Ultra High Magnetic Field (UHF) MR scanners (7 Tesla and higher) have strong potential to unveil anatomical, functional and chemical information that is not accessible at lower field strengths and could allow for earlier, non invasive diagnoses. Important obstacles, however, must be solved to obtain high quality data at UHF. Arguably, the most challenging problems relate to Radio Frequency (RF) propagation in large biological samples at UHF. First, the reduced RF penetration leads to increased tissue heating, which limits the types of scans that can be performed within safety limits. Second, transmit B1 fields are severely distorted and inhomogeneous, corrupting images and spectral acquisitions. It has been shown that RF issues can be addressed with new technologies such as B1 Shim and Parallel Excitation, that both require multiple transmit RF coils. This, in turn, requires magnitude B1 mapping for each RF coil, with two main subsequent issues: long scan times and high RF peak power. Indeed, conventional B1 mapping cannot be used with numerous coils as it typically requires several minutes of scan time per coil. Furthermore, conventional approaches necessitate large flip angles, which is not generally feasible because generating a large flip angle over a large region (head or torso) from a single transmit coil element would require levels of RF power beyond hardware and/or patient safety limits. Recent approaches allow for faster B1 mapping but are still problematic at high field with multiple channels. In this proposal we introduce novel techniques and algorithms aiming at mapping transmit B1 profiles for multiple transmit coils in a short time and with limited RF peak power. The first mapping approach relies on merging information from small flip angle (linear regime) and large flip angle (sinusoidal regime) data. A new category of B1 shim algorithms will be optimized for minimizing the needed amount of large flip angle data. Assuming that in many clinical applications approximate B1 estimation will provide sufficient improvement in image quality, an additional technique is proposed, allowing for even faster B1 approximation in low flip angle regime. This technique relies on a new formalism utilizing transmit and receive B1 information in transceiver arrays at UHF. All experiments in this proposal will be conducted on human scanners operating at 7T and 9.4T equipped with multi transmit capability. It is expected that those novel B1 mapping methods will greatly facilitate clinical use of B1 shim and Parallel Excitation at UHF.

Public Health Relevance

In this proposal we introduce new methods to calibrate the transmit profile of multiple radiofrequency coils in human scanners operating at 7Tesla and 9.4Tesla. Those new methods are expected to be significantly faster and to require less RF peak power than conventional approaches. This should greatly facilitate the development of clinical applications on ultra high magnetic field MR scanners.

Agency
National Institute of Health (NIH)
Institute
National Institute of Biomedical Imaging and Bioengineering (NIBIB)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21EB009133-02
Application #
8204623
Study Section
Special Emphasis Panel (ZRG1-SBIB-J (80))
Program Officer
Liu, Guoying
Project Start
2011-01-01
Project End
2012-12-31
Budget Start
2012-01-01
Budget End
2012-12-31
Support Year
2
Fiscal Year
2012
Total Cost
$188,750
Indirect Cost
$63,750
Name
University of Minnesota Twin Cities
Department
Radiation-Diagnostic/Oncology
Type
Schools of Medicine
DUNS #
555917996
City
Minneapolis
State
MN
Country
United States
Zip Code
55455
Wu, Xiaoping; Schmitter, Sebastian; Auerbach, Edward J et al. (2016) A generalized slab-wise framework for parallel transmit multiband RF pulse design. Magn Reson Med 75:1444-56
Deelchand, Dinesh K; Marjańska, Małgorzata; Hodges, James S et al. (2016) Sensitivity and specificity of human brain glutathione concentrations measured using short-TE (1)H MRS at 7 T. NMR Biomed 29:600-6
Liu, Jiaen; Zhang, Xiaotong; Schmitter, Sebastian et al. (2015) Gradient-based electrical properties tomography (gEPT): A robust method for mapping electrical properties of biological tissues in vivo using magnetic resonance imaging. Magn Reson Med 74:634-46
Schmitter, Sebastian; Wu, Xiaoping; Uğurbil, Kâmil et al. (2015) Design of parallel transmission radiofrequency pulses robust against respiration in cardiac MRI at 7 Tesla. Magn Reson Med 74:1291-305
Zhang, Xiaotong; Liu, Jiaen; Schmitter, Sebastian et al. (2014) Predicting temperature increase through local SAR estimation by B1 mapping: a phantom validation at 7T. Conf Proc IEEE Eng Med Biol Soc 2014:1107-10
Jiaen Liu; Xiaotong Zhang; Schmitter, Sebastian et al. (2014) Gradient-based magnetic resonance electrical properties imaging of brain tissues. Conf Proc IEEE Eng Med Biol Soc 2014:6056-9
Sohn, Sung-Min; DelaBarre, Lance; Gopinath, Anand et al. (2014) RF Head Coil Design with Improved RF Magnetic Near-Fields Uniformity for Magnetic Resonance Imaging (MRI) Systems. IEEE Trans Microw Theory Tech 62:1784-1789
Schmitter, Sebastian; Wu, Xiaoping; Auerbach, Edward J et al. (2014) Seven-tesla time-of-flight angiography using a 16-channel parallel transmit system with power-constrained 3-dimensional spoke radiofrequency pulse design. Invest Radiol 49:314-25
Schmitter, Sebastian; Wu, Xiaoping; Adriany, Gregor et al. (2014) Cerebral TOF angiography at 7T: Impact of B1 (+) shimming with a 16-channel transceiver array. Magn Reson Med 71:966-77
Zhang, Xiaotong; Liu, Jiaen; He, Bin (2014) Magnetic-resonance-based electrical properties tomography: a review. IEEE Rev Biomed Eng 7:87-96

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