Three-dimensional imaging of magnetic nanoparticles using multiple pickup coils and field-free line

Abstract

We performed three-dimensional detection of magnetic nanoparticle (MNP) samples using third-harmonic signal detection. In this method, a combination of five pickup coils and a gradient field with a field-free line was used to acquire three-dimensional MNP sample position information. The resulting two-dimensional maps of the signal fields generated by the MNP samples are sufficient for three-dimensional MNP image reconstruction. In the experiments, two MNP samples with different Fe contents were set at different positions. Two-dimensional field maps were measured using the five pickup coils, and the three-dimensional MNP sample distribution was then reconstructed from these field maps by solving an inversion problem. We demonstrated three-dimensional detection of two MNP samples where we reconstructed the three-dimensional positions and the Fe contents of these two MNP samples with reasonable accuracy. These results indicate the feasibility of the proposed system for threedimensional magnetic particle imaging.

Three-dimensional detection of magnetic nanoparticles using a field-free line with weak field gradient and multiple pickup coils

“…It is important, however, to clarify how much the G value can be decreased without degrading the spatial resolution for MPI when multiple pickup coils are used. As shown previously, 12,15) we can increase information on the spatial distribution of the MNP sample by increasing the number of pickup coils. However, it is not clear how much the degradation of the spatial resolution arising from the smaller G value can be compensated by using information obtained with multiple pickup coils.…”

“…Figure 1(a) shows a schematic depiction of the MPI system, which has previously been described in detail. 11,12) The system consists of three sets of coils, which are called the AC excitation, DC gradient and pickup coils. A magnetic field B was applied to the MNP sample using the excitation and gradient coils as follows…”

“…For this purpose, we have been developing an MPI system using a weak field gradient and multiple pickup coils. 11,12) It was shown by us 13) and Ref. 14 that the field gradient can be decreased without degrading the spatial resolution when we use an AC excitation field with a small amplitude.…”

“…We also showed that the spatial resolution can be improved by using multiple pickup coils for signal detection. 12) This is because information on the spatial distribution of the MNP sample can be increased by using different field maps obtained with multiple pickup coils, 12,15) compared with the conventional case of using a single pickup coil. Based on these results, we developed the MPI system using the FFL and five pickup coils, as reported in our previous paper.…”

“…Based on these results, we developed the MPI system using the FFL and five pickup coils, as reported in our previous paper. 12) In that system, we used a small field gradient (G = 0.1-0.21 T m −1 ) and a relatively low AC excitation field (2 mT at 3 kHz). We successfully demonstrated three-dimensional imaging of two MNP samples.…”