ISMRM 21st Annual Meeting & Exhibition 20-26 April 2013 Salt Lake City, Utah, USA

UTE: Methods & Applications
Thursday 25 April 2013
Room 255 EF  16:00 - 18:00 Moderators: Michael Carl, Peder E. Z. Larson

16:00 0761.   High-Bandwidth ZTE Imaging with Sub-Millisecond TR
Markus Weiger1, David Otto Brunner1, Benjamin E. Dietrich1, and Klaas P. Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Zero echo time (ZTE) imaging is a promising alternative for direct MRI of tissues with short T2. With respect to the commonly applied 3D UTE method employing rapid gradient ramping after RF excitation, the hardware demands are shifted towards the RF domain by excitation after setting the gradient. For imaging at high bandwidth as required for resolving short T2, very rapid T/R switching is required, which was implemented for a human whole body scanner. In addition sub-millisecond TR was realised to improve SNR efficiency. With these measures, initial results were obtained for musculoskeletal imaging in healthy human volunteers.

16:12 0762.   
Zero Echo Time (ZTE) Imaging with Anisotropic Field-Of-View
Cheng Li1, Alan C. Seifert1, Jeremy F. Magland1, and Felix W. Wehrli1
1Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States

Relative to ultrashort echo-time (UTE), zero echo time (ZTE) imaging offers higher SNR and reduced image blurring for short-T2 imaging. However, ZTE imaging is time-consuming since it is inherently 3D and a complementary scan is needed to fill the missing central k-space portion. In this work, we designed a ZTE sequence with anisotropic filed-of-view (FOV) tailored to the elongated shape of the target anatomy to reduce the scan time. Point-spread function simulation verified the intended FOV shape. Both proton phantom imaging and ex-vivo cortical bone phosphorus imaging demonstrates the practicality of anisotropic FOV ZTE imaging.

16:24 0763.   Adiabatic Inversion Recovery Prepared Ultrashort Echo Time (IR-UTE) Imaging of Bound Water in Cortical Bone
Shihong Li1,2, Michael Carl3, Eric Chang1, Won C. Bae1, Christine Chung1, Graeme M. Bydder4, and Jiang Du1
1Radiology, University of California, San Diego, San Diego, CA, United States, 2Huadong Hospital, Fudan University, Shanghai, China, 3Global Applied Science Laboratory, GE Healthcare, San Diego, CA, United States, 4Radiology, University of California San Diego, San Diego, CA, United States

Bone is a composite material consisting of mineral, organic matrix and water. There is mounting evidence showing that there are age and disease related changes to the organic matrix. However, there are no techniques available for direct imaging of the organic matrix in vivo. Magnetic resonance imaging (MRI) has been employed to indirectly evaluate the organic matrix via direct imaging of water bound to collagen in cortical bone. In this study we investigated the adiabatic inversion recovery prepared ultrashort echo time (IR-UTE) sequence to evaluate bone water bound to the organic matrix.

16:36 0764.   
SWIFT with Magnetization Preparation: Signal Partitioning and 3D Measurement of Adiabatic T1rho in Osteochondral Specimen -permission withheld
Jinjin Zhang1,2, Mikko J. Nissi1,2, Djaudat Idiyatullin1, Shalom Michaeli1, Michael Garwood1, and Jutta Maria Ellermann1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States, 2Department of Orthopedic Surgery, University of Minnesota, Minneapolis, Minnesota, United States

SWIFT is an emerging technique that allows imaging of almost all biological objects including tissues having ultrashort T2 relaxation times (down to a few µs). Besides nearly pure proton density weighted contrast, SWIFT can provide other types of contrasts, including T1, T2, T1rho, and T2rho by utilizing magnetization preparation blocks. In the present work we describe the theory and experimental setup to generate T1rho contrast in MP-SWIFT images and demonstrate T1rho quantification in osteochondral specimens. Additionally, the same concept of magnetization preparation is utilized to separate the different spin pools in an osteochondral specimen (fast relaxing spins and slow relaxing fatty or non-fat tissue).

16:48 0765.   Off-Resonant Reconstruction of Balanced 3D-Radial Acquisitions with Half-Echo Sampling for Unique Cell Tracking Contrast
Clemens Diwoky1, Daniel Gungl2, Andreas Reinisch2, Nicole Anette Hofmann2, Dirk Strunk2, and Rudolf Stollberger1
1Institute of Medical Engineering, Graz University of Technology, Graz, Austria, 2Stem Cell Research Unit, Dept. of Hematology, Univ. Clinic of Internal Medicine, Medical University of Graz, Graz, Austria

Within this work, SPIO labelled cells are given a unique contrast feature in order to enhance their detectability. Our approach is based on a motion-insensitive 3D radial balanced SSFP acquisition with half-echo sampling and a simple post-processing step. Adding a frequency shift to each half-echo before reconstruction, a unique ring-shaped contrast around voxels containing a strong magnetic perturber (e.q. a single labeled cell) is produced. In-vitro and in-vivo images as well as a full intra-voxel signal simulation are presented to show this unique contrast.

