Traditional Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
Compressed Sensing & Receive Arrays

Tuesday May 10th
Exhibition Hall  13:30 - 15:30

2857.   Array Compression for 3D Cartesian Sampling  
Tao Zhang1, Michael Lustig1,2, Shreyas Vasanawala3, and John Pauly1
1Electrical Engineering, Stanford University, Stanford, CA, United States, 2Electrical Engineering and Computer Science, University of California Berkeley, Berkeley, CA, United States, 3Radiology, Stanford University, Stanford, CA, United States

Array compression is a technique to reduce data size and reconstruction computation for large coil arrays. In this work, a data-driven array compression for 3D Cartesian sampling is proposed. A slice-by-slice array compression method with autocalibrating parallel reconstruction using 3D synthesis kernels is designed. Faster reconstruction and similar image quality is achieved compared with reconstruction results using the original large arrays.

2858.   k-Space Channel Combination for Non-Cartesian Acquisitions Using Direct Virtual Coil (DVC) Calibration 
Philip James Beatty1, Atsushi Takahashi2, Kevin M Johnson3, and Jean H Brittain4
1Global Applied Science Laboratory, GE Healthcare, Thornhill, Ontario, Canada, 2Global Applied Science Laboratory, GE Healthcare, Menlo Park, California, United States, 3Medical Physics, University of Wisconsin - Madison, Madison, Wisconsin, United States, 4Global Applied Science Laboratory, GE Healthcare, Madison, Wisconsin, United States

k-Space channel combination for multi-channel acquisitions promises to reduce reconstruction latency by combining data across channels during data acquisition and reducing the number of Fourier transforms required for data reconstruction. In this work, a method is proposed that enables k-space channel combination for non-Cartesian acquisitions. The proposed approach combines Direct Virtual Coil (DVC) channel combination calibration with conventional convolution gridding. Image quality is evaluated using radial and spiral data sets.

2859.   Compressed Sensing with Compressed Channels 
Feng Huang1, Wei Lin1, George Randy Duensing1, and Arne Reykowski1
1Invivo Corporation, Gainesville, Florida, United States

In MRI, imaging using receiving coil arrays with a large number of elements is an area of growing interest. With increasing channel numbers, longer reconstruction times have become a significant concern. Channel compression has been proposed to reduce the processing time. However, channel compression technique has to balance speed and preservation of signal. In this work, a novel technique using relative sensitivity maps is proposed for faster channel-by-channel compressed sensing. The proposed method is much faster than conventional channel compression technique, and preserves the signal significantly better.

2860.   GRAPPA Operator Enhanced Initialization for Improved Multi-channel Compressed Sensing 
Feng Huang1, Wei Lin1, George Randy Duensing1, and Arne Reykowski1
1Invivo Corporation, Gainesville, Florida, United States

The combination of partially parallel imaging (PPI) and compressed sensing has shown great potential for fast imaging. Fourier transform of the partially acquired data is conventionally used as the initialization of the iterative reconstruction algorithm. A good initialization is crucial for the convergence speed and accuracy of iterative algorithms. In this work, it is proposed to use GRAPPA operator to efficiently generate initialization for multi-channel compressed sensing. Using self-feeding Sparse SENSE as a specific example of multi-channel compressed sensing algorithm, experimental results show the advantages of the proposed method over conventional scheme.

2861.   SpRING: Sparse Reconstruction of Images using the Nullspace method and GRAPPA 
Daniel Stuart Weller1, Jonathan R Polimeni2,3, Leo Grady4, Lawrence L Wald2,3, Elfar Adalsteinsson1, and Vivek Goyal1
1EECS, Massachusetts Institute of Technology, Cambridge, MA, United States, 2A. A. Martinos Center, Dept. of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 3Dept. of Radiology, Harvard Medical School, Boston, MA, United States, 4Dept. of Image Analytics and Informatics, Siemens Corporate Research, Princeton, NJ, United States

SpRING combines compressed sensing (CS) with GRAPPA to recover a sparse image from multi-channel, undersampled k-space data. The combined method operates in the nullspace of the observation matrix, holding the acquired data fixed without resorting to complicated procedures for constrained optimization. Whereas GRAPPA amplifies the noise present in the image and CS over-smoothes non-sparse details, the combined method strikes a balance to improve SNR and preserve details. We analyze the noise amplification properties of the combined algorithm using g-factors computed using Monte Carlo trials to illustrate its superiority over GRAPPA and CS alone for real data.

2862.   A Method to Combine Compressed Sensing with Auto-Calibrating Parallel Imaging Reconstruction for Cartesian Acquisition 
Kang Wang1, Philip Beatty2, James Holmes2, Reed Busse2, Jean Brittain2, and Frank Korosec1
1Medical Physics, University of Wisconsin-Madison, Madison, WI, United States, 2Global Applied Science Laboratory, GE Healthcare

This abstract presents a framework that combines compressed sensing (CS) with auto-calibration parallel imaging (acPI) reconstruction for undersampled Cartesian acquisition. In data acquisition, a two-step undersampling scheme is used. For reconstruction, an acPI method is integrated into the CS L1 norm minimization process, such that both the coherent and incoherent aliasing artifacts associated with the undersampling can be suppressed in the iteration. The feasibility of the new method was validated using 3D contrast-enhanced peripheral MR angiography data sets

2863.   Impact of Coil-Neighbors of Target points in Autocalibration of ESPIRiT 
Anja Brau1, Peng Lai1, Srihari Narasimhan2, Babu Narayanan3, and Vijaya Saradhi2
1Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States, 2Computing & Decision Sciences Lab, GE Global Research, Bangalore, India, 3Medical Image Analysis Lab, GE Global Research, Bangalore, India

As part of the calibration step for Compressed Sensing & Parallel Imaging algorithms like ESPIRiT and L1-SPIRiT, computation of kernel weights involves obtaining a least squares fit for predicting target points in the calibration region using a set of source points in their neighborhood, separately for each coil. If we do not use the coil neighbors of the target location, the linear system needs to be solved only once. We observe that using this approach, we get significant computational benefit and still obtain similar image quality for high channel count reconstructions.

2864.   CS-SENSE Reconstruction Using a Two-level Variable Density Sampling Pattern 
Mariya Doneva1,2, Peter Börnert1, and Alfred Mertins2
1Philips Research Europe, Hamburg, Germany, 2University of Luebeck, Luebeck, Germany

The synthesis of CS and parallel imaging is of consierable interest. Several works have proposed a combination of SENSE and CS as an iterative sparsity constrained SENSE reconstruction. Typically a variable density pseudo-random sampling is used as a compromise between regular and irregular sampling. Based on the properties of CS and SENSE, we propose a two-step CS-SENSE reconstruction, in which the two reconstruction steps are used to recover distinct parts of k-space and apply a two-level variable density sampling pattern.

2865.   Single-signal Based Parallel Imaging Using Compressed Sensing 
satoshi Ito1, Hirotoshi Arai1, and Yoshifumi Yamada1
1Research Division of Intelligence and Information Sciencs, Utsunomiya University, Utsunomiya, Tochigi, Japan

In this paper, we propose a novel image reconstruction method in which CS and PI are executed using only single set of signal. Since the distribution of PSFT signal strongly reflects the distribution of the object, the application of a weighting function to the PSFT signals has a similar effect as the application of the weighting function to the object. Therefore SENSE reconstruction using a single signal is feasible by producing another folded image having another weighting function. Here, we propose a new imaging method which combine CS and PI using single signal to achieve higher reduction factor.

