Radiography Mid-Term Lecture

Front 1

Wavelength & Frequency

Back 1

A sound wave has a long wavelength and a low frequency. X-rays have a short wavelength and a high frequency. X-rays that have a short wavelength will penetrate more easily than those with a long wavelength.

Front 2

Cathode

Back 2

• Small wire (filament) made of tungsten
• produces electrons when heated
• # of electrons depends on mA applied
• Higher the mA, the hotter the filament, the more electrons produced
• focusing cup - directs electrons towards anode

Front 3

Anode

Back 3

• Target
  
• Where electrons strike
• Made of tungsten
• Rotating or stationary
• 99% heat

Front 4

How it Works

Back 4

Filament - mA applied - Electrons produced - Electrons hit target - electrons accelerated across tube - kV applied between cathode & anode - Heat & x-rays produced

Front 5

Image Receptors

Back 5

• Cassettes
  
• Intensifying Screens
• X-Ray Film
• Film-Screen Systems

Front 6

Intensifying Screens

Back 6

• Sheets of phosphor crystals bound to plastic layer and affixed to lining of cassettes
  

Front 7

Composition of Film

Back 7

1. Transparent polyester base

- Flexible support with thin adhesive

2. Emulsion

- Bound to base by adhesive

- Consists of gelatin with silver halide microcrystals dispersed in it

3. Silver Halide

- Billiona of crystals per cc of emulsion

4. Supercoat

- Clear protective material to prevent damage to delicate emulsion

Front 8

Screen Film

Back 8

• Screen
• Screened film is highly sensitive to visible light from the intensifying screens, and less to ionizing radiation
• Very efficient because less x-rays are required = safety

Front 9

Non-screen Film

Back 9

• Non-screen film exposed by direct action of ionizing radiation
• Greater exposure required
  
• Greater detail of image
• particularly valuable in bone or dental radiography
• dental film

Front 10

Quantity

Back 10

• Quantity or intensity of x-rays is defined as:

- "The amount of energy flowing per second through a unit area perpendicular to the direction of the beam.

• the # of x-rays traveling from tube to image receptor in a specific period of time
• Quantity of x-rays = mA (how many)

- affects the intensity of the beam produced

Front 11

High or Low

Back 11

• Higher mA allows for lower time (s)
• Lower time = less motion
• Motion is most common artifact
• Use High mA whenever possible

Front 12

Quality

Back 12

• Quality of x-ray beam is determined by its penetrating power.
• shorter wavelength has higher penetrating power
• Density (degree of blackness)
• Contrast (difference between the adjacent densities)
• Detail & Definition (sharpness or clarity)

Front 13

kVp

Back 13

• kVp = faster el
• Faster el = increased penetrating power of x-rays
• Increased penetrating power = more x-rays reaching image receptor
• more x-rays reaching image receptor = lower mAs settings
• lower mAs settings = lower time

Front 14

Effect if kV

Back 14

• 3 major influences of increased kV

- Increased penetrating power

. Increased density (blackness)

. High scale of contrast, loss of detail

. Increased scatter

• Decrease in kV = lack of density, white image with no contrast or detail perceptible