Cone Beam Computed Tomography: Anatomy & Interpretation part 1

Field of View

Reduce volume size to region of interest

What does reducing the field of view do?

• Lower radiation dose (ALARA)

• Increase resolution

• Improve image quality

• Less anatomy to review

What are the dental applications of CBCT in oral surgery?

• Dento-alveolar trauma

• Pathology (intraosseous lesions)

• Impacted 3rd molar extraction and orthognathic surgical planning)

What are the dental applications of CBCT in periodontics?

Implant and surgical planning

What are the dental applications of CBCT in orthodontics?

• Airway and cephalometric analysis

• Impacted and supernumerary teeth

What are the dental applications of CBCT in endodontics?

• Root canal morphology

• Fractures

• Resorption

What are the dental applications of CBCT in oral medicine?

• Temporomandibular joints

• Osteonecrosis

What is the main metric for resolution

Voxel size (minecraft, bigger pixels- blocky)

What is the relationship between voxel size and volume size?

As we increase FOV (or volume), voxel size increases

When there is evident or suspected soft-tissue involvement, what is the preferred modality?

MDCT is the preferred CT modality

What can you not really see in CBCT imaging, but can see in MDCT

Pathoses: Soft Tissue

Why is MDCT better for soft tissue windowing?

It has a higher/better contrast resolution

• It enables soft tissue eval that is not possible with CBCT

• IV contrast improves detection of soft tissue conditions due to enhancement (inflammation, malignancy, lymph node involvement)

What does the ADA have to say about the use of CBCT in Dentistry?

• It is considered adjunct to standard oral imaging modalities, you have to use it when conventional radiography is insufficient

• You also need appropriate clinical justification

• It is NOT used for screening purposes

• You have to use it when the diagnostic yield is expected to benefit patient care and enhance patient safety/improve clinical outcomes

What does the AAOMR say about radiology in dental implantology?

• CBCT should be considered as the modality of choice for preoperative imaging of implant sites

• You have to use PAs for post-op implant assessment in the absence of clinical signs or symptoms

• DO NOT use CBCT for interval/periodic assessment of clinically asymptomatic implants

What does CBCT allow in implant planning?

• Visualization of implant site in all dimensions

• Reliable, accurate measurements

• Evaluation of bone density and cortical thickness

• Assessment of adjacent vital structures

What are the discrepancies using CBCT and PAs in implant planning?

Intraoral imaging is limited by superimposition and distortion (particularly in the buccal-lingual dimension)

• Measurements from PA showed -1.7 to +2.1mm discrepancies compared to CBCT

• PAs overestimate measurements 66% of the time

• Panoramic is limited by superimposition, distortion and magnification

Dual scan

Image fusion

What is image fusion?

The integration of 2+ imaging datasets, examples include

• Intra-oral scan

• Cast/model

• Dual scan

What is image guided navigation in implant planning?

Real-time virtal guidance based on planned implant

What is a good modality for assessing impacted 3rd molars, why?

CBCT is better than panoramic because you can see the number of roots, apical divergence, direct contact with IAC and predicting IAN exposure during surgery but was NOT better at predicting postoperative complications

What is the evidence that CBCT Is better than a pano for assessing 3rd molars?

There is none - no evidence that CBCT improves prediction of treatment outcomes or helps prevent complications

But it is still advised that CBCT be utilized bc it indicated the proximity to IAC

What is the best modality for endodontics?

Intraoral radiographs should be considered the modality of choice because there are indications for limited field of view in CBCT

What are the indications for limited field of view in endodontics?

• Contradictory or nonspecific clinical signs and symptoms

• Suspect extra canals or complex morphology

• Identification/localization of calcified canals

• Non-healing previously treated teeth

• Limited dentoalveolar trauma, root fractures, luxation, and/or displacement of teeth, and localized alveolar fractures

• External and internal resorptive defects

• Assess endodontic treatment complications

What are the findings in CBCT in endodontics?

