This document provides an overview of cone-beam computed tomography (CBCT) imaging. It discusses the principles of CBCT imaging, including how CBCT uses a rotating x-ray source and detector to obtain multiple 2D images that are reconstructed into a 3D volume. It describes the components of image production, clinical considerations for CBCT scans, common artifacts, and applications of CBCT imaging such as implant planning and assessment of pathology. In conclusion, CBCT is presented as an effective diagnostic imaging technique that produces high resolution 3D images of the maxillofacial region at lower radiation doses and costs compared to medical CT.

1. MOHIT KAPOOR
FINAL YEAR

2. CONTENTS
 INTRODUCTION
 PRINCIPLES OF CBCT IMAGING
 COMPONENTS OF IMAGE PRODUCTION
 CLINICAL CONSIDERATIONS
 IMAGE ARTIFACTS
 ADVANTAGES AND DISADVANTAGES
 APPLICATIONS
 CONCLUSION

3. INTRODUCTION
CBCT IMAGING
 Most significant technology advancement in
maxillofacial imaging
 In this, the imaging shifts from 2D to a
volumetric approach.

4. PRINCIPLES
 CBCT imaging is performed
using a rotating platform
carrying an x-ray source
and detector

5.  A divergent cone shaped or pyramidal source of radiation
is directed through region of interest (ROI)
 X-ray source and detector rotate around a rotation
center, fixed within center of the ROI

6. • During rotation, multiple sequential planer
projection images are obtained while the x-ray
source and detector move through an arc of 180
to 360 degree
• Single projection image form raw primary data,
which is individually known as - basis, frame or
raw image
• Usually several hundred 2-D basic images are
formed from which the image volume is
calculated.
• Complete series of images is called PROJECTION
DATA

7. Components of CBCT
 1. IMAGE PRODUCTION
 2. VISUALISATION
 3. INTERPRETATION

8. COMPONENTS OF IMAGE
PRODUCTION
X-ray
generation
X-ray
detection
Image
reconstruction

9. X-RAY GENERATION
Patient Stabilization
Sitting, Standing, Supine
 With all system, immobilization of the patient’s head
is more important than position because any
movement degrades the final image
 Immobilization of head by -
Chin cup OR Bite fork

10. CHIN CUP BITE FORK

11. X-ray generator
X-ray generation
continuous or pulsed
 When pulsed- exposure time is up to 50% less than
scanning time (this technique reduces patients radiation
dose)
 ALARA (As Low As Reasonable Achievable) principle of dose
optimization states that CBCT exposure factor should be
adjusted on the basis of patient’s size.

12. Scan Volume / field of view(FOV)
It is the amount of area to be exposed in a single
scan
DEPENDS ON -
* Detector size and shape
* Beam projection geometry
* Ability to collimate the beam
Shape – cylindrical or spherical

13.  It is desirable to limit the field size to the
smallest volume that images the ROI.
 This procedure reduces unnecessary
exposure to the patient and produces the
best image by minimum scattered radiation,
which degrade image quality.

14. CLASSIFICATION OF CBCT UNIT ACCORDING TO FOV

15. SCANNING OF ROI GREATER THAN FOV OF DETECTOR

16. Scan factor
 Number of images forming the “projection data”
throughout the scan is determined by-
1. Detector frame rate (no. of image acquired per sec.)
2. Completeness of the trajectory arc (180 to 360)
3. Rotation speed of source and detector

17. IMAGE DETECTOR
Larger and bulkier Lighter in weight
Circular basis image area Rectangular
Spherical volume Clindrical volume
Cesium iodide scintillator
CBCT units
Image intensifier
tube/charge-coupled
device(II/CCD)
Flat panel
detector(FPDs)

18. Voxel- Volume element
 Individual volume element is VOXEL
 Voxels form the volumetric data set
 CBCT units provide voxel resolution
 that are isotropic - equal in all 3 dimension
 Determinant of voxel is- Pixel size of detector
Detector with small pixel
Capture few x-ray photon per voxel

19. 3. RECONSTRUCTION
basis projection frames
volumetric data
a single CBCT rotation take less than 20 sec
produce 100 to 600 individual projection frames
Each with more than 1 million pixel with 12 to
16 bits of data assigned to each pixel
These data processed to create volumetric data set(voxel) by a
sequence of software algorithms
a process known as RECONSTRUCTION

20. 2 STAGES OF RECONSTRUCTION PROCESS
1) Preprocessing stage-
 performed at acquisition computer
 Inherent pixel imperfections should be corrected
 Exposure normalization
2) Reconstruction stage-
 Corrected images are converted into a special
representation called a sinogram
 Sinogram is a composite image developed from multiple
projection images
 The final image is constructed from the sinogram with
a filtered back-projection algorithm.

