TRADITIONAL POSTER - ismrm

Poster Sessions
2838. Electromagnetic and Thermal Simulations of Experimentally-Verified B1 Shimming Scheme with
Local SAR Constrains
Lin Tang 1 , Tamer S. Ibrahim 2
1 School of Electrical and Computer Engineering, University of Oklahoma; 2 Departments of Bioengineering and Radiology, Univeristy
of Pittsburgh, Pittsburgh, PA, United States
In this work, using 3D numerical simulations and verifications with a 7T scanner equipped with a transmit array system we conduct a comprehensive study
using B1 shimming for potential 7T whole-body applications. Different from previous works [2], this study includes the optimizations of the B1+ field,
local/average SAR and the resulting temperature elevation in the tissue.
2839. Simulation and Comparison of B1+ Mapping Methods at 3T
Christopher Thomas Sica 1 , Zhipeng Cao 1 , Sukhoon Oh 1 , Christopher M. Collins 1
1 Penn State College of Medicine, Hershey, PA, United States
RF inhomogeneity greatly affects the quality of MR imaging at high field strength, and compensation methods typically require accurate B1+ maps for
optimum performance. Comparison of B1+ mapping methods based on experimental results alone is limited by lack of knowledge of the true B1+ field
distribution. MRI simulation allows for comparison of the true, input B1+ field distribution with a simulated map. This study simulates AFI and a flip angle
series method at 3T, utilizing MRI and electromagnetic field simulations. The simulation maps correspond closely to the input B1+ and one another.
Experimental maps deviate significantly from one another.
B1 Mapping
Hall B Tuesday 13:30-15:30
2840. 3D Phase Sensitive B1 Mapping
Steven Paul Allen 1 , Glen R. Morrell 2 , Brock Peterson 1 , Daniel Park 1 , Josh Kaggie 2 , Ernesto Staroswiecki 3 ,
Neal K. Bangerter 1
1 Department of Electrical and Computer Engineering, Brigham Young University, Provo, UT, United States; 2 Department of
Radiology, University of Utah, Salt Lake City, UT, United States; 3 Department of Radiology, Stanford University, Stanford, CA,
United States
Accurate quantification of tissue sodium concentration is an important component of several potential applications of sodium MRI. Quantitative analysis of
sodium concentrations requires accurate measurement of B1. However, the low SNR typical in sodium MRI makes accurate B1 mapping in a reasonable
time challenging. Phase-sensitive B1 mapping techniques are particularly robust in low SNR environments. In this work, we apply phase sensitive B1
mapping to sodium MRI, and compare it to a standard dual angle B1 mapping method. The phase sensitive method is shown to perform much better than
the dual angle method, allowing rapid acquisition of reliable sodium B1 maps.
2841. Image Inhomogeneity Correction in Human Brain at High Field by B 1 + and B 1 - Maps
Hidehiro Watanabe 1 , Nobuhiro Takaya 1 , Fumiyuki Mitsumori 1
1 Environmental Chemistry Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
We propose a correction method of image inhomogeneity at high field. The inhomogeneity is originated from B 1 - and measurable B 1 + . We confirmed that a
ratio map of B 1 - to B 1 + (ρ) has a similar spatial pattern throughout human various brains from experimental results. The ratio map ρ in human brain was
calculated from B 1 + maps and images obtained with adiabatic pulses. Then, B 1 - was calculated by ρ× B 1 + . Homogeneous intensity was achieved in the
corrected images by B 1 + and B 1 - . Water fractions in gray and white matters obtained from corrected M 0 image were in good agreement with reported values.
2842. Signal to Noise Ratio Analysis of Bloch-Siegert B 1 + Mapping
Mohammad Mehdi Khalighi 1 , Laura I. Sacolick 2 , Brian K. Rutt 3
1 Applied Science Lab, GE Healthcare, Menlo Park, CA, United States; 2 Imaging Technologies Lab, General Electric Global Research,
Garching b. Munchen, Germany; 3 Department of Radiology, Stanford University, Stanford, CA
The Bloch-Siegert method (BS) has been recently introduced as a fast, robust and accurate method for B 1 + mapping. To compare it with other existing
methods, we derived analytical expressions for SNR in BS, Actual Flip Angle Imaging (AFI) and Double Angle (DA) B 1 + maps. Both theoretical and
experimental comparisons show that the BS method has a higher SNR at low flip angles than the other methods, despite the shorter scan time of the BS
method, making it a promising choice for B 1 + mapping for parallel transmit pulse design, especially in situations where there is highly non-uniform B 1
+
across the object.
2843. Sa2RAGE - A New Sequence for Rapid 3D B 1 + -Mapping with a Wide Sensitivity Range
Florent Eggenschwiler 1 , Arthur Magill 1,2 , Rolf Gruetter 1,3 , José P. Marques 1,2
1 EPFL, Laboratory for Functional and Metabolic Imaging, Lausanne, Vaud, Switzerland; 2 University of Lausanne, Department of
Radiology, Lausanne, Vaud, Switzerland; 3 Universities of Geneva and Lausanne, Department of Radiology, Switzerland
Sa2RAGE is based on the rapid acquisition of two images with low flip angles just before and after a saturation pulse. The ratio of the signals from the
images can be linked to a specific B 1 + . Optimization of the sequence parameters allowed the derivation of a protocol that performs 3D B 1 + -mapping in ~30s
(matrix size 64x64x16) with limited T 1 dependence. Experimental work showed the accuracy of the B 1 + -mapping over a 10 fold range of B 1 + . In-vitro and invivo
B 1 + maps were performed to demonstrate the applicability of the method on the context of parallel transmission.