Removing Meningial Regions

  In addition to tumor, meningial tissues immediately surrounding the brain, such as the dura or pia mater, receive gadolinium infused blood. As a result they can have a high T1 signal intensity that may interfere with the knowledge base's assumption in Section 3.5.2 that regions with the highest T1 value are most likely tumor. These extra-cranial tissues can be identified and removed via anatomical knowledge by noting that since they are thin membranes, meningial regions should lie along the periphery of the brain in a relatively narrow margin.

  

Figure 10: Removing Meningial Pixels. A ``ring'' that approximates the brain periphery is created by applying a $7\times7$erosion operation to the intra-cranial mask (a), resulting in image (b). Subtracting (b) from (a), creates a ``ring'', shown in (c). By overlaying this ``ring'' onto a tumor segmentation (d), small regions of meningial tissues (e) can be detected and removed. The unusual shape of the intra-cranial region is due to prior resection surgery.

Figure 10 shows that an approximation of the brain periphery can be used to detect meningial tissues. The unusual shape of the intra-cranial region is due to prior resection surgery. The periphery is created by applying a $7\times7$ erosion operation to the intra-cranial mask and subtracting the resultant image from the original mask, as shown in Figure 10(a-c). Each component or separate region in the refined tumor mask is now intersected with the brain periphery. Any region which has more than 50% of its pixels contained in the periphery is marked as meningial tissue and removed. Figure 10(d) shows a tumor segmentation which is intersected with the periphery from Figure 10(c). In Figure 10(e), the pixels that will be removed by this operation are shown and they are indeed meningial pixels.