Film vs Digital imaging

Question 1

When were dental xrays discovered?

Answer 1

dental xrays were discovered in early 1900’s by CODAK

Question 2

Film imaging

Answer 2

• requires chemcials to process
• require time to develop
• provides superior image quality
• more radiaition

Question 3

Digital imaging

Answer 3

• no chemical neded
• instant viewing
• image emacement with coputer software
• less radiation
• PSP and CCD/CMOS

Question 4

Xray film

Answer 4

• Base = clear flexible celliouose acetate material (plastic)
• Film emulsion = silver halide crystals in a gelatin material
• intensifying screen = coated with fluorescent phosphor to reduce amount of exposure needed

Question 5

Film speed

Answer 5

• faster the film, the less exposure it needs
• A>B>C>D>E>F
• D and F are most popuraly used
  Film speed is determined by several factors
• larger crystal = faster film
• double emulsion = faster film
• radiosensitive dyes added to the emulsion = faster film

Question 6

Film Imaging

Answer 6

• xray photons will chemically change silver halide crystals into neutral silver atoms in the emulsion layer to create a latent image
• radiolucent (dark) = photons pass through tissue to reach film
• radiopaque (light) = photons are attentuated and do not reach the film

Question 7

What is a latent image?

Answer 7

is an invisible image which has all the ionized silver atoms that are focused into certain areas and them all of the metallic silver is later converted to a visible image through the chemical processing

Question 8

Chemical processing

Answer 8

1. developing - makes the metallic silver atoms turn black we turn that invisible latent image into a visible image
2. fixing - where we wash away any exposed or undeveloped silver grains
3. washing - wash away any residual chemicals from the previous two steps
4. drying - so we can actually read the finished film

Question 9

Developer solution

Answer 9

• converts exposed crystals into metallic silver grains that are seen as dark on a radiograph
• phenidone = first electron donor that reduces silver ions to metallic silver at latent image site
• hydroquinone = provides an electron to reduce oxidised phenidonne to its original state
  The developer is what actually convert to invisible to a visible image

Question 10

Fixer solution

Answer 10

• removes undeveloped silver halide crystals from the emulsion
• ammonium thiosulfate = cleaning agent, remove undeveloped silver halide crystals
• aluminium salts = tanning agent, hardens and perserves the emulsion
• acetic acid = acidifier, maintaining the fixers level of acidity and also neutralises the developer
• sodium sulphate = preservative, prolongs shelf life of the solution
  water = solvent, dissolves the other ingredients

Question 11

PSP

Answer 11

• photo stimulate phosphor
• barium fluorohalide plates capture and store xray energy from dental exposure and then they are read by a scanner and sent to your computer

Question 12

CCD/CMOS

Answer 12

CCD= charged coule device
CMOS = completentary metal oxide semiconductor
- sillicon sensor chip captures xray and rapidly displays image on monitor

Question 13

Detector characteristics

Answer 13

> = better than
- contrast resolution = ability to distinguish shades of gray - Film > digital
(film has continuous greyscale whereas digital greyscale - limited to a certain amount of gray levels)
- spatial resolution = ability to distinguish two close points - film > CCD/CMOS > PSP
detector latitude = exosure range providing useful image intensities - PSP > CCD/CMOS > FILM
- detector sensitivity = dose required to achieve standard gray level - CCD/CMOS is half F-speed film

Question 14

Radiographic quality assurance

Answer 14

Program implemented to ensure optimal and consistent operation of each comonent in the imaging chain

• daily task = record all errors
• weekly task = review error log
• monthly tasks = examine PSP plates for scratches, inspect aprons for tears
• Yearly tasks = machines calibrated by health physicist, verify digital sensors with phantom

Question 15

Troubleshooting

Answer 15

• underexposed - inadequate exposure time, inadequate development time, chemicals were old, developer solution out of date, tempreture was too low
• overexposed - exposure time too long, overdeveloped the image, exposed to light
• creases - dark radiolucent sharp line going through image
• static electricity - black tree-branch lines
• film placed backwards - tire truck appearance called the herringbone effect