医学交流课件：OPTIMIZING YOUR.pptVIP

ABDOMEN- Physics OPTIMIZING YOUR MACHINE OPTIMIZING YOUR MACHINE Ultrasound is a dynamic process Constant interaction between you and your machine is required TRANSDUCERS IDEAL TYPE OF TRANSDUCER? Mechanical vs electronic Linear, convex, phased array, sector scanner Scan head shape Frequency Depends on use and available money! Mechanical Sector Transducer Does not allow variable focussing Elements are mechanically rotated Small footprint – intercostal scanning Moving parts subject to wear More prone to damage when dropped Electronic Transducers Multiple crystals fire together or sequentially Multi-element transducers are called arrays Linear Convex Phased Linear Array Transducer Rectangular FOV Often limited skin contact Wide near-field, limited depth Best for musculoskeletal application, superficial structures Highest lateral resolution High frequencies (up to 25mHz) Convex Array Transducer = curvilinear 60°, 90°, 120° Wide near-field Even wider far- field Best for abdominal scans Phased Array Transducer Phased Array Transducer Limited near-field visibility compared with linear-array or curvilinear-array transducers Useful for evaluation of deeper structures Best for heart (intercostal windows) Transducer Care Do not apply alcohol directly onto surface Clean/wipe after every scan Freeze image when not in use Heat sensitive – do not sterilize Settings - Power Intensity (Amplitude) of sound Adjusting power effects entire screen Related to artefact production The lower the power setting, the less likely artefacts will occur Settings - Gain Amplification and reject controls Intensity of sound decreases with depth Amplification of returning echoes Selects gain (vs Overall Gain) Not equal to power Settings - Gain Overall Gain Uniform amplification of all returning echoes regardless of depth Settings - Gain Time Gain Echoes returning from deeper structures are weaker than those arising from more superficial structures