Development of MRI system for dentistry

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To develop a small-sized MRI for dentistry, we developed an MRI phantom and designed a magnetic circuit. We then developed trial units of the magnetic circuit and of a maxillofacial MRI system, collected image data signals, and reconstructed the MR images. Based on this research, we applied for a patent on the unilateral magnetic circuit.1. Development of phantom: We developed a phantom having human-tissue equivalent T1 and T2 relaxation times, and human-tissue-equivalent (except for fat) conductivity. Any shape of the phantom can be made, as it is in gel form.2. Design of a magnetic circuit algorithm: A spatially uniform magnetic field is difficult to generate with a magnetic circuit using an open-type magnet because of its structure. To overcome this, we conceived a "scaled evolution strategy method", which enabled us to effectively reduce the number of objective functions.3. Trial development of magnetic circuit: Based on the above design method, we developed a lateral magnetic circ … More uit.4. Trial development of a maxillofacial MRI system: We developed a relatively small magnetic circuit into which the patient's head can be positioned. We also constructed an MRI unit, and reconstructed MR images from the obtained data.5. Development of lateral magnetic circuit: Generally, the magnetic field of a unilateral magnetic circuit decreases with the increase of distance from the surface of the magnetic circuit. In our research, however, we designed a unilateral magnetic circuit having three-dimensionally uniform distribution in a target volume apart from the magnetic circuit surface. By means of combination of 16 magnetic blocks, the directions of the magnetic fields in the target region became parallel to the surface of the magnetic circuit. Using the 3-dimensional finite element method, a magnetic circuit 400 mm x 400 mm x 200 mm in size had a magnetic flux density of 64.5mT in a region of interest (ROI) 55 mm from the surface of the magnetic circuit. The uniformity was 28 ppm when the ROI size was 10 mm x 10 mm x 1 mm, and 613 ppm when 20 mm x 20 mm x 10 mm in size. Less