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Ultrasound EquipmentsUltrasound Equipments

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Ultrasound EquipmentsUltrasound EquipmentsThe Physics of Ultrasound.

The Principles of Ultrasound Diagnostic Equipment.

Image Processing.

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The Physics of UltrasoundThe Physics of UltrasoundThe term ultrasound refers to acoustical wavesabove the range of human hearing (frequencies higher than 20000 kHz).Ultrasound waves are vibrations or disturbancesconsisting of alternating zones of compression and rarefaction in physical medium such as gas, liquid, or solid matter.It will be studied the following:

FrequencyVelocityGenerationReflectionBeam patternResolution

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Humans can hear only a limited rang of frequencies (Audible spectrum).The frequency range of audible sound is approximately 20 Hz to 20 kHz.Frequencies lower than 20 Hz are Infrasound and frequencies higher than 20 kHz are called UltrasoundDiagnostic ultrasound equipments used ultrasound frequencies in the range of approximately 1 MHz to 10 MHz

20 kHz

Ultrasound FrequencyUltrasound Frequency

0

Infrasound DiagnosticUltrasound

Audible sound

10 MHz20 Hz 1MHzUltrasound

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Velocity of ultrasound wavesVelocity of ultrasound wavesThe table shows velocity of ultrasound waves to each material of human bodyThe average velocity in human body is about 1530 m/sec, this average velocity will be significant in the study of equipment principles, which will be explained later

Material Velocity m/secAir 330

Blood 1570Brain 1540Fat 1450

Soft tissue 1540Kidney 1560Liver 1550

Muscle 1580Skull bone 4080

Water 1480

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Generation of ultrasound wavesGeneration of ultrasound wavesPiezo-electric effect:

Transducer without any voltage appliedIf we apply voltage in pulses the transducer will expand and contractBy applying this voltage in very quick pulses we can vibrate the transducer and produce the ultrasound waveIf any external forces is applied to the transducer a voltage is generatedThis phenomena is called piezo-electric effect

~

Ultrasound waves

Ultrasound waves

Tran

sduc

er

Voltage

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VoltageVoltage--ultrasound conversionultrasound conversionIn the practice high voltage pulses of about 100 V are applied to the transducerThe transducer converts the voltage pulses into the ultrasound waves, which my be transmitted into the human body

Transmission

Ultrasound waves

Object

Transducer

Pulses

TransducerVoltage

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VoltageVoltage--ultrasound conversionultrasound conversionWhen the ultrasound waves reach an object they are reflected back to the transducerThe reflection echoes are then converted by the transducer into voltage to be used as reception signals

Transducer

Reflection

Transducer Ultrasound waves

Object Echoes

Voltage

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VoltageVoltage--ultrasound conversionultrasound conversion

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Ultrasound waves transmitted in the human body.At the border of different structures some of the transmitted waves are reflected back according to the acoustic impedance different between two structures.Acoustic impedance:

Z: Acoustic impedanceρ: DensityC: velocity

Ultrasound reflectionUltrasound reflection

CZ ∗= ρ

TransmittedU.S. wave

PenetratedU.S. wave

ReflectedU.S. wave

AAA CZ ∗= ρ

BBB CZ ∗= ρ

AAA CZ ∗= ρ

BBB CZ ∗= ρ

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Acoustic impedanceAcoustic impedanceThe table shows acoustic impedance of each material in the human bodyThe average impedance is about 1.6Acoustic impedance of each material is different from each other and that is why U.S. waves are reflected from the different structures

Material Acoustic impedance

Air 0.00043Blood 1.62Brain 1.6Fat 1.38

Soft tissue 1.6Kidney 1.62Liver 1.66

Muscle 1.7Skull bone 7.8

Water 1.52

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Ultrasound beam patternUltrasound beam pattern

As it shown above, if there no acoustic lens on the transducer surface, the ultrasound beam is transmitted in a straight line in the near field then begins divert from a certain point in the far field as shown above. This is called an unfocused beamIf there an acoustic lens on the transducer surface the ultrasound beam will be focused and convert as a certain point called the focal pointWe can say generally the focused beam can obtain a clearer image.

