High-definition fibre tractography is new tool for brain imaging
19 September 2012
A technique called high-definition fibre tractography (HDFT) can trace the course of nerve fibre connections within the brain with more accuracy. It has the potential to improve the accuracy of neurosurgical planning and to advance scientific understanding of the brain's structural and functional networks.
the technique is reported in the August issue of Neurosurgery, official journal of the Congress of Neurological Surgeons.
In the new report, Dr Juan C Fernandez-Miranda and colleagues of University of Pittsburgh describe and illustrate the use of the HDFT to track the course of the nerve fibres that make up the white matter of the brain. The researchers write, "Our HDFT approach provides an accurate reconstruction of white matter fibre tracts with unprecedented detail in both the normal and pathological human brain."
Seeing white matter tracts in living brain
Dr Fernandez-Miranda and coauthors report on the development and evaluation of the HDFT technique, including initial findings in healthy people and patients with various brain lesions. The new technique adds advanced digital processing and reconstruction techniques to current methods of tractography — a method used to trace the course of bundles of white matter fibres, or "tracts", in the brain.
Tractography using a technique called diffusion tensor imaging (DTI) has been available for more than a decade. However, DTI has some important limitations: it can't show the complex course of white matter fibre tracts as they cross each other, and it can't accurately show the starting point and ending points of white matter tracts. The researchers call these the "crossing problem" and the "termination problem," respectively.
Over the past three years, Dr. Fernandez-Miranda and colleagues have been working on refining new fibre mapping techniques — such as high-angular resolution diffusion imaging and diffusion spectrum imaging — to study the structural connections of the brain.
They write, "In an attempt to more effectively solve the crossing and termination problems, we have focused on optimizing these methods to obtain what we refer to as HDFT."
Through a combination of imaging processing and reconstruction and tractography methods, HDFT can track white matter fibre tracts from their origin, through complex fibre crossings, to their termination point, with resolution of one millimetre or less.
For brain researchers, HDFT provides an unprecedented level of detail to solve both the crossing and termination problems. Colour-coded images show the complex architecture of white matter fibres, as they cross each other in complex patterns. The HDFT images accurately replicate known features of the brain anatomy, including the folds and grooves (gyri and sulci) of the brain and the characteristic shape of brain structures.
To evaluate how the new technique might be used for surgical planning, the researchers analyzed HDFT images obtained in patients with cancers and other brain lesions. In patients with brain cancers, HDFT clearly showed the disruption of brain tissue caused by rapid tumour growth. Importantly, it was able to show the absence of white matter fibres within the tumour itself in two types of brain cancers.
In patients with brain blood vessel malformations, HDFT provided information likely to be useful in planning the safest approach to surgery. The ability to differentiate displacement versus disruption of fibres may become a critical factor in determining whether or not damage caused by brain lesions is reversible.
The researchers emphasize that much more research will be needed to refine the HDFT technique and to evaluate its scientific and clinical uses. "From a clinical perspective, we show that accurate structural connectivity studies in patients facilitate white matter damage assessment, aid in understanding lesional patterns of white matter structural damage, and allow innovative neurosurgical applications," the researchers write. They also believe that structural connections shown by HDFT will provide a useful complement to efforts to map the functional connections of brain networks, such as the Human Connectome Project.