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Computed Radiography

Computed Radiography Test

voxel 3D pixel
IRD image reader device-reads latent image on CR cassette
what are some other terms for CR *indirect capture *cassette-based *film-less
what is the process of latent image acquisition *x radiation ionizes europium sites causing them to release free eletrons *free electrons are moved to a higher energy band called F center *F center holds electrons in bound state *# of trapped electrons is equal to absorbed radiation
nyquist frequency *determines the maximum spatial resolution for a given sampling frequency by IRD *states that if the desired spatial resolution is (x) the sampling frequency must be 2(x) -increasing the sampling frequency increases the time it takes to display an image
needle/columnar phosphor phosphor crystals arranged as needles or columns
turbid phosphor phosphor crystals distributed throughout a phosphor layer
europium *impurity that allows luminescence *has ecxess electrons at ground level *activator *storage property
when should you use a grid *kVp higher than 60 *whent the part being xrayed is at least 12cm thick
radiopaque cannot be penetrated by xrays
radioluscent easily penetrated by xrays
dicocm header *header with pt name and medical record number, and other pt info, that cannot be edited by RT
artifact any unwanted density
what are the different types of ADC in the IRD *photomultiplier tube *photodiode *CCD
what is the relationship between scanning freq. and contrast and resolution the higher the scanning frequency, the higer the contrast and resolution
how do you change brightness and contrast in CR *use window and level/width *ROI box
ROI range/region of interest-box shaped area of an anatomic structure on a reconstructed digital image defined by the operator by moving the cursor
MTF modulation transfer function- measure of the quality of a detector system, determined by the systems contrast and spatial resolution quality
banding *frequency of scan does not meet grid frequency -can be prevented by using appropriate grid
flat panel artifacts *dust/dirt *scratches *pixel malfunction *gost images
software artifacts *inorrect histogram *auto-rescaling not working *image too compressed
subject artifacts *piercings on pt *any metal or artifacts on pt *collimation off
speed class *CR image acquisition operation that affects certain factors
when should you erase xray plates *unsure of what is on them *hasnt been used in 48 hrs *erase twice if double exposed or used on large pt
how long after exposure should you process an imaging plate *within 1hr to avoid degeneration -latent image loses 25% of its energy within 8hrs
what will happen if you turn tube with grid you will get grid lines
which way is the correct way to place your cassette *blue line down if lengthwise *blue line to your right if crosswise
what are the layers of a CR cassette *backside *antistatic/backing layer *base *reflective/anti-halo layer *phosphor layer *protective coat/layer
what is the backside of the cassete made of lead, also contains lead foil on the inside
antistatic/backing layer *mounted to the back of cassette *prevents handling artifacts *contains barcode *prevents static energy
reflective/anti-halo layer *prevents laser light from bouncing back and causing fog or noise *anti-halo is blue *reflective is white
phosphor/active layer *acquires latent image
protective layer/overcoat *toward tube *prevents handling artifacts *allows cleaning
what is the material that is on the outer covering(tube side) made of carbon or bakelite
what are the two ways that phosphor crystals are aranged in a psp plate *needle/columnar *turbid
what does speed class affect *exposure index *auto-rescaling *image appearance -the slower the speed the better the contrast
what is the purpose to the exposure index to tell the range of exposures that are acceptable
what is the first step in the conversion of a latent image to manifest image in the IRD *there is an initial low level laser scan that sets boundries for collimation of the image and test to make sure latent image matches histogram selected before setting aut-rescaling
what is the second step in the conversion of a latent image to manifest image in the IRD *high level lase scan to release trapped electrons from f center and back into their regular state, causing emision of light
what is the third step in the conversion of a latent image to manifest image in the IRD *light is captured by CCD, which converts it to an electronic signal
what controls contrast resolution *dynamic range *quantization
Created by: bigad1982