RAD 120 Exposures I | Chapter 12 | Exam notes

prime factors

technical factors that affect x-ray emission that are under direct control of technologist

1. mAs

2. kVp

3. distance

Three principal factors that affect x-ray emission are under the direct control of the radiographer:

1. quantity

2. quality

The x-ray beam can be described in terms of:

quantity

measure of the NUMBER of x-ray PHOTONS in the useful beam

• output

• intensity

• exposure

what are the other names for x-ray QUANTITY?

• mAs

• kVp

• Distance

• Filtration

what factors affect QUANTITY?

Quality

measurement of the PENETRATING ability of the x-ray BEAM

• energy of the beam

• penetration power of the beam

farther

highest energy photons travel _____ than low-energy photons therefore, MORE penetrating

HVL

what is QUALITY numerically represented by?

• kVp

• Filtration

what factors affect QUALITY

mA

MEASUREMENT of x-ray tube CURRENT

• NUMBERS of ELECTRONS crossing the tube from anode to cathode

• directly proportional to tube current

mAs

unit used to describe the PRODUCT OF TUBE current

1. mAs

the PRIMARY controller of x-ray QUANTITY is 1.________

• PRIMARY controller of IR EXPOSURE

mAs = mA * time

what is the formula of mAs?

x-ray exposure doubles

when mAs doubles, 1.___________

there are more electrons in the current

when mA is increased, what happens to the electrons in the current?

there will be more target interactions

when mA is increased, more electrons in the current, what happens to the target interaction?

there will be more x-ray photons produced

when mA is increased, more electrons in the current, more target interactions, what happens to the number of x-ray photons produced?

there will be more ALLOWED time for thermionic emssion

if time is increased, what happens in thermionic emission?

• there will be more electrons burned off

• more target interactions

• more x-ray photons produced

if time is increased, more allowed time for thermionic emission, what happens to the electrons being burned off, target interactions, and x-ray photons?

SID

Source to image distance

inverse relationship

distance and quantity have what relationship?

A. decrease

when SID is increased, exposure A._____

B. increases

when distance is decreased, the exposure B.______

I₁/I₂ = D₂²/D₁²

inverse law expression:

• mR

• more photons striking the IR

• more exposure
  

In SHORTER SID, what happens to the photons and exposure

• x-ray photons miss the IR

• less photons striking IR

• less exposure

In LONGER SID, what happens to the photons and exposure

1. more

as tube ages, there is 1.______ inherent filtration due to vaporize tungsten on window

exposure doubles

when kVp is increased 15%, what happens to the exposure

half exposure

when kVp is decreased 15%, what happens to the exposure

• exposure will be in half

• double mAs

if want to maintain exposure, how would you adjust these technical factors:

kVp: decrease 15%

mAs: ?

• doubles the exposure

• cut mAs in half

if want to maintain exposure, how would you adjust these technical factors:

kVp: increase 15%

mAs: ?

exposure indicator (EI)

number assigned by computer that indicates how much exposure IR has received.

Deviation index (DI)

standard deviation from perfect exposure

0

what is the perfect exposure?

mAs₁/mAs₂ = D₁²/D₂²

the exposure maintenance formula is:

kVp = increase

if it’s less bony detail on the picture, what must be adjusted?

• not enough penetration power

• can’t see enough bones

double mAs

if the radiograph is underexposed, it will be a grainy image, what factor must be adjusted?

• not enough photons forming the image

greater energy

increasing the energy of an incident electron will result in the production of an x-ray photon with _______

x-ray quantity

the product of tube current and exposure time is equal to _______

prime

the factors that affect x-ray emission under the direct control of the radiographer are called _____ factors

1. double mAs

2. increase kVp by 15%

what would double exposure?

15%

by what increments should kVp be adjusted?

image receptor exposure

what is the exposure indicator a measurement of?