Tomography – method of producing three dimensional images of internal structures, imaging sections or sectioning through the use of any kind of penetrating wave.the device used in tomograpohy is called tomograph where as the image produced is called a tomogram.
Was actually developed for angiography in 1980
We live in a 3 dimensional world with 3 dimensional people yet we comfortably depend on 2 d images and systems to plan intricate diagnosis and treatment plans
Any kind of computed tomography consists of an x ray source and detector mounted on a rotating gantry .during rotation of the gantry , the xray source produces radiation while the receptor records the residual x rays after attenuation by the patients tissues.these recordings constitute the raw data that is reconstructed by computer based on complex alogrithms to generate cross sectional images. These basis images are similar to cephalometric images except each one is a little offset from the other.
CT first scans in slices the reconstructs
CBCT scans the whole Region of interest, then slices it ..
An x-ray machine is essentially a camera. Instead of visible light, however, it uses X-rays to expose the film. X-rays are like light in that they are electromagnetic waves, but they are more energetic so they can penetrate many materials to varying degrees. When the X-rays hit the film, they expose it just as light would. Since bone, fat, muscle, tumors and other masses all absorb X-rays at different levels, the image on the film lets you see different (distinct) structures inside the body because of the different levels of exposure on the film.
Center of rotation lies within the center of the object being imaged
Ccd sensors, the area odf focus is less and requires stiching of the image. Binary system of ???
One scan can produce about 500 -600 images.each image is known as a basis projection .not only lateral projections, but also antero posterior.
Minimizes scattered radiation.
Reducing object to detector distance and increasing object to source distance also gives good resolution but obviously produces magnification of the image Smallrer Fov have larger voxels and better images.
Pixel- voxel-Accuracy of linear measurements from cone-beam computed tomography-derived surface models of different voxel sizes Janalt Damstra Am J Orthod Dentofacial Orthop 2010,0.25 and 0.4 did not make a difference
As low as reasonably achievable
Sensor needs some time to get processed as an image so there is a lag time where there is no registration of the x ray beam , this can be avoided by pulsed. Machines that have an option of pulsed exposure also have longer lifes than the other
People who could benefit with a lesser scan time- children, a person who cannot stand still.
The ability of the image to revale fine detail .This is dependent on the pixel size. Cbct has poor contrast resolution.
For example a voxel of 1mm may contain both bone and adjacent soft tissue , in this case the displayed pixel is not of either bone nor soft tissue .it becomes an average of the brightness of the different tissues.
Cupping artifacts from beam hardening occur when x-rays passing through the center of a large object become harder than those passing through the edges of the object due to the greater amount of material the beam has to penetrate. Because the beam becomes harder in the center of the object, the resultant profile of the linear attenuation coefficients appears as a "cup"
American academy of oral and maxillofacial radiology ICRP 2007 CHART
1 micro serviet euals 100 milirem , therefore to produce any problems we have to reach above 1000 milirems , 10000 micro serviets..
European sedentex guidlinesssss 2012
ICRP – international commission on radiological protection
They need us to do more good than harm
Letter to the author airway assessment in 2015 in response to schendel et als article about osp , he stated that the airway is not always static and can change in a person the very next day
Moonyung lee 2015 angle orthod newly defined landmarks
Melissa 2015 angle orthod –only 5% chances of perforating a root
Holdaway and park and burstone Facial asymmetry
Cbct over estimates the amount
Los angeles, straight c white showed just how important it was to take a cbct when there was an unerupted tooth or severe root resorption
Accuitomo CBCT scanner, Kyoto japan , small and large leasions
• What is CBCT?
• Why 3D?
• How does CBCT work?
• Principles of CBCT
Field of view
• Advantages and disadvantages
• Applications in dentistry
• Applications in Orthodontics
• Its is the most significant technological advancement in maxilla facial
• It is a form of xray computed tomography
• X rays are divergent forming a cone
• Cone beam technology was first introduced in the European market in 1996 by
QR s.r.l. (NewTom 9000) and into the US market in 2001
• October 25, 2013, during the "Festival della Scienza" in Genova, Italy, the
original members of the research group:AttilioTacconi, Piero Mozzo, Daniele
Godi and Giordano Ronca received an award for the cone-beam CT invention.
