ISMRM 24th Annual Meeting & Exhibition • 07-13 May 2016 • Singapore

Scientific Session: New Techniques for CEST & MT

Tuesday, May 10, 2016
Room 324-326
10:00 - 12:00
Moderators: Julio Cardenas, Phillip Zhe Sun

Simultaneous Multi-Slice Spiral-CEST Encoding with Hankel Subspace Learning: ultrafast whole-brain z-spectrum acquisition
Suhyung Park1, Sugil Kim1,2, and Jaeseok Park3
1Center for Neuroscience Imaging Research, Institute for Basic Science (IBS), Suwon, Korea, Republic of, 2Department of Brain and Cognitive Engineering, Korea University, Seoul, Korea, Republic of, 3Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of
Chemical exchange saturation transfer (CEST) imaging has been introduced as a new contrast mechanism for molecular imaging, and typically requires long saturation preparation and multiple acquisitions of imaging data with varying saturation frequencies (called z-spectrum). Since the z-spectrum acquisition is inherently slow and takes prohibitively long imaging time, it has been very difficult to introduce CEST z-spectrum into a clinical routine. In this work, we propose a novel, simultaneous multi-slice (SMS) Spiral CEST encoding with Hankel subspace learning (HSL) for ultrafast whole-brain z-spectrum acquisition within 2-3 minutes, in which: 1) RF segmented uneven saturation is employed to reduce the duration of saturation preparation, 2) Spiral CEST encoding is employed to acquire SMS signals, and 3) SMS signals are projected onto the subspace spanned by the complementary null space, selectively reconstructing a slice of interest while nulling the other slice signals. 

Superfast CEST Spectral Imaging (SCSI)
Iris Yuwen Zhou1, Jinsuh Kim2, Takahiro Igarashi1, Lingyi Wen1, and Phillip Zhe Sun1
1Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, United States, 2Department of Radiology, University of Illusions at Chicago, Chicago, IL, United States
To resolve metabolites at different chemical shift offsets, complete Z-spectrum is conventionally obtained by varying saturation offset from scan to scan, which is time consuming and not suitable for studying dynamic changes. To overcome this, we innovatively combined superfast Z spectroscopy with chemical shift imaging (CSI) and developed Superfast Chemical exchange saturation transfer (CEST) Spectral Imaging (SCSI). It provides fast Z-spectral CEST information with spatial resolution. While conventional CSI measures dilute metabolites, the proposed SCSI exploits CEST mechanism to investigate the interaction between metabolites/contrast agents and tissue water, providing sensitivity enhanced measurements of metabolites and pH information.

Clinically relevant rapid 3D CEST imaging with hexagonal spoiling gradients, optimised B1, and symmetric z-spectrum sampling
Robert C. Brand1, Nicholas P. Blockley1, Michael Chappell2, and Peter Jezzard1
1FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom, 2IBME, University of Oxford, Oxford, United Kingdom
Clinical 3D CEST has been hindered by slow acquisition times and z-spectra artefacts that affect fitting. Here, we demonstrate various sequence improvements, including: 1) hexagonal gradient spoiling that minimises ghosting, shortens TR and reduces confounding T2 sensitivity; 2) low readout flip angles combined with symmetric z-spectrum sampling that better maintains the steady state between samples and eliminates the need for T1-restoration periods; and 3) exchange-rate matched 360° CEST pulses that reduce direct water saturation to minimise T1 sensitivity and increase CNR. Together, these improvements result in high-quality whole-brain 39-offset z-spectra measurements at 3mm isotropic resolution in 2:59 minutes.

Conjoint measure of 3D ASL and 3D APT in the lesion proximal regions for differentiating metastasis tumor from glioblastom
Rui Li1, Bing Wu2, Chien-yuan Lin3, Xin Lou1, YuLin Wang1, and Lin Ma1
1Department of Radiology, PLA general Hospital, Beijing, China, People's Republic of, 2GE healthcare MR Research China, Beijing, China, People's Republic of, 3GE heathcare Taiwan, Taipei, Taiwan
Differential diagnosis is challenging due to similar appearance using conventional imaging such as T1 contrast enhanced and DWI. In this work, we use the measure of spatially matching 3D arterial spin labeling (ASL) and 3D amide proton transfer (APT) in the lesion proximal regions to differentiate metastasis and glioblastom, in the hypothesis that glioblastom  infiltrates into sourrounding tissues whereas metastasis tumors have clear biological boundaries.

Blind Compressed Sensing-based Ultrafast Chemical Exchange Saturation Transfer (CEST) Imaging
Hye-Young Heo1,2, Sampada Bhave3, Mathews Jacob3, and Jinyuan Zhou1,2
1The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, United States, 2F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States, 3Department of Electrical and Computer Engineering, University of Iowa, Iowa City, IA, United States
CEST imaging, such as amide proton transfer (APT) imaging, is a novel, clinically valuable molecular MRI technique that can give contrast due to a change in water signal caused by chemical exchange with saturated solute protons. However, its clinical translation is still limited by its relatively long scan time because a series of RF saturation frequencies are unavoidably acquired. Here, we present a highly accelerated CEST imaging technique (up to 10-fold) using a novel blind compressed sensing framework.

