Figure 7. (a) The distribution of pixel values of relative re-circulation (rR) in a patient with a grade 3 glioma. Note that the distribution of the values fits normal distribution with a skewness value of 0.45. (b) A similar distribution graph from a patient with a glioblastoma multiforme. Note the marked skew of the data to the right side due to an increase of pixels with high values. This gives rise to a skewed distribution with a skewness of 1.22. (c) The distribution of rR values within a group of gliomas of varying grades. A clear relationship between grade can be identified with far higher values of skewness in grade 4 tumours than in grade 2 and 3. (d) A scattergram showing the distribution of mean values of relative cerebral blood volume (rCBV) on the x-axis and skewness of rR on the y-axis. The points represent grade 2 (triangles), grade 3 (diamonds) and grade 4 (circles) gliomas.