Combining MRI scans could help spot where tumours are short of oxygen, helping to personalise treatment

The Cambridge Science Festival kicks off today, and scientists from the Cancer Research UK and EPSRC Imaging Centre – based in Cambridge and Manchester – will be on hand at an event on Sunday 26 March to talk about the latest developments in cancer imaging. In a series of guest posts ahead of the event, our scientists explore what the future holds for 3 different ways to scan or take pictures of tumours. The first, from PhD student Adam Featherstone, looks at MRI.

All tumours are different. The balance of faulty genes and molecules that help them grow, and their appearance on scans, is unique to each tumour.

These differences can be seen between patients, but also between tumours within the same patient.

In fact, regions inside the same tumour can behave remarkably differently to each other in terms of how the cells may grow and their potential to spread.

As tumours grow, some areas can become starved of oxygen, which encourages cells to adapt and change their behaviour in order to survive. In some cases it’s these regions of low oxygen (known as hypoxia), and its effect on cell behaviour, that can lead to tumours becoming resistant to treatments, including certain drugs and radiotherapy.

This means that a one-size-fits-all approach to treatment, where all patients with a particular type of cancer receive the exact same treatment, may not be the best way to tackle the disease. Being able to find out exactly which parts of tumours are short of oxygen is therefore really important as it can show who might benefit from a hypoxia-specific drug, for example.

Unfortunately, most methods doctors have for measuring tumour hypoxia require taking samples of the tumour (biopsies) or inserting measuring probes into the patient. These are far from ideal as they are highly invasive and may not even be possible depending on where the tumour is.

In the Quantitative Biomedical Imaging Laboratory at The University of Manchester, we focus on an entirely different way of measuring hypoxia: MRI. We believe that combining MRI scans and analysis techniques could track down hypoxia, helping doctors to choose better treatment plans for their patients in the future.

What’s new in MRI?

MRI helps us see different tissues inside the body by using magnetic fields and radio waves to measure the slight magnetisation that water molecules naturally carry. And it does this without exposing the patient to radiation, which can be harmful.

We can use MRI to capture images of the inside of a patient’s body, telling us where a tumour is. But we can also repeatedly image the same area of tissue over many minutes. We can then stitch these images together to create an MRI ‘movie’, which we refer to as dynamic MRI.

To help build up these images, we give the patient something known as a ‘contrast agent’, which lights up in the image if the tissue changes to tell us how it’s behaving.

Our research involves 2 types of dynamic MRI, each of which uses a different contrast agent.

The first is injected into a vein in the patient’s arm so it can reach tissues via the bloodstream, causing parts of the MRI image to appear brighter in relation to how much blood the tissue is receiving. If the tumour lights up, this tells us it’s receiving a working blood supply.

In the second type of scan, the patient wears a breathing mask that switches from delivering normal air (21% oxygen) to pure (100%) oxygen. This causes a change in the brightness of the MRI image in relation to how much oxygen is in the tissue. If the tumour lights up, this tells us it’s got plenty of oxygen.

Our lab, most recently in collaboration with The Institute of Cancer Research, London, showed that by combining these two scanning techniques we can get a clearer picture of hypoxia inside mouse tumours.

Specifically, regions of tumours that light up with the scan that monitors blood supply but don’t light up with the oxygen-detecting scan we believe show hypoxia.

This study found 3 categories of tumour tissue (regular, hypoxic, and dead), which matched with the invasive methods of measuring hypoxia. And it lays the vital groundwork in potentially establishing a less invasive clinical measure of hypoxia.

But, as exciting as it is that these MRI techniques can measure tumour hypoxia, the oxygen-detecting scan is relatively new and the combination of the two scans is newer still. Because of this, we don’t know if simply looking at the bright spots on different scans is making full use of the dynamic MRI.

How do we take it further?

For my PhD research, I’m investigating whether we can extract even more information from these types of MRI images. I want to know if we can identify more than 3 types of tissue, and perhaps locate different levels of hypoxia in tumours.

If it’s possible to make better use of dynamic MRI, we could provide even more useful information to doctors for fine-tuning treatments. And the approach could also be adapted to monitor how well treatments are working.

To do this, I first combine the images from the 2 different scans of the tumour. I then create what’s known as a feature map, which looks a bit like how a thermal camera might show areas of hot and cold. A feature map is an image of the tumour where every pixel has been given a numerical value, and this value tells me something specific about how that part of the tumour is behaving.

I then write computer software to identify and group patterns in these feature maps, creating a region map. In these maps the colour shows areas of the tumour that behave in a similar way but in a distinct way to areas of a different colour. I can then study these region maps to see exactly how these regions are behaving, and how they spread out over the tumour as it grows.

An example of the information that can be extracted from dynamic MRI scans. Credit: Adam Featherstone

While this research (like all research) is not without its challenges, it looks promising for one day helping doctors to reliably and routinely measure hypoxia in each patient’s tumour.

The combination of the 2 scans is now being tested in clinical trials, looking at how well the techniques work in people, and is a great example of the progress that research into imaging techniques such as MRI can make in the fight against cancer.

Adam