2866.   Parallel Compressed Sensing MRI Using Reweighted L1 Minimization 
Ching-hua Chang1, and Jim Ji1
1Texas A&M University, College Station, Texas, United States

The combination of Compressed Sensing (CS) with multiple receiver coils has drawn great attentions because of their potentials to significantly reduce acquisition time in MRI. The former emerged by exploring the sparsity of MR images, and the latter can reduce scan time by resorting to parallel MRI (pMRI). CS can be used as regularization method and is integrated to take advantages of the sensitivity information from multiple receiver coils. In this abstract, we propose to use a reweighted nonlinear conjugate gradient L1 minimization method to enhance the reconstruction of parallel CS-MRI.

Traditional Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
Reconstruction in Parallel Imaging

Wednesday May 11th
Exhibition Hall  13:30 - 15:30

2867.   Scalable anti-aliasing image reconstruction in the presence of a quadratic “phase-scrambling” gradient using the fractional Fourier transform 
Jason Peter Stockmann1, Gigi Galiana2, Vicente Parot3,4, Leo Tam1, and Robert Todd Constable2
1Biomedical Engineering, Yale University, New Haven, CT, United States, 2Diagnostic Radiology, Yale University, New Haven, CT, United States, 3Biomedical Imaging Center, Pontificia Universidad Católica de Chile, Santiago, Chile, 4Department of Electrical Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile

Scalable image reconstruction from phase-scrambled data has previously been performed by expressing the signal equation as a Fresnel transform, which has the form of a chirp convolution. Scaling is achieved by varying the frequency of the chirp kernel that is multiplied by and deconvolved with the data. This approach has the form of a fractional Fourier transform (FrFT) but has not been previously described as such in the MR community. In this work, the relationship between the Fresnel transform and the FrFT is elucidated. The FrFT is then used to reconstruct alias-free scalable images from undersampled data that have been phase-scrambled using a powerful Z2 gradient coil.

2868.   Fast Image Reconstruction for Generalized Projection Imaging 
Gerrit Schultz1, Daniel Gallichan1, Marco Reisert1, Maxim Zaitsev1, and Jürgen Hennig1
1University Medical Center Freiburg, Freiburg, Germany

Recent approaches in signal localization rely on encoding with strongly nonlinear and even ambiguous field geometries. When more than two encoding fields are involved, image reconstruction becomes highly time-consuming because the encoding matrix does in general not have a sparse structure. However, for a large class of sampling trajectories, the imaging process can intuitively be interpreted as “sparse” image projections. In this abstract, we show that the finite duration of the acquisitions destroys the sparsity. However, with some loss of resolution along frequency-encoding the encoding matrix can be sparsified, which speeds up the reconstruction by up to two orders of magnitude.

2869.   Fast image reconstruction in the presence of dynamic higher-order fields 
Bertram Jakob Wilm1, Christoph Barmet1, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Zurich, Switzerland

MRI in the presence of higher-order fields poses a complex reconstruction problem. An accelerated algebraic reconstruction approach is proposed by expanding the higher-order field terms into a weighted sum of optimized basis functions. Thereby image reconstruction can be performed by utilizing the computational efficiency of Fast Fourier Transforms. Acceleration by orders of magnitude is achieved with a minimal loss in computational accuracy.

2870.   Combination of arbitrary gradient encoding fields using SPACE RIP for reconstruction (COGNAC) 
Jakob Assländer1,2, Martin Blaimer2, Felix A Breuer2, Maxim Zaitsev1, and Peter M Jakob2,3
1Medical Physics, Department of Diagnostic Radiology, University Medical Center Freiburg, Freiburg, Germany, 2Research Center Magnetic Resonance Bavaria (MRB), Würzburg, Germany,3Department of Experimental Physics 5, University of Würzburg, Würzburg, Germany

COGNAC is a reconstruction method that allows encoding with arbitrary gradient fields. In this work a non-linear, radially symmetric gradient is used for frequency encoding, projecting the object onto concentric rings. For encoding the angular direction, conventional gradients were used in addition to the spatial information of the receiver coil array. Reconstruction is done with SPACE RIP, where an encoding matrix describes both, coil sensitivity profiles and phase encoding. This gives one the freedom to adjust sampling strategies to better complement the geometry of receiving coils and use non-linear gradients for reduction of peripheral nerve stimulations.

2871.   Accelerating Parallel Acquisition Reconstruction with Sparse Matrix Transformations 
Josh M Speciale1, Charles A Bouman1, and Thomas M Talavage1,2
1School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, United States, 2Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States

Parallel imaging approaches are effective at reducing scan acquisition time. However, increasing numbers of receive coils and higher acquisition acceleration factors add to the complexity of reconstructing acquired images. Our intent is to determine if complexity of image reconstruction can be reduced using sparse representations of the matrices involved without sacrificing image quality. The sparse matrix transform (SMT) approach to approximating the singular value decomposition of the SENSE unfolding matrix enables it to be represented by a series of sparse rotation matrices. This reduces the number of multiplies in the unfolding process, reducing reconstruction complexity and time.

2872.   Data Driven Reconstruction of Inconsistent K-Space Data 
Kevin Michael Johnson1, Walter F Block1,2, Scott B Reeder1,3, and Alexey Samsonov1,3
1Medical Physics, University of Wisconsin - Madison, Madison, WI, United States, 2Biomedical Engineering, University of Wisconsin - Madison, 3Radiology, University of Wisconsin - Madison

Artifacts in MR often arise from data inconsistency; however, existing solutions to handle inconsistent data are often not robust, ineffective or incompatible for many applications. In this work, formulate image reconstruction to include data inconsistency from both stochastic noise and systematic bias. With k-space data inconsistencies estimated from the repetitive sampling of the center of k-space of a radial trajectory, we demonstrate improved image quality and improved noise performance in both a digital phantom and in-vivo for fast spin echo applications.

2873.   An Augmented Lagrangian Method for Regularized MRI Reconstruction Using SENSE 
Sathish Ramani1, and Jeffrey A Fessler1
1EECS Department, University of Michigan, Ann Arbor, Michigan, United States

Based on the augmented Lagrangian (AL) formalism, we present a new method for MR image reconstruction from undersampled sensitivity encoded data using a combination of total-variation and l1-regularization. We introduce a set of constraint variables and convert the original unconstrained reconstruction problem into an equivalent constrained task. We then construct an AL function (that includes a Lagrange multiplier term and a penalty term) and iteratively minimize it (while taking care to update the Lagrange multiplier) by applying an alternating scheme that decouples the minimization process with respect to the constraint variables, leading to a simple (AL) algorithm. Numerical experiments with real MR data illustrate that the proposed AL algorithm converges faster than both general-purpose optimization methods such as the nonlinear conjugate gradient (NCG) algorithm and state-of-the-art MFISTA.

2874.   Iterative and joint reconstruction from calibration and image data for parallel imaging 
Yu Li1, and Charles L. Dumoulin1
1Radiology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, United States

The presented work introduces a new approach to reconstructing images iteratively and jointly from calibration and acquired image data in parallel imaging for accelerating MRI. Unlike a conventional parallel imaging technique that seeks a reconstruction solution "unidirectionally" from calibration to real image data, the new technique optimizes the reconstruction "bidirectionally" between low resolution/fully sampled calibration data and high resolution/undersampled real image data. This iterative and joint reconstruction offers high image quality when acquired data, including both calibration and image data, are not sufficient for a conventional reconstruction technique, thereby improving parallel imaging performance.

