Visualising tumours

27 September 2016

Interview with

Dr Sarah Bohndiek, The University of Cambridge

Sarah Bohndiek's Vision Lab at the University of Cambridge is using light to fight cancer. She joined Kat Arney to show how...

Kat - So tell us a bit about this - how important is imaging - being able to see stuff, to fighting cancer, to diagnosing it and to treating it?

Sarah - Well imaging is very important in the journey of a cancer patient. So if you think about the development of the disease early on, many of the symptoms of cancer are nonspecific. So patients will often go into their GP and report these nonspecific symptoms, who will refer them into the hospital.

Now if we didn't have imaging techniques like X-rays, or Magnetic Resonance Imaging (MRI), then we'd have to surgically open up the patient and search for the tumour mass.

Kat - Oh my God!

Sarah - So having these non-invasive imaging techniques allows us to non-invasively have a look inside the patient and search for any abnormal lumps bumps which shouldn't be there in the normal anatomy. So it's very important at diagnosis but then it's also very important when we come to treatment, for example.

So if we think about setting up radiotherapy. Many solid tumours are treated with doses of radiation which are shaped and formed to target the tumour mass, and if we weren't able to see noninvasively where that mass was, then we might misdirect our dose and could cause side effects to off-target tissues.

So it's important in diagnosis, in treatment, and then many patients undergo follow-ups so they'll come back routinely to the hospital to have scans over time to check that their tumour is shrinking, and so that's how we manage to monitor that the tumour is responding to any therapy that's been given.

Kat - So you've mentioned a couple of techniques - a CT which uses X-ray, MRI which uses magnetism. But what are you doing - you're using a different form of waves aren't you?

Sarah - That's right. So we're trying to use visible light and light that's just outside that visible region. And the reason for that is that CT and MRI and other conventional imaging technologies that we're familiar with in hospitals are relatively expensive and require patients actually to go into the hospital and have a scan that's operated by a specialist person. If we could make more cost-effective technologies that could be distributed to GP surgeries, for example, then we might be able to actually improve the journey of a cancer patient where they can get a faster diagnosis rather than having to go into the hospital.

Kat - So, you've got a little demo here to demonstrate one of the techniques that you're using. Talk me through it - what's the technique and show us how this actually works?

Sarah - So the technique is called "photoacoustic imaging" and it's based on a physical concept called the "photoacoustic effect," and this effect is quite readily understandable. If you think about going out into the sunshine on a hot day, the light energy that the Sun is beaming down will be converted into heat energy in our skin, so light is often converted into heat. So that's the photo part of the photoacoustic effect.

So the acoustic part is the heat being converted into sound. So the advantage of this technique is that we can measure how light is absorbed in tissue but we can image it using sound which penetrates much more deeply into the tissue. I mean, we know we can't see through each other so that means that visible light doesn't penetrate very deep into the tissue, but sound does. And so, using the combination of light energy to create sound, means that we can get much better images.

Kat - so you've got a nice little demo here - How does this work?

Sarah - So the demo that I've got is a Coke Zero can..

Kat - Other sugary drinks are available - non-sugary drinks!

Sarah - Thanks Kat. So the reason for using this is the can has a black coating on it and black is very strongly absorbing of light. You can do this at home with any regular camera flash that you have in your house. You can put it close to the coke can... so I'm now going to put the camera flash right up close to the coke can.

Kat - About how far away would you say that is?

Sarah - So about a centimetre from the coke can.

Kat - OK. Flash right up against the can...

Sarah - And I'm going to flash it... and you hear a little 'ping' of the coke can.

Kat - Wow! It's like someone's kind of flicked it with a finger.

Sarah - Exactly. So I'll just do it again so everyone can hear it...


Kat - Wow!. OK, so that is the light basically being turned into sound?

Sarah - Yes. So that's the energy coming from that camera flash being turned into a 'ping' of sound. And so that's exactly what we're doing with the photoacoustic effect when we use it for imaging cancer. So we send a 'ping' of light in; In this case we use a pulse of laser light, and that pulse of laser light gets absorbed and it produces a sound wave which we can detect using regular ultrasound transducers.The same systems that you would use when you're imaging a foetus during pregnancy, and we can use those to detect the sound.

Kat - So you're listening to the light coming back at you?

Sarah - Exactly. And so the advantage of doing this is that ultrasound penetrates much deeper into the tissue than light does, but light gives us much more better contrasts.  When we do ultrasound imaging we're just looking at reflection of sound off of boundaries so we're not looking at any particular kind of molecular information or any functional information.

Whereas when we use light, light is absorbed by a number of different molecules in the body, including haemoglobin in our blood cells. And haemoglobin has a different absorption spectrum so it absorbs light differently with different colours depending on whether it's bound to oxygen or not. So that means, in a tumour, we would be able to develop a map of the level of blood that's present in the tumour, so how many blood vessels are feeding it and also, how well oxygenated that blood is, so how well the nutrients are being delivered.

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