Radiology

Define radiograph vs radiography vs radiology vs radiographer vs radiologist

Radiograph = recorded image after xray passes through a patient

Radiography = art and science of taking a radiograph

Radiology = study and interpretation of radiographs and other diagnostic imaging modalities

Radiographer = person with special expertise in taking radiographs

Radiologist = special clinician whose study allows them to accurately interpret radiographs and other diagnostic imaging

Explain Ionising vs Non-ionising radiation

Electromagnetic Radiation = all ionising and non-ionising forms

• all travel at 300,000 km/s

• various frequency and wavelength determines their ability to travel through objects and heating ability = also effects on people

Ionising Radiation

• high energy and frequency + short wavelength

• enough energy to cause chemical change / bread bonds = damage living tissue

• ionisation = when an electron is given enough energy to break away from an atom

• Examples: Gamma Rays, Xrays, UV Light

  • Gamma Rays = originate from the nucleus of decaying radionuclide

    • Ex: nuclear medicine or scintigraphy (most energetic photon)

  • Xrays = produced when electrons interact within an atom

    • Ex: radiography, fluoroscopy, CT (least energetic photon)

Non-ionising Radiation

• low energy and frequency + long wavelengths

• enough energy to excite molecules → vibrations = heat

• Examples: UV, Visible, Infared, Microwaves, Radio

Explain the components of an Xray Tube and how Xrays are produced

• electrons go from cathode (positive charge) → anodes (negative charge)

• when electrons his the anode and suddly stop they release energy by either:

  • Braking = Bremsstrahlung Radiation

    • electrons slows down and does a U turn around the nucleus, then goes back in the direction it came from

  • Ejecting = Characteristic Radiation

    • projectile electron smashes into electron, then darts out of the atom and all the other electrons jump to fill the void

• Xray beams diverge from a point source and travel in straight lines

• obey the inverse square law

• attenuate differently through different tissue due to differences in atomic number, mass density and xray energy

• when electrons reach anode, a number of varying intensity xrays are produced in all directions

  • low energy xrays are filtered out with aluminium filter to reduce absorbed dose

How does energy and anode positions effect Xrays?

• low exposure (bright image) → high exposure (dark image)

• Xray photons = 1%, vs heat produced = 99% → use oil to dissipate heat

• Focal spot is the anode = electrons are focused here (from cathode)

  • larger focal spot = larger heat dissipation BUT decreases image quality due to Penumbra Effect

• Penumbra Effect = ability to increase focal spot size to assist in heat dissipation without effecting the projected size by using the Line Focus Principle

Anode Heel Effect

• Xray beam has central rate and many divergent beams (cathode → anode)

  • cathode side has more intensity than anode side

• place thickest part of anatomy on the cathode side, to ensure more even exposure of varying thickness of tissue

  • increased distance = reduce anode heel effect

  • reduce field of view + smaller image receptors = uniform/central beam

Stationary vs Rotating Anode

• Stationary anode = limited use due to poor heat dissipation

• Rotating anode = increased surface area so better heat dissipation, also allows you to use a smaller focal spot for improved image quality

What happens when Xray’s interact with matter?

1. Penetration

   • through an object unaffected

   • limited attenuation

   • image is black as gas does not absorb xray photons

2. Absorption

   • absorbed by an object due to the photoelectric effect

   • demonstrates attenuation

   • image is white/radiopaque as photons reach the image receptor

     • bones = absorb many photons (high attenuation) = white

     • soft tissue = absorb some photons (varied attenuation) = grey

3. Scatter

   • scattered by object due to “Compton scatter”

   • demonstrated attenuation

   • photons are deflected from expected course = degrades image quality

     • can use a grid to reduce the effect of scattered radiation

What are the 3 exposure factors for Xray production?

kVP = Kilovoltage Peak

• potential energy difference across the tube

• determines the energy of electrons = penetrating power of the photons → contrast

• quality of the xray

mA = milliamperage

• tube current

• number of electrons from filament = number of xray photons produced → density

• quantity of xray

Time (seconds)

• timing of the tube current

• mA x time (s) = mAs

• mAs value with a high mA and short time = best

• quantity measurement

Effects / damage caused by radiation

• Cellular

  • change nucleus, DNA and organelles

  • cellular death, scaring or altered cell metabolism

  • may lead to somatic change (cancer) or genetic depending what cells

• Somatic Change = directly harmful → cancer, cateract, radiation burn

• Genetic Change = future harm → damage to DNA of germ cells

How (including units) can you measure radiation?

