some brilliant people are standing in for me here.

First is Alex from Brainbook, he's a brain surgeon.

There's nothing gruesome in this video,

but there is the answer to a question I never knew I had,

how do neurosurgeons find their way around inside the brain?

- Neurosurgery is fraught with risk.

The brain is packed with almost 100 billion neurons

compartmentalised into complex bundles of nerves

and other structures that make you who you are.

Small parts of your brain are vital for allowing you

to speak, move, think, learn and love.

As neurosurgeons, we operate in and around

these vital structures and spend a great deal of time

learning the anatomy so that we can operate safely.

The room for error can be millimetres

as we manoeuvre around blood vessels and critical nerves

and damaging any of these can cause either life changing

or life ending complications.

No matter how good the surgeon and no matter

how good their knowledge, we can still go astray

and need a helping hand.

Neurosurgery is a specialty that's inherently

intertwined with cutting edge technology,

and we can use that to guide us

when we're navigating the brain.

Today I'm going to show you how neurosurgeons

can use infrared and electromagnetic image guidance systems

to show us exactly where we are in the brain

during critical operations like brain tumour surgery,

or inserting biopsy needles deep into the brain.

This is a Medtronic StealthStation S8.

It's a combination of hardware and software

that uses special trackable instruments,

such as this pointer and this stilette.

To be able to guide the neurosurgeon,

the system tracks the position of these instruments

in relation to the surgical anatomy

and sends that information to the software.

The software then displays the instrument's position

on either the CT or MRI scan of that patient.

The system can track instruments either optically

using an infrared camera or electromagnetically.

With optical tracking, this camera sends out

and then detects infrared light

that's reflected from these silver balls.

The camera then transmits the instrument's location

to the navigation software.

Similarly, with electromagnetic tracking,

the emitter emits a low energy magnetic field

with unique characteristics at every point.

The electromagnetic instruments contain sensors,

which allow the navigation software

to identify the instrument's location within the electromagnetic field.

For the software to display the instrument's location

in relation to images of the patient, you've got

to help the software by creating a map

between points on the patient and points in the images.

This process is called registration,

and it's essentially the same for both optical

and electromagnetic types.

After registration is complete, whenever the surgeon

touches a point on the patient using one of these tracked instruments,

the computer uses the map

to identify the corresponding point on the images.

This identification is called navigation.

And now I'm going to show you both systems in action.

Here we've got an MRI scan of a brain model

that we're going to use.

Coming up, you see this white blob, which is supposed

to be a simulated brain tumour on the MRI scan.

Up here, you can see an eye coming into view,

and then the nose.

So this is the brain that's going to correspond with the model.

In the bottom right hand corner, we're using infrared tools,

and you can see the pointer coming into reference

with the reference array that we've got fixed

to the patient's head.

We're going to be doing registration as we mentioned before,

marking out lots of points with the infrared pointer.

Now we can verify the registration.

We've got 1.5 millimetre accuracy,

which will do for this simulation.

So, we're going to touch the tip of the nose on the model

and you can see in the MRI that that correlates well.

Let's look at the inner part of the eye and that looks good.

The outer part of the eye and the tip of the ear,

and this is all looking like

it's corresponding really nicely.

We put the pointer into this hole that's pre made,

we're on the tumour, so that's looking good as well.

And this is a pre made craniotomy or trapdoor in the skull

that's going to allow us to just access the tumour straight away.

In real life, we'd make this hole

and that would take about 45 minutes to an hour,

having cut through the skin and drilled off this bone.

So we can operate around this tumour and see exactly

where we are in the brain avoiding critical structures

like blood vessels, nerves and parts of the brain

that are important for speaking and seeing, for example.

Now let's move on to the electromagnetic form of navigation,

which is also called axiom guidance.

We're going to be using a Rowena neurosurgical simulator

and thanks a lot to Susie Glover from Delta

and Stephanie Brown from NHS Healthcare Horizons.

This model is quite cool because it actually has fluid systems within it

and here you can see us actually scanning it

and we're going to take these CT images and plug them into the software.

Here you can see we've put the model in pins,

but we don't usually do that because it can interfere

with the electromagnetic system.

We're going to be using this stilette to guide

a piece of tubing deep into the brain's fluid reservoirs.

This pointer is what we're going to use to do a registration.

This is the actual catheter that we're going to be inserting

deep into the brain and we'll take out

the little metal stilette that comes with it,

and insert the tracked axiom stilette

that comes with the electromagnetic system.

So now that catheter is tracked, we can use this pointer

to mark out exactly what trajectory we're going to be using

and see where we're going to need to make a cut

and then later on where we're going to make a burr hole

which is a small hole in the skull

that allows us to access the brain.

Now we're going to mark it with a red marker in this case

and start drilling.

[high speed drilling]

Once we've made the hole and done a bit more work

in real life, we're ready to put the catheter in.

On the right so you can see that the StealthStation

is showing us how far we need to go and shows us a target

that we've pre-planned.

We're going to follow that trajectory

and make sure the green dots line up.

As we advance the catheter down,

it gives us a countdown in millimetres.

Once we reach zero, we should be in the ventricle system

and as I take out the metal stilette from inside the tubing,

fluid should start coming out.

And there we are, we are in. And in real life

we'd now secure this catheter and get out of there.

- Go and subscribe to Brainbook, start with his video

on a day in the life of a neurosurgeon on call.

Next week, we go from brain surgery to settling on Mars.