Specific absorption rate during magnetic resonance imaging
Abstract
A patient in Magnetic Resonance Imaging (MRI) is exposed to the time varying gradient and radio-frequency (RF) fields. The RF magnetic field induces current in the human body. The local power deposition inside human body is function of the location of the patient in the MRI coil, the RF frequency, and the coil geometry. Medical implants may concentrate the induced RF currents, resulting in potentially large temperature rise near an implant. Since, human subjects can not be used for testing, measurements of RF-induced temperature rise in implants in phantoms are used to predict the in-vivo temperature rise. This work focuses on the numerical computation of both, power deposition inside such phantoms, and on the distribution of the deposited power inside the human body using Finite Difference Time Domain (FDTD). Power absorbed in a sphere of uniform conductivity was compared with the theoretical values. Results from the commercial software (www.remcom.com) were in agreement with the results form the software developed in this work. The whole body birdcage coil was used for the calculations. Both high pass and low pass configurations of the birdcage coil were studied. Inside phantoms, for landmarks in the torso, the power deposition was concentrated near the edges. Also, SAR and temperature rise distributions were calculated around the tips of generic straight implants. Inside the human model a large concentration of the absorbed power was observed where the hands were touching the body. SAR was a strong function of landmark for both phantoms and the human model as expected.
Degree
Ph.D.
Advisors
Nyenhuis, Purdue University.
Subject Area
Electrical engineering
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