2875.   Highly accelerated myocardial perfusion MRI using k-t SLR with parallel imaging 
Sajan Goud Lingala1, Yue Hu2, Edward Dibella3, and Mathews Jacob1
1Biomedical Engineering, University of Rochester, Rochester, NY, United States, 2Electrical and Computer Engineering, University of Rochester, Rochester, NY, United States, 3Radiology, University of Utah, Salt Lake city, UT, United States

We consider the problem of minimizing the trade-offs between the image parameters (spatio-temporal resolution, volume coverage and the SNR) routinely observed in myocardial perfusion MRI. In this context, we propose to use our accelerated k-t SLR scheme (which exploits the low rank and sparsity properties of the dynamic data) in combination with parallel imaging. Experimental results and comparisons show that, our proposed scheme provide superior reconstructions with better fidelity at high accelerations (>10), while existing schemes such as k-t PCA, k-t FOCUSS and TV based spatio-temporal regularizers have limitations characteristic to their method of operation

2876.   Accelerated Variable Density Spiral at 7 Tesla using Parallel Imaging 
Peter Börnert1,2, Wei Lin3, Feng Huang3, Tim Nielsen1, Andrew Webb2, and Matthias JP van Osch2
1Philips Research Laboratories, Hamburg, Germany, 2Department of Radiology, C.J. Gorter Center for high field MRI, Leiden University Medical Center, Leiden, Netherlands, 3Philips Healthcare, Invivo Corporation, Gainesville, United States

Spiral imaging is a very efficient and versatile MR sampling that can find interesting applications at 7T. But the spiral is sensitive to off-resonance effects, a problem especially present at high fields, resulting in a loss of spatial resolution. Parallel imaging could help to reduce such off-resonance artifacts by shortening the acquisition window. In this work, a rapid, non-iterative k-space-based parallel imaging reconstruction method is proposed. It estimates the missing k-space data and allows after appropriate image combination off-resonance correction in a very efficient way. This approach was successfully tested at 7T in vivo applications resulting in improved image quality.

Traditional Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
Parallel Imaging
Thursday May 12th
Exhibition Hall  13:30 - 15:30

2877.   Flexible Virtual Coils (FVC) for Faster Channel-by-Channel Partially Parallel Imaging 
Feng Huang1, Wei Lin1, George Randy Duensing1, and Arne Reykowski1
1Invivo Corporation, Gainesville, Florida, United States

In MRI, imaging using receiving coil arrays with a large number of elements is an area of growing interest. With increasing channel numbers for parallel acquisition, longer reconstruction times have become a significant concern. Channel compression, direct virtual coil (DVC) and synthetic coil (ST) have been proposed to reduce the processing time of channel-by-channel partially parallel imaging (PPI) techniques [4]. In this work, a technique called flexible virtual coils (FVC) is proposed to enable faster and more accurate reconstruction than these existing techniques.

2878.   Impact of Direct Virtual Coil Channel Combination on Reduced Field-of-View Artifacts 
Philip James Beatty1, James H Holmes2, Scott B Reeder3, and Jean H Brittain2
1Global Applied Science Laboratory, GE Healthcare, Thornhill, Ontario, Canada, 2Global Applied Science Laboratory, GE Healthcare, Madison, Wisconsin, United States, 3Departments of Radiology and Medical Physics, University of Wisconsin - Madison, Madison, Wisconsin, United States

Combining parallel imaging with reduced field-of-view acquisitions is challenging since such acquisitions violate underlying assumptions of many parallel imaging reconstruction methods. Direct Virtual Coil (DVC) parallel imaging is a data-driven technique that delivers similar image quality to coil-by-coil approaches, such as GRAPPA, while reducing memory and compute requirements by over 10X for high channel count coil arrays. This work compares images reconstructed with DVC channel combination and sum-of-squares (SoS) channel combination, revealing subtle differences within the wrapped region.

2879.   Combination of Partial k-Space and Direct Virtual Coil Parallel Imaging 
Philip James Beatty1, Ananth Madhuranthakam2, Shaorong Chang3, Ersin Bayram3, and Jean H Brittain4
1Global Applied Science Laboratory, GE Healthcare, Thornhill, Ontario, Canada, 2Global Applied Science Laboratory, GE Healthcare, Boston, Massachusetts, United States, 3GE Healthcare, Madison, Wisconsin, United States, 4Global Applied Science Laboratory, GE Healthcare, Madison, Wisconsin, United States

Partial k-space acquisition is an important technique to reduce scan time or shorten echo time and is often used together with parallel imaging. In this work, we combine a partial k-space acquisition with the Direct Virtual Coil (DVC) parallel imaging reconstruction method. In vivo imaging results compare coil-by-coil reconstruction results to DVC.

2880.   Phase-Constrained Synthetic Target Algorithm for Non-Cartesian Parallel Image Reconstruction 
Meihan Wang1, Weitian Chen2, Micheal Lustig3, Peng Hu4, Michael Salerno5, Christopher Kramer5, and Craig Meyer1
1Biomedical Engineering, University of Virginia, Charlottesville, VA, United States, 2GE Healthcare, 3UC Berkeley, 4University of California, Los Angeles, 5University of Virginia

Synthetic Target (ST) is a rapid self-calibrated parallel reconstruction method. The original ST works well for spiral and Cartesians, yet suffers from aliasing for radial trajectories. In this abstract, we improved our original Synthetic Target algorithm by adding a phase constraint in the training process. The resultant images have higher SNR than the original ST for radial trajectories. We also compared our method with another iterative parallel reconstruction algorithm in terms of image quality and computation time.

2881.   An Augmented Lagrangian Method for MR Coil Sensitivity Estimation 
Michael John Allison1, and Jeffrey A Fessler1
1Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, Michigan, United States

Accurate coil sensitivity estimates are required to avoid artifacts in many parallel imaging techniques. Existing regularized methods provide sufficiently accurate estimates, but often at a high computational cost. We propose an iterative technique that uses Augmented Lagrangian principles to efficiently compute sensitivity estimates. Our method generated sensitivity estimates for a challenging breast phantom dataset in half the time required by a conjugate gradient algorithm. We therefore conclude that our AL approach provides an efficient strategy for accurately estimating coil sensitivities.

2882.   Improved parallel imaging with GRAPPA with large virtual coils arrays for time-resolved applications 
Simon Bauer1, Bernd Andre Jung1, Alexey A Samsonov2, Matthias Honal1, and Michael Markl1
1Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Department of Radiology, University of Wisconsin, Madison, Wisconsin, United States

Parallel imaging is based on the measurement of the MR signal with multiple receiver coils, where each coil modulates the signal with its sensitivity profile. The motion of an object can also be seen as a modulation of the object. Therefore, a time resolved measurement of a moving object can be considered as an acquisition with multiple (virtual) receiver coils along the temporal dimension. In this work we used a phantom and an in-vivo measurement to compare GRAPPA to a parallel imaging reconstruction which uses a combined virtual coil array consisting of the coil array and all time frames.

2883.   Iterative parallel imaging reconstruction of time-resolved data using 3D variational regularization 
Florian Knoll1, Kristian Bredies2, and Rudolf Stollberger1
1Institute of Medical Engineering, Graz University of Technology, Graz, Austria, 2Institute for Mathematics and Scientific Computing, University of Graz, Graz, Austria

Constrained iterative image reconstruction of undersampled data from multiple coils has shown its high potential to deliver images with excellent image quality from highly accelerated measurements. To eliminate aliasing artifacts, regularization methods are facilitated, which introduce a-priori knowledge about the structure of the desired solution. Usually, regularization is applied only in 2D, and data is reconstructed slice by slice. While this approach reduces the size of the problem and therefore the amount of memory that is needed in the computation, it neglects the potential of introducing a-priori information in the third dimension. This work introduces an approach which treats a whole 3D volume of images as a single data set, and also includes 3D regularization. Results are presented for undersampled spiral angiography data from the 2010 ISMRM image reconstruction challenge.

