Magnetic resonance methods to enable motion robust thermography in abdominal organs during transcutan ablations

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The standard method for monitoring temperatures using Magnetic Resonance Imaging (MRI) requires acquiring two MR images at different time points, which introduces errors. This thesis presents a physically and mathematically motivated method to calculate temperature information from a single MR image. In homogeneous tissue with linearly changing susceptibility, the MR signal phase can be described as a harmonic function. Utilizing this harmonic behavior and the Laplace equation, a reference-less Proton Resonance Frequency (PRF) method is introduced, enabling non-invasive temperature calculation from one phase image acquired during heating. For this method, a thin border must be placed around the heating target area. Temperature data in and around the thermal zone was analyzed using an exponential fit based on the Bioheat equation proposed by Pennes. The reference-less online temperature monitoring was tested on patients undergoing liver thermotherapy, with and without breathing triggers. Results indicate that this method can predict necrosis and serve as a safety tool during local thermal therapies. The reference-less approach offers flexibility for clinical use, eliminates the need for respiratory triggers, enhances temporal resolution, and removes inter-scan motion artifacts, as well as issues related to temperature estimation due to tissue swelling or shrinking.