diagnostic imaging lecture 2 Flashcards
explain conventional radiography? How are they processed?
x-ray film needed, cassettes. automatic or manual film processor (develop, fix and rinse and dry) dark room or view box.
3 main types of radiographic image acquisition?
conventional, computed radiography (CR), Digital radiography (DR)
What is a double emulsion x-ray film?3 layers? what does each layer rovide?
responds to x-rays faster. polyester base with silver halide emulsion and then protective coating on each side. base is for structural strength, adhesive binds the emulsion to the base. the coat provides protection for the silver halide against mech damage.
What do silver halide crystals consist of?
light sensitive material in the emulsion. sensitivity increased by having a mixture of 1% silver iodide and 90-99% silver bromide.
what happens when silver halide crystals exposed to light?
electron in silver bromide released by light energy. silver atom is formed at the sensitivity speck and this is turned to metallic silver. - this produces the latent image.
How is the latent image formed?
greater number of silver halide crystals that have been transferred to metallic silver - the blacker the film and greater film density.
what are the advantages of an automatic film processor for conventional radiography?
reduces film processing time by 4 . silver halide cyrstals that are not exposed are removed during fixing.
what does the developer do in conventional radiography?
what does the fixer do?
what does the wash do?
it causes cataylsis of the reaction which reduces the reamining silver ion into grain of metallic silver
the fixer prevents further development and removes undeveloped silver bromide from the film
the wash removes fixer chemicals which would discolour the film over time.
before processing any films what should you do? what should this include?
you should permanently identify them (date, medical record number, animal name, owner name and practice name. )
what is the difference between non-screen and screen x ray films. ? which one is better?
non-screen - used direct exposure to x ray and use cardboard holders. results in high personal and patient exposure.
screen - single or double emulsion. 95% of film exposure is from ight given off by the intensifying screen.
what is the intensifying screen used for screen x ray films?
reduces person exposure and patient exposure
increases the contrast.
x ray photons may either? (2) they either interact with what or what? if they are absorped? what is the Compton effect? what is the coherent effect?
they are either scattered or absorped. they either interact with the orbital electrons (diagnostic) or the nucleus of the atoms. if they are absorped then they are completely removed from the x-ray film. compton - 90-180 degree deflection
coherent - in the same direction.
what is a grid used for?
use to absorb scatter radiation to improve the radiographic contrast. this is recommened when body thickness is over 10 cm. (good picture)
what are the main advantages of CR?image caprtued in?
computed radiography. it is filmless, no darkroom and no chemistry. image is captured in casettes containing phosphor storage layer. creates image in DICOM FORMAT. and the image is sent and stored in PACS.
phosphor - how does it work in CR?
stirage phosphor. a laser beam then stimulates it to reases its stored light energy.
