Square-Wave Inverter Excitation for Magnetic Nanoparticle Tomography

Abstract

The imaging of magnetic nanoparticle (MNP) distributions is a promising biomedical imaging technique for detecting cancers [1]. A method is magnetic nanoparticle tomography (MNT), in which multiple magnetic sensors are used to detect the harmonic signal of MNPs [2] [3]. In our previous study [2] [3], a linear amplifier power supply with low power efficiency was used to generate the excitation magnetic field. In this study, a square-wave inverter was alternatively used to provide high efficiency. However, the third harmonic excitation field was generated by the general square-wave inverter excitation, degrading the imaging performance. Therefore, we developed a method to suppress the third harmonic by shifting the switching phase of the inverter. The experimental setup is shown in Fig. 1. A full-bridge inverter was used to generate a square excitation voltage. Generally, a square-wave voltage was generated by shifting the switching phase of the left- and right-arms by 180°. The square voltage generated using this method contained the third harmonic. We developed a method to suppress the third harmonic by shifting the switching phase by 120°. In this case, the third harmonic does not appear theoretically. The Resovist MNP sample (500 mg-Fe / 150 mg) was arranged and magnetized by an alternating-current magnetic field in the Z-axis using an excitation coil. The sample moved on the x-y plane, and the third harmonic signal of the MNPs was obtained using 16 detection coils. The distance between the excitation coil and the sample was set to 35 mm. Figs. 2(a) and (b) show the third harmonic signal distribution from MNPs using 180° and 120° shifts, respectively, detected by a detection coil. The signal from the MNPs was masked by the excitation field noise (Fig. 2(a)). In contrast, the peak and trough were visible. The results show that the proposed method increases the feasibility of MNT using a square wave inverter excitation. This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Number JP21H01342).  Fig.1. Experimental setup  Fig. 2. Third harmonic signal distributions of MNPs using (a) 180° and (b) 120° shifts (The cross mark indicates the position of a detection coil.)