• Odds of CBCT locating a lesion are 2x as good as PAs

• CBCT has high accuracy for tooth fractures

• High confidence in positive result

• Negative result should be interpreted with caution esp. in previously treated teeth

• **Fairly significant limitations in the study (resolution is not that good- might not see tiny fractures)

  • Can make artifacts

  • Not 100% reliable for predicting fractures

What are the clinical recommendations regarding the use the CBCT in Orthodontics?

The pediatric population is radiosensitive

• They are 2-10x more prone to radiation-induced carcinogenesis than mature adults

• Higher rate of cellular growth and longer life expectancy

How has CBCT demonstrated use in Orthodontics?

It has demonstrated clinical efficacy in treatment planning for impacted maxillary canines, unerupted teeth, severe root resorption, severe skeletal discrepancies

In what cases should CBCT be USED in orthodontics?

When clinical question cannot be adequately answered by conventional imaging

In what cases should CBCT be AVOIDED in orthodontics?

Solely to produce a lateral cephalometric and/or panoramic view if it would result in higher radiation exposure than conventional imaging

What would you use CBCT for when looking at the airway?

Obstructive sleep apnea (OSA); severe OSA patients had significantly narrower cross-sectional area at uvula, more inferiorly positioned hyoid bone, and thicker soft palate

What are the risk factors for obstructive sleep apnea (OSA)?

• Obesity

• Decreased muscle tone of upper airway

• Sleeping on back

• Relaxants: ETOH, CNS depressant meds

• Narrow nasal passages

• Enlarged tonsils, adenoids, uvula, soft palate, tongue

• Skeletal discrepancies

What are the measurements made in CBCT for airway analysis?

• Cross sectional area and volume

• Narrow minimum cross-sectional area has been
  associated with OSA

• Use and applicability of these measurements is
  controversial

What are the limitations of using CBCT for airway analysis/OSA?

• Airway size and shape are variable depending on head posture and breathing stage

• Does not accurately reflect airway during sleep

What is the use of CBCT for evaluation of TMJ?

What is the initial imaging exam for patients with TMD symptoms?

Panoramic

• It is not sensitive to small changes

• Entire condylar surface is not clearly depicted (obscured by superimposition and distortion)

What is used for the evaluation of osseous abnormalities in TMJ evaluation?

CBCT and MDCT are equivalent for evaluation

• MDCT with contrast is recommended if malignant lesion is suspected

• MRI has superior soft tissue resolution to MDCT and the only technique that shows the disk

CBCT in TMJ disorders

When taking a CBCT for TMJ evaluation, what should the patient do?

Be in occlusion. Open-mouth CBCT has limited impact on TMD diagnosis and management

The what are the display modes of CBCT

1. Multiplanar reformation

2. Orthogonal projections

What are the types of multiplanar reformations?

1. Linear oblique

2. Curved oblique

3. Serial transaxial

What are the volume renderings of orthogonal projections in display modes?

Direct volume rendering

• Ray sum

• Maximum intensity projection

Indirect volume rendering

What are the standard orthogonal planes?

What are multiplanar reformations?

Display of data in different sections/planes

non-orthgonal or oblique

The options are software dependent

What are some awys you can optiminze imaging?

Using contrast and brightness

• adjust for clear distinction between dentin and enamel, soft tissue and air, cortical and trabecular bone

• Thin cortical bone should be distinct

• Enhancements: smoothing or sharpening

Enhancements of image optimization

What is indirect volumetric rendering?

• Computationally complex

• Uses segmentation process to produce volumetric surface reconstruction with depth

What is Ray Sum (Direct) volumetric rendering?

• Image slab created by increasing number of adjacent voxels included in display

• Gives appearance of anatomic superimposition (2D)
  without magnification or distortion

What is Maximum Intensity Projection (Direct) volumetric rendering?

• Displays only highest gray level voxels along an
  imaginary beam path

• Useful in representing bony surface morphology

What are some task-specific tools?

It is dependent on software

• Inferior alveolar canal tracing

• Virtual implant planning

• Surgical guide and restoration design

• Superimposition

  • Overlay scans taken at different time points to assess change

• Cephalometric analysis

• Airway analysis

• TMJ viewer

• Endodontic specific reformats and volumetric renderings

What are some liability considerations when taking a CBCT?

