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Interpolation

In addition to a pair of images and a particular transformation, the cost function requires that a method of interpolation be defined. That is, some method of calculating what the intensity is in the floating image at points in between the original voxel (or grid) locations. This is necessary in order to know the intensity at corresponding points in the images after the geometrical transformation has been applied to the floating image. Interpolation methods that are commonly used are: trilinear (also called linear or, in 2D, bilinear), nearest neighbour, sinc (of various kernel sizes and with or without various windowing functions; e.g. Blackman), spline and Fourier. The choice of method has some impact on cost function smoothness, although all interpolation methods except nearest neighbour are continuous. However, the choice of method becomes most critical for motion correction as the transformed image intensities are needed for later statistical analysis.

Peter Bannister 2002-05-03