Echo 1: Introduction to echocardiography Flashcards
Explain the piezoelectric effect in echo
-Pressure is generated when an electrical current is applied to the crystal
-Crystal expands and contracts to produce compressions and rarefactions (ultrasound waves)
-Crystal is struck by returning echoes which are converted into electrical currents
-These are converted into a digital display
How is image produced from ultrasound waves?
-Transducer transmits short bursts of US
-Waits for reflected US to return before transmitting next burst
-Measures time taken between emitting and return (roundtrip time)
-Uses this and propagation velocity to calculate distance between transducer and reflector
-Transducer can also determine intensity of the returning signal to build display
Uses of Doppler echo
-Measurement of velocity and direction of RBCs
-Assessment of stenotic and regurgitant valves
-Assessment of cardiac shunts
-Estimation of pressures
How is Doppler used to determine speed of blood flow?
-Frequency of returned US increases if RBCs move towards transducer
-Frequency of returned US decreases if RBCs move away from transducer
-Change in frequency = Doppler shift
-Greater Doppler shift = Faster blood flow
What is spectral doppler?
-Signal above baseline = flow towards probe
-Signal below baseline = flow away from probe
-Density of signal represents number of RBCs moving at a particular velocity
What is tissue doppler?
-Provides useful velocity information on the longitudinal function of the left ventricle in systole and diastole
Direction of blood in colour doppler
Blue away from probe
Red towards probe
What are the 3 types of resolution in echo?
Axial - distinguish between 2 points ALONG the US beam
Lateral - distinguish between points ADJACENT to each other
Temporal - ability to detect motion over time (Hz)
What is gain in echo and how should it be adjusted?
-Increases the amplitude of all returning signals
-Should be adjusted so that blood pool is black and myocardial tissues are grey
-Increase gain to improve visualisation of poor reflectors
-Decrease gain to improve visualisation of strong reflectors
What is time gain compensation (TGC)?
-Counteracts the effect of attenuation
-Attenuation - loss of amplitudes and intensity of US signal occurs exponentially with increase in depth
Optimised gain
High gain
Low gain
Good TGC
Bad TGC
-Bottom slider too left
-Can’t see posterior wall
Bad TGC
-Top slider too left
-Can’t see anteroseptum
What is the focal zone?
-Highest resolution of the US beam occurs at focal zone
-Focal zone placed at area of interest
How does sector width/depth affect frame rate?
-Increasing sector width/depth reduces frame rate
-Decreasing sector width/depth increases frame rate but reduces field of view
Parasternal view
-Right ventricle top
-Left ventricle left
Parasternal short axis (AV level)
-mercedes benz
Parasternal short axis (LV base)
-fish mouth
Parasternal short axis (LV mid)
Parasternal short axis (LV apex)
Apical 4 chamber
