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Test - module #4-#6
med. imaging module 4, 5, 6 test objectives
| Question | Answer |
|---|---|
| name 2 types of digital receptors | cassette-less capture (DR-direct capture) and cassette-based capture (CR-indirect capture) |
| name the 2 types of cassette-less capture (DR-direct capture) | direct acquisition and indirect acquistion |
| explain how direct acquisition DR works | x-rays come in, amorphous-Selenium (x-ray photoconductor) converts x-rays to electrical charge, electrical signal interacts with TFT (thin film transistor) |
| explain how indirect acquisition DR works | x-rays come in, x-rays are converted to light via cesium-iodide (scintillator phosphor), light converted to elecrtic charge via amorphous-Silicon (photodiode), electric signal interacts with TFT |
| explain how CR (indirect capture) works | cassette with plate, put under pt, set technique, expose it, stick whole cassette in processor, processor opens cassette and captures image and clears plate (exposes to fluorescent light) - reusable |
| A-D converter (ADC - analog to digital converter) | converts analog (electronic) signal from image sensor to a number digital signal(binary system)- numbers representative of color (0,1 - black and white) |
| binary | 0 & 1 - representative of color (black and white) |
| bit depth | groups of numbers - numbers for black, white, and greys - number of bits per pixel, how many shades of grey/black/white in a pixel |
| digital | numerical representation of an image - using bits to show an image |
| name 3 ways an image can be stored | GIF, JPEG, and TIFF (JPEG is the best) |
| GIF | graphics interchange format - used for logo and icon storage - similar to JPEG |
| JPEG | joint photographic experts group - standardized format for storing images on a computer (preferred format for image storage) |
| TIFF | tagged image file format - used for publishing and faxing |
| pixels | picture element - individual squares (smallest) 2-D images that make up matrix |
| resolution | how clear and sharp is the image - best image has large matrix with several pixels (more pixels, better resolution, better picture) |
| matrix | entire picture |
| voxel | 3-D matric (volume element) |
| lossy compression | loss of quality of image during compression and decompression of image |
| lossless compression | no loss of quality of image during compression and decompression of image |
| what is digital imaging | graphical representation of an object (dealing with numbers) - shades of black/white/grey are assigned numbers (can be altered, made up of pixels, the more pixels the better resolution) |
| explain cassette-less (DR - direct capture) | electronically readable, flat-panel detector, captures image directly |
| what does a TFT do? | Thin film transistor - stores electronic signal |
| explain cassette-based (CR- indirect capture) | have a cassette like in film-screen imaging, screen, no intensifying screen only phosphor plate |
| DQE | detective quantum efficiency - how efficient are they, how efficient can it convert x-rays to a signal to a useful image |
| spatial resolution | how detail oriented is my image (higher for DR and CR than silm-screen cassette) |
| scatter | CR and DR are very sensitive to scatter (sensitive to low energy photons) |
| contrast (CR & DR) | higher contrast with CR & DR because they're much more sensitive, still control using kV and mAs |
| density (CR & DR) | higher density with CR |
| explain dynamic range | availability of black/white/grey, range of shades of grey that I can see |
| dynamic range (CR & DR) | dynamic range is higher for CR & DR vs. film-screen (infinite range of numbers for CR & DR, more shades) |
| explain latitude | how much wiggle room do i havewith an image, how much error can I make and still have a decent image |
| latitude (CR & DR) | latitude is higher for CR & DR (more space and wiggle room) than for film-screen |
| speed (CR & DR) | CR & DR are faster than traditional film-screen imaging, less pt dose |
| pixel | picture element, composed of several shades of G/B/W (bits) |
| pixel density | several different shades of B/W/G, # of pixels per millimeter, (increased pixel density, increased resolution) |
| pixel pitch | measurement from center of pixel, to center of another pixel, (micrometer or microns), more pixels, better resolution |
| pixel size | larger matrix, smaller pixel, better resolution, smaller pixel, more pixels the image has, better resolution |
| rescaling | computer automatically alters image to get a better image - cleans it up |
| how does bit depth affect contrast | bit depth is how many shades of g/B/&W are in a pixel, the more shades of grey (the bigger the bit depth) the less the contrast |
| DQE | the percentage of x-rays that they capture and convert to useful image. DR is most efficient at capturing and converting to images that CR |
| rules for good image acquisition with cassette-based systems (CR) | patient positioning, (straight over cassette), proper technique (select correct kV and mAs), kVp (low kV, good contrast, quality), mAs (density, quantity, low mAs - quantum mottle, high mAs - black image), |
| cont. | image plate selection (high resolution - lose image quality, stress fractures and mammograms), standard resolution for everything else, imaging plate size (proper size for what you're imaging), grid use (need grid with CR&DR, clean up scatter, more sens. |
| cont. | collimation (collimate area imaging, good contrast - bigger field, more interaction, more scatter, want good clarity and resolution (smallest area possible)) |
| rules for good image acquisition with cassette-less systems (DR) | detector size (select proper size, not too large will collect scatter), rapid succession of filming (give machine time in between films), collimation (film smallest area possible), use of grids (CR&DR are more sens. to scatter, grids absorb scatter |
