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Radiation euipment
digital radiography and PACS author carter/veale
| Question | Answer |
|---|---|
| In CR, what device is the radiogrphic image recorded on that consists of a thin sheet of plastic? | imagine plate |
| what is the very thin, tough, clear plastic that prtects the phosphor layer? | protective layer |
| where in the imaging plate is the PHOTOSTIMULABLE PHOSPHOR located? | the phosphor or active layer |
| what is does the PHOSPHOR layer do in the CR imaging plate? | the photosimulable phosphor "traps" electrons during exposure; also contains a dye that differentially absorbs the stimulating light to prevent as much spread as possible |
| what is BARIUM FLUOROHALIDE? | the family in which photostimulable phosphor layer is made from |
| what is the purpose of the REFLECTIVE layer in the CR imaging plate? | sends light in a forward direction when released in the cassette reader. may be black to reduce the spread of stimulating light and the scape of emitted light. SOME DETAIL IS LOST IN THIS PROCESS |
| What is the purpose of the CONDUCTIVE layer in the CR imaging plate? | absorbs and reduces sttic electricty |
| What is the purpose ot the COLOR layer in the CR imaging plate; Where is it w/in the plate? | Absorbs the stimulating light but reflects emitted light; between the active and support layers |
| What is the SUPPORT layer do in the CR imaging plate? | Semirigid material that gives the imagin sheet some strength |
| What is the BACKING layer do in the CR imaging plate? | A soft polymer that protects the back of the cassette. |
| What is the purpose of the BARCODE LABEL/BARCODE STICKER on the CR imaging plate? | Allows the technologist to match the image info w/ the patient-identifying barcode on the exam request. For each new exam the barcode label must be matched w/it's appropriate pt-identifying exam request |
| How is the exposure recorded using Computed Radiography? | the remnant beam (what didnt get absorbed) interacts w/e`s in the barium fluorohalide crystsal contained w/in the imaging plate. This interaction stimulates(gives energy)e`s in the crystal, allowing them to enter the conductive layer. |
| How is the exposure recorded using CR cont'? | In the conductive layer the electrons are trapped in crystals of the color/phosphor center. The trapped signal will remain for hours or days. trapped signal is never completely lost |
| What is the purpose of the LASER? | aka light amplification of stimulated emission of radiation, is a device that creates and amplifies a narrow, intense beam of coherent light. |
| What is a RASTER pattern and where does it occur? | When the cassette is put into the reader, the imaging plate is extracted and scanned w/a helium laser beam or solid-state diodes.The pattern is from left to right, returns back to left, scans left to right, returns back to left... |
| Describe the beam in the cassette reader. | 100mm wide w/wavelength of 633 nm; helium or solid-state diode. Red laser light is emitted at approximately 2eV and the extra energy allows the trapped e`s to escape the active layer where they emit visible blue light at an energy of 3eV. |
| What is the PHOTOMULTIPLIER? | Electronic device that amplifies light and sends it to a digitzer. |
| What does "digitizing the signal" refer to? | Refers to assigning a numerical value to each light photon. |
| That does "analog" refer to? | Refers to a device or system that represents changing values as continuously variable physical quantities. ex: a wrist watch |
| In the digitizing process... | the light signal, each phosphor storage center is scanned, & the released e`s enter a digitzer that divides the analog image into squares (matrix) and assigns each square in the matrix a # based on the brightness of the square. |
| What is a PIXEL? | Each square that gets digitized. Typical # pixels in a matrix ranges fr: 512X512 to 2500X2500. The more pixels-the higher image resolution. |
| Describe spatial resolution. | One way the image is digitized, by position or spatial resolution. It's the amt of detail present in any image |
| The thinner the phosphor layer... | the higher the resolution |
| In film/screen the best resolution... In CR the best resoluion is... | ...10-lp/mm ...2.55 to 51-lp/mm |
| Which has better image detail, film/screen or CR? | Film screen |
| In CR, what is the speed refering to? | Time it takes the laser beam to read the imaging plate which is roughly equivalent to 200 speed film/screen. The "speed" is a reflection of the AMOUNT of photstimulable luminescence (PSL) given off by the imaging plate while being scanned by the laser. |
| How often should imaging plates be erased? | At least once a week to earase any background radiation and/or scatter. |
