Having been the subject of more than 200 MRI scans and performing many more in the course of her research, Rebecca is the perfect person to teach us all about brain imaging techniques, how they work and what they can be used for. 3750 years ago, if you wanted to look at someone's brain then you had to drill a hole in their head. Known as trepanning, there is evidence to show that it was possible for people to survive the experience. The 1600s saw the introduction of scientific rigor in medicine but didn't stretch much past asking patients what was wrong with them and performing dissections to try and get a baseline for what was "normal". They had no objective measures - the ability to perform the same test over and over again.
In more modern times, the search has been on for a non-invasive, non-ionising way of investigating the body, which is both completely harmless and repeatable lots of times. X-rays have been used for over 100 years and machines used to be shown off at dinner parties as a status symbol, while ultrasound is the most common form of investigation in the UK.
In 1974, Nuclear Magnetic Resonance scanning began, taking advantage of the fact that the body is transparent to radio waves. Since then Nottingham has really been the world's epicentre for MRI, with Sir Peter Mansfield winning the Nobel Prize for Physiology or Medicine in 2003 for the work that he had done at the University of Nottingham regarding his discoveries concerning MRI. The technology can have many different uses from examining what is wrong in a patient to seeing whether a medicine is actually helping.
In the 1970s it took many tens of minutes to get an image, these days it is possible to get a decent image of the brain in just seven minutes. Despite the improvements of the technology over the years, it is still necessary to make trade offs between contrast (bright and dark), spatial resolution (detail) and temporal resolution (time taken). So, something with great contrast showing all of the tiny details would take a long time.
But how does a functional Magnetic Resonance Imager (fMRI) machine actually work? On a basic level, it's taking a photograph using radio waves rather than the visible spectrum. There are different levels of iron in oxygenated and deoxygenated blood. The magnetic field generated by the machine changes around deoxygenated blood and so you can tell which parts of the brain are using more oxygen.
A typical experiment would last for around 10-20 minutes with snapshots of the brain taken every 2 seconds. The subject are then given stimuli and the machine can then measure the blood concentrations in the brain. It is then possible to generate many different sorts of images. However, these are initially greyscale and colour is added to them in order to differentiate which parts of the brain are being used.
MRI scanners are incredibly loud, up to as much as 130 decibels. This isn't particularly helpful for Rebecca as her research is all in hearing. The huge magnets in the machine also mean that anyone with a cochlear implant can't use it. Fortunately, there are other imaging techniques available such as near-infrared spectroscopy. This offers faster sampling than MRI but with less source information and it can only get information from close to the scalp.
Rebecca is looking at the damage caused to hearing caused by noise exposure. This includes "hidden" hearing loss, which is often not detected by standard audiometry and can be the inability to hear at certain wavelengths. So, are there safe expose levels when it comes to noise exposure? What happens in the brain and how does it process sound? Using the scanner, it's possible to see results in real time and it shows that brain stem response is different to cortex response.
Field strength increases every few years, providing more energy in less time. In 1977, the machine at the University of Nottingham was 0.5 Tesla but in 2005, one was installed that was 7 Tesla. These days most MRI machines in the western world are 3 Tesla. This can be important as some IUDs are only safe at 1.5 Tesla.
But why are MRI scanners so loud? Well, the technology that inside isn't that different to that which is in a loudspeaker, only scaled up to many times the size. This then requires a lot of current, which is why the things are so noisy. We also learn that MRI machines are never turned off, despite what you might see in US medical dramas, as they take two days to switch on. Finally, it seems that the biggest threat to the future of MRI is a lack of helium on the planet. It is used to cool down the magnets but the price of it has tripled in just four years - think about that next time you're buying a balloon off that guy outside the Exchange Arcade.
SciBar returns to The Vat & Fiddle at 7:30pm on the 30th of August where Professor Richard Bowtell talks on New Ways Of Imaging The Brain At Work