Near field

far field

Nearfield

Farfield

Lens Focalpoint

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ResolutionResolutionThey are two major parameters, which influence the diagnostic image quality these are axial and lateral resolutionResolution can be defined as the ability of the equipment to distinguish two separate objects

DΔY

Transducer

ΔX

ΔX: Axial resolutionΔY: Lateral resolution

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Axial ResolutionAxial ResolutionAxial resolutions describe resolution in the axial directionAxial resolution is determined by the U.S. wave length and frequencyIf the U.S. beam use a short wave length as is shown above we can distinguish two separate objects which are based closed together in line in axial direction. This is because wave length of the U.S. beam is shorter than the distance between the two objects.

High frequency

Low frequency

A-Mode display

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Axial ResolutionAxial ResolutionIf the U.S beam uses a longer wave length as shown below, we can not distinguish two separate objects, this is because the wave length is longer than the distance between the two objectsBecause a higher frequency main a short wave length, we can say generally: that the higher the U. S. frequency, the higher the axial resolution

High frequency

Low frequency

A-Mode display

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Lateral ResolutionLateral Resolution

A

B

AB

A

B

A

B

DisplayedObject size

Near fieldConvergence

far fieldDivergence

Lateral resolution describes resolution in the lateral directionIf the U.S. beam is wide, as shown in the top figure, the displayed object size may be bigger than the actual object size so lateral resolution is poor.If the U.S. beam is narrow the displayed object size will be a closer to the actual size so lateral resolution is better.Generally speaking: the narrow the U.S. beam, the higher the lateral resolution.

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RelationshipRelationshipThis table shows the relationship between frequency,resolution and penetrationIn general, the higher the U.S frequency the higher the resolution and the lower the penetration.Conversely , the lower the U.S frequency the lower the resolution but the higher the penetration.To determine a wide range of diagnostic requirements we need a wide range of U.S. frequenciesThat is why there is a wide selection of probe frequency for studies of different organs.

Frequency Low HighResolution Poor GoodPenetration Good Poor

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The principles of ultrasound diagnostic The principles of ultrasound diagnostic equipmentequipment

Ultrasound Equipment

Display Mode

Electronic Focus

Two Dimensional Scanning

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Principles of ultrasound equipmentPrinciples of ultrasound equipmentUltrasound Equipment: U.S diagnostic equipment uses a pulse reflection system

Pulse generatorT-Delay

ReceiverR-Delay

D.S.C

TV-monitorOrgan

Digital ScanConverter

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Principles of ultrasound equipmentPrinciples of ultrasound equipmentPulse generator: A pulse circuit generate a high voltage pulses, then the T-delay line circuit applies appropriate delay time for each transmitted pulse for electronic focusing of the U.S. beamWhen the U.S. probe touches the patient skin surface U.S. waves are transmitted to the patientThe delayed high voltage pulses are applied to the piezo-electric transducer elementsThey produce the U.S. waves, which will entire the patient, and are reflected back by the intern structures.

Pulse generatorT-DelayOrgan

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Principles of ultrasound equipmentPrinciples of ultrasound equipmentThe reflected echo signals are received by the same probeThen they are input into the R-delay line circuit to compensate for the transmission delay factor of the pulses and mix the echo signals.Then the receiver circuit amplifies the mixed echo signal from the R-delay line

OrganReceiverR-Delay

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Principles of ultrasound equipmentPrinciples of ultrasound equipmentIn new equipment the echo signals are produced using a digital scan converter D.S.CSo that the image data is thought enter the frame menuand read sequentially out in a format suitable for display on TV-monitor. The result is real time imaging

ReceiverR-Delay

D.S.C

TV-monitorOrgan

Digital ScanConverter

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AbsorptionAbsorptionThis table shows the absorption of MHz U.S. waves in each materialAbsorption is measured in decibels per centimeters (dB/cm)Note that absorption in air and skull bone is very high as shown in the tableIf absorption is very high the U.S waves can not pass throughAs a general rule U.S diagnosis is not restructures containing gas or structures hidden behind bon such as lung, stomach and brain.