21. CLINICAL CONSIDERATION
1.Patient selection criteria
 It provides a radiation dose to the patient higher than
radiation dose of other dental radiograph
 When periapical or panoramic view cannot provide the
necessary information
 Used as adjunctive diagnostic tool

22. 2. Patient preparation
Appropriate personal radiation barrier protection
 Leaded apron - for pregnant patients and children
 Lead thyroid collar- to reduce thyroid exposure
 Before scan, remove all the
 Metallic object
 Eyeglass
 Jewelry
 Metallic partial denture

23. Patient motion can be minimized by
Head stabilization
Chin cups to posterior or lateral head support
 Patient should be directed to remain still as
possible before exposure, to breathe slowly
through nose, and to close the eyes.

24. 3. Imaging protocol
 Develop to produce image of optimal quality with the
least amount of radiation exposure to the patient
PARAMETERS
 Exposure settings
 Spatial resolution
 Scan time and number of projections

25. 1. Exposure setting
 Quality and quantity of x-ray beam depend on
i. Tube voltage(kVp)
ii. Tube current( mA)
 CBCT unit manufacturers approach setting exposure in 2
ways-
1. Selection of fixed exposure setting
2. Allow operator manual adjustment of kVp or mA

26. 2. Spatial resolution
 Ability of an image to reveal fine detail
 Determined by
i. Pixel size
ii. Beam projection geometry
iii. Patient scatter
iv. Focal spot size
v. Number of basis images
vi. Reconstruction algorithm

27. 3. Scan time and number of projection
adjusting the detector frame rate
increase the number of basis image projections
reconstructed image with fewer artifacts and better image
quality

28. 4. Archiving, export, and distribution
 Process of CBCT imaging produces 2 data products
1. Volumetric image data from the scan
2. Image report generated by the operator
 Both set of data must be archived and distributed
 However the export of image data is in Digital Imaging
And Communications in Medicine standard version 3
(DICOM v3) file format.

29. IMAGE ARTIFACTS
 An artifact is any distortion or error in the image
Image
artifacts
Inherent
Procedure
related
Introduced
Patient
motion
artifact

30. 1. INHERENT ARTIFACTS
 Can arise from limitations in the physical processes
 Beam projection geometry, reduced trajectory rotational
arcs, and image reconstruction methods produce 3 type
of artifacts
Scatter
Partial volume averaging
Cone beam effect

31. Scatter-
 Result from x-ray photons that are diffracted from
their original path after interaction with matter
Partial volume averaging-
 It occur when the selected voxel size of the scan is
larger than the size of the object being imaged

33. Cone beam effect-
 Is a potential source of artifacts, especially in the
peripheral portion of scan volume
 Can result in
i. Image distortion
ii. Greater peripheral noise
 Clinically, the effect can be reduced by positioning of ROI
in the horizontal plane of x-ray beam.

34. 2. Procedure related artifacts
 Under sampling of the object can occur when too few basis
projections are provided for image reconstruction or when
rotational trajectory arc are incomplete
 Reduced data sample leads to:-
1. misregistration
2. noisier image
 which appear as fine striations in the image

37. 3. Introduced artifacts
 An x-ray beam pass through an object ,lower energy photons
are absorbed in preference to higher energy photons, this
phenomenon is known as beam hardening
 Can result in 2 type of artifacts
1. Distortion of metallic structure as a result of differential
absorption, known as cupping artifact
2. Streaks and dark bands, which when present b/w 2 dense
objects ,create extinction or missing value artifacts

39. 4. Patient motion artifacts
 Can cause misregistration of data which appear
as double contours in the reconstructed image
 Problem can be minimized by restraining the
head and using a short scan time as possible

41. ADVANTAGES OF CBCT
 Less cost
 Less space required rapid, quick scanning time
 Radiation dose reduction
 Image accuracy
 Reduced image artifacts
 Unlimited number of views
 Imaging can be obtained at any angle
 Superior representation of bony structure
 Powerful diagnostic 3D planning tool

42. DISADVANTAGES OF CBCT
Image noise –
 Because radiation from the source transmitted
through tissue in the body, the receptor receives
non uniform information from radiation scattered in
many directions-termed as noise
Poor soft tissue contrast-
 Scattered radiation contributes to increased noise of
the image which reduces the contrast of the cone
beam system

43. APPLICATIONS

44. IMPLANT SITE ASSESSMENT
 Provides cross section view of
i. alveolar bone height, width, and angulations
ii. accurate distance from vital structure such as inferior
alveolar canal in mandible and maxillary sinus

45. ORTHODONTICS
1. Used in identification of root resorption
2. Display of position of impacted or supernumerary teeth
3. Relation to adjacent structure
4. Cephalometric analysis

46. TMJ
 provide multiplaner or 3 D image of condyle and
surrounding structures

47. MAXILLOFACIAL PATHOSIS
 Useful in assessment of trauma
 Visualizing the extent and degree of involvement of
benign odontogenic or non odontogenic as well as
osteomyelitis

48. MANDIBULAR THIRD MOLAR
POSITION
 To check the relationship of the third molar with the
inferior alveolar canal during extraction
 To prevent the nerve damage

49. CONCLUSION
 CBCT imaging is an effective volumetric diagnostic
imaging technology that produces accurate, high
resolution images of diagnostic quality in formats
enabling volumetric visualisationof the osseous
structures of the maxillofacial region at lower doses
and costs.

50. THANK YOU