Unit 1 Exam

Refers to various techniques for producing images of internal structures (anatomy) and/or function (physiology) that are used for diagnosis

Diagnostic imaging

Entire Volume of Tissue between source and image receptor is projected onto 2D image

True

Produces x-rays

X-ray source

Receives/detects x-rays

Image receptor

Shows the radiograph/image

Image display device (for digital imaging)

Components that contribute to radiographic image formation and display

Imagine chain

Path of radiation (x-ray beam) must include ______ and _____

anatomy of interest; receptor

Consists of x-ray photons, travels in straight lines, and is divergent

features of x-ray beam

reduction in x-ray beam intensity as it travels through the anatomy

attenuation

the _____ and ____ the structure, the more x-rays are absorbed and the more the beam is attenuated

thicker; denser

Differentially attenuated by structures of different density

Incident beam

Carries information from incident beam to receptor

Transmitted beam

Black/dark structures, less radiodense, attenuating structures

Radiolucent

White/light structures, more radiodense, attenuating structures

Radiopaque

This property of an object refers to ability to attenuate or absorb xrays

Radiodensity

metal > enamel > dentin & cementum > bone > muscle > fat

MEDCBF

order of decreasing density as it appears

Range of densities on an image. Defines as difference in densities between light and dark regions

Contrast

Shows both light and dark areas with few shades of gray in-between

High contrast

Shows various light and dark shades of gray

Low Contrast

Imaging sharpness, spatial resolution, contrast resolution, magnification, distortion

What are these?

Parameters of radiographic image quality

Measures how well a boundary between two areas of differing radiodensity is revealed (ex, dark radiolucent structure and white radiopaque structure)

Sharpness

Measures how well an image reveals small objects that are close together

Spatial Resolution

Difference between object size on image and actual object size

Size distortion

Increase in size of object on image compared to actual size of object (caused by divergent paths of x-ray photons in a beam)

Magnification

Difference in appearance of object shape on image compared to actual object shape (unequal magnification of different parts of the same object)

Shape Distortion

______ should be as SMALL as possible

Focal spot, Object-receptor distance

____ should be as LONG as possible

Source-receptor distance

_____ should be parallel to the long axis of the object

Receptor

_____ should be perpendicular to the object and receptor

Central beam

An area on target of X-ray tube where x-rays are produced

Focal spot

Focal spot size for dental, panoramic, and cone beam CT machines range from ______

0.4 - 0.8 mm

A smaller focal spot yields a

sharper image

Xrays produced at different points in the focal spot that pass through the same point on an object

will NOT hit the same spot on the receptor

Blurring of object edges

geometric unsharpness, penumbra, adumbration

A larger focal spot creates a wider zone of geometric unsharpness

loss of image sharpness

Increasing _____ distance reduces x-ray beam divergence, minimizes image magnification as x-rays in the center of beam travel nearly parallel

Source-object

Increasing _____ distance reduces x-ray beam divergence, reduces geometric unsharpness as x-rays in the center of beam travel nearly parallel

source-object; source-receptor

Decreasing _____ distance reduces x-ray beam divergence, reduces geometric unsharpness and minimizes image magnification as x-rays in the center of beam travel nearly parallel

Object-receptor

Define SID and SOD

SID = source to image distance (source-receptor distance)

SOD = source to object distance

Magnification caused by an increased object-receptor distance can be minimized by ________________

Increasing the source-object distance

Occurs when not all the parts of an object are at the same source-to-object and/or object-to-receptor distance

Image shape distortion

Minimizing shape distortion can be done by

Aligning the object and image receptor parallel with each other. Aligning the central ray perpendicular to both the object and image receptor

Which root appears disproportionately longer?

Palatal roots, compared to buccal roots

Image of object is shorter than true object.

Object is not parallel to receptor

Central ray is perpendicular to receptor, NOT object

Foreshortening

Image of object is longer than true object.

Object is not parallel to receptor

Central ray is perpendicular to object, NOT receptor

Elongation

What is happening here

Foreshortening

What is happening here

Insignificant Distortion

What is happening here

Elongation

1. Use as small a focal spot as practical (determined by manufacturer, can’t be changed)

2. Increase the source-to-object distance

3. Minimize the object-to-receptor distance

Where are these principles important?

Maximizing Image Sharpness

If focal spot is small, what happens to image sharpness?

Increases

If focal spot is large, what happens to image sharpness?

Decreases

If source-receptor distance is short, what happens to image sharpness and image magnification

Image sharpness decreases, Image magnification Increases

If source-receptor distance is long, what happens to image sharpness and image magnification

Image sharpness increases, image Magnification Decreases

If object-receptor distance is short, what happens to image sharpness and image magnification

Image sharpness increases, Image magnification decreases

If object-receptor distance is long, what happens to image sharpness and image magnification

Image sharpness decreases, Image magnification increases

If source-object distance is short, what happens to image sharpness and image magnification?

