what is the wave equation?
c=fλ
c = speed of ultrasound in soft tissue (1540 m/s CONSTANT)
f = frequency (Hz)
λ = wavelength (m)
what is the speed of ultrasound in soft tissue?
1540 m/s
what frequency is considered an ultrasound?
anything above 2 MHz
what is acoustic impedance?
the barrier between soft tissue, blood and bone - some waves are reflected back and some are absorbed (the change in difference us density)
what are the physics of ultrasound?
- above 20 kHz
- mechanical longitudinal wave
- acoustic impedance
- C = frequency x wavelength
- propagation velocity (m/s) = frequency (hz) x wavelength (m)
- C = a constant 1540 m/s
what does higher and lower frequencies mean?
high frequencies mean a better spatial resolution and poorer penetration
lower frequencies mean a poorer spatial resolution and better penetration
the colours of density in an ultrasound?
least dense = black
most dense = white
how does piezo crystal work?
if you apply electrical current to a piezo crystal it will develop an ultrasound
what is an ultrasound?
a level of wave activity we cannot hear
what are the types of resolution?
- spatial resolution
- axial resolution
- lateral resolution
what are echos normally requested for?
- patient is haemodynamically unstable e.g. they have a cardiac tamponade
- pulmonary embolism
- vegetations on valves
what is a cardiac tamponade?
life threatening condition caused by rapid or excessive accumulation of fluid, blood or pus in a pericardial space
this restricts heart filling and severely lowers blood pressure
what position is a patient supposed to be in for PLAX, PSAX, Apical ECHO view?
left lateral decubitus (left hand side to move lungs away)
with left arm placed above or behind the patient’s head (to move intercostal muscles out of the way)
how to achieve PLAX?
- transducer in 3rd or 4th intercostal space left of sternum
- probe marker towards right shoulder (10 o’clock)
- patient in left lateral decubitus position
what are the ECHO windows?
- parasternal long axis (PLAX)
- parasternal short axis (PSAX)
- Apical view 4C, 5C, 2C, 3C (perspective from the apex)
- subcostal view
- suprasternal view
how to achieve PSAX?
- start from PLAX view
- rotate transducer 90 degrees clockwise so marker points towards left shoulder (2 o’clock)
how to achieve apical 4CV?
- 5th - 6th intercostal space (around V5 position)
- probe marker pointed towards the patient’s shoulder (3 o’clock)
- patient in left lateral decubitus position
how to achieve apical 5CV?
- start from apical 4CV
- tilt probe anteriorly
- the LVOT and the aortic valve will appear (between left and right atria)
how to achieve apical 2CV?
- start from apical 4 CV
- rotate transducer anticlockwise 60-90 degrees (probe marker towards 12 o’clock)
- the left ventricle and left atrium are visible
how to achieve apical 3CV?
- start from 4CV
- rotate transducer anticlockwise 60-90 degrees (probe marker towards 11 o’clock)
- tilt probe slightly anteriorly to bring the aorta into view
- you will see LV, LA and LVOT
how to achieve subcostal view?
- patient needs to be supine with knees slightly bent to relax abdominal muscles
- probe marker pointing towards 3 o’clock
- you will see LA, LV, RA, RV, LIVER
how to achieve suprasternal view?
what is the typical depth of view?
10-15 cm (but it can change)
what are the machine settings?
- probe
- depth (10-15 cm)
- sector size
- focus
- gain (amplification of the image)
