Advanced Sequences & Techniques
Tuesday 21 April 2009
Room 313BC 10:30-12:30

Moderators:

 Sonia Nielles-Vallespin and Klaus Scheffler
 
10:30  251. Young Investigator Award Finalist:  B0 and B1 Correction Using the Inherent Degrees of Freedom of a Multi-Channel Transmit Array
    Jeremiah Aaron Heilman1, Jamal J. Derakhshan1, Matthew J. Riffe1, Natalia Gudino1, Jean Tkach1, Christopher A. Flask1, Jeffrey L. Duerk1, Mark A. Griswold1
1Case Western Reserve University, Cleveland, OH, USA
    We present methods that capitalize on the inherent degrees of freedom in a mutli-channel transmission array to correct the effects of B0 and B1 variations within the context standard slice selective and chemically selective pulses. A new method called Parallel excitAtion for B-field insensitive fat Saturation preparaTion (PABST) utilizes the frequency and amplitude freedom to improve uniformity and efficacy of CHESS pulse fat saturation in the presence of off-resonance without increasing the length of the pulse or requiring iterative optimization. A similar technique, utilizing phase and amplitude freedoms to tailor the axis of rotation across the FOV, can correct for off-resonance effects in TrueFISP and potentially eliminate banding.
     
10:50 252. Sampling Strategies for MRI with Simultaneous Excitation and Acquisition
    Markus Weiger1, Klaas Paul Pruessmann2, Martin Tabbert3, Franek Hennel4
1Bruker BioSpin AG, Faellanden, Switzerland; 2Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; 3Bruker BioSpin MRI GmbH, Ettlingen, Germany; 4Bruker BioSpin MRI GmbH, Germany
    The concept of simultaneous excitation and acquisition (SEA) introduced with the SWIFT technique enables MRI of samples with very short T2 also under B1 constraints. Within this framework we suggest a number of improved sampling strategies, addressing reconstruction stability, SNR, and artefacts related to pulse errors. High-quality SEA images of short-T2 samples acquired at a bandwidth of 100 kHz are presented.
   

 
11:02 253. A New Short TE 3D Radial Sampling Sequence: SWIFT-LiTE
    Jang-Yeon Park1, Steen Moeller1, Ryan Chamberlain1, Michael Garwood1
1Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, USA
    UTE imaging and SWIFT are techniques for imaging hard tissues with short T2 relaxation times on the order of a few tens to hundreds of microseconds. However, implementation of UTE and SWIFT on clinical MRI systems can be challenging due to unique hardware requirements. In some cases, achieving short TE < 1 ms (not ultrashort TE) is all that is required. This can be relatively easily accomplished with the new sequence introduced here, which is called SWIFT-LiTE (SWIFT with Limited TE). SWIFT-LiTE is a 3D radial sampling sequence and can effectively cover the short TE range of > ~0.5 ms.
     
11:14 254. A Low Power Imaging Alternative to BSSFP
    Walter R.T. Witschey1, Ari Borthakur2, Mark Elliott2, Erin Leigh McArdle2, Ravinder Reddy2
1Biochemistry and Molecular Biophysics, University of Pennsylvania, Philadelphia, PA, USA; 2Radiology, University of Pennsylvania, Philadelphia, PA, USA
   

Spin locked steady-state free precession (slSSFP) is shown to maintain a balanced gradient echo steady-state with significantly lower power than a bSSFP acquisition with similar contrast. The independence of locking power on the observable contrast is shown for MnCl2 doped samples in the motional narrowing regime. slSSFP was shown to mimic bSSFP contrast in knee tissues but the dependence on low frequency relaxation dispersion remains to be explored.
     
11:26 255. Spin Locked Steady-State Free Precession Imaging
    Walter R.T. Witschey1, Ari Borthakur2, Mark Elliott2, Abram Voorhees3, Ravinder Reddy2
1Biochemistry and Molecular Biophysics, University of Pennsylvania, Philadelphia, PA, USA; 2Radiology, University of Pennsylvania, Philadelphia, PA, USA; 3Siemens Medical Solutions USA, Inc., Malvern, PA, USA
    A high SNR efficiency, fast imaging technique is described which makes use of spin locking pulses interleaved with short periods for data acquisition. The technique was implemented at low flip angle to obtain high resolution T2-weighted images at 7T and the resulting steady-state was shown to be nearly identical to bSSFP over a wide range of relaxation times.
     
