TRADITIONAL POSTER - ismrm

Poster Sessions
2850. Enhanced Parallel Imaging Acceleration with a B1 Accelerated Reconstruction Sequence (BARS)
Gigi Galiana 1 , Jason P. Stockman 1 , Robert Todd Constable 1
1 Diagnostic Radiology, Yale University, New Haven, CT, United States
This work presents an approach to accelerated imaging via RF and surface coil localization using a multiwindow acquisition. The sequence can be described
as creating “effective sensitivity profiles” for each acquisition window using the in-plane RF profiles to multiply and sculpt the sensitivity profiles of
multichannel receivers. Rectangular RF profiles are chosen so as to efficiently encode along the phase encode-direction, improving the ability to unwrap
aliasing caused by extreme undersampling along this direction. We present both numerical studies and experimental verification of the approach.
2851. Comparison of Different Methods for B1+/flip Angle and Reception Sensitivity Mapping
Valentina Hartwig 1,2 , Nicola Vanello 3 , Giulio Giovannetti 1 , Maria Fillomena Santarelli 1 , Luigi Landini 3
1 Institute of Clinical Physiology, CNR, Pisa, Italy, Italy; 2 Department of Electrical Systems and Automation, University of Pisa, Pisa,
Italy, Italy; 3 Department of Information Engineering, University of Pisa, Pisa, Italy, Italy
Knowledge of transmission field B1+, and reception sensitivity maps is important in high field (>=3T) human Magnetic Resonance (MR) imaging for
several aspects: these include post acquisition correction of intensity inhomogeneities, that may affect the quality of images, and modelling and design of
radiofrequency (RF) coils and pulses. Moreover, in recent works, it has been demonstrated that B1 maps can be used for the direct calculation of tissues
electrical parameters and for estimating the local Specific Absorption Rate (SAR) in vivo. In this study a comparison among known methods for B1+/flip
angle and reception sensitivity mapping is introduced.
2852. Simulataneous B1 and B0 Mapping at 7T
Walter RT Witschey 1 , Ravinder Reddy 1 , Mark A. Elliott 1
1 Radiology, University of Pennsylvania, Philadelphia, PA, United States
A modification of the actual flip angle (AFI) method for measuring B1 is presented which simultaneously acquires spatial maps of both B0 and B1, allowing
for accurate calculation of the radiofrequency field in the presence of off-resonance effects. An analytical expression for the actual B1 field is derived, given
the apparent flip angle and the B0 map. Application of the new method is demonstrated at 7 tesla in phantom images.
B1 Insensitive RF
Hall B Wednesday 13:30-15:30
2853. BIR-4 Based B1 and B0 Insensitive Velocity Selective Pulse Trains
Eric C. Wong 1 , Jia Guo 2
1 Radiology and Psychiatry, UC San Diego, La Jolla, CA, United States; 2 Bioengineering, UC San Diego
The BIR-4 pulse was recently shown to be useful for B1 and B0 insensitive T2 preparation. We report here an extension of this concept that includes the use
of symmetrical gradient pulses inserted at the zero points of the BIR-4 pulse to impart velocity selectivity. The resulting velocity selective module is time
efficient, and has better B1 insensitivity than existing methods based on adiabatic double spin echoes. Application to velocity selective arterial spin labeling
is demonstrated.
2854. Broadband, Shallow Tip NMR Pulse Design Providing Uniform Tipping in Inhomogeneous RF Fields
Hui Liu 1 , Gerald Matson 1,2
1 CIND, Veterans Affairs Medical Center, San Francisco, CA, United States; 2 Pharmaceutical Chemistry, University of California, San
Francisco, San Francisco, CA, United States
Although high-field MRI offers increased signal-to-noise (S/N), the non-uniform tipping produced by conventional RF pulses leads to spatially dependent
contrast and sub-optimal S/N, thus complicating the interpretation of the MR images. The aim of this research was to develop broadband RF pulses with
immunity to B1 inhomogeneity. To accomplish this, we developed an optimization routine based on optimal control theory to design RF pulses with a
desired range of immunity to B1 inhomogeneity and to resonance offset. The resulting pulses were more efficient than analogous pulses in the literature.
These pulses have promise for certain MRI experiments at high field.
2855. Adiabatic Pulses Revisited Through Averaging
Bahman Tahayori 1,2 , Leigh Andrea Johnston 1,2 , Peter Mark Farrell 1,2 , Iven Michiel Yvonne Mareels 1,2
1 EEE Department, The University of Melbourne, Melbourne, Victoria, Australia; 2 NICTA Victoria Research Laboratory, Melbourne,
Australia
In this paper, the Bloch equation is scaled and averaged consequently to find the magnetization behaviour in a simple way with a negligible error for
adiabatic passages. The novel framework presented here may be used to optimise the modulation functions of the adiabatic passages.
2856. Hyperbolic Secant Parameter Optimization for Non-Selective Inversion at 7 T
Jay Moore 1,2 , Marcin Jankiewicz 1,3 , Adam W. Anderson 1,4 , John C. Gore 1,4
1 Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States; 2 Department of Physics and Astronomy,
Vanderbilt University, Nashville, TN, United States; 3 Department of Radiology and Radiological Sciences, Vanderbilt University,
Nashville, TN, United States; 4 Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States
Results include 3D δB 0 and B 1 + field maps in the human brain at 7 T. Hyperbolic secant pulses with a range of bandwidths are evaluated for non-selective
inversion uniformity in this context. Numerical optimization of hyperbolic secant waveform parameters (β and μ) is shown to result in noticeably improved
inversion uniformity as compared to pulses with the same bandwidth and μ=5.