Radiographic Image Characteristics

What are the two forms of image acquisition?

1. Conventional Film
2. Digital

What are the two parts of conventional film?

1. intraoral films
2. extraoral films

How are conventional films processed?

chemical processor

How is the image of conventional film displayed?

hard copy

What are the three parts of digital?

1. PSP plates
2. CCD/CMOS Intraoral sensors
3. Flat panel detectors

How are digital images processed?

scanners + computers

How are digital images displayed?

soft copy + hard copy

What two reasons make it so that we will always get an image?

1. receptors are designed to respond to radiation
2. response is based on type of receptor (film vs digital)

What is the imaging goal?

produce an image with optimum diagnostic quality + minimal radiation exposure

What two factors influence degree and pattern of darkness?

1. energy + intensity of x-ray photons
2. subject composition

Radiographic density

high density: dark (overexposed)
low density: white (underexposed)

What are the primary controlling factors of radiographic density?

1. milliamperage
2. exposure time
3. distance

What is the linear relationship between mAs and density?

mAs directly control number of x-ray photons produced

How does the inverse square law affect distance?

intensity of x-ray beam reduces as focal spot to object distance increases

How does kVp affect density?

increase kVp, increase density, penetrability, # of x-ray photons

How does the object size/thickness affect density?

thicker the object = more beam is absorbed
image density decreases resulting in a lighter image

What is image contrast?

difference shades to ensure structure visibility

What is the primary controlling factor of image contrast?

kVp - HIGH energy (kVp) penetrates tissues more evenly resulting in LOW contrast

High contrast

- few shades of gray
- low kVp
- short scale of grey

Low contrast

- many shades of grey
- high kVp
- long scale of grey

What is an additional image contrast influencing factor?

subject contrast - various anatomic structures have absorption difference

What is radiographic noise?

appearance of uneven density - degrades quality + limits visibility

What is projection geometry?

effects of focal spot size, position of object + sensor on image clarity, magnification, distortion

What is the difference between image sharpness and spatial resolution?

sharpness - how well a boundary between differing radio density is revealed
resolution - how well close, small objects are revealed

What three factors effect sharpness + resolution?

1. focal spot size
2. distance between receptor + object
3. distance between focal spot + object

What is the relationship between focal spot size + sharpness?

smaller focal spot = shaper image

What is the relationship between receptor distance + sharpness?

smaller distance = shaper image

What is the relationship between focal spot distance + sharpness?

larger distance = sharper image

What is the importance of image sharpness?

seeing the enamel-dentine junction + compact-cortical bone interface

What is the function of resolution?

ability to show small structures separately

Dark shade is called

radiolucent

Light shade is called

radiopaque