comparison of CT and CBCT -INTRODUCTION TO CT, CBCT - DIFFERENCES BETWEEN CT AND CBCT - CLINICAL USES IN ORTHODONTICS

2. COMPARISON OF CT AND
CBCT
DONE BY:
AMRITHA JAMES,CRI
GUIDED BY:
DR. KARUNANATHI MDS, DR.SARANYA DEVI, MDS
Department of orthodontics

3. contents
 Computed tomography
 Introduction
 How does a CT work?
 Image reconstruction in CT
 Artifacts
 Indications of CT
 Advantages and disadvantages of
CT
 Cone beam computed
tomography
 Introduction
 How does a CBCT work?
 Principle of CBCT
 Image formation
 Artifacts
 Indication of CBCT in
orthodontics
 Advantages and disadvantages of
CBCT
 CT vs. CBCT

4. CT
 CT scanner was invented by Godfrey
Newbold Hounsfield in Hayes, England
 A CT scan makes use of computer-
processed combinations of many X-
ray images taken from different angles to
produce cross-sectional (tomographic)
images.

5. How does a CT work?
 A CT scanner consists of an x-ray tube that emits a finely collimated
fan shaped x-ray beam directed through a patient to a series of
scintillation detectors.
 These detectors measure the number of photons that exit the patient.
 The detectors form a continuous ring around the patient and the x-
ray tube moves in a circle within the fixed detector ring.
 This information is used to construct a cross- sectional image of the
patient.

7. Image reconstruction
 Many scans are progressively taken as the object is gradually passed
through the gantry. They are combined together by the mathematical
procedure known as tomographic reconstruction.

8.  The x ray beam attenuation data is collected in a grid
pattern called a matrix.
 Each square in the matrix is made up of pixel which
represents the x ray attenuation of small finite volume of
tissue(voxel) or volume element.
 Typical matrix in CT are 256*256 or 512*512 pixels.

9.  Each pixel is assigned a CT number
(hounsfield unit) representing tissue
density.
 This number is proportional to the
degree to which the material within
the voxel has attenuated the x-ray
beam.
 Water is the reference and assigned a
value of zero.
 Tissues more denser than water have
a positive number.

10. Image display
 Areas of high density with high CT number appear white on the
greyscale.
 Areas of low density with low CT number appear black on the
greyscale.

11. 3 step process of CT imaging

12. Artifacts
 Aliasing Artifact or Streaks
 These appear as dark lines which
radiate away from sharp corners.
 It occurs because it is impossible for
the scanner to take enough projections
of the object, which is usually
metallic.
 Ring Artifact
 Probably the most common
mechanical artifact, the image of
one or many 'rings' appears within
an image. This is due to a detector
fault.

13.  Noise Artifact
 This appears as gaining on the image
and is caused by a low signal to noise
ratio. This occurs more commonly when
a thin slice thickness is used. It can also
occur when the kV or mA is too low.
 Motion Artifact
 This is seen as blurring which is caused
by patient movement.
 Beam Hardening
 This can give a 'cupped appearance'. It
occurs when there is more attenuation in
the center of the object than around the
edge. This is easily corrected by
filtration .

14. Indications of CT in dentistry
1. Evaluation of extent of any suspected pathology in the head and
neck, including tumors, cysts and infection.
2. Determination of location and extent of facial fractures.
3. Radiographic pre surgical evaluation for implant placement.

15. ADVANTAGES OF CT
1. CT completely eliminates the superimposition of images of
structures outside the area of interest.
2. Because of the inherent high-contrast resolution of CT, differences
between tissues that differ in physical density by less than 1% can
be distinguished.
3. Data from a single CT imaging procedure consisting of either
multiple contiguous or one helical scan can be viewed as images in
the axial, coronal, or sagittal planes, depending on the diagnostic
task. This is referred to as multiplanar reformatted imaging.

16. DISADVANTAGES OF CT
 Time consuming
 Expensive for routine clinical use
 High radiation exposure
 Expensive equipment and hence is not always accessible

17. CBCT
 CBCT is a variation on traditional
computed tomography (CT)
 Unlike traditional CT scanners, in CBCT
an X-ray tube and detector panel rotate
around the patient capturing data with a
cone-shaped X-ray beam instead of the
“slices” CTs are typically known for.
 Images are then reconstructed using
algorithms to produce 3-dimensional
images at high resolution. CBCT machine

18. NewTom 9000 / NewTom 3G i-CAT

19. HOW DOES A CBCT WORK?
 All CBCT scanners consists of an x ray source and detector mounted
on a rotating gantry.
 During rotation of the gantry, the x ray source produces a divergent
cone shaped radiation, while the receptor records the residual x rays
after attenuation by patients tissues.
 The x ray source and detector moves through an arc of 180 to 360
degree to produce multiple planar projection images.
 Theses images constitute the raw primary data which is then
reconstructed by a computer algorithm to generate cross sectional
images.

21. Components of image production
1. X-ray generation
2. X- ray detection: Image sensor- PSP (photo stimulable phosphorus
plates),CCD sensors, FPD (flat panel detector)
3. Image reconstruction

22. Image reconstruction

23. PRINCIPLE OF CBCT
 FIELD OF VIEW:
 Collimation of x ray beam by adjustment of FOV limits the radiation to one
Radius Of Interest.
 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.

