The advantages of high field MR Imaging have brought with it the disadvantages of increased power delivered to MRI coils. This has forced the MR community to struggle with a method to determine specific absorption rates in tissues subjected to MRI procedures. For transmit/receive surface coils, the electric field is highest at the capacitors. For a birdcage coil, the electric field increases as the square of the distance outwards from the center of the coil. It is the interaction of the electric field with the tissue which theoretically causes local heating. However, it is unclear what, in practice this heating might be, if at all. We have found a temperature dependent chemical shift for Na4HTm[DOTP]2-. This shift is very near 0.5 PPM per oC, both for a solution and in agarose. We then constructed a large agarose phantom with Na4HTm[DOTP]2- and performed 30 minute long imaging experiments, both with the birdcage and the surface coils. We monitored the chemical shift during the experiment and found it to not change at all. In addition, phase images of the phantom describe areas of local heating in the sample. In the phase images, we found no areas of local heating, in either the surface coils or the birdcage coil, even right on top of the capacitors. These preliminary results indicate the usefulness of this compound for determining heat deposition by MRI coils.
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