Tetsuya Matsuda

Magnetic Particle Imaging (MPI) is an imaging modality that directly detects the nonlinear responses of magnetic nanoparticles (MNPs). Spatial encoding is achieved by saturating the magnetic moment of MNPs almost everywhere except in a special point called the field-free region in which a magnetic field vanishes. Recently, MPI sensitivity was improved using a field-free line (FFL) in which a field-free region was formed as a line. An MPI with a FFL device was developed using a neodymium magnet and an iron yoke to image objects with a small amount of magnetic nanoparticles, such as in biological systems. We have been developing MPI equipment for detecting amyloid-β, a causative agent of Alzheimer's disease. We attached amyloid-β probes to nanoparticles. In our development, we discriminated between magnetic particles that are bound to biological tissue from those that are suspended in the brain. We focused on the differences in relaxation times due to the change in the hydrodynamic diameter between the bound and unbound particles. Because the bound particles have a larger apparent particle size and do not rotate when an AC magnetic field is applied, the relaxation time is different from the unbound particles. Since the differences in the responses to the AC magnetic field appear as relaxation times, we investigated a particle-discrimination method using these differences and studied the magnetization response of magnetic nanoparticles using our developed MPI device.

Research and development for the practical application of a med-ical-use magnetic resonance imaging system (MRI) superconduct-ing magnet that does not require liquid helium started as the New Energy and Industrial Technology Development Organization's (NEDO) supported project in fiscal 2016. Development of a liquid helium-free medical MRI superconducting magnet has been de-sired. Another purpose is to reduce the size and weight of high magnetic field magnets. By using the high temperature supercon-ducting coil, it is possible to make the 3T magnet of the same shape, weight, leakage magnetic field as 1.5T magnet. In this pro-ject, we are developing a half size active shield-type 3T REBCO coil for MRI. This magnet has active shield coils with a maximum diameter of 1200 mm, and its room bore diameter is 480 mm. This magnet is one of the world's largest magnets using a REB-CO wire with an accumulated energy of 1.6 MJ at the rated mag-netic field. It generates a magnetic field of high homogeneity and stability necessary for imaging. In this paper, we report the half-size active shield-type 3T coil and its cooling system that can re-duce the initial cooling time.