General Q1-10

Question 1

Appoint imaging methods:

Answer 1

Radiology
Fluoroscopy
Computer tomography
Magnetic resonance imaging
Ultrasonography
Endoscopy

Question 2

Characterize X-rays:

Answer 2

X-rays = electromagnetic radiation
* Have no charge, no mass and cannot be felt
* Penetrate all matter to some degree
* Ionizing
* Cause some substances to fluorescence

Question 3

Describe the physical nature of X-radiation (photons, beam, quality, mA, kV, operating console, heat):

Answer 3

Photons = produced in a tube. Electrons sent from a cathode collide with the atoms of target element of the anode.
Beam = photons with different range of energy.
Quality = increased number of electrons means more photons are produced and increased intensity of beam. Increased speed of electrons means more energic beam causing beam with higher quality.
mA (milli ampere) = number of electrons produced by cathode. Controlled by the amount of electric current passing through the cathode (filament).
kV (kilovoltage) = strength/speed of electrons
Operating console = allows control of x-ray tube current and voltage, to ensure proper quantity and quality of x-ray beam.
Heat = much of the electron energy is converted to heat, the more the anode needs to rotate to dissipate heat.

Question 4

Name components of the X-ray device:

Answer 4

3 main components:
1) Operating console - kV, mA
2) Generator - supply power to the x-ray tube
3) X-ray tube - External (tube support, protective housing, glass/metal envelope), Internal (has vacuum). Internal consists of cathode (thermionic emission) and anode (flat disc that draws electrons).

Other components:
Collimator (primary grid) - limit primary x-rays and prevent non-useful radiation leaving tube
Secondary grids - between patient and film to reduce scattered radiation from entering the film and improves image contrast
X-ray film - inside cassette, turns black when hit by X-rays

Question 5

Describe the development of X-rays in short terms:

Answer 5

1) X-rays (photons) = a form of energy with the ability to penetrate tissue
2) Photons are absorbed by tissue
3) Photons pass through the tissue
4) Photons hit and interact with and expose the x-ray film
5) Produce a picture

Question 6

Explain the physical nature of CT:

Answer 6

CT (computed tomography):
X-ray beam rotates around the body to ger a series of x-ray projections.
* creates 3D image
* generated on computer screen; photons that pass through the tissue are transformed into electrical signals that the computer understands
* assess all the tissues and fluids, and differentiates
* more accurate
Amount of x-rays absorbed determine the density of tissue, and are assigned a Hounsfield unit or CT number.
* High density (bone etc) absorbs to a greater degree
* Low density (lungs etc) absorbs less

Question 7

Explain the physical nature of MRI in short term:

Answer 7

MRI (magnetic resonance imaging):
1) Hydrogen proton spins around its axis, act as many tiny magnets.
2) Body is placed in a strong magnetic field. Passing of electric currents through wire loops, proton will all line in the same direction.
3) Short bursts of radio waves are sent to the body, knocking the protons out of alignment.
4) Radio waves are turned off, protons realign. This sends out radio signals picked up by recievers.
5) The info is sent to a computer which process all the signals and generates a 3D image.

High water and fat is white, bone is black due to low water.

Question 8

Explain sciascopy and skiagraphy:

Answer 8

Sciascopy: Static image. Process of copying radiographs. Emulsion side of copy film faces X-ray, and the pair of films is exposed to UV-light.

Skiagraphy: movement (x-ray movie) = fluoroscopy - a dynamic method of imaging organs using x-rays. X-ray beam is passed through the body and image is transmitted to a monitor so the movement of body part can be seen in detail.

Question 9

Explain differences between CT and MRI:

Answer 9

CT: X-ray beam rotate around the body to get a series of x-ray projections. Creates 3D image on a computer screen: X-ray photons pass through tissues and are transformed into electric signals that the computer understands.

MRI: Large tube with powerful magnets. Uses strong magnetic fields, radio waves and the body’s natural magnetic properties (hydrogen molecules) to produce detailed image inside the body.

Question 10

Where and how are x-rays formed?

