Unit 3 Test Part 2

What are patient factors?

The thickness and opacity of tissues influence the image

Common rule: the thicker the part being examined, the greater he radiation absorption

Differential Absorption

The manner in which tissues in the body absorb or attenuate radiation. All do not attenuate the same

What patient factors influence the differential absorption?

Age, physique, pathology (underlying conditions), hollow or dense organs, use of contrast media to visual anatomical structures (ex. Barium in Fluoro)

What will you find in every x ray?

Absorption and scatter

Type of tissue

Bones absorbs more radiation than fat and air. Air transmits more radiation than fat and bone

What are the 4 variables to create an image?

Amperage or mA

Time

Kilo voltage (kVp)

Distance or SID

What is milliamperage (mAs)

Milliamperage x time is the total amount of radiation to patient

mAs and time are always used together to make your total amount of radiation

mAs is always QUANTITY

Where does milliamperage come from ?

The cathode side of the tube

What is kVp?

Force that comes out of the tube also controls the QUALITY of the x ray beam

All about the energy of the beam and the penetrating ability

How do you find mAs?

mA x time = mAs

how to find time?

Divide mAs by mA

How to find mA

Divide mAs by mA

If you’re going from KV to V what do you do?

Move decimal places 3 places to the right

If you are going volts to KV what do you do?

Move the decimal 3 places to the left

kVp is an important factor regarding what?

Image quality- need to have proper penetration of the part before any other factors are considered

We must make sure the kVp is correct before we set the mAs

Lower kVp results in

More absorption

Higher kVp results in

More transmission through the tissue

What is SID

The intensity of the radiation beam

The closer the x ray tube is to the patient the more intense the x ray beam is and vise versa

What is the inverse square law?

if the distance from the x ray tube and the patient is doubled, the intensity is ¼ as great. Or if the distance is cut in ½ the intensity is 4 times greater

What is the formal for the inverse law

Starting radiation over X equals new distance squared over over old distance squared

Cross multiply towards the end

The intensity of the radiation is 50R at 40” SID. What is the new intensity if the distance is changed to 70” SID

X=16.32 or 16R

Exposure factors

Depends on the body part being imaged

The patients size and shape

Patient’s condition: sick, healthy, underlying disease etc.

Hypersthenic

Massive 5%

Sthenic

(Average) 50%

Hyposthenic

(Slender) 35%

Asthenic

(Very slender) really tall, 10%

The thinner the patient the…

The more radiation transmitted (radiation that exits the body)

The thicker the patient the…

The more radiation absorbed

The mAs and kVp is directionally proportional to what

The number of electrons produced at the cathode side and directionally proportional to the voltage applied to the tube

Factors that assess image quality

Density/ receptor exposure

Contrast

Spatial resolution

Distortion

What are the difference in density

Under exposure (too bright)

Overexposure (insufficient brightness)

Slight underexposure

Optimal density

An image with excessive brightness

Not enough mAs

Image with insufficient brightness

Too much mAs

Absorbed radiation

Creates increased brightness or white areas on the displayed image

Transmitted radiation on image

Creates decreased brightness or black areas on the displayed image

contrast

difference between densities or differences between bright levels

If the density is insufficient the contrast will be too. They work together

Long scale

Many diagnostic densities but a small difference between them. Low contrast high kVp

Short scale

Few diagnostic densities with large difference between them. High contrast low kVp

Example chest

What is the most detrimental Influencing factor to contrast

Fog

What is the most popular cause of fog

Scatter radiation