Nonrigid registration for subtraction CT angiography applied to the carotids and cranial arteries.
OBJECTIVE
Computed tomography angiography (CTA) is an established tool for vascular imaging. However, high-intensity nonvascular structures in the contrast image can seriously hamper luminal visualization. This is an issue for three-dimensional visualization, where high-intensity structures might cover the underlying vasculature. But also in two dimensions, calcified plaques adjacent to the contrast-enhanced vessel lumen impede correct determination of the vessel boundary. High-intensity structures can be eliminated using subtraction CTA, where a native image is subtracted from the contrast image. However, patient and organ motion limits the widespread application of this technique. We propose to use nonrigid image registration to solve this problem.


METHODS
For each patient, a native image and a contrast image are recorded, respectively, before and after contrast administration. The native image is registered to the contrast image using an automatic intensity-based nonrigid three-dimensional registration algorithm. Both images are merged in a fused image, allowing the user to switch between a view of the arteries, the bone or both. The procedure has been applied to 95 patients.


RESULTS
In all cases, subtraction CTA using nonrigid registration allows for a significantly better artifacts removal than subtraction CTA without registration. Image quality of all images was judged adequate for clinical use. The average total processing time for each dataset is about 30 minutes.


CONCLUSIONS
Nonrigid registration can allow for a great reduction in subtraction artifacts for subtraction CTA, resulting in a clear view of the vasculature.
Loeckx
Dirk
D
Medical Image Computing, ESAT/PSI, Faculty of Engineering, Katholieke Universiteit Leuven. Dirk.Loeckx@uz.kuleuven.ac.be
Coudyzer
Walter
W
Maes
Frederik
F
Vandermeulen
Dirk
D
Wilms
Guido
G
Marchal
Guy
G
Suetens
Paul
P
D000465:Algorithms; D000792:Angiography / Q000379:methods*; D016477:Artifacts; D050197:Atherosclerosis / Q000000981:diagnostic imaging; D002339:Carotid Arteries / Q000000981:diagnostic imaging*; D017536:Carotid Artery, Common / Q000000981:diagnostic imaging; D016893:Carotid Stenosis / Q000000981:diagnostic imaging; D003287:Contrast Media; D006257:Head / Q000098:blood supply*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods; D012886:Skull / Q000098:blood supply; D013382:Subtraction Technique; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*
D003287:Contrast Media