Film and Digital Radiology - digital receptors Flashcards
What is the basic difference between digital and film receptors/radiology?
how the x-ray beam is dealt with after it has interacted with the patient. E.g. how the x-rays are captured, converted into an image and stored (the photon interaction is the same).
Out of the different types of film receptors, what ones are single and multi use?
film = single
digital = multi use
What diff digital receptors do you get?
- Phosphor plate
- Solid-state sensor
What diff film receptors do you get?
- direction action film
- indirect action film receptors
How is an image created from x-rays and a digital x-ray recptor?
- When the x-ray beam passes through an object some of the x-ray photons are attenuated, creating an “x-ray shadow”
- The x-ray shadow is basically the image “information” held by the x-ray photons after an x-ray beam has passed through an object
- The image receptor detects this x-ray shadow & uses it to create an image
Why is the x-ray shadow lighter in the middle and darker on the outside? (when a radiograph is taken of a ball)
- there is more attenuation in the centre (more x-ray absorbed) as the beam is passing through the widest diameter of the ball
- There is less attenutaion on the outside as the x-rays are passing through air
How is the x-ray image displayed on digital receptors? (how does the receptor measure the attenuation and how does this make a difference?)
The receptor measures the x-ray intensity at defined areas which are arranged in a grid
Each are is given a value which corresponds to a shade of grey
Each of these sqaures are called pixels
How do the number of pixels influence the x-ray image?
more pixels = better detail = higher resolution
Increasing the resolution of an x-ray will do what?
It will provide a more diagnostic image UP TO A LIMIT (eventually increased pixilation will not provide any clinical benefit)
Why are digital receptors limited to the number of pixels it has?
Because its a small space - manufacturing challenges
What is the greyscale bit depth?
- describes the number of shades of greys that have been used to represent the image
Radiographs are usually processed in at least how many bits? (greyscale)
at least 8 (256 shades of grey)
In what ways can you manipulate a digital image to view it? (that you cant do with a film)
- Contrast
- negative contrast
- emboss
- magnify
What format are digital images kept as?
DICOM (digital imaging and communications in medicine)
What is good about the digital format that images are kept in (DICOM)?
- It is an international standard format for handling digital medical images
- It is used to transmit, store, retrieve, print, process and display images
- Allows imaging to work between different software, machines, manufacturers, hospitals & countries without compatibility issues
- Stores other info such as patient ID, exposure, date
Describe how an image is created using phosphor receptors (the process).
- The receptor is exposed to x-ray beam within the patients mouth
- The phosphor crystals in the receptor are excited by the x-ray energy, resulting in the creation of a latent image
- An image stored by the phosphor crystals in the receptor which we cannot see
- The receptor is then scanned by a laser
- The laser energy causes the excited phosphor crystals to emit visible light
- This light is detected by the scanner and created the digital image
What different types of solid state sensor do you get?
- CCD (charge-coupled devices)
- CMOS (comolimentary metal oxide semiconductor)
What is found on a solid state sensor to help aid orientation of the image?
an identification dot located in the corner of the receptor
(However, this is only effective if the receptor was positioned correctly during exposure)
