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Cbct

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cone beam tomography in orthodontics

Publicada em: Saúde e medicina
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Cbct

  1. 1. Dr.Rabab Khursheed Cone Beam Computo Tomography
  2. 2. Contents • What is CBCT? • History • Why 3D? • How does CBCT work? • Principles of CBCT Components used Field of view voxel scan time resolution Dicom file • Artifacts • Advantages and disadvantages • Applications in dentistry • Applications in Orthodontics
  3. 3. What is CBCT ?
  4. 4. • Its is the most significant technological advancement in maxilla facial imaging • It is a form of xray computed tomography • X rays are divergent forming a cone
  5. 5. History • 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 oct 2010
  6. 6. "Prima Immagine Cone-Beam-1994-07-01-3" by Daniele Godi - Own work.
  7. 7. Why 3D? • 3 D visualization of manifested disease/deformation/malocclusion • diagnostic accuracy • Better understanding • To the point treatment planning
  8. 8. How does CBCT work? Xray source Detector Raw data Rotates Records after attenuation by patient tissues Reconstructed by complex algorithms
  9. 9. Components used • X-ray generator • Image sensor • Image reconstruction
  10. 10. X-ray generator • 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- anode cathode tube envelop tube housing • Collimator Size of the anode matters.smaller the size of the anode intensity of the x ray increases
  11. 11. • 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
  12. 12. Image sensor • PSP (photo stimulable phosphorus plates) • CCD sensors • FPD (flat panel detector) direct indirect A sensor which has smaller pixel size has better resolution . One pixel can be 0.007 to 0.3mm size. A sensor which has a higher bit rate, can identify more areas of black and white .
  13. 13. Image reconstruction
  14. 14. Principles of cbct
  15. 15. Field of view • Collimation of x ray beam by adjustment of FOV limits the radiation to one ROI • 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.
  16. 16. 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.
  17. 17. 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 xray photons per voxel and result in more noise. • To balance it out a good scanner has higher dosage of radiation
  18. 18. Grayscale • 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.
  19. 19. Exposure settings • 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.
  20. 20. • Can be pulsed or continuous . • Rotation of 180 degrees or 360 degrees
  21. 21. Scan time • 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.
  22. 22. Resolution • The ability of an image to differentiate between two closely placed objects. • Two types- spatial resolution contrast resolution • 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.
  23. 23. DICOM file 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 medicine) format. This is the international standards organization – refrenced standard for all diagnostic imaging Includes x ray, visible light images and ultrasound
  24. 24. Artifacts Any distortion or error in the image that is unrelated to the subject being studied. 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
  25. 25. Inherent 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 • Scatter • Partial volume averaging • Cone beam effect
  26. 26. • 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’
  27. 27. • 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
  28. 28. • 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 reconstruction. • Clinically it can be reduced by placing the ROI in the horizontal plane of the xray beam.
  29. 29. 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
  30. 30. Introduced artifacts • 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 artifact ii. Streaks and dark bands which when present between two dense objects create extinction or missing artifacts. 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
  31. 31. 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 AAOMR
  32. 32. 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 may cause. • Should be used only when a periapical or an opg cannot provide necessary information for patient diagnosis and treatment planning.
  33. 33. Required characteristics for an ideal CBCT image for diagnosis • Good density and contrast • Sharpness • Good resolution • Accuracy of image • Free of artifacts • Free of noise
