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Science 9&10 test

12 13 14 15

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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