Hatcher DC -Operational principles of cone beam computed tomography JADA
"Prima Immagine Cone-Beam-1994-07-01-3" by Daniele
Godi - Own work.
• 3 D visualization of manifested disease/deformation/malocclusion
• diagnostic accuracy
• Better understanding
• To the point treatment planning
How does CBCT work?
Rotates Records after
• High voltage generator which modifies incoming voltage and current to provide
the x ray tube with the power needed to produce an x ray beam of desired peak kilo
voltage (kVp) and current (mA)
• X ray tube-
Size of the anode matters.smaller the
size of the anode intensity of the x ray increases
• Exposure factors can be controlled manually or automatically
• Scout images
• KvP 60 to 90
• mA 6 to 10
• Pulsed or continuous x ray generation
• 180 or 360 degree rotation of the x ray generator and sensor
• PSP (photo stimulable phosphorus plates)
• CCD sensors
• FPD (flat panel detector)
A sensor which has smaller pixel size has better resolution . One pixel can be 0.007 to 0.3mm
A sensor which has a higher bit rate, can identify more areas of black and white .
Field of view
• Collimation of x ray beam by adjustment of FOV limits the radiation to one
• These depend on the detector size and shape, beam projection geometry
and the ability to collimate or not
• It is desirable to limit the field size to the smallest volume that can
accommodate the region of interest.
Region of interest beyond FOV?
• Obtaining data from two or more separate scans and superimposing and
overlapping the regions of the CBCT data using refrence points,
• A software is used to stich or blend the images together
• Disadvantage being scanning the regions of interest double times so
increase in doage of radiation.
• The spatial resolution is determined by individual volume elements called
• These are cubic in nature equal in all dimensions
• The principle determinant of voxel size is the pixel size of the detector.
Detectors with smaller pixel size capture fewer xray photons per voxel and
result in more noise.
• To balance it out a good scanner has higher dosage of radiation
• The ability of a cbct scan to display differences in attenuation.
• This parameter is called bit depth of the system and determines the number
of shades of grey available to display the attenuation.
• All current CBCT machines have 12 bit detectors and are capable of
identifying 4096 shades of gray . A 16 bit detector can identify 65,536
shades of grey, but this would mean the file sizes and image processing time
would increase by folds.
• ALARA principle
• Can controlled either automatic or manual adjustment of kVp or mA
• Scout exposure- high energy x rays can be avoided by taking an initial scout
exposure, the amount of electrons generated by the patient is registered on
the sensor and the exposure settings are adjusted.
• Can be pulsed or continuous .
• Rotation of 180 degrees or 360 degrees
• Average time for one cbct scan may vary from 7-30 seconds.This is the scan
time including the initial scout image scan
• It also varies if half a rotation or a full circle rotation is used.
• Standard scan- 3-4 seconds, lower resolution , reduced scan time.
• The ability of an image to differentiate between two closely placed objects.
• Two types-
• Spatial resolution – the ability to visualize the difference between two objects of
different radio density
• Contrast resolution – ability to differentiate two objects of the same color type.
Cbct produces two data products
• The volumetric image data from the scan
• Image report generated by the operator
All of these images are svae in the DICOM (digital imaging and communication in
This is the international standards organization – refrenced standard for all diagnostic
Includes x ray, visible light images and ultrasound
Any distortion or error in the image that is unrelated to the subject
Occurs at the interface of the material with a completely different
radiological property from the subject being imaged
• Inherent artifacts
• Procedure related artifacts
• Introduced artifacts
Can result from limitations in physical processes involved in the accusation of
the CBCT data.the beam projection geometry of the CBCT , reduced trajectory
rotational arcs and image reconstruction methods produce the following three
types of artifacts
• Partial volume averaging
• Cone beam effect
• Scatter results from x ray photons that are diffracted from their original
path after interaction with matter
• The scattered photons that are captured by the sensors contribute to over
all image degradation called ‘quantum noise’
• Partial volume averaging happens when the selected voxel size of the scan
is larger than the object being imaged.