Separation of intracellular and extracellular Z-spectra by DiffusionCEST
Kevin Ray1, Gogulan Karunanithy2, Andrew Baldwin2, Michael Chappell3, and Nicola Sibson1
1Oxford Institute for Radiation Oncology, University of Oxford, Oxford, United Kingdom, 2Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, United Kingdom, 3Institute of Biomedical Engineering, University of Oxford, Oxford, United Kingdom
CEST-MRI is an imaging technique which is sensitive to tissue pH, and has generated pH-weighted images in acute stroke patients. One key assumption regarding CEST-MRI is that the signal is predominantly intracellular. This assumption has implications in the application of CEST-MRI for pH measurement of tumours, which are generally associated with extracellular acidosis. This study developed a novel pulse sequence, combining stimulated echo acquisition mode diffusion and CEST imaging. Using this novel pulse sequence, the intracellular and extracellular contributions to the acquired Z-spectrum were isolated in a simple cell system and post-mortem mouse brain.

Multi-echo Parametric VARiation Saturation (MePaVARS) enabling more specific endogeneous CEST imaging
Xiaolei Song1,2, Yan Bai1,3, Meiyun Wang3, and Michael T. McMahon1,2
1The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, United States, 2F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States, 3Department of Radiology, Henan Provincial People’s Hospital, Zhengzhou, China, People's Republic of
Existing CEST methodologies have difficulties in discriminating agents with small difference in chemical shift. As CEST signal is very sensitive to saturation power (B1) and length (tsat), indicating a second route to indentify agents by modulating the saturation conditions. We utilized the Multi-echo Parametric VARiation Saturation (MePaVARS), to separate faster and slower exchanging endogeneous CEST metabolites and molecules according to their differences response to B1. In simulations and phantoms, MePaVARS allowed extraction of faster-exchanging Glutamate from the slower-exchanging Creatine, based on its oscillation patterns. A preliminary study for mice bearing prostate tumor further validated the feasibility of MePaVARS in vivo

Implementing single-shot quantitative CEST/T1? measurements using bSSFPX
Shu Zhang1, Robert E Lenkinski1,2, and Elena Vinogradov1,2
1Radiology, UT Southwestern Medical Center, Dallas, TX, United States, 2Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States
Recently properties of bSSFP were explored to detect exchange processes (bSSFPX), similar to CEST or off-resonance T experiments. We expand the study and implement a transient bSSFPX experiment that acquires bSSFP spectra continuously as the effective saturation time increases, allowing observation of the approach of magnetization to the steady state in a single shot. The magnetization dynamic is governed by the effective field and relaxation times parallel or perpendicular to it. Work is in progress to derive an exact quantification model. The method leads to fast acquisition of time-dependent data and may speed up QUEST-like quantification of the exchange processes.

IHMT: Is it misnamed? A simple theoretical description of "inhomogeneous" MT.
Alan P Manning1, Kimberley L Chang2, Alex MacKay1,3, and Carl A Michal1
1Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada, 2Department of Neurology, University of British Columbia, Vancouver, BC, Canada, 3UBC MRI Research Centre, Department of Radiology, University of British Columbia, Vancouver, BC, Canada
Inhomogeneous MT (IHMT) shows promise for myelin-selectivity. Images acquired with soft prepulses at positive and negative offsets simultaneously show a reduced intensity compared to images with a single positive or negative offset prepulse. The leading hypothesis is that this works due to inhomogeneous broadening of the lipid proton line. Our results contradict this. We show that IHMT can be explained by a simple spin-1 model of a coupled methylene pair, and that it occurs in homogeneously-broadened systems (hair and wood). We propose the relevant timescales for IHMT are the dipolar coupling correlation time and the prepulse nutation period.

In vivo quantitative Magnetisation Transfer in the cervical spinal cord using reduced Field-of-View imaging: a feasibility study
Marco Battiston1, Francesco Grussu1, James E. M. Fairney2,3, Ferran Prados1,4, Sebastien Ourselin4, Mara Cercignani5, Claudia Angela Michela Gandini Wheeler-Kingshott1,6, and Rebecca S Samson1
1NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, University College London, London, United Kingdom, 2UCL Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom, 3Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, University College London, London, United Kingdom,4Translational Imaging Group, Centre for Medical Image Computing, UCL Department Medical Physics and Bioengineering, University College London, London, United Kingdom, 5CISC, Brighton & Sussex Medical School, Brighton, United Kingdom, 6Brain Connectivity Center, C. Mondino National Neurological Institute, Pavia, Italy
Quantitative Magnetization Transfer (qMT) Imaging techniques offer the possibility to estimate tissue macromolecular fraction, which has been shown to be specific for myelin in the brain and spinal cord. To date, applications of qMT in the spinal cord have been hampered by prohibitive protocol duration. We propose a novel approach for qMT in the spinal cord based on the combination of off-resonance saturation and small field-of-view imaging, with the potential of reducing the scan time needed to perform qMT in the spinal cord.

The International Society for Magnetic Resonance in Medicine is accredited by the Accreditation Council for
Continuing Medical Education to provide continuing medical education for physicians.