2884.   PILARS: Parallel Imaging with Large ARrays and Sinc-interpolation 
Shuo Feng1, and Jim Ji1
1Texas A&M University, College Station, Texas, United States

Large arrays make it possible to use parallel imaging to significantly accelerate MR imaging speed. However, the need for auto calibration signals (ACS) limits the actual acceleration factors achievable with large arrays. This paper presents a novel method for parallel imaging with large arrays. The method uses Sinc kernels for interpolation that only requires one phase parameter to be estimated. Phantom experiments using a 64-channel system show that the new method provides higher acceleration factors, comparable reconstruction quality, and fast reconstruction speed.

2885.   Automatic Coil Selection for Streaking Artifact Reduction in Radial MRI 
Yiqun Xue1, Jiangsheng Yu1, Hyun Seon Kang1, Sarah Englander1, Mark A Rosen1, and Hee Kwon Song1
1Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States

In radial MRI, streaking artifacts arising from regions of bright signal intensity can contaminate an entire image. The situation is exacerbated in large FOV imaging using coil arrays where the high sensitivities of local coils can detect signal from peripheral regions of the FOV in which gradient field distortions often cause signal intensities to become highly concentrated. In this abstract, we describe an algorithm which can automatically identify those coils whose images contain streaking artifacts and by excluding these coils, we demonstrate marked improvements in image quality.

2886.   Using RF to Create Nonlinear Virtual Coil Profiles 
Gigi Galiana1, Jason Stockmann2, Leo K. Tam2, and Robert Todd Constable1,2
1Diagnostic Radiology, Yale University, New Haven, CT, United States, 2Biomedical Engineering, Yale University, New Haven, CT, United States

Since surface coil profiles are not usually arranged for optimal encoding along the undersampled direction, we address this with a sequence that uses RF excitation to create virtual coil profiles. These virtual coil profiles can be chosen to optimally complement the undersampled data, and previous work showed that encoding with bar-like RF profiles significantly improved the achievable acceleration of Cartesian undersampled data. With the increasing availability of high powered nonlinear gradient sets, other shapes are possible that can better complement the azimuthal arrangement of multichannel coils. Exploiting this flexibility, we present an implementation of ring-like RF profiles (BARings) and the acceleration enhancements they can bring to multichannel radial acquisitions.

2887.   Parallel Imaging Using a 3D Concentric Cylinders Trajectory 
Kie Tae Kwon1, Holden H Wu1,2, Michael Lustig1,3, and Dwight G Nishimura1
1Electrical Engineering, Stanford University, Stanford, CA, United States, 2Cardiovascular Medicine, Stanford University, Stanford, CA, United States, 3Electrical Engineering and Computer Science, University of California at Berkeley, Berkeley, CA, United States

The 3D concentric cylinders trajectory is an efficient and robust trajectory with fewer excitations than a comparable 3DFT trajectory and benign off-resonance effects. In this work, we applied an efficient parallel imaging strategy to 3D concentric cylinders, which decomposes the 3D non-Cartesian parallel imaging reconstruction into a series of 2D Cartesian reconstructions. Combined with the centric-ordered sampling scheme, this trajectory can be used to efficiently capture transient responses in a magnetization-prepared sequence.

2888.   Reconstructing Undersampled Non-Cartesian Data with Calibrationless Parallel Imaging 
Daniel Neumann1, Felix A. Breuer1, Peter M. Jakob2, Gregory Lee3, Mark A. Griswold3, and Nicole Seiberlich3
1Research Center Magnetic Resonance Bavaria (MRB), Würzburg, Germany, 2Dept. of Experimental Physics 5, University of Würzburg, Würzburg, Germany, 3Dept. of Radiology, Case Western Reserve University, Cleveland, Ohio, United States

Non-Cartesian imaging has many known advantages over Cartesian imaging; however, complex parallel imaging techniques are required for such non-standard trajectories. In this work, we first use Calibrationless Parallel Imaging (CPI) to iteratively reconstruct fully-sampled and undersampled variable density spiral data. This method requires no explicit calibration data or coil sensitivity maps and offers robust reconstructions using in-vivo spiral data for acceleration factors up to 4. Our results suggest that CPI with GROG may overcome the problems of reconstructing images from accelerated non-Cartesian measurements using parallel imaging.

2889.   Non-Cartesian Parallel Imaging Reconstruction Using PRUNO-GROG 
Jian Zhang1, and Ajit Shankaranarayanan2
1Global Applied Science Lab, GE HealthCare, Bethesda, MD, United States, 2Global Applied Science Lab, GE HealthCare, Menlo Park, CA, United States

Pseudo-Cartesian GRAPPA in conjunction with GROG (PCG-GROG) is an effective algorithm to reconstruct non-Cartesian parallel imaging data. However, the PCG reconstruction is usually a cumbersome task as different fitting patterns need to be determined point by point. PRUNO is a generalized auto-calibrated reconstruction algorithm, in which local nulling kernels are independent of the acceleration factor and undersampling patterns. We can thus replace the PCG step with PRUNO to bring out a more convenient and accurate algorithm, termed PRUNO-GROG. Promising preliminary results are shown on both phantom and in vivo images.

2890.   Prospects of Parallel ZTE Imaging 
Thomas Oberhammer1, Markus Weiger2,3, Franciszek Hennel3, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, 2Bruker BioSpin AG, Faellanden, Switzerland, 3Bruker BioSpin MRI GmbH, Ettlingen, Germany

ZTE is an MRI technique with 3D radial centre-out encoding and zero echo time, particularly suited for imaging samples with short T2. ZTE data is inherently incomplete in the k-space centre, which can be addressed by algebraic reconstruction, however, possibly entailing noise amplification and correlation. In this work, the principles of parallel imaging are applied for improving the noise behaviour in ZTE imaging. By means of 1D and 2D simulations it is demonstrated, that, beyond the original purpose of accelerated data acquisition, sensitivity encoding is also capable of handling the ZTE-specific problem of incomplete sampling in central k-space.

2891.   Comparing Gridding and Masking in 3D Parallel Reconstruction 
Nicholas Ryan Zwart1, and James Grant Pipe1
1Neuroimaging Research, Barrow Neurological Institute, Phoenix, Arizona, United States

Parallel image reconstruction methods synthesize data to replace undersampled or non-sampled gaps in k-space. The SENSE parallel imaging algorithm is generalized for the reconstruction of non-cartesian k-space trajectories through the use of a gridding step within each iteration. In an effort to reduce the number of computations, a method of masking k-space was introduced as a replacement for this step. This work compares the two techniques.

2892.   Phase constraints for parallel imaging with PEPI 
Kenneth Otho Johnson1, and Craig H Meyer1
1Biomedical Engineering, University of Virginia, Charlottesville, VA, United States

Pretty Easy Parallel Imaging (PEPI) provides a fast framework for non-Cartesian reconstruction of undersampled data. Here a phase constraint is added that helps reduce aliasing artifacts and improve convergence.

