Neural Imaging – Pictures of the Brain (the ultimate selfie!)

At Design Your Life, we look a lot at how we can change our brains. But how do we know that our brains change?

Warning: this one gets a little geeky!

The latest advances in science and technology have let us take a long hard look into our minds. Perhaps not in the mind-reading way, that some presume. No 1984 Ministry of Truth nightmares…yet.

Neuroimaging (pictures of the brain) are designed to look both at the structure of the brain and how parts of it function.

The blueprint of the mind

Structural imaging (pictures designed to look at the structure of the brain) look at the different materials of the brain. Yes, the brain isn’t all just the same ‘goop’. The head and brain consists of the skull, grey matter, white matter and cerebrospinal fluid. I know, I know, that’s a lot of things to put into your head. Pardon the pun.

Grey matter is made up of what they call neuronal cell bodies. You can think of this as the main stuff in the brain. Hence, the saying “Use your grey matter”.

White matter, is the axons and support cells. These are like the wires that connect parts of the brains and the scaffolding that holds it all together.

Cerebrospinal fluid is like the infrastructure of the brain. It helps send to some messages like the postman. It carries out waste like the garbage collector and it provides a protective cushion like the police officer.

Ever heard of a CT scan? Maybe on those medical dramas on TV that I’m too squeamish to watch (there is a reason I chose psychology over medicine!). CT scans became synonymous with pictures of the brain. But how do they work? Each of the different elements of the brain absorb X-rays differently. The skull absorbs the most and the cerebrospinal fluid the least with grey and white matter sitting in between. These produces a cool black and white picture of the brain. From this we can see its structure. Like blueprint of a building. It shows where the walls are, where the hallways are, where the rooms are.

However, while CT scans become synonymous with pictures of the brain, they did come with some downsides. The first was that they used a small amount of radiation. The second was that their resolution wasn’t the best. Resolution allows scientists to see the fine details of the brain. The greater the resolution, the more details we can see.

But, as flat screen TVs replace the old tube TVs and MP3s replace CDs which replaced vinyl, new technology allowed us to overcome these downsides and improve give us even better pictures of the brain.

So what was the flat screen of neuro-imagery? It is called magnetic resonance imaging (MRI).

MRI has been touted as one of the most important advances in medicine last century. Rightfully so, it’s inventors Sir Peter Mansfield and Paul Lauterbur were given the Novel Prize in 2003.

So what makes MRI so good?

Well, it doesn’t have that pesky radiation problem that CT scans had. Always a good thing! Unless you think the radiation will give you superpowers!

Also, it has much better spatial resolution. As you remember, this means that it can see brain in far greater detail. In our blueprint analogy, this means that the two rooms next to each other, actually look like two rooms and not one big room.

In addition to being able to see greater detail, it can also better tell the difference between grey matter and white matter. So we can see the ‘meat’ of the brain against the ‘wires’ and ‘scaffolding’ that hold it all together.

So, how many of you want to know how MRIs work?

If you are reading this book, I take it that you’re are a Curious Coconut and are eager to learn about MRIs. However, even, I understand that this may be a bit too technical (and by that I mean…‘geeky’) for some. If so, feel free to skip ahead.

Are you still here? Nice. Let’s geek it out and look at MRIs.

I find MRIs to be truly ingenious. One of those things that are so simple and so ingenious that you sit and wonder why you didn’t think of it. However, even with my 3 semesters of university physics and astrophysics, I get lost in the detail. So let’s look at MRI physics…without going into the physics! (queue the collective sigh of relief)

As you would know, most of our body is made up of water. We hear this when we exercise in the heat. We hear this from companies trying to sell bottles of water that cost more that petrol. Seriously, how is something that is free from the tap cost as much as something like fuel. Someone, digs a hole…nothing…digs another hole…nothing and so on. Then when they find oil, the build a rig, pump it out from under the ground. Ship it across the world to a refinery. Refine it. Truck it to the local petrol station and store it underground until you are ready to drive up and pump it into your car. And bottled water costs more than this?!...but I digress. Right, the body is mainly water. Our brain is no different. However, different types of tissue in our brain have different amounts of water in them.

Now to the chemistry. Can you remember the chemical formula of water? If not, it was also probably on one of those overpriced water commercials. It is H2O (not H2GO!). Water molecules have a weak magnetic field. In water, these are randomly oriented. Some are pointing up, some around pointing down, some around pointing to your left…well you get the picture. When the MRI scan starts, it uses a strong magnetic field across the brain. This causes some of the water molecules to point in the same direction. Once this happens, a radio pulse knocks the water molecules that have aligned themselves by 90 degrees. This causes a measurable change in the magnetic field which is sensed by the MRI. 

Lost yet? If you weren’t, you are doing better than I did the first, second, third and maybe tenth time! Think of the water molecules like lots of little compasses. However, initially, they don’t have a north pole to point at and are randomly pointing. When the MRI starts, it is like creating a north pole. Suddenly, some of the compasses point in the same direction. Next the radio pulse, is like someone who flicks the compasses pointing north by 90 degrees. After this, the compasses slowly return to north. Different tissues return at different speeds an allows the sensor to determine the structure of the brain.

Everyone has their own job to do

The second type of neuro-imagery is functional imaging.

If structural imaging is the blueprint of the brain and shows the rooms and hallways, functional imaging shows what each room is for. It shows, which rooms are the toilets, which are conference rooms, which are the kitchens etc. Not a perfect analogy but I hope you get the gist.

Picture the blood in the brain like cars in a city. If we know where the cars go during specific events, we can try and work out what those locations are for. During school drop off time, the cars go to the schools. We can predict that the place that the cars go are the schools. When the football is on, the cars go to the stadium. Functional imaging works by looking at where the blood goes during specific events and predicts that these parts of the brain are used for those functions.

Picture those cars driving around. But if you can’t see the cars, it is hard to know where they go. What if we put our own cars in there that beeped their horns intermittently. And we had sensors to know where the beeping was coming form. Our cars would follow the existing cars but we would know where they were going but listening to the beeping.

Positron emission tomography (PET) works in this way. PET uses a radioactive tracer which is injected into the blood stream. As the tracer decays it releases positrons which can be detected by sensors around the head. However, injecting radioactive tracers isn’t as appealing to patients as it sounds.

Bring back the flat screen TV…I mean MRI.

Yes, you guessed it, MRI can do functional imaging too. In this case, we call it fMRI.

However instead of using radioactive tracers, fMRI uses the oxygen in our blood to measure blood flow. When neurons (the cells in our brain) are being used heavily, they use more oxygen. In the process they convert one chemical into another (for the chemistry geeks out there, oxyhemoglobin to deoxyhemoglobin). This product is strongly magnetic and distorts the magnetic field. It is this distortion that is measured by the fMRI. Using the car analogy this is like measuring the traffic by measuring the amount of exhaust gases left from the cars as they travel.