| Wht is involved in the Preprocessing, Processing and Forwarding the Image? | Once imagin plate has been read, the signal is sent to computer, then to the monitor where the technologist can manipulate the image (postprocessing), and send it to the Quality Control (QC) station and ultimately to PACS. |
| Why is is important to select the correct body part and position from the exam menu? | Because in order for proper conversion to take place. If inproperly selected the algorithms wil misinterpret the image. |
| Kilovoltage Peak is chosen for what? Value range? | Chosen for penetration and the type and amount of contrast desired. 45-120 kVp |
| What is mAs selected for? | to provide the correct number of photons needed for a particular part. |
| Insufficient mAs will cause _______. | quantum noise or quantum mottle |
| What are the two factors to be considered when selecting a CR imaging cassette? | SIZE (pixel size is an amportant factor in determining resolution) and the TYPE |
| What happens when the grid chosen is unaligned? | Will cause a wavy artifact on the image known as MOIRE pattern |
| What causes the moire effect? | Grid lines that are projected onto the imaging plate when using a stationary grid can interfere w/the image. The grid lines and scanning laser are parallel. |
| What are the four Grid Selection Factors? | Grid frequency, Grid ratio, Focus, Size |
| What is grid ratio? | the height of the lead strips to the distance between the strips. Higher the ratio-the more scatter radiation is abosorbed by the lead strip |
| What is Grid frequency? | number of grid lines per centimeter or lines per inch. |
| What is the recommended grid frequency for digital imaging receptors? | 103 lines per inch or greater. |
| Most grids chosen by radiography departments are what type? | Parallel and focused |
| what is a focused grid? | Consist of lead strips angled to coincide w/the deversion of the x-ray beam and must be used w/in specific distances using a precisely centered beam. |
| What is a parallel grid? | Are less critical to beam centering but should not be used at distances less than 48 inches. |
| Why is grid size important for the image? | the smaller the grid the hight the sampling rate. |
| What is the definition of collimation? | the reduction of the area of beam that reaches the patient through the use of two pairs of lead shutters encased ina housing attached to the x-ray tube. |
| What is shuttering? | Through postexposure image manipulation can be accomplished. A black background can be added around the original collimation edges, virtually elliminating the distracting white or clear areas. |
| What does collimation do with the compton effect? | Decreases compton scattering? |
| what is the exposure indicator number? | a numerical representation of the amount of exposure absorbed by the imaging plate, usually the mean value |
| Which systems use S for their exposure indicator number? What is the number? | Fuji, Phillips, Konica 1mR at 80 kVp has a value of 200 |
| Which systems use EI or exposure index? What is the number? | Kodak 1mR @ 80 kVp aluminum/copper filter yield value of 2000 |
| The amount of light given off by the imaging plate is a result of the radiation exposure the plate has received. The light converted into a signal that is used to calculate _________ | exposure indicator number |
| What does the exposure indicator number measure? | the amount of radiation the was absorbed by the plate |
| What is lgM? | logarithm of the median expousure; term used to express exposure to the imaging plate |
| what is a histogram? | a graphic representation of the numerical tone values of an x-ray exposure. Generated by dividing a scanned area into pixels and determining the signal intensity for each pixel; can be calculated for specific anatomy and procedures |
| what is the image data recognition phase for kodak? | Segmentation |
| what is the image data recognition phase for Agfa? | collimation |
| what is the image data recognition phase for Fuji? | exposure data recognition |
| What is automatic data recognition? | The image recording range is already determined. The tech. just selects whether the field is divide for multiple exposure & in what pattern the exposure will be made. Collimation is automatically recognized & the latitude (L) & sensitivity (S) r adjusted |
| What does semiautomatic mode do in image data recognition and preprocessing? | the latitude balue of the histogram is fixed, and only a small reading area is used. NO collimation detection |
| What is Multiple manual selection mode? | The area of interest is selected by the technologist, aids in cross-table exams when body part may not alight w/selected imaging plate regions |
| What does fixed mode do in data recognition and preprocessing? | The user selects the exposure index, or sensitivity number, and the value of the latitude from a menu. |
Created by:
clbrock0620
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