Magnetic Nanoparticle Imaging Using Second Harmonic Signals for Sentinel Lymph Node Detection

Abstract

We developed a magnetic nanoparticle (MNP) imaging system that uses the second harmonic signal of MNPs. Detecting the second harmonic signal, we could significantly decrease the interference of the excitation field and obtain a clear signal from MNPs. We showed that the present system can detect a 100-μg MNP sample located at a depth of 30 mm from the pickup coil. We also developed a method to accurately estimate the sample position. For this purpose, we measured the contour map of the signal field. From the measurement of the x and y components of the signal field, Bx and By, we could estimate the sample depth z. With the estimated z, the contour map of the Bz field was converted to an MNP distribution map using a mathematical technique called singular value decomposition (SVD). We could clearly distinguish two MNP samples separated by Δx = 20 mm and located at z = 20 mm. We also show the robustness of the SVD analysis by demonstrating that the MNP distribution can be accurately estimated even when a ±5 mm error exists in the depth estimation. This simple imaging system will be useful for in-vivo application, especially for sentinel lymph node detection.