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computed radiology
computed radiography
| Question | Answer |
|---|---|
| CR or computed radiography uses what? | imaging plate |
| CR | is indirect capture , cassette-based and film-less. |
| CR is used where? | HHPO,POI, TLI, HMC fugi portables, and DR/DF rooms will allow for use of CR imaging plates. |
| the tube side of the cassette is made out of what? | radiolucent (black side) carbon fiber or backer light material |
| radiolucent | allows xray beam to penetrate |
| the back side of a cassette is made out of what? | radio-opaque lead foil which prevents back scatter which would fog the IP (imaging plate) |
| radio-opaque | does not allow x ray beam to penetrate |
| what is the purpose of a cassette in CR? | it holds and protects the IP (imaging plate) and contains the bar code to ID |
| the bar code allows for the detection of what? | the correct patient and histogram (projection) |
| IP | imaging plate |
| where is the imaging plate? | mounted inside the cassette onto the backside of the cassette |
| is the IP reusable? | yes |
| the imaging plate is the acquisition or capture of what ? | the latent image |
| what is the latent image? | the invisible image on an imaging plate prior to processing |
| IP construction/ #1 backing | antistatic layer mounted onto the backside of the cassette which protects from handling artifacts. also contains bar code information |
| IP construction/ #2 base | made up of polyethylene terephalate which provides mechanical support for phosphor layer |
| IP construction/ #3 anti-halo/reflective layer | anti-halo- blue tint and reflective layer- white color coupled together to prevent laser light from penetrating but allows reflected light to be emitted to phosphor. helps reduce noise (grainy appearance) |
| IP construction/ #4 phosphor (active) | photostimulable phosphor (PSP- gives off light twice ), which collects or acquires the latent image |
| PSP construction needle/columnar phosphor | phosphor crystals arranged as needles or columns |
| PSP construction trubid phosphor | phosphor crystals distributed throughout a phosphor layer. less patient does also lost of detail/spatial resolution |
| PSP | barium fluorohalide doped with europium x halide (gives off light) can be bromide,chlorine or iodine, etc |
| europium/activator | impurity to allow luminescence has excess e- at ground level |
| IP construction/ #5 protective layer | protects from handling artifacts. points towards the tube and allows for cleaning- approx 3 months |
| what is used when cleaning the protective layer? | denatured alcohol and gauze pad |
| acquisition of latent image | (invis image on IP) x radiation ionizes europium sites causing them to release free e- free e-s are moved to a higher energy band called f center. f center holds e- in bound state. # of trapped e-s is equal to absorbed radiation |
| f center stands for what? | fabre, which means color |
| what is on the CR console? | exam list screen (Worklist)- patient data and bar code reader |
| LUT | look up table is where the gray scale rendered or default visible manifest image appears after processing. where widow width or range can be adjusted. changing the window level changes brightness or density. image data from histogram is rescaled also |
| practical tips for CR imaging plate | erase plate if unsure of what is on it or it has not been used in 48 hours. erase plate a 2nd time if double used or large patient/part which prevents ghosting. process within 1 hr of exp to avoid image denigration (fading)latent image loses 25% in 8 hrs |
| practical tips continued | do not turn tube w/ grid or you will get grid lines. blue line down if LW/ to your right if CW |
| IP sensitive to radiation | to low intensity radiation, back ground exp on stored IP responds to 60 uR. avg back ground in room is 40-80 uR per day |
| IP sensitive to scatter | do not leave IP in rooms because of back s/s |
| speed class | CR image acquisition operation that affects exposure index and auto rescaling |
| auto rescaling | software that rescales image brightness to present level over exposure range of 100 |
| image appearance | determined by receptor exposure. average value is 200 |
| S number | is the sensitivity number. inversly related to the level of exposure that the psp plate receives. doubling expo. reduces S value by half. incr. the expo. a PSP plate receives decreases the S #. decreasing tthe expo a PSP plate receives incr. the S # |
| image display | konica, FUGI, and phillips range 100-200 (HHMC,TLI,POI) above underexposed, high quantum mottle noise due to low MAs/ below overexposed |
| EI | exposure index- logarithm based exposure index directly related to the exposure level a PSP plate receives |
| ROI | region of interest - area that you collimate to level of interest |
| when does the EXI appear? | when 1 mR reaches the IR varies per manufacturer |
| TEI | target exposure index- when image is optimally exposed. determined by facility |
| what leads to corruption of EI? | poor centering, incorrect collimation, lead shields, metallic object in the body and if unable to use at least 33% of IR |
| Agfa | log base |
| lgM | logarithm of a histogram median. directly related to expo. a PSP plate receives an is log based |
| IR | image reader device |
| processing the latent image | load the cassette into the IRD. IP scanned twice by helium neon laser beam |
| 1st scan | pre read or slow scan, done at low intensity. used to set boundaries of collimation for the image & determines range of pixel densities |
| 2nd scan | fast progressive scanning/ 2nd phase of light. main read for fast scan increased intensity. scanned by narrowly collimated laser for maximum detail. laser causes phosphors to emit stored latent image in the form of light photons |
| PMT | photo multiplier tube which is the A-D converter |
| conversion of latent into manifest image | laser causes trapped e- at f center to be released called photostimulated excitement. e- go back to europium site and give off bluish purple light called photostimulated luminance. light is collected and sent to the PMT. PMT converts light into elect. si |
| slow scan | 1st scan which uses a constant motor driven system to precisely move IP along long axis of laser which helps reduce banding artifacts. laser scans perpen. to grid lines to prevent aliasing artifacts |
| aliasing artifacts/ grid moire | due to imaging grid lines across pixels. choose grids with thinner lead strips |
| shuttering/cropping | prevents eyestrain because of the white border. do not crop off anatomy of interest |
| stitching | used in scoliosis treatment |
| LSR | limiting spatial resolution- an indicator of the detectors ability to resolve small structures |
| MTF | measure of spatial resolution. best method to express image quality of detector system |
| system malfunctions | ghost image, dead pixels, erasure, readout problems, printer distortion, banding and laser jitter |
| ghost image | electrons staying in f center. to prevent double erase |
| dead pixels | can cause white spots and or dust |
| what corrects banding | high frequency progressive scanning and thinner grid lines prevent banding. |
Created by:
eckoultd1972
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