MRI mapping of nerve fibres helps brain surgeons preserve brain
24 November 2013
A novel technique for interpreting MRI scan data produces
images of the brain’s nerve network that can guide neurosurgeons to
preserve critical brain functions such as vision, speech and memory.
The technique, called tractography or diffusion tensor imaging
(DTI), has been used by University of California San Diego Health
System neurosurgeons to guide brain tumour surgery.
Tractography scans, which map the oriented water molecules in
nerve fibres, can reveal tiny open paths between the nerve fibres to
reach brain tumours. The scans display the neural network in
multiple colours. Other current imaging techniques such as computed
tomography (CT) and conventional magnetic resonance imaging (MRI)
cannot achieve this type of visual display.
Tractography image showing nerve network around
a brain tumour
“The brain can be mapped by tracking the movement of its water
molecules,” said Clark Chen, MD, PhD, neurosurgeon and vice-chairman
of neurosurgery at UC San Diego Health System. “Water molecules in
brain nerves move in an oriented manner. However, outside the
nerves, the molecules move randomly. Neurosurgeons at UC San Diego
can use these distinct properties to locate important connections
and to guide where surgery should occur or not.”
“There are no margins for error in the brain. Every centimetre of
brain tissue contains millions of neural connections so every
millimetre counts,” said Chen. “With tractography, we can visualize
the most important of these connections to avoid injury. In doing
so, we will preserve the quality of life for our patients with brain
Anthony Chetti is one of the beneficiaries of tractography-guided
brain surgery. Chetti developed a tumour in the region of the brain
called the occipital lobe, the portion of the brain responsible for
processing visual information. He underwent a complete excision of
the brain tumour without any damage to his vision.
“Anytime that you are told that you can potentially lose your
vision, you are scared,” said Chetti, a San Diego school teacher.
“But when Dr. Chen shared the tractography images with me and showed
me how he was going to avoid injury to the connection between my eye
and the occipital lobe, I was reassured. When I woke up from
surgery, I asked for my glasses immediately and began running
systems checks. I could see the clock. I could read the words on a
sign. It was immediately evident that there were no problems."
“There is no way of predicting where these fibres would lie
except with tractography,” said Chen. “I believe that many brain
tumour patients will benefit from tractography-guided surgery. By
observing the flow of water molecules, we can visually reconstruct
the complex symphony of brain connections. The resulting images are
not only accurate but breathtakingly beautiful, giving us a glimpse
into the extraordinary human mystery of the brain.”