FINAL ch.8, 9, 10

Chapter 8

What is Characteristic Radiation?

Projectile electron collides with inner-shell electron, removed from target atoms = ionized

What fills the inner shell vacancy (characteristic)? and what is produced?

Outer shell; x-ray emission

What does each photon have?

Has specific energy equal to the difference in binding energies of two shells involved

Projectile Electron=

Photoelectron

Which shell = characteristic x-ray? with what energy?

Only K Shell

with at least 69 keV = Diagnostic radiograph

higher atomic # of target = ?

increased energy

What is Brems Xrays?

Projectile electron passes nucleus of target atom, slows down, changed course and leaves with reduction KE

Which interactions happen in the tube?

Characteristic and Bremsstrahlung

What is lost in Brems X-rays?

energy lost

What do most X-rays = ?

Brems (diagnostic Range)

<69 kVp = what type of interaction?

Brems X-rays

over 69 kVp = Which interaction?

Characteristic and/or Brems

X-ray Emission Spectrum

illustrated relative number of x-rays at each energy levels, from 0 - 100 keV

aka Characteristic Xray

discrete, Specified Spectrum

Characteristic Xray Spectrum binding energy

= 69keV (limited energies)

Mono energetic

one energy

Poly energetic

many energies

Factors that affect size and position of x-ray spectrum

1. mAs

2. kVp

3. added filtration

4. target material

5. voltage waveform

mAs

Change in mAs is DIRECTLY PROPORTIONAL to change in amplitude of spectrum

Examples of mAs increase

if doubled 200 mA to 400 mA = twice the # of projectile electrons (from cathode to anode) = mAs doubled but energy is the same

increase in mAs = ?

increase in amplitude

increase in quantity =

NO change in quality

kVp increase

When kVp is increased = amplitude of spectrum increased BUT also more high energy emitted

kVp High Energy =

• higher potential for multiple penetrability

• increase both energy and quality

Increase voltage ripple =

Decrease quantity and decrease in quality

The shift of the characteristic x-ray spectrum to higher energy will occur because of

an increased in atomic number

Useful characteristic x-rays are produced in tungsten

by ionization of a k-shell electron

Characteristic x-ray

are characteristic of target Z

Brems radiation is produced by

a conversion of projectile electron kinetic energy to electromagnetic energy

If an average radiographic technique is used

most x-rays are bremsstrahlung

In bremsstrahlung x-ray production

the projectile electron is from the cathode

When Brems X-ray is produced

a projectile electron will lose enegry

The wavelength of an x-ray

becomes longer as projectile electron kinetic energy is reduced

An increase in mAs will

increase the number of bremsstrahlung x-rays

The area under the curve of the x-ray emission spectrum us representative of

the total number of x-rays

Normally the x-ray emission spectrum contaisn

both characteristic and bremsstrahlung x-rays

The characteristic x-ray emission spectrum principally depends on which of the following?

target material

The x-ray emission spectrum that represents several energy levels comes from

the x-rays emitted from the tube

Both the shape and position of the characteristic x-ray emission spectrum

correspond to target electron binding energies

Characteristic radiation is produced when

a vacancy in an electron orbit is filled

The x-ray emission spectrum is a plot of

the number of x-rays versus energy

The amplitude of the brems x-ray emissiono spectrum

has max value at an energy approx one third of the kVp

On s general x-ray emissiong spectrum, what 2 items are affected?

Quantity and Quality

Most of the x-rays produced at the target are

Bremsstrahlung

In order to construct an x-ray emission spectrum, one must know the

number of x-rays at each energy intervals

The wavelength of an x-ray is

inversely proportional to its energy

Minimum wavelength is related to

the KE of the Projectile Electron

The region of the x-ray emission spectrum associated with minimum wavelength

highest-energy brems x-ray

To calculate minimum x-ray wavelength, one must know the value of

kVp

Chapter 9

What does nomogram do?

