Term
| Why has digital radiography been slow to evolve? |
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Definition
- conventional screen film radiography has been used for decades and done it well, no pressing need to convert to digital
- the lg field of view (14 x 17 in radiographic image) and high spatial resolution of radiography require lg amts of digital data (4 – 32 MB) and demand high-quality monitors for viewing when compared with MRI, CT, and US |
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Term
| What was the first digital radiography introduced? |
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Definition
| in the early 1980s by Fujifilm Medical Systems (CR) |
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Term
| What is the main difference between digital radiography and conventional film-based radiology? |
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Definition
| - that radiographic images are electronically captured, recorded, and viewed at a computer terminal, replacing radiographic film and the view box |
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Term
| The conventional screen-film cassette is replaced by a reusable image receptor known as the? |
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Definition
- a reusable image receptor (detector)
- receives x-rays just as conventional intensifying screens do
- intensifying screens or other scintillation devices expose a “digital plate” that transforms emitted light to an electrical latent image |
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Term
| What is the PACS used for? |
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Definition
- PACS = picture archiving and communication system
- the broad term for computers and components used to capture, transfer, store and display medical digital info |
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Term
| List and explain two disadvantages for using screen-film radiography. |
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Definition
- requires fairly narrow exposure factors to produce a diagnostic quality radiograph. because x-ray film has a limited linear response, relatively small underexposure or overexposure may yield an unacceptable image. this is why a technique chart is req’d
- the image cannot be adjusted once made. because the digital image can be manipulated after it is made, overexposure and underexposure are a thing of the past w/ digital |
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Term
| What does the kVp do for the digital image? |
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Definition
| - unlike traditional screen-film radiography, kVp (kilovoltage potential) has little effect on the contrast or latitude of the digital image. |
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Term
| Digital images have more latitude than film images. What do they mean by latitude? |
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Definition
latitude = shades of gray
- they can display high-contrast body parts while simultaneously displaying soft tissues
- this high gray-scale (high latitude) is desirable because it allows observation of minor differences in radiation attenuation that may not be visible with film |
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Term
| The exposure latitude is very beneficial in digital radiography. List 2 advantages of the exposure latitude |
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Definition
- the need for retakes resulting from overexposure and underexposure is reduced and mostly eliminated
- images that are too light/dark that would be discarded on radiographic film can be adjusted with the digital image management software |
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Term
| What is the advantage of being able to zoom an image using digital radiography? |
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Definition
| - to scrutinize the film as if using a magnifying glass to view a radiographic film |
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Term
| Why are repeat radiographs significantly reduced with digital radiography? |
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Definition
- images that are too light/dark that would be discarded on radiographic film can be adjusted with the digital image management software
- exposure-related retakes should be essentially eliminated
- patient-motion artifacts can be reduced by reducing radiographic exposure time (selecting a higher kVp and a corresponding lower mAs technique – recall that kVp is no longer a factor in radiographic image contrast and latitude and this can be done w/o altering image contrast) |
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Term
| List some advantages of image storage and transport with digital radiography. |
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Definition
- quick access and viewing is simply a computer search
- easy transferability of images via email
- CD can be made for other vets or for the client |
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Term
| List a few disadvantages of digital radiography |
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Definition
- changing and getting used to a new imaging system
- personnel training
- cost |
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Term
| Define the acronyms HIS, RIS and PACS |
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Definition
HIS
- hospital information system, a computer program that allows pt info to be entered into the hosp computer system.
- can be used for elec record keeping
- ideally, the HIS communicates with the dig imaging system directly or via a RIS
RIS
- radiology information system. a computer sys that handles all the info needed to perate a rad dept. RIS manages pt info, scheduling of imaging procedures, radiology reporting, and a database allowing case search capabilities.