Image sharpness decreases, Image magnification increases

If source-object distance is long, what happens to image sharpness and image magnification?

Image sharpness increases, Image magnification decreases

Circumstances that suggest a need for diagnostic imaging

Selection criteria

Examples of selection criteria

Clinical evidence of an abnormality, high probability of disease that is not clinically evident

Patient age/demographic social/medical/dental hx

Exception: BTW for detection of early interproximal caries

1. Should record the complete area(s) of interest

2. Have the least possible amount of distortion

3. Have optimal density and contrast to facilitate interpretation

What radiographs SHOULD do

Projections show the entire length of tooth and surrounding peri-radicular bone

PA

Projections show only the crowns of teeth and adjacent alveolar crests

BTW

Projections show an area of teeth and bone larger than periapical images

Occlusal

Consists of PAs and BWs (18-20 images) )14-16 PAs_

FMX

attached to tubehead aperture to direct x-ray beam

Position indicating device, also called a “cone” or “aiming cylinder”

Receptors have __ active side that needs to face source

1

What type of receptor uses a photostimulable phosphor plate (PSP)?

Indirect

What type of receptor uses a solid state, direct digital sensor (CCD/CMOS), corded?

Direct

This projection technique is preferred, produces images with less distortion, anatomy may prevent strict adherence

Position receptor parallel to long axis of teeth and direct central xray perpendicular to both

Paralleling Technique

Another word paralleling technique

Right-angle, long cone, or extension cone technique

In the paralleling technique, where is the receptor placed for maxillary imaging?

Toward the center/height of the palatal vault

In the paralleling technique, where is the receptor placed for mandibular imaging?

Deep in the lingual vestibule, pushing tongue out of the way toward midline

Anatomic constraints of the paralleling technique

Shallow palate/vestibule, presence of tori

Long cone is used to ____ the source-object distance

Increase

Distance from source to edge of cone ranges from ____

8-20 inches

Distortion is likely, used when anatomy is tricky

Bisecting Angle Technique

2 triangles are equal when they share 1 complete side and have 2 equal angles

Cieszynski’s rule of isometry

Receptor is positioned close to lingual surfaces of teeth, mentally bisecting angle between long axis of teeth and long axis of receptor. Xray tube positioned at right angle to bisecting line

Process of the Bisecting Angle Technique

In bisecting angle technique, actual length of tooth will be equal to that on image, except for

Multirooted teeth

What is the bone distortion of the bisecting angle technique

Alveolar ridge is projected coronal to its true position, and the alveolar bone height is distorted around teeth

Where does the cone point in + angulation

Cone points downward

Where does the cone point in - angulation

Cone points upward

Angle between x-ray beam and line ____ to floor/occlusal plane in vertical angulation

Parallel

What vertical angulation error results in vertical angle being too small (under-angulation)

Elongation

What vertical angulation error results in vertical angle being too large (over-angulation)

Foreshortening

Geometrically accurate (w/ long cone), reproducible, good periodontal bone levels, zygomatic process above upper molars

Advantages of paralleling technique

Positioning can be uncomfortable, position can be hard for operator, anatomy sometimes makes technique impossible

Disadvantages of paralleling technique

Receptor positioning is comfortable, simple and quick, adequate for most diagnostic purposes if done correctly

Advantages of bisecting technique

Foreshortening and elongation can distort image, not reproducible, perio bone levels are poorly shown, requires skill, and zygomatic process overlies upper molar roots

Disadvantages of bisecting technique

___ projection geometry produces images that are more reliably accurate for periodontal bone level evaluation than ____

BTW; PAs

Where is the vertical beam angle placed for bitewings

Parallel to occlusal plane, perpendicular to receptor, 0-10 degrees to compensate for curve of Wilson

Where is the horizontal beam angle place for bitewings

Directed through interproximal spaces, getting open contacts between teeth is ideal

When are Vertical bitewings done

When a pt has moderate-severe alveolar bone loss. Orientation increase chance alveolar crests are captured.

Primary objectives of periapical projections

Capture full length of root and 2-3mm of periapical bone, entire crowns and open contacts, and capture all interproximal bone levels

Occlusal images are used where

Pediatrics for evaluation of developing dentition

Receptor is only available in film (not digital), “tube” side is positioned toward the jaw to be examined, vertical angulation is steep, standardized projections have a desired relationship between the central ray, receptor, and region being examined

Occlusal Technique

Occlusal localizes in mesiodistal and buccolingual dimensions

Periapical localizes in mesiodistal and S-P dimensions

ID position of object relative to surrounding anatomic landmarks on both projections

Right angle technique

Uses changes in relative positions of two separate objects that occurs when the image projection angle is changed

SLOB Rule

SL in SLOB rule

“Same lingual”

lingual objects shift in same direction as tubehead

OB in SLOB rule

“Opposite Buccal”

buccal objects shift in opposite direction from tubehead