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RAD100Chapter7 Terms
Chapter 7 Terms
| Term | Definition |
|---|---|
| Histogram | a graph showing the distribution of pixel intensities (brightness levels) in a digital image, plotting exposure levels (X-axis) against the count of pixels at that level (Y-axis) |
| Automatic Rescaling | Process by which images are produced with uniform brightness and contrast, regardless of the amount of exposure |
| Window Level (WL) | Controls image brightness |
| Window Width (WW) | controls image contrast |
| Pixel | Picture element and the smallest component of the matrix |
| Matrix | Series of picture elements (pixels) or detector elements arranged in rows and columns |
| Film | has best spacial resolution |
| Digital | has best contrast resolution |
| Filtration | a thin layer of aluminum (sometimes copper) below the tube inside the collimator box to remove low energy (low kVp) photons from the primary beam |
| kVp (kilovolt peak) | the max possible energy of any given photon in the beam |
| Collimation | restriction of X-Ray beam |
| Inverse Square Law | Describes the relationship between radiation intensity and distance from the source of the radiation As you increase SID, you decrease exposure As you decrease SID, you increase exposure |
| mAs Distance Formula (Direct Square Law) | As you increase SID, you must increase mAs As you decrease SID, you must decrease mAs |
| Radiographic Grids | Absorbs scatter radiation from the patient that would hit the IR |
| Grid Ratio | Can be described by grid frequency and grid ratio height of lead strip ÷ width of interspace |
| Grid Frequency | number of lead lines per unit length EX: 40 lines per cm |
| Contrast | the visible difference between any two selected areas of brightness levels within the displayed radiographic image. |
| High Contrast | Few grays, mostly black to white Short-scale contrast |
| Low Contrast | Many grays, but little difference among those grays Long-scale Contrast |
| Differential absorption | Variation of attenuation based on the properties of the matter (body parts, objects, etc.) |
| Attenuation | Process by which a beam of radiation is reduced in energy when passing through tissue or other materials |
| Digital imaging Too low mAs = not enough photons | appear “grainy” - called quantum mottle |
| Digital imaging Too high mAs = pixel overload | appears “burnt” – too dark to see detail, Image is saturated |
| Spatial Resolution | Degree of accuracy of the structural lines actually recorded in the image |
| Contrast Resolution | Ability to distinguish between very subtle differences in image receptor exposures and differentiate them from the noise in the image |
| Grid | Device consisting of thin lead strips designed to permit primary radiation to pass while absorbing scatter radiation |
| Kilovoltage Peak (kVp) | Measure of the potential difference, which controls the quality and affects the quantity of x-ray photons produced in the x-ray tube |
| Source-to-Image Receptor Distance (SID) | Distance between the source of the x-rays (usually the focal spot of the x-ray tube) and the image receptor |
| Image Receptor (IR) | Device used to capture the image for recording, such as photo-stimulable phosphor imaging plate or a digital flat-panel detector |
| Image Receptor (IR) Exposure | Amount of ionizing radiation received by the image receptor |
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