24.  REGION OF INTEREST BEYOND FOV:
 Data from two or more separate scans are superimposed and
overlapped using reference points
 A software is then used to stich or blend the images together

25.  VOXEL:
 The spatial resolution is determined by individual volume elements
called voxels.
 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 x-ray photons per voxel
and result in more noise. To balance it out a good scanner has higher
dosage of radiation
 All current CBCT machines have 12 bit detectors and are capable of
identifying 4096 shades of gray .

26. IMAGE FORMATION
 Image formed can be visualized
as
 2D trans-axial, multi-planar
reformatted
 3D techniques such as surface
reconstruction and volume
rendering
 A combination of 2D and 3D
techniques
saggital(A), coronal (B), and axial (C) planes.

27. THE MECHANISM OF CBCT ACQUISITION

28. artifacts
 Any distortion or error in the image that is unrelated to the subject
being studied is called an artifact.
 Occurs at the interface of the material with a completely different
radiological property from the subject being imaged. They can be
classified into
1. Inherent artifacts
2. Procedure related artifacts
3. Introduced artifacts

29. STREAKING ARTIFACT MOVEMENT ARTIFACT BEAM HARDENING
METAL ARTIFACT

30. CBCT IN ORTHODONTICS
Impacted Tooth Root Resorption associated
with impacted teeth
Developmental anomalies
Root Fracture Evaluate the residual alveolar
bone thickness
Evaluating the bony defect
caused by cleft palate

31. Temporomandibular Evaluation
Nerve Mapping
Ceph Tracing
Airway Analysis

32. Advantages of CBCT
 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
resolution
 Economical, comfortable and
safe

33. Disadvantages of cbct
 Poor contrast resolution, thus
soft tissue cannot be viewed
 Artifacts
 Image noise

34. Ct vs cbct

35. CT CBCT
1. Traditional CT uses a high-
output, rotating anode X-ray
tube.
1. Cone beam tomography utilizes a
low-power, medical fluoroscopy
tube that provides continuous
imaging throughout the scan.

36. CT CBCT
2. Traditional computerized
tomography records data with a
fan-shaped X-ray beam onto
image detectors arranged in an
arc around the patient.
2. The advanced cone beam
technology uses a cone-shaped
X-ray beam that transmits onto a
solid-state area sensor for image
capture.

37. CT CBCT
3. Produces a single slice image
per scan. Each slice must
overlap slightly in order to
properly reconstruct the images.
3. Produces the complete volume
image in a single rotation.

38. CT CBCT
4. Slower due to spiral motion.
Scan time is longer.
4. The single-turn motion image
capture used in CBCT is quicker
than traditional spiral motion of
CT. Average time for one cbct
scan may vary from 7-30
seconds.

39. CT CBCT
5. Has high radiation dose.
The average medical CT scan of the oral
and maxillofacial area can reach levels
of 1,200– 3,300 microsieverts. To
collect adequate
5. Has lower radiation dose as a
result of no overlap of slices.
Radiation exposure using the
standard full field of view from an
i-CAT® CBCT machine is 36
microsieverts.

40. CT CBCT
6. To collect adequate formation,
there is overlapping of
radiation.
6. No overlap of slices

41. CT CBCT
7. Only one jaw can be visualized
at one time.
7. Both jaws can be imaged at the
same time.

42. medical CT 120 kV, 100 mAs CBCT 110 kV, 10 mAs
CT CBCT
8. High-contrast resolution 8. Poor contrast resolution, thus soft
tissue cannot be viewed.

43. CT CBCT
9. Cost is high 9. Cost of equipment is
approximately 3-5 times less than
traditional Medical CT
CT CBCT
10. Can cause claustrophobia 10. The open design of the cone
beam CTs virtually eliminates
claustrophobia and greatly
enhances patient comfort and
acceptance

44. CT vs CBCT

45. CONCLUSION
 CBCT is the future of orthodontics and its applications in
orthodontics seem almost limitless. CBCT imaging provides insight
into treatment planning that is unachievable with other imaging
methods, and allows clinicians to provide more predictable patient
care, however CBCT should be used with careful consideration ,it
should not be used where 2D imaging suffices.

47. references
 CBCT in Orthodontics: The Wave of Future
Jiwanasha Manish Agrawal, Manish Suresh Agrawal, Lalita Girish Nanjannawar,
Anita D Parushetti
 Facing the facts: dental CBCT vs. medical CT scans
By Bruce Howerton, DDS, MS
 The clinical application of cone beam CT in orthodontics
Moiz Ahmad Khana, Syed Sheeraz Hussainb
 Using cone beam technology in orthodontics Edward Lin
 Applications of CBCT in dental practice: A review of the literature
Hadi Mohammed Alamri, BDS n Mitra Sadrameli, DMD and Mazen Abdullah
Alshalhoob, BDS Mahtab Sadrameli, DMD, MAGD Mohammed Abdullah Alshehri,
BDS, AEGD
 2D / 3D Cone-Beam CT images or conventional radiography: Which is more reliable?
Carolina Perez Couceiro**, Oswaldo de Vasconcellos Vilella***