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RT 111 Test review

ch 14,16,17,18

Radiographers can produce patterns that help radiologist make a ________ Diagnosis
What catches light, transforms it to nervous signial, trasmits it to brain for processing? Human Eye (Anatomic design mechanics)
What part of the eye gathers and focuses light? Aqueous humor,cornea,iris,and the lens
What are the retnia cells that transforms light to nervous signals? Rods and Cones
What nerves trasnmit nervous signal to the brain? Optic nerve
What is corneal malformations due to incoming light not properly focusing on the retnia? Visual correction
What is myopia, hyperopia, and presbyopia? Nearsidedness, Farsidedness, Old eyes
What can affect what or how we see things? Mental perception
What are primarily located within the fovea centralis? Cones
What covers the rest of the retina? Rods
What emit neurologic impulses when stimulated by light? Rods and Cones
What is photopic vision? Daylight vision and color vision CONES
How many light photons do you need to emit a neurologic impulse? >100
Cones are MOST sensitive to what color light? yellow
High concentration of cones at fovea centralis results in what daylight vision? sharp
Cones improve what kind of perception? contrast in an x-ray
Cones detect changes in what? brightness
What is scotopic vision? Night vision, dim light, RODS
How many light photons does it take to generate neurologic impulse? 15
What is bleached out by high light levels? Rhodipsin
Rods are MOST sensitive to what color light? green (cannot preceive colors in low light)
How are dim objects best viewed? peripherally
What is visual phenomenon associated with viewing extremely small objects? Threshold detection
Threshold detection is dependent on resolving power of what? total imaging system (MUST minimize noise(ie. fog, scatter,etc.) to increase detection)
When the visual system has difficulty perceiving contrast defferences that are distant from ea other its called what? boundry effect
What % of difference is needed for objects that are close together for the boundry effect? 2%
What % of difference is needed for objects that are far apart for the boundry effect >20%
What changes should be 25-33% to be visual to the eye? Density
Percepual illusions that occur when the eye perecieves a boundry is what? Mach effect
What kind of difference is in a long boundry that might not beable to see in a sm boundry? Suttle
What compresses the density scale and makes the boundry more distinct? Edge enhancement
On a step wedge, the step appears lighter the closer you get to what? The next darker step
Moving the eyes while viewing an image improves what? Contrast perception
What cells of the retina reach a saturation point quickly? Photosensitive
Moving the eyes minimizes what? optical saturation
When intense light from the view box hits the eye directly its called what? veil glare
What happens in veil glare? decrease contrast perception
With viewing distance, what varies? Intensity
With viewing distance, what changes? results
Hystological, pathological, anatomical, and physiological are all apart of what? Pattern Recognition
Comparing mental images of patterns is known as what? Pattern Recognition
What is the radiographers challange? Controlling image in space
Visualizing the object of intrest floating within the body is the start of what? Controlling image in space
Art & skill does what to an object? manipulate
What are the 3 things you need to know about the structures to think 3D? Location, shape, relationship to one another
What is a single x-ray missing? Depth
How many 90 degree views do you need to perceive depth in radiography? two
Anterior to posterior, Medial to lateral, and superior to inferior are what kind of views? Dimensional views
The thicker the body part, what increases? photons or attenuation
The reduction in x-ray photons remaining in the beam after passing through a given thickness of materials is called what? Attenuation
Cutting the beam intensity in 1/2 is called what? Half value layer
what are the 4 major substances that account for variable attenuation? Air, fat, muscle, bone
The # 1 substance is what? bone
Results in increase area of exposure on the IR is due to what? Air
Air has what for tissue density? low
What on the film least attenuates the beam? Black
What substance tissue density is less than muscle? Fat
Slightly hgher atomic # and tissue density than fat is what substance? muscle
What is the atomic # for air? 7.78
What is the high atomic # of element found in the body? calcium
what substance has the greatest tissue density? bone
Bones do what to the IR? decrease area of exposure
The IR exposure will be altered by changes in amount or type of tissue being irradiated, is known as what? subject density
How are subject density and film density related? Inversely related
The degree of differential absorption resulting from differing absorption characteristics of tissues of the body is known as what? Subject contrast
What does subject contrast show? different shades of gray
During subject detail, what are teh 3 recorded details that the structures are dependent on? Position, Body placement to IR, and size of the part
Unless the paitent is positioned specifically to demonstrate a particular structure, it may not be accurately represented on the IR is know as what? Subject distortion
Subject distortion is misrepensentation of what 3 things? lenght, width, and shape
What improves radiographic contrast in the image that absorbs scattered readiation before it reaches the IR? grid
What is responsible for the dark area on the image? Transmission
what is responsible for the light areas on the image? Absorption
What reates fog and lowers contrast on the film? scatter
When do you use a grid? Part thickness is >10cm OR kVp >60
Grids are made up of what? Radiopaque lead strips and radiolucent interspace material (alum)
Who created crosshatched grids? Dr.Gustav Bucky
what allows primaryradiation to reach the IR and absorbs most scatteered radiation? grids
what is the primary disadvantage of grid use? grids lines on film
who gave improvements to the grid? Dr. hollies potter
what are the grid dimensions? h,D
What is the tipical ration range for grids? 5:1 to 16:1
what is the grid ratio formula? h/D
what is more efficent in removing scatter? higher grid ratio
The # of lead strips per inch or cm is called what? Grid frequency
what is the grid frequency range? 60-200 lines /in OR 25-80 lines/cm
when are very high fequency grids used? digital imaging systems
what is the most important factor in grids efficiency? lead content
Lead content is measured in what? g/cm2
when is lead content greater in a grid? High ratio low frequency
what kind of grid has horizontal and vertical lead strips? criss-cross or cross hatched
the primary beam must be centered how to the grid? perpendicular
what kind of grid has lead strips that run the length of the cassette and allows the primary beam to be angled along the long axis of the grid without obtaining "cut-off"? Linear grid
In a focused linear grid, how are the lead strips angled? to match divergence of the beam
Scatter is absorbed by lead strips in a focused linear grid, where will the primary beam align? interspace material
with focused linear grids, improper centering that results in peripheral cut-off and is only useful at preset SID distance with a higher ratio grids that require careful alignment with the tube is known as what? narrow positioning lattitude
grid use monts ______________ grid above the cassette 17x19
what are two types of grid movement? reciprocating and oscillating
motor drives grid back and forth during exposure is known as what type of grid movement? reciprocating
Electromagnet pulls grid to one side and releases it during exposure is known as what kind of grid movement? Oscillating
what is the grid conversion factor? GCF = mAs with grid / mAs without a grid
what are the two criteria that is evaluated diring the grid performance evaluation? selectivity and contrast improvement ability
highly selective grids are better at removing scattered radiation and high lead content grids are more selective during what evaluation? selectivity
What uses the "K" factor and compares radiographic contrast of an image with a grid to radiographic contrast of an image with out a grid? contrast improvement ability
off-level, off-center, off-focus, upside-down, moire effect are all examples of what? grid errors
what technique is used as an alterative to a grid? Air gap technique
10" air gap has a similar clean up of what grid ratio? 15:1
high frequency grids can prevent this phenomenon? moire effect
What effect iswhen grid lines are paralle to scan lines in a digital system? moire effect
Created by: Amison86