physical principles of utz

8/6/2019 Physical Principles of Utz

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Course Objectives

Identify history & define ultrasound

Define piezoelectric effect

Define frequency & wavelength; identify their relationship Define bandwidth

Define attenuation; identify relationship to frequency

Define resolution & its components; identify relationshipto frequency

Identify basic transducer types

Define electronic array

Differentiate between sector & linear array

Identify types of image display

Identify artifacts useful to diagnosis

Discuss safety of medical ultrasound


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History of Ultrasound

Piezoelectricity discovered by the Curies in

1880 using natural quartz

SONAR was first used in 1940s war-time

Diagnostic Medical applications in use

since late 1950s


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Ultrasound: Physical Definition

Sound waves greater than 20,000 Hertz orcycles per second

Infrasound U

20,000 Hz


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Ultrasound: Medical Definition

Diagnostic Medical Ultrasound is the use of

high frequency sound to aid in the diagnosis

and treatment of patients.

Frequency ranges used in medical

ultrasound imaging are 2 - 15 MHz


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Piezoelectric Effect

Definition: The principle of convertingenergy by applying pressure to a crystal.

The reverse of the piezoelectric effect

converts the energy back to its originalform.


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Piezoelectric Effect andUltrasound Transducers

A transducer converts one type of energy

into another.

Based upon thepulse-echo principle

occurring with ultrasound piezoelectric

crystals, ultrasound transducers convert: Electricity into sound = pulse

Sound into electricity = echo


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Pulse

Pulse of sound is sent to soft tissues

Sound interaction with soft tissue =

bioeffects

Pulsing is determined by the transducer or

probe crystal(s) and is not operator

controlled


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Echo

Echo produced by soft tissues

Tissue interaction with sound =

acoustic propagation properties

Echoes are received by the transducer

crystals

Echoes are interpreted and processed by

the ultrasound machine


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Frequency

Number of complete cycles per unit of time

Man-made transducer frequency ispredetermined by design

Ultrasound transducers are referred to by

the operating, resonant or main frequency


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Wavelength

Definition: The distance betweenconsecutive cycles of sound.

Transducer frequency

Transducer wavelength


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Transducer Frequencies

2.5 MHz

3.5MHz

5.0 MHz

7.5 MHz

10.0 MHz

Deep abdomen,OB/Gyn

General abdomen,

OB/Gyn Vascular, Breast, Gyn

Breast, Thyroid

Breast, Thyroid,

Superficial veins,

Superficial masses


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Bandwidth

All ultrasound transducers contain a range

of frequencies, termed bandwidth

Broad bandwidth technology produces

medical transducers that contain more than

one operating frequency, for example:

2.5 - 3.5 MHz for general abdominal imaging

5.0 - 7.5 MHz for superficial imaging


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Attenuation

Definition: The reduction in power andintensity as sound travels through a

medium.


Depth of penetration

Higher frequencies attenuate, or are

absorbed, faster than lower frequencies


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Time Gain Compensation

Operator controlled adjustment tocompensate for the attenuation of

sound as it travels into the tissue

Must be adjusted manually for each

tissue type examined and may be

manipulated throughout an exam to

optimize the image


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RESOLUTION

The ability to differentiate between

structures that are closely related, both in

terms of space and echo amplitude Wavelength (frequency) dependent

Gray Scale Resolution

Axial Resolution

Lateral Resolution


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Frequency vs. Resolution


Resolution and image detail

Higher frequency transducers provide

better image resolution better gray scale resolution

improved ability to distinguish fine detail


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Frequency and Resolution

3.5 MHz 7.5 MHz


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Gray Scale Resolution

Adequate gray scale resolution allows for

the differentiation of subtle changes in the

tissues

Dynamic Range determines how many

shades of gray are demonstrated on animage


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Dynamic Range

Decreased DR Increased DR


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Axial & Lateral Resolution

Spatial Resolution describes how physically

close two objects can be and displayed

separately.Axial: along the beam path

Lateral: perpendicular to beam path

All current equipment has an overall spatial

resolution of 1.0 mm or less.


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Frequency Summary

High frequency improved

resolution

depth of penetration

loss

higher frequency

transducers for

superficial uses

Low frequency poorer resolution

full depth of

penetration

lower frequency

transducers for general

abdominopelvic uses


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Machine Components

Transducer

Beam Former

Receiver

Memory

Display


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Transducer Types

Mechanical

Oscillating

Rotating

Electronic

Linear Arrays

Curved Arrays

Phased Arrays


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Electronic Arrays

Groups of piezoelectric material workingsingly or in groups

Transducer126873 4 5 621


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Electronic Transducers

Sector Array crystals are placed

parallel or in

concentric rings transducer face is

curved

produces sector orpie-shaped image

Linear Array crystals are placed

parallel

transducer face is

flat

producesrectangular image


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Display Field of View

Field Of View -- the display of the echo

amplitudes

shape dependent on transducer type and

function


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Field of View Shapes

SECTOR FOV

produced by

oscillatingrotating

curved arrays

phased arrays

typically used in

abdominal application

LINEAR FOV

produced by

linear arrays

typically used in

superficial application


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Sector Linear


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Display Modes

B Mode

B Color

M Mode D Mode or Doppler

spectral

audio

color

Color/Doppler/PowerAngio -- slow flow


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B-Mode M-Mode


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Duplex and Triplex Imaging


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Artifacts

Portions of the displaywhich are not a true

representation of the

tissue imaged

Medical Diagnostic

Ultrasound imaging

utilizes certain

artifacts to

characterize tissue


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Artifacts

The ability to differentiate solid vs. cystic

tissue is the hallmark of ultrasound imaging

Acoustic Shadowing andAcoustic

Enhancementare the two artifacts that

provide the most useful diagnosticinformation


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Shadowing

Diminished sound or loss of sound

posterior to a strongly reflecting or strongly

attenuating structure Strong reflectors

large calcifications, bone

Strong attenuators solid tissue, significantly dense or malignant masses


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Shadowing


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Enhancement

Increased through transmission of the sound

wave posterior to a weakly attenuating

structure Gain curve expecteda certain loss or

attenuation with depth of travel

Occurs posterior to

simple cysts or weakly attenuating masses


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Enhancement


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Bioeffects

Prudent use assures patient safety

Effects at intensities higher than those used

in diagnostic medical ultrasound include:

cavitation

sister chromatid exchange


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AIUM Statement

No confirmed biological effects on patients

or operators caused by exposure at

intensities typical of diagnosticultrasound

...current data indicate that the benefitsoutweigh the risks.

Summary


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Summary

Ultrasound > 20,000 Hz

Piezoelectric Effect = pulse-echo principle

Frequency & wavelength are inversely proportional

Broad bandwidth enables multihertz probes

Attenuation & frequency are inversely related

Resolution determines image clarity

Electronic Arrays may be sector or linear

Display mode chosen determines how image is registered

Shadowing & Enhancement are the artifacts most used in

ultrasound diagnosis

Diagnostic Medical Ultrasound is safe!

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