Test 3 Flashcards by kara baker

How and why do technique systems provide consistent image quality

By reducing variability so you can reduce repeats and avoid excessive or dose

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What is the primary goal of technique systems

To provide consistent image quality

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What are the advantages of a Fixed kV

Decrease or dose
Provide more information on image
Consistent image contrast and density
Wide exposure latitude
Reduce tube wear
Decreased time settings=less motion
Easy to remember

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Disadvantages of a fixed Kv

More scatter
Lower contrast
Less visibility (grayer image)

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Advantages to a variable Kv

Permit small incremental changes with changing body part thickness
Higher image contrast
Enhanced visibility of fine detail
Increased perception of resolution

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Disadvantages of a variable Kv

Increased or dose
Less info on image
Inconsistent image contrast and density
Narrow exposure latitude
Increased tube wear

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What are computerized exposure control systems

It utilizes vast databank of technique systems
Inherent part of control console
Tech chooses exam and computerized factors appear
Factors may be modified to meet non routine conditions

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7 steps to building a technique chart

Produce phantom images - measure part ️size
Select optimal phantom image - selected by radiologist
Extrapolate technique chart - use 15% rule and adjust for part thickness
Phantom testing
Clinical trials
Clinical fine tuning
Ongoing fine tuning o

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What is AEC

It is sensors in the Bucky that stops exposure when image reaches appropriate density

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Advantages of AEC

Fewer repeats
Decreased pt exposure
Increased efficiency of dept

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Limitations of AEC

Requires skill techs - positioning and knowledge of AEC devices

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How does tech control time with AEC

Higher MA = shorter time

Lower MA = longer time

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What tech factors does tech set when using AEC

MA KV AND SID

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What are two types of AEC devices

Phototimers

Ionization chambers

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Characteristics of Phototimers

Located behind the IR
“Old fashioned”
Photomultiplier tube and fluoroscopic screen
Terminates when appropriate amount of LIGHT from screen reaches the photomultiplier tube

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Characteristics of ionization chamber

Located between pt and IR
“Modern”
Gas filled ionization chamber
Terminates exposure when proper amount of RADIATION is detected by ionization o air in chamber

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What is another name for the two AEC devices

Phototimers

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Why are the two most important decisions when using AEC

Patient positioning
Detector/chamber/cell selection
* detector must sample radiation coming directly from area of interest

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Without proper ________ of _________ AEC may actually increase repeats and or dose

Knowledge of positioning

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What are 5 causes of improper image density when using AEC

Inaccurate positioning(#1 cause)
Poor collimation
Wrong “speed” IR (film/screen)
Equipment failure
Pt conditions

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What is minimum response time (MRT)

Lag time between AEC recognizing enough radiation, sending signal to terminate exposure , and switch thrown to end exposure

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What is the equipment limitation for MRT in older and newer equipment

Older = 30 millisec
Newer = 1 millisec

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What is the upper limit set by the safety device on AEC

600 mAs

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What would cause the back up tune to activate

Excessively large pt
Wrong detector selected
Wrong tube selected
Incorrect tube/Bucky alignment
Incorrect back up timer setting

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T/F in order to produce the correct density the radiation reaching the AEC chamber must come from the part of interest

True

T/F increased scatter will produce an overexposed image when using AEC

False (underexposed)

Will a photocell covered by heavy absorber produce an overexposed, underexposed, or no change image

Over exposed

When the primary beam strikes the photocell will that produce an overexposed underexposed or no change image

Underexposed

When you want to image bone but the photocell is covered by soft tissue .... Overexposed underexposed or no change

Underexposed

Using table Bucky but selected wall Bucky...... Overexposed underexposed or no change

Overexposed

Imaging an AP lumbar spine but have selected outer chambers...... Overexposed underexposed or no change

Underexposed

Poor collimation when imaging an obese pt and using a high Kv.... Overexposed underexposed or no change

Underexposed

What is photographic properties

The visibility of recorded detail

What is geometric properties

The sharpness I recorded detail

Why is radiographic density

The amount of overall blackness produced on the processes image

What is radiographic contrast

Is the degree o difference or ratio between adjacent densities Scale of contrast Long scale=low contrast Short scale=high contrast

What does radiographic density determine

The completeness o the image recorded upon the radiographic film. It is the overall blackening of the film caused by the intensity of radiation