| image acquisition and extraction of cassette based systems (CR) | x-rays interact with phosphor, converts x-rays to light, energy is stored in phosphors, energy is converted to an analog signal, analog signal converted to digital image |
| image acquisition and extraction of cassette-less systems (DR) | direct - x-rays absorbed by photoconductor, converts to electric signal, signal sent to TFT, TFT converts signal to image indirect - x-rays, photon converted to light, light converted to signal, signal to TFT, TFT to image |
| name image acquisition errors | exposure field recognition, histogram analysis, and inappropriate rescaling |
| explain exposure field recognition | incorrect technique aor area being imaged (collimation, scatter) |
| explain histogram analysis | scale of greys - want your field to be centered to get a correct histogram analysis |
| explain inappropriate rescaling | computer does automatic rescaling - don't rely on it (if image is too light, will have quantum mottle after rescaling) (if image is too dark - computer will try to rescale down, not enough contrast) |
| describe the risks of artifacts in digital imaging | an artifact is anything causing an increase or decrease in density, any unexpected material causing undesired objects to show up |
| list examples of artifacts | imaging plate artifacts (dust or dirt on plate), plate reader artifacts (processor not working, rollers need cleaning), printer artifacts (printer not working, causes poor quality image), operator error (wrong technique, jewelry, wrong menu options) |
| examples of imaging plate artifacts | scratches on plate, static hairs |
| explain proper means of scatter control | low energy scatter is produced from the patient) optimal exposure, collimation, grid use |
| explain optimal exposure for scatter control | the more radiation coming from machine, the more interactions with pt, the more scatter is produced - want to keep technique down |
| explain collimation for scatter control | smaller field, less scatter, less radiation to pt |
| explain grid use for scatter control | grids cut down on the amount of scatter caused by interaction with the pt muddying up film |
| explain Moire' pattern | lines will show up on film if the grid isn't lined up perfectly with cassette/reader (use moving grid and line up grid perfectly) |
| describe the response of digital systems to background radiation | CR&DR are much more sensitive to low energy radiation/background radiation. CR&DR will pick up background radiation causing image to be less clear/crisp |
| evaluate the effect of a given exposure change on histogram shape | low kV - wide histogram, a lot of contrast/latitude high kV - narrow histogram, less contrast/latitude |
| what has biggest effect on histogram | kV |
| define automatic rescaling | when the computer looks at a picture and decides what needs to be done to create a better quality image |
| name problems with automatic rescaling | quantum mottle (if image is too light, not enough density, not enough mA) and loss of contrast (if image is too dark, can't see difference in shades of grey, too much exposure) |
| what is the symbol for kodak receptors (vendor specified values) | EI - exposure index |
| what is the symbol for Agfa receptors (vendor specified values) | lgM - Log mean exposure |
| what is the symbol for Fuji/Philips/Konica?Minolta receptors (vendor specified values) | S - sensitivity |
| base sensitivity value for kodak | 2000 |
| base sensitivity value for Agfa | 2.6 |
| base sensitivity value for Fuji/Philips/Konica/Minolta | 200 |
| Other factors affecting digital detectors | reader needs to be calibrated, pt needs to be centered, and correct collimation needs to be used |
| explain DAP | dose area product - cG/m2 - how much cG pt is receiving per meter squared |
| name 5 post processing procedures with digital imaging | subtraction, frequency processing, edge enhancement, gradient processing, black/white reversal |
| explain subtraction | after i take an image, it pops up on screen, can reverse or get rid of any overlying anatomy (reversing brightness) |
| explain frequency processing | when you apply a filter to the image to better see anatomy to get diagnostic information, supressing some pixels/frequencies |
| explain smoothing | (low-pass filtering) - average out the pixel value (the greys), smoothes/blurs them |
| explain edge enhancement | (high-pass filtering) - artificial increase in frequency, remove a lot of grey pixels, increases density (can sometimes cause quantum mottle/noise) |
| explain gradient processing | altering the brightness (density) and contrast (black and white) of an image ((best post processing tool) |
| name the 2 types of gradient processing | window level and window width |
| explain window level | alters brightness, the higher the window level, the more white is seen, less density, |
| explain window width | amount of contrast (greys) in an image, icrease window width, decrerase contrast, wider window width - more greys, less contrast....more narrow window width - less greys, more contrast |
| explain black and white reversal | what shows up black will look white and what shows up white will look black |
| explain shuttering | adding a black background to better see the image |
| explain equalization | (similar to shuttering), light areas (with low exposure) are made darker and areas that are dark (with a lot of exposure) are made lighter - equalizes everything out |
| discuss the effects of excessive processing | decreases visibility of anatomic structures, can be misdiagnosed |
| describe contrast concerning digital imaging | contrast is more driven by window width (not driven by kV - used for penetration of the body) |
| describe density concerning digital imaging | driven by window level and pixels (not driven by mAs) |
| describe spatial resolution concerning digital imaging | recorded detail and clarity, smaller pixel size and more pixels in matrix, better spatial resolution (films - recorded detail) (digital imaging - spatial resolution) |
