X-Ray Module 3

What is the anode heel effect?

Distribution of radiation intensity more on the cathode side than the anode side

Why is the intensity reduced as it travels through the “heel” of the anode?

Travels a longer path through the anode

How much can radiation intensity vary across the useful beam?

45%

Which portion of the X-ray tube should be positioned over the thinner portion of anatomy?

Anode

Which portion of the X-ray tube should be positioned over the thicker part of anatomy?

Cathode

What are the main factors that alter the anode heel effect?

Anode angle

X-ray field size

Distance

How does anode angle effect the heel effect?

Smaller the angle, greater the heel effect

How does x-ray field size effect the heel effect?

Large the field size, greater the heel effect

How does distance effect the heel effect?

Shorter the distance, greater the heel effect

How is characteristic radiation produced?

Projectile electron interacts with inner-shell electron of target atom

How is an x-ray produced?

Outer-shell electron drops into the inner shell

What is the x-ray energy equal to?

The difference in binding energies of the orbital electrons involved

Which shell in tungsten is the only shell that can produce high enough energy for diagnostic x-rays?

K

What is the required x-ray tube potential for K-characteristic x-rays?

69 kVp

What happens if <69 kVp?

No useful characteristic x-rays produced

What kind of spectrum do characteristic x-rays have?

fixed energies

discrete emission energies

How is Bremsstrahlung radiation produced?

Projectile electron misses target electron, but come close to nucleus

What does Bremsstrahlung mean?

German

“Slowing down” / “braking”

How are x-rays made during Bremsstrahlung?

As electron changes direction and slows down, loss of kinetic energy in converted to x-ray

What happens when the electron come closer to nucleus?

More it bends its path

Slows down more

Produces higher energy x-ray

What kind of spectrum does Bremsstrahlung have?

Range of energies

Continuous emission

At 100 kVp, what percentage of x-ray beam is characteristic?

15

At 100 kVp, what percentage of x-ray beam is bremsstrahlung?

85

How can total number of x-rays emitted be determined?

Adding together number of x-rays at each energy

On a graph, where is the total number of x-rays emitted?

Under the curve

Generally, how does the curve change?

Always same shape

relative position can change

How does a change is mA or mAs affect x-rays?

proportional change in amplitude of x-ray emission spectrum at all energies

How doe kVp change affect x-ray spectrum?

Both amplitude and position

What would happen with a 15% increase in kVp?

Doubles mAs

How does filtration work with x-rays?

Absorbs low energy x-rays

Allows high energy x-rays to pass

What is increasing the average energy of the beam called?

Beam hardening

What will happen when you add filtration?

Reduce x-ray intensity and increase average energy

What does the atomic number affect?

Quantity and energy of x-rays

What happens if you increase the target atomic number?

Increase efficiency of x-ray production

Increase energy of characteristic and bremsstrahlung x-rays

What does the atomic number affect?

Quantity and energy of the x-rays

What happens when the % ripple is lower?

Higher the x-ray intensity (mAs) and energy (kVp)