2D Quantitative Imaging of Magnetic Nanoparticles by an AC Biosusceptometry Based Scanning Approach and Inverse Problem

Abstract

The use of magnetic nanoparticles (MNPs) in biomedical applications requires the quantitative knowledge of their quantitative distribution within the body. AC Biosusceptometry (ACB) is a biomagnetic technique recently employed to detect MNPs in vivo by measuring the MNPs response when exposed to an alternate magnetic field. The ACB technique presents some interesting characteristics: non-invasiveness, low operational cost, high portability, and no need for magnetic shielding. ACB conventional methods until now provided only qualitative information about the MNPs’ mapping in small animals. We present a theoretical model and experimentally demonstrate the feasibility of ACB reconstructing 2D quantitative images of MNPs’ distributions. We employed an ACB single-channel scanning approach, measuring at 361 sensor positions, to reconstruct MNPs’ spatial distributions. For this, we established a discrete forward problem and solved the ACB system’s inverse problem. Thus, we were able to determine the positions and quantities of MNPs in a field of view of 5×5×1 cm3 with good precision and accuracy. The results show the ACB system’s capabilities to reconstruct the quantitative spatial distribution of MNPs with a spatial resolution better than 1 cm, and a sensitivity of 1.17 mg of MNPs fixed in gypsum. These results show the system’s potential for biomedical application of MNPs in several studies, for example, electrochemical-functionalized MNPs for cancer cell targeting, quantitative sensing, and possibly in vivo imaging.

Quantitative imaging of magnetic nanoparticles in an unshielded environment using a large AC susceptibility array

“…The mathematical approach of both the forward and inverse problems for quantitative 2D ACB imaging has been described by Biasotti et al [ 24 ]. Briefly, considering distinct pick-up coils and a FOV composed of voxels, the induced voltage in the -th pick-up coil, generated by a MNP mass ( ) in the -th voxel, can be calculated by Faraday’s law and is given by: …”

“…Despite the advantages of acquisition with high temporal resolution and the potential for real-time imaging, the absence of a direct correlation between pixel intensity with MNPs mass restricts the application of the ACB system to qualitative analysis. To overcome this limitation, Biasotti and co-workers employed a scanning approach to the single-sensor ACB system by establishing a forward problem and solving the corresponding inverse problem, obtaining 2D quantitative images of an MNPs spatial distribution [ 24 ]. Though it is suitable for ex vivo biodistribution studies or in vivo quantifications limited to a specific organ, this ACB setup is limited for future real-time imaging applications due to the prolonged scanning times.…”