Answer 10

1) patient is placed between x-ray tube and x-ray film
2) x-ray beam pass through the subject and undergo absorption by tissues
3) the rest of the beams that is not absorbed is recorded by the film
3) the film produces an image

Question 11

Describe the film and how does it work:

Answer 11

The film responsible for image production = emulsion consisting of gelatine with tiny granules of silver bromide.
1. Silver bromide is sensitive to x-ray photons
2. When exposed, silver bromide precipitate and appear black, unexposed crystals white.
3. Amount of precipitated silver determines how black, grey or white that part of the film appears.
4. This is directly related to the number of x-rays that react with that part of the film.

Question 12

Describe x-ray interactions with tissue (degree of absorption):

Answer 12

Degree of absorption depends on three factors:
* Atomic number of tissue: high atomic number, more absorption, more radiopaque
* Thickness of tissue: the thicker tissue, more radiopaque
* Superimposition density: additive density of superimposed objects

Question 13

Name the five radiographic densities, radiopaque to radiolucent:

Answer 13

1. Metal: white (all x-rays are absorbed)
2. Bone: nearly white
3. Soft tissue/fluid: mid-grey
4. Fat: dark grey
5. Air/gas: black

Question 14

Explain radiolucency and radiopacity:

Answer 14

Radiolucency: quality of permitting the passage of radiant energy such as x-rays (increased = blackness).
Radiopacity: ability of obstructing the passage of radiant energy (increased = whiteness)

Question 15

What is digital radiography?

Answer 15

Direct-readout electronic x-ray detectors either use as a direct technique or indirect technique for converting x-rays into electrical charge.

Question 16

Explain the difference between development radiography direct and indirect digitalization:

Answer 16

Direct digitalization:
* directly converts x-ray photons into electrical charge, image immediately appear
* bypass the need to connect the cassette to computer
Indirect digitalization:
* first converts x-rays into visible light, then electrical charge
* need to put cassette into computer

Question 17

Explain film processing in dark room:

Answer 17

1) Development (reduction): 3-5 min, chemicals convert exposed crystals of silver bromide into grains of metallic silver
2) Rinsing: 10 sec, remove excess developing solution
3) Fixing: 10 min, immersion in fixing solution to stop development and make the image permanent
4) Washing: water tank, 15-30 min
5) Drying

Question 18

Explain the difference between primary and secondary radiation:

Answer 18

Primary radiation:
* Comes directly from source
* Beam is used to produce a radiographic image
* Emerge through window in the x-ray tube
* When exposed you are hit directly by the x-rays originating from the x-ray machine

Secondary radiation:
* Low energy x-ray photons from the primary radiation, not sufficient to pass through the patient and is scattered
* Fog the film –> unclear image
* Partly absorbed or scattered by the patient
* Comptoms effect: low energy photon continues to travel in random directions (safety hazard)

Question 19

Explain the difference between a primary and a secondary screen:

Answer 19

Primary screen: focuses the primary radiation to create a clear picture. Is situated in the collimator (primary grid).

Secondary screen: prevents blurring of the picture by secondary radiation and oblique x-rays. Secondary gris between the patient and the film. Absorb or align the x-rays to only allow straight x-rays to enter the film –> better quality of the image.

Question 20

Explain magnification:

Answer 20

Enlargement of a radiograph image of an object in relation to actual size. Occurs when the distance increases between object and film.

Question 21

Explain distortion:

Answer 21

Misrepresentation of the true shape of an object. Caused by unequal magnification of different parts of the same object. Distorsion is reduced by ensuring that the object and the film is parallel.

Question 22

Explain superimposition:

Answer 22

When two objects/organs overlap. The overlapped area appear more radiopaque than the rest of the object/tissue.

Question 23

Explain the Silhouette effect:

Answer 23

When two objects of the same radiopacity is in contact and the two margins are impossible to differentiate.

Question 24

Explain the Collimator:

Answer 24

Device which limits the primary x-rays and prevents non-useful radiation leaving the x-ray tube, which would otherwise increase the dose recieved by the patient or cause fogging of the image. This also improve radiation safety.

