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Chapter 8
key words
| Question | Answer |
|---|---|
| Artifact | an erroneous portion of an image or tracing that does not accurately represent the subject of the image or measurement being recorded |
| Backscatter | radiation from the cassette back and the cassette tray that is scattered back toward the film |
| Digital imaging | the process of acquiring images of the body using x-rays displaying them digitally, viewing and storing them on a computer complete file |
| Digital radiography (DR) | one of the two types of digital imaging systems; is cassetteless. The phosphor is bonded to a flat panel detector built into the x-ray table or chest board |
| Direct conversion | detectors convert the x-ray energy directly to an electric signal through an amorphous selenium detector |
| Indirect conversion | a two step process in which the x-ray energy is first converted to light & then converted into electrical signal using a scintillator |
| Scintillator | a device that glows when hit by the high-energy x-ray photons and often is made of cesium iodide |
| Photostimulable phosphor | a phosphor used in computed radiography (CR) plates to absorb the x-ray energy and store it until it is processed by a special unit and laser light |
| Analog | image comprised of continuous shades of gray from black to white |
| Digital | an array of small picture elements (pixels) that forms a matrix; each pixel is recorded as one numerical value representing one shade of gray quantization) |
| Spatial resolution (digital) | determined primarily by the number of pixels in an image & therefore the size of each pixel |
| Image size (digital) | the dimensions of the field of view (fov) with in patients body not the size of displayed image |
| Dynamic range (digital receptors) | range of exposures over which a detector can acquire image data and display contrast comparable to film latitude |
| Contrast resolution (digital) | smallest exposure change (signal) difference that can be captured by a detector controlled by the dynamic range of the detector and quantization |
| Windowing | an option of post processing to improve the film |
| Window level | a part of windowing that adjusts the brightness; it identifies the type of tissue to be in focus (soft tissue or bone) |
| Window width | (contrast) – determines the gray scale rendition of that tissue & therefore the image contrast |
| Solarization | saturation or white out of a digital image |
| EI# - Exposure index number | the amount of radiation hitting a detector |
| S# - Sensitivity number | indicates the amount of luminescence (light) given off by the IP (image plate) while being scanned by the laser. Is inversely proportional to the amount of radiation that strikes the IP (doubling the exposure mAs results in 1/2 the S# |
| Post processing | the further adjusting of any image of a body part with the use of computer software |
| ALARA | keep mAs as low as reasonably achievable |
| Picture archival and communication system (PACS) | an extensive networked group of computers, services and archives the image |
| Computed radiography | one of the two types of digital imaging systems that is cassette based, the body part is obtained using storage phosphor in the cassette |
| Radiolucent | referring to a substance that is easily penetrated by x-rays; an area of the film through which a moderate amount of light from the view box is transmitted |
Created by:
mdtodd
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