PACS
- picture archiving and communication system
- the broad term for computers and components used to capture, transfer, store and display medical digital information
- allow communication between computers
- some form of PACS is needed to realize all the advantages of digital rad |
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Term
| Describe the origin of a digital rad |
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Definition
- a conventional rad is produced by a series of analog signals, from x-ray formation and interaction w/ the pt, to capture of x-rays by the intensifying screen, which in turn emit light that exposes the radiographic film. the final image results by development of silver halide contained w/in the emulsion of the x-ray film
- the origin of a digital image is identical to conventional radiography
- the difference is the conversion of the analog signal (light emitted from scintillation screens) to an electronic digital signal by use of a digital radiographic device |
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Term
| Describe the analog signal. |
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Definition
- a voltage waveform that is continuous; at any point in time there is a voltage value
- its electrical value is represented as a voltage value
- a digital signal is produced from an analog signal by way of an analog-to-digital converter (ADC). the ADC samples the analog waveform and transforms it into a “stepped” representative signal
- the more times the analog signal is digitally samples, the closer the digital waveform is to the original analog waveform
- the freq of digital sampling is the sampling rate – sampling rates in the 10s to 100s of thousands per second are needed to accurately digitally replicate an analog waveform |
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Term
| Explain the two types of digital receptors |
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Definition
- Indirect systems use a two-part process, converting x-ray energy first to light and then to an electronic (digital) signal. The indirect digital systems incl photostimulable phosphor (PSP) imaging plates (used in CR), CCD’s and silicon flat panel receptors
- Direct digital radiography (DDR). A digital radiography system in which there is direct conversion of x-ray energy into an electronic (digital) signal. Although DDR offers the best in digital radiography resolution, the technology is currently expensive and not commonly used even in human medicine yet due to high manufacturing costs |
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Term
| Define CR in a digital imaging system |
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Definition
- computed radiography
- a type of digital that uses a phosphostimulable phosphor detector screen
- the PSP screen absorbs and stores most of the incident x-ray energy (latent image) which is to be “read out” later
- because PSP screen store energy, they are also known as storage phosphors or CR imaging plates
- by contrast, conventional screen-film intensifying screens do not store energy, instead they emit light instantaneously upon x-ray interaction, in turn exposing the radiographic film (latent image production), which is later developed into a radiograph
- CR system can be thought of as using a filmless cassette
- one PSP imaging plate is used per exposure. following exposure, the CR cassette is taken to a laser CR reader unit (also known as an Image Reader Device [IRD], “CR processor”, or plate reader, among others) for processing the latent image |
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Term
| What occurs after exposure of the CR cassette? |
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Definition
1. the CR cassette is placed into the CR reader, where it Is automatically opened and the CR plate removed
2. as the CR plate moves through the processor, it is scanned by a helium-neon laser beam. The laser light stimulates release of trapped x-ray energy stored in the CR plate as visible light
3. The released visible light is collected by fiberoptics to a photomultiplier tube, producing an electrical signal
4. the electrical signal is digitized and stored on a computer
5. The CR plate is then exposed to a bright white light, erasing any residual latent image
6. The CR plate is returned to the cassette, ejected from the CR reader, and ready to reuse |
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Term
| Explain Image plate artifacts. |
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Definition
- CR image plates are susceptible to cracking as they bend inside the plate reader. Cracks occur first along the edges of the plate and progress centrally to interfere with the image
- cracks are areas w/o PSP and therefore show as white lines or “cracks” on the CR image
- Debris w/in the CR cassette such as dirt or hair will block light and also appear as a sharp area of “white” image void. This is analogous to dirt w/in a conventional screen cassette. these could be confused with a FB w/in the pt if not recognized
- plate reader artifacts are caused when the CR plate has been improperly erased or not used for 24 hrs or longer
- ghost images from extraneous radiation from scatter rad, “cosmic rays” etc can cause a type of CR image fogging
- this is why CR plates must be erased before use if stored for > 24 hrs
- flat panel detectors are less sensitive but not immune to ghost image artifacts |
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