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RT 111 Test review
ch 14,16,17,18
| Question | Answer |
|---|---|
| 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
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