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Siamak BakhtiariConsultant in Emergency Medicine
Objectives
� Physics - how does an ultrasound machine work
� Turning on & setting up USS machines
� Knobology and use of ultrasound controls
� Obtaining basic images and maximising quality
� The boundaries and pitfall in USS
History
How does it work
Structure of the machine
� Transducer to produce, transmit and receive ultrasound waves
� Computer for interpretation and storage of the acquired data
� Monitor to display the image
Sound waves
� Ultrasound is > 20 KHz
� Ultrasound machines work in megahertz range – mostly 2 to 20 MHz
Transducer
Transducer
Sound waves
� The speed of sound varies in different body tissues
Transducer
� High frequency� Superficial penetration� High resolution
� Low frequency� Deep penetration� Low resolution
What happens to the sound waves in the body?
Reflection
Refraction
Scatter
Absorption
Attenuation
The combined effect of scattering and absorption is called attenuation.
Ultrasonic attenuation is the decay rate of the wave as it propagates through material.
Echogenicity
� Hyperechoic: more echogenic than surrounding tissue
� Hypoechoic: less echogenic than surrounding tissue
� Isoechoic: same echogenicity as surrounding tissue
� Anechoic: absence of echoes
Setting up the machine
� Patient’s information
� Information governance
� Occupational health issues
� Appropriate environment
� Cleaning the machine
Knobology and use of ultrasound controls
Ultrasound modes
� A mode: Amplitude modulation
� B mode: Brightness modulation
� M mode: Motion mode
A mode
� Amplitude Modulation
� Display of amplitude spikes of different heights
� Still in use - Ophtalmology
B mode
� Display of 2D map of data
� The most common form of ultrasound imaging
B mode
� Doppler
� Power Doppler
� Colour Doppler
� Spectral Doppler (pulse wave)
Power Doppler
Colour Doppler
� Toward the probe = RED
� Away from the probe = BLUE
Spectral Doppler
M mode
� Display of a one-dimensional image that
is used for analysing moving body parts
Obtaining basic images
Transvers plan
Sagittal plan
Coronal plan
Depth
� Depth of field of view
Time Gain Compensation - TGC
Gain
� Overall brightness of the image
Time Gain Compensation - TGC
Probe markers
Probe markers
Typeequationhere.
Probe orientation
Probe orientation
How to hold the probe
Probe movements
Black & White
� Structures like Bones and stones appears as white and called hyperechoic
� Fluid allows most sound waves through and appears as black and called hypoechoic
� Air is the enemy
Artefacts
Practitioner
� Probe position
� Control settings
Patient
� Motion
� Gas
� Anatomy
� Shadowing
� Enhancement
Acoustic shadow
Acoustic or Posterior enhancement
� Increased echoes deep to structures that transmit sound exceptionally well
Image mirroring
� Seen when there is a highly reflective
surface in the path of the primary beam
Reverberation
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