X-ray Production and Making a Radiograph

Radiograph

medical image depicting patient anatomy; shadow of anatomy creating using x-rays (form of electromagnetic energy)

Electromagnetic radiation

a form of energy that exhibits wavelike behavior as it travels through space

Photons

massless, chargeless, packets of energy that can travel at the speed of light

Velocity is equal to....

wavelength x frequency

Energy of photons is directly proportional to ____________ and inversely proportional to ____________

frequency; wavelength

Wavelength and frequency are ____________ proportional

inversely (as wavelength goes up, frequency goes down and vice versa)

Higher energies have _________ frequency and ___________ wavelength

higher; lower

X-ray machine components

X-ray tube, control panel, and table

X-ray tube

heart of the x-ray generating system; consists of cathode and anode that creates the X-ray

Cathode of X-ray

tungsten filament that is the source of electrons for the X-ray

What controls the current flowing thorugh the cathode?

the milliampere setting (mA)

*higher mA, more current, more electrons

Anode of X-ray

target for electrons coming from cathode; tungsten

Two technique settings of the control panel

1.) kVp

2.) mAs

mAs setting

milliapere per second; determines how many electrons are available to interact with anode

kVp setting

controls the electric potential difference between the cathode & the anode

Higher kVp settings give the projectile electrons greater kinetic energy & produce...

a beam with x-rays of greater quantity and quality

kVp determines the _________ of electrons, and therefore the _________ they possess

speed; energy

Two types of anodes

1.) rotating

2.) stationary

rotating anode

disc that rotates about the center; area that electrons coming from cathode strike is spread out over the disc area, allowing for greater heat absorption

Because the rotating anode can absorb more heat, we can use ___________ technique settings

higher

When might higher technique settings be useful?

larger patients and thicker body parts where higher energy photons are required

Stationary anode

chunk of tungsten that doesn't move; electrons coming from cathode always strike the same place, so has lower heat absorption

Because the stationary anode can absorb less heat, we can use ___________ technique settings

lower

When might lower techhnique settings be useful?

in portable machines that you can carry around

What happens at the anode?

electrons come from the cathode to strike the anode and interact with tungsten ions; this creates a lot of heat

Though interaction with tungsten ions, electrons create _______ _______

X-ray photons

Two processes for creating X-ray photons

1.) General radiation (bremsstrahlung)

2.) Characteristic radiation (binding energy)

General radiation (bremsstrahlung)

electron slows as it passes through the tungsten nucleus; as it slows, it gives up energy that is released as an x-ray photon

The more an electron slows during general radiation, the __________ energy it gives off

higher

Characteristic Radiation (binding energy)

electron coming from cathode strikes an inner shell electron of tungsten and kicks it out of orbit; an outer shell electron of tungsten drops in to fill its place, which releases energy as an X-ray photon

The majority of photons in the x-ray beam are _________ of the peak kVp setting

1/3

There are many ______ energy x-rays created and these are not useful because...

low; they cannot contribute to image creation and can create scatter

What is done with the low energy x-rays produced?

They are filtered out using an aluminum sheet

aluminum sheet

absorbs energy from low energy x-rays while high energy x-rays flow through

Why does the X-ray beam need to be shaped?

-to reduce personnel and patient exposure

-to maintain image quality by reducing scatter

How is the x-ray beam shaped?

collimation

collimation

process by which the x-ray beam is shaped; paired lead sheets opposite each other are able to be adjusted to encompass the anatomy of interest

Collimator field

light created by a light bulb lights up area that is created by the lead sheets, depicting anatomy of interest and where x-ray beams are going to travel

The radiographic image is created due to...

differences in x-ray photon absorption of tissues

The image created depends on (4):

-x-ray energy

-tissue thickness

-physical density

-atomic number (Z) of tissue

The image is really a ____________

shadow

Three things that can happen when an X-ray photon enters the patient

1.) nothing

2.) X-ray photon stopped completely

3.) x-ray photon deviated

Three things that can happens when an X-ray photon enters the patient: Nothing

x-ray photon passes through patient in a straight line from the anode to the imaging plate and creates a black/gray area on radiograph in that spot

Three things that can happens when an X-ray photon enters the patient: X-ray photon stopped completely

complete absorption of photon occurs, creating a white area on radiograph

Three things that can happens when an X-ray photon enters the patient: x-ray photon deviated

photon is scattered, which degrades the image, and contributes to exposure

*no longer contributing to the actual image of patient

*can contribute to patient exposure

Photoelectric effect

occurs when x-ray photon is completely absorbed; most useful to radiology

Photoelectric effect is reposible for __________ on an image

contrast

The photoelectric effect is due to what type of radiation?

