Strategies of Localization & Imaging Methodology
Monday 3 May 2010
Room A4 11:00-13:00 Moderators: Anke Henning and M. Albert Thomas

11:00 23.

Focused RF in High Field 1H-MRSI: Outer Volume Suppression by Local Excitation
Vincent O. Boer1, Ingmar J. Voogt1, Hugo Kroeze1,2, Bart Leo van de Bank1, A H. Westra2, Peter R. Luijten1, Dennis W.J. Klomp1
1Radiology, UMC Utrecht, Utrecht, Netherlands; 2MTKF, UMC Utrecht, Utrecht, Netherlands

An alternative to SAR demanding outer volume suppression is proposed for 7T MRSI. Low power suppression is achieved by using focused RF to locally saturate subcutaneous signals by using an RF headband; a close fitting, small element, eight-channel transmit receive array. Two sets of RF shims are defined to drive the RF headband; a ‘ring’ mode for outer volume suppression close to the elements and a quadrature mode for water suppression and excitation of the brain. High spatial resolution MRSI is shown within a short scan time.

11:12   24.

Motion Artifact Reduction Using Bipolar Diffusion Gradients in Diffusion-Weighted Echo-Planar Spectroscopic Imaging
Yoshitaka Bito1, Koji Hirata1, Toshihiko Ebisu2, Yuko Kawai3, Yosuke Otake1, Satoshi Hirata1, Toru Shirai1, Yoshihisa Soutome1, Hisaaki Ochi1, Masahiro Umeda3, Toshihiro Higuchi4, Chuzo Tanaka4
1Central Research Laboratory, Hitachi, Ltd., Kokubunji-shi, Tokyo, Japan; 2Neurosurgery, Nantan General Hospital, Nantan-shi, Kyoto, Japan; 3Medical Informatics, Meiji University of Integrative Medicine, Nantan-shi, Kyoto, Japan; 4Neurosurgery, Meiji University of Integrative Medicine, Nantan-shi, Kyoto, Japan

Diffusion-weighted echo-planar spectroscopic imaging (DW-EPSI), using bipolar diffusion gradients, has been developed to reduce motion artifacts. Signal loss in signal accumulation, which is detrimental in diffusion-weighted spectroscopic measurements, is estimated by numerical analysis using bipolar diffusion gradients. Reduction of motion artifacts is demonstrated by applying DW-EPSI, using bipolar diffusion gradients, to a phantom and a rat brain in vivo. The results suggest that the effectiveness and limitations of this technique in reduction of motion artifacts and numerical analysis is helpful in investigating errors due to motion.

11:24 25. 

Spatial Localization Accomplished by Sensitivity Heterogeneity
Li An1, Steven Warach1, Jun Shen2
1National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States; 2National Institute of Mental Health, National Institutes of Health, Bethesda, MD, United States

This work demonstrates a new method that allows multi-compartmental spatial localization based on the heterogeneity of sensitivity profiles of phased array receiver coils.  This method offers an alternative to SENSE-CSI for performing spectroscopy using phased array coils. It allows the user to manually prescribe compartments following natural anatomical or physiological boundaries to reduce partial volume artifacts associated with conventional CSI and SENSE-CSI. In vivo application using PRESS and an eight-element phased array head coil demonstrates that this method can extract spectra from stroke tissue and normal tissue in 4 seconds.

11:36 26. 

Selective Homonuclear Polarization Transfer at 7T: Single Shot Detection for GABA in Human Brain
Jullie W. Pan1, Nikolai Avdievich1, Hoby P. Hetherington1
1Yale University School of Medicine, New Haven, CT, United States

Given its important role as the major inhibitory neurotransmitter, GABA is a well known target for detection in human brain. However, because of its overlap with many other resonances, editing is required for its unambiguous detection. We describe implementation of selective homonuclear polarization transfer to detect the C4 3.0ppm GABA in a single shot in human brain. This is based on a broad T1 based inversion pre-sequence suppression with a J-refocused acquisition. As implemented in human brain, we demonstrate the performance of this approach at 7T in spectroscopic imaging format with 1.44cc resolution.

11:48 27.  

Fast 3D Proton Spectroscopic Imaging of the Human Brain at 3 Tesla by Combining  Spectroscopic Missing Pulse SSFP and Echo Planar Spectroscopic Imaging
Wolfgang Dreher1, Peter Erhard1, Dieter Leibfritz1
1Dept. Chemistry, University of Bremen, Bremen, Germany

One of the limitations of the fast spectroscopic imaging sequence “spectroscopic missing pulse SSFP” are the rather long minimum total measurement time for 3D measurements with large matrix size. This drawback is eliminated by acquiring the echo-like signal under a symmetrically oscillating read gradient in slice direction. The sequence was implemented on a 3 Tesla head scanner and applied to healthy volunteers. Within 4:19 minutes only, a 3D measurement of the brain was performed with 32x32x16 matrix size and 0.33 ml nominal voxel size using weighted k-space averaging with a maximum of four accumulations in the k-space center.

