therapeutic ultrasound Flashcards
what is an ultrasound?
- form of mechanical energy, which when applied to the body has both thermal and non- thermal effects
what is sound energy?
- mechanical vibration at increasing frequency
what is the normal human sound range?
- 16 Hz to 15-20,000 Hz
what is it called beyond the normal human sound range? what is it usually between?
- beyond the limit is called ultrasound
- usually between 1.0-3.0 MHz
what is 1MHz equal to?
- 1 mil cycles per sec
what ultrasounds are available?
- different sizes and types of ultrasounds are available
what are soundwaves? what do they consist of?
- longitudinal waves consisting of compression and rarefaction
what do particles of a material do?
- oscillates about a fixed point rather than move with the wave itself
what must there be for a pulsed shortwave?
- must be a thermal component
what happens to the energy levels in a pulsed shortwave?
- energy levels within the walls will diminish as energy is transferred to material
what is different for different tissues regarding pulsed shortwave?
- energy absorption and attenuation
what is frequency?
- number of times a particle experiences a complete compression/ refraction cycle in 1 second
what is a wavelength?
- distance between two equivalent points on the waveform in the medium
what is the average tissue wavelength at 1MHz compared to 3MHz?
- 1MHz= 1.5mm
- 3MHz = 0.5mm
what is velocity?
- speed that the wave travels through the medium
what is the saline velocity? is this the same for all tissues?
- approx. 1500m sec-1
- most tissues are similar
how do you work out velocity?- give the equation
velocity = frequency to wavelength
V = F. I
what is a transducer?
- part of ultrasound containing crystal
- converts electrical energy to sound
is US beam uniform? what does this mean?
- US beam is not uniform
- so changes depending on distance from transducer
what happens near treatment head?
- when near field/ frenzel zone, significant interference
is energy in near field greater than the machine’s output?
- energy in near field can be 12-15 times greater than the machine’s output
how do you work out the length of near field?
- r^2/l
what does r stand for?
- radius of transducer crystal
what does l stand for?
- US wavelength
what is the zone beyond the near field known as? how is it described?
- known as Fraunhofer zone
- beam more uniform and divergent
what is beam nonuniformity ratio (BNR) ?
- quality indictor of US applicators (transducers)
- gives an indication of near field interference
what does beam nonuniformity ratio (BNR) numerically describe?
- describes the ratio of intensity peaks to mean intensity
what does each tissue present? what is it determined by?
- presents impedance to sound waves
- determined by density and elasticity
what is BNR for most?
- BNR would be 4-6
when does maximum energy transfer occur?
- occurs when the impendance of adjacent media is similar
- large differences = ^ reflection and reduced transmission of energy
when does the most significant impedance difference occur?
- occurs at steel/ air interface
what is a coupling media?
- suitable coupling medium e.g., gel, oil, cream or water is essential to minimise air gaps to reduce total reflection
what should the coupling media be?
- should be fluid (to fill up available spaces), viscous and allow for maximum absorption, attenuation and disturbance
what media is preferred and why?
- gel- based media preferred over oils and creams while water is a good alternative but lacks viscosity
how do you avoid bacterial contamination?
- treatment heads should be cleaned with an alcohol- based swab between treatments to reduce microbial transmission
what happens when a US wave encounters a boundary at an angle of 90 degrees?
- refraction occurs
- changing the beam’s path
why is pathway angled?
- because beam through 2nd medium will not be the same as its path through original
what is US energy absorption described as?
- exponential
- superficial tissues absorb more energy
is there a point of complete absorption?
- no but energy levels decrease with depth as a greater proportion of energy absorbed
what is half value depth?
- depth where half the surface energy is available
what do half value depths vary by?
- vary by tissue type and frequency
what is the half value depth of 3MHz compared to 1MHz?
- 3MHz= 2cm
- 1MHz= 4cm
what tissues absorb more effectively?
- tissues with higher protein content e.g., ligaments, tendons, fascia absorb US more effectively that those with high water content e.g., blood, fat
what is ranking done by?
- ranking by absorption capacity
- critical for clinical decision making
- high collagen tissue particularly effective absorbers
what limits the effectiveness of US energy?
- cartilage and bone reflect much of the US energy
what is more effective when implicating ultrasounds clinically?
- targeting highly absorptive tissues is more effective than low absorption capacity
what is a pulsed output? what is the common pulse ratios?
- common pulse durations are 2ms with variable off periods
- typical pulse ratios are 1: 1 and 1: 4
what is a relevant factor in dosage calculations ?
- proportion of time that the machine is on compared with off
how is pulse ratio (duty cycle) different to pulse frequency?
- if 1:4;
duration at 2ms= on for 2ms and off for 8ms= 100Hz
duration increased to 4ms= on for 2ms and off for 16ms= 50Hz
what affects the number of cycles per second?
- adjusting pulse duration
what is the normal pulse time?
- 2ms meaning 100 pulses of ultrasound energy delivered per second
how does ultrasound help in tissue healing?
- enhances tissue healing by speeding up recovery and improving repair quality
what are the thermal effects of heating the tissue?
- promotes hyperaemia
- aids in chronic inflammation resolution
what are non- thermal effects primarily attributed to?
- cavitation
- acoustic streaming
what is cavitation?
- involves the formation of gas- filled voids within tissues and body fluids
what is stable cavitation?
- formation of gas bubbles by accumulation of dissolved gas in the medium (approx 100cycles)
what does stable cavitation enhance and promote ?
- enhances acoustic streaming
- promotes cellular activity
what is unstable cavitation?
- formation of bubbles at low pressure part so bubbles collapse very quickly
- releasing large amounts of energy> potentially harmful to tissue viability
what is acoustic streaming?
- small scale fluid movement around a vibrating structure and surface of stable cavitation gas bubble
what does acoustic streaming affect?
- affects diffusion rates and membrane permeability
- influences metabolic processes
what permeability is altered and what does this cause due to acoustic streaming?
- sodium ion permeability is altered
- changes cell membrane potential so alteration in enzyme control mechanisms like protein synthesis
what is micromassage?
- mechanical effect where sound wave travelling causes molecules to vibrate
what does micro massage enhance and effect?
- enhances tissue fluid interchange
- affects tissue mobility
how does ultrasound aid inflammation stage?
- stimulates mast cells, platelets, white blood cells and macrophages
- act as inflammatory optimiser
how does ultrasound aid proliferation stage?
- positively influences fibroblasts, endothelial cells and myofibroblasts
how does ultrasound aid remodelling stage?
- improves collagen fibre orientation and transition from type III to type I collagen
when are ultrasounds used?
- fracture repair
- wound healing
- stress fracture diagnosis via pain response
- chronic sinusitis
- pain management
- knee osteoarthritis
what are the contraindications of ultrasound?
- malignant tumour
- pregnancy
- CNS tissue
- joint cement
- plastic components
- pacemaker
- thrombophlebitis
- eyes
- reproductive organs
what are the cautions of ultrasounds?
- acute inflammation
- epiphyseal plates
- fractures
- breast implants
