Prime Factors

Question 1

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

Answer 1

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

Question 2

What is quantity?

Answer 2

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

Question 3

What is quantity prime controller ?

Answer 3

mAs and also affected by kVp,distance, and filration

Question 4

What is quality?

Answer 4

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

Question 5

High energy photons travel farther in…

Answer 5

tissue

Question 6

What is the prime controller of quality?

Answer 6

Kvp and also directly affected by filtration

Question 7

what does milliamperage per second (mAs) measure?

Answer 7

The xray tube current

Question 8

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

Answer 8

-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

Question 9

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

Answer 9

directly proportional to the number of xray photons created

Question 10

mAs x s = or
tube current x exposure time

Answer 10

mAs

Question 11

can adjust mA and time separately to result in

Answer 11

same xray exposure

Question 12

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

Answer 12

Exposure Index (EI)

Question 13

Exposure index does not indicate…

Answer 13

Patient dose

Question 14

Index range and values vary from vendor to vendor

Answer 14

ex) S#
EX#
EI#

Question 15

EI value must fall within a specified range

Answer 15

-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

Question 16

mAs is the prime controller of…

Answer 16

image receptor exposure

Question 17

There’s a direct proportional relationship between …

Question 18

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

Answer 18

the same IR exposure

Question 19

Increasing the kVp will cause an increase in…

Answer 19

the speed and energy of the electrons applied across the tube

Question 20

As kVp increases so does…

Answer 20

the number of electrons interactions at the target (quantity)

Question 21

15% increase in kVp=

Answer 21

double number of photons

Question 22

Double kVp=

Answer 22

number of photons increases about 4 times

Question 23

Greater photon energy=

Answer 23

more penetrability

Question 24

kVp affects both…

Answer 24

quality and quantity of xray beam

Question 25

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

Answer 25

in image contrast

Question 26

Contrast is..

Answer 26

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

Question 27

Contrast helps with the ability...

Answer 27

to distinguish the differences between tissues or structure

Question 28

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

Answer 28

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

Question 29

What is the 15% rule?

Answer 29

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

Question 30

kVp should not be used to control....

Answer 30

the IR exposure

Question 31

At a lower kVp...

Answer 31

more radiation is absorbed by the patient

Question 32

Higher kVp and lower mAs will reduce..

Answer 32

patient dose but at the expense of contrast

Question 33

The intensity of the x-rays vary....

Answer 33

greatly with distance

Question 34

What is inverse square law?

Answer 34

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

Question 35

Intensity is measure in?

Answer 35

Roentgen (R)

Question 36

Increasing distance causes...

Answer 36

a decrease of exposure

Question 37

When do we use Direct Sqaure Law?

Answer 37

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

Question 38

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

Answer 38

the radiographer

Question 39

The radiographer should select the kvp based on...

Answer 39

the desired contrast

Question 40

The radiographer should adjust...

Answer 40

mAs to provide the appropriate total exposure to the receptor

Question 41

Distance is generally set based on the desired beam geometry

Answer 41

A distance is selected based on the procedure