Quizlet from girl

physics

Scatter is produced during a __________ interaction

compton

Not part of the useful beam and has NO redeeming qualities

scatter

factors that affect scatter

kVp and irradiated material

Image quality is improved when the amount of scatter reaching the IR is __________

reduced

collimator shutters thickness?

1-2 mm in lead

purpose of collimator shutters

reduce # of photons thatll exit and cause secondary radiation

would you collimate more or less on a thicker patient?

upper shutters of collimator purpose

attenuate extra focal radiation

lower shutters move

transversely

what is "cropping"?

called post processing, editing the image afterwards; increases exposure, collimate before

best method to reduce overall patient dose

beam restriction

types of restriction devices

collimator(most effective), automatic collimation, cone/cylinders, aperture diaphragm

collimator mirror is _______ and it is considered _________ filtration

fixed; added

automatic collimation and what is PBL?

HEW (act of 1974); cannot open wider than field size
PBL: positive beam limitation

purpose of cone/cylinders

limits size of radiation field

extension cylinders

more affective attenuating extra focal/off focus radiation than a collimator

aperture diaphragm

Flat sheet of metal, usually lead with a hole cut in the center and attached to the x-ray tube port (least affective)

why use beam restriction?

reduce patient exposure
to produce a clear image with better contrast

increasing collimation, ____________ size of radiation field

decreases

_________ wavelength = increased energy and frequency

short

________ wavelength= decreased energy and frequency

long

as beam restriction increases, field size

decreases

as part thickness increases, volume ____________, and scatter ______________.

increases; increases

as attenuation increases, part thickness ____________, and HVL ____________

increases, increases

0.3 LGM represents a _____ change in IR exposure

2x

true or false; mAs will NOT negatively influence scatter production

true

Why is more scatter created in bone than in soft tissue?

high atomic numbers make photons have a greater chance of striking an electron and interacting with these materials

Grid is useful when.....

patient thickness is > 10cm
Over 70-80 kVp

function of the grid

remove scatter and secondary radiation from reaching the IR and to improve contrast

description of grid

strips of lead (Pb) separated by interspace material (lead totally attenuates x-rays)

true or false; a grid does NOT prevent scatter radiation; it decreases scatter from reaching the IR

true

does adding a grid to image production increase mAs?

yes

Grid ratio formula

strip height (h) / interspace width (d)

lines per inch formula

lines/ inch = 25.4 / D + d (D= interspace width; d=lead strip width)

contrast improvement factor (k)

Contrast obtained with a grid compared to contrast without a grid

Grid lead content

amount of Pb content within a grid measured in grams

to increase lead lines per inch, ___________ the thickness of lead strips or interspace material

decrease

as thickness of individual lead strips __________, a less noticeable artifact (grid lines) is produced on the finished image

decreases

What is grid cut off?

The grid blocks so many photons that you cause quantum mottle

upside-down focused grid cutoff

upside down grid, produces bilateral peripheral cutoff, exposure affected only in the center

lateral distance decentering focused grid cut off

CR is not centered but is set at proper SID, uniform loss across image

Off-level grid cutoff

grid surface is not perpendicular to CR, uniform loss across image

Distance decentering grid cutoff

CR is centered but SID is off, bilateral peripheral cutoff

lateral and focused grid distance decentering combined grid cutoff

uneven exposure across IR, underexposed under target when SID is above; underexposed on side away when SID is below

Moire grid cutoff

zebra like pattern

linear grid

all lead strips within grid are parallel

Crossed or cross-hatched grid

lead lines that run at right angles to one another

Non-focused grid

strips run parallel, fluorscopy, unlimited SID

focused grid

Grid for general-purpose use; the lead strips are aligned to the direction of the diverging primary x-ray beam.

stationary grid

high-frequency grid that does not move during the exposure (PRODUCES grid lines)

Reciprocating grid

a moving grid moving back and forth several times during x-ray exposure; attenuates 25% more scatter than stationary

Define grid ratio

the ratio of the height of the lead strips to the distance between the strips

How does an off-level grid error occur?