2893.   Null Space Imaging with Compressed Sensing for Rapid Parallel Imaging 
Leo K Tam1, Jason P Stockmann1, Gigi Galiana2, and Robert Todd Constable1,2
1Biomedical Engineering, Yale University, New Haven, Connecticut, United States, 2Diagnostic Radiology & Neurosurgery, Yale University, New Haven, Connecticut

Recent advances in accelerating MRI scans include compressed sensing and the utilization of nonlinear magnetic encoding fields. The two methods collect data in a targeted manner and disperse residual aliasing artifacts to make them less apparent. In the current work, a parallel nonlinear magnetic encoding method using first and second order in-plane spherical harmonics, Null Space Imaging (NSI), is combined with a compressed sensing algorithm to reconstruct highly accelerated images with fidelity. The work suggests that compressed sensing and parallel imaging with higher order gradients may be a synergistic approach towards robust reconstructions of accelerated scans.

2894.   Virtually Independent Gaussian Channel Nulling (VIPGen) Image Reconstruction for Functional Magnetic Resonance Inverse Imaging (fMRInI) 
Shr-Tai Liou1, Hsiao-Wen Chung1, Wei-Tang Chang2, Wen-Kai Tsai2, and Fa-Hsuan Lin2,3
1Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, Taiwan, 2Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, Taiwan, 3MGH-HST Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States

Single-shot volumetric MR inverse imaging (InI) can achieve 100 ms temporal resolution and 5-10 mm spatial resolution with the whole head coverage. Different approaches have been proposed to reconstruct InI images with high spatial resolution or high computational efficiency. Here we propose the virtually independent parallel Gaussian channel nulling (VIPGen) reconstruction. The group analysis in our visuomotor experiments shows that VIPGen provides good spatial resolution similar to the sources reconstructed by the eigenspace L1 norm minimization and high statistical values, while the computing time is comparable to the L2 norm minimization.

2895.   Dictionary-Based Sparsification and Reconstruction (DIBSAR) 
Berkay Kanberoglu1, Lina J. Karam1, and David Frakes1,2
1School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ, United States, 2School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ, United States

An alternative method to ABSINTHE (Atlas based sparsification of image and theoretical estimation) is proposed. ABSINTHE achieves sparsification by performing a principle component analysis (PCA) on the aliased undersampled image. Better sparsification can be achieved by using K-SVD. K-SVD provides flexibility of dictionary design parameters which can be important for the image approximation. The proposed method shows that K-SVD is able to reconstruct similar quality images in comparison to the traditional ABSINTHE method while using half the number of basis images required by PCA.

2896.   Image Deformation Based ABSINTHE 
Eric Pierre1,2, Nicole Seiberlich3, Vikas Gulani4, Pierrick Bourgeat2, Olivier Salvado2, and Mark Griswold3
1Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2ICT Centre, CSIRO, Brisbane, QLD, Australia, 3Radiology, Case Western Reserve University, Cleveland, Ohio, United States, 4Radiology, Case Western Reserve University, Cleveland, United States

In order to improve the GRAPPA reconstruction of an undersampled object at high reduction factors, the previously introduced ABSINTHE technique required a large training set of MR signal with matching coil configuration. This study seeks to further increase the effectiveness and applicability of ABSINTHE by allowing the addition of any MR image to the training set regardless of its coil configuration. Furthermore, it introduces key image preprocessing steps which noticeably increase the relevance of each image in the training set. An improved image quality is shown in simulated and in vivo data compared to GRAPPA and the previous ABSINTHE technique.

2897.   Parallel Magnetic Resonance Imaging Reconstruction by Image Editing 
Jun Shen1
1NIMH, Bethesda, Maryland, United States

A new method is introduced here for parallel magnetic resonance imaging reconstruction that is based on the concept of two-step spectral editing in magnetic resonance spectroscopy (MRS). It uses a unitary 2×2 Fourier matrix (1 1;1 -1) for encoding and decoding. Although image editing is performed in the image domain, it does not suffer from the deficiency associated with SENSE when the prescribed field of view in phase-encoding direction is smaller than the region occupied by the object. Instead, the appearance of the aliasing in the reconstructed image is exactly the same as in the unaccelerated image.

Traditional Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
Parallel Transmission & RF Pulse Design

Monday May 9th
Exhibition Hall  14:00 - 16:00

2898.   B1+ inhomogeneity compensation using 3D parallel excitation is enhanced by simultaneous linear and nonlinear gradient encoding 
William A Grissom1, Laura Sacolick1, and Mika W Vogel1
1GE Global Research, Munich, Germany

3D parallel spokes excitation pulses have been proposed for compensating flip angle inhomogeneities induced by inhomogeneous B1+ at high field. While flip angle homogeneity improves with increasing spokes pulse duration and an increasing number of parallel excitation channels, competing desires to limit off-resonance sensitivity and system complexity limit these pulses' effectiveness in practice. We show that nonlinear gradient phase encoding is well-suited to this application and that simultaneous linear and nonlinear phase encoding can significantly improve spokes pulse performance, enabling shorter pulse durations and fewer transmit channels for a desired level of flip angle homogeneity.

2899.   A Spatial-Spectral Pulse Approach for Reduced FOV Excitation Using Second-Order Gradients 
Chao Ma1, Kevin F. King2, Dan Xu2, and Zhi-Pei Liang1
1Electrical and Computer Engineering, University of Illinois, Urbana, Illinois, United States, 2Global Applied Science Lab, General Electric Healthcare, Waukesha, Wisconsin, United States

This paper presents a method to design RF pulses for reduced FOV excitation using second-order gradients and spatial-spectral pulses. By taking advantage of the spatial dependence introduced by the second-order gradients, a thin disk can be excited using a 2D spatial-spectral pulse, i.e. covering 2D excitation k-space instead of 3D excitation k-space in the case of using the first-order gradients. The proposed method was validated using Bloch equation simulation.

2900.   Multi-dimensional refocusing pulses for parallel transmission by optimal control 
Weiran Deng1, Cungeng Yang1, and V. Andrew Stenger1
1Medicine, University of Hawaii John A. Burns School of Medicine, Honolulu, HI, United States

Multi-dimensioanl refocusing RF pulses for parallel transmission are useful for spin-echo imaging at high magnetic fields. The design of such pulses is challenging because it requires a nonlinear approach to "pancake-flip" the spins with different in-plane phases. We designed a refocusing pulse with 2D spiral k-space trajectory for eight transmitters using a two-process optimal control approach that flips the Y-component of spins from the +Y to -Y direction and leaves the X-component intact. The performance of the pulse was demonstrated using Bloch equation simulation.

2901.   Adapted Tx-SENSE excitation to account for inhomogeneous slice refocusing at 7T 
Tomasz Dawid Lindel1,2, Frank Seifert1,2, Martin Dietterle1,2, Thoralf Niendorf2, and Bernd Ittermann1,2
1Physikalisch-Technische Bundesanstalt, Braunschweig und Berlin, Germany, 2Berlin Ultrahigh Field Facility, Max-Delbrück-Centrum für Molekulare Medizin, Berlin, Germany

2D spatial excitation using Tx-SENSE is frequently combined with a conventional, slice selective refocusing pulse to restrict the signal in the third dimension. Severe B1+ inhomogeneities of the refocusing pulse at 7T compromise the resulting image quality even if B1 shimming is applied. We present phantom experiments with adapted Tx-SENSE pulses to address this problem.

