Cultural physics

Titan I date and venue

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Sandra ThomasClinical Marketing & Education ManagerSonoSite Ltd – Middle East,India & Africa

Ultrasound Physics

And

Obtaining an Image


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•What is ultrasound?•How is it generated?•What happens to it?•What do things look like?•Other stuff – Doppler etc

Agenda


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What is Ultrasound?

•Infrasound0-20 Hz

•Audible Sound20 Hz to 20,000 Hz

•Ultrasound>20,000 Hz (or 20 KHz)

•Medical Ultrasound2 MHz to 15 MHz


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Generation of Ultrasound

•Transducer converts energy from one form to another

•Piezoelectric effect•Electrical energy applied to crystal(s) causes dimensional change (mechanical energy)

•Dimensional change produces sound wave

•Reception of reflected beam is reverse of generation


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All of the above occur simultaneously in real time scanning so we can see motion

Image Generation

1. Initiate sound wave by system

2. Transmission through medium

3. Reflection from structures

4. Signal returns to system


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2D images of tissue traversed by ultrasound scan. Displays motion by showing images of tissue under the transducer as it is being scanned

2D Real-time ultrasound


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Ultrasound Resolution

Resolution is the ability to identify closely separated interfaces

• Resolution has two components1. Axial resolution – ability to distinguish 2 reflectors

along the path of the beam• Depends on pulse length/frequency• In practice axial resolution is 0.5mm for high

frequency transducers2. Lateral resolution

• Ability to distinguish 2 reflectors as individual elements which are perpendicular to the US beam

• Depends on beam profile/scan line density


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Axial Resolution Lateral Resolution

Depends on pulse length (frequency)

Depends on beam profile/line density


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Interaction of Ultrasound with Tissues

Positives:

Reflection- occurs at boundaries between tissues of differing acoustic impedances.

Best reflection when beam is perpendicular to boundary

07.39.12 hrs __[0000007].mp4


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Interaction of Ultrasound with Tissues

Positives:

Reflection- occurs at boundaries between tissues of differing acoustic impedances.

Best reflection when beam is perpendicular to boundary


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Multibeam technology…• Real time acquisition software

• Improves image quality : more detail, more tissue signature

• Artifact reduction

• Improves contrast resolution

Standard Multibeam


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Multibeam technology…Standard acquisition

Multibeam


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Benefits…

Improves contrast resolution

Increases tissue information

Standard Multibeam


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What is the effect of frequency ?

Frequency = Resolution

Frequency = Resolution

Frequency =

Frequency = Penetration

1Penetration


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Effect of frequency shift10MHz


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7.5MHz


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5MHz


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10MHz


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Transducers

38mm

1 mm

•Transmits and receives the ultrasound beam•Contacts the patient’s skin•Takes thin slices of object being imaged•Rotate or angle to change views


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Transducer Orientation Markings

vertical protrusion

horizontal protrusion

groove

Markings are located on oneside of transducer only andcorrespond to orientation markeron screen


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Transverse Transducer Orientation


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Transverse Transducer Orientation

Skin surface

Blood vessel

Groove towards patient’s rightOrientation marker

Right Left


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Longitudinal Transducer Orientation


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Longitudinal Transducer Orientation

Skin surface

Blood vessel

Groove towards patient’s headOrientation marker

Head Feet


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NEAR

FAR

Image Appearance

Tissue = Grey

Blood = Black


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Ultrasound appearances

Artery

Vein

Muscle

Tendon

Nerves – LS

TS

Anechoic - black Pulsatile

Anechoic - black Compressible

Hyperechoic fascia Hypoechoic muscle

Hyperechoic Tubular (fibrillar)

Discontinuous hypoechoic lines separated by hyperechoic lines(fasicular)

Multiple round hypoechoic areas(fasicles) surrounded by hyperechoic halo (connective tissue, perineurium)


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Appearance of nerves

TS

LS


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Femoral Nerve

NerveArtery Vein


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Brachial Plexus - interscalene


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Image Optimisation - Gain

One of the commonest mistakes in ultrasound imaging is the use of incorrect gain settings.

Insufficient gain can result in missed structures of low reflectivity.

Excessive gain can result in false echoes or over saturation, which may obscure important diagnostic image characteristics such as shadowing or enhancement

Amplification of returning echoes


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Gain

Near

Far

Overall


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Near Gain


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NEAR

FAR

Image Optimization

Depth adjustment

The choice of correct depth setting is a trade-off between achieving adequate field of view to resolve all relevant structures and maximising detail resolution


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NEAR

FAR

Image Optimization-Depth

Tissue = Grey

Blood = Black

Too close Too far Just right

Increasing the depth allows you to visualize deeper structures

Adjust the depth so that the target is centered in the image


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NEAR

FAR

Tissue = Grey

Blood = Black

Doppler Ultrasound

Doppler Effect based on work by Austrian physicist Johann Christian Doppler

Apparent change in received frequency due to relative motion between a sound source and sound receiver

Source moving TOWARD receiver = HIGHER frequency

Source moving AWAY from receiver = LOWER frequency


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NEAR

FAR

Tissue = Grey

Blood = Black

Doppler Ultrasound

Color Power Doppler-venous & arterial flow


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DCPD


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NEAR

FAR

Tissue = Grey

Blood = Black

Acoustic Couplants

• Air/tissue interface allows little ultrasound transmission so gel is needed on skin to exclude air

•Best quality image requires an air free coupling between ALL surfaces


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NEAR

FAR

Tissue = Grey

Blood = Black

Acoustic Couplants


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And finally……..

Aoccdrnig to rscheearch at Cmabrigde Uinevrtisy, it deosn’t mtlaer in what oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be in the rghit pclae.

The huamn mnid deos not raed ervey lteter but the word as a wlohe


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Median Nerve Common extensor Tendon


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And finally………really!

What happens when you…………….

1. Have nothing to do

2. Own a sharp knife

3. Have a large lime

4. Own a patient cat……………………


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Thanks for listening!

Cultural physics

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