Image intensity in each image case is not the same resulted from different conditions in taking MRA pictures. So a normalization method need to be found in order to compare image intensity of pixels in each case.

In this median intensity normalization method, median value of each image set is acquired as a norm. It is assumed that white matters of brain take a large part in an image set. A normalized method should acquire white matter with same value.

The mean value of median pixel value from all 162 image cases are calculated as a norm, each image is then adjusted linearly according to the scale of norm and its median value.

More stable and effective methods are still testing.