Rad 115 Week 1 & 2

SID

Source to Image Distance

SID increases → beam intensity increases

SOD

Source to Object Distance

OID

Object to Image Distance

Kvp

Kilovoltage peak

mAs

Milliamperage per second

IR

Image Receptor

Who discovered x-ray?

Wilhelm Roentgen

What year was the X-ray discovered?

1895

What was the first X-ray?

Bertha’s Hand

mAs

• Quantity of photons in x-ray beam

• time the beam is on

• directly proportional to exposure (mAs up → exposure up → image darker)

• Measured in R

• NO relationship with distance, distance doesn’t change mAs

kVp

• controls quality and intensity of x-ray beams

• inversely proportional to contrast (kVp up → contrast down)

• Represented by HVL

• kVp increase → quantity increase → Scatter increase → contrast down

HVL

Thickness of material that turns R in half

• reduces intensity (mAs and quantity)

Filtration

Reduces quantity of x-rays overall, and increases penetration

• removes the low energy x rays

Long wavelength x-ray photons

• have low energy

• Stay in the object and cause ionization and maybe cancer

• More harmful than short wave photons

When kVp increases

• mAs increases because of the increase in speed

• Current increases

• Quantity increases

• penetrability increases

• contrast decreases

X-rays travel at

• at the speed of light

• in sine waves

• in a straight line

All x-ray machines must have filtration of 2.5mm of aluminum

To absorb longer wavelengths

the red area is the ______, and the highest point

crest

The blue area is the _________ and the distance between 2 crests

Wavelength (WL)

The yellow area is the

Amplitude

What is the process of x-ray production?

1) electrons come through the cathode on the negative side of the x-ray tube

2) The tungsten filaments heat up and create an electron cloud (thermionic emission)

3) the negatively charged electrons from the thermionic emission are attracted to the anode on the positive side of the tube, and hit the tungsten target.

4) heat and x-rays are released upon impact

Distance (d)

When distance decreases, magnification decreases

x-ray intensity decreases as distance increases

Formula for mAs

mAs= mA x S

SDD

Source to detector distance

1 second is how many milliseconds?

1000

Soft X-rays

Low-energy waves, long wave length

cause more harm than hard x-rays

Hard X-rays

High-energy x-rays, short wave length

mA

• Milliamperage

• determines beam quantity or intensity

• High mA → High Current → more x-rays

• Low mA → Low Current → fewer x-rays

Electric Current, equal to electric charge of 1 coulomb per second

Ampere (A)

Tube Current

Direct relationship with beam intensity (quantity)

quantity up → number of electrons up → patient dose up

Exposure Time

Direct relationship with intensity/quantity of beam

Time increase → quantity increase

generally, less than 1 second

decimals, fractions, milliseconds (ms), S

Equation for mAs (controls quantity)

mA x seconds = mAs

mAs Reciprocity

Same IR/DD exposure resulting from different mA and times

ex) 3mA x 2s = 6 mAs

6mA x 1s= 6 mAs

Density

• old term

• amount of silver in hard copy film

• overall blackness of film

• NOT related to brightness

IR/DD Exposure

• new term referring to image property of visibility

• mAs

• has nothing to do with brightness

• one of the photographic properties

15% Rule

• 15% increase in kVp = 2x exposure

• 15% decrease in kVp =1/2x exposure

Maintenance

• decrease kVp 15%, double mAs

• increase kVp 15%, halve mAs

Inverse Square Law

relationship of x-ray quantity/intensity to distance

I ₁ / I ₂ = D ²₂ / D ²₁

I₁ x D₁² = I₂ x D₂²

Exposure Maintenance Formula/ Direct Square Law

Maintains same IR/DD exposure when SID is changed

mAs ₁ / mAs ₂ = D ²₁ / D ²₂

Standard Tabletop SID

40” or 100cm

Standard Chest SID

72” or 180 cm

Why is the standard chest SID greater?

So that the chest is not magnified

Overexposure is

too dark

a result of high quantity or mAs

Underexposure is

Too light

result of low quantity or mAs

kVp is usually

75 to 100

based on desired contrast

mAs is adjusted to meet ..

exposure needs

Prime Factors

1. millamperage-second (mAs)

2. kilovoltage (kVp)

3. distance (d)

X-ray quantity is affected by

• mAs

• D

• kVp

• Filtration

X-ray Quality is affected by

• kVp

• Filtration