1. Optimum Gray Level Narendhran Vijayakumar 02/08/2008

2. Image properties ModalityNo of bits DimensionFOVResolution (pixels per mm) T2FLAIR16512x512220mmx220mm2.327 DWEPI16256x256280mmx280mm0.914 DIFFRAD16256x256256mmx256mm1.000 2

3. Choosing Gray Levels Tradeoff between accuracy and computation time Ways to determine effective gray levels – Histogram Involves guess work – Entropy measure Guessing not required 3

4. Entropy measure of T2 FLAIR 4

5. Mutual Information 5

6. Conclusion Effective number of gray levels – 11 bits => 2048 Levels MI of T2FLAIR/Radial diffusion – Higher than T2FLAIR/DWEPI – Quantitatively proves Radial Diffusion is better 6