X-ray Imaging

Question 1

What three specifications affect the quality of an X-ray image?

Answer 1

Exposure factors
Focal spot
Filtration

Question 2

Why is it important to turn off an X-ray machine when not in use?

Answer 2

When connected to a power supply, the area around it is considered a ‘controlled area’ with access restrictions.

Question 3

How does kV affect X-rays produced?

Answer 3

The higher the kV, the greater the potential difference across X-ray tube, and the faster the electrons will travel between cathode and anode.
Therefore resultant X-rays will have a higher energy.

Question 4

What is the typical kV range, and how does increasing this affect the exposure?

Answer 4

Typical range 40-120kV
kV affects penetrating power of X-rays produced, so need to increase kV to X-ray thicker parts of body
An increase of 10kV approximately doubles the exposure

Question 5

How does mA affect the X-rays produced?

Answer 5

The greater the mA, the hotter the cathode filament gets, and the more electrons are available to be accelerated across the tube.
If more electrons hit the anode, then more X-rays are produced (energy of X-rays is not changed)

Question 6

How does increasing exposure time affects X-rays produced?

Answer 6

Increasing time of exposure results in an increase in the number of X-rays produced

Question 7

What are typical mA values, and how does increasing this affect the exposure?

Answer 7

Typical 20-60mA (portable) 1000mA (fixed)
mAs govern quantity of X-rays produced
Increase in mAs needed to radiograph thicker parts of the body
Doubling the mAs doubles the exposure

Question 8

What do we need to decide on for each region when setting up an exposure chart?

Answer 8

kV
mA
s
Distance
Use of a grid

Question 9

What is the relationship in increase in kV and mAs?

Answer 9

An increase in 10kV is approximately equivalent to doubling the mAs

Question 10

What is the focal spot? Describe the ideal size.

Answer 10

Focal spot = the area of the anode hit by electrons

Ideally as small as possible - ‘point source’ of X-rays

Question 11

When would we use fine focus on an X-ray machine?

Answer 11

Used for smaller/thinner areas of anatomy - smaller focal spot.

Question 12

What is the difference between the actual and effective focal spot?

Answer 12

Angle of anode allows electrons to hit a larger area (actual focal spot), while source of X-ray beam is effectively smaller (effective focal spot)

Question 13

What is the penumbra of an image?

Answer 13

Slight margin of blurring around edge of a structure - increases with larger focal spot.

Question 14

What is filtration of X-rays?

Answer 14

Low-energy X-rays insufficient to penetrate patient, so filtered out by thin sheet of aluminium over window of X-ray tube.

Question 15

Name the three different types of X-ray machine.

Answer 15

Portable
Mobile
Fixed

Question 16

Describe portable machines.

Answer 16

Small, compact, easily moved
Can be operated from normal electrical socket#
Relatively low output
Often ‘linked’ exposures

Question 17

Describe mobile machines.

Answer 17

Larger and heavier than portable (wheeled)
Can still usually be operated from normal electrical socket
Higher output than portable machines

Question 18

Describe fixed machines.

Answer 18

Permanent installations - tube on a gantry
Wired to specialised 3-phase electrical supply
Much higher potential output

Question 19

How does collimation help in X-raying imaging?

Answer 19

Reduces unnecessary radiation of patient

Reduces production of scattered radiation (improves image quality, less personnel exposure)

Question 20

What is the Inverse Square Law and why is it important?

Answer 20

Intensity of beam at given point is inversely proportional to square of distance from X-ray tube
Important in radiation safety and exposure for the X-ray image formed

Question 21

Define film focal distance (FFD) and explain what this means for the exposure factors.

Answer 21

FFD = distance from X-ray tube to X-ray image receptor
If FFD is altered, mAs will need to be altered to produce a comparable radiograph (old mAs x new distance squared / old distance squared = new mAs)

Question 22

Define object film distance (OFD).

Answer 22

OFD = distance between the object being radiographed and the X-ray detector

Question 23

How does Object Film Distance affect magnification and how can we reduce this?

Answer 23

If OFD increases, image will be magnified
Keep patient area of interest as close to cassette as possible
Can use marker of known size to determine degree of magnification of image

Question 24

How does Object Film Distance (OFD) affect image sharpness and how can we reduce this distortion?

Answer 24

Large OFD increases size of penumbra around edges

Keep area of interest parallel to cassette and perpendicular to X-ray beam

Question 25

In what 3 ways might X-rays interact with matter?

Answer 25

X-ray photons pass through unchanged, in a straight line and do not lose energy (useful image) X-ray photons are absorbed, proportion depends on nature of material X-ray photons are scattered, lose some energy, degrade image quality and pose radiation hazard

Question 26

What factors affect the absorption of X-rays?

