Surgeons face difficult decisions when dealing with cancer, with brain cancers removing too much too soon can lead to disability, taking too little and the disease returns. But scientists say a new laser can help doctors quickly find the outside edge of a tumor. Our health correspondent James explained why conventional brain surgery is so complicated.

If you just think of another cancer. You find a tumorous growth and then you go "right we've got to get that out." And what you can do is you can just take a section either side. Easy peasy to take it out. Once you get to the brain, it gets a little bit more difficult because you can't go "Okay, there's the tumor. Let's take you know a nice 5 centimetres around either side. We are just to make sure we've got all of it out", because if you do that you'll be left with a profound disability. So one of the great challenges when it comes to brain surgery is only operating on what you have to operate on. It's like a cloud, when it comes to brain surgery. You know where the middle of the tumor is but where the edge of it is gets a little hazy.

So tell us about this new method.

The idea of this method is that you use a laser to analyze the brain sample for you. And what happens is it changes the properties of the laser depending on what the chemicals are inside the different cells. And a cancer cell is chemically very different to normal brain tissue. So that allows surgeons to very easily spot where the edge of the cloud of that brain tumor is. Now it's only been tested for trying to work out where the edge of a tumor is. So they think it's working quite well. Well, it's really laborious. What you have to do is you've taken sample of brain tissue, you have to go away, freeze it, press it down so it's flat, put all kinds of dies on it so that it stains the tissue so you can actually see it and then put it under a microscope. And that process can take 40, 50 minutes. And it's one of the reasons why brain surgery can take such a long time.

So as you say, this is, at this state is still just a study. What are the implications then?

Well the grand hope is that not only can you make surgery much quicker but you make sure you are actually getting rid of all of the brain tumor. So the aim really is the aim of all medical research, to make something safer and benefit patients.