17:00 0766.   Off-Resonance Saturation Enhanced Phase Contrast of the Brain at Ultra-Short TE
Chunlei Liu1,2, Wei Li1, and Peder Larson3
1Brain Imaging and Analysis Center, Duke University, Durham, NC, United States, 2Department of Radiology, Duke University, Durham, NC, United States, 3Radiology and Biomedical Imaging, UCSF School of Medicine, San Francisco, CA, United States

Susceptibility contrast of the brain is generally obtained at long echo times. At such long TE, the short-T2 components are largely attenuated and contribute minimally to phase contrast. We show that strong phase contrast of the brain can be generated at ultra-short TE (64 micro seconds) by off-resonance saturation. Our data suggest that the saturated short-T2 components of white matter have negative frequency shift. Off-resonance saturation together with UTE offers a new way to generate phase contrast and to probe tissue microstructure. UTE provides the advantage of high efficiency, high SNR and minimal susceptibility-induced distortion while saturation enhances contrast.

17:12 0767.   Decoupling of Tx/Rx Coils Using a Tx-Array System: Application to UTE and CEA
Ali Caglar Ozen1,2 and Ergin Atalar1,2
1Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, 2National Magnetic Resonance Research Center (UMRAM), Ankara, Turkey

A novel method for decoupling that provides over 80dB isolation between receive and transmit coils is developed. Transmit array technology is utilized to cancel the individual B1 induced currents in the receive coil by adjusting relative amplitudes and phases of transmit array elements. As an application of this method, MRI with concurrent excitation and acquisition (CEA), where MR signal is acquired during RF excitation, is implemented and spectroscopy and frequency-swept imaging techniques are demonstrated. CEA enable observation of spin characteristics during RF excitation as well as zero-TE. Preliminary results are represented for spectroscopy and imaging of ultra-short T2 samples.

17:24 0768.   Comparison of Sequences for MR-Based Cortical Bone Imaging and Tissue Classification in the Pelvis at 3.0T with Subsequent Generation of Electron Density Maps and Digitally Reconstructed Radiographs
Michael Helle1, Christian Stehning1, Melanie S. Traughber2, Nicole Schadewaldt1, Heinrich Schulz1, Steffen Renisch1, and Stefanie Remmele3
1Philips Research Laboratories, Hamburg, Germany, 2Philips Healthcare, Cleveland, Ohio, United States, 3Hochschule Landshut (FH), Landshut, Germany

Emerging MRI applications, e.g. radiation therapy planning, benefit from superior display of tissue contrast and the delineation of tumor and critical organs. However, utilizing MRI for standalone radiation therapy simulation would require the generation of electron density (ED) maps and segmentation of cortical bone for the creation of digitally reconstructed radiographs (DRRs). In this study, we introduce a new approach based on a Cartesian T1-Dixon acquisition for tissue classification and cortical bone imaging to generate ED maps and DRRs of the pelvis at 3.0T. Results of a Cartesian T1-Dixon acquisition are compared qualitatively with a combined UTE-multi-echo Dixon sequence.

17:36 0769.   
Rapid Acquisition of PET Attenuation Maps from Highly Undersampled UTE Images Using Sparse-SENSE Reconstruction
Andrew Peter Aitken1, Christoph Kolbitsch1, Tobias Schaeffter1, and Claudia Prieto1
1Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom

Attenuation correction (AC) maps that accurately depict bone are required for precise PET reconstruction. Segmented AC maps can be obtained from ultrashort echo time (UTE) MR imaging. However, the clinical use of high resolution UTE in simultaneous PET/MR is limited by the long scan time (>7 minutes for the head). We show, in prospectively undersampled acquisitions, that compressed sensing combined with parallel imaging can be used to reduce the scan time to less than one minute, while retaining accurate AC-maps with respect to those produced from fully sampled data.

17:48 0770.   On the Reproducibility of MR-Based PET Attenuation Correction Using a Probabilistic Atlas-Based Method -permission withheld
Kevin T. Chen1,2, Daniel B. Chonde2,3, and Ciprian Catana4
1Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States, 2Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States,3Biophysics, Harvard University, Boston, MA, United States, 4Massachusetts General Hospital, Charlestown, MA, United States

We have previously implemented an MR-based PET attenuation correction (AC) method using dual-echo ultrashort echo time (DUTE) and morphological MR images to segment the tissue classes most relevant for attenuation correction (i.e. bone, soft tissue and air cavities). Attenuation maps generated from these segmented images were previously demonstrated to agree well with those generated using the “sliver standard” segmented CT method. In this work, the reproducibility of the probabilistic atlas-based method for generating the attenuation maps was studied by comparing the maps obtained from the MR data acquired in nine subjects at three time points.