Absorbed Dose = Gy (Gray) = radiation required to deposit energy of 1 Joule in 1kg of tissue

Equivalent Dose = Sv (Sievert) = absorbed dose x radiation weighting factor (Wr)

• weight factor accounts that for different types of radiation, there are different abilities to damage biological tissue

Effective Dose = Sv (Sievert) = sum of (equivalent dose x tissue weighting factor) for each organ or body part irradiated

• indicates each organs sensitivity to radiation

Maximum Permissible Dose (MPD) = the absolute max - all radiation is damaging

• QLD occupational limit = 20 mSv / year

• non-occupational limit = 1 mSv / year (comes from space, food, water)

Radiation Badges = all you to measure and record types of radiation

• ALARA = as low as reasonably achievable

• Radiation Safety Act (1999) and Radiation Safety Regulations (2021) explains that you must have a licence to operate check equipment, safety plan

Explain the 4 Pillars of Radiation Safety

Time = limit time as much as possible

• Dose creep allows radiographs to be edited to reduce repeats at varied exposure

• Overexposed film = black vs underexposed film = white

Distance = inverse square law (further = safer)

Shielding = PPE such as lead gowns, thyroid collar, lead gloves, hand/arm shields, glasses

Common Sense = rooms are labelled with a warning light visible from outside, certified by gov

Restraining patients for Xrays

Chemical = anaesthetic and sedation

Manual = positioning aids

Physical = staff restraining with PPE (avoid where possible)

Large animals = many people required to be around to restrain or hold machine. Also due to animal side require higher exposures

• collimate beam as much as possible

• PPE

• distance - inverse square law

• effective chemical or manual restraint = best radiograph the 1st time

Explain Film radiology

• intensifying screens turn xray photons into visible light

• visbile light is more efficient at exposing film than xrays

  • lower exposure = reduce respiratory blur

  • lower radiation to patient and operator

Advantages = cheap, no technological fauts/risk loosing data, easily portable

Disadvantages = time consuming, physical storage, need a dark room + lots of chemcials

Explain the types of digitised radiography

CR = Computed radiography	DR = Digital radiography
Use a cassette which is read by a CR reader (big machine)	Directly from plate to computer screen (wired or wireless)
Advantages can manipulate image post processing electronic storage easy to share files	Advantages can manipulate image post processing electronic storage easy to share files instant radiographs
Disadvantages expensive exposure creep need larger server for digital image storage need to be erase CT plates regularly	Disadvantages very expensive exposure creep need larger server for digital image storage digital panels are easily damage + expensive to replace

Both store on CD, DVD, Hard Drives or PACS (Picture Archive Communication System)

Stores as DICOM (Digitial Imaging and Communications in Medicine) files

What are grids?

• reduce scattered radiation that reaches the image receptor (film, CR or DR)

• grids placed between patient and image receptor - act as a filter

• only used when body thickness is >10cm

• often made from aluminium and lead (does not absorb photons)

• Bucky’s = grids that are fixed to the xray table but can oscillate or vibrate to eliminate grid lines on images

What are the 4 things that effect radiographic quality?

Density

• degree of blackness of a film

• effected

  • mAs (increased mAs → more Xrays = black)

    • double mAs = double film density

  • time and temperature of film

Contrast

• difference in density between the two adjacent areas in film

  • high contrast = large difference of black vs white → bone

  • low contrast = small different so mostly grey → soft tissue

• primarily affected by kVp → increased kVp = lower contrast

  • increase kVp by 20% = doubles film density

  • more Xray photons pass through patient to cassette = more energy and more scatter = less contrast

Definition - sharpness + superimposition

• Sharpness = ability to define an edge, dependant on crystal size in screen/film

  • magnification: increased distance → increases magnification

  • distortion: unequal magnification of different parts of same object

  • penumbra effect: blurred edge due to focal spot not aligned

  • motion: movement whilst taking image

  • screen: unpreventable light diffusion decreases quality

• Superimposition

  • always take from two views to avoid overlying structures

Scatter

• reduces quality of image

• increases with = increased patient thickness, kVp and field size (poor collimation)

• decreases with = using a grid, decreasing field size (good collimation)

What is a radiographic artifact?

