Comparison of the accuracy of voxel based registration and surface based registration for 3D assessment of surgical change following orthognathic surgery.
OBJECTIVE
Superimposition of two dimensional preoperative and postoperative facial images, including radiographs and photographs, are used to evaluate the surgical changes after orthognathic surgery. Recently, three dimensional (3D) imaging has been introduced allowing more accurate analysis of surgical changes. Surface based registration and voxel based registration are commonly used methods for 3D superimposition. The aim of this study was to evaluate and compare the accuracy of the two methods.


METHODS
Pre-operative and 6 months post-operative cone beam CT scan (CBCT) images of 31 patients were randomly selected from the orthognathic patient database at the Dental Hospital and School, University of Glasgow, UK. Voxel based registration was performed on the DICOM images (Digital Imaging Communication in Medicine) using Maxilim software (Medicim-Medical Image Computing, Belgium). Surface based registration was performed on the soft and hard tissue 3D models using VRMesh (VirtualGrid, Bellevue City, WA). The accuracy of the superimposition was evaluated by measuring the mean value of the absolute distance between the two 3D image surfaces. The results were statistically analysed using a paired Student t-test, ANOVA with post-hoc Duncan test, a one sample t-test and Pearson correlation coefficient test.


RESULTS
The results showed no significant statistical difference between the two superimposition methods (p<0.05). However surface based registration showed a high variability in the mean distances between the corresponding surfaces compared to voxel based registration, especially for soft tissue. Within each method there was a significant difference between superimposition of the soft and hard tissue models.


CONCLUSIONS
There were no significant statistical differences between the two registration methods and it was unlikely to have any clinical significance. Voxel based registration was associated with less variability. Registering on the soft tissue in isolation from the hard tissue may not be a true reflection of the surgical change.
Orthodontic Department, Glasgow Dental School, University of Glasgow, Glasgow, United Kingdom.
Anas
A
Almukhtar
Medical Device Unit, Department of Clinical Physics and Bioengineering, NHS Greater Glasgow and Clyde, Glasgow, United Kingdom; Honorary Research Fellow, Glasgow Dental School, University of Glasgow, Glasgow, United Kingdom.
Xiangyang
X
Ju
Discipline of Orthodontics and Paediatric Dentistry, Faculty of Dentistry, The University of Hong Kong, Hong Kong, Hong Kong SAR.
Balvinder
B
Khambay
Orthodontic Department, Glasgow Dental School, University of Glasgow, Glasgow, United Kingdom.
James
J
McDonald
Oral and Maxillofacial Surgery Department, Glasgow Dental School, University of Glasgow, Glasgow, United Kingdom.
Ashraf
A
Ayoub
D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005145:Face / Q000473:pathology / Q000601:surgery; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D057909:Orthognathic Surgery / Q000379:methods; D011184:Postoperative Period; D057234:Preoperative Period; D012189:Retrospective Studies