Registration:
Input: Images , and initial velocity field
Output: Transformation from to
Pre-registration: through SURF related affine transformation or
ELASTIX to globally register and
Repeat
Demons registration:
 (i) Find updates mapping to
 (ii) Smooth updates:
 (iii) Update velocity field:
       (approximated with )
 (iv) Smooth velocity field:
 (v) Calculate traditional similarity metric SSD.
until convergence
Algorithm 2: SURF/ELSTIX related registration framework.