Development of MRI system for dentistry

为了研制小型牙科核磁共振成像，我们研制了核磁共振成像体模，并设计了磁路。然后，我们开发了磁路和颌面MRI系统的试验单元，收集了图像数据信号，并重建了MR图像。在此基础上，我们申请了单侧磁路的专利。幻影的开发：我们开发了一种具有人体组织等效T1和T2松弛时间和人体组织等效（脂肪除外）电导率的幻影。任何形状的幻影都可以制成，因为它是凝胶状的。磁路算法的设计：由于开式磁体的结构，磁路很难产生空间均匀的磁场。为了克服这个问题，我们设想了一种“规模化进化策略方法”，使我们能够有效地减少目标函数的数量。磁路的试制：在上述设计方法的基础上，我们研制了一种横向磁路。颌面MRI系统的试验开发：我们开发了一个相对较小的磁路，病人的头部可以被定位。我们还构建了一个MRI单元，并根据获得的数据重建了MR图像。横向磁路的发展：一般情况下，单侧磁路的磁场随着离磁路表面距离的增加而减小。然而，在我们的研究中，我们设计了一个单侧磁路，在远离磁路表面的目标体积内具有三维均匀分布。通过16块磁块的组合，使目标区域的磁场方向与磁路表面平行。利用三维有限元方法，在距离磁路表面55mm的感兴趣区域（ROI）内，尺寸为400mm x 400mm x 200mm的磁路的磁通密度为64.5mT。当ROI尺寸为10 mm × 10 mm × 1 mm时，均匀性为28 ppm，当ROI尺寸为20 mm × 20 mm × 10 mm时，均匀性为613 ppm。少

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