Higher field (7T) MRI offers many potential advantages to clinical and scientific studies, including increased sensitivity and in many cases improved contrast. Demonstration of this potential in specialized studies has resulted in the proliferation of 7T and even 9.4T human scanners. There are, however, outstanding methodological challenges to bringing these systems from the research to the clinical arena. One of the most limiting issues is the ability to achieve uniform image contrast over the body. The source of this confound is the shortened RF wavelength in biological tissues leading to spatial inhomogenieties of the transmit B1 field, which, in turn lead to contrast variations in many sequences. In a conventional T1 weighted volume acquisition, the image contrast can change over an order of magnitude over the head at 7T. RF excitation in the presence of time-varying gradients offers the potential of multi-dimensional selective excitation. In this scheme, the excitation is shaped to mitigate the B1 pattern measured in the head. The principal challenge is to encode the 3D excitation in a short enough time to be useful for a wide variety of sequences, including 2D slice selective sequences as well as 3D (non-selective) acquisitions. We propose a development program to test the ability the spatially shaped pulses to mitigate B1 inhomogeniety in the head at 7T.
Our first aim i s to develop the RF transmit arrays needed to decrease the length of time spent encoding these pulses using the transmit SENSE method.
Our second aim i s to improve the methods used for calculating the accelerated pulses and test the limits of the transmit SENSE approach in the head at 7T, including high flip angle excitations.
Our third aim i s to build the methodology that will be needed to safely and accurately monitor local SAR levels for transmit arrays and assess the SAR penalty associated with constructive interference from the E fields of the multiple transmit channels

Public Health Relevance

This project will impact public health by developing technology to increase the diagnostic power of MRI to detect, identify and follow the efficacy of treatment in brain pathology. The project will enable the increased sensitivity of ultra-high field MRI to be utilized in clinical diagnostic imaging by addressing the most problematic technical barrier to its clinical use.

Agency
National Institute of Health (NIH)
Institute
National Institute of Biomedical Imaging and Bioengineering (NIBIB)
Type
Research Project (R01)
Project #
3R01EB006847-02S1
Application #
7631512
Study Section
Biomedical Imaging Technology Study Section (BMIT)
Program Officer
Liu, Guoying
Project Start
2007-09-15
Project End
2011-05-31
Budget Start
2008-06-05
Budget End
2009-05-31
Support Year
2
Fiscal Year
2008
Total Cost
$102,334
Indirect Cost
Name
Massachusetts General Hospital
Department
Type
DUNS #
073130411
City
Boston
State
MA
Country
United States
Zip Code
02199
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Guérin, Bastien; Villena, Jorge F; Polimeridis, Athanasios G et al. (2018) Computation of ultimate SAR amplification factors for radiofrequency hyperthermia in non-uniform body models: impact of frequency and tumour location. Int J Hyperthermia 34:87-100
Guerin, Bastien; Serano, Peter; Iacono, Maria Ida et al. (2018) Realistic modeling of deep brain stimulation implants for electromagnetic MRI safety studies. Phys Med Biol 63:095015
Fan, Qiuyun; Nummenmaa, Aapo; Wichtmann, Barbara et al. (2018) Validation of diffusion MRI estimates of compartment size and volume fraction in a biomimetic brain phantom using a human MRI scanner with 300?mT/m maximum gradient strength. Neuroimage 182:469-478
Golestanirad, Laleh; Angelone, Leonardo M; Iacono, Maria Ida et al. (2017) Local SAR near deep brain stimulation (DBS) electrodes at 64 and 127 MHz: A simulation study of the effect of extracranial loops. Magn Reson Med 78:1558-1565
Vinding, Mads S; Guérin, Bastien; Vosegaard, Thomas et al. (2017) Local SAR, global SAR, and power-constrained large-flip-angle pulses with optimal control and virtual observation points. Magn Reson Med 77:374-384
Golestanirad, Laleh; Iacono, Maria Ida; Keil, Boris et al. (2017) Construction and modeling of a reconfigurable MRI coil for lowering SAR in patients with deep brain stimulation implants. Neuroimage 147:577-588
Guérin, Bastien; Villena, Jorge F; Polimeridis, Athanasios G et al. (2017) The ultimate signal-to-noise ratio in realistic body models. Magn Reson Med 78:1969-1980
Davids, Mathias; Guérin, Bastien; Malzacher, Matthias et al. (2017) Predicting Magnetostimulation Thresholds in the Peripheral Nervous System using Realistic Body Models. Sci Rep 7:5316
Golestanirad, Laleh; Keil, Boris; Angelone, Leonardo M et al. (2017) Feasibility of using linearly polarized rotating birdcage transmitters and close-fitting receive arrays in MRI to reduce SAR in the vicinity of deep brain simulation implants. Magn Reson Med 77:1701-1712

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