- controls scale of contrast increasing image noise production reducing image contrast

Radiographic technique Flashcards by Aleesha Cruz

The combination of the radiation quantity (mR/mAs) and radiation quality (HVL)

Exposure factors

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What are the 4 main exposure factors?

KVP, mA, Exposure time, SID

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controls how fast the electrons are sent across the tube

kVp

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Controls Quality

KVP

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Controls Quantity

mAs (directly proportional)

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Beam penetrability of KVP

high energy, greater penetrating ability, more compton effect(scatter)

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KVP

controls scale of contrast
* increasing image noise production
* reducing image contrast

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affects number of x-rays produced (not energy)

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mA, quantity, and patient dose are ____ proportional

directly

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determines the number of photons radiation quantity, OD and patient dose

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mA stations are usually

50, 100, 200, 300, 400 & 600

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Three phase exposure time

1 ms

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single phase exposure time

<8ms

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Short exposure time ______ image blur.

reduces

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Must ________ mA when using short exposure times to maintain x-ray intensity

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Formula for mAs

mAs= (mA) x (S)

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key factor of optical density

mAs

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mAs

changes the number of electrons

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states the OD will be constant for any combination of mA and exposure time that results in constant mAs

Reciprocity Law

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Distance affects x-ray ________ not _______

intensity; quality

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Determine required change in mAs after a change in SID to maintain OD

square law

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half-wave rectification

drops to zero

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Full wave rectification

consistent but always drops to zero

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3 phase power

6 or 12 pulse, energy higher, nearly constant output

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high frequency

less 1% ripple, much better overall

Hypersthenic

5% population, massive type, chest and abdomen are very broad, lungs are short and wide, stomach is high and transverse

Sthenic

average body type, represents 50% of population, active or strong, stomach is more J-shape and lower, more slender version of hypersthenic

Asthenic

opposite of hypersthenic, 10% of population, very frail and of poor muscle tone, narrow, long, shallow diaphragm is low, heart is long and slender, abdominal cavity rests mainly in the pelvic region

Hyposthenic

35% of population, modification of the asthenic build, stomach is j-shaped and extends into the iliac crest region, high splenic flexure

As thickness increases, ______ radiation is necessary for penetration.

soft tissue technique

low kvp and high mAs

Extremity technique (soft tissue and bones)

low kvp

Chest technique (high contrast)

high kvp

Abdomen (low contrast)

middle kvp

Pathology

the destructive decrease or constructive increase in mass or composition has a direct effect on technical consideration

image quality factors

Optical density, contrast, image detail, distortion

The degree of blackening of the finished radiograph

Optical density

when OD is high...

took dark, over exposed

when OD is low...

too light, under exposed

OD and mAs are _______ proportional.

directly

when only mAs is changed it is either.........

halfed or doubled

___% increase required for visible change in OD for mAs.

30%

____% increase is required for visible change in OD for kvp

square law formula

mAs2/mAs1=(SID2)^2/(SID1)^2

15% rule: To maintain OD a ___ increase in kvp would require a reduction of ____ the mAs

15%; half

variation in OD between adjacent atomic structures

Contrast

Contrast is controlled by

KVP (penetrability of the primary beam)

The range of OD from the whitest portion to the blackest portion of the radiographic image

scale of contrast

Short scale

low kvp, short scale, high contrast, "bone work"

high contrast radiographs used when an increase in contrast is desired produces greater differences in black and white

short scale

Long scale contrast

low contrast, many shades of grey, high kvp, "chest images"

radiographs having optimal radiographic density and contrast to visualize area of interest

photographic properties

5% rule

an increase in kvp by 5% may be accompanied by reduction in mAs by 30% to produce the same OD at a slightly reduced contrast scale.

Sharpness of small structures or spatial resolution of the image

image detail

image detail is evaluated by

sharpness and visibility

the amount of clarity or blur in the visualization of the structural lines or borders of tissues in the image

sharpness

Sharpness controlled by

FFS, SID, OID, intensifying screen

The contrast resolution of ability to see the detail of the radiographic image

Visibility

Loss of Visibility

refers to any factor that causes a deterioration or obscuring of the image detail (fog)

The misrepresentation of object size and shape due to position of the tube, the anatomic part, and or image receptor

Distortion

disadvantage of distortion

elongation, foreshortening

advantage of distortion

allow better visualization of anatomy

technique charts based on

1. variable kvp 2. fixed kvp 3. high kvp 4. AEC

VARIABLE KVP CHART

- varies according to thickness of anatomic part - provides radiographic with shorter scales of contrast - Ma and time stays the same, but you measure for kvp

Fixed kVp chart

- developed by arthur fuchs - kVp stays constant, mAs varies - provide radiographs with longer scale of contrast - seen group small, average, large

high kvp chart

- Used for barium exams, contrast exams, cxr, - ensures adequate penetration - requires a decrease in mAs - reduces patient dose

AEC

- the use of computer assisted automatic/electric timers and photocells - needs selection of kvp and od settings - patient positioning must be accurate - terminated when the image receptor has received the appropriate radiation exposure to correspond with OD settings - most AECs have 2s override

Radiographic technique Flashcards

(67 cards)