Medical Image Registration: Theory, Algorithm, and Case Studies in Surgical Simulation, Chest Cancer, and Multiple Sclerosis - Biomedical Image Analysis - page 7

registration himself, assisted by software supplying a visual or numerical impres-
sion of the current transformation, and possibly an initial transformation guess.
Semi-automatic , where the interaction required can be of two different natures:
the user needs to initialize the algorithm, e.g., by segmenting the data, or steer
the algorithm, e.g., by rejecting or accepting suggested registration hypotheses.

1.2.5 Optimization Procedure

There exists two possible ways of finding the transformation parameters. Either
they are computed directly from the available image information, or they are
looked for based on a certain optimization criterion. Many applications use more
than one optimization technique, frequently a fast but coarse technique followed
by an accurate yet slow one (as shown later).

1.2.6 Modalities Involved

Four classes of registration tasks can be recognized based on the modalities
that are involved. In monomodal applications, the images to be registered be-
long to the same modality, as opposed to multimodal registration tasks, where
the images to be registered stem from two different modalities. The other two
are modality to model and model to modality registration where only one image
is involved and the other modality is either a model or the patient himself. The
model to modality is used frequently in intraoperative registration techniques.
Monomodal tasks are well suited for growth monitoring, intervention verifica-
tion, rest-stress comparisons, ictal-interictal comparisons, subtraction imaging
(also DSA, CTA), and many other applications. The applications of multimodal
registration are abundant and diverse, predominantly diagnostic in nature. A
coarse division would be into anatomical-anatomical registration, where images
showing different aspects of tissue morphology are combined, and functional-
anatomical, where tissue metabolism and its spatial location relative to anatom-
ical structures are related.

1.2.7 Subject

There can be intrasubject registration involving images for the same pa-
tient, intersubject registration involving images for different patients and atlas