[...]... Hospital Brussels, Belgium XXI CHAPTER CHAPTER 1 1 From 3-D Volumetric Computer Tomography to 3-D Cephalometry Filip Schutyser, Johan Van Cleynenbreugel 1. 1 1. 1 .1 1 .1. 2 1. 1.3 1. 1.4 CT Imaging of the Head 2 CT Scanner 2 Characteristics of a CT Dataset 3 Radiation Dose 5 3-D Image Volume 7 1. 2 3-D Scene Approach 8 1. 3 1. 3 .1 1.3.2 1. 3.3 Virtual Cephalograms 10 Conventional 2-D Cephalograms 10 Generation... 3 .1 Standardized Virtual Positioning of the Skull 94 3.2 Computing of Virtual Lateral and Frontal Cephalograms 96 3.3 Definition of the Nasion and Sella 3-D Cephalometric Landmarks 99 3.4 Set-up of the Anterior Cranial Base (S-N) Plane 10 6 3.5 Set-up of the 3-D Cephalometric Reference System 10 7 3-D Scene Approach 8 1. 3 1. 3 .1 1.3.2 1. 3.3 Virtual Cephalograms 10 Conventional 2-D Cephalograms 10 Generation... and add depth dimension (b, c) Finally the bone is cut and split (d) 9 CHAPTER 1 From 3-D Volumetric Computer Tomography to 3-D Cephalometry a b Fig 1. 11 For a lateral cephalogram, the patient is positioned in a standard way in the X-ray machine 1. 3 Virtual Cephalograms 1. 3 .1 Conventional 2-D Cephalograms Cephalometric X-ray images are widely accepted in daily routine The patient is installed in a standard... the Virtual Cephalogram 10 Visualization of Virtual Cephalogram and 3-D Data 11 1. 3.4 Benefits of This Environment 11 CHAPTER 2 Basic Craniofacial Anatomical Outlines Gwen R J Swennen 2 .1 3-D CT Anatomy of the Skull 14 2.2 Multi-planar CT Anatomy of the Skull 37 2.2 .1 Axial CT Slices 37 2.2.2 Virtual Coronal (Frontal) CT Slice Reconstructions 46 CHAPTER 4 3-D Cephalometric Hard Tissue Landmarks Gwen... Fig 1. 12 A virtual cephalogram is computed from the CT image volume A virtual parallel X-ray beam is sent through the patient Extra radiation dose is avoided, and the geometrical relationship is known 1. 3.3 Visualization of Virtual Cephalogram and 3-D Data The orientation of the virtual X-ray image plane is perpendicular to the bundle of rays Therefore, this X-ray image can be added to the 3-D scene as... Swennen 4 .1 Definition of 3-D Cephalometric Hard Tissue Landmarks 11 6 4.2 Set-up of 3-D Cephalometric Hard Tissue Landmarks 17 4 4.3 Additional 3-D Cephalometric Hard Tissue Landmarks 18 1 2.2.3 Virtual Sagittal CT Slice Reconstructions 64 2.3 Virtual X-Rays of the Skull 76 XIX Contents CHAPTER 5 CHAPTER 8 3-D Cephalometric Soft Tissue Landmarks Gwen R.J Swennen 3-D Cephalometry and Craniofacial Growth... CT and virtual cephalograms To avoid extra radiation dose, and to achieve this geometric relationship, lateral and frontal cephalograms are computed from the CT data In this way, an unlimited number of virtual X-ray images of the skull can be computed (Chap 2) To compute a virtual X-ray image, a bundle of parallel rays is cast through the CT volume (Fig 1. 12) Each CT number is associated with an opacity... dose values should be compared with the classical cephalogram and orthopantogram (OPG) doses Table 1. 1 gives an overview of the doses, and shows the equivalent time to have the same dose as natural background radiation 12 days OPG CHAPTER ination doses as low as reasonably achievable (ALARA principle) The average equivalent dose due to natural sources is estimated at about 3 mSv per year in US For a multi-slice... orbital fissure; 12 Sphenozygomatic suture; 13 Zygomatic bone; 14 Zygomaticofrontal suture; 15 Supraorbital margin; 16 Supraorbital foramen; 17 Frontonasal suture; 18 Nasal bone; 19 Internasal suture; 20 Nasomaxillary suture; 21 Vomer; 22 Middle nasal conchae; 23 Inferior nasal conchae; 24 Frontomaxillary suture; 25 Infraorbital margin; 26 Infraorbital foramen; 27 Maxilla; 28 Frontal process of maxilla;... Swennen 6 .1 3-D Cephalometric Planes 230 6.2 Set-up of 3-D Cephalometric Planes 240 CHAPTER 9 Clinical Applications Gwen R J Swennen Case 1 309 Case 2 322 CHAPTER 7 3-D Cephalometric Analysis Gwen R J Swennen 7 .1 3-D Cephalometric Hard Tissue Analysis 244 7 .1. 1 Linear Hard Tissue Analysis 244 7 .1. 2 Angular Hard Tissue Analysis 2 51 7 .1. 3 Orthogonal Arithmetical Hard Tissue Analysis 254 7.2 7.2 .1 7.2.3 . CT Imaging of the Head 2 1. 1 .1 CT Scanner 2 1. 1.2 Characteristics of a CT Dataset 3 1. 1.3 Radiation Dose 5 1. 1.4 3-D Image Volume 7 1. 2 3-D Scene Approach 8 1. 3 Virtual Cephalograms 10 1. 3 .1 Conventional. Conventional 2-D Cephalograms 10 1. 3.2 Generation of the Virtual Cephalogram 10 1. 3.3 Visualization of Virtual Cephalogram and 3-D Data 11 1. 3.4 Benefits of This Environment 11 CHAPTER 1 CHAPTER 1 1 CHAPTER. generated and co-visualized with the 3-D data, taking into ac- count the geometrical relationships. In this way ,a com- bined 2-D and 3-D approach opens the way towards re- liable and repeatable 3-D analysis