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Science 9&10 test
12 13 14 15
| Question | Answer |
|---|---|
| Factors that contribute to the quality of the X-ray image P93 | Visibility and Sharpness (how accurately lines are recorded) |
| Difference between high/low contrast, and long scale/short scale contrast | High-variation in tissue/chest (bones and soft tissue) Low-little variation in tissue/abdomen (soft tissue) |
| What is subject contrast and what contributes to it ? | Softer tissues have poor absorption properties. Hard to visualize w/o contrast media. When tissue is very soft like this we can say that it has very poor subject contrast |
| Distortion is what? 2 types are what? | Misrepresentation of size or shape. Size distortion (magnification) increase in image size Shape distortion (elongation +foreshortening) |
| What is a resolution test pattern for? | Measures & Records line Pairs Per Millimeter. |
| Line pairs per milliliter | Greater number of line pairs per millimeter, the greater the resolution |
| Define resolution | The ability of the system to distinguish between two adjacent structures. Detail capability. |
| What is spatial resolution? | Recorded detal. Refers to the the smallest object that can be detected in an image. Refers to the number of pixels utilized in construction of the image. |
| Shape distortion vs size distortion | Some size distortion with OID and SID. Shape distortion is elongation or foreshortening of the anatomy. |
| How does oid and Sid effect magnification ? | As SID increases, magnification decreases. As OID decreases, magnification increases. |
| How does shape distortion occur and how is it corrected? | CR placement, Tube placement, IR placement |
| What is an artifact? | any unwanted image in the x-ray. +/- density |
| What is Quantum noise and how to correct it | Photon Dependent. Visible as brightness or density fluctuations. Means fewer photons reaching the IR to form the image. |
| A Pixel is | individual Picture elements within the recorded Matrix. Recorded as a single numerical value, that's represented as a single brightness level on a display monitor. |
| Bit depth is | Number of bits in each pixel. More depth = more shades of grey 8 bits = byte, 2 bytes =word |
| Fov field of view is what | Given area. 1024x1024 2048x2048 |
| Matrix is what | How a digital image is recorded. A combination of rows and columns, small, usually square "picture elements" (pixels) |
| Dynamic range in relation to Digital imaging | Optical densities range .05 - 2 OD. Range of exposure intensities an IR can detect. |
| Where is a foreign body? | X-rays can detect radio-opaque foreign bodies such as glass and metal |
| Contrast resolution | more shades of gray |
| Window width and level (high/low) | Window Width adjusts contrast Window Level sharpness of contrast. |
| Pixel pitch is what? | The pixel spacing or distance measured from the center of a pixel to an adjacent pixel (effects spatial resolution) |
| What is grey scale | the number of different shades of gray that can be stored and displayed by a computer system |
| How to fix Quantum Noise ? | Increase number of photos reaching the the IR. mottle/noise. |
| What is the 15% rule and how is it used? | A 15% increase in KVP has the same effect as doubling the mAs. A 15% decrease in KVP has the same effect as decreasing the mAs by half. |
| Several questions about the 15% rule | |
| KV - other terms that mean the same thing are: | energy, penetrating power, quality, potential difference |
| Inverse square law | Relationship btwn distance and x-ray beam intensity. The intensity of the x-ray is inversely proportional to the square of the distance from the source. |
| Connection between Kv & scatter, and contrast | Higher kVp reduces # of interactions, increases # of x-rays transmitted. Then more compton scattering than x-ray occurs (PE Effect) and more scatter exits the patient. As a result images with lower contrast are produced. |
| How does sid effect beam intensity | As SID increases, the x-ray intensity is spread over a larger area. This decreases the overall intensity of the x-ray reaching the IR. |
| How does Sid and oid effect magnification | A long SID creates less magnification than a short SID. Increasing OID increases magnification and decreases spatial resolution. Decreasing the OID decreases magnification and increases spatial resolution. |
| How does Sid and oid effect record of detail? | OID, SID and focal spot size all affect the angle of the x-ray beam, which affects recorded detail/spatial resolution. The longer the SID, the more of the central part of the x-ray beam is used. The more angled x rays are absorbed by the collimator |
| What is SOD | Source to Object |
| What’s the magnification formula? | SOD=SID (72in) - OID (3in) =69 MF = SID (72in) / 69in MF = 1.044 |