• radiographic flaws not normally present on an xray that are produced by artificial means

• Examples

  • motion = blurring, mostly during inspiration/expiration or poor sedation

  • magnification = object distance from machines which distorts size

  • distortion = unequal magnification on the same object, poor positioning

  • foreign object = positioning aids, clips, random objects not relevant

    • monitoring equipment or legit foreign bodies inside patient don’t count

  • mal-aligned grid = incorrect position, distance, angling or if upside down

  • mal-aligned centring/collimation = divergence of beam from anatomy

  • double exposure / ghosting = only in CR imaging, when not clearing plate between scans which would lead to layered Xray images

Explain Fluoroscopy

• uses Xray

• “video Xray” = watch images in real time

• black and white colours are inverted

• often used in theatre using a C-arm = low dose

Advantages	Disadvantages
functional imaging (swallowing) helpful in biopsy procedures for need placement	ionising radiaton possibility for high doses due to long time being used high exposure dose to staff patients may move due to unable to have GA

Explain Computed Tomography (CT)

• use Xray

• cross sectional image of anatomy

• CT table goes through gantry (donut), whilst Xrays emitted through

• measured in Hounsfield Units (HU)

  • high HU = white vs low HU = black

• tube rotates very quickly at 0.5-1 second/rotation = noisy

• allows for continuous data in many planes (axial, sagittal and coronal)

  • Multi-Planar Reconstructions (MPR)

• animals must have GA /very heavy sedation to ensure they are still

• can use iodine contrast (IV or oral) due to high xray attenuation (positive contrast) but can cause fatal SE

Advantages	Disadvantages
excellent for identifying cross-sectional anatomy good at imagining organs with different attenuation reasonably fast	uses ionising radiation very high radiation dose (x150 xray) expensive iodine contrast is risky

Explain Nuclear Medicine (NM or Scinetigraphy)

• use Gamma radiation

• high sensitivity but low specificity

• used to target an area of interest by injecting a radionuclide bound drug to region → produced gamma photons

• patient will continue to emit radiation post procedure, measure half life

  • keep animals post exam or have limited contact until dose decayed

Advantages	Disadvantages
excellent for demonstrating pathology and functional abnormalities can discern acute conditions not identifiable on radiographs until chronic	used ionising radiation patients are injected with radioactive substance risk of radiation to handlers patients are radioactive contaminants post procedure

Explain Ultrasound (US)

• does not use radiation

• uses reflection of soundwaves to form images

  • piezoelectric crystals in transducer probe produce soundwaves when electric current is applied

  • transducer identifies echoes to form image

• types of images

  • anechoic (no echo) = fluid filled structure - bladder

  • hypoechoic (not many echoes) = soft tissue - healthy liver

  • hyperechoic (many echoes) = solid structure - bone

• operator technique and interpretation has a large influence on image quality

• ideally need to clip hair and use a gel

• often need sedation or GA

Advantages	Disadvantages
live representation of organs and structures separates solid vs fluid does not use ionising radiation	does not image bone or gas structures well does not show deep structures (only superficial) highly operator dependant

Explain Magnetic Resonance Imaging (MRI)

• does not use radiation

• can be open or closed

• gold standard for soft tissue imaging

• uses very strong magnets - nothing in room!

  • Hydrogen nuclei exhibits small magnetic properties due to positive proton

  • hydrogen in water, fat and tissue have different magnetic properties

  • use large magnetic field and radio frequencies to determine different signals and therefore tissue types

• contrast can be used = gadolinium

• takes a long time, so need sedation or GA

Advantages	Disadvantages
excellent soft tissue definition does not use ionising radiation non invasive	very long scan times movement (blood) degrades image safety risk with metal objects very expensive