Physics Ch 14,16,17 Flashcards
Location of the rod and cone cells
Cones- fovea centralis
Rods- remainder of retina
Which cells control photopic (daylight) vision
Cone cells
Which cells require relatively bright light to function
Cone cells
Which cells are sensitive to yellow light
Cone cells
What cells have a higher visual acuity?
Cone cells
What cells control scotopic (night) vision
Rods
What cells are sensitive to low light levels
Rods
Humans are unable to perceive colors in extremely low-light situations because of this
Rod cells are more sensitive to green light
Glare
When bright light causes temporary blindness in both humans and animals
Where does human image conversion occur?
In the rod and cone cells
What parts of the eye gathers and focuses light?
Lens
Iris
Cornea
Aqueous humor
LICA
What part of the eye converts images to nervous impulses?
Fovea centralis. Special cells of the retina
What part of the eye transmits impulses to the brain?
Optic nerve
What is the primary job of Rod and cone cells of the eye?
Image conversion ( in the retina)
Which cells in the eye are sensitive to yellow light?
Cones
What causes colorblindness?
A lack of cones sensitive to a particular color or colors
Most cones are located in the ______ ________in high concentration
Fovea centralis
Cones can detect changes in brightness which is also known as__________.
Contrast perception
Rods are sensitive to as little as ______photons
15
Rod cells function by photosensitization of ____________
Rhodopsin
Attenuation
Reduction in the total number of X Ray photons remaining in the beam after passing through a given thickness of material (patient).
Remnant beam (exit beam)
- The beam that comes out of the patient
- less intense than the entrance beam
- contains radiologically significant info needed by radiologist to make diagnosis
When the patients thickness is increased the attenuation and exposure factors (increases/decreases)
Increases
X rays are attenuated exponentially, what does that mean?
- reduced by a certain percentage for each given thickness of material they pass through
- never reaches 0, each succeeding thickness of material reduces the # of photons by only a fraction of the previous amount.
When the patients thickness is increased the attenuation and exposure factors (increases/decreases)
Increases
high-atomic number materials attenuate (greater/lower) percentage of the beam then low-atomic number materials
Greater
Attenuation
Reduction in the total number of X Ray photons remaining in the beam after passing through a given thickness of material (patient).
Remnant beam (exit beam)
- The beam that comes out of the patient
- less intense than the entrance beam
- contains radiologically significant info needed by radiologist to make diagnosis
When the patients thickness is increased the attenuation and exposure factors (increases/decreases)
Increases
high-atomic number materials attenuate (greater/lower) percentage of the beam than low-atomic number materials
Greater
Higher atomic numbers have an (increase/decrease) in attenuation
Increase ( like bone + contrast agents)
Bone produces (less/more) image receptor exposure
Less
Density
- The quantity of matter per unit of volume measured in kilograms per cubic meter.
- how tightly the atoms of a given substance are packed together
When density is increased, like with bone, attenuation is (greater/less) then other substances, such as lung tissue
Greater
What is the greatest variable the radiographer faces when performing a radiographic procedure?
The human body and its tissues
What does the body primarily consist of (at the atomic level) ?
Hydrogen, carbon, nitrogen, and oxygen
Three different ways patients affect attenuation of image
- patient thickness
- tissue density
- atomic number
How does air appear on a radiograph, why?
Black. Air has significantly lower tissue density, so it absorbs fewer photons as they pass meaning more reach the IR.
Where is air naturally present?
Lungs, sinuses, small amount in the GI tract and on an ABD X-Ray it’s seen in the stomach and colon
How does fat appear on an image
Looks grey (perirenal fat capsule around the kidneys allows us to pick them out on an image)
How does muscle appear on a radiograph?
Less grey than fat (psoas muscles on abdomen)
What is a greater attenuater of the beam (fat/muscle)?
Muscle
How does bone appear on a radiograph, why
- White
- Ca has a higher atomic #, and bone has a high density.
- therefore, bone absorbs the beam and there is less exposure to IR
There are no rods in the______ ________.
Fovea centralis
A visual phenomenon involving the perception of extremely small or faint detail is _______ ________.
Threshold detection
Minimizing background exposure and other artifacts such as visual noise….helps with ________
Threshold detection
Why does the boundary effect occur?
Because the visual system has trouble perceiving contrast differences that are distant from each other
The ________ ________occurs when the eye perceives a boundary. Each time there is a change in exposure, there is also a change intensity of impulses sent to the brain
Mach effect
_________ __________ compresses the entire grayscale while making the boundary appear more distinct than it really is
Edge enhancement
Contrast perception is greatly increased when a ________motion is used.
Scanning
Because photosensitive cells in the eye can integrate a limited amount of information, eye movement avoids _________of the optical nerves.
Saturation
In simple terms, define veil glare.
Brightlight scatters inside the eye and decreases contrast perception. (occurs when an intense bright light floods the eye directly)
The fovea centralis creates a blind spot at a viewing distance of _________
9 inches
Pattern recognition involves comparing…..____________
Mental images of patterns
What is the true domain of the radiologists medical knowledge and competence?
Pattern recognition
True or false?
Radiological positioning requires knowledge about shape and location of skeletal and soft tissue structures and an in depth understanding of their anatomical relationship
True
How do radiological technologist achieve a 3-D view
By taking two images as close to 90° to one another as possible
What are the dimensional views required for all exams?
Anterior to posterior, medial to lateral, superior to inferior
Define attenuation;
Reduction of the total number of x-ray photons after passing through a given thickness
The results of x-rays interacting with matter and being absorbed or scattered
Attenuation
X-rays are attenuated exponentially, meaning….
They are reduced by a certain percent for each given thickness
The __________ beam is altered as it passes through the patient
Incident
What type of beam exits the patient and goes to the IR?
The remnant beam
How tightly the Atoms of a given substance are packed together
Density
What is the greatest variable the radiographer faces when performing a radiographic procedure
The patient
At the atomic level, the body consists primarily of
______,_______,_______,_____.
Hydrogen, carbon, nitrogen, and oxygen
What is the atomic number of calcium which is found in bones and teeth?
20
What 4 major substances account for most of the variations and x-ray absorption in the body?
Air, fat, muscle and bone
Which has a higher effective atomic number and greater tissue density? Fat or muscle
Muscle
What 4 properties does the patient have an impact on when it comes to radiographic quality?
Density/image receptor exposure, contrast, recorded detail and distortion
Subject contrast is…
The difference of densities on an image
Subject density is….
The impact the patient has on the radiographic density/image receptor exposure
Greater sharpness will result when the anatomical part is _________ to the image receptor
Closer
