Magnetic particle imaging with use of second harmonic response of magnetization

Magnetic particle imaging (MPI), as introduced by Gleich and Weizenecker, is based on utilizing the nonlinear magnetization response M for detection of superparamagnetic iron oxide nanoparticles (MNP). The excited M contains not only the fundamental excitation frequency ω0 but also its harmonics when applying an ac excitation magnetic field. To improve the detection sensitivity for the magnetization M of MNP and the imaging technique based on the detection of a second harmonic response, a 2D imaging system consisting of four magnetic fields, dc bias field Hdc, ac modulation field Hac, gradient field of Z-axis and gradient field of X-axis have been constructed. The advantage of the detection of a second harmonic response is that no large ac modulation field Hac is required. This study demonstrated a MNP detection method using a second harmonic of magnetic response. The position of the 10-microlitre MNP sample was clearly indicated in 2D imaging.