Update: Diffusion tensor imaging

Diffusion tensor imaging

J.Sales-Llopis

Neurosurgery Department, University General Hospital of Alicante, Foundation for the Promotion of Health and Biomedical Research in the Valencian Region (FISABIO), Alicante, Spain

Diffusion tensor imaging (DTI) provides a measure of the directional diffusion of water molecules in tissues.

Indications

Conventional white matter (WM) imaging approaches, such as diffusion tensor imaging (DTI), have been used to preoperatively identify the location of affected WM tracts in patients with intracranial tumors in order to maximize the extent of resection and potentially reduce postoperative morbidity.

Preoperative diffusion tensor imaging (DTI) is used to demonstrate corticospinal tract (CST) position. Intraoperative brain shifts may limit preoperative DTI value, and studies characterizing such shifts are lacking.

For nonenhancing intraaxial tumors, preoperative DTI is a reliable method for assessing intraoperative tumor-to-CST distance because of minimal intraoperative shift, a finding that is important in the interpretation of subcortical motor evoked potential to maximize extent of resection and to preserve motor function. In resection of intra-axial enhancing tumors, intraoperative imaging studies are crucial to compensate for brain shift 1).

Spinal cord

The measurement of DTI indexes within the spinal cord provides a quantitative assessment of neural damage in various spinal cord pathologies. DTI studies in animal models of spinal cord injury indicate that DTI is a reliable imaging technique with important histological and functional correlates.

DTI is a noninvasive marker of microstructural change within the spinal cord. In human studies, spinal cord DTI shows definite changes in subjects with acute and chronic spinal cord injury, as well as cervical spondylotic myelopathy. Interestingly, changes in DTI indexes are visualized in regions of the cord, which appear normal on conventional magnetic resonance imaging and are remote from the site of cord compression. Spinal cord DTI provides data that can help us understand underlying microstructural changes within the cord and assist in prognostication and planning of therapies 2).

Pediatric stroke

Plasticity of the developing motor tracts is a contributor to recovery of motor function after pediatric stroke. The mechanism of these plastic changes may be functional and/or structural in nature.

In a case of a 3-year-old girl demonstrating reorganization of the pyramidal tracts after an extensive left MCA territory stroke secondary to head trauma. Reorganization is characterized using serial diffusion tensor imaging (DTI) of the pyramidal tracts which contain the CST.

Imaging shows decreased ipsi-lesional fractional anisotropy (FA) suggestive of Wallerian degeneration and increased contralesional FA.

These results point to plastic reorganization of the pyramidal tract post-stroke and the utility of DTI in recognizing these changes 3).

Pulsed arterial spin labelingDTI, and MR spectroscopy are useful for predicting glioma grade. Additionally, the parameters obtained on DTI and MR spectroscopy closely correlated with the proliferative potential of gliomas 4).

Intracranial meningiomas

For predicting the consistency of intracranial meningiomas.

Limitations

DTI, has limitations that include its inability to resolve multiple crossing fibers and its susceptibility to partial volume effects.

Therefore, recent focus has shifted to more advanced WM imaging techniques such as high-definition fiber tractography (HDFT).

Abhinav et al. illustrate the application of HDFT, which in their preliminary experience has enabled accurate depiction of perilesional tracts in a 3-dimensional manner in multiple anatomical compartments including edematous zones around high-grade gliomas. This has facilitated accurate surgical planning. This is illustrated by using case examples of patients with glioblastoma multiforme. They also discuss future directions in the role of these techniques in surgery for gliomas 5).

1) Shahar T, Rozovski U, Marko NF, Tummala S, Ziu M, Weinberg JS, Rao G, Kumar VA, Sawaya R, Prabhu SS. Preoperative Imaging to Predict Intraoperative Changes in Tumor-to-Corticospinal Tract Distance: An Analysis of 45 Cases Using High-Field Intraoperative Magnetic Resonance Imaging. Neurosurgery. 2014 Jul;75(1):23-30. doi: 10.1227/NEU.0000000000000338. PubMed PMID: 24618800.
2) Vedantam A, Jirjis MB, Schmit BD, Wang MC, Ulmer JL, Kurpad SN. Diffusion tensor imaging of the spinal cord: insights from animal and human studies. Neurosurgery. 2014 Jan;74(1):1-8. doi: 10.1227/NEU.0000000000000171. PubMed PMID: 24064483.
3) George E, Heier L, Kovanlikaya I, Greenfield J. Diffusion tensor imaging of pyramidal tract reorganization after pediatric stroke. Childs Nerv Syst. 2014 Jan 14. [Epub ahead of print] PubMed PMID: 24420673.
4) Fudaba H, Shimomura T, Abe T, Matsuta H, Momii Y, Sugita K, Ooba H, Kamida T, Hikawa T, Fujiki M. Comparison of Multiple Parameters Obtained on 3T Pulsed Arterial Spin-Labeling, Diffusion Tensor Imaging, and MRS and the Ki-67 Labeling Index in Evaluating Glioma Grading. AJNR Am J Neuroradiol. 2014 Jul 3. [Epub ahead of print] PubMed PMID: 24994829.
5) Abhinav K, Yeh FC, Mansouri A, Zadeh G, Fernandez-Miranda JC. High-definition fiber tractography for the evaluation of perilesional white matter tracts in high-grade glioma surgery. Neuro Oncol. 2015 Jun 27. pii: nov113. [Epub ahead of print] Review. PubMed PMID: 26117712.

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