Brain parenchyma undergoes motion driven by blood pulse pressure changes over the cardiac cylce. Studies have documented these brain tissue dynamics in Chiari malformation type I (CMI), but these studies are generally limited to tracking a few locations in the image. In the current study, we employed displacement encoding with stimulated echoes magnetic resonance imaging (DENSE MRI) to quantify brain tissue displacement and principle strains on a pixel-wise basis at the midsagittal plane in CMI individuals and controls. We hypothesized that brain motion and principal strain in the brain stem and cerebellum would be higher in CMI patients compared to control subjects.
Nineteen individuals with a documented clinical diagnosis of CMI and 16 controls with no history of central nervous system or cardiovascular disorders were included. In-house MATLABbased software was used to post-process and analyze the DENSE images and determine timedependent tissue displacement and principal strains in the brainstem and the cerebellum. Temporal Peak, spatial Mean Displacement (PMD) was calculated in each pixel as temporal maximum of the spatially-averaged displacement waveform for the brainstem and cerebellum. Values for compression and extension principle strains were created using similar methodology.
CMI individuals exhibited higher displacement than controls; cerebellar PMD was 52% higher in in CMI patients than controls (0.17±0.10 vs. 0.084±0.03 mm, p<0.05). Similar results were seen in the brainstem. Compression and extension principle strains in the cerebellum were 51% and 46% larger in CMI individuals than control subjects, respectively (p < 0.05).
Discussion and Conclusion
The major finding of this study is that tissue displacement and principle strains in brain parenchyma is elevated in CMI individuals compared to control subjects. Tissue displacement or strain may be a new biomarker to assess the functional severity of CM1. Further research will investigate links between brain displacement and strain and CMI pathophysiology and symptomology.