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varkey chapter 10 SG
| Question | Answer |
|---|---|
| The random fluctuation in the optical density of the image is known as | radiographic noise |
| What is spatial resolution? | Ability to image small objects that have high subject contrast. Limited to pixel size. |
| Name two other terms that can be used instead of spatial resolution. | -detail -recorded detail |
| Name the factors that control/affect detail. | -motion/geometric blur - focal spot size -SID/OID |
| What factors affect the visibility of detail | -Image contrast -optical density |
| What is Quantum Mottle? How does it appear on the image? | The random nature by which x-rays interact with the IR. Image produced with few x-rays has high quantum mottle, image produced with low number x-rays has low quantum mottle. |
| What is Quantum Mottle? How does it appear on the image? continued... | Less quantum mottle produces smoother x-rays, more produces less smooth x-rays. Quantum mottle caused by low mAs. To fix higher mAs, low kVp. |
| How can you minimize quantum mottle? | Use of high mAs, low kVp, and slower image receptor |
| What is contrast resolution? | The ability to distinguish between many shades of gray from black to white (visibility of detail) |
| What factors affect contrast resolution? | -Dynamic Range: number of gray shades imaging system can produce -Postprocessing: Allows visualization of all shades of gray -Signal-to-noise ratio (image noise): limits contrast resolution. |
| How does speed affect detail? | faster speed=more noise, less detail slower speed = less noise, more detail |
| If the speed of the image receptor is doubled, what will you do to maintain the density? | mAs must be halved |
| What is sensitometry? | Study of relationship between intensity of exposure and the blackness (density) on a radiograph |
| When creating a sensitometric curve what is plotted on the X-axis and on the Y-axis? | -Log relative exposure on x-axis -optical density (OD) on y-axis. |
| What are the three parts of a characteristic curve? | -Toe -Straight line portion -Shoulder |
| What part of the characteristic curve represents optimum contrast? | straight-line portion (steeper slope higher contrast) |
| What part of the characteristic curve represent over exposure? | The shoulder Dmax |
| What part of the characteristic curve represent under exposure? | The Toe Dmin |
| Density can be measured using a | densitometer |
| What is the formula for calculating optical density? | Optical Density = log(L_0/L_t ) where L0 = Level of light incident and Lt = Level of light transmitted |
| If 36000 light beams strike on a radiographic film and 36 light beams pass through it, what is its optical density? | log(L_0/L_t ) , log(36000/36) = 3 |
| What is the diagnostically useful density range for a radiographic image? | OD range 0.25-2.5 |
| What is the range of base plus fog density? | 0.1-0.3 OD |
| Radiographic contrast is the product of | IR contrast and Subject contrast. |
| Film contrast is related to the | range of optical density (slope) of the straight-line portion part of the characteristic curve. |
| If two characteristic curves are given to you, how will you identify the one that is faster? | The one positioned closer to y-axis is faster |
| If two characteristic curves are given to you, how would you identify the one that has more contrast? | The curve with the steeper slope has a higher contrast |
| If two characteristic curves are given to you, how will you identify the one that has narrow latitude? | Latitude range of exposures over which IR responds with OD in useful range. Wider latitude has a wider range of exposures. Graph with narrow latitude has short gray-scale (steep slope) |
| If two characteristic curves are given to you, how will you identify the one that has short scale contrast? | Short scale contrast corresponds to steeper slope, narrow latitude |
| If two characteristic curves are given to you, how will you identify the one that has long scale contrast? | Long-scale contrast corresponds to less slope, wider latitude |
| If two characteristic curves are given to you, how will you identify the one that has less latitude? | One with less latitude will have more narrow range of exposures corresponding to straight line portion (useful OD in 0.25-2.5) |
| Latitude and contrast are _______ proportional | Inversely |
| What are the three Principal Geometric factors that affect radiographic quality? | Magnification, Distortion, and Focal-spot blur |
| What are the two formulas that can be used to calculate the Magnification Factor (MF)? | • MF = Image Size/Object Size • MF = SID/SOD • Image Size/Object Size = SID/SOD |
| What are the factors that affect magnification? | SID and OID |
| How can you minimize magnification? | Large SID, Small OID |
| What is shape distortion? | Unequal magnification of different portions of the same object |
| What are the factors that affect distortion? | Object thickness, object position, and the shape of the object |
| . Which object will be distorted the most? (Thicker object/thinner object)? | thicker |
| Which object will be distorted the most? (Object in the path of the CR/object away from the CR) | object away from CR |
| If the image of an object is smaller than the object, the image is said to be | foreshortened |
| If the image of an object is longer than the object, the image is said to be | elongated |
| What is spatial distortion? | Misrepresentation in image of actual spatial relationships among objects. Occurs when multiple objects positioned at various OIDs |
| Focal spot blur is (small or large) on the anode side and (large or small) on the cathode side of the image. | small (anode side) Large (cathode side) |
| Name the six factors that affect subject contrast? | -Patient thickness, - tissue mass density, - effective atomic number of tissues being examined, -object shape, -kvp, -motion blur (movement of patient) |
| _______is the most important influence on subject contrast | Kvp |
| Low kVp produces______ -scale contrast | short |
| High kVp produces______-scale contrast (Short scale or long scale) | long |
| Low kVp produces______ contrast (High or low) | high |
| Motion blur will be more visible when using_____ SID (long or short?) | short (Large SID less motion blur ) |
| Motion blur will be more visible when using______ OID (long or short?) | large (Small OID reduces motion blur) |
| As the speed of the image receptor increases, radiographic noise___________ (Increased or decreased) and spatial resolution is _________. (Increased or decreased) | increased (radiographic noise) decreased (spatial resolution) |
| How can you reduce focal spot blur? | -Small effective focal spot, long SID, and short OID reduce focal spot blur. *Large effective focal spot, short SID, Long OID create focal spot blur. |
| Define density: | Overall blackening of an image due to exposure of the silver in the emulsion |
| What are the factors that affect density? | mAs |
| Define contrast | kVp, shades of gray. IR contrast x subject contrast = radiographic contrast |
| What are the factors that affect contrast? | • OID • Grids • Collimation • Filtration • patient size • kVp |
| What is contrast resolution? | -Visibility of detail Ability to distinguish anatomical structures of similar subject contrast |
| What are the factors that affect contrast resolution ? | Compression (improves spatial resolution and patient dose as well), kVp, filtration |
| What is spatial resolution? | Ability to image small objects that have high subject contrast |
| What are the factors that affect spatial resolution? | Motion blur, geometric blur, and screen blur |
| Define noise | random fluctuation in OD of the image |
| How can you reduce noise? | Reduce quantum mottle by using high mAs, low kVp, and a slower IR. |
| How kVp affect radiation dose to the patient? | Higher kVp = greater radiation dose to patient |
| How kVp affect contrast on an image? | Higher kVp = lower contrast, lower kVp = greater contrast |
| What is the relation between the scale of contrast and latitude? | Wider latitude = less contrast (longer gray-scale), narrower latitude = greater contrast (shorter gray-scale) |
| What causes foreshortening and how can you reduce it? | Reduce angle of inclination of part from IR. Place part to central part of beam (lateral deviation from central axis increases foreshortening) |
| What is the primary factor that control optical density? | mAs |
| What are the factors that affect detail? | Spatial resolution = detail |
Created by:
daniel.velazco004