• Boundaries in the resultant image may have a step appearance or
homogeneity of pixel intensity level.
• Selection of the smallest accusation voxel can reduce this
• Cone beam effect is a potential source of artifacts , especially in the peripheral portions of
the scan volume.
• Because of the divergence of the x ray beam as it rotates around the patient in a horizontal
plane, structures at the top and bottom of the image are exposed only when the xray
source is on the opposite side of the patient.
• This results in large image distortion and streak artifacts and peripheral noise.
• This is minimized by the incorporation by manufacturers of various forms of cone beam
• Clinically it can be reduced by placing the ROI in the horizontal plane of the xray beam.
Procedure related artifacts
• When very few basis images are taken or the time between the images are
too long, undersampaling of the object can occur.this leads to aliasing
artifacts or striations in the image.
• Scanner related artifacts can also appear as a circular projection.This could
be due to the misalignment of the xray source to the detector
• Beam hardening
• Cupping artifact
• Extinction or missing value artifact
As an xray beam passes through an object , lower energy photons are absorbed in preference to higher
energy photons.This is called beam hardening , which results in two types of artifacts ,
i. Distortion of metallic structures as a result of differential absorption known as the cupping
ii. Streaks and dark bands which when present between two dense objects create extinction or
In clinical practice it is advised to reduce the field of view, modify patient position, or separate the
dental arches to avoid scanning regions susceptible to beam hardening
Effective radiation dosage
• FOV>15 cm – 52 to 1073 µSv
• FOV 10 to 15cm – 61 to 603 µSv
• FOV of < 10 cm- 18 to 333 µSv
• Multislice CT -426-1600 µSv
• Panaromic – 6-50 µSv
• Cephalogram- 2 -10 µSv
• IOPA- 2-8 µSv
Patient selection criteria
• the ALARA principal must always be applied.
• There should be justification of the exposure to the patient so that the total
diagnostic benefits are greater than the individual determinant the radiation
• Should be used only when a periapical or an opg cannot provide necessary
information for patient diagnosis and treatment planning.
Required characteristics for an ideal CBCT
image for diagnosis
• Good density and contrast
• Good resolution
• Accuracy of image
• Free of artifacts
• Free of noise
• Rapid scan time
• Beam limitation
• Image accuracy
• Reduction in patient radiation dose
when compared to medical ct
• Interactive display modes
• Multiplanar reformatting
• 3 dimensional volume rendering
• Better images with good spatial
• Economical, comfortable and safe
• Motion artifacts due to increased
• Scan volume in sufficiency
• Poor contrast resolution, thus soft
tissue cannot be viewd
• Image noise is detrimental
European SEDENTEXCT guidelines for CBCT
aid the patient
setting up each
must always be
where you can
be done for
under go critical
examination for safety
regular routine tests
training for all those
guidleines for radiation
protecyion for staff
the evaluation should
be done by a
education and training
19.Small FOV for
18.Dentists who are
not previously trained ,
should be trained
• Localised applications of CBCT for the developing dentition
• Generalized application of CBCT for the developing dentition
• Dental caries diagnosis
• Periodontal assessment
• Assessment of periapical disease
• Dental trauma
• Implant dentistry
• Bony pathosis
• Facial trauma
• Orthognathic surgery
• Temporomandibular joint
• Periapical lesions
• Periodontal problems related to pdl or gingiva
• Soft tissue assessment
• Very small lesions (smaller than voxel size)
