PURPOSE: White matter (WM) and gray matter (GM) respond differently to ischemia and thrombolytic treatment. Being able to differentiate WM/GM in CT enables tissue dependent perfusion analysis and automated detection of stroke related pathology. In this work we show the feasibility of segmenting WM/GM in 4DCT images of acute ischemic stroke patients.
METHOD AND MATERIALS: In total 18 stroke patients who received both a 4DCT and followup MR scan were included in this retrospective study. CT imaging was done on a 320 row scanner with 19 or 24 volumetric acquisitions after contrast injection resulting in 512x512x320 isotropic voxels of 0.5 mm. T1w imaging was done on a 1.5T MR scanner resulting in approximately 384x318x26 voxels of 0.6x0.6x5.5 mm. The MR image was segmented with FSL tools and served as reference standard to train and evaluate the method. The method starts with brain segmentation by atlas registration followed by a refinement using a geodesic active contour with dominating advection term steered by a gradient based speed function. Within the segmented brain, three groups of features are then extracted: intensity, contextual and temporal, including a multiscale representation of the temporal average image weighted according to the exposures of the individual time points to maximize the signaltonoise ratios. In total 120 features were then fed into a nonlinear support vector machine with Gaussian radial basis kernel. A leaveonepatient out cross validation was carried out. Segmentation results were visually inspected for overall quality. Dice coefficient (DC) and 95th percentile Hausdorff distance (HD) were reported.
RESULTS: The segmentations were evaluated as good with the separation of WM/GM at the cortex good to excellent. GM segmentation at the cortex had generally less thickness variations compared to the reference standard. DC were 0.79+-0.06 and 0.77+-0.06, 95% HD were 8.71+-3.22 and 7.11+-3.93 mm, for WM and GM, respectively.
CONCLUSION: WM and GM segmentation in 4DCT is feasible.
CLINICAL RELEVANCE/APPLICATION: WM and GM segmentation in 4DCT enables tissue dependent perfusion analysis and may increase sensitivity of detecting core and penumbra. Volume measurements of WM and GM normalized with the contralateral side may yield an important diagnostic parameter in the acute phase of ischemia.