siamak bakhtiari consultant in emergency medicine · 2019. 2. 23. · objectives physics - how does...

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