11:38 256. Sodium-MRI Using a Density Adapted 3D Radial Acquistion Technique
   

Armin Michael Nagel1, Frederik Bernd Laun1, Marc-André Weber2, Christian Matthies1, Wolfhard Semmler1, Lothar Rudi Schad3
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany; 2Department of Diagnostic and Interventional Radiology, University Hospital Heidelberg, Heidelberg, Germany; 3Computer Assisted Clinical Medicine, University Heidelberg, Mannheim, Germany
    A density adapted 3D radial projection reconstruction pulse sequence (DA-3DPR) is presented that provides a more efficient k-space sampling than conventional 3D projection reconstruction sequences (3DPR). The gradients of the DA-3DPR sequence are designed such that the averaged sampling density in each spherical shell of k-space is constant. Benefits for low SNR applications are demonstrated with the example of sodium imaging. In simulations of the point-spread function, the SNR is increased by the factor 1.66. Using analytical and experimental phantoms, it is shown that the DA-3DPR sequence allows higher resolutions and is more robust in the presence of B0-inhomogeneities.
     
11:50 257. 3D Dynamic MRSI for Hyperpolarized 13C with Compressed Sensing and Multiband Excitation Pulses
   

Peder E. Z. Larson1, Simon Hu1, Michael Lustig2, Adam B. Kerr2, Sarah J. Nelson1, John Kurhanewicz1, John M. Pauly2, Daniel B. Vigneron1
1Radiology and Biomedical Imaging, University of California - San Francisco, San Francisco, CA, USA; 2Electrical Engineering, Stanford University, Stanford, CA, USA
    We have developed and applied a compressed sensing acquisition and reconstruction scheme for repeated accelerated acquisitions for 3D dynamic time-resolved MRSI for hyperpolarized carbon-13 studies. This sequence also uses multiband RF excitation pulses to efficiently utilize the hyperpolarized magnetization. The compressed sensing exploits the spectral sparsity and temporal redundancy while the multiband pulses take advantage of the different metabolite concentrations in order to obtain dynamic serial 3D MRSI with a time resolution of 5 s over 50 seconds after injection of hyperpolarized [1-13C]-pyruvate.
     
12:02 258. Accelerated Slice-Encoding for Metal Artifact Correction
    Brian A. Hargreaves1, Wenmiao Lu2, Weitian Chen3, Garry E. Gold1, Anja C. Brau3, John M. Pauly4, Kim Butts Pauly1
1Radiology, Stanford University, Stanford, CA, USA; 2Electrical & Electronic Engineering, Nanyang Technological University, Singapore, Singapore; 3Applied Science Lab, GE Healthcare, Menlo Park, CA, USA; 4Electrical Engineering, Stanford University, Stanford, CA, USA
    Techniques have recently been proposed to correct the susceptibility-induced distortions in MR images near metallic implants. The slice-encoding for metal artifact correction (SEMAC) method applies additional slice encoding, which almost completely corrects in-plane and through-plane distortions at a cost of additional scan time. Here we show that with a linear reconstruction SEMAC imaging can be performed with spin echo trains and both parallel imaging and partial Fourier imaging to provide flexible contrast in reasonable scan times.
     
12:14 259. MR Imaging at Sub-Millisecond Frame Rates
    Steven M. Wright1,2, Mary P. McDougall1,2
1Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA; 2Biomedical Engineering, Texas A&M University, College Station, TX, USA
   

Spatial encoding using radiofrequency coils can provide extremely fast imaging speeds as the localization is not the result of a time integral of a gradient pulse. In this abstract the combination of Single Echo Acquisition (SEA) imaging and an echo-planar readout is demonstrated, resulting in 64 x 64 images obtained at frame rates exceeding 1000 images per second. Applications being investigated include imaging of extremely rapid flow, and the monitoring of the evolution of transverse magnetization during 2D RF pulses generated with EPI gradient trajectories by modifying the pulse sequence to enable a single image during the flyback period.