Answer 26

``` Atomic number (high Z = more absorption) Physical density (higher density = more absorption) Thickness of tissues (thicker tissues = more absorption) ```

Question 27

Describe how bone, gas and soft tissue would appear on a radiograph.

Answer 27

Bone = high Z, good absorber, white on image Gas = low density, poor absorber, black on image Soft tissue = intermediate Z and density, intermediate absorber, grey on image

Question 28

How are grids used and what do they do?

Answer 28

Used when radiographing thicker areas (approx. >10cm thick) Placed between patient and cassette Reduce amount of scattered radiation reaching the film - improve image quality

Question 29

How do grids affect exposure factors and why does this happen?

Answer 29

Some scattered radiation will pass through spacing material Some of primary X-ray beam will be absorbed by lead So higher mAs needed if using a grid

Question 30

What is a grid ratio and give some typical examples?

Answer 30

Height of lead strips divided by width of spacing material | Typical ratios 6:1 - 12:1

Question 31

How does grid ratio affect exposure factors?

Answer 31

High grid ratios most effective at removing scatter BUT remove more of primary beam So higher exposure is needed

Question 32

How do lines per cm on a grid affect exposure factors?

Answer 32

More strips of lead per cm = more scatter removed BUT more primary beam absorbed too So higher exposure needed

Question 33

What is a grid factor and what does it depend on?

Answer 33

Grid factor = number by which the mAs must be multiplied if a grid is used Depends on grid ration, lines/cm

Question 34

Name the 5 types of grid.

Answer 34

``` Parallel Focused Pseudo-focused Cross-hatched Moving/Potter Bucky ```

Question 35

Describe a parallel grid.

Answer 35

Lead strips parallel and of equal height Some increase in amount of primary beam absorbed towards edges, since beam is diverging Cheap, can be used either way up, at any FFD or centring point

Question 36

Describe a focused grid.

Answer 36

Lead strips slope more towards periphery of grid, no cut-off of image Must be used right way up Centre of X-ray beam must be at centre of grid, appropriate FFD used More expensive than parallel grids

Question 37

Describe pseudo-focused grids.

Answer 37

Lead strips parallel but height reduces towards periphery of grid Reduction in grid ratio at periphery compensates for grid cut-off

Question 38

Describe cross-hatched grids.

Answer 38

Tow sets of lead strips at right angles to each other Very efficient at removing scattered radiation Require high exposures, accurate centring, are expensive

Question 39

Describe moving/Potter Bucky grids.

Answer 39

Parallel grids mounted permanently beneath radiolucent tabletop Oscillate rapidly during exposure Means that fine lines (from stationary grid) are blurred out and not seen X-ray cassette/detector stays stationary beneath grid so image remains sharp

Question 40

Describe Computed Radiography (CR) and how it is carried out.

Answer 40

Uses cassettes containing a 'storage phosphor' plate Plate is erased by bright light and can be re-used Process takes around 1-2 mins

Question 41

Describe Digital Direct Radiography (DR).

Answer 41

Electronic detector directly captures X-ray image | Image is displayed immediately on monitor

Question 42

What information do we need to set before taking an X-ray image?

Answer 42

Patient information Anatomical region of interest Size of animal

Question 43

What do we need to know about our machine's 'exposure index' (EI)?

Answer 43

Manufacturer's name for value | Whether it is a proportional or inversely proportional measure of exposure

Question 44

How can we manipulate a digital image?

Answer 44

``` Filters / algorithms Contrast / brightness Size (zoom in/out) Orientation (flip/rotate) Annotation / measurement ```

Question 45

How can digital X-ray images be stored?

Answer 45

As computer files - dicom format (digital imaging and communications in medicines) On PACS software (picture archiving and communication system) Need regular backup!

Question 46

What are the advantages of digital radiography?

Answer 46

``` Decreased running costs Time saving Improved images in some cases Easy image retrieval and storage Easy communication of images Portable - instant images in the field ```

Question 47

What image quality factors should be assessed?

Answer 47

``` Opacity Contrast Sharpness Patient positioning Centring of X-ray beam Collimation of X-ray beam ```

Question 48

Define radiographic opacity.

Answer 48

Degree of blackening of the radiograph.

Question 49

What is radiographic opacity influenced by?

Answer 49

Patient (tissue type and thickness) Exposure factors Digital algorithm/processing

Question 50

Define radiographic contrast.

Answer 50

Difference in radiograph opacity between adjacent areas on an image.

Question 51

What influences radiographic contrast?

Answer 51

The inherent contrast of part being radiographed (Z number, density) Digital algorithm selected Amount of scatter reaching film

Question 52

Define radiographic sharpness.

Answer 52

The ability to distinguish fine detail on an image.

Question 53

What decreases radiographic sharpness?

Answer 53

Movement (animal, table, X-ray tube) Scattered radiation Object film distance

Question 54

List the miscellaneous digital image artefacts that occur.

Answer 54

``` Double exposure Digital exposure errors 'Uberschwinger' or rebound artefact Ghost artefact Moire artefact Dirt on light guide (CR only) ```

Question 55

What is an 'uberschwinger' or rebound artefact?

Answer 55

Occurs when there is a large density difference between adjacent objects (excessive 'edge enhancement' by computer algorithm Most commonly seen around orthopaedic implants Important to recognise as can mimic implant loosening

Question 56

What is a ghost artefact?

Answer 56

Incomplete erasure of a CR plate before use | May also occur if CR plate exposed to light

Question 57

What is a Moire artefact?