2902.   A fast parallel excitation pulse design for efficient selection and ordering of PE locations with B0 field inhomogeneity 
Daehyun Yoon1, Jeffrey A Fessler1, Anna C Gilbert2, and Douglas C Noll3
1Electrical Engineering, University of Michigan, Ann Arbor, MI, United States, 2Mathematics, University of Michigan, Ann Arbor, MI, United States, 3Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States

We present a novel method for selecting and ordering efficient phase encoding(PE) locations in an Echo-Volumar trajectory for parallel excitation considering B0 field inhomogeneity. Recently several parallel excitation algorithms were presented enforcing sparsity on the number of chosen PE locations, but none of them considered off-resonance during excitation. We observed from simulation that this could lead to significant degradation in excitation accuracy where strong off-resonance is present. We developed a fast greedy algorithm to select and order efficient PE locations considering B0 field inhomogeneity, and demonstrate from simulation that our algorithm can significantly improve the excitation accuracy.

2903.   Localized MR-Spectroscopy in Arbitrarily Shaped Voxels Using Parallel Excitation Pulses with Large Spectral Bandwidth 
Peter Ullmann1, Jeff Snyder2, Martin Haas2, Johannes Thomas Schneider1,2, and Wolfgang Ruhm1
1Bruker BioSpin MRI GmbH, Ettlingen, Germany, 2Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany

Spatially-selective excitation (SSE) offers great potential for volume-selective MR-spectroscopy by allowing the excitation of arbitrarily shaped voxels which can be used to mitigate partial-volume effects and to increase SNR. In order to excite arbitrary voxels with high spatial resolution and large spectral bandwidth this study combines segmented SSE pulses with parallel RF transmission which enables significant reduction of the number of segments. Experiments on a 9.4T animal scanner demonstrate that by using segmented parallel excitation pulses complex-shaped voxels can be excited with good spatial selectivity and spectra with broad spectral range and high resolution can be acquired from these voxels.

2904.   Accounting for B1 void using optimized transmit pulses in ultra high field MRI 
Ling Xia1, Tingting Shao1, Minhua Zhu1, Guofa Shou1, Feng Liu2, and Stuart Crozier2
1Department of Biomedical Engineering, Zhejiang University, Hangzhou, China, People's Republic of, 2School of Information Technology & Electrical Engineering, University of Queensland, Brisbane, Australia

This work presents a novel approach to account for the limited coverage of RF energy in ultra high field MRI. Based on the recently developed parallel transmission technology, an optimized 3D tailored RF (TRF) pulse has been proposed to upgrade the RF excitation. The pulse is designed with an adaptive stack-spiral trajectory that is tailored according to the high-weight k-space area, which is most responsible for the desired excitation pattern. An iterative RF pulse design method is employed to ensure the excitation accuracy. Test simulations show that the proposed scheme optimally upgrades the excitation over the whole imaging area which includes deep domain where RF energy can be difficult to penetrate at ultra high field.

2905.   TOF Angiography in the human brain at 7T using 3D Parallel Excitation: Initial results 
Sebastian Schmitter1, Xiaoping Wu1, Edward J Auerbach1, Michael Hamm2, Josef Pfeuffer3, Kamil Ugurbil1, and Pierre-Francois Van de Moortele1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, 2Siemens Healthcare, Charlestown, MA, United States, 3MR Application Development, Siemens Healthcare, Erlangen, Germany

One of the main challenges in ultra-high-field imaging is the spatial inhomogeneity of transmit B1. In cerebral time-of-flight (TOF) angiography this inhomogeneity results in spatially varying background suppression and thus suboptimal contrast. Parallel transmission (pTX) proved to generate homogeneous excitation by using independent RF waveforms on multiple transmit channels. So far, however, pTX methods have not been used at a large scale in clinical applications, and it remains to be demonstrated that this approach provides reliable results in clinical MR protocols. In this report we demonstrate the successful implementation of Spoke 3D RF pulses in multi-slab TOF angiography at 7T.

2906.   Improved Navigator Performance by Parallel Transmission 
Manuel Walther1, Kay Nehrke2, Ingmar Grässlin2, Ulrich Katscher2, Markus Eblenkamp1, Erich Wintermantel1, and Peter Börnert2
1Chair of Medical Engineering, Technische Universität München, Garching, Germany, 2Philips Research Laboratories, Hamburg, Germany

Parallel transmission has been used to overcome B1 homogeneity limitations and to improve the performance of multi-dimensional RF pulses by shortening their duration. One of the simplest multi-dimensional RF pulses is the pencil beam which finds application as a navigator to sense respiratory motion. As modern high-field systems (3T and beyond) are especially prone to off-resonance effects, shorter pulse durations are necessary to overcome this problem. However, accelerated pulses also cause aliasing artifacts. Transmit SENSE, replacing gradient encoding with transmit sensitivity encoding, has been found to significantly improve the performance of these accelerated navigator pulses, allowing pulse durations of 1.7ms.

2907.   Adiabatic B1 Shimming Algorithm for Multiple Channel Transmit at 7T 
Priti Balchandani1, Mohammad Mehdi Khalighi2, Scott Sigao Hsieh1,3, Kawin Setsompop4, John Pauly3, and Daniel Spielman1
1Radiology, Stanford University, Stanford, California, United States, 2Global Applied Science Laboratory, GE Healthcare, Menlo Park, California, United States, 3Electrical Engineering, Stanford University, Stanford, California, United States, 4A.A. Martinos Center for Biomedical Imaging, Harvard Medical School, Massachusetts General Hospital, Charlestown, Massachusetts, United States

Adiabatic B1 shimming is a hybrid imaging approach which exploits the flexibility offered by multiple transmit channels to ensure the B1-immunity of adiabatic RF pulses over the entire spatial region of interest. We developed a simulated annealing optimization algorithm to determine the amplitude and phase adjustments to adiabatic RF pulses played on individual transmit channels. The values were chosen to maximize uniformity of the flip angle while limiting RF amplitude and minimizing worst-case SAR. The final shimming algorithm was applied to 2-channel and 8-channel 7T B1 transmit maps and the resultant values were tested in simulation. Highly uniform flip angles were achieved.

2908.   Minimum-Duration Adiabatic Spectral-Spatial Refocusing Pulses 
Adam B. Kerr1, Duan Xu2, Peder E.Z. Larson2, Daniel B. Vigneron2, and John M. Pauly1
1Electrical Engineering, Stanford University, Stanford, CA, United States, 2Radiology and Biomedical Imaging, UCSF, San Francisco, CA, United States

Minimum-duration adiabatic spectral-spatial refocusing pulses are designed by using an alternate frequency sweep than the conventional hyperbolic secant pulse. A 55% reduction in pulse duration from 26 to 11.7 ms is demonstrated, at the cost of higher SAR and larger spectral transition bands. This approach will provide a significant decrease in the minimum TE for PRESS-localized MRSI sequences that use two of these pulses.

2909.   A Low-Power Asymmetrically-Selective Adiabatic Pulse 
Adam B. Kerr1, Duan Xu2, Peder E.Z. Larson2, Daniel B. Vigneron2, and John M. Pauly1
1Electrical Engineering, Stanford University, Stanford, CA, United States, 2Radiology and Biomedical Imaging, UCSF, San Francisco, CA, United States

A novel adiabatic full-passage pulse has been designed demonstrating a 33% peak power reduction compared to a classic hyperbolic secant (HS) pulse, while maintaining the spectral selectivity at one frequency edge. The new pulse is used to design the two adiabatic spectral-spatial pulses for a PRESS-localization, but with spectral profiles offset and reversed to achieve full HS selectivity. The peak power reduction will enable the higher spectral bandwidths demanded at high field without compromising selectivity.

