|Advanced MRS Localization & Imaging Methodology|
Sensitivity Encoded VAPOR-FIDLOVS at 7T: Mapping the
Anke Henning1, Alexander Fuchs1, James B. Murdoch2, David Foxall2, Peter Boesiger1
1University and ETH Zurich, Zurich, Switzerland; 2Philips Medical Systems, Cleveland, USA
For MRSI acquisition at 7T direct acquisition of the Free Induction Decay Localized by Outer Volume Suppression (FIDLOVS) is proposed to minimize SNR loss due to short T2 relaxation times. To that, a broadband frequency-modulated excitation pulse for slice-selection and a numerically optimized outer-volume-suppression scheme, which considers T1 relaxation of skull lipid, B1 inhomogeneity, saturation band crossing and is based on broadband PPR-pulses, for in-plane localization are applied. The resulting signal-to-noise ratio (SNR) and spectral resolution enable mapping of 15 metabolites. The high SNR is also the base for highly spatially resolved metabolite mapping accelerated by sensitivity encoding.
Single-Shot Proton MR Spectroscopic Inverse Imaging
Fa-Hsuan Lin1, 2, Shang-Yueh Tsai2, Yi-Ru Lin3, Ricardo Otazo4, Graham Wiggins1, Lawrence Wald1, John Belliveau1, Stefan Posse4
1Massachusetts General Hospital, Charlestown, Massachusetts, USA; 2National Taiwan University, Taipei, Taiwan; 3National Taiwan University of Science and Technology, Taipei, Taiwan; 4Univesity of New Mexico, Albuquerque, New Mexico, USA
A proton spectroscopic inverse imaging (SInI) acquisition and reconstruction protocol is introduced to measure 2-dimensional spectroscopic maps in a single excitation with high spectral resolution. Combining with echo-planar readout for spectral and 1D spatial information, we use the solution of the minimum-norm estimate (MNE) inverse problem along the other spatial dimension from all channels of a coil array. Feasibility of short TE proton MRSI was demonstrated on 3 T scanners equipped with a 32-channel array. This method enables flexible tradeoff between phase encoding and parallel imaging to maximize spectral width for applications in dynamic single-shot MRSI.
Spectroscopic Imaging at 7 T
Yoshitaka Bito1, Koji Hirata1, Toru Shirai1, Yukari Yamamoto1, Yoshihisa Soutome1, Toshihiko Ebisu2, Masahiro Umeda3, Yuko Kawai3, Toshihiro Higuchi3, Chuzo Tanaka3
1Hitachi, Ltd., Kokubunji-shi, Japan; 2Nantan General Hospital, Japan; 3Meiji University of Oriental Medicine, Japan
A fast lactate-discriminating echo-planar spectroscopic imaging (EPSI) technique suitable for 7-T MRI is developed. The technique uses just a single TE measurement for acquiring lactate-discriminated images, in which the TE is chosen to shift the echo peak of a lactate signal away from that of an overlapping lipid signal. The optimum TE at 7 T is calculated so that the lipid signal is sufficiently suppressed while the lactate signal is not attenuated so much. Acquisition of discriminated lactate images is demonstrated by applying this technique to a phantom and a rat.
Diffusion Weighted Spectroscopy: A Novel Approach to
Determine Macromolecule Resonances at 14T
Nicolas Kunz1, Cristina Cudalbu1, Vladimir Mlynarik1, Stéphane V. Sizonenko, Rolf Gruetter1, 2
1Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; 2University of Lausanne and Geneva, Switzerland
Quantification of the neurochemical profile by 1H-MRS critically depends on the estimation of the contribution of macromolecule resonances to the spectrum. As the linewidth of macromolecules does not increase with B0, the resonances attributed to macromolecules are increasingly difficult to distinguish from those of coupled spin systems. Due to heterogeneity of T1, in the metabolite-nulled spectra residuals attributed to metabolites are still observed. The study shows that an IR 1H-MRS sequence combined with diffusion weighting allows near-complete removal of metabolites signals and excellent definition of the spectral contribution of macromolecules due to one order of magnitude smaller ADC of macromolecules.
Superresolution Parallel Spectroscopic Imaging
Ricardo Otazo1, Fa-Hsuan Lin2, Graham Wiggins2, Ramiro Jordan1, Stefan Posse1
1University of New Mexico, Albuquerque, New Mexico, USA; 2Massachusetts General Hospital, Boston, Massachusetts, USA
Standard parallel imaging may produce artifacts when applied to MR spectroscopic imaging (MRSI) due to coil sensitivity variation within the typical large voxels in low spatial resolution MRSI. In this work, a novel approach for accelerating the spatial encoding process of MRSI known as Superresolution SENSE (SURE-SENSE) is presented. Acceleration is performed by acquiring the low spatial resolution representation of the object being imaged and intra-voxel reconstruction is performed using coil sensitivity maps acquired with higher target spatial resolution. The method is particularly suitable for array coils with a large number of small elements that present stronger sensitivity variation. We show feasibility of the method for human brain MRSI using Proton Echo Planar Spectroscopic Imaging (PEPSI) and a 32-channel receiver array coil.
