Flashcards in Final Exam Deck (23)
What are the two principle components of film?
Emulsion and Base. Emulsion is coated on both sides of the base and consists of photon sensitive silver halide grains, and suspension vehicle. The base is a plastic supporting material. A Silver halide crystal is chemically altered when struck by an x-ray photon, creating the latent image. Film's silver grains are about 8 um's
Which way should the dot on the film packet be oriented?
Toward the occlusal surface in PA's.
Which way should the plain side of the film packet (opposite side of dot) be oriented?
Toward the source of the radiation.
What is the bump on the developed film?
It represents the plain side of the film packet.
Which types of film are the fastest and slowest?
C film is the slowest and F film is the fastest. C has larger crystals and takes less time but the pixelation is greater so the detail is worse. F film gives the best detailed image.
What is the purpose of a cassette?
It requires less radiation to expose film. But also offers decreased definition.
What are the six things that can influence the amount of transmission of light through the film.
3. exposure time
4. focal spot to film distance
5. subject density
6. subject thickness
What is the principal purpose of a grid with the film?
To reduce the scatter or fog on a radiograph.
What are the five processes of processing the film in the dark?
What is the ratio between processing temperature and time?
For every 10 degrees Celsius increase in temperature, the rate of reaction doubles. The more heat entropy coming into the reaction, the quicker the reaction occurs.
What are the three main advantages of digital radiography?
1. Lower patient exposure
2. Faster radiographs
3. More eco friendly
What are the three main types of digital sensors?
What is the standard language for the electronic communication of digital images?
What is the definition of contrast resolution?
The ability to distinguish different densities in an image.
What is the definition of spatial resolution?
The ability to distinguish fine detail.
What is the definition of sensor latitude?
The ability to capture a range of exposures. PSP has the greatest latitude.
How does a sensor work and what is a scintillator?
X-ray photons are converted to visible light as they hit the CsI scintillator. This light is channeled via the fiberoptic taper to the CCD. The scintillator is what converts x-ray photons to light photons.
How many shades of grey can a sensor see as compared to the human eye?
65, 365 shades vs 64 shades
What are some of the limitations of panoramic views?
Linear measurements are undependable. Magnification varies among different units. Anatomical vertical axis vary. X-ray beam is not oriented right angle, foreshortening and elongation.
But panos are always distorted in both size and shape.
What is focal trough and what are implications?
Patient must bite down on bitestick in order for patient to be in focal trough. The clearer the image.
What does it mean if you have too much spinal cord in a Panoramic?
Patient is too far forward
How does a cone-beam CT scan work?
The x-ray beam passes through the patient and is captured on a silicon flat panel or image intensifier CCD detector. It captures hundreds of images and produces them into voxels, which can be as small as 0.125 nm. Effective dose ranges from 6 to 477 uSv