2D magnetic nanoparticle imaging using magnetization response second harmonic
Abstract A detection method and an imaging technique for magnetic nanoparticles (MNPs) have been investigated. In MNP detection and in magnetic particle imaging (MPI) the most commonly employed method is the detection of the odd harmonics of the magnetization response. We examined the advantage of using the second harmonic response when applying an AC magnetic modulation field and a DC bias field. If the magnetization response is detected by a Cu wound coil detection system, the output voltage from the coil is proportional to the change in the flux, dph/dt Thus, the dependence of the derivative of the magnetization, M on an AC magnetic modulation field and a DC bias field were calculated and investigated. The calculations were in good agreement with the experimental results. We demonstrated that the use of the second harmonic response for the detection of MNPs has an advantage compared with the usage of the third harmonic response, when the Cu wound coil detection system is employed and the amplitude of the ratio of the AC modulation field and a knee field H ac H k is less than 2. We also constructed a 2D MPI scanner using a pair of permanent ring magnets with a bore of ph 80 mm separated by 90 mm. The magnets generated a gradient of G z =3.17 T/m transverse to the imaging bore and G x =1.33 T/m along the longitudinal axis. An original concentrated 10 ml Resovist solution in a ph 2x3 mm 2 vessel was used as a sample, and it was imaged by the scanner. As a result, a 2D contour map image could be successfully generated using the method with a lock in amplifier.