- Physics 1
- lasers
- basics
- Light Amplification and Stimulated Emission of Radiation
- 3 components
- excitation energy source
- lasing medium
- optical resonator and outlet coupler
- excitation energy source excites molecules in lasing medium, some spontaneously decay and release a photon (spontaneous emission), which is reflected in the optical resonator back to the losing medium where it collides with another atom, releasing 2 photons in parallel, of the same wavelength and monochromatic. This results in a cascade and amplification of light energy which can be delivered to tissues. A small percentage of the radiation is emitted through the outlet coupler (partially reflective mirror)
- types
- CO2
- 10,600nm (IF)
- shallow penetration
- resecting airway tumours, good haemostasis
- Nd-YAG
- 1064 / 1320nm (near IF)
- good penetration
- good for vascular malformations, ophthalmic surgery and tattoo removal
- pulsed dye
- 577 - 585nm
- red blood cells
- good for port wine stains
- argon
- 488 - 514 (blue green spectrum)
- retinal surgery
- definitions
- gas
- a compressible fluid where molecules are so spread apart that their intermolecular forces are negligible
- vapour
- a substance below its critical temperature, so compression to liquid is possible
- fixed gas
- a substance above its critical temperature
- latent heat
- energy change associated with a change in state of a substance in either direction per unit mass without changing its temperature
- J/kg
- of fusion
- from solid to liquid or vice versa
- of vapourisation
- from liquid to vapour or vice versa
- at critical temperature = 0 J/kg
- SI units (SMMACK)
- base
- second
- metre
- mol
- ampere
- candela
- kelvin
- kilogram
- derived
- equations
- waves
- f = c / λ
- light: c = 3 x 10*8, sound = 300
- heat capacity
- c = e / mt
- heat capacity = energy / mass x temperature
- specific heat capacity = amount of energy required to heat 1g of a substance by 1 degree
- flow
- Reynold’s number = density x velocity x length /viscosity
- pressure
- pressure = density x acceleration (due to gravity) x height
- pressure
- absolute
- referenced to a vacuum
- = 1 atm when not in use
- gauge
- referenced to atmospheric pressure
- = 0 when not in use
- flow
- laminar
- turbulent
- always turbulent through an orifice
- ultrasound
- 2.5 - 15MHz
- 1540m/s in tissue
- wavelength and frequency of wave is changed when it reflects back from a substance
- MRI
- theory
- magnetic field aligns atoms with an odd number of nucleons, bursts of radiofrequency are then applied and are taken up by hydrogen nuclei which are then knocked out of alignment. The energy is then released and picked up by an external radiofrequency coil.
- numbers
- 1 Tesla = 10,000 Gauss = 1 weber/m2
- Earth’s magnetic field: 1 Gauss
- Safety line: 0.5 mTesla (5 Gauss)
- Second line: 50 Gauss
- danger for ferromagnetic objects
- medical equipment may fail
- MRI: 0.2 - 3 Tesla
- setup
- Faraday cage radiofrequency shield built into MRI room
- liquid helium around magnets at -270 C reduces resistance, insulated by a vacuum
- CI’s
- implanted surgical devices
- cochlear implants, pacemakers, neurovascular clips
- prostheses, general surgical clips, sternal wires and heart valves are normally ok!