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Pre Exposure > Prime Factors > Flashcards

Prime Factors Flashcards

1
Q

What are 3 principle factors that affect xray quality and quantity?

A

Miliamperage per second (mAs)
Kilovoltage
Distance
They are under the direct control of the radiographer

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2
Q

What is quantity?

A

-Measure of the number of xray photons in the useful beam
-aka output, intensity or exposure

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3
Q

What is quantity prime controller ?

A

mAs and also affected by kVp,distance, and filration

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4
Q

What is quality?

A

Measure the penetrating ability of the xray beam or distance it travels in matter

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5
Q

High energy photons travel farther in…

A

tissue

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6
Q

What is the prime controller of quality?

A

Kvp and also directly affected by filtration

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7
Q

what does milliamperage per second (mAs) measure?

A

The xray tube current

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8
Q

What is the measure of the xray tube current?
(3)

A

-number of electrons crossing the tube from cathode to anode per second
-as mA increases, so does the number of electrons
-As time increases so does the number of electrons

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9
Q

mA and time are both directly proportional to the number of electrons crossing the tube and…

A

directly proportional to the number of xray photons created

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10
Q

mAs x s = or
tube current x exposure time

A

mAs

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11
Q

can adjust mA and time separately to result in

A

same xray exposure

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12
Q

IR exposure is assessed by reviewing numeric exposure value known as the…

A

Exposure Index (EI)

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13
Q

Exposure index does not indicate…

A

Patient dose

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14
Q

Index range and values vary from vendor to vendor

A

ex) S#
EX#
EI#

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15
Q

EI value must fall within a specified range

A

-any number over or under the range is an over or underexposed image
- May vary depending on the body part
-Some systems may be the inverse

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16
Q

mAs is the prime controller of…

A

image receptor exposure

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17
Q

There’s a direct proportional relationship between …

A
18
Q

As long as mAs is constant, any combo of mA and time will create…

A

the same IR exposure

19
Q

Increasing the kVp will cause an increase in…

A

the speed and energy of the electrons applied across the tube

20
Q

As kVp increases so does…

A

the number of electrons interactions at the target (quantity)

21
Q

15% increase in kVp=

A

double number of photons

22
Q

Double kVp=

A

number of photons increases about 4 times

23
Q

Greater photon energy=

A

more penetrability

24
Q

kVp affects both…

A

quality and quantity of xray beam

25
Q

An increase in kVp causes an increase in penetrability and decreases…

A

in image contrast

26
Q

Contrast is..

A

A characteristic of image quality; visibility of detail or different between IR exposure levels

27
Q

Contrast helps with the ability…

A

to distinguish the differences between tissues or structure

28
Q

A primary beam with higher kV will result in an overall…

A

rise in penetration through tissues and will result in lower contrast radiograph or longer scale of contrast (more shades of grey)

29
Q

What is the 15% rule?

A

an increase or decrease in kVp by 15% which will cause a doubling or halving mAs

30
Q

kVp should not be used to control….

A

the IR exposure

31
Q

At a lower kVp…

A

more radiation is absorbed by the patient

32
Q

Higher kVp and lower mAs will reduce..

A

patient dose but at the expense of contrast

33
Q

The intensity of the x-rays vary….

A

greatly with distance

34
Q

What is inverse square law?

A

doubling of distance increases the area 4x’s which decreases the intensity by 1/4

35
Q

Intensity is measure in?

A

Roentgen (R)

36
Q

Increasing distance causes…

A

a decrease of exposure

37
Q

When do we use Direct Sqaure Law?

A

to compensate for IR exposure changes when distance changes must be made

38
Q

Setting the appropriate mAs, kvp, and distance is the responsibility of..

A

the radiographer

39
Q

The radiographer should select the kvp based on…

A

the desired contrast

40
Q

The radiographer should adjust…

A

mAs to provide the appropriate total exposure to the receptor

41
Q

Distance is generally set based on the desired beam geometry

A

A distance is selected based on the procedure

Pre Exposure (10 decks)

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