Interpretation Bias & Basics

What are the steps for the overview of interpretation principles?

1. Select appropriate image type

2. Make sure image is diagnostic

3. Identify presence of any abnormalities in the image

4. Determine what the abnormality is (differential diagnosis)

What is image selection?

Effectiveness of imaging refers to likelihood that it will meet diagnostic objectives

Imaging should be guided by

1. The perceived nature or severity of abnormality (size and accessibility)

2. Efficacy of technique to accurately reveal characteristic radiologic features of abnormality

3. Amount of image detail required (density, contrast and spatial resolution)

4. Radiation dose, accessibility and cost to patient

What are intraoral images good for?

1. Highest spatial resolution relative to other modalities in dentistry

2. Best for evaluating diseases involving teeth and supporting structures

What are panoramic images good for?

1. Allows examination of more extensive disease involving a larger area (includes TMJs, more of maxillary sinuses)

2. Lower image resolution and more artifact than intraoral

What are CBCT and MDCT images good for?

Indicated when there is a need to evaluate anatomy in multiple dimensions without anatomical superimpositions

What are MRI images good for?

Soft tissue evaluation (more info than MDCT but at a lower resolution and hard tissues less well visualized)

What are imaging steps?

What are intraoral images?

Full-mouth radiographic series (FMX) or intraoral complete series- survey of whole mouth intended to display crowns and roots of all teeth, periapical areas, interproximal areas and alveolar bone including edentulous areas

• Periapical images

• Bitewing images

What are periapical images good for?

• Optimal to demonstrate roots, supporting structures (periodontal ligament and lamina dura), and peri-radicular alveolar process

• Limitation is geometric distortion

What are bitewing images good for?

• Optimal for revealing interproximal caries

• Project the crests of the alveolar processes relative to adjacent teeth with minimal distortion

What is a panoramic image?

Visualization of a larger region of anatomy than intraoral images

What is the main disadvantage to panoramic images?

Lack of fine anatomic detail (lower spatial resolution than intraoral)

What are some other disadvantages to a panoramic image?

• Susceptibility to patient positioning and movement

• Unequal magnification and geometric distortion across image

• Complex pattern of superimposition of anatomic structures challenges interpretation

• Occasionally overlapping structures can hide lesions (ex. cervical spine)

Why is a panoramic image not as useful as IOs?

• It doesn’t detect small carious lesions, fine structure of periodontium, or early periapical disease

• It doesn’t provide much additional useful information beyond an FMX for most patients

  • Panoramic combined with BWs and selected PAs could provide diagnostic information similar to FMX

What is image quality?

Reliability of an image in its representation of the true state of anatomy examined

What are the parameters of radiographic image quality?

• Image sharpness

• Spatial resolution

• Contrast resolution

• Magnification

• Distortion

What is the quality criteria for radiographs?

1. Should record the complete area/s of interest on the image

2. Have the least possible amount of magnification and distortion

3. Have optimal contrast and spatial resolution to facilitate interpretation for the diagnostic task

What should quality criteria do for your image?

1. Assess whether the diagnostic objectives of the imaging examination were adequately met

2. If not, determine which additional images to take and/or which images need to be retaken to meet the diagnostic objectives

What is a systematic search strategy?

• Improves detection of abnormalities

• Helps avoid “satisfaction of search”

what is the systematic search strategy for a periapical image?

You would look for:

• crown

• root structure

• pulp chamber and root canal system

• periodontal ligament space

• lamina dura

what is the systematic search strategy for a panoramic image?

You would look for:

• Posterior border of maxilla

• maxillary sinus floor

• zygomatic process of maxilla

• infraorbital rim

• condyles

what is the systematic search strategy for a CBCT image?

You could look for review of captured anatomy through entire volume in axial, coronal, and sagittal planes

What is diagnostic reasoning?

Method of identifying features of the abnormality that will assist in arriving at a plausible interpretation or diagnosis

What is important for interpretation accuracy?

Feature memorization is generally less effective than understanding basic disease mechanisms

What is a non-analytic strategy for diagnostic reasoning?

• Assumes viewing abnormality in its entirety on a global level leads to a more holistic diagnostic hypothesis

• Deliberate search for features that support the hypothesis

• “pattern recognition”

• Success is limited by experience level

What is an analytical strategy for diagnostic reasoning?

• Step-by-step analysis of all features which are used to make interpretation/diagnosis

• Reduces bias and premature closure of decision-making process

How can analytical and non-analytical strategies be complementary?

They can be used together but

• Avoid use of non-analytical alone

• Avoid rote memorization of lesion features

What are the steps for the analytical strategy?

1. Describe lesion features

2. Interpret significance of observed features

   a. Use features to determine disease category

   b. Narrow down to differential diagnosis- short list of most likely entities

What is the acronym for analytical strategy?

L- location

E- Edge (border)

S- shape/size

I- internal content

O- other structures

N- number

What is the description for lesion?

• Localized/generalized

• Single/multifocal

• Unilateral/bilateral

• Epicenter/position in jaw

What is the description for external border/edge (periphery)?

• Well or poorly defined

• corticated or non-corticated

What is the description for internal content/structure/pattern?

• Lucent/opaque/mixed

• Septations

• Calcifications

What is the description for other effects on structures/anatomy?

Teeth, inferior alveolar canal,, maxillary sinuses, cortices, trabecular pattern

What is the description for number?

Solitary or multiple

What is the first step in the analysis of intraosseous lesions?