Material Absorption at 1 MHz dB/cm

Air 12Blood 0.2Brain 0.9Fat 0.6

Soft tissue 0.8Kidney 1Liver 0.9

Muscle 2.3Skull bone 13

Water 0.002

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Relationship between Depth and TimeRelationship between Depth and TimeThe average velocity of U.S. in the human body is about1530 m/secAt this velocity an U.S. wave will take about 6.5 μsec to travel from the probe transducer to a target 1 cm below the skin as shownAn additional 6.5 μsec is required for the U.S. wave to return to the probe transducerAs a result the total time taken for the U.S. wave to be transmitted and received to and from a target, which is 1 cm from the transducer, is about 13 μsec as shown

13 μ secSoft tissue

1 cm

Pulse Echo

sec5.610015301

1:1530:sec1

μ=∗

=

⇒≡

cmX

cmXm

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Relationship between Depth and TimeRelationship between Depth and TimeThe U.S. transmission timing and reception period are determined by rate pulseThe rate pulse allows a reception period of up to 260 μsec. This 260 μsec translate to distance of about 20 cm depth in the human bodySo we can say generally that the maximum scanning depth is limited to this 20 cm

Depth[cm]

260 μ sec

Pulse Echo

Depth time1 cm = 13 μsec

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Display ModeDisplay ModeWe will explain some of the display modes for U.S. imaging.Here we will take about 3 of the most common modes. they are:

1) A-Mode

2) B-Mode

3) M-Mode

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Principles of APrinciples of A--ModeModeA-mode display gives information about the distance between tissue boundaries e.g. to measure organ thicknessIf we observe an iconoscopes display, let the vertical direction be the time or depth axis and let the horizontal direction be the amplitude of the received signal waveThis display method is called Amplitude Mode or justA-Mode

Depth[cm]

Amplitude0

A-ModeAmplitude-Mode

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Principles of BPrinciples of B--ModeModeThe B of B-Mode stands for brightnessShifting the position of U.S. transmission and reception results in scanningEcho signals received and then go to intensity modulation so that across sectional image can be displayed on CRTUsing this display method we can see internal structure I a patient study

B-ModeBrightness-Mode Depth

[cm]

Width[cm]

⇒Intensity

modulation

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Principles of MPrinciples of M--ModeModeHere we illustrate M-Mode. The M of m-mode stands for motion.This display mod is useful for studying moving targets such as inertial mitralvalveThe transducer position should remain fixed when using this mode, while the display mode used customarily screened in a movement code scrollingScrolling allows movement of the valve to be displayed as an image

M-ModeMotion-Mode

Time[sec]

Intensitymodulation

Depth[cm]

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Principles of MPrinciples of M--ModeMode

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A, B and MA, B and M--ModeMode

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Principles of Electronic FocusPrinciples of Electronic FocusIn actual practice a block of transmission elements are driven for transmission each U.S. waveThat the transducer elements are not driven at the same time, the first U.S. pulse will be driven from transducers 1and n then transducers 2 and n-1 and so on

1

2

n-1

n

Inputpulses

Delay linecircuit

Delayedpulses

TransducerArray

FocalPoint

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Principles of Electronic FocusPrinciples of Electronic Focus

This sequential driving causes the U.S. beam to convert at a focal point and that is called Electronic focusingThe distance of the focal point from the probe is determined by the delay time between transmission pulses.

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T&RT&R--Delay LineDelay LineFor transmission a pulses input to the transmission delay lineThe transmission delay line generates a delay time between pulses to achieve a desired focusing distanceFor reception the echo signals are input to the reception delay line, where they are a phase corrected and mixed together.