Answer 57

Bands across the image | Can arise with CR systems due to interference between frequency of laser reader and number of lines/cm of grid

Question 58

What happens if there is a dirt on the light guide (CR only)?

Answer 58

Emitted light blocked by dirt from reaching photomultiplier tube Seen as a line along the image Line is orientated in direction imaging plate moves during the reading process CR plate reader cleaning and maintenance should be performed routinely to prevent this occurring

Question 58

What happens if there is a dirt on the light guide (CR only)?

Answer 58

Emitted light blocked by dirt from reaching photomultiplier tube Seen as a line along the image Line is orientated in direction imaging plate moves during the reading process CR plate reader cleaning and maintenance should be performed routinely to prevent this occurring

Question 59

Define contrast media.

Answer 59

Contrast media = agents that are more or less opaque than surrounding tissue.

Question 60

What is the purpose of contrast media?

Answer 60

To see structures not normally/poorly visible, e.g. ureters, urethra, spinal cord To gain more information about soft tissue structures, e.g. bladder, kidneys, GI tract

Question 61

What are the two types of contrast media?

Answer 61

Positive contrast, e.g. barium/iodine - white on radiograph | Negative contrast, e.g. air/CO2 - black on radiograph

Question 62

Describe barium as a contrast agent.

Answer 62

``` Used in GI tract Various formulations, powder/suspension Inert, non-toxic Reasonably palatable Cheap Good mucosal detail (liquid barium) No osmotic effect ```

Question 63

Describe iodine as a contrast agent.

Answer 63

Water-soluble organic iodine-containing preparations 2 main groups - ionic / non-ionic IV use Renal excretion

Question 64

What are the disadvantages of ionic iodinated contrast media?

Answer 64

Irritant extra-vascularly Toxic in large doses - do not repeat studies multiple times Viscous Contraindicated IV in CV or renal insufficiency Contraindicated for myelography

Question 65

What are the disadvantages of non-ionic iodinated contrast media?

Answer 65

Slightly more expensive Viscous Side-effects may still occur, although rare (anaphylaxis, urticaria, vomiting, pyrexia)

Question 66

What are the advantages of negative contrast media?

Answer 66

Cheap Simple to use Relatively safe Can combine with positive - double contrast study

Question 67

What are the disadvantages of negative contrast media?

Answer 67

Very small risk of air embolism Poor mucosal detail Produce less contrast than positive contrast agents

Question 68

Why do we carry out plain radiographs before contrast radiographs?

Answer 68

Check radiographic quality Check patient preparation Look for radiological diagnosis Look for radiopaque lesions that may be obscured by contrast

Question 69

What alternative methods to contrast radiography have become more popular?

Answer 69

Endoscopy has replaced many GI studies Ultrasound +/- colour Doppler - portosystemic shunts, UT investigations CT and MRI have replaced myelography to a degree

Question 70

Describe a barium swallow.

Answer 70

Indications = dysphagia, regurgitation, suspected rupture Shows pharynx and oesophagus Liquid barium/barium and food OR iodinated contrast if suspected rupture Care if swallowing problems, risk of aspiration

Question 71

Describe a barium 'follow-through' study.

Answer 71

Evaluates stomach and small intestine (e.g. if vomiting cat/dog) Liquid barium by mouth/stomach tube Radiographs taken immediately then at intervals Final images at 24hrs / when all barium in colon Largely superseded by ultrasound and endoscopy

Question 72

Describe a barium enema.

Answer 72

``` Evaluates large intestine Liquid barium infused into rectum post-enema Can follow with air (double contrast) Messy and difficult to interpret Technique superseded by endoscopy ```

Question 73

What contrast media do we use for the urinary tract?

Answer 73

Water-soluble iodinated contrast medium | NEVER barium - cannot use IV and irritant in bladder, can cause granulomatous cystitis

Question 74

Describe excretory urography.

Answer 74

Identify/assess kidneys and ureters Bolus of contrast given into peripheral vein Radiographs taken immediately (nephrogram), 5 mins (pyelogram), 10 mins (ureterogram), 15 mins (ureterovesicular junction)

Question 75

Describe cystography.

Answer 75

Delineates bladder Contrast introduced via urinary catheter Pneumocystogram (air only) = bladder location, shows large masses or marked thickening Positive contrast cystogram (iodinated contrast) = leakage Negative contrast cystogram (both agents) = delineation of wall and content

Question 76

Describe (vagino-)urethrography.

Answer 76

Delineates urethra (and vagina) Water-soluble iodinated contrast medium, introduced via Foley catheter into distal urethra/vestibule Radiograph taken at end of injection Indications as for cystography

Question 77

Describe myelography.

Answer 77

Delineates sub-arachnoid space Localises lesions of spinal cord NON-ionic water-soluble contrast medium (ionic causes seizures/arachnoiditis) CT and MRI have largely replaced myelography

Question 78

What nursing considerations should we have for myelography?

Answer 78

Keep head elevated to prevent media entering the brain, as this could cause the patient to seizure A patent IV catheter should be available IV diazepam should be available