2910.   Mapping inversion efficiencies of adiabatic pulses at 7T 
Mayur Narsude1,2, José Marques1,2, Florent Eggenschwiler1, and Rolf Gruetter1,3
1Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédéral de Lausanne, Lausanne, Vaud, Switzerland, 2Department of Radiology, University of Lausanne, Lausanne, Vaud, Switzerland, 3Department of Radiology, University of Geneva, Geneva, Switzerland

Transmit B1 field inhomogeneous distribution encountered at high magnetic field (7T and above) makes it difficult to achieve homogeneous inversion in the whole brain region. In the presented study, few inversion RF pulses are studied for their inversion efficiencies using in vivo B1 mapping and in-vitro measurements. It is demonstrated that whole brain inversion is possible at 7T at the cost of somewhat higher SAR. The observed inversion efficiencies in the CSF regions were as predicted by the model with slight deviations, which are likely due to T1rho during the inversion, in the white matter regions.

2911.   Nonuniform and multidimensional Shinnar-Le Roux RF pulse design 
William A Grissom1, Graeme C McKinnon2, and Mika W Vogel1
1GE Global Research, Munich, Bavaria, Germany, 2GE Applied Science Lab, GE Healthcare, Milwaukee, Wisconsion, United States

The Shinnar-Le Roux (SLR) RF pulse design algorithm is currently the most widely-used method for designing one-dimensional RF pulses on constant gradient waveforms due to its ease of use and optimality. Presently, no analogous method exists for designing multidimensional RF pulses on non-Cartesian gradient trajectories. In this work the SLR pulse algorithm is generalized to nonuniform and multidimensional excitation pulses via a novel problem parameterization and design problem framework. The method is validated and compared to methods conventionally used for large-tip-angle spiral and spectral-spatial pulse design.

2912.   B1+-insensitive slice-selective pulses constructed from optimized non-selective composite waveforms 
Jay Moore1,2, Marcin Jankiewicz1,3, Adam W Anderson1,4, and John C Gore1,4
1Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, 2Physics and Astronomy, Vanderbilt University, Nashville, TN, United States, 3Department of Radiology and Radiological Sciences, Vanderbilt University, 4Department of Biomedical Engineering, Vanderbilt University

Non-selective composite RF pulses are numerically optimized for insensitivity to static and RF field variations and subsequently transformed into slice-selective pulses via RF shape modification and execution of an oscillating gradient waveform. Pulse designs accommodate the gradient performance and maximum RF amplitude limits of a commercial 7 T human scanner while significantly reducing signal variations due to B1+ inhomogeneities in the human brain.

2913.   Broadband refocusing pulses with B1 robustness and energy constraints 
Martin A Janich1,2, Rolf F Schulte2, Markus Schwaiger3, and Steffen J Glaser1
1Chemistry, Technische Universität München, Munich, Germany, 2GE Global Research, Munich, Germany, 3Nuclear Medicine, Technische Universität München, Munich, Germany

Broadband RF pulses are of great interest for improving selectivity and reducing chemical shift displacements in localized spectroscopy. Slice-selective broadband refocusing pulses with immunity to B1 variations are designed using optimal control theory. Pulses are optimized under energy constraints, are compared to a broadband SLR pulse, and applied in a PRESS experiment.

2914.   Practical Non-selective Refocusing Pulses for 7 T MRI 
Marcin Jankiewicz1,2, Jay Moore1,3, Adam Anderson1,4, and John Gore1,4
1Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, 2Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States, 3Physics and Astronomy, Vanderbilt University, United States, 4Biomedical Engineering, Vanderbilt University

We evaluate a sample of short, low-SAR, non-selective refocusing pulses using a 3D SE-EPI sequence at 7 T. With only a two-fold increase in SAR relative to a block pulse, several refocusing options were found to increase signal in low B1+ regions by a factor of 2.

2915.   High Bandwidth Dualband Selective Saturation RF Pulses for Prostate Proton MRSI 
Galen D Reed1, Adam B Kerr2, Peder E.Z Larson3, Eugene Ozhinsky3, John Kurhanewicz3, and Daniel B Vigneron3
1Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, United States, 2Electrical Engineering, Stanford University, Palo Alto, California, 3Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California

Very Selective Saturation (VSS) pulses are critical for PRESS localized spectroscopy by providing outer volume suppression and reducing chemical shift artifacts. Since these bands are placed in parallel pairs, cosine modulation can be applied to excite two bands in a single pulse, thereby saving time in the suppression pulse train by eliminating redundant crusher gradients. This abstract demonstrates the design of an increased bandwidth dual band selective saturation pulse based on a convex optimization filter design (for optimizing selectivity) and biased-probability Monte Carlo root flipping algorithm (for minimizing computation time). These pulses were designed and tested in patient exams incorporating prostate MRSI

2916.   Global Minimum Peak RF Design for Large Time-Bandwidth Saturation Pulse 
Christine Law1, and Sonal Josan2
1University of Oxford, Oxford, Oxfordshire, United Kingdom, 2SRI International

We demonstrate a convex optimization technique to design minimum peak RF saturation pulses. This method achieves global minimum peak RF amplitude without the need of exhaustive search over possible phase profiles. Our technique accept passband/stopband ripple and time-bandwidth product as inputs. But to formulate as a convex problem, we make use of autocorrelation function of the rf waveform and employ the technique of convex iteration. We compare our technique with exhaustive search in small time-bandwidth case and show a result for large time-bandwidth design.

2917.   Dynamic Gradient Spatial-Spectral Pulse 
Xiaocheng Wei1, and Yongchuan Lai1
1MR, GE Healthcare, Beijing, Beijing, China, People's Republic of

In this study, a new Spatial-Spectral (SpSp) pulse, called as Dynamic Gradient SpSp (DG-SpSp) pulse, is designed to achieve better minimum slice thickness performance under certain peripheral nerve stimulation (PNS) limitations. And the payment of this improvement is tiny increment of TR time.

2918.   Time-Efficient Slab Selective Water Excitation 
Gregory R Lee1, Jean A Tkach1,2, and Mark A Griswold1,3
1Radiology, Case Western Reserve University, Cleveland, OH, United States, 2Radiology, Imaging Research Center, Cincinnati Children's Hospital Research Foundation, Cincinnati, OH, United States, 3Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States

At 3T and above, spectral-spatial (SPSP) subpulse durations of less than 1 ms are needed in order to selectively excite either water or fat spins. With such short subpulses, RF power limits prohibit the excitation of sharp spatial slabs when using traditional SPSP pulse designs. In the present work, a new algorithm for alternating between minimum-time VERSE gradient waveform reshaping and RF pulse redesign is presented. The algorithm can produce much sharper spatial slabs while preserving the spectral profile. In addition, there is flexibility in the specification of the SPSP excitation pattern and tip-down time within the pulse.

2919.   Maximizing MR Signal for 2D UTE Slice Selection in the Presence of Rapid T2 Relaxation 
Michael Carl1, Jing-Tzyh Alan Chiang2, and Mark Bydder2
1Global Applied Science Laboratory, GE Healthcare, San Diego, CA, United States, 2University of California, San Diego, United States

We have derived an analytic expression for the steady state transverse magnetization resulting from VERSE corrected 2D UTE excitation RF pulses, which we used to predict the optimum flip angles (generalized Ernst angles) for short T2 tissues. Simulations and experimental verifications support the validity of the derived results.