Characteristic Radiation (binding energy)

The photoelectric effect is more likely to occur with ________ atomic number tissues and ______ x-ray energy

higher; lower

The photoelectric effect is why bones are _________

white; bones possess atoms with higher atomic number, like minerals

Compton effect

not helpful in radiology; deviation of x-ray from initial path

What occurs with the compton effect?

an x-ray photon kicks outer shell electrons out of orbit, is richoched off in another direction, and can't contribue to the image

Compton effect is aka...

scatter!

Compton effects leads to...

-unnecessary radiation exposure

-lowers image contrast and creates false information

The compton effect is more likely to occur when using...

high kVp techniques

Radiographic image density

related to the number of x-ray photons that each the imaging plate

Black areas = _____ x-rays made it to imaging plate

Gray areas = _______ x-rays made it to imaging plate

White aras = _______ x-rays made it to imaging plate

more

some

no

Number of x-ray photons is determined by the ___________ technique setting and energy of x-ray photons is determiend by the ____________ technique setting

mAs

kVp

To create a good quality image, there must be a ___________ between mAs and kVp

balance

Underexposure

images are too white

Overexposure

images are too dark

Doubling the mAs _________ the density

doubles

*relationship is 1:1

Density is doubled when what happens to kVp

kVp + 10%

Density is halved when what happens to kVp

kVp - 10%

If anatomy is too light (underexposed) kVp was too ________

low (not enough energy to penetrate anatomy)

If anatomy is too dark (overrexposed) kVp was too ________

high (too much energy)

If kVp is decreased, mAs has to be __________. Why?

increased; to maintain the density of original image (if it was appropriate)

What else can influence density?

focal film distance

Focal film distance

distance between the spot electrons are striking on the anode and the imaging plate

Shorter Focal film distance = _______ intense x-ray beam, more _________ image

more; dense

the more dense an image, the _________ it is

darker

Longer Focal film distance = _______ intense x-ray beam, less _________ image

less; dense

the less dense an image, the _______ it is

lighter

How to begin the radiograph

1.) measure patient

2.) set technique settings (based on patient/where taking image)

3.) program kVp and mAs according to technique chart

4.) make exposure

How to measure patient

-Measure thickness for both the lateral measurements and ventral/dorsal measurements

-thickest area

Technique chart

-lists kVp and mAs based on thickness

-grouped by anatomy

-with or without grid

Radiographic opacity

the degree of object whiteness or blackness created by variable x-ray absorption/penetration; appearance of the patient in the image

Five radiographic opacities:

1.) metal

2.) mineral

3.) soft tissues

4.) fat

5.) gas

Tissue Z

atomic number of atoms composing a tissue

Tissue Z affects likelihood of photoelectric effect, but all soft tissues have the ________ average Z

same

However, the physcial density of soft tissues is __________

different

The physical density of tissues also effects the ___________ and radiographic ____________

attenuation; opacity

As kVp increases, contrast ______________. Why?

decreases; compton effect (more scatter, more gray)

As kVp decreases, contrast ________. Why?

increases; photoelectric effect dominates, less scatter, less gray

Thorax technique

-high contrast due to gas in the lungs and soft tissue of the heart

-needs less contrast to depict anatomy (to show more shades of gray)

-need to use high kVp to create low contrast

Abdomen technique

-low contrast tissue since everyting is fat or soft tissue

-needs more contrast (to show fewer shades of gray, enhances teh contrast between them)

-mid-range kVp is preferred technique

Musculoskeletal technique

-high contrast due to bone and soft tissue

-needs less contrast (to show more shades of gray)

-low kVp is prefered technique

Increasing the kVp will cause the __________ effect

compton (scatter)

What can be done to deal with scattering?

-collimate

-using a grid

Collimation helps to avoid ____________

scatter

Grids

plate that is mounted in the table; creates grid lines that can be removed in digital systems

Grids are needed when the patient thickness is over ________ cm

10 cm

What is a grid made of?

lead strips that absorb errant photons, and a space betwen them made of aluminum

Grid ratio

the ratio of the height of the lead strips to the distance between them

High grid ratio, ________ scatter gets through

Lower grid ratio, __________ scatter gets through

less

more

Grids are supposed to absorb scattered photons, but can also absorb _________ photons

non-scattered (that were supposed to contribute to the image)

Four consequences of radiograph being a 2-D image of a 3-D object

1.) magnification and distortion

2.) familiar becoming unfamiliar

3.) loss of depth perception

4.) summation

Distortion

due to divergence of x-ray beam as it fans out to create image; anatomy at edge of image will cast a larger shadow that is not representative of its shape

Distortion is common when imagaing ___________

spines

Magnification and blur

objects further from imaging plate cast a larger shadow and edges will be more blurry