  34. 34. Advantages • 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 Disadvantages • Scatter • Artifacts • Motion artifacts due to increased scan time • Scan volume in sufficiency • Poor contrast resolution, thus soft tissue cannot be viewd • Image noise is detrimental
  35. 35. European SEDENTEXCT guidelines for CBCT (2012)
  36. 36. Principals 1.History and clinical examination 2.Benefits should outweigh risks 3.New information to aid the patient 4.Not be repeated routinely 11.Quality assurance programs for setting up each CBCT facility 6.Diagnosis with lower radiation imaging is questionable 5.Reffering dentists must provide sufficient information to radiologists 12.Aids to accurate positioning must always be used 10.Resolution compatible with adequate diagnosis yet low radiation should be used. 7.Thourough clinical evaluation report should be made 9.Use small volume doses where you can 8.Should not be done for soft tissue assessment
  37. 37. 13.ALL new installations should under go critical examination for safety 14.CBCT machines should undergo regular routine tests 16.Adequate practical and theoretical training for all those involved 15.European guidleines for radiation protecyion for staff 20.For non dentoalveolar areas, the evaluation should be done by a radiologist 17.Continuing education and training 19.Small FOV for dentoalveolar regions and teeth 18.Dentists who are not previously trained , should be trained
  38. 38. Justified referrals • 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 • Endodontics • Dental trauma • Implant dentistry • Bony pathosis • Facial trauma • Orthognathic surgery • Temporomandibular joint
  39. 39. • Segmental mandibulectomy • Alveolar fractures • Airway assessment • Root canal volume • 3 D cephalometry
  40. 40. Limitations • Periapical lesions • Caries • 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 • Artifacts • High scan time can cause motion artifacts
  41. 41. Orthodontic applications
  42. 42. INDIA UNIT MODEL MANUFACTURER NEWTOM 3G/NEWTOMVGi QR,Inc ,Italy ACCUITOMO 3D ACCUITOMO- TOMOGRAPH/VERAVIEWPACS 3D J-MORITA,JAPAN KODAK KODACK 9000/9500/9300 CBCT CARESTREAM HEALTH GALILEOS GALILEOS SINORA DENTAL SYSTEMS, GERMANY PROMAX 3D CBCT PLANMECAOY, FINLAND
  43. 43. CBCT machines available
  44. 44. Accuracy and reliability of cone-beam computed tomography measurements: Influence of head orientation ,Amr Ragab Et al , AJODO 2011
  45. 45. Comparison of transverse analysis between posteroanterior cephalogram and cone-beam computed tomography by Kyung-Min Lee et al , Angle Orthod. 2014
  46. 46. Three-dimensional monitoring of root movement during orthodontic treatment, Robert et al ,Am J Orthod Dentofacial Orthop 2015
  47. 47. Accurate registration of cone-beam computed tomography scans to 3-dimensional facial Photographs, Kyung-Yen Nahm, Am J Orthod Dentofacial Orthop 2014
  48. 48. Accuracy of cone-beam computed tomography in detecting alveolar bone dehiscences and fenestrations, Liangyan Sun et al Am J Orthod Dentofacial Orthop 2015
  49. 49. Impact of cone-beam computed tomography on orthodontic diagnosis and treatment planning, Ryan J et al Am J Orthod Dentofacial Orthop 2013
  50. 50. Diagnostic accuracy of 2 cone-beam computed tomography protocols for detecting arthritic changes in temporomandibular joints , SumitYadav, Am J Orthod Dentofacial Orthop 2015
  51. 51. Incidental findings arising with cone beam computed tomography imaging of the orthodontic patient, Sheelagh et al , Angle Orthodontist, Vol 81, No 2, 2011
  52. 52. Conclusion 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 imaging suffices.
  53. 53. • White and Pharrow , oral radiology edition 7, 2014 • European SEDENTEXCT guidelines for CBCT (2012) • ICRP – international commission on radiological protection 2007 publication • American academy of oral and maxillofacial radiology 2009 • Prima Immagine Cone-Beam-1994-07-01-3" by Daniele Godi - Own work • Hatcher DC -Operational principles of cone beam computed tomography JADA oct 2010 References
  54. 54. • 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 Orthop 2015 • 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 References
  55. 55. • Three-dimensional monitoring of root movement during orthodontic treatment, Robert et al ,Am J Orthod Dentofacial Orthop 2015 • 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 , AJODO 2011
  56. 56. • 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.

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