IPE exam 5 AEC, technique charts, beam restriction

AEC is programmed to terminate the _____

exposure time

AEC is also commonly referred to as

phototiming or Automatic Exposure Detection (AED)

AEC can help improve _______ of our image quality.

consistency

what device may be used to ensure consistency of radiographic quality from one exposure to the next?

Automatic Exposure Control (AEC)

what is a radiation detection device that measures the ionization of air in a gas-filled chamber?

ionization chamber

which cell of the ionization chambers has the most influence on the overall exposure when more then one is activated?

the cell receiving the most radiation

When a predetermined level of ionization is reached in the ionization chamber, what does the machine do?

the exposure is terminated

how is the minimum reaction time for AEC determined?

length of time necessary for the AEC to respond to the radiation and for the exposure to be terminated; modern chambers have less than 0.001 second (1/1000 second; 1 millisecond)

Backup timers should be set at _____% of the expected exposure time.

150

Federal law required automatic termination at ______ mAs when working above ______ kvp

600; 50

increasing kVp can _______ the exposure time, but will also _______ contrast

reduce; decrease

a high mA will lead to a ______ in the exposure time

decrease

what program suggests a kVp, mA and active chambers for a given exam?

Anatomically Programmed Radiography (APR)

AEC devices are equipped with _____ _____ that allow the radiographer to adjust the amount of present radiation detected in the cells before termination

density controls (changes the detector sensitivity)

how are the density control buttons indicated on the control panel?

-2, -1, 0, 1, 2

zero indicates neutrality

density control buttons changes exposures by what measure?

some predetermined amount or increment expressed as a percentage- common increment is 25%

*routinely using density controls to produce an acceptable radiograph indicates a possible problem with the AEC device

density controls should not be used to compensate for changes in part thickness

true; AEC does this automatically

1 multiple choice option

too tight collimation around ionization chambers (chamber "clipping") can lead to the chambers operating as it the tissue is _____

dense , leading to overexposure

too wide collimation can lead to an increase in scatter which can lead to an _______ image

underexposed

written tables to help radiographers obtain a consistent, standardized image while using the lowest radiation dose possible

technique chart

a technique chart

all of the above

3 multiple choice options

a thorough technique chart should include the following:

kVp

mA

backup exposure time or mAs

SID

focal spot size

use of grid and grid ratio

AEC detector(s)

acceptable exposure indicator range

a way to measure the path of the central ray; measures the thickness of the patient's part being examined

calipers

how are technique charts typically developed?

based on patient's thickness

designed for average/typical patient

do not consider pathology and condition of patient

adjustments should be made for history and condition

what are the two main types of technique charts?

variable kVp

fixed kVp

when using a variable kVp chart, the _____ remains the same for that particular body part no matter the patient

mAs; kVp is varied based on different patient part thickness as measured with calipers

what rule does the variable kVp- fixed mAs chart used to account for patient thickness?

(2 kVp x part cm) + 30 kVp = new kVp

If the kVp is dropped very low when using a variable kVp chart it is possible to:

under penetrate the body part

1 multiple choice option

when using the fixed kVp chart, _____ is varied according to part thickness as measured with calipers

mAs; assumes optimal kVp for the part being x-rayed (exception is considerably large patients)

optimum kVp for small extremities

50-60

optimum kVp for large extremities

70

optimum kVp for skull

80

optimum kVp for abdomen and ribs

80

optimum kVp for barium-based contrast studies

120

optimum kVp for iodine-based contrast studies

68

optimum kVp for chest with a grid

120

optimum kVp for chest without a grid

80

optimum kVp for spine

80

optimum kVp for pelvis and hip

80

Fixed kVp chart: it makes sense to adjust only mAs since its the controlling factor of _____; a minimum change of _______% is required since anything less is not significant

IRE; 30

which chart is better suited for use with digital imaging receptors?

fixed kVp

1 multiple choice option

using a fixed kVp chart generally uses a higher kVp, which gives:

all of the above

3 multiple choice options

photons in a higher kV beam will have higher energy, they will be more likely to _______ patient's body

pass straight through

1 multiple choice option

at the ______ kVp settings, the change in exposure is more noticeable if the kVp is change (15% rule)

lower

1 multiple choice option

which chart can better control motion?

fixed kVp chart; using a high kVp and lower mAs (reciprocity law)

Variable technique (change to both kVp and mAs) charts provide a way to alter routine settings due to:

pathological conditions

patient age

ability to cooperate

BMI

casts

contrast media

Casts will require an increase in ____

kVp

kVp for wet plaster cast

8-10 kvp increase

kVp for dry plaster cast

5-7 kVp increase

kVp for fiberglass cast

3-4 kVp increase

Additive pathology will lead to a ______ in IR exposure if the technique is not adjusted

decrease

Destructive pathology will lead to an _____ in IR exposure if the technique is not adjusted

increase

Pediatric patients are more radiosensitive, and they are smaller, so the technical factors can be ______

reduced

Geriatric patients typically have bones that are not as dense, thus require a _____ in technical factors

decrease

if the patient was given contrast media, such as barium, the technical factors will need to be _____ due to the higher atomic number of the contrast

increased

if you decide not to use a grid for an exam that typically uses one, than your technique will need to be ___

decreased

the best practice for digital radiography is to use the ______ within the optimal range for the part and position along with the _______ that will still provide adequate exposure to the image receptor

highest kVp; lowest mAs

which type of technique will produce the least radiation dose to the patient?

high kVp technique

2 multiple choice options

what device is attached to the opening in the tube housing and is used to regulate the size and shape of the beam?

beam restrictor

beam restriction reduces the number of _____ ______ being emitted from the tube

primary photons; the helps reduce the amount of scatter, you may sometimes have to increase your technical factors

scattered photons are not part of the useful beam

true

1 multiple choice option

where is scatter produced?

in the patient's body when the primary photons hit the patient's atoms and are deflected with a loss of energy

what is the most used beam restrictor in radiography?

collimator

what are the types of beam restrictors?

1. aperture diaphragms

2. cones and cylinders

3. collimators- aka variable aperture diaphragm

what is the most simplest type of beam restrictor?

aperture diaphragms; made of a sheet with a hole in the center and is placed directly below the tube window (size and shape of hole determine size and shape of beam) ^ no longer use today

which team restrictors are circular aperture diaphragms with metal extensions?

cones and cylinders

which beam restrictor has two sets of lead shutters at right angles to one another that move in opposing pairs?

the collimator

what are the parts of the collimator?

1. light source

2. mirror

3. two sets of shutters

what is the purpose of the light bulb in the collimator?

shows the exact configuration of the x-ray field

target of the tube and the light bulb should be the same distance from the center of the mirror

bottom shutters reduces _______ along the edges of the beam

penumbra (unsharpness)

upper shutters help reduce the amount of _______ ______ reaching the IR by absorbing radiation

off-focus radiation

Features of the shutters

all of these

3 multiple choice options

what is a positive beam limiting device (PBL) ?

automatically collimates the beam to the size of the image receptor

by limiting collimation to the area of interest we are:

improving image quality

decreasing patient dose

what are ancillary devices?

lead blockers and lead masks; help give the beam a specific shape *such as when we place lead blockers behind a patient for a lateral lumbar