Biomedical Engineering Reference
In-Depth Information
FIGURE 4.4
Serial MRI examination of a patient with a mild head injury: (a) baseline scan; (b) follow-
up scan three days later; (c) difference image (b) minus (a); (d) difference image after
registration of (b) to align it with (a); (e) segmented version of (a) used to exclude extra-
cranial tissues; (f) subtraction image showing the result of registering (b) to (a) using only
the segmented data in (e). Residual signals in the brain in (d) result from an inability of the
registration algorithm to find a rigid-body transformation that accommodated both the brain
and the changed hematoma. Excluding the soft tissue changes using the segmented image
(e) allows the registration algorithm to determine a rigid-body transformation for the brain
alone. The difference image (f) reveals that the brain is unchanged.
FIGURE 4.5
Example of spine registration showing two scans of the patient in different positions: (a)
first position, (b) second position, (c) segmentation of vertebrae treated as rigid bodies by
the algorithm, and (d) first image transformed to the coordinates of the second using a
nonrigid registration algorithm.
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Note that although the images shown are all 2D, the
algorithm works on the 3D images.
