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Selecting the best index for following the temporal evolution of apparent diffusion coefficient and diffusion
Carola van Pul1, Jan Buijs, Maurice J A Janssen
1Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands. c.vanpul@mmc.nl
Background And Purpose:
Diffusion-weighted (DW) MR imaging is a useful technique for detecting ischemia. In adults and neonates, however, temporal changes on DW images after ischemia complicate interpretation. Our purpose was to investigate the temporal evolution of the apparent diffusion coefficient (ADC), diffusion-tensor (DT) imaging components, and anisotropy in neonatal brain after hypoxic-ischemic white matter injury and to determine which anisotropy index is preferable.
Methods:
DT images were obtained with single-shot echo-planar imaging, by using pulsed field gradients in six directions. Sixteen volunteers and 10 term neonates with normal MR images were evaluated to obtain reference values. Among the anisotropy indexes of fractional anisotropy (FA), relative anisotropy (RA), volume ratio (VR), linear (CI) and planar (Cp) diffusion, and axial anisotropy (Am), simulations were performed to select the most appropriate indexes for clinical practice. The ADC, DT imaging components, and anisotropy were evaluated as a function of time after onset of symptoms in 11 neonates with hypoxic ischemia.
Results:
In neonates, changes in lesions were characterized by a large decrease (40%) in all eigenvalues, with a stronger decrease in the direction perpendicular to the fibers, resulting in increased anisotropy indexes. The temporal evolution of the relative change in ADC did not show a significant trend (P >.05). The relative change in anisotropy decreased linearly with time (P <.05), with the strongest trend in anisotropy index Am.
Conclusion:
In clinical practice, anisotropy indexes FA, RA and Am appear to be useful. Am is the best index to monitor anisotropy changes. DT imaging provides information about diffusion parallel and perpendicular to white matter fibers, which helps the interpretation of physiologic changes after hypoxic-ischemic injury.
Insights
Diffusion tensor imaging reveals changes in neonatal brain white matter after hypoxic-ischemic injury. Axial anisotropy (Am) is the most effective index for monitoring these diffusion changes over time.
Area of Science:
- Neuroimaging
- Biomedical Engineering
- Pediatric Neurology
Background:
- Diffusion-weighted (DW) MR imaging is crucial for detecting ischemia.
- Temporal changes in DW images complicate interpretation in adults and neonates.
- Hypoxic-ischemic white matter injury in neonates presents unique diagnostic challenges.
Purpose of the Study:
- Investigate the temporal evolution of diffusion-tensor (DT) imaging components after neonatal hypoxic-ischemic white matter injury.
- Evaluate changes in apparent diffusion coefficient (ADC) and anisotropy.
- Determine the most suitable anisotropy index for clinical practice.
Main Methods:
- DT images acquired using single-shot echo-planar imaging with pulsed field gradients.
- Reference values established from healthy volunteers and neonates.
- Simulations performed to select appropriate anisotropy indexes (FA, RA, VR, CI, Cp, Am).
- Evaluation of ADC, DT components, and anisotropy over time in neonates with hypoxic ischemia.
Main Results:
- Neonatal lesions showed decreased eigenvalues with increased anisotropy.
- Relative change in ADC did not exhibit a significant temporal trend.
- Relative anisotropy change decreased linearly with time, most notably for Am.
- Axial anisotropy (Am) demonstrated the strongest trend in monitoring anisotropy changes.
Conclusions:
- Anisotropy indexes like FA, RA, and Am are clinically useful for assessing neonatal hypoxic-ischemic injury.
- Axial anisotropy (Am) is the optimal index for monitoring anisotropy changes.
- DT imaging provides valuable insights into diffusion parallel and perpendicular to white matter fibers, aiding interpretation of physiological changes.
