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Detection limit of magnetic nanoparticles improved

A newly developed pick-up coil makes magnetic particle imaging even more efficient

PTB-News 1.2018
Especially interesting for

biomedical applications and res

earchmagnetic particle imaging (MPI) technology

(magnetic) nanoparticle research

In cooperation with industrial partners, PTB has developed a pick-up coil for a novel imaging method called magnetic particle imaging (MPI). This coil has already been successfully implemented and tested at the MPI system in Berlin. The new coil considerably improves the sensitivity of the technique. Quantities of magnetic nanoparticles as small as a few nanograms can now be detected.

Figure: a) Reconstructions of varying nanoparticle quantities, each measured with a conventional transmitreceive coil system (top) and with the receive-only coil (bottom). The red dots represent the sample positions. b) Product layout of an optimized 1D receive-only coil

Magnetic nanoparticles exhibit unique magnetic properties which are utilized in a number of biomedical applications, both therapeutic and diagnostic. The tracking of cells or medicine inside the body is an example of this type of application. The particle surface can be modified in such a way that the particles bind to certain cells. These particles’ magnetic properties allow them to interact in a non-invasive way; they can thus be used in various manners. One of these possibilities is magnetic particle imaging (MPI), a quantitative, radiation-free medical imaging method which exploits the physical properties of magnetic nanoparticles for diagnostics. After such nanoparticles have been introduced into the body, they can be excited by means of magnetic (alternating) fields. The distribution of the nanoparticles can eventually be reconstructed with millimeter precision from the measured signal. A great advantage of MPI compared to other imaging procedures is that not only are the nanoparticles represented, but they can also be quantified at each image point. Furthermore, the procedure enables dynamic images with a temporal resolution of up to 21 ms. These are two considerable advantages for functional biomedical applications.


The decisive aspect for most application fields is the sensitivity of the detection system to exceedingly small amounts of magnetic nanoparticles. In this context, the sensor plays a key role in realizing the full potential of the technique. In cooperation with Bruker, PTB in Berlin has developed a new pick-up coil for MPI which ensures enhanced signal acquisition. In order to characterize this coil, a prototype was installed and tested at the institute’s own MPI scanner at the Rudolf Virchow Hospital in Berlin. Direct comparison with the previous transmitreceive hardware system shows that the new receive-only coil is four times as sensitive as the previous design, and offers enhanced suppression of interfering noise. This allows nanoparticle quantities as small as a few nanograms to be detected, i.e. the detection limit has been improved by one order of magnitude.

The findings obtained by PTB through this prototype have decisively supported the future potential of MPI to be used in preclinical research.


Frank Wiekhorst
Department 8.2
Phone: +49 30 3481-7347
E-mail: frank.wiekhorst(at)ptb.de

Scientific publication

J. Wells, H. Paysen, O. Kosch, N. Löwa, F. Schmitzberger, M. Makowski, J. Franke, L. Trahms, F. Wiekhorst: Characterizing a preclinical magnetic particle imaging system with separate pickup coil. IEEE Transactions on Magnetics 53:1–5 (2017)