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Yonsei University tracks CNS fibers with Diffusion Tensor Imaging

Best Practice
Dr. Lee, Seung-Koo, M.D. Seoul, Yonsei University College of Medicine Korea

Yonsei University tracks CNS fibers with Diffusion Tensor Imaging (DTI)

Yonsei University (Yonsei, South Korea) conducts white matter imaging using diffusion tensor imaging (DTI) for two to three cases every day, exploring neural connections in addition to the neuropathology of stroke, cerebral palsy/periventricular leukomalacia, and malformation of cortical development. DTI also figures significantly in pre-surgical localization and avoidance of the corticospinal tract in brain tumor and epilepsy cases. Because the white matter in the brain and spinal cord is responsible for communication between the brain's grey matter regions and between the grey matter and the rest of the body, its depiction and the diagnosis of diseases affecting it are crucial, according to Seung-Koo Lee, M.D.
Dr. Seung-Koo Lee Yonsei University, Seoul
Dr. Seung-Koo Lee
Yonsei University, Seoul

 

In March 2002, just one year after acquiring their Intera 1.5T, Yonsei University radiologists began to conduct DTI with high angular diffusion (32 directions). Yonsei scientists' and clinicians' enthusiasm for the DTI technique even spurred them to develop their own processing program, called DoDTI, for highly sophisticated, multi-featured and user-friendly diffusion tensor analysis.

 

In March 2005, Yonsei installed an Achieva 1.5T system and an Achieva 3.0T system. Achieva series systems have proven to be excellent platforms for DTI studies, with their robust DWI software and superb diffusion sensitivity. Recently, Yonsei physicians have begun to acquire higher resolution DTI with the 3.0T system.

 

DTI 1.5T 3.0T
DTI
1.5T
3.0T

  DTI and fiber tractography of a normal volunteer. Philips SameScan was used to acquire

  identical scans in both 1.5T and 3.0T scanners.

  Left: Color-coded vector maps at the level of basal ganglia. On lower resolution images,

  1.5T and 3.0T provide nearly the same quality DTI maps with high SNR. However, higher

  resolution with 1.4 mm isovoxel images clearly demonstrate the difference between 1.5T

  and 3.0T, i.e. clear differentiation of the posterior limb of the internal capsule with higher

  SNR at 3.0T (arrows).

  Center and Right: Fiber tractography drawn from ROI at optic chiasm. With the same resolution,

  optic radiation is more easily traced on a 3.0T image than a 1.5T image.

 

DTI joins DWI in stroke imaging

As the leading cause of death in Korea, stroke is one of the most intensely studied pathologies at Yonsei, where diffusionweighted imaging (DWI) has been a critical tool in shedding light on a stroke's aftermath. Now, DTI is adding to Yonsei's battery of imaging tests for stroke.

 

 "We use DTI to determine the degree of corticospinal tract injury in the brain as a means of predicting clinical outcome," Dr. Lee says. "Although the findings don't affect the final diagnosis or interventional plan, we are obtaining data from patients who aggravated clinically after admission and this information could help narrow down the severity of stroke and the patient's prognosis."

Cerebral palsy studies investigate motor dysfunction

DTI can help identify the source of motor dysfunction in cerebral palsy children with periventricular leukomalacia (PVl), Dr. Lee says. "We're looking for abnormalities on white matter tracts in the corpus callosum, thalamic radiations and sensory fibers," he observes. "DTI studies have shown decreased fractional anisotropy of the corpus callosum and decreased volume of thalamocortical fibers and periventricular white matter."

 

The precise mechanism of spasticity in cerebral palsy is still unclear, he adds, but further investigation of defects in neural connections among thalami, cerebral cortex and cerebellum may provide answers to these questions.

Focus on the growing cortex

Yonsei clinicians are exploring the maturation and white matter connection processes of the developing brain and using DTI to visualize malformation of cortical development. The diagnostic goal is to determine seizure foci and clearly detect subcortical abnormalities in cortical dysplasia in regions where anomalous development is suspected.

 

"Typically, clinicians use PET and SPECT to detect cortical abnormalties," Dr. Lee says. "Now, DTI also is capable of showing minute subcortical changes, even with normal findings on T2-weighted or FLAIR images."

Planning the route to disease

Imaging modalities are increasingly used to plan surgical routes to treat tumors or epilepsy lesions in the brain and spine that avoid critical normal structures or demonstrate whether a lesion infiltrates or merely displaces organs and tissue. In the case of white matter structures, DTI's role at Yonsei centers on avoidance of the corticospinal tract during surgery.

 

"The relationship between the lesion and corticospinal tract is a key parameter that our protocol - which includes both DTI and BOLD fMRI - can help determine," he says. "Then, surgeons will have the information they need to plan surgical or biopsy paths."

DTI still evolving

Paired with SENSE, DTI at Yonsei is a rapid, simple procedure that takes just 10 minutes for data acquisition and five minutes for post-processing. SENSE reduces susceptibility artifacts, speeds acquisition and in combination with the single shot EPI technique provides relatively motion-free data, Dr. Lee explains. The major challenge with DTI moving forward, according to Dr. Lee, is standardizing DTI interpretation.

 

"Adequate interpretation of DTI data is still difficult because DTI is still a solely qualitative method," he says. "Fiber tracking post-processing is quite operator-dependent. Therefore, a more robust algorithm and automated post-processing procedure should be developed. The fast rate at which progress is made in DTI methodology, however, is extremely encouraging."



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Best Practice
Achieva 1.5T, Achieva 3.0T
Release 1
Brain, Neuro
 

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