TRADITIONAL POSTER - ismrm

Poster Sessions
average flip angle is used to calculate the transmit gain setting needed to produce the desired flip angle. This is shown here at 3 Tesla in the brain, shoulder,
abdomen, breast, and wrist with a total scan time for a robust implementation of 1.6 seconds.
2831. Fast and Robust B 1 Mapping at 7T by the Bloch-Siegert Method
Mohammad Mehdi Khalighi 1 , Laura I. Sacolick 2 , W Thomas Dixon 3 , Ron D. Watkins 4 , Sonal Josan 4 , Brian
K. Rutt 4
1 Applied Science Lab, GE Healthcare, Menlo Park, CA, United States; 2 Imaging Technologies Lab, General Electric Global Research,
Garching b. Munchen, Germany; 3 General Electric Global Research, Niskayuna, NY, United States; 4 Department of Radiology,
Stanford University, Stanford, CA, United States
B 1 + mapping is a critical step in the design of RF pulses for parallel transmit systems. We used the Bloch-Siegert (BS) B 1 + mapping method and a 2-channel
parallel transmit enabled 7T scanner to produce fast, robust and accurate B 1 + maps through the human brain. Both B 1 + magnitude and phase are obtained
from a single sequence, employing +/-4kHz off-resonance BS pulses. B 1 + magnitude and phase maps acquired with a 26s BS scan are compared with those
acquired with a 640s classical double angle scan, showing that the BS method is a very good candidate for efficient B 1 + mapping at 7T.
2832. Practical Vector B1 Mapping at 7T
Douglas Kelley 1,2 , Janine Lupo 2
1 Applied Science Laboratory, GE Healthcare, San Francisco, CA, United States; 2 Radiology and Biomedical Imaging, University of
California, San Francisco, San Francisco, CA, United States
Compensation of B1 variations in vivo requires mapping both the magnitude and the phase of each channel's RF magnetic field. Since the field distribution
is strongly dependent on the specific size, shape, and positioning of the tissue, such mapping must be made for each subject. We present a practical method
for acquiring these maps within 10 minutes in phantoms and human subjects at 7T.
2833. Compressive B1 + Mapping: Towards Faster Transmit Coil Sensitivity Mapping
Mariya Doneva 1 , Kay Nehrke 2 , Alfred Mertins 1 , Peter Börnert 2
1 Institute for Signal Processing, University of Lübeck, Lübeck, Germany; 2 Philips Research Europe, Germany
The potential to accelerate the B1 + mapping measurement by means of compressed sensing (CS) was investigated. Joint sparsity constraint accounting for
the common sparsity support in different TX channels, and higher dimensional undersampling space, also including the coil dimension, allow for
considerable acceleration even for the low resolution data acquired in B1 + mapping. The basic feasibility of the proposed method is evaluated on simulations
and in vivo data from a 3T 8-channel parallel transmit system.
2834. Simultaneuous B 0 and High Dynamic Range B 1 Mapping Using an Adiabatic Partial Passage Pulse
Kim Shultz 1 , Greig Scott 1 , Joelle Barral 1 , John Pauly 1
1 Electrical Engineering, Stanford University, Stanford, CA, United States
We present a simultaneous δ B 0 and high-dynamic range B 1 mapping technique using an adiabatic partial passage pulse. The double angle method, the gold
standard for B 1 mapping, requires 66% longer to acquire the same B 1 range. The high dynamic range is useful for mapping the fields from ablation wires or
surface coils, where significant B 0 variation will also be present.
2835. Fast B1+ Mapping with Validation for Parallel Transmit System in 7T
Joonsung Lee 1 , Borjan Gagoski 1 , Rene Gumbrecht 1,2 , Hans-Peter Fautz 3 , Lawrence L. Wald 4,5 , Elfar
Adalsteinsson 1,5
1 Electrical engineering and computer science, Massachusetts Institute of Technology, Cambridge, MA, United States; 2 Physics,
Friedrich-Alexander-University Erlangen, Erlangen, Germany; 3 Siemens Healthcare, Erlangen, Germany; 4 Department of Radiology,
A. A. Martinos Center for Biomedical Imaging, Cambridge, MA, United States; 5 Harvard-MIT Division of Health Sciences and
Technology, Massachusetts Institute of Technology, Cambridge, MA, United States
We present a fast B1+ mapping method for parallel transmit system and validate the performance on water phantom in 7T. The measured flip angle matches
with the flip angle simulated by the Bloch equation.
2836. Image-Guided Radio-Frequency Gain Calibration for High-Field MRI
Elodie Breton 1 , KellyAnne McGorty 1 , Graham C. Wiggins 1 , Leon Axel 1 , Daniel Kim 1
1 Research Radiology - Center for Biomedical Imaging, New York University Langone Medical Center, New York, NY, United States
The purpose of this study was to develop a rapid, image-guided RF transmitter gain calibration procedure for high-field MRI and evaluate its performance
through phantom and in vivo experiments at 3T and 7T. Using a single-shot TurboFLASH pulse sequence, a series of “saturation-no-recovery” images was
acquired by varying the flip angle of the preconditioning pulse. In the resulting images, the signal null occurs in regions where the flip angle of the
preconditioning pulse is 90°, and the mean signal within a region-of-interest can be plotted as a function of the nominal flip angle to quantitatively calibrate
the RF transmitter gain.
2837. No Inversion Double Angle Look-Locker (NiDALL) for Flip Angle Mapping
Trevor Wade 1,2 , Charles McKenzie 1,3 , Brian Rutt 4
1 Imaging Research Laboratories, Robarts Research Institute, London, ON, Canada; 2 Biomedical Engineering, The University of
Western Ontario, London, ON, Canada; 3 Medical Biophysics, The University of Western Ontario, London, ON, Canada; 4 Diagnostic
Radiology and Richard M Lucas Center for Imaging, Stanford University, Stanford, CA, United States
The double angle Look-Locker method is an efficient 3D method of mapping transmit B1 inhomogeneity. It makes uses inversion pulses and samples the
recovering magnetization using SPGR trains at two different angles. This leads to two time constants that can be combined to find the achieved flip angle. If
the SPGR trains at the two angles are interleaved the inversion pulses can be omitted entirely, and the same information can still be extracted. This reduces
SAR, simplifies data analysis and still yields nearly the same performance in terms of measuring the flip angle.