Open-Type Magnetically Shielded Room Combined With Square Cylinders Made of Magnetic and Conductive Materials for MRIs

摘要

To improve the comfort of hospital patients, we have developed a new open-type magnetically shielded room (MSR) for magnetic resonance imaging (MRI), constructed by stacking square cylinders composed of magnetic material on the inside and a conductive material on the outside. The magnetic cylinder shields against leakage of the magnetic field from the MRI, while the conductive outer cylinder prevents intrusion of the electromagnetic field from outside by waveguide attenuation. First, the optimal design of the magnetic cylinder was determined, using 3-D magnetic field analysis with a simple cubic MSR. Second, the validity of the analysis and the practical realization of the designed MSR were investigated using a small experimental model. Finally, from a design perspective and the standpoint of saving space, the optimal combination of electromagnetically shielded glass and conductive cylinders made of aluminum was studied by measuring the electromagnetic shielding effect. As the optimal design of an open-type MSR for an MRI, we have adopted a combination of single-layered electromagnetically shielded glass together with stacked cylinders. These cylinders are made of a square cylinder, 144 $times$ 144 mm and 300 mm long, made of silicon steel (thickness $t=1 $mm) and divided into three parts along the axial direction, placed inside a second square cylinder made of aluminum, 150 $times$ 150 mm and 300 mm long $(t=3 {hbox{mm}})$. This MSR construction technique creates an open, spacious feeling inside the facility and can be easily fabricated at low cost.