Using MRI to see the optic nerve more clearly

Magnetic resonance Imaging (MRI), is something people with MS are very familiar with, it creates diagnostic pictures of the brain and spinal cord by using magnetic fields rather than x-ray beams.

MRI machines create large magnetic fields which then rapidly change causing specific atoms in the body to change their magnetic fields to match the extremely powerful magnetic fields in the MRI machine. These changes in the atom’s magnetic field are temporary, and depending on the chemical makeup of the tissue the atoms drop back to their natural state at different times. The MRI machine then detects these subtle changes and builds up an image of the body from billions of these minute changes and how long they last.

Typically, when a person with MS has an MRI, there are a range of pictures that are generated by using varying strengths and timings of the magnetic pulses. These are referred to as sequences. The different types of sequences capture different sorts of information, for example whether there is active lesions or older lesions with less inflammation. However, these sequences are not useful for picking up more detailed changes in myelin structure in the brain.

Now a team of Australian researchers led by Ms Sanuji Gajamange,  a postgraduate scholar funded by MS Research Australia, and Dr Scott Kolbe have investigated a new technique which may help by detecting things previously missed by traditional MRI techniques, including more microscopic details.

In a relatively small study published in the journal NeuroImage: Clinical the researchers have imaged the optic nerve of 17 people with a history of optic neuritis (inflammation and myelin damage in the optic nerve) and 14 healthy individuals without optic neuritis (controls).

They used a new technique developed by Professor Alan Connelly from The Florey Institute of Neuroscience and Mental Health, Melbourne, to explore nerve fibres of the optic nerve in the people who had experienced optic neuritis. Their technique can detect the density of nerve fibres and the orientation of the fibres, whereas most common imaging focuses on the presence of ‘larger’ features, such as lesions and other structural changes.

This technique has been previously used to investigate changes in motor neurone disease, epilepsy and in brain development. It does not require new MRI equipment but is a new way to interpret some of the signals induced by the changes in magnetic fields of the atoms in the body.

Using their technique, they showed that those who had experienced acute optic neuritis had a reduced nerve fibre density in the pathways taking visual information from the eyes to the rest of the brain. Whilst this might appear to be obvious, all novel techniques require validation to confirm that they can detect known changes. In addition, given that this study was carried out on people with a relatively short history of disease and that they could detect differences suggests that this is a very sensitive technique which may be able to detect changes that occur before any clinical disability or clinical signs are obvious. It could also be used to measure myelin repair in clinical trials to test new myelin repair treatments – a much-needed missing element in MS research.

The team is hoping to expand this study and look for associations between the pathways of damaged nerve fibres  and changes in other areas of the brain not necessarily directly associated with vision. Hopefully, techniques like this can help us detect disease activity early and monitor responses to treatment to help optimise treatment and prevent the accumulation of MS symptoms.

Rohan Greenland The May 50K

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Using MRI to see the optic nerve more clearly