Reception

T-delay line

R-delay line

TransmissionSame Transducers

DelayTime

DelayTime

Inputpulses

MixedEcho

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BB--Mode Scanning MethodMode Scanning MethodNext we will explain some of the types of B-Mode scanningHere we will explain the two most common scanning modesThey are:

Linear scanning

Sector scanning

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Principles of Linear ScanningPrinciples of Linear Scanning

In practice many tiny transducers called transducer elements arrayed in straight line The U.S. scanning beam is produced by simultaneously driving a block of several transducer elements.

PulsesGenerator

123n

TransducerArray

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Principles of Linear ScanningPrinciples of Linear ScanningThe block is new to across the links of the elements array by electronic switchingThis effect moving the scanning beam across the links of the transducerOne scanning line of the U.S. image is produced from the information gathered between each switching interval of the U.S. beam

PulsesGenerator

123n

TransducerArray

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Linear ScanningLinear ScanningOn the left hand side is the probe and the shape of the beamOn the right hand side is the display format of linear scanningThe advantages of linear scanning are a large field of view at shallow regions of the body and easier identification of skin orientation

TV DisplayFormat Probe

Beam shape

This is the actual B-Mode real time image display of linear scanning

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Principles of Sector ScanningPrinciples of Sector ScanningFor sector scanning all the transducer elements are used for transmission and reception

TransducerArray

Pulse Generation

T-delayline

Delaytime

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Principles of Sector ScanningPrinciples of Sector ScanningThe angle of the U.S. beam is changed by the delay time between transmission pulses as shown

TransducerArray

Pulse Generation

T-delayline

Delaytime

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Sector ScanningSector ScanningOn the left hand side is the probe and the shape of the beamOn the right hand side is the display format of sector scanning

The advantages of sector scanning are: a large field of view at deep region of the bodyand a small skin contact area

TV DisplayFormat

Shape

Probe

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Sector ScanningSector ScanningTherefore the sector probe can transmit U.S. waves to a very small acoustic window such as between the ribs to exam the heart as shown

This is the actual B-Mode real time image display of sector scanning

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Image ProcessingImage ProcessingSTC

Dynamic range

Echo enhancement

Combination focus

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Sensitivity Time Control (STC)Sensitivity Time Control (STC)The transmitted U.S. waves attenuated gradually through absorption as they penetrate the human bodyThis mains that echoes reflected from near the skin surface will be stronger than echoes reflected from deep regions of the human body

Gain

STC Gain compensation

Compensated Echo

ReceivedEcho

penetration

TransducerThe STC or sensitivity time control can be used to compensate for this difference in echo signals strength from shallow to deep regions as shownAs echo strength decreases over distance, gain of the signal for different depth can be increased independently, so that the echoes all have the same strength

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Sensitivity Time Control (STC)Sensitivity Time Control (STC)

STC

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Dynamic RangeDynamic RangeDynamic rang of the image is defined as the center of request strongest echo signals which can be displayed The dynamic range control is to adjust the display range of the U.S. image The dynamic range actually uses a wide band operational amplifierIn the figure we can see the amplification factor of the amplifierHere the strength of the signal is too great to be displayed at this dynamic rangeIf we have a larger dynamic range, a greater range of signal intensities can be displayed

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Dynamic RangeDynamic RangeBy changing the amplification factor the range of the output echo signals is changed as shownHere the dynamic range has been increased to cover the highest signal strengthIf dynamic range is too wide, observation of the image becomes difficult because the image contents to many similar signalsIf the range too narrow, contrast increases but too narrow range will increase areas of intense darkness or brightness as signals beyond the ranges are lost

