kilovoltage (kVp)

exposure factors controlled by radiologic technologist

kVp

mAs

SID

voltage (potential difference)

measure of the difference in electrical potential between 2 points in a circuit

voltage happens between the flow of

cathode to anode

volt (V) is the units of

electrical potential or potential difference

volt (V)

the force with which electrons travel

kilovolts equals

1000 volts

kilovolts (kV) is a unit used to describe the

kinetic energy of the electrons flowing in the tube

electron volt (eV)

energy one electron will have when it is accelerated by an electrical potential of 1 volt

electron volt is the measurement of the

binding of an electron

kiloelectron volt (keV) unit used to measure

xray energy

kiloelectron volt

1000 electron volts

kilovoltage peak (kVp)

technologist set at operators console

highest energy of the beam

increasing kVp, will increase

speed and energy of electrons applied across the table

emission spectrum

average primary beam photon has a keV energy of approximately 30-45% of the selected kVp

incoming line current- US households

60 Hz alternating current at 110 volts

incoming line current- xray systems

60 Hz alternating current at 220-240 volts

high voltage transformer

convert incoming line voltage to kilovolt levels

1 kilovolt = 1000 volts

xray generators includes

step up transformers

rectified current

alternating current flows first in one direction. then alternates to flow in the opposite direction. only 1/2 of the wave is useful unless the current is rectified

all modern equipment uses

rectifiers

generator types

single phase

three phase

high frequency

more efficient generators produce xray beams with a

higher average energy

beam intensity increases

radiograpghic quality- main components

contrast

exposure intensity

detail

distortion

contrast

controlled by computer algorithms

kVp contriibutes to subject contrast

exposure intensity

beam quantity

controlled by mAs (directly proportional manner)

influenced by kVp

kVp controls the

penetrability (quality) of beam

mAs _____ quantity

kVp ______ quantity

controls

affects

kVp

-increases speed and energy of electrons applied across the xray tube

-high energy increases number of electrons applied across the tube to the anode

-not in a directly proportional manner

-increases the number of interactions at the anode

-increased speed and energy of electrons results in production of xray photons with higher energy

kVp determines

to what extent the xray beam will penetrate the pts tissues

(kvp) all tissues must be sufficiently penetrated to visualize

fine details

low kVp

long wavelength xrays

low penetrability

-results in white parts of our image

examples of when to use low kVp

fingers, hand, feet, ankles

high kVp

short wavelength

greater penetrability

examples of when to use high kVp

chest, abdomen, hip, pelvis

penetrability is expressed as

beam quality, HVL, or beam hardness

high kVp is required to penetrate

thick, dense body part

the quality (intensity) of photons increases with an increase in kVp

-greater number of electrons will reach the target

-higher kVp results in increased interactions at the anode

emission spectrum

kVp affects both quality and quatity

increases kVp quality

average energy increase (curve shift to the right)

increased kvp= quantity

amplitube increase (total number of photons)

contrast

the ratio, or percentage difference, between

two adjacent brightness levels

scale of contrast

number of useful visible IR exposures, or shades of gray

high contrast

drastic difference in adjacent brightness or densities

low contrast

subtle difference between adjacent brightness or densities

HIGH contrast LOW kvp

black and white with very few shades of gray

great differences between adjacent densities

high contrast - low kvp

long wavelength

low penetrability

few shades of gray- black and white

-short scale of contrast

LOW contrast HIGH kvp

more discernable shades of gray

minimal differences between adjacent densities

low contrast- high kvp

short wavelength

greater penetrbility

more shades of gray

-long scale of contrast

15% rule and exposure quality

expresses the effect of the kvp on IR exposure

15% increase in kVp will _______ exposure intensity

double

15% decrease in the kVp will decrease exposure intensity by

one half

what kVp should be used for a particular exam?

criteria

penetrability required

contrast required

high kVp and low mAs techniques _______ pt dose

reduces

fixed kVp technique chart

select kVp that will penetrate body part

vary mAs according to specific pt

fixed kVp technique chart

vary mAs according to specific pt

-measure thickness of body part to determine the amount of mAs

fixed kVp technique chart

double mAs for every ____ cm of body part thickness

4

variable kVp technique chart

-vary kV to achieve different densities

-maintain mAs at specific level of particular body part

-for every 2 cm of body thickness, vary kVp by 2

variable kVp technique chart

for every ___ cm of body thickness, vary kVp by ___

2cm

2

anatomically programmed radiography systems combine AEC system with exposure factors to

specific anatomical procedures

anatomically programmed radiography systems

control console provides choice of region with suggested

exposure factors

exposure factors may be modified