Oral radiology: Radiographic Properties

what are photographic proproperties

1. density

   1. control

   2. influence

2. contrast

   1. control

   2. influence

Factors affecting photographic properties

What are geometric properties

Factors affecting geometric properties

What does density mean and its types

Density = degree of darkinging on readiograph

• Radiolucent = dark are on image

  • created by more exposure of film/sensor ← radiaton passing through less dense anatomy

• Radiopaque = light are on image

  • radion absorbed by dense anatomy → film is less exposed

How well does radioation pass through: Metal, Air, Muslce, Bone?

Darkest/Most exposure/ less dense anatomy → Lightest/least exposure/less dense anatomy

Air (Radiolucent))→ Muscle → Bone →Metal (Radioopauqe)

Factors that can effect image density

• Quantity of photons that interact with image

• Controlled by milliamperage-seconds (mAs)

  • more mA→ more photons → more density

  • xray beam intensity is proportional to mA = more mA→ stronger beam

  • more time photon hit → more density

• Influenced by kVp, collimation, FFD, filtration, patient factors

Denisty relationship to kVp, mA, exposure time, collimation

more kVP = more density

more mA = more Density

more time = more Density

shape beam => reduce fog => decrease density

What happens as kVp increases to its peak voltage value

xray intensity increases

• slowly at first then it speeds up as it reaches its peak

Inverse square law

xray beam relationship is inverse to the square of distace betweeb target

How does Filtration and patient factors influence density

Filtraton= decrese density by removing low energy photons → less quantity of photons

Patient factors

• thicker the person → more beam attenuated (beam loose intensity as it moves through matter) →lighter image (more white)

• denser person = dense structure in subject → greater attenuation of xray beam → lighter image

Patient factors to note for xrays

• Anatomic location

  • Anterior, posterior, maxillary molar

• Age

  • >50 years or <10 years

• size

  • Large or small

• Oral Status

  • Edentulous or dentate

for these things adjust mA, leace kVp alone

What is constrast? types of contrast?

range or diffrence of density between light and dark regions on radiograph

• High (short gray scale)

  • reduced range of grays between black and white on image and major diffrences

  • black and white image

    • it will be WHIIIITE AND BLAAAACK image

• Low (long gray scale)

  • vast range of grays between black and white

  • gray image with slight diffences

what effects contrast

Controled by kVp

influenced by

• Collinmation

• Filtration

• Patient Factors

contrast relationship between kVp, Collimation, filtration, patient factors

• More kVp => stronger beam=> more penetrating power => less contrast

  • Has inverse relationship

• Collimation shapes xray beam → reduces fog→ increases contrast

• filtration → remove longer weaker waves → stronger beam→ decreases contrast

Patient Factors that effect contrast

variation of Thickness across body parts

Variation of tissue density(mass)

Effective atomic number: higher atomic # => Higher Contrast

• ex: amalgam vs tooth structure

the subject contrast is proportional to amount of rays leaving adjacent section of subject]- what

What effect if any does the following (when increased) have on density?: mA, kVp,FFD, Collimation,Filtration

mA: increases

kVp: increases

FFD: decreases

Collimation: decreases

Filtration: decresses

What effect if any does the following (when increased) have on contrast?: mA, kVp,FFD, Collimation,Filtration

mA: n/a

kVp: decreases

FFD: n/a

Collimation: increases

Filtration: decresses

Image Sharpness

how defined (or good) is a boundary between areas of diffrent densities

image Spatial Resolution

How well will small objects that are close tgr be revealed

Penumbra

Photons coming from different spots on the focal spot → zone of unsharpness on radiograph

smaller penumbra = sharper image

usally are created when hit edge of object

Componets of Image definition

• image sharpness

• image resolution

Factors that effect image definition

• Controlled by focal spot size, focal spot to object distance, object to film distance

• influenced by ;

  • motion

  • kVp & mA

  • screens

  • patients

  • image receptor

  • technique

3 ways to manipulate focal spot to control Penumbra

1. Spot size

   1. use effective small focal spot and small angle to generate a small penumbra

2. Focal spot to object distance

   1. Increase destance between focal spot and object with a long open ended cylinder; longer distance = smaller pneumbra

3. object to film distance

   1. decrease distance between object and /film/sensor; decrese distace =

*These are actually the first 3 principles in order

Main influence of Image definition

Motion (tube, object, sensor)

Types of Distortion

Size: magnification of object (image object bigger than actual object)

• controlled by FFD (focal to film distance) and object to film distance (OFD)

• when calculating top gonna always be a larger number than the bottom

Shape: magnification of different parts of objects unequally

• so make sure to line the object up carefully

  • Types of shape distortion:

  • Dimensinal: 3D object to 2D media

  • Elongation: object looks longer on fim then irl

  • Foreshortening: object looks shorter on film than irl

• *principle 4 : film needs to be parallel to long axis of object

• *Principle 5: Central ray needs to be perpendicular to object AND film

Elongation and foreshortening caused by what

Elongation: ray is perpendicular to object but not to film

Foreshortening: film perpendicular to film but not to object

Shape techniques that effect distortion

• Bisecting Angel:

  • put film as close to teeth as possible

  • perpendicularly angle cenral ray bisects the angle between the teeth and the film/sensor.

• Paralleling Technique

  • place film paraelle to long axis of tooth

    • will lesses distortion

    • usual method

What are the 5 Principles

1. Use as small an effective focal spot as practical

2. Increase the distance between the focal spot and the object by using a long, open-ended cylinder

3. Minimize the distance between the object and the film

4. Position the film/sensor parallel to the long axis of the

   object

5. Orient the central ray perpendicular to the object and

   film/sensor.

Properties of radiographic image

Density: mAs, kVp

Contrst: kVp

Magnification/Unsharpness: Focal Spot, FFD,OFD

Shape distortion: Alignment