2920.   Hadamard encoded iMQC high-resoultion NMR spectroscopic method in inhomogeneous fields 
Yushan Chen1, Congbo Cai1, Fenglian Gao1, Shuhui Cai1, and Zhong Chen1
1Communication Engineering and Physics, Fujian Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, Fujian, China, People's Republic of

Intermolecular multiple quantum coherences (iMQCs) caused by long-range dipolar interactions possess some appealing unique properties for high-resoultion NMR spectroscopy in inhomogeneous fields. In this abstract, a new iMQC method involving Hadamard encoding is proposed to obtain high- resolution 1D NMR spectrum in inhomogeneous fields within a short acquisition time. Its application on simple and complex systems was tested. Experimental results indicate that the spectral line-width can be considerably reduced and the signal to noise ratio can be improved.

Traditional Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
B0 & B1: Quantification & Correction

Tuesday May 10th
Exhibition Hall  13:30 - 15:30

2921.   Spatial field monitoring using navigator echoes 
Maarten J. Versluis1,2, Andrew G. Webb1,2, Peter Boernert2,3, Mark A. van Buchem1, and Matthias J.P. van Osch1,2
1Radiology, Leiden University Medical Center, Leiden, Netherlands, 2C.J. Gorter Center for high field MRI, Leiden University Medical Center, Leiden, Netherlands, 3Philips Research Europe, Hamburg, Germany

Strongly T2*-weighted sequences are very sensitive to variations in the magnetic field due to, for example, respiration and body movements. This effect is more apparent at high magnetic field strengths (7 Tesla). Using navigator echoes it is possible to estimate and correct for global field changes. In this work we have improved this method by including the sensitivities of the different coil elements in the receive array to estimate the local field variations. Including the spatial encoding along the read out axis of the navigators yielded the best results.

2922.   Optimised Acquisition of Magnetic Field Correlation Mapping for Improved Precision 
Catherine Anusha Mallik1, Gareth J Barker1, and David J Lythgoe1
1Centre for Neuroimaging Sciences, Institute of Psychiatry, King's College London, London, United Kingdom

Magnetic field correlation (MFC) is a temporal correlation function sensitive to iron levels. MFC is measured by collecting asymmetric spin echo data, at multiple (typically five or more) echo shifts. Here we use simulations to show that precision of MFC estimates can be improved by acquiring data at only two time-shifts and using the time saved to increase the number of signal averages (maintaining overall scan time). We show how the averages should be distributed between the two shifts and, with the final optimised protocol, collect in vivo data to show the improvement over a standard, five point, scheme.

2923.   Slice-by-Slice Grey Matter Optimised Z-shimming for fMRI Applications 
Stephen James Wastling1, David John Lythgoe1, and Gareth John Barker1
1Centre for Neuroimaging Sciences, Institute of Psychiatry, King's College London, London, United Kingdom

Previous workers have shown the feasibility of recovering signal in regions of GE-EPI images with susceptibility-induced signal dropout by combining two images acquired using different z-shim gradients. We have demonstrated that by constraining the algorithm used to select the two z-shims to grey matter voxels on a slice-by-slice basis improves signal recovery over their whole-brain optimisation scheme.

2924.   Robust Transmitter Calibration during Continuous Table Movement 
Alto Stemmer1, and Berthold Kiefer1
1Healthcare Sector, Siemens AG, Erlangen, Germany

In MR examinations that acquire the data at multiple different table positions it can be more efficient to perform the calibration steps, which are necessary to determine or compensate patient specific load, during continuous table movement. In this work reliable transmitter calibration results during continuous table movement with 50 mm/sec are obtained with a three RF pulse sequence that employs a flow compensated gradient scheme along the direction of movement.

2925.   A Fast B1 Mapping Method for Transmit/Receive Coils for Parallel Transmit (pTx) Applications 
Tiejun Zhao1, Hai Zheng2, Anthony DeFranco3, Tamer Ibrahim2,3, Yongxian Qian3, and Fernando Boada2,3
1Siemens Healthcare, Siemens Medical Solutions, Pittsburgh, Pennsylvania, United States, 2Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

For a successful parallel transmit experiment, the B1 map must be known for each Tx channel. As the number of the transmit channel increases, the total scan time of B1 mapping could increase significantly. In light of this, there is a tremendous motivation to find a fast B1 mapping method for pTx applications in the recent years. In this abstract, we proposed and demonstrated a fast technique to estimate B1+ map for pTx experiments using only a set of small tip angle images, which can be obtained under 2min for a 8-channel Tx/Rx coil with whole brain coverage.

2926.   Interference Bloch-Siegert B1 Mapping for Parallel Transmit 
Laura Sacolick1, William A. Grissom1, Guido Kudielka1, Wolfgang Loew2, and Mika W. Vogel1
1GE Global Research, Munich, Germany, 2Cincinnati Children's Hospital Medical Center, Cincinnatti, OH, United States

Bloch-Siegert B1 mapping is presented here for high channel count parallel transmit application. Compared to single transmit coils, parallel transmit systems present unique problems of acquiring many B1 maps quickly, and measuring low amplitude B1 fields from individual coil elements. Here we present a scheme where the complex B1 field amplitude and phase are determined from Bloch-Siegert B1 maps acquired sequentially for the composite field of all but one transmit channel.

2927.   Fast Spin Echo Bloch-Siegert B1 Mapping 
Laura Sacolick1, Seung-Kyun Lee2, William A. Grissom1, and Mika W. Vogel1
1GE Global Research, Munich, Germany, 2GE Global Research, Niskayuna, NY, United States

A fast spin echo based Bloch-Siegert B1 mapping is presented here for rapid B1 field mapping. In cases where T2* causes significant signal loss in long-echo time gradient echo images, spin echo based B1 mapping is desired. The fast spin echo uses only two off-resonance RF pulses per echo-train, resulting in lower SAR and significant B1 map acceleration. The static Bloch-Siegert phase shift causes signal loss from the non-CPMG condition, but one can reconstruct a B1 map with high SNR even for phase shifts >90 degrees with a CPMG sequence. The B1 mapping shown here is applied for both parallel and single transmit systems.

2928.   Joint B0 and B1 Mapping from Tagged Rapid 2D Acquisitions 
Wayne R Dannels1, and Andrew J Wheaton1
1Toshiba Medical Research Institute, Mayfield Village, OH, United States

A single 2D acquisition with RF tagging prepulses is used to generate both B1 maps and B0 maps. It has previously been shown that RF spatial tagging in conjunction with k-space data processing yields a rapid method for 2D B1 mapping. Now it is shown that the same acquisition can simultaneously yield 2D B0 maps without any increase in acquisition time or modification of the pulse sequence.

2929.   Turbo Spin Echo Bloch Siegert Shift B1+ Mapping 
Thomas Christian Basse-Lüsebrink1, Volker Sturm1, Thomas Kampf1, Guido Stoll2, and Peter Michael Jakob1
1Experimental Physics 5, University of Wuerzburg, Wuerzburg, Bavaria, Germany, 2Neurology, University of Wuerzburg, Wuerzburg, Bavaria, Germany

An interesting method for B1+ mapping based on the Bloch-Siegert (BLS) shift was recently presented for gradient echo (FLASH) and Spin Echo (SE) sequences. This method uses off-resonant pulses before signal acquisition to encode the B1 information into the signal phase. Fast B1+ mapping is possible since the repetition time has only minor influence on the quality of the phase information. In the present study, the use of BLS B1+ mapping was extended to CPMG-based Turbo-Spin-Echo (BLS-CPMG-TSE) imaging. For fast B1+ mapping phantom as well as in vivo 2D and 3D experiments were performed to evaluate the proposed method.