What are the 2 controlling factors that affect density

Milliamperage and time

What 9 things influence density

``` kvp SID Grid Film screen speed Collimation Anatomic part (thickness of part) Anode heel effect Tube filtration Film processing ```

MA and exposure time control the _______ of radiation reaching the image receptor

Quantity

MAs and density have what kind of relationship

Proportional (direct) | Double mAs double density

To make a visible change in density the minimum amount of change in mAs is approximately ________

30%

How does kvp influence density?

It alters the energy and amount of penetrating ability of the xray beam

Electron speed is determined by_______

The voltage

As the voltage increases

The electrons travel faster The greater the energy of the X-rays produced The greater the penetrating ability of the X-rays

Changing the Kv by 15% will have the same effect on density as

Doubling or doing the mAs by half

Using the 15% rule

To increase density - add 15% to kvp To decrease density - subtract 15% from kvp To maintain density - when increasing Kv by 15% divide mAs by 2 when decreasing Kv 15% multiply mAs by 2

When would you change kvp to change density

When change is contrast Is also desired

SIDS effect on density

Inverse square law - doubling SID decreases density to 1/4

The inverse square law states that the intensity o the xray bean is ________ _________ to the square of the distance from the source

Inversely proportionate

As SID increases density _______ | As SID decreases density _______

Decreases | Increases

When SID is increased what must be done to maintain density

Increase mAs

Exposure maintenance formula (SID and density)

MAs 1 = SID1^2 -–—— --------- MAs 2 SID 2^2

If adding a grid the mAs must be ________

Increased

Formula for grid and mAs

Mas1 = GCF1 ------- ------- Mas2 GCF2

Grid conversation factors

No grid ➡️ 1x 5: 1➡️2x 6: 1➡️3x 8: 1➡️4c 12: 1➡️5x 16: 1➡️6x

A radiograph was taken without a grid using 3.2 mAs. If an 8:1 grid is used what would the new mAs be?

3. 2 mAs ; 8:1 grid : GCF 4 | 3. 2 x 4 = 12.8

The greater the speed of the film screen the ________ the amount of density produced on radiograph

Greater

Increasing the film screen speed requires a _______ to be made to the mAs

Decrease

Film screen systems are classified by their

Relative speed factor (RS)

Formula for film screen and mAs

MAs 1 = RS 2 -------- -------- MAs 2. RS1

A thick body part absorbs more radiation which will reflect (more or less) density

Less

A thin body part transmits more radiation which will reflect (more or less) density

To maintain density when imaging a thicker body part the mAs needs to be

Increased

For every change in part ️thickness of 4 cm the mAs must be adjusted by a factor of

When using a fixed mAs and variable kvp each cm increase in pt ️thickness requires a(n)

Increase in 2 kvp

There is a decrease in the primary xray beam intensity in the (cathode or anode) side of the tube

Abide

Place the thickest part under the (cathode or anode) end will help decrease visibility of the anode heel effect

Cathode

Density is one of two ________ properties that comprise visibility of detail

Photographic

What is the range of densities visible to the human eye

Photographic optical .25-2.5

Which is worse to be too dark or too light in density

Too light

The controlling factor for density is the

MAs

The text indicates there are ______ potential factors affecting density with _____ being negligible

13 | 2

T/F a dark radiograph has recorded too much information

True

Whenever s choice must be made between excess and insufficient density the wise decision is always the choice of the lighter image

False

T/f an AEC system controls time not milliamperage

True

T/f the configuration of the generator is another important consideration in how kvp affects density

True

When in doubt it is advisable to adjust density by a step at a time

False

T/f as SID Increases density decreases

True

T/f as OID increases density increases

False

t/f as filtration increases density decreases

True

T/f Restricting the primary beam increases density

False

The density of the radiographic image is the

Easiest prime technical factor to evaluate Result o black metallic silver deposited on the radiograph Degree of overall blackness

The _______ factors should be used as the principal method for adjusting radiographic density

Controlling

Which generator produces the least amount of radiographic density

Single phase, 2 pulse

Which generator produces the greatest amount of radiographic density

A high frequency generator

Which factor influences the average energy of photons reaching the radiograph film

Kvp

The 15% rule changes

Density and contrast

The relationship between exposure and SID is

Inversely proportional