Fast Spectroscopic Imaging Using Uniform Wideband
Parallel Excitation on 7T
Borjan Aleksandar Gagoski1, Kawin Setsompop1, Vijay Alagappan2, Franz Schmitt3, Ulrich Fontius3, Andreas Potthast4, Lawrence Wald2, 5, Elfar Adalsteinsson1, 5
1Massachusetts Institute of Technology, Cambridge, Massachusetts, USA; 2MGH, Charlestown, Massachusetts, USA; 3Siemens Medical Solutions, Erlangen, Germany; 4Siemens Medical Solutions, Charlestown, Massachusetts, USA; 5Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts, USA
In this work we combine spiral CSI readouts with parallel RF transmission to mitigate B1+ inhomogeneities. We limit this initial demonstration to the low flip-angle domain where excitation k-space analysis holds, and apply “spokes”-based slice selective RF design to an eight channel transmit system at 7T. The 8 transmit channels enable reduced-duration, slice-selective RF pulses that implement excellent wide band B1+ mitigation over a 600 Hz bandwidth. The goal of this work is to demonstrate efficient spiral CSI encoding with B1+-mitigated spatial-spectral excitation over a spatial FOV and frequencies of interest for 1H brain spectroscopic imaging.
Parallel Spectroscopic Imaging
Reconstruction with Arbitrary Trajectories Using K-Space Sparse Matrices
Meng Gu1, Chunlei Liu1, Daniel Spielman1
1Stanford University, Stanford, USA
Parallel reconstruction has been successfully applied to magnetic resonance spectroscopic imaging to reduce scan times. To reconstruct undersampled MRSI data with arbitrary k-Space trajectories, image-domain based iterative-SENSE algorithm and k-Space based PARS algorithm have been proposed at costs of long computing times. In this abstract, a new k-Space-domain based parallel spectroscopic imaging reconstruction with arbitrary trajectories using sparse matrices is applied to MRSI with spiral trajectories. It achieves MRSI reconstruction with reduced computing times. The results are demonstrated in an in-vivo study. Results very similar to that reconstructed with fully sampled spiral k-Space data are obtained with different reduction factors.
Reduction of Acquisition Time in Magnetic Resonance
Spectroscopic Imaging Using 3D Wavelet Encoding Method: Comparison to
Chemical Shift Imaging
Richard Young1, Hacene Serrai1
1National Research Council Institute for Biodiagnostics, Winnipeg, Canada
This work describes the extension of the wavelet encoding method in MRSI from 2 dimensions to 3 dimensions. The obtained in-vivo results demonstrate the usefulness of the wavelet encoding method in reducing the acquisition time as compared to CSI. In addition, wavelet encoding appears to preserve the spatial distribution better than the CSI (phantom results not shown). As expected a reduction in signal-to-noise ratio is noticed in wavelet encoding; however, this reduction is minimum.
|17:36||602.||Voxel Shift and Interpolation for Hadamard-Encoded MR
Lazar Fleysher1, Roman Fleysher1, Songtao Liu1, Oded Gonen1
1NYU School of Medicine, New York, New York, USA
While spatial Fourier gradient phase-encoding and spatial Hadamard radio-frequency encoding are two established MR localization techniques, the absence of voxel-shift and interpolation post-processing algorithms for the latter has always placed it at a discouraging disadvantage. In this paper we present a method for voxel-shift and interpolation of Hadamard-encoded data.
|Spectroscopic Imaging with Volume Selection by
Unpaired Adiabatic π Pulses: Theory and Application
Julien Valette1, Jang-Yeon Park1, Olli Gröhn1, Kamil Ugurbil1, Michael Garwood1, Pierre-Gilles Henry1
1CMRR, University of Minnesota, Minneapolis, Minnesota, USA
In spectroscopy, volume selection can be advantageously achieved using adiabatic π pulses, which enable high bandwidth and B1 insensitivity. In order to avoid the generation of non-linear phase profiles, these pulses are usually used in pairs. However, in the context of spectroscopic imaging, a high enough spatial resolution may limit phase dispersion within each pixel when using only one pulse per selected spatial dimension, yielding a reduced TE and reduced power deposition. In this work, the feasibility of this approach is explored theoretically and experimentally, using a new adiabatic sequence named Pseudo-LASER in the rat brain at 9.4 T.