Design and implementation of a MRI compatible and dynamic phantom simulating the motion of a tumor in the liver under the breathing cycle

In the context of cancer treatment by proton therapy, research is carried out to use magnetic resonance imaging (MRI) to perform a real-time tracking of tumors during irradiation. The purpose of this combination is to avoid damaging the healthy tissue surrounding the tumor with the proton beam, while using a non-ionizing imaging method. Therefore, it is necessary to validate the tracking algorithms and real-time MRI sequences. This master thesis is dedicated to the design and implementation of a dynamic MRI-compatible phantom simulating the motion of a tumor in a liver subjected to the breathing cycle. This phantom is a device representing a liver with hepatocellular carcinoma, a stomach and a pancreas, with a movement similar to the one induced by respiration, faithful to the anatomy and the magnetic properties of the human body. Many anatomical or mobile phantoms already exist, but the purpose here is to combine a reliable representation of the human body with the creation and the evaluation of a programmable movement in the same device. The phantom, designed by following the Pahl and Beitz process, is composed of surrogate organs made of CAGN gels. These organs are placed in a box filled with water and attached to an elastic membrane. A programmable electro-pneumatic system creates a movement, similarly to a human diaphragm, by inflating and deflating the membrane. The relaxation times of the synthetic organs belong to a range corresponding to the human organs values (T1 = [458.7-1660] ms, T2 = [39.3-89.1] ms). The displacement of the tumor is tracked in real time by a camera inside the MRI. The amplitude of the movement varies from 12.8 to 20.1 mm for a periodic and repeatable movement. Irregular breath patterns can be created with a maximum amplitude of 40 mm.