west test 4 chap 15

what two types of xrays are responsible for the radiographic image

those that pass through the patient without interaction and those that are compton scattered within the patient and come out of patient

image forming xrays

these are x rays that exit the patient(also called remnant xrays) and interact with the ir

off focus radiation

happens when projectile estray and interact at positions on the anode other than the focal spot, they also increase image blur

what is the primary effect of collimation

it reduces patient radiation dose by restricting the volume of tissue irradiated and it improves image contrast

as scatter radiation increases

the rad image loses contrast and becomes more gray and dull

whats special about the variable-aperture collimation

its the most commonly used beam restricting device in radiography

first stage entrance collimation

it controlls off focus radiation, its made of PB(lead), and the shutter blades protrude from the top of the collimator into the x ray tube

second stage collimation

its made of PB(lead), 3 mm thick and has long and cross blades

what are light localizing collimators

positive beam limiting devices that automatically size the collimated beam to size of the ir

characteristics of a positive beam limiting device

they have small lamp and mirror, their projected light field coincides with the x ray beam, and under no circumstances do their light fields exceed the size of the image receptor

scatter radiation

every radiographic procedure apart from mammography, produce scatter radiation if there is interaction of photons with soft tissue

what causes fog

the detection of scattered photons, it also does not add info to the content in the image

what percentage of xrays incident on the patient reach the ir

1%

what 3 factors contribute to increased scatter radiation

increased kvp, increased field size, increased patient thickness

what are the 3 types of beam restricting devices

aperture diaphragm, cones or cylinders, collimators

more scatter is produced for

thick body parts, high kv levels, and large collimated areas

grids ____ have anything to do with the production of scatter radiation

do not

scatter clean up

use of grid, and air gap technique

when using a grid or air gap technique what happens to patient dose

the radiation dose increases

grids are used ____ scatter has been produced

after

as kv increases, compton interactions_____, and photoelectric effect ____

increases, decreases

what is the techs dose

compton scatter

what is the patients dose

Photoelectric(PE)

when the kvp goes up what happens

patient dose goes down, more scatter is produced, and reduced contrast

whats the percentage of xrays that reach the image receptor

1%

brems and k- characteristics are interactions between

electrons and the anode target when x rays are produced

classical, photoelectric, and compton scatter are interactions between

xrays and matter(body)

interactions between electrons and the anode create what type of radiation

bremsstrahlung and k-characteristic radiation

what makes or breaks the type of interaction

kv level

the curve on the xray emmision graph represents what

brems

what represents the spike

characteristic

what causes brem specifically

incident electrons deflecting with resulting energy loss and when electrons approach a nuclear charge and causes change in direction and loss of energy, essentially causing the first stated thing

what causes characteristic radiation specifically

incident electrons ejecting an inner shell tungsten electron, an orbital electron moving to fill in the space of an inner shell, or transitions of electrons from outer to inner shells

the two major interactions that occur when xrays strike the body that are categorized as ionization events are

photoelectric effect and compton scattering

photoelectric effects are responsible for what

contrast and the total amount of incident radiation absorbed

compton scattering is responsible for what

scatter radiation and incident radiation being partially absorbed

a third form of interaction is called classical and its a

excitation event that only occurs 5% of the time but does NOT cause ionization

PIICT- P meaning

Photoelectric

PIICT- I meaning

inner shell electron interaction with an x ray photon

PIICT- I meaning

ionization event

PIICT- C meaning

contrast

PIICT-T meaning

totally absorbed

As PE goes up, KV goes__, and Z# goes ___

down, up

CLOIPS- C

compton

CLOIPS-L

loosely bound electron

CLOIPS-O

outer shell electron

CLOIPS-I

ionization event

CLOIPS-P

partial absorption of incident photon

CLOIPS-S

scatter producer

what does bremsstrahlung mean

breaking radiation/slowing

What is Bremsstrahlung radiation?

incident electrons that are deflected with energy loss

when the xray beam field size is increased what happens to scatter

it increases

patient does goes down what happens to spatial resolution

goes up

what is the most common light localizing device

variable- aperture collimator

as the fov goes down, what happens to scatter

goes down

when collimation goes up

scatter goes down

are there any circumstances where the xray beam should exceed the size of the ir

no

cylindar cones

they are metal cylinders that attach to the bottom of the collimator and are used to tightly restrict the beam to a small circle

when making a large collimation field small

you need to increase mass

when making a small field large you need to decrease mass

when going from 14x17 to 10x12

increase mass 20%

when going to 8x10

increase mass 30%

when going to 5x7

increase mass 50 percent

what is the aperture diaphram

its a flat piece of lead with a circle or square opening in the middle that is placed really close to the xray tube window, and it has no moving parts

how does the grid(antiscatter grid) work

it is placed between the patient and ir and uses geometry to reduce the amount of scatter radiation that would reach the ir

when using a grid what happens to techniques

techniques need to go up which inturn increases patient dose

are grids radiation protection devices

no

what are grids for

they are devices that improve radiographic film quality by increasing contrast

when should a grid be used

when patient body part thickness is greater then 10cm or when kvp is above 60

what is a antiscatter grid

its essentially a regular grid that uses a series of slits that separate highly attenuated septa which are made of lead, in order to absorb scatter from primary x rays

what is a grid ratio

its the ratio of the height to width of the interspaces in the grid

what are the 3 grid designs

parallel, crossed, and focused

what are parallel grid designs

they are the simplest type of grid, essentially all the lead strips are parallel

what are crossed grid designs

they are parallel grid designs that run across each other and they clean up better then parallel

what are focused grid designs

they are essentally parallel grid strips that angle towards the center

focal length

determines the amount of slant of the slits in the grid

grid frequency

refers to the number of gird bars per unit length.

what is the bucky factor

it is the ratio of the entrance exposure to the patient when the grid is used to the entrance exposure without the grid

what is the formula for the bucky factor

B=patient dose with grid over patient dose without grid

what happens when the contrast improvement factor goes up

grid ratio goes up

what is the greek symbol for selectivity

its sigma(sideways m)

what is sigma primarily influenced by

the total lead content in the grid

what is grid cutoff

the undesirable absorption of primary xrays

its the _____ disadvantage of parallel and crossed grids

main

linear 5:1 and 6:1 grids have a

very wide positioning latitude

linear 16:1 have

narrow positioning latitudes

when patient dose goes up

grid ratios go up

high grid ratios are usually used for

high kvp examinations

patient dose at high kvp is

less than that of low kvp

air gap technique is an alternative to

using a grid

for every additional cm of air gap increase mas by

10%

at 10-15 cm, we see a visible change in

oid

the main disadvantage of using an air gap technique is

the possible image magnification with focal spot blue

what is air gap technique most commonly used for

chest radiography and cerebral angiography

when was the virtual grid introduced

fuji in 2014

what is a virtual grid

digitally reconstructed radiography

how does it work

computer algorithms take out most of the scatter produced

what happens when you use a virtual grid

reduces patient dose, improves image contrast, and its easier to use than grids

as patient thickness goes up

compton scatter goes up

what improves spatial and contrast resolutions while also lowering patient dose

compressing anatomy