Sir Peter Mansfield Imaging Centre

Investigation of long-lived magnetization in tissue using optically pumped magnetometers

Supervisors: Richard Bowtell and Matt Brookes

Description of project / Current research interests:

Previous work on post mortem tissue has provided evidence that  residual magnetization is produced when small magnetite deposits are exposed to a magnetic field2. Since under normal circumstances, tissue iron is sequestered in ferritin as ferrihydrite3, it has been suggested that the presence of magnetite indicates a failure of iron regulation4. Such failure has been associated with neurodegenerative diseases, including Alzheimer’s and Parkinson’s diseases. As ferritin does not display remanent magnetization at body temperature, detection of long-lived magnetization in the human body might provide a way of detecting the presence of magnetite, and thus exploring the effect of disease on iron dysregulation. Fields from remanent magnetization are also a confounding factor when measurements of brain activity are made using MEG on human subjects who have recently undergone an MRI scan. 

In pilot experiments, we have used a conventional cryogenic magnetoencephalography (MEG) scanner to detect remanent fields from the human body after brief exposure to a magnetic field. This residual magnetization persists on a time scale of hours, showing a measurable decay during this period. We have also now gained significant experience of using optically pumped magnetometers (OPMs) for measuring the weak magnetic fields generated by brain activity and have demonstrated the advantages that OPM MEG offers5. We would now like to exploit the OPM’s capabilities in investigating the origin of long-lived tissue magnetization – these include capability to bring detectors much closer to the skin surface thus enhancing sensitivity and spatial specificity, the possibility to make simultaneous measurements of two components of the magnetic field, rapid recovery from exposure to a strong magnetic field, allowing magnetization and subsequent measurement to be carried out without moving the subject.  

The aim of this project is to integrate an existing system for magnetizing tissue with the OPM MEG array and to use this set-up to characterize the dependence of tissue magnetization (in vivo and in vitro) on the spatiotemporal form of the polarizing field. The resulting information will provide a better understanding of the source of magnetization. The project will involve experimentation, data analysis and some theoretical work. Expertise and skills developed in the project would include those required for operation of the OPM-MEG array and the polarizing system, along with data analysis, electromagnetic field modelling and physiology. The project could be readily extended to form a 3-year PhD project focusing on the broader investigation and exploitation of recently identified long-lived tissue magnetization.

  1. M. Hamalainen et al., Reviews of Modern Physics 65, 413 (1993).
  2. J.L. Kirschvink, A. Kobayashikirschvink, and B.J. Woodford, PNAS 89, 7683 (1992).
  3. J.F. Schenck and E.A. Zimmerman, NMR in Biomedicine 17, 433 (2004).
  4. Y. Gossuin et al, NMR in Biomedicine 18, 469 (2005).
  5. E. Boto et al, NeuroImage, 149, 414, 2017.