When the tube is angled across the long axis of the grid strips

Filtration

placing some type of absorbing material for the purpose of attenuating low energy/ low wavelength x-rays from the primary beam

true or false; filtration is NOT beneficial to the patient

False; it is beneficial and less photons are reaching them

inherent filtration (high atomic #)

filtration that is a result of the composition of the tube and housing

added filtration (aluminum mostly)

any filtration that occurs outside the tube and housing before the image receptor

glass envelope is made of

Pyrex glass

insulating oil is within tube housing and based on _________

thickness

true or false; collimator assembly is fixed and includes the mirror

true

why do we use added filtration?

if inherent is not enough; need ATLEAST 2.5 mm of filtration if kev is > 70 (fed. law)

As the xray tube filament ages, inherent filtration __________.

increases

when vaporization occurs what 3 changes happen?

1. fluency will continuously decrease
2. amplitude energy will increase (kevavg.)
3. minimum photon energy will increase (kevmin)

why use aluminum with added filtration?

attenuates the same as a human body does and produces an absorption coefficient like human soft tissue/muscle

Increasing filtration, _________ wavelength, and ___________ kev

decreases; increases

As energy (kev) increases, PE interactions may be suppressed and __________ Compton interactions

increase

_________ (increasing or decreasing) Compton interactions can cause image contrast to decrease

increasing

increasing filtration, ___________ subject contrast

decreases

Primary beam intensity decreasing, radiation output __________, and IR exposure _____________

decreases; decreases

Thickness of filtration increasing, ___________ the overall # of x-rays

decreases

INCREASING filtration thickness will _____________ IR exposure

DECREASE

wedge filter

most common type of compensating filter

trough filter

double wedge; allows visibility of both lungs and T-spine

ingot filter

used for hips

little prism filter

helps prevent IR exposure from top to bottom

bommerang filter

used for facial and nasal bones, and AC joints

Ferlic filter

used for shoulders

define HVL

the amount of absorbing material it takes to reduce the x-ray intensity to half of it's original value

When more than one filtering material is used, as in a compound filter, how are the materials arranged in relationship to the x-ray source?

Compound filters place the highest-atomic-number material closest to the tube and the lowest-atomic-number material closest to the patient.

What are the two most common compensating filters?

wedge and trough

What is total filtration?

inherent filtration + added filtration

How does filtration affect patient dose and beam intensity?

reduces the patient dose by eliminating low-energy photons from the primary x-ray beam. It also removes a portion of the useful beam, which reduces the overall beam intensity.

what is subject contrast?

The degree of differential absorption resulting from the differing absorption characteristics of the tissues in the body

factors influencing subject contrast (influence whether or not an interaction will occur)

tissue type
density
thickness
atomic number (Z)
tissue pathology

atomic number of adipose tissue

5.9

atomic number of muscle/water

13.8/20

binding energies of k-shell electrons
adipose tissue= ? kev
bone/calcium= ? kev

0.5 kev
4.04 kev

true or false; below 30 kvp, great different in photoelectric absorption occur between soft tissue and structures

true

least to most dense tissues in human body

air, adipose tissue, hollow organ, muscle, solid organ, bone, tooth enamel

least to most PE interactions

air, adipose tissue, hollow organ, muscle, solid organ, bone, tooth enamel

true or false; tissue thickness differences influence the likelihood for a particular interaction to occur

true, a PE or compton interaction

bone has the _________ e-/cm^3, and therefore attenuates the most radiation

greatest

Absorbed/ ______ interactions = high brightness/ white shade

PE

Scattered/ _________ interactions= intermediate brightness/ shades of grey

compton

transmission= low brightness and ________ shades

black

true or false; As kVp is increased, Compton scattered x-ray photons' angles of deflection decrease, increasing the likelihood that scattered photons reach the image receptor (IR)

true

air does not attenuate and is the color _______

black

fat attenuation is small and the color is _______

dark grey

other soft tissues attenuation is medium and the color is ______

grey