN UMR 7179, Brunoy, France, 6CEA/DSV/iMETI/SEPIA, Fontenay-aux-Roses, France, 7EA 2027, Université Paris 8, Saint-Denis, France
This study describes the possibility to image glutamate concentration alterations using gluCEST. Injection of brain homogenates of Alzheimer’s disease (AD) patients in susceptible mice can induce or accelerate the pathology, suggesting a “prion-like” mechanism. Here, two groups of mouse lemur primates were injected with brain homogenate of either AD (n=4) or age-matched control patients (n=3). They were characterized by MRS, showing modifications in metabolic profile, especially a decrease in glutamate concentration (-16.5%). GluCEST images showed a decrease of gluCEST contrast (-17.6%) reflecting glutamate concentration variation. These results suggest that glutamate level could be a surrogate marker of disease progression.