Open Type of Magnetically Shielded Room Combined With Cancelling Coils for Magnetic Resonance Imaging

摘要

Recently, Magnetic Resonance Imaging (MRI) has come into wide use as a method of creating images of the inside of a human body in the hospitals, etc. MRI has some advantages over other methods, such as the fact that it does not entail radiation exposure, as both Computed Tomography (CT) scans and X-rays do. However, as the strong flux density of more than 1T is applied inside MRI, the leakage flux outside becomes problems because it leads to malfunctions in heart pacemakers, a quartz clocks, and so on. Therefore, MRI is usually installed in a magnetically shielded room (MSR) in order to reduce the leakage flux to less than 0.5mT outside the room. In an ordinary MSR, the room is surrounded by ferromagnetic materials and the inner space is completely closed by a wall with exception of a small operation window. The space enclosed by the wall causes patients a great deal of stress and discomfort because they are isolated from the operators and the scenery outside. Therefore, an open type of MSR should be developed in order to improve the experience for patients. An open type of MSR using the magnetic bars instead of the magnetic walls has already been proposed [1]. However, the proposed MSR cannot generate a sufficiently open feeling because the width and interval of the bars cannot be enough small due to the requirements of the shielding performance.