While human patients and healthy subjects are being imaged at 3T, 7T, and soon, 10.5T, more data and understanding of RF safety at these ultra-high field strengths are needed. The overall objective of this renewal proposal therefore is to extend the RF heating studies in the human head of our previous grant to the investigation of RF heating in the human body for ultra-high field MRI applications. Safety will be better assured and imaging performance improved by developing the means to accurately predict and measure RF temperature contours in human anatomy. Through development of new theory, technology, methodology, and experimental approach, these means will be achieved by accomplishing the following aims. First, a more fundamental understanding of the electrodynamics and thermodynamic nature of RF induced heating and heat transfer in anatomy will be furthered through mechanistic improvement of the empirical Pennes Bioheat Equation. Second, this new theoretical model will be validated at high field Larmor frequencies by invasive, direct measurement of RF heating in anesthetized porcine models, by fluoroptic thermometry. The porcine model is required as an intermediate step toward understanding and measuring RF heating in humans. Toward this end, the third aim is to develop a noninvasive NMR thermometer that is accurately and precisely calibrated by the invasive fluoroptic measurement. Once confidence is gained in predicting and noninvasively measuring temperatures in pigs, these methods will be applied or correlated to monitoring RF heating in humans and so accomplishing the final aim of this study. With new understanding, data, and thermal measurement methods, high field human MRI will become safer.
While humans are being imaged at 3T, 7T, and soon, 10.5T, more data and understanding of RF safety at these ultra-high field strengths are needed. These RF safety issues were investigated for head imaging in the previous grant. The objective of this renewal proposal therefore is to continue the investigation of high frequency RF heating in the human body to improve RF safety and imaging performance for ultra-high field MRI. Safety will be better assured by developing means to accurately predict and image RF heating contours in human anatomy.
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