Regardless of the primary purpose for the scan, the complete volume must be interpreted by an appropriately qualified provider

• Interpreting provider is held to the standard of a specialist

• Interpreting provider must be able to recognize significant findings

• Endodontists and endo residents had interpretation accuracy of 60% compared to gold standard (consensus of experienced endodontist + OMFR) for limited FOV CBCTs

• High rate of errors – missed lesions and false positives – by orthodontists and ortho residents

• Findings must be documented in patient chart

What are some incidental findings in CBCT?

“Any abnormal or pathological finding that is unrelated to
the original purpose of the imaging test or tests being
performed.”

• Presence of significant incidental findings in CBCT scans
  well-documented

  • Incidence of ~24-94%

  • Most are not life-threatening

  • Frequency of incidentally found malignancy: 0.003 to 1.4%

• Case report: 66yo female who had CBCT (80mm) for maxillary implant planning

  • Incidentally noted left sphenoid sinus mass

  • Further evaluation confirmed metastatic renal cell cancer
    Incidental finding of metastatic malignancy

Example of a CBCT report

What is the other responsbility that you as a provider need to do in addition to taking the CBCT?

You need to be able to export and archiving it. Properly store it

• CBCT volumes must be saved and stored like other patient images

  • Must be able to provide patients (and other providers) with usable copies

• DICOM Digital Imaging and Communications in Medicine
  Standard format for image archiving and transmission

  • Used by all viewing software

What term do you use to talk about radiographic density instead of radiolucent?

Hypodense

What term do you use to talk about radiographic density instead of radiopaque?

Hyperdense

List some tips for interpretation

✓ Use a systematic approach
✓ Start with panoramic rendering
✓ View entire volume in all 3 standard planes
✓ Focus on region(s) of interest last
✓ Avoid satisfaction of search

To ensure you don’t miss any incidental findings and/or pathology, review this list of anatomical structures contained in the FOV in all imaging places (axial, sagittal, coronal)

✓ Oral cavity (dentition, paradental bone)
✓ Nasal cavity
✓ Paranasal sinuses
✓ Cranial base
✓ Orbits
✓ Airway
✓ Temporomandibular joints
✓ Cervical spine

List all the anatomical structures you’d find in the mandible

• Body

• Ramus

• Coronoid process

• Mylohyoid ridge

• Submandibular fossa

• Inferior alveolar canal

• Mental foramen

• Lingual canal

• Genial tubercles

List all the anatomical structures you’d find in the TMJ & Temporal Bone

• Mandibular condyle

• Glenoid fossa

• Articular eminence

• Styloid process

• Mastoid process

• Mastoid air cells

• External auditory canal

List all the anatomical structures you’d find in the Maxilla

• Tuberosity

• Hard palate

• Nasopalatine canal

• Incisive foramen

• Anterior nasal spine

• Zygomatic process of maxilla

• Zygomatic arch (zygomatic & temporal bones)

List all the anatomical structures you’d find in the nasal cavity

• Nasal concha (inferior, middle, superior)

• Nasal septum

• Nasal bones

• Nasolacrimal duc

List all the anatomical structures you’d find in the paranasal sinuses

• Maxillary sinus

  • Ostium

  • Uncinate process

• Sphenoid sinus

• Frontal sinus

• Ethmoid air cells

List all the anatomical structures you’d find in related to orbits

• Orbit

• Infraorbital foramen (maxillary bone)

• Optic canal (sphenoid bone)

• Superior orbital fissure

• Inferior orbital fissure

List all the anatomical structures you’d find in soft tissues and airway

• Nasopharynx

• Oropharynx

• Soft palate

• Tongue

• Palatine tonsils

• Epiglottis

List all the anatomical structures you’d find in cervical spine and other

• Anterior arch of C1

• Dens of C2

• Pterygoid plates (medial, lateral)

• Pterygopalatine fossa

• Pterygomaxillary fissure

• Hyoid

• Sella turcica