Estimates intensity of x-ray beam

How is an increase in mAs relates to kVp?

Increase mAs (increase quantity of photons) and not related to energy (kVp)

Increase kVp = ?

decrease in mAs

increase in kVp, decrease in mAs = ?

OD (optical density) remains constant = decrease patient dose

Inverse Square Law equation

Terms related to Inverse Square Law

New Intensity + Patient Dose, Distance, Intensity

What is Inverse Square Law?

Radiation intensity varies inversely with the square of the distance from the target

Radiation intensity = ?

dose patient receives

What is the equation for Square Law?

What is the purpose of filtration?

Reduce (filters out) low energy x-ray

Why is filtration good for patients?

Reduce patient dose

What is the size for metal filters in x-ray?

X-ray unit have metal filters: 1-3mm Al

What does filtration do?

reduces quantity (x-rays) useful beam

What is a disadvantage of filtration?

Reduces image contrast

Hard X-rays =?

high quality and high penetrability

Soft x-rays = ?

low quality and low penetrability

Why is enough kVp needed for x-rays?

ENOUGH kVp IS NEEDED TO PENETRATE THE BODY AND THROUGH THE IR

What is a half value layer?

Thickness of absorbing material necessary to reduce x-ray intensity to half its original value

What is the range of HVL for a diag. X-ray?

Diagnostic x-ray beam has HVL range of 3-5mm Al or 3-6cm soft tissue

What do higher x-rays have?

High energy x-rays have higher penetrability and thicker HVL’s

What does HVL have an influence on?

HVL is influences by type of rectification, total filtration and kVp

HVL = … quality ?

Beam Quality

What is HVL?

Some kind of filtration

Increase HVL will increase what?

IF YOU INCREASE HVL = INCREASE PENETRABILITY = DECREASE PATIENT DOSE

Increase kVp will increase what two things?

kVp - increase kVp = increase quality = increase HVL

What is the purpose of filtration? (name 2)

Reduce patient dose

Increase quality

Increase in filtration = increase in ? , decrease ?

increase quality, decrease quantity

What will there be less of on patient?

Less dose skin and organs exposure

What is considered inherent filtration?

includes glass or metal envelop, oil (insulator and tube housing

How thick is added filtration?

1.0mm Al

How thick is mirror collimator?

1.0mm Al

Total Filtration?

2.5mm Al

What are compensating filters?

Comes in many shapes and sizes are usually made of Al or plastic

Why are compensating filters used?

Used to provide more uniforms density on the radiograph due to irregular anatomy

What is the anatomic number for Al?

13

What are the types of filters?

Wedge

Trough filter

bow tie

conic filter

Why are these filters useful?

These filters are useful in maintaining image quality not radiation protection devices

What are keywords for x-rays happening inside the tube

Electron, Target (anode), interaction

What is x-ray quantity inversely proportional to?

Distance

Why is a minimum HVL required for diag. x-ray beam?

A minimum HVL is required for diagnostic x-ray beam because a lower HVL would result in an increased absorbed dose to the patient with no improvement in image quality

When filtration is added to an x-ray tube, which is principally a function of which of the following

kVp

As filtration is added to an x-ray beam

low energy x-rays are removed more readily than high-energy x-rays

a minimum HVL is required for diag. x-ray beam because

a lower HVL would result in an increased absorbed dose to the pt with no improvement in image quality

An X-ray beam can be made to have higher effective energy in which of the following

A filtration is added

Reducing kVp will do which of the following in regards to filtration

soften the x-ray beam

Adding filtration to an x-ray beam will do which of the following in regards to filtration

increase quality

HVL is defined as

a thickess of materail that will halve x-ray quantity

The inherent filtration in a general purpose radiographic x-ray tube is usually equivalent to

.5mm AL

How many HVL’s are required in order to reduce the intensity of a beam of monoenergetic photons to less than 10% of its original value?

4