4 Mastering the Art of Image Acquisition

Radiography provides image of …?

internal anatomy ---- not visible on clinical examination (we need high quality or diagnostic radiographs for this)

what term describes the Reliability of image to represent true state of anatomic region?

image quality (diagnostic radiograph)

what are the 3 parameters of diagnostic radiographs?

1. detail (image sharpness and resolution)

2. contrast resolution

3. magnification and distortion (we want minimal)

what are the 5 principles of projection geometry in radiography?

• X-rays should originate from a small Focal Spot

• SOD should be as long as possible

• ORD should be as short as possible

• Long axis of object should be parallel to the receptor

• Central ray should be perpendicular to receptor

X-rays should originate from a …?

small Focal Spot (smaller focal spots produce a sharper image)

however, reality is that they originate from an area and not a point source

SOD should be as short/long as possible

long

• makes X rays less divergent

• sharper images

• less magnification

clinically, how is a long SOD achieved?

collinated extensions in intra-oral radiography (8, 12, or 16 inches)

ORD should be as short/long as possible

short

• less magnification

• sharper image

clinically, how is a short ORD achieved?

• place anatomy of interest closest to receptor

• however, intra-oral imaging can be challenging

Long axis of object should be ______ to the receptor

parallel

• decreases distortion

• improves image sharpness

Central ray should be _________ to receptor

perpendicular

• reduces geometric distortion

image shape distortion is a result of…?

unequal magnification of different parts of same object

how can image shape distortion be minimized?

• position image receptor parallel to long axis of object

• orient central ray perpendicular to object and image receptor

what happens when central ray is perpendicular to the image receptor but the object is not parallel with the image receptor?

foreshortening

what happens when central ray is perpendicular to the object but not to the image receptor?

elongation

foreshortening (long axis of teeth not parallel to receptor)

foreshortening (receptor not parallel to object)

image should look like this

elongation

what is the paralleling technique?

The central ray is directed at right angle to the central axes of Object and Receptor (preferred method to minimize distortion)

what is the bisecting angle technique?

The central ray is directed at a right angle to the imaginary plane that bisects the angle formed by the image receptor and the central axis of the object (less frequently used because of more distortion)

the bisecting angle technique is less frequently used but can be useful in what pt populations?

Useful in patients with severe gag reflex and small mouth opening

what term describes How well a boundary between two areas of differing radiodensity is revealed?

sharpness

what term refers to the ability of an imaging system to differentiate between two nearby objects?

spatial resolution (aka How well a radiograph reveals small objects that are close together)

sharpness and resolution are _____________

interdependent

sharpness + resolution = __________

detail

what 5 factors affect detail (sharpness + resolution)?

1. focal spot size

2. SOD

3. OFD

4. movement (tube or patient)

5. contrast resolution

what term describes the overall degree of darkening of a radiograph?

radiographic density (how dark image is)

what structures are more radiolucent?

• air space

• foramen, canal, suture, fossa, pdl space

• soft tissue

what structures are more radiopaque?

• cortical bone

• amina dura

• dentin enamel

• metal restorations

how do artifacts such as lead aprons, film reversal, earrings, and thyroid collars affect density?

lighter areas in film

what term refers to the difference in densities between the light and dark regions in radiograph?

contrast

the range of densities observed on a radiograph is a result of…?

attenuation/ absorption of xray photons

how does scatter radiation affect radiographic contrast?

produces fog (overall darkening reduces contrast)

localization can be used to observe what type of pathoses?

• impacted/supernumerary tooth

• root canal

• foreign bodies

• fractures

describe the right angle technique.

Obtain 2 radiographs at 90 degrees to each other of the area of interest. For example,

• periapical and occlusal radiographs

• Lateral cephalometric and postero-anterior view of skull

what radiographic techniques can be used in localization?

• right angle technique

• tube shift technique

• special studies

what is the SLOB rule (tube shift technique)?

Same

Lingual

Opposite

Buccal

• Images of objects that are superimposed can be separated by changing the angle of projection

• Object moves in the same direction as x ray tubehead → Lingual Object

• Object moves in the opposite direction as x ray tubehead → Buccal Object

apply the SLOB rule (tube shift technique) to determine if the impacted tooth is lingual or buccal

impacted tooth moves distally as tube move (same direction), therefore it is lingual

As the tube is moved mesial, the impacted premolar moves distal

Opposite= Buccal to the root of 1st premolar

Tube Moves= Mesial, Impacted tooth moves= Mesial

SAME= LINGUAL to the roots of 2nd premolar and 1st molar

more canine is showing so it has moved mesially

pink arrow is buccal canal

buccal

not sure about this one ask professor