Neurovascular Visualization from 3D MR Data

Multiscale line filtering was applied to postcontrast gradient-echo (SPGR) MR images of the brain for the purpose of vessel enhancement so as to use the enhanced vein structures as landmarks for brain tumor resection [26,27]. The MRI dataset consisted of 192 sagittal slices of 256 x 256 pixels. The pixel dimensions were 1.0 mm2, while the slice thickness was 1.2 mm. The DSA images obtained from the same patient were also available, and used to compare with the vessel visualization with the MRI data. We used 80 slices corresponding to the right half of the head, and trimmed a region of 220 x 150 pixels from each slice. Sinc interpolation was performed for the trimmed images to obtain isotropic voxel sampling (the left frame of Fig. 10.4(a)). Multiscale line filtering was applied to the interpolated images using y23 = y12 = 1.0, a = 0.25, a\ = 0.8 pixel, s = 1.5, and n = 3 (the right frame of Fig. 10.4(a)). The original and line-filtered images were visualized using the volume-rendering technique [28,29] (Fig. 10.4(b)).

It is quite difficult to perceive the vessels through the skin in the volume-rendered original images, but almost the same vein structures as in the DSA image (Fig. 10.4(c)) can be clearly seen in the volume-rendered line-filtered images. Although the vessels and the skin had almost the same intensity level in the original images, the line filter could mostly remove the effect of the skin since it has a sheet-like structure. As a side effect, the line filter also gave high levels of response to the rims of biopsy holes in the skin and skull. It is a current limitation of our formulation that the line filter gives a high level of response to rim structures as well as to line structures. In order to remove rim structures, a procedure such as the nonlinear combination of the first derivatives for line detection from 2-D images [3, 30], needs to be extended for use with 3-D images.

Figure 10.4: Neurovascular visualization from 3-D MR data. (a) Original (left) and line-filtered (right) cross-sectional images. (b) Original (left) and line-filtered (right) volume rendered images. (c) DSA (digital subtraction angiography) image at a vein phase.

Figure 10.4: Neurovascular visualization from 3-D MR data. (a) Original (left) and line-filtered (right) cross-sectional images. (b) Original (left) and line-filtered (right) volume rendered images. (c) DSA (digital subtraction angiography) image at a vein phase.

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