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Computed Radiography
Computed Radiography Test
| Question | Answer |
|---|---|
| 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
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