| discuss exposure myths associated with digital imaging | mAs - quant. of photons (not enough - quantum mottle) kVp - quali. of photons, penetration through body. collimation - big area, more pt dose. grid - need grid more than with film b/c CR&DR more sens. to background rad. (pt thicker than 12-15cm use grid) |
| cont. | SID - increased SID, increase mag. speed class - still need enough mAs to have correct quant. of exposure and good/clear image. fog - more of a problem for DR&CR b/c more sens. to background rad. |
| discuss ALARA | as low as reasonably achievable dose for pt |
| dose creep | radiologists stopped paying attention to techniques and started using higher and higher radiation level (pt getting higher doses) |
| how to keep pt dose to a minimum | collimate (smaller field), use proper kVp and mAs, fast screen/processor speeds |
| describe pt benefits gained through telemedicine | can have medical advice at any time within or outside of the facility (tests read, images looked at by someone) makes it easier for pt to not have to carry images to diff. facilities, quicker, easier |
| what modality types are incorporated into PACS | (picture archival communication system) - RIS (radiology info sys), HIS (hospital info sys), and billing info |
| define accession number | a unique number given to each item to be archived (pt name, info etc.) |
| define DICOM | digital imaging and communications in medicine - ability to allow different systems of a PACS system to communicate with each other |
| data flow | image modalities (HIS, RIS, billing) goes into PACS which goes into DICOM - DICOM allows PACS to commuinicate |
| describe HIPAA concerns with electronic information | (health insurance portability and accountability act) - electronic information can be lost, sent to incorrect places, deleted, changed, and possibly be hacked into |
| describe image viewing and dispay units used | CRT (cathose ray tube) and LCD (liquid crystal display), can view image on screen, DRR, and archive it on a disk |
| define DRR | digitally reconstructed radiograph |
| when are DRR's used in radiation therapy dept. | DRR is when you take an image on a screen and print it out, can be used to transport image to another facility (can see it better anatomyon screen, better dynamic range) |
| discuss storage capabilities for archival of digital information | can archive images and info. on DVD, CD, tape, can store it in RIS, HIS, PACS, DICOM, on site, off site |
| imaging plate layers | (PSP - photostimulable phosphor) protective layer, phosphor layer (does all work - trap electron), light reflective layer (no light allowed through), conductive layer (does all work - absorbs electrons trapped in psp layer), support layer, backing layer |
| thinner the psp layer | better resolution |
| if set 50% or less than ideal exposure | you will get quantum mottle/noise |
| if set 200% or greater than ideal exposure | see loss in contrast and lots of density |
| if using grid | need higher mAs (adjust technique b/c grids absorb rad./ |
| exposure indicators - increaser sensitivity | decrease amount of exposure you need (faster), less pt dose |
| define archive | where records are stored and preserved |
| explain HIS info | address, pt info, age, old chart, insurance, DOB |
| explain RIS info | images and pictures |
| explain image manager | stores record by a file # (accession number) |
| short term storage | on site |
| long term storage | off site |
| teleradiology | no radiologist on site, call someone off site and have them look at radiographs |
| CAD | (computer aided diagnosis) - computer diagnoses you and looks at radiograph |
| PACS id the abbreviation for what | picture archiving and communication system |
| DICOM is the abbreviation for what | digital imaging and communications in medicine |
| thin film transistors (TFT) are used in which process | digital radiography (both direct and indirect acpture) |
| the image prior to processing but after exposure is termed | latent image (invisible) |
| which of the following must be processed in a reader | computed radiography |
| what is responsible for pre-processing contrast with both CR & DR | kVp (window width) |
| which of the following is responsible for noise or quantum mottle of an image | excessively low mAs |
| what can be used to save data from PACS | disk, DVD, CD, tape |
| list 2 types of monitors that can be used for display of information on PACS | CRT (cathose ray tube) and LCD (liquid crystal display) |
| name a disadvantage and an advantage for CRT | dis - throws off a lot of heat adv - can be viewed at any angle w/o distortion or deterioration of the image |
| name a disadvantage and an advantage for LCD | adv - better in ambient light (no shadows) dis - the further you move away from the screen the more th eimage deteriorates |
| what system typically stores data on the patients general medical information | HIS - hospital info sys |
| the active layer of an imaging plate in computed radiography is composed of | photostimulable phosphor |
| what layer of the imaging plate is present for absorption and reduction of static electricity | conductive layer |
| the amount of detail present on an image is termed | spatial resolution |
| what is selected for "penetration" of the image subject | kVp |
| Moire' pattern is an artifact caused by | incorrect grid alignment |
| what involves adding a black background around an image to clear up distracting pr clear areas | shuttering |
| what uses material composed of amorphous selenium | digital radiography (direct capture) |
| what is a term for the measurement of percentage of x-rays that are absorbed once they hit the detector | exposure indicator |
| what improves spatial resolution | smaller pixels and a larger matrix |
| the most common image post-processing parameters are those for | brightness, density, and contrast |
Created by:
Kayleeh18