Lecture 1 Basics Of Radiology

Front 1

Who discovered X-rays?

Back 1

Wilhelm Conrad Rontgen
In 1895

Front 2

What is the difference b/w an X-ray and a gamma ray?

Back 2

X-rays are produced outside the body and gamma rays are created from atoms within the body

Front 3

*How are x-rays produced?

Back 3

When high speed electrons strike a metal target.

Front 4

*What are the 3 key requirements for x-ray production?

Back 4

1) Cathode electron source
2) Method to accelerate electrons
3) Anode target

Front 5

*How are electrons produced at the cathode?

Back 5

Electricity passes through a Tungsten filament and the filament becomes hot and releases electrons in a surrounding cloud

Front 6

*What tightens the electron cloud produced at the cathode?

Back 6

The focusing cup tightens the cloud, it's negatively charged therefore repelling the electron cloud=tightens cloud

Front 7

What determines if there is a large or small focal spot when taking an x-ray?

Back 7

Whether using a large or small Tungsten filament in the cathode

Front 8

What is the mA control on an x-ray machine?

Back 8

Milliamps- the strength of the current that passes through the Tungsten filament

Front 9

What happens to the size of the electron cloud when the mA is increased?

Back 9

Stronger the current the larger the electron cloud

Front 10

True or false. The Tungsten filament is an important part of the anode.

Back 10

False, the filament is part of the cathode

Front 11

*What method is used to accelerate the electrons produced by the filament?

Back 11

The voltage difference b/w the cathode and anode
Cloud of electrons at cathode is attracted to the anode (positively charged Tungsten target)

Front 12

*What regulates the voltage difference b/w the cathode and anode in an X-ray machine?

Back 12

kVp

Front 13

How does the energy difference b/w the anode and cathode affect the energy of the x-ray?

Back 13

Higher difference=higher energy
Higher energy=higher velocity e-
Higher velocity e-=higher energy X-rays

Front 14

Why does the anode rotate?

Back 14

To dissipate the heat produced from the electrons hitting the anode

Front 15

*What are the 2 major types of electron interactions that occur with the tungsten at the anode?

Back 15

1) Characteristic X-ray generation
5% of x-rays of diagnostic imaging
2) Bremsstrahlung radiation
95% of X-rays in diagnostic imaging

Front 16

True or false. The Bremsstrahlung radiation is responsible for 85% of the X-rays used in diagnostic imaging.

Back 16

False, 95%

Front 17

When are X-rays actually generated?

Back 17

Once the electrons hit the Tungsten-get the characteristic X-ray generation and Bremsstrahlung radiation

Front 18

What produces characteristic X-rays?

Back 18

The electron produced at the cathode of the x-ray tube ejects an orbital electron from the K shell. The outer shell electron of a higher energy fills the void of the inner shell and the difference in energy levels is emitted as an x-ray photon.

Front 19

* True or false. Characteristic x-rays result in a broad, continuous range of x-ray energies.

Back 19

False, x-rays of specific energy are released

Front 20

*What does the energy of a characteristic x-ray depend on?

Back 20

The material-the differences o binding energies b/w the orbital electrons.

Front 21

*What produces Bremsstrahlung radiation?

Back 21

Fast electrons approach the nucleus of the Tungstenand slow as it loses energy, this energy is emitted as x-rays
(e- close to nucleus=very slow=higher energy x-ray

Front 22

*True or false.Bremmstrahlung radiation results in a broad, continuous range of X-ray energies.

Back 22

True

Front 23

What does the energy of Bremsstrahlung radiation depend on?

Back 23

How close the electron gets to the nucleus

Front 24

The maximum energy of the Bremsstrahlung radiation continuum is equal to what?

Back 24

kVp

Front 25

At what energy do you see the Characteristic radiation peaks on a graph of number of x-rays vs energy? why?

Back 25

2 at about 60-this is the energy released by the k & L shell of tungsten

Front 26

*What are the 3 results of increasing the kVp?

Back 26

*1) Higher energy x-rays
2) More electrons from cathode accelerated to anode
*3) More X-rays

Front 27

*What are the 4 interactions of x-rays with matter?

Back 27

1) Coherent scatter
2) Photoelectric effect
3) Compton scatter
4) None (goes straight through)

Front 28

True or false. Coherent scatter degrades image quality.

Back 28

True

Front 29

What is coherent scattering?

