Magnetic Particle Imaging (MPI) is a tracer technique for imaging which has been established about 20 years ago using very small iron-oxide nanoparticles for signal generation. An alter-native – yet to some extend related – approach using the same type of particles was implemented in a previous DFG funded project. This so-called Rotating Drift Spectroscopy (RDS) exploits the rotational behaviour of such particles when exposed to external rotating fields. Due to intrinsic as well as extrinsic properties of the particles they cannot follow the external field without a lag. This allows evaluation of these properties, e.g., environmental viscosity or temperature. This project’s goals were: 1st Development and implementation of a mobile RDS spectrometer. 2nd Implementation of imaging strategies and apparatus using the rotational drift effect. 3rd Improved understanding of the underlying physics of the motion of particles in rotating fields. Goal 1: During this project, a mobile RDS setup was build, the “RDSkop”, and its ability to detect environmental parameters was demonstrated on the examples of changing viscosity or temperature. Furthermore, intrinsic parameters were evaluated by scanning and distinguishing different kinds of nanoparticles. Additional result: The COVID pandemic triggered evaluating RDS as a method for fast screening of samples for COV-19-antibodies, i.e., for detecting infections. In combination with MPI strategies a new method called Critical Offset Magnetic PArticle SpectroScopy (COM-PASS) was developed, which allows a rapid detection of antibodies within seconds with a sensitivity and specificity comparable to the gold-standard PCR tests. A corresponding spectrometer has been developed in another small DFG-funded project. Goal 2: For RDS imaging (RDSI) an additional spatial encoding is required. Therefore, an offset field is used to align the magnetic particles in the beginning and then different readout methods can be used to effectively do a spectroscopic fingerprinting of the particles point by point. This spatial encoding is achieved by a field in the scanner varying between linear and rotational excitation with changes between the two modes being spatially dependent. Using system simulations and establishing suitable sequences an RDSI system was built. Goal 3: In the previous project a numerical solution describing the motion of particles in rotating magnetic fields was shown. The mathematical research was continued and a fully analytical closed expression for description of the motion in the edge case of vanishing thermal interactions was found. This closed expression can be used to verify numerical simulation and as a basis for finding more general descriptions. With these above-mentioned results of the proposal’s work-program we were able to advance RDS(I) further towards application and – with COMPASS – establish a spectroscopic technique with very high potential for application.
Volker C. Behr (Thu,) studied this question.