Preclinical Magnetic Particle Imaging: an interview with Professor Jeff Bulte, Johns Hopkins

Thought leader series

Please can you introduce yourself and your subject area?

I'm Jeff Bulte, professor of Radiology and Director of Cellular Imaging at the Institute for Cell Engineering at Johns Hopkins University School of Medicine, Baltimore, Maryland in the United States. I lead a group of about 20 to 25 people who focus their research on imaging cells.
There are some similarities between MRI and MPI, so we can learn what can be achieved with these techniques using the same kind of nanoparticles and targeting molecules. We can then start demonstrating the potential applications.

Why did you enter the field of Magnetic Particle Imaging (MPI) research?

I've been imaging cells with MRI for a long time (for 25 years), but I got into MPI research about ten years ago.
We became interested in the potential MPI has for providing very good cell quantification. It has a very high sensitivity and can be used for hotspot imaging, just like radionuclide imaging can, as a tracer technique. There are some advantages of MPI over MRI and that's why I got interested in it.

What makes MPI technology unique in comparison to other imaging modalities?

What makes it unique is that it's a hotspot technique based on magnetic nanoparticles. We're looking at super-paramagnetic magnetization.
Unique features are the technique’s extreme sensitivity, its potential for use in cell quantification and the ease of image interpretation, because there's no confusing background signal as there is with some other techniques.
Having said that, it may well also be that it needs combining with other techniques such as CT and MRI to co-localize the anatomy or tissue with these hotspots of particles.

Can you share any up-to-date research results with us?

Yes, I think what I've seen at this meeting today – and there’s more to come – is that a lot of people are able to produce images. Originally, there was more theoretical calculation, quantification and mathematical development of particles and a lot of progress has been made since then.
The goal is to eventually make clinical scanners. If things continue at the current pace, we will develop small scanners, then bigger animal scanners and bigger machines. The pace of development is very fast at the moment.
Going forwards, I think this meeting has grown so much in the last few years and is on its way up, almost like a snowball effect. The more people get involved, the faster development becomes.

What are the main limitations?

One limitation is the poor availability of workable machines, which are mainly only available in Germany. The magnetic nanoparticles also need to be commercially available and eventually there need to be clinical preparations.

What will be the main applications of MPI?

I think one of the main applications of MPI will be angiography – blood flow measurements and looking at vessel obstructions in a very fast, real-time scan mode.
I also think cell imaging will be an application because the technique is so sensitive. For instance, we can label a patient's cells with these particles, inject them back into the patient and if they have an infection or any inflammation we do not know the location of, these cells will home in on the area, which we can then image. I think these are wonderful applications.

What are the next steps?

I think the next step would be the construction of a clinical scanner because then everybody gets interested, especially the physicians who control a lot of the politics at medical schools. That would be great.
The other thing that's missing is a second imaging technique that can co-localize those hotspots with the anatomy of the tissue. For instance, combining an MPI scanner with MRI or CT, would also be great and that might be the next phase of development. However, that would involve a lot of engineering because the magnetic fields may not be compatible and one field may affect the other one.
I would just like to see the technique ubiquitously available in academic centers as an additional clinical tool that can be applied for faster and more specific diagnosis of disease.