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Dynamic RangeDynamic Range

Input

output

Time

Time

InputEcho

DisplayLimit

OutputEcho

0

DRUP

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Dynamic RangeDynamic Range

Input

output

Time

Time

InputEcho

OutputEcho

0

DRUP

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Echo Enhancement (E.E)Echo Enhancement (E.E)Echo enhancement is to enhance the definition of the U.S. imageIf for example a square wave is the input to the echo enhancement circuit, both edges of the square wave can be enhanced as shown in the top figureThe practical application of echo enhancement is to enhance the borders of internal structures in diagnostic images as shown belowThe higher membrane enhancement liver select the greater the enhancement Echo

EnhancementCircuit

Input Output

Image Image

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Principles of combination focusPrinciples of combination focusCombination focus has multiple focal points to narrow beam width from shallow to deep regionsThe first U.S. pulse is focused in the near field The reception data from the first pulse in the near field is told in the digital memoryAfter that the second U. S. pulse is emitted focusing in the far fieldThen the near and far field reception data are combined by the digital memoryAnd so on the TV monitor we see a higher resolution image in both, the shallow and deep regions using the combination focus

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Principles of combination focusPrinciples of combination focus

FocalPoint

FocalPoint

Depth[cm]

NearFocus

FarFocus Combination

Focus

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Types of Ultrasound ProbesTypes of Ultrasound ProbesLinear Array:

frequency range app. from 5 MHz to 13 MHzLength from 30 to 60 cmApplications: (Small Parts), (Orthopedics, Breast, Musculoskeletal)

Convex array:frequency range app. from 3.5 MHzto 9 MHzLength from 20 to 60 cmApplications: Abdomen, GYN, OB, Urology

Micro-convex: Application: Pediatrics

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Types of Ultrasound ProbesTypes of Ultrasound ProbesPhased array:

frequency range app. from 2 MHz to 8 MHzangle from 60 to 90 cmApplications: cardiology (heart)

Multi-Plane TEE-Transducer:with a frequency range of 4.0 to 8.0 MHz and an image plane rotation between 0 and 180 deg,

Adult

Pediatric

Multi-PlaneTEE-Transducer

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Types of Ultrasound ProbesTypes of Ultrasound ProbesFingertip / Intraoperative

frequency range app. from 5 MHz to 10 MHz

Endocavityfrequency range app. from 5 MHz to 10 MHzApplication: Endovaginal, Endorectal

Endoscopic / Mini-probesfrequency range app. from 5 MHz to 20 MHz

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Doppler EffectDoppler EffectThe Doppler effect is simply what someone moving away from a source of sound, such as a whistle experiences.That person will hear a pitch lower than the pitch heard by a person standing stillLikewise, someone moving toward the whistle will hear a higher pitch

Doppler effect

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Doppler EffectDoppler EffectThe diagram shows a Doppler transducer placed on the skin and aimed at an angle, θ, towards a blood vessel, which contains blood flowing with a velocity of u m/s, at any instant. The transducer emits ultrasound waves of frequency, fo, and echoes generated by moving reflectors in the blood, e.g. red blood cells, have a frequency, fr. The difference between these two frequencies, Δf, is related to the velocity of the flowing reflectors throught the following equation:

where v is the velocity of sound in the medium.So, for instance, when ultrasound with a frequency in the range 2-10 MHzis applied in medicine to detect blood flowing in arteries (where typical velocities are 0-5 m/s), the equation above reveals that the frequency differences will be in the audible range of sound frequencies, i.e. 0-15 kHz. Their signals can therefore be fed through speakers so that this sound can be heard

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Doppler EffectDoppler EffectUsing Doppler effect to measure blood flow

An ultrasonic blood flow meter

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Types of US Doppler TechniqueTypes of US Doppler TechniquePulsed-wave Doppler (PW Doppler)

Continuous-wave Doppler (CW Doppler)

Color Flow Imaging (CIF)

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Types of US Doppler TechniqueTypes of US Doppler TechniqueBlock diagram of a Doppler system

U. ST&R

PhaseDetection

FrequencyAnalysis

FFT

FrameMemory

DSC

ColorFlow

Imaging Monitor

VideoRecorder

VCR