Radiography Flashcards
Properties of xrays (7)
no mass
invisible
speed of light
travel in straight line
penetrate all matter
cause fluorescence
ionise atoms
Safety measures
Time - minimum time exposure, minimum number of images
Distance - maximum distance from source, chemical restraint
Shielding - PPE
+ Equipment maintenance
Radiation Protection Advisor
External to practice
Radiation Protection Supervisor
Internal to practice
Ionising Radiation
has enough energy to ionise atoms and damage biological tissue
Non-ionising Radiation
less energetic - doesn’t cause ionisation
Absorbed Dose
Radiation absorbed by an object (Gray, Gy)
Equivalent Dose
Absorbed dose x radiation weighing factor
How harmful the radiation is to biological tissues (Sievert, Sv)
Effective Dose
Equivalent dose x tissue weighing factor
Radiosensitivity of different organs and risk of stochastic effects (Sievert, SV)
Stochastic Effects
Effects which occur with no threshold dose - random probability
Deterministic Effects
Occur at a specific dose threshold, with dose dependant severity
Direct Damage
Breaks molecular bonds within cells
Indirect Damage
Interaction with water leading to creation of free radicals which break cell bonds
Photoelectric Absorption
Ejection of inner cell election from a photon which ionises other atoms
important for exposure at low energy
Compton Absorption
Ejection of an outer shell election which ionised other atom
Photon diverts in a different direction with less energy - scatter
Characteristic Radiation
Radiation produced by photoelectric absorption
Bresstahlung Radiation
Braking radiation - scattered radiation
Border Obliteration
Difficulty telling apart adjacent tissues with same radiopacity
Mass Effect
Displacement of structures due to adjacent space occupying lesions
Reduction of Scatter (5)
Collimation - reduced volume of tissue exposed
Compress patient - as above
Film grids - absorb scatter - use at thickness >10cm
Alternative filtration devices
Lead backing to film cassettes - prevents back scatter
Grids
> 10cm thickness
parallel lead strips
grid ratio - higher = more absorbed scatter
grid factor = how much exposure factors must be raised to compensate for grid
Contrast improvement ratio = measure of improvement in contrast due to grid
Kilovoltage (kV)
Intensity of beam
Miliampere-seconds (mAs)
Rate of xray production in tube
Quality
Penetrating power of beam - affected by kV
Intensity
Amount of radiation in the beam - affected by kV and mAs
PCCELA - Pink Camels Collect Extra Large Apples
Positioning
Centring
Collimation
Exposure
Labelling
artefacts
Right lateral
y shaped diaphragm crura
more consistent cardiac silhouette
lees of lung field obstructed by diaphragm
Left lateral
parallel lung crura
Dorsoventral
Single smooth hump diaphragm
Heart more cranial and left
Ventrodorsal
3 diaphragm humps
Clock face to locate part of heart affected
Aortic arch - 12 o’clock
Main pulmonary trunk - 1
Left auricle - 2
Left ventricle - 4
Right ventricle - 7
Right atrium - 10
Normal Heart Size
Lateral
- height - 2/3 thorax
- width - 2.5-3.5 intercostal spaces
DV
- max 2/3 width of thorax
Vertebral Heart Score
VHS = length + width (in intervertebral spaces)
Dog - 8.5-10.5
Cat - 7.5
Causes of enlarged heart (5)
pericardial effusion - gross enlargement, globoid shape
mitral valve disease - left side atrial enlargement, straightening of caudal margin, trachea displacement
right atrial enlargement - cranial enlargement
right ventricular enlargement - increased sternal contact in lateral view
enlarged vessels - bulge at point of entry
Difficulties in interpretation (5)
atelectasis - effect of crushing dependant lung in lateral
breed differences
age - thymus
nodules - easily mixed up with end on blood vessels
skin folds - can look like pneumothorax
