What factors affect images?
Intensity of X-ray beam.
Operator variables:
- Exposure time
- mA vs time
- kVp - intensity
- Set up of film/sensor
How does exposure time affect images?
Directly proportional to the effect on X-rays.
How does mA vs time affect images?
Direct effect on quantity of photons.
mA x time (seconds) = mAs
- mA and seconds = inversely proportional to maintain same quantity of radiation.
How does kVp affect images?
- Homogeneous – photons of identical energy.
- Heterogeneous – photons of varying energy.
- Quality – energy of photons.
- Quantity – number of photons.
- Intensity – total energy in beam (quality x quantity/area x time).
- kVp determines maximum energy of X-rays produced (quality).
- Higher kVp = higher kinetic energy of electrons higher energy in X-rays.
Hard X-rays = more penetrating.
Soft X-rays = low energy.
How does setup of film/sensor affect images?
Intensity of beam decreases as distance from source increases.
Describe the structure of the X-ray tube
- Cathode (-ve) = heated lament of tungsten – electron source.
- Anode (+ve) = target (small piece of tungsten) in angled face of large copper block to allow efficient heat removal.
- Focusing/position indicating device (PID) aims stream of electrons at focal spot on target.
- Kilovoltage peak - high-voltage between cathode and anode accelerates electrons from negative filament to positive target.
- Current flows from cathode to anode – measure of quantity of electrons being accelerated.
- Surrounding lead casing absorbs unwanted X-rays as radiation protection measure (X-rays emitted in all directions).
- Surrounding oil = heat removal.
What are bitewings for?
- Interproximal caries.
- Condition of crestal alveolar bone.
What are vertical bitewings for?
Patients with advanced periodontal disease.
What are technique errors associated with bitewings?
- Overlap.
- Improper film placement.
- Cone cutting.
How does cone cutting occur?
If X-ray tube isn’t positioned properly, X-ray beam may not cover entire film – results in white area on film.
How does radiolucent areas show up?
Remnant radiation collected by sensor produces darker density areas or radiolucent areas.
What are periodicals used for?
Show alveolar bone and root structure. Endodontics. Before extractions/crown/bridge prep. Trauma. Periodontal disease.
What techniques are associated with PAs?
- Paralleling.
- Bisected angle.
What difficulties are associated with PAs?
Mandibular 3rd molars. Gagging. Endodontics. Edentulous alveolar ridges. Children. Patients with disabilities.