Localize the abnormality

• Anatomic position (epicenter)

• Localized or generalized

• Unilateral or bilateral

• Single or multifocal

What is the second step in the analysis of intraosseous lesions?

Assess periphery and shape of abnormality

• Well defined (corticated, punched out, sclerotic, soft tissue capsule)

• Poorly defined (blending, invasive)

• Shape (circular, scalloped or irregular)

What is the third step in the analysis of intraosseous lesions?

Analyze the internal structure

• Totally radiolucent or totally radiopaque

• Mixed radiolucent and radiopaque (describe the pattern)

What is the fourth step in the analysis of intraosseous lesions?

Assess the effects of the lesion on adjacent structures

• Teeth, lamina dura, periodontal ligament space

• Inferior alveolar nerve canal and mental foramen

• Maxillary sinus

• Surrounding bone density and trabecular pattern

• Outer cortical bone and periosteal reactions

What is the fifth step in the analysis of intraosseous lesions?

Formulate an interpretation

What is epicenter?

The geometric center of the lesion

• Midpoint of the mesial-distal, superior-inferior, and buccal-lingual extensions

• May assist in determining cell or tissue type the lesion is derived from

  • less accurate with very large or poorly defined lesions

How is the epicenter relative to the inferior alveolar canal?

• Within IAC → more likely neural or vascular

• Above IAC → more likely odontogenic

• Below IAC → more likely nonodontogenic

• Epicenter in ramus, coronoid or condyle or within maxillary sinus more likely non-odontogenic

What can narrow interpretation?

The extent of the lesion, whether it is generalized or localized

• Metabolic and endocrine processes tend to uniformly impact structures

• Few lesions tend to be multi-focal which can narrow diagnosis

In order to know where the lesion is, what do you have to do?

• Describe the lesion extent in multiple dimensions (ex. superior-inferior, medial-lateral) relative to other structures (ex. teeth)

  • Peri-coronal, peri-apical, inter-radicular

• Certain lesions tend to be found in certain locations

  • Location alone should never be used as sole feature when formulating diagnosis

What are the types of periphery/borders? And what do they mean?

• Well defined

  • If you can confidently (*mostly*) trace the border

  • Tends to be benign

• Poorly defined

  • Difficult to exactly delineate or reproducibly draw

  • Tends to be malignant

• Zone of transition

  • How quickly normal bone transitions to abnormal

  • Narrow vs. wide

What do you see in a well defined border?

• Punched out – sharp, narrow zone of transition; non-corticated

  • Term tends to be strongly associated with multiple myeloma

• Corticated – thin, radiopaque line of bone at lesion periphery

  • Associated with benign, slow-growing process

• Sclerotic – wider, more diffuse zone of transition

  • Reflects ability of lesion to stimulate bone production (reactive bone formation)

• Radiolucent periphery – rim of radiolucency representing soft tissue

  • Generally with outer corticated border and inner/internal radiopacity

  • Associated with benign, slow-growing lesion

What do you see in a poorly defined border?

• Blending – gradual, wide zone of transition

  • Focus on trabeculae rather than marrow spaces

• Invasive – wide zone of transition with few or no trabeculae between lesion periphery and normal bone

  • Focus on enlarging radiolucency at expense of normal trabeculae

  • Also called permeative – lesion appears to grow through trabeculae producing finger-like extensions

  • Associated with rapid growth and aggressive and malignant lesions

Size can be measured depending on what?

imaging modality

Lesion may have a particular shape or be irregular

• Circular or “hydraulic” shape (inflated or water-filled balloon) is characteristic of a cyst

• Unilocular

• Scalloping – series of contiguous arcs or semicircles that may develop around roots of teeth or in adjacent bone or cortices (sometimes see this called lobulated or loculated)

  • May reflect mechanism of lesion growth

  • Can be seen in cysts and benign neoplasms

What are three basic categories of internal structures?

• Entirely radiolucent – normal bone resorbed

• Entirely radiopaque – lesion filled with mineralized matrix

• Mixed radiolucent and radiopaque (mixed density)

What do you need to look at for mixed radiolucency and radiopacity?

• Examine shape, size, pattern, and density of the opaque/calcified material

  • Ex. enamel is more opaque than bone

• In 2D imaging, can be challenging to determine whether the perceived radiopacity is located within the lesion itself or buccal or lingual to lesion

What are some things to look for in internal structures?

• Abnormal trabecular patterns – variations in numbers, lengths, thickness and orientations of trabeculae

• Internal septation –

  • Multilocular – compartments created by septations (striations of bone within lesion)

    • Can represent normal, trapped, residual bone

    • Can be manufactured/created by lesion

    • Appearance of septa (length, thickness, orientation) can indicate nature and pathogenesis of lesion

• Dystrophic calcification – mineralization in damaged soft tissue (ex. chronically inflamed cysts)

• Amorphous bone –dense often cortical-like bone but poorly organized

• Tooth structure – enamel, dentin, pulp

What are effects on adjacent structures?

• Used to infer biologic behavior of lesion

• May aid in diagnosis

• Understanding disease mechanisms that gives rise to changes is required

• Ex. periapical inflammatory disease can stimulate bone resorption (rarefaction) or formation (sclerosis)

• Ex. space-occupying lesion (cyst, benign neoplasm or tumor) slowly creates its own space by displacing teeth and other adjacent structures

• Ex. malignancy tends to be fast growing and destructive to bone, but usually leaves the teeth