| What’s a grid and what’s it used for? | The use of grids can improve image quality and diagnosis in chest X-rays. ... As radiographers, we know that the whole purpose of using grids in radiography is to reduce scatter radiation, thereby increasing radiographic contrast. |
| Know body habitus' | Hyper- Large 5% Sthenic-Average person. (50%) Hypo-smaller 35% Asthenic. Extremely tiny. 10% "normal" is sthenic or hyposthenic |
| What’s a compensating filter and how is it used? | A filter (usually aluminum, usually wedge-shaped) in front of the collimator to (reduce) a portion of the primary beam so as to compensate for varying body part thicknesses in the same field of view. INcreases exposure to PT. More uniform exposure to IR. |
| Single phase vs a 3 phase generator | Single-phase gens produce 1 voltage that alternates continuously. 3 phase generators produce 3 separate waves of AC power that operate in sequence = continuous flow of energy & that the power level never dips as it does with single-phase generators. |
| How does using a grid effect the technique you use? | Thus, using grids with higher ratios and higher frequencies cleans up more scatter radiation, which increases contrast more than low-ratio and low-frequency grids. |
| Decreasing collimation means what? | collimation means decreasing the size of the projected field, so increasing collimation means coning in/decreasing field size, and decreasing collimation means increasing field size/opening up |
| When do you use a grid? | body part thickness is over 10 cm kVp is above 60 - because scatter becomes enough of an issue to degrade the image |
| How does high KV effect absorption? | Reduces absorption. The amount of radiation delivered to a patient's body must be increased to compensate for the radiation absorbed by the grid. more power decreases attenuation. Increases transmission. |
| Know the relationship between grid ratio and scatter absorption | The grid ratio is a measure of the height of the lead strip to the interspace distance, and is a good measure of the selectivity of primary to scatter transmission. |
| Difference between long scale/short scale contrast | Short Scale Contrast - Black and white Long Scale Contrast - lots of grey to black |
| Photographic quality effected by... | Patient Technique Collimation Grids |
| Digital characteristics | brightness, contrast, spacial resolution, noise |
| x-ray density | overall blackness |
| Optical density/densitometer | measures blackness |
| a quality x ray must include | all the above; Accuracy, Minimal Unsharpness, Visibility |
| Visibility factors include | brightness/density, contrast |
| Image with increased brightness will have | decreased density on film |
| Increasing quantity of radiation (mA) | increase density |
| Tissues that attenuate x ray beam equally have | low contrast |
| System that can handle 10 lp/mm instead of 6 has | improved sharpness |
| Unwanted exposure to IR will increase | fog |
| Range of exposure intensites an IR can detect is | dynamic range |
| FOV | Large Matrix size will have more pixels |
| grayscale range depends on | pixel bit depth |
| contrast can be lowered by increasing | window LEVEL (lower level) |
| IR exposed to excessive ratioation would result in | increased pt exposure |
| amount of light transmitted is | optical density |
| dignostic densities should fall within which region of curve | straight line |
| High contrast film would have | steep and narrow slope |
| for Every Change in Part thickness of 4-5 CM | adjust mA by 2 |
| Changing KV by 15% has the same effect as changing mA | by a factor of 2 |
| High KvP | low contrast |
| low kvp | High contrast |
| Smaller focal spot | increases spatial resolution |
| Generators with more efficient output require lower exposure technique | 3 phase more efficient |
| mAs and exposure reaching IR | direct relationship |
| mA and time | inverse proportional relationship |
| Increasing mA has NO effect on | brightness |
| change in kVp will affect | density, compton, contrast |
| what has same effect as doubling mAs? | increasing kVp by 15% |
| what does not effect spacial resolution? | Grid |
| The amount of remnant radiation will decrease when increasing | tissue thickness |
| Image using 70kVP 15 mAs at 40 sid. If at 30 SID, what would be adjusted? | 70 @8.4 |
| What effects intensity, scatter to IR, magnification and spatial resolution? | OID |
| A diagnostic range is created using 80@10 and grid of 12:1. what if grid is removed? | 80@2 |
| what is magnification factor when using 72 sid and 1.5 in OID | 1.021 |
| How is the primary beam affected when increasing tube filtration? | increase # of higher energy x-rays |
| Single gen | less mass |
| Under 6 decrease kVp by 15% | due to bone mass reduced |
Created by:
carey7059
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