Ch11: Secondary Factors Flashcards by Alyssa Dosch

What sizes of filaments are there?

Large (1-1.2mm)
Small (0.5-0.6mm)

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What is the purpose of the filaments in the cathode?

affects heat of tube (tube loading capacity)
affects spatial resolution/sharpness of anatomy

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T/F The smaller the focal spot means better spatial resolution or recorded detail.

True

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T/F Larger focal spots create heat on a larger surface which could cause heat damage to the tube.

False
Smaller focal spots disperse heat on a smaller area, creating possible heat damage to the tube

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Does focal spot size have any affect on the exposure?

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How does focal spot size affect spatial resolution?

larger size decreases spatial resolution
larger size increases the area of un-sharpness
beam divergence occurs

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T/F Distance is a factor that will either increase or decrease exposure dose to people/objects.

True
As distance (from the beam) increases, the exposure dose decreases

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T/F As SID increases, the exposure to the IR increases.

False
As SID increases, the amount of radiation hitting the IR will decrease. (as long as the technique remains the same)

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How do you fix a low EI if the distance is too far?

Increase your mAs

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SID stands for…

source to image receptor distance

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SID affects… (quantity/quality)

quantity
affects amount of radiation reaching the IR/patient

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What is another abbreviation for SID?

FFD
Focal Film Distance

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T/F Beam intensity will change when distance changes.

True
Amount of radiation (beam intensity) on the IR will change at different distances
(quantity)

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T/F Increased SID will increase exposure, intensity, and patient dose.

False
Increasing SID will decrease all those amounts

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T/F Decreased SID will increase patient dose.

True
Exposure Index and intensity will also increase

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Does SID and exposure index have a inverse or direct relationship?

inverse

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Does SID and patient dose have a inverse or direct relationship?

inverse

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Does SID and beam intensity have a inverse or direct relationship?

inverse

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What is the inverse square law?

Intensity of radiation at a given distance from the source is inversely proportional to square of the distance
(Intensity 1 / Intensity 2) =
(distance2^2 / distance1^2)

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If you were to double your distance (SID) from 50in to 100in, how has your intensity changed?

intensity has decreased by 1/4

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What situation would you use the inverse square law formula?

finding intensity of radiation when distance changes (as long as technical factors remain unchanged)

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When would you use the direct square law formula?

maintaining exposure when SID changes, calculating mAs to compensate for change in distance (as long as other factors remain the same)

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T/F As distance increases (SID), the beam becomes more perpendicular to the subject and increases magnification.

False
increasing the distance will decrease magnification
the beam does become more perpendicular

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As SID increases, mAs should _____ to keep the exposure the same

increase

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Direct Square Law or Exposure Maintenance Formula

mas 1 / mas 2 = (SID1^2 / SID2^2)

If SID decreased, but you did not change your mAs technique, what would happen to the EI?

increase

How do you find what % of SID is OID?

OID / SID

As SID increases, while OID remains unchanged, how does that affect magnification?

decreases as SID increases

What does OID stand for?

Object to Image Receptor Distance

As OID increases, how does that affect the amount of radiation on the IR?

less radiation strikes the IR as OID increases

T/F OID creates an air gap which prevents scatter and increases contrast

True

OID increases, and magnification....

increases

Why does OID create magnification?

the exit beam diverges after leaving the patient, increasing the size appearance of an object

OID has what affect on spatial resolution?

inverse relationship OID increases, spatial resolution decreases OID decreases, spatial resolution increases

T/F Rule of thumb for projections is to keep the body part of interest furthest from the IR.

False

Magnification Factor Formula

MF = SID / SOD

SOD stands for....

Source to Object Distance

Why is the Magnification factor always over 1?

the object is being magnified the factor as a percent would be over 100% because the image is larger than the initial object

Which combo will create the best spatial resolution? 40 mAs, 80 kvp, 40in SID, 4in OID 50 mAs, 70 kvp, 50in SID, 4in OID 120 mAs, 90 kvp, 40in SID, 2in OID 10 mAs, 75 kvp, 50in SID, 2in OID

10 mAs, 75 kvp, 50in SID, 2in OID Separate the mas and kvp b/c it doesn't matter find the magnification factor (divide SID by SOD) lowest mag factor = better spatial resolution

How do you calculate the object's true size from a magnified image?

Find the SOD if not given (SID - OID) Calculate mag factor (SID / SOD) Calculate object size by dividing the image size by the mag factor

What types of distortion occur with Central Ray/object alignment?

elongation foreshortening off center/clipping

How does angulation of the ray affect the amount of exposure to the IR?

angulation increases SID, so it decreases exposure

What is the primary purpose of a grid?

absorbs scatter radiation increase image contrast (by cleaning up fog/scatter)

Why would you use a grid?

larger anatomy creates excess scatter used on anatomy larger than 4 inches

How do you need to adjust your technique when using a grid?

when adding in a grid, you need to increase your mAs

Why do you need to adjust technique when adding a grid?

grids will absorb scatter and radiation in general so it will reduce the overall amount of radiation hitting the IR you need to increase mAs to increase the quantity to maintain the EI

What does the grid ratio mean?

It is the number of lead strips per one inch

What happens to patient dose when you add a grid? Why?

dose increases b/c you have to increase your mAs You increase mAs to maintain EI and/or have adequate exposure increased mAs = increase pt dose

What happens if you do not adjust mAs when you add or get rid of a grid?

quantum noise/fog

T/F A smaller light field means there is more beam restriction and more collimation.

True

Why is a smaller light field preferred?

less tissue is irradiated and less scatter better contrast

T/F A larger light field means more beam restriction and less collimation and will result in better contrast.

False Large Light field means.... less collimation less beam restriction more scatter and more tissue irradiated lower/poor contrast

A tech asks you to make your collimation bigger, what do they mean?

Open the light field lessen beam restriction

Collimation has a larger affect on the image when you use...

no grid high kVp large light field

T/F Beam restriction affects the amount of scatter produced.

True

What are some secondary factors?

Generator output Tube filtration Compensating Filters SID/OID Beam Restriction Grids

A higher frequency generator requires (more/less) exposure techniques.

less

What affect does tube filtration have?

amount of high penetrating photons higher energy beam more scatter

What are compensating filters?

placed in the xray tube/beam to produce more uniform exposure requires more mAs which will increase patient dose/exposure

What are some patient factors?

body habitus part thickness age (pediatric pts) pathology/replacements

For every 2 inch increase in part thickness, the mAs needs to...

almost double increase mAs by 2

What are two patient factors that affect contrast?

thickness and atomic number (bony or replacements)

What do you need to adjust for peds patients?

fast exposure times to decrease movement decrease kVp (b/c thickness of parts is smaller)

What are the four body habitus/types from thickest to thinnest?

hypersthenic sthenic hyposthenic asthenic

Whenever possible, use a (low/high) kVp and a (low/high) mAs.

high kVp low mAs

To consider radiation protection, what should you remember when collimating?

always collimate to include only the necessary anatomy

For radiation protection, should you always use a grid?

No only use when necessary built into (usually) table and wall bucky only needed for large body parts

Because digital imaging auto-corrects images, what should you always check to avoid overexposing your patient?

Exposure Index number