ch 13 Flashcards by Shanna H

Prime exposure factors

KVP, MA, Time, SID

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KVP controls ____

image contrast

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KVP is primary control of ___

quality

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KVP controls energy and therefore ___

beam penetrability

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Higher quality means higher ____

energy

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Increased KVP= _____ scatter, = _____ contrast

increased, decreased

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MA controls _____

image density or brightness

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MA also controls _____ that are produced

of xrays

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If time doesn’t change changing MA will change the ____ of xrays

quantity

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Changing from 100 to 200 MA

Doubles exposure and patient dose

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Xray systems are often identified by their

maximum MA

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Reducing time reduces ____

motion blur

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MAS=

MA x Time

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When time is decreased, MA must be ____ to retain the same _____

increased, OD/brightness

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Newer units time is displayed in

milliseconds

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Single phase unites can go as low as

1/120 seconds or 8ms

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3 phase and high frequency generators can go as low as

1 ms

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If time is halved, MA is

doubled

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What type of generator only allows the tech to select MAS, not MA and time seperately

Falling load generators

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The ____MA and ____ time is automatically used for falling load generators

Highest, shortest

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Distance effects exposure and intensity with no effects on

quality of radiation

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Standard SIDS are used to ensure

continuity

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More SID=less ____ & ____ and increased ___

magnification, blur, spatial resolution

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____ MAS must be used with a longer SID

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what allows a rad tech to calculate new MAS after a change in SID

Direct Square Law

New MAS/Old MAS = (SID)^2 New /(SID)^2 Old

imaging system characteristics

Focal spot size, filtration, high voltage generation

Focal spot size controls

detail

Large focal spots for thick objects such as

abdomen and pelvis

Small focal spots for

detail radiography

Filtration increases beam

quality

Result of filtration is _____ scatter and ____ image contrast

increased, decreased

Inherent filtration is ____ equivalent required

2.5 mm Al

Metal or glass envelope provides inherent filtration which is equal to ____ equivalent

0.5mm Al

Collimator provides inherent filtration which is equal to ____ equivalent

1.0 mm Al

Adding filtration ___ patient dose

decreases

Compensating filters are mounted on

collimator

Wedge shaped filters are useful for

spine, cross table hips, leg

Half wave generators produces the ____ quality as full wave but half the ____ of xrays

same, quantity

Full wave has no

dead time

Three phase and higher frequency generators produce higher

quantity & quality

Patient factors include

habitus, thickness, composition, pathology

Sthenic

strong, active

Hyposthenic

thin but healthy

Hypersthenic

overweight, large frame

asthenic

small, frail

Thicker patients require more

xray radiation

Thickness measured with

calipers

Soft tissue uses ___ KVP and ____ MAS

low, high

Soft tissue are low subject ___

contrast

Chest uses ___ & ____ scale of contrast

low, long

____ pathology causes tissue to be more radiolucent

destructive

____ pathology causes tissue to be more radiopaque

constructive

Image quality factors

Optical density, contrast, detail, distortion

Degree of blackening on the finished radiograph

Optical density

Black =

OD of 3 or greater

Image quality factors

Optical density, contrast, detail, distortion

Degree of blackening of the finished radiograph

Optical density

Black =

OD of 3 or greater

Clear =

OD of 0.2 or less

High OD is caused by

overexposure

Low OD is caused by

underexposure

MAS and SID are factors controlling

Change is MAS of ____ % is required to produce a visible change

30%

MAS is ____ or ____ as a general rule

halved, doubled

KVP also changes OD, however it also effects ___

contrast

____ is used if OD is the only factor that needs to be adjusted

MAS

A ____ % changed in KVP is needed to produce a visible change in OD

Changing the KVP by ____ % is equal to halving or doubling the MAS

15%

Contrast function is to make

anatomy more visible

____ is the controlling factor in contrast

KVP

High KVP = ____ contrast = ____ scale

low, long

Low KVP= _____ contrast= _____ scale

high, short

Relationship between contrast and KVP is

inverse

If an image is too low contrast, KVP must be ____

lowered by 15%

If KVP is lowered, to achieve the same OD, MAS must be

doubled

If an image is too high contrast KVP must be

raised by 15%

If KVP is raised, to achieve the same OD, MAS must be

halved

Sharpness of appearance of small structures on the radiograph

Detail

evaluated by recorded detail and visibility

image detail

Best measured by spatial resolution

recorded detail/sharpness of detail

Structural lines and borders

amount of blue in image

Recorded detail/sharpness of detail is controlled by

focal spot size, SID, OID

Best detail = ____ focal spot, ___ SID, and ____ OID

smallest, longest, lowest

best measured by contrast resolution

visibility of detail

visibility of detail is affected by

fog, scatter

Misrepresentation of an objects size or shape

distortion

Poor part or tube alignment can cause

elongation or foreshortening

Ability to distinguish between and to image similar tissues

contrast resolution

spatial resolution is

recorded detail

contrast resolution is

visibility of detail

ability to image small objects that have high subject contrast

spatial resolution

distortion is primarily controlled by

patient positioning

MAS remains ___ and KVP is ____ according to part and thickness for variable KVP chart

constant, varied

KVP is varied ___ per cm

2 KVP

Variable KVP chart results in higher ____ and lower ____

patient dose, exposure latitude

KVP is ____for each body part and MAS is ____ for each body part in fixed KVP chart

set, changed

Fixed KVP chart results in lower ____ and greater ____

patient dose, exposure latitude

High KVP chart is usually greater than

100 KVP

High KVP chart generally provides lower

patient dose

Radiation intensity is measured with ___ or ____ between patient and IR

photocell or ionization chamber

For AEC tech must position properly and select

OD and backup time

APR stands for

Anatomically programmed radiography

APR uses microprocessor to select

KVP, MAS, backup time, OD, etc