Back 29

A photon interacts with an object and changes direction
-No absorption of photon
-No ionization
-X-ray looses no energy

Front 30

Which x-rays undergo coherent scatter?

Back 30

Very low energy x-rays

Front 31

True or false. Coherent scatter is the source for most occupational radiation.

Back 31

False, Compton scatter is the source of most occupational radiation

Front 32

True or false. The amount of x-rays that undergo Coherent scatter is only 5%.

Back 32

True

Front 33

*What is the biggest contributor to radiographic contrast?

Back 33

Photoelectric effect

Front 34

*What is the photoelectric effect?

Back 34

X-ray energy is completely absorbed (by the patient)

Front 35

*The probability of a photoelectric interaction is directly proportional to what?

Back 35

Z^3
Z=atomic number

Front 36

How does the photoelectric effect result in contrast?

Back 36

Small differences in atomic composition of neighboring tissues lead to big differences in the number of x-rays absorbed=radiographic contrast

Front 37

What is the photoelectric effect inversely proportional to?

Back 37

The cube of x-ray energy (kVp)
1/E^3

Front 38

True or false. The photoelectric effect is more likely with low energy x-rays.

Back 38

True, inversely proportional to x-ray energy (kVp) so less likely with high energy x-rays

Front 39

What produces Compton scatter?

Back 39

X-ray interacts with outer shell electron in atom of patient's tissues and ejects outer-shell electron resulting in ionization of the target atom and a change in x-ray direction=scatter

Front 40

*True or false. Compton scatter does not change the direction of the x-ray.

Back 40

False, it does change the x-ray direction=scatter
(Coherent scatter changes direction only slightly)

Front 41

True or false. Compton scatter doesn't change the x-ray energy.

Back 41

False, it reduces x-ray energy. Coherent scatter doesn't decrease energy of x-ray

Front 42

What is the probability of Compton scatter directly proportional to?

Back 42

The total number of electrons in the patient
-physical density (g/cm^3)
-e-/g

Front 43

True or false. Most matter contains the same e-/g.

Back 43

True, this results in poor tissue contrast

Front 44

The probability of Compton scatter is inversely proportional to what?

Back 44

X-ray energy
1/E

Front 45

What are the 2 types of radiographs?

Back 45

Conventional radiographs
Digital radiographs

Front 46

What are conventional radiographs?

Back 46

Films viewed using a light box

Front 47

What are the 2 main systems of digital radiography?

Back 47

1) Computed radiography
2) Direct Digital radiography

Front 48

What are digital radiographs?

Back 48

Where radiograph exists as DICOM file and displayed on a monitor.

Front 49

What comprises a radiographic x-ray film?

Back 49

Silver halide crystals bound to a polyester base.

Front 50

Relatively speaking, do more x-rays hit a film when it is black or white?

Back 50

Black-means lots of x-rays went straight through

Front 51

Do films usually have singe or double layers of emulsion?

Back 51

Double

Front 52

*What happens to the silver halide crystals in a film after exposure to light/x-rays and development?

Back 52

Converts to metallic silver

Front 53

**Are x-ray films more sensitive to light or x-rays?

Back 53

LIGHT

Front 54

How does developed and exposed silver in a film appear?

Back 54

black

Front 55

*What 5 things determines the 'blackness' of an x-ray film?

Back 55

1) The number of x-rays hitting the film
2) Energy of the x-rays
3) Distance from the x-ray tube to the film
4) Film and screen speeds
5) Film development conditions

Front 56

*What determines the number of x-rays that hit a film?

Back 56

1) mAs
2) Patient attenuation

Front 57

*What determines the energy of x-rays?

Back 57

kVp

Front 58

What determines the distance from the x-ray tube to the film?

Back 58

Focal spot to film distance

Front 59

What are 3 film development conditions that affect the blackness of the film?

Back 59

Temperature, time and concentration of chemicals.

Front 60

*Intensifying screens for x-ray cassettes contain a _______ layer.

Back 60

Fluorescent

Front 61

*What is the function of intensifying screens on x-ray cassettes?

Back 61

Converts x-ray energy to light
Color of light emitted is matched to color sensitivity of film

Front 62

Where are intensifying screens located?

Back 62

Inside cassette, adjacent to film

Front 63

Why do we want the film and intensifying screen in contact?

Back 63

To ensure optimal light transfer by minimizing light diffusion from phosphor (fluorescent layer) in screen to film

Front 64

What are the 3 steps in 'developing' a film?

