- USS for regional
- Principles of USS
- US transducer utilses frequencies of 2-15MHz
- Most use polycrystalline ferroelectric materials eg lead zirconate titanate (PZT)
- These have piezoelectric properties. When a current is applied, it expands and contracts producing pressure sound waves
- The reverse also occurs and the voltage change can be amplified to form the receiving signal
- The US beam is reflected at interfaces depending on the difference in acoustic impedance and the angle of the USS beam
- Reflectivity is greatest when the object being visualised is perpindicular to the angle of the USS beam
- High frequency probes give good resolution but poor penetration
- Low frequency has better penetration but poorer resolution
- Common artefacts
- Post-cystic enhancement
- Increased brightness behind fluid structures
- Acoustic shadowing
- Highly reflective surfaces (bone) reflects almost all the sound beam, throwing a shadow over deeper structures
- Anisotropy
- Image dependent on the angle of the USS beam
- Air
- Not possible to see through air filled cavities
- Advantages
- Ability to visualise target nerves and surrounding structures
- Allows for patient variability
- Determine depth, angle and path of the needle to target the nerve
- Real time visualisation of local spread
- Allows procedure to ba carried out safely in anaesthetised patients and even repeated if ineffective
- Portable and safe
Link:www.youtube.com/results?search_query=basic+principles+of+ultrasound
- CEACCP
Link:ceaccp.oxfordjournals.org/content/7/1/20.full.pdf