HIGH FIELD NMR HEATING AND IMAGE DISTORTION IN THE HEAD

University Of Puerto Rico At Humacao, Humacao PR

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Abstract

Since its inception, magnetic resonance imaging (MRI) has always been questioned with respect to heating and radio frequency (RF) penetration at high fields. Although the clinical community is now comfortable with routine imaging up to field strengths of 2.0T, there are still federal guidelines on how much power deposition is allowed, and image uniformity. These two problems are exacerbated as the field strength increases. There is a constant dire to increase field strength because of the concomitant increase in signal-to-noise and hence the ability to image system with better resolution. Today there are many systems at 3.0T and 4.0T and newer yet higher field strength systems are planned for several sites including a 6.0T systems at the University of Michigan and 7.0T system at the University of Minnesota. As the frequency so does the tissue conductivity and the RF non- uniformity in the brain. These two factors are responsible for potential heating problems and image quality, respectively. It is important to reassess the role of high frequency effects given the thrust to higher and higher fields. The research will focus on two key questions. First, how does image non-uniformity and power deposition depend on the frequency and, second, how do they depend on the compartmentalization in the brain. It is felt that this compartmentalization is responsible for the lack of problems in MRI and the success of being able to image at current high fields. The head was chosen because this is the focus of high field imaging at this time, especially for the study of stroke and functional brain imaging. However, our results will be easily extended to large objects to understand the problems associated with imaging the body. The models developed will also be used by the PI and consultant as teaching tools for students having an interest in the medical physical profession.