Back 64

1) Develop (exposed silver)
2) Fix
3) Wash (unexposed silver)

Front 65

What is the purpose of film development?

Back 65

Amplifies the latent image by 10^8

Front 66

What does the developer do to the film?

Back 66

Turns exposed silver crystals black

Front 67

How is film development accomplished?

Back 67

Chemical process
-Time & temperature sensitive
-Multiple chemicals in solution

Front 68

What happens during the fixing of a film?

Back 68

Stabilizes developed silver & solubilizes unexposed silver halide crystals

Front 69

You develop a film but it comes out milky or cloudy looking, what went wrong?

Back 69

Inadequate fixing

Front 70

What is washing a film?

Back 70

washes fixer from radiograph

Front 71

What happens if a film is not washed thoroughly enough?

Back 71

Unremoved fixer reacts w/ silver in the film, forming silver sulfide= smells like rotten eggs

Front 72

*You take an x-ray but your film comes out and smells like rotten eggs, what happened?

Back 72

The film was not properly washed
Film will also turn brown w/ age

Front 73

What does digital radiography use instead of film?

Back 73

Digital x-ray sensors

Front 74

*Compare contrast resolution and spatial resolution in digital and conventional radiographs.

Back 74

Contrast resolution=digital is better
Spatial resolution=film is better

Front 75

Are conventional or digital radiographs more forgiving to over/underexposure?

Back 75

Digital

Front 76

True or false. Digital radiography takes more technique to produce a similar image to conventional radiographs.

Back 76

False, digital radiography requires less technique

Front 77

What is technique?

Back 77

mAs & kVp

Front 78

What are the 2 advantages to digital radiography?

Back 78

1) Allows immediate image viewing
2) Ability to digitally transfer image
-Teleradiology
-Consultation

Front 79

What is used instead of a film with computed radiography?

Back 79

Imaging plate

Front 80

The imaging plate used for computed radiography is coated with what?

Back 80

Photostimulable phosphors

Front 81

What happen when x-rays strike the imaging plate?

Back 81

Energizes/traps the electrons in a higher energy state=latent image

Front 82

How is the latent image on the imaging plate converted to an actual image?

Back 82

The plate reader extracts the imaging plate from a cassette and scans it with a red laser to release the image.

Front 83

How are imaging plates cleared?

Back 83

White light
(Red light releases image)

Front 84

What limits the resolution of computed radiography?

Back 84

The size of the laser in the ADC which converts the latent image into the digital image, can't make laser smaller so can't get better spatial resolution

Front 85

*What comprises the imaging plate used for digital radiography?

Back 85

Is an array of detector elements
-Built into table or portable
-Has to be connected to computer

Front 86

What are the 2 types of direct digital radiography?

Back 86

Direct: converts x-ray energy directly into an electrical signal
Indirect: converts x-ray energy into light, light is converted into an electrical signal

Front 87

*What are the 3 fates of x-rays after leaving the tube?

Back 87

1) Absorbed in patient
2) Scattered by patient
3) Pass through unchanged

Front 88

*True or false. X-rays must pass through the patient to reach the film.

Back 88

True

Front 89

*True or false. Differential scattering of x-rays in patients is what leads to differential darkening of film.

Back 89

False, differential absorption!

Front 90

*The amount of x-ray absorption depends on what 4 factors?

Back 90

1) Density of tissue- e-/g (Compton)
2) Atomic number of elements in tissue (photoelectric)
3) X-ray energy
4) Thickness of tissue

Front 91

**What are the 5 opacities (differential x-ray absorption)?

Back 91

1) Air
2) Fat
3) Soft tissue/fluid
4) Bone/mineral
5) Metal

Front 92

Why does mineral appear different from fat on an x-ray?

Back 92

Because mineral has a higher atomic number so has a greater photoelectric effect

Front 93

Where is air normally found in x-rays?

Back 93

Lungs & intestines

Front 94

Where is fat normally visible on radiographs?

Back 94

B/w abdominal organs

Front 95

The 'soft tissue' opacity includes what 3 things?

Back 95

1) Parenchymal organs
2) Muscle
3) fluids e.g. blood, bile, urine

Front 96

How does contrast material appear on radiographs?

Back 96

Metal opaque

Front 97

Does an overexposed film appear white or black?

Back 97

Black -too many x-rays hit film

Front 98

On radiographs, what can be mistaken for thin bone?

Back 98

Very thick soft tissues can look the same as thin bones.