An approach to standardize the MR image intensity scale

Despite the many advantages of Magnetic Resonance (MR) images, they lack a standard image intensity scale. MR image intensity ranges and the meaning of intensity values vary even for the same protocol (P) and the same body region (D). This causes many difficulties in image display and analysis. We propose a two-step method for standardizing the intensity scale in such way that for the same P and D, similar intensities will have similar meaning. In the first step, the parameters of the standardizing transformation are "learnt" from an image set. In the second step, for each MR study, these parameters are used to map their histogram into the standardized histogram. The method was tested quantitatively on 90 whole brain FSE T2, PD and T1 studies of MS patients and qualitatively on several other SE PD, T2 and SPGR studies of the brain and foot. Measurements using mean squared difference showed that the standardized image intensities have statistically significantly (p < 0.01) more consistent range and meaning than the originals. Fixed windows can be estabilished for standardized images and used for display without the need of per case adjustment. Preliminary results also indicate that the method facilitates improving the degree of automatation of image segmentation.