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78 Cards in this Set
- Front
- Back
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what is the measure for x-ray beam intensity
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x-ray quantity measured in roentgens (R or mGya)
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define a roentgen
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is a measure of the # of ion pairs produced in air by a quantity of x-rays
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quantity
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is the # of x-rays in the useful beam
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what are the factors controlling quantity
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mAs, kVp, distance, filtration
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the quantity is _____ to the mA striking it
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directly proportional
(double mAs double quantity) |
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I1 = mAs1
I2 - mAs2 |
I = intensity
mAs = current |
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mAs is a measure of what
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the total # of electrons traveling from the cathode to the anode to produce x-rays
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how does kVp change quantity
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proportional kVp squared (double kVp 4 times the quantity)
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x-ray quantity is ________ to square of the SID
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inversely proportional
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to maintain a constant OD if SID is increased the mAs must be ______ the SID squared
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increased
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adding filtration _____ patient dose
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reduces
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quality of the beam is
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penetratebility
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quality is identified by
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HVL
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attenuation
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reduction in x-ray intensity due to absorption & scatter
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quality & HVL are effected by
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kVp & filtration
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define HVL
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is the thickness of absorbing material needed to reduce the x-ray intensity by half is original value
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types of filtration
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inherent .05 mm Al
added 1 mm Al |
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compensating filters are used when
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anatomy has varing density
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radiolucent
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x-rays pass thru object
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radiopaque
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x-rays are absorbed by object
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compton effect is inversely proportional to
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x-ray energy
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photoelectric effect is
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inversely proportional to 3rd power of x-ray energy
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compton effect or scatter in
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interacts with outer shell electron. ionizes atom & scatters x-ray
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compton scatter _______ contrast
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reduces
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the probability of compton scatter ______ with increased kVp
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decreases
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photoelectric effect occurs with
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inner shell electron interaction
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the kinetic energy of the photon is _____ during photoelectric interactions
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absorbed
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photoelectric interactions are more likely to occur with high or low Z # atoms?
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high atomic number
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image fog is caused by which interaction
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compton scatter (no image value at all)
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___% of photons reach the IR
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1% reach IR
.05% create the image |
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at low energies most interactions are
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photoelectric
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compton interactions are predominate at _____ energy levels
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high
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to image small diferences in soft tissue you must use ____ kVp to get max differential absorption
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low
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interaction between x-rays and tissue is __________ to the density of the tissue
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proportional
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air is what kind of contrast agent
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negative
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barium & iodine are what kind of contrast agents
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positive (higher # than tissue)
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attenuation
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is the product of absorption & scatter
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absorption & attenuation depend on what factors
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Z number of tissue, mass density of tissue, & x-ray energy
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exit or image forming beam
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beam that leaves the patient
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what parts make up film
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base & emulsion
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what is the adhesive layer
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inbetween the base & emulsion layers (provides uniform adhesion)
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overcoat
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geletin outer layer that protects the emulsion layer
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purpose of the base
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fondation of film, provide a rigid structure for the emulsion layer
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base is made of
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lucent semi rigid polyester
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define dimensional stability
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base of the film helps it to maintain its shape & size during processing
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what other older bases where used
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glass - easy to brake
cellulose nitrate - flammable |
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"safety base" is made of
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cellulose triacetate in 1920's
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new bases are made of
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polyester - stronger, thinner, more stable
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why is the emulsion called the heart of the film
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tha material that interacts with x-rays or light from the screen and transfers the information
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emulsion is made of
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mixture of gelatin & siver halide crystals
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function of gelatin
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provide mechanical support to silver halide crystals
(clear & porus) |
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silver halide is made of
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silver bromide (98%) & silver iodide (high Z #s) resulting in latent image formation
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sensitivity centers
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during exposure photoelectrons and siver ions are attracted to the sensitivity spots
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what effects film speed
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size & concentration of silver halide crystals
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latent image
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x-rays - photoelectric interaction with silver halide. energy is deposited. invisible before development.
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manifest image
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developed image
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Gurney-Mott theory
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theory of latent image formation
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what interacts to form the latent image.
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radiation with the silver & halide
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secondary electrons are attracted to ______
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sensitivity center
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during latent image formation what interactions with x-ray are taking place
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compton & photoelectric - causing secondary electrons
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processing
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the chemical reaction that transorms the latent image into the manifest image
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high contrast film is
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black and white
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low contrast film is
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shades of gray
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the contrast of IR is inversly proportional to its exposure latitude .....
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exposure latitude - range of exposure techniques that are produced
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what determines latitude as med, high, highest
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depends on size & distribution of the silver halide crystals
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speed
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the sensitivity of the screen-film combination to x-rays and light
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what determines speed
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concentration and amount of silver halide crystals
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why us double emulsion film
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twice the speed
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converting power
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a more efficent use of silver in newer emulsions
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crossover
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is the exposure of an emulsion by light from the oposite side of the radiographic intensifying screen
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spectral matching
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the use of rare earth screens with their corosponding film
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safelights
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incandescent lamps with color filters, used in dark rooms
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halation of a image
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reflection of light from screen back on to film causes a halo on the image
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extremity exams use
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fine grain, high detail screens, double emulsion film as the IR
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mamography exams use
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single emulsion film, green emitting screens
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duplicating film is used
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to duplicate existing images
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laser beam modulations are sensative to what color light
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red,
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cini film is
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35 mm film used for cardiac catheterization
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