• Fractures of the tooth
• Root canals, accessory canals
• Assessing bone density
• High scan time can cause motion artifacts
UNIT MODEL MANUFACTURER
NEWTOM 3G/NEWTOMVGi QR,Inc ,Italy
ACCUITOMO 3D ACCUITOMO-
KODAK KODACK 9000/9500/9300 CBCT CARESTREAM HEALTH
GALILEOS GALILEOS SINORA DENTAL SYSTEMS,
PROMAX 3D CBCT PLANMECAOY, FINLAND
Accuracy and reliability of cone-beam computed tomography
measurements: Influence of head orientation ,Amr Ragab Et al , AJODO
Comparison of transverse analysis between posteroanterior cephalogram
and cone-beam computed tomography by Kyung-Min Lee et al , Angle
Three-dimensional monitoring of root movement during orthodontic
treatment, Robert et al ,Am J Orthod Dentofacial Orthop 2015
Accurate registration of cone-beam computed tomography scans to 3-dimensional
facial Photographs, Kyung-Yen Nahm, Am J Orthod Dentofacial Orthop 2014
Accuracy of cone-beam computed tomography in detecting alveolar bone
dehiscences and fenestrations, Liangyan Sun et al Am J Orthod Dentofacial
Impact of cone-beam computed tomography on orthodontic diagnosis and
treatment planning, Ryan J et al Am J Orthod Dentofacial Orthop 2013
Diagnostic accuracy of 2 cone-beam computed tomography protocols for
detecting arthritic changes in temporomandibular joints , SumitYadav, Am
J Orthod Dentofacial Orthop 2015
Incidental findings arising with cone beam computed tomography imaging of the orthodontic patient,
Sheelagh et al , Angle Orthodontist, Vol 81, No 2, 2011
This technique hugely expands the fields for diagnosis and treatment
possibilities, not to forget many more research frontiers as well.however CBCT
should be used with careful consideration ,it should not be used where 2D
• White and Pharrow , oral radiology edition 7, 2014
• European SEDENTEXCT guidelines for CBCT (2012)
• ICRP – international commission on radiological protection 2007
• American academy of oral and maxillofacial radiology 2009
• Prima Immagine Cone-Beam-1994-07-01-3" by Daniele Godi -
• Hatcher DC -Operational principles of cone beam computed
tomography JADA oct 2010
• Incidental findings arising with cone beam computed tomography imaging of the
orthodontic patient, Sheelagh et al ,Angle Orthodontist,Vol 81, No 2, 2011
• Diagnostic accuracy of 2 cone-beam computed tomography protocols for detecting
arthritic changes in temporomandibular joints , SumitYadav,Am J Orthod Dentofacial
• Impact of cone-beam computed tomography on orthodontic diagnosis and treatment
planning, Ryan J et al Am J Orthod DentofacialOrthop 2013
• Accuracy of cone-beam computed tomography in detecting alveolar bone dehiscences and
fenestrations, Liangyan Sun et al Am J Orthod DentofacialOrthop 2015
• Accurate registration of cone-beam computed tomography scans to 3-dimensional
facial Photographs, Kyung-Yen Nahm, Am J Orthod DentofacialOrthop 2014
• Three-dimensional monitoring of root movement during
orthodontic treatment, Robert et al ,Am J Orthod Dentofacial
• Comparison of transverse analysis between posteroanterior
cephalogram and cone-beam computed tomography by Kyung-
Min Lee et al , Angle Orthod. 2014
• Accuracy and reliability of cone-beam computed tomography
measurements: Influence of head orientation ,Amr Ragab Et al ,
• ScarfeWC, Farmna AG, Sukovic P. Clinical applications of cone beam
tomography in dental practice. J Can Dent Assoc. 2006;72:75–80.
• Ludlow JB, Ivanovic M. Comparative dosimetry of dental CBCT devices and
64-slice CT for oral and maxillofacial radiology. Oral Surg Oral Med Oral
Pathol Oral Radiol Endod. 2008;106:106–114
• Upadhyay M,Yadav S, Patil S. Mini-implant anchorage for en-masse
retraction of maxillary anterior teeth: a clinical cephalometric study. Am J
Orthod Dentofacial Orthop. 2008; 134:803–810.