Sensitivity Improvement of Magnetic Nanoparticle Imaging by Compensation with Digital-to-Analog Converter

In the application of the magnetic nanoparticle (MNP) imaging technique, which uses a large ac magnetic field and detects harmonic signals, it is important to attenuate the fundamental signal generated by the magnetic field used for excitation. In this article, we propose a method to reduce this fundamental signal using a compensation circuit with a digital-to-analog (D/A) converter, which can be interpreted as an electrical bridge. We apply the proposed method to an MNP imaging system. The system contains one excitation coil that generates an ac magnetic field and 16 pickup coils that detect the third-harmonic signals from the MNP samples. The position of an MNP sample containing $100~\mu \text{g}$ of Fe was estimated using this system via an inverse problem analysis. The results demonstrate that the fundamental signal is suppressed successfully and also show that the distance between the estimated and actual positions of the MNP sample is less than 10 mm at a depth of 50 mm.