Contrast-enhanced magnetic resonance angiography (MRA) is used to obtain images showing the vascular system. To detect stenosis, which is narrowing of for example blood vessels, maximum intensity projection (MIP) is typically used. This technique often fails to demonstrate the stenosis if the projection angle is not suitably chosen.
To improve identification of this region a color-coding algorithm could be helpful. The color should be carefully chosen depending on the vessel diameter.
In this thesis a segmentation to produce a binary 3d-volume is made, followed by a distance transform to approximate the Euclidean distance from the centerline of the vessel to the background. The distance is used to calculate the smallest diameter of the vessel and that value is mapped to a color. This way the color information regarding the diameter would be the same from all the projection angles.
Color-coded MIPs, where the color represents the maximum distance, are also implemented. The MIP will result in images with contradictory information depending on the angle choice. Looking in one angle you would see the actual stenosis and looking in another you would see a color representing the abnormal diameter.
Source: Linköping University
Author: Edsborg, Karin