. 2016 Jun 3;10:236. doi: 10.3389/fnins.2016.00236

Algorithm 1.

Longitudinal Rigid Registration between 2 Images

Input: I_j with j = 1, …, N−1, the image not necessarily aligned with the reference I₀.

Output:

I_{j}^{a l}

with j = 1, …, N−1, the image after rigid alignment with the reference I₀.

Find the rigid transformation

ϕ_{1}^{j}

that aligns I_j to I₀

H_{j} = I_{j} \circ ϕ_{1}^{j}

Skull-strip (SS) I₀ and H_j

J_j = SS(H_j) and J₀ = SS(I₀)

Find the rigid transformation

ϕ_{2}^{j}

that aligns J_j to J₀

K_{j} = J_{j} \circ ϕ_{2}^{j}

Compose the 2 previously found transformations

ϕ_{R}^{j} = ϕ_{2}^{j} \circ ϕ_{1}^{j}

Apply the composed transformation to the input image I₁

I_{j}^{a l} = I_{j} \circ ϕ_{R}^{j}