12:00 28. 

Spectrally Selective Phosphocreatine Imaging on a 9.4T Whole-Body Scanner Using a Spatial-Spectral RF Pulse
Yi Sui1,2, Haoyang Xing2, Theodore Claiborne2, Keith R. Thulborn2,3, Xiaohong Joe Zhou2,4
1Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, United States; 2Center for Magnetic Resonance Research, University of Illinois Medical Center, Chicago, IL, United States; 3Department of Radiology, University of Illinois Medical Center, Chicago, IL, United States; 4Departments of Radiology, Neurosurgery and Bioengineering, University of Illinois Medical Center, Chicago, IL, United States

In this study, we report a spatial-spectral (SPSP) pulse that is tailored for selectively exciting the phosphocreatine (PCr) resonance at 9.4T while suppressing all other major phosphorus metabolites including inorganic phosphate and adenosine triphosphates. Using this pulse in conjunction with a RARE sequence, we have obtained PCr images from phantoms (50 mM) and the lower extremity of human volunteers in 10 minutes on a 9.4T whole-body scanner. With an in-plane spatial resolution of 7.5mm  x 7.5mm, the PCr images show anatomic details with an adequate signal to noise ratio (SNR=14).

12:12  29. 

1H MR Spectroscopy of the Human Prostate Using an Adiabatic Sequence with a SAR Optimized Endorectal RF Coil
Catalina Arteaga1, Uulke A. van der Heide1, Marco van Vulpen1, Peter R. Luijten2, Dennis W.J. Klomp2
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands; 2Radiology, UMC Utrecht, Utrecht, Netherlands

Prostate 1H MRSI at 7T with fully adiabatic sequences like full-LASER allows polyamine detection. In addition, choline and creatine levels can also be depicted in prostate cancer patients even with hormone therapy.  We showed that fully adiabatic sequences can overcome the B1 inhomogeneities compared to semi-adiabatic sequences.

12:24   30. 

High Resolution GABA Mapping in Vivo Using a Slice Selective MEGA-MRSI Sequence at 3 Tesla
He Zhu1,2, Ronald Ouwerkerk1,3, Richard A.E. Edden1,2, Peter B. Barker1,2
1Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States; 2F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States; 3The National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD, United States

A spin echo based MEGA-MRSI sequence was developed to acquire MEGA-edited spectra of γ-aminobutyric acid (GABA) in an entire slice with excellent sensitivity. Co-editing of lipid and NAA signals was greatly suppressed by a dualband pre-saturation sequence and integrated outer volume suppression (OVS) pulses. Experiments in normal volunteers were performed at 3 Tesla using a 32-channel head coil. High signal-to-noise ratio spectra and metabolic images of GABA (and glutamate) were acquired from 4.5 cm3 voxels in a scan time of 17 minutes.

12:36 31.

Qualitative Detection of Ceramide and Other Metabolites in Brain Tumor by Localized Correlated Spectroscopy
Rajakumar Nagarajan1, Whitney B. Pope1, Noriko Salamon1, Linda M. Liau2, Timothy Cloughesy3, M Albert Thomas1

1Radiological Sciences, University of California Los Angeles, Los Angeles, CA, United States; 2Neurosurgery, University of California Los Angeles, Los Angeles, CA, United States; 3Neurooncology, University of California Los Angeles, Los Angeles, CA, United States

Magnetic resonance spectroscopy (MRS) provides metabolic information about brain tumors complementary to what can be obtained from anatomic images. In contrast to other metabolism-based imaging techniques, MRS yields multiparametric data, does not require ionizing radiation, and can be performed in conjunction with magnetic resonance imaging studies. Magnetic resonance spectral patterns have been shown to be distinct for different tumor types and grades. Two-dimensional (2D) localized correlated spectroscopy (L-COSY) in patients with high and low grade gliomas provides better dispersion of several metabolites such as N-acetylaspartate (NAA), creatine (Cr) choline (Cho), ceramide (Cer), phosphoethanolamine (PE), glutamine/glutamate (Glx), lactate (Lac), myo-inositol (mI), taurine (Tau), etc. which has been a major difficulty in 1D MRS.

12:48 32.

Increased Signal-To-Noise in High Field Localized Spectroscopy of the Temporal Lobe Using New Deformable High-Dielectric Materials
Andrew Webb1, Hermien Kan1, Maarten Versluis1, Nadine Smith1
1Radiology, Leiden University Medical Center, Leiden, Netherlands

The intrinsic B1 non-uniformities from standard volume resonators at high field are particularly problematic for localized spectroscopy of areas such as the temporal lobe, where low signal-to-noise results from a reduced B1 field. Using a recently developed high dielectric constant material placed around the head, increases in signal-to-noise of ~ 200% can be achieved in such problem areas without reducing the sensitivity in other areas of the brain.



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