Question 25

Explain Penetration:

Answer 25

The ability of the photons to pass through objects. Objects of low specific gravity will absorb less, thus more photons penetrate it. The object will appear radiolucent on the image.

Question 26

Explain absorption:

Answer 26

The ability of the tissues to absorb and stop the photons passing through the body. With higher specific gravity, more photons are absorbed and the film appears more radiopaque.

Question 27

Explain radiolucency:

Answer 27

The ability of permitting the passage of radiant energy such as x-rays (AIR). Increased radiolucency = increased blackness.

Question 28

Explain radiopacity:

Answer 28

Ability of stopping the passage of radiant energy such as x-rays (METAL). Increased radiopacity = increased whiteness.

Question 29

What does the radiographic cassette consist of?

Answer 29

1. Front/outer covering composed of material of low atomic number and density
2. Foam layer
3. Intensifying screen
4. Emulsion
5. Film

Question 30

What is the role of intensifying screens?

Answer 30

To reduce the amount of exposure of the film to create a clear image. Allow much lower mAs, and less scatter and patient exposure.

Question 31

What are the possibilities of radiograph identification by intensifying screens?

Answer 31

1) a radiopaque marker is added during the primary exposure (lead letters on write-on tape)
2) a light marker can be used prior to processing (exposure to light in dark room)
3) digital labelling before x-raying
Radio ID: name of practice, animal and owner, date.

Question 32

Describe radiographic films:

Answer 32

Non-screen films:
* used without intensifying films
* high amount of mAs required
* extremely fine images
* film is wrapped in thick, light-proof paper
* small dental films
Screen films:
* designed for use in cassettes
* less detailed/fine image due to the intensifying screen

Question 33

What are the three basic types of protection against x-rays?

Answer 33

1) Shielding
2) Distance
3) Time

Types of protection:
* Lead clothing
* Physical barrier (wall with lead)
* Monitoring of x-ray exposure
* Distance increasing
* Decrease duration (time) of exposure
* Remove unnecessary personnel
* Keep mAs and kV to correct level

Question 34

Explain the concept of dosimeter, density and opacity:

Answer 34

Dosimeter: small monitoring device that record any radiation they are exposed to, worn on the trunk beneath the lead apron.

Density: measure of overall darkness of the image. Ratio between the light hitting the film and the light being transmitted through the film.

Opacity: measure of penetration ability. Darkening of the film by the primary beam hitting with little hindrance.

Question 35

What factors influence exposure and how?

Answer 35

kV and mA - Overexposed, underexposed or unbalanced proportion between the two.

Question 36

Explain how kV and mA influence exposure:

Answer 36

Kilovoltage: contribute to blackening and contrast.
* min kV depends on the size of the animal as the photons must have enough energy to reach the film.
* influenced by the potential difference between the cathode and anode.
* by increasing kV, we increase the energy of each electron so that the photons produced have more energy –> increased penetration power and quality

Milliampere:
* mAs (per second) control the electrical current to the cathode = number of x-ray photons produced during exposure. Contribute to overall film blackening.

Question 37

When do we use a raster?

Answer 37

Raster = special type of collimotor/grid located inside the cassette.
Thin bars of lead that only allow the x-rays from the focus to hit the film –> reduces the scattered radiation and improve image quality.

Question 38

Describe the errors that may occur during making of radiograph:

Answer 38

The machine:
* wrong settings: under/overexposure - too light/dark image
* patient: position, movement
* grid: used to avoid excess scatter and reduce fog
* artefacts: manmade objects, large focal spot - blurred image, magnification, damage to film, fogging, dirty/damaged screens, foreign objects ON patient

Question 39

Describe errors that may occur during development of the radiograph:

Answer 39

• Exposure to light
• Wrong processing in the dark room (foggy, splash drops)
• Rough handling
• Automatic processing - dirty

Question 40

Describe errors in the assesment of radiograph:

Answer 40

Labelling: left/right side should be labelled
Assessment: assess whole image, minimum 2 angles
Artefacts: superimposition or silhouette effect
Hypothesis: radiology is not a diagnostic method, only confirm hypothesis