Exposures

The human eye gathers light, focuses the light, converts it to nervous impulse and transits it to the brain for processing

gathers light to nerve impulse

Transmits nerve impulses to the brain

• Aqueous humor
• Cornea
• Iris
• Lens

• daylight vision- vision is controlled by the CONES they require relatively bright light to function they can see long=yellow
• Medium= green
• Short= violet
• -good focus-good contrast perception

-night vision- vision is controlled by the RODS very sensitive to low levels and unable to see bring lights

Can not seen colors—but come best see green if any

-good peripheral vision

recognition and interpretation of what we see

• Perception of extremely small or faint detail
• Is affected by background noise
• Noise= fog(Compton scatter)
• Artifacts=jewelry

• Hard to see the difference in colors with colors are not close together
• The longer the boundary the easier to tell the difference between shades

Nerve impulse and what our brain perceives with bright light or a big change

• See a thin white strip b4 a big change in contrast
• Scanning motions can help to reduce this or when gradually change contrast

• Bright light shining out sides of view box
• Can’t judge contrast

Distance makes light diverge. It also changes blind spots. Humans have a blind spot at 9 inches. It also changes the cell so you don’t overuse a cell

Faster when techs hang radiographs correct

2 radiographs 90 degrees apart from one another

the name tells what is being superimposed

• Incedent photons and outer shell electrons
• compton interactions (high kvp)

Density increase and Contrast decrease

As kvp increase there is more comptons interactions which increase scatter and decrease contrast.

As volume increases scatter increases

• Field size
• Patient thickness

• The higher the atomic number the less scatter
• Bones. Contrast media

• Large field size= more scatter produced
• Small field size= less scatter produced

• - Aperature diaphragms
• - Cones and cylinders
• - Collimaters

• they increase penumbra
• dont decrease off focus
• dont decrease stem

• Reduce penumbra
• Reduce off focus

Senses size and orientation of the cassette

• Penumbra- fuzzy borders-reduces detail -
• Off focus- xray photons being created at tube and not at focal spot

Keep the scatter from hitting the cassette

• Kvp
• Irradiated material
• beam restrictors

Reduction in the total number of x-ray photons and the lower energy of the beam

• Absorption
• scatter

• Continue on their way
• Be absorbed
• Change direction

Exponentially

Through transmission

Thicker the patient the more attenuation

higher the atomic number the more attenuation *photoelectric absorbtion

• More dense the more the attenuation
• More tissue density the less radiographic density

• Higher the electrons the more attenuation
• Calcium-bones=more attenuation

• air
• fat
• muscle
• bone

• Air- least
• Fat-second least
• Muscle-second most
• Bone-most attenuation

• More subject density less radiograph density
• less subject density more radiograph density

Amount of differential absorption

• Chest- high subject contrast
• Mammography- low subject contrast

Age and size is what affects contrast

• How patient affects Sharpness of structure as it appears on film
• Highest detail when have the part is closest to film
• We rely on where part lies on body and where patient is to the film
• Less detail larger patients

• Misrepresentation of size and shape of structure
• Magnification-size
• Angle-sharp
• Larger the patient-less detail- more distortion – has to do with subject size

patient

• Kvp- 5- 15 %
• A place where there used to be or is supposed to be air turns into something more dense
• As additive disease gets worse radiographic density gets less (whiter)

• mAs- 25- 50 %
• a place that used to be a dense tissue turns to air or a less dense tissue
• as destructive disease gets worse radiograph density gets greater (blacker)

• good patient history
• observe patient
• clinical assessment
• luenectomy
• old exams

higher the kvp the more scatter= contrast then decrease

• Thin flat rectangular device- in contains radiopaque (absorb) lead strips sepaorated by radiolucent( pass through) space material
• Used body part greater than 10 cm
• Used when kvp higher than 60 =kvp penetrating power

• Higher the grid ratio= closer the strips = more scatter clean up= higher the contrast
• Beam has to be pretty straight

• Number of grids lines per inch
• Higher grid frequency the thinner the strips= less scatter cleanup= lower contrast

high grid ratio (close) – and less grid frequency (thick)

• linear- can angle longitudinal
• Criss cross (cross hatched)- can not angle

Parallel- all grids run up and down = will never touch Use with longer SID

• Focused-lead strips angle to match the beam Tube is supposed to be aligned to the convergence line o Have to be in the correct focal range
• Not too much room for error

Lower grid ratio makes more room for error

• Grid strips move perpendicular to the way they run
• Strips run length of bucky and table

• When use grid you have to increase mAs
• Higher the grid ratio the higher the GCF
• Higher ratio higher the mAs

• Off level- one but not the other is angled—parallel and focused
• Off center- tube is not aligned to grid -- focused
• Off focus- center good the rest bad-- focused
• Upside down- center good the rest bad -- focused