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G. Wayne Moore, B.Sc., MA, FASE

Ultrasound Beamformation and Image ReconstructionAAPM 2009 Conference

What we will coverWhat we will coverWhat we will coverWhat we will cover

• Historical Perspective of Ultrasound Technology

• Ultrasound and Tissue Water

• Partition of Ultrasonic Imaging Events

• Image Quality Advances

• Ultrasound System Architecture Changes

• Beamformation Analysis and Test Device

• Modern Approaches to Solving Old Imaging Problems

• Newer Approaches to Image Reconstruction – 2D Matrix Arrays

• Test Fixture and 3D Volumetric Image Reconstruction Analysis

• What’s Coming in the Future for Ultrasound

WeWeWeWe’’’’re Just re Just re Just re Just ““““Bags of WaterBags of WaterBags of WaterBags of Water””””!!!!

• An archetypal person has about 40 L of body fluid

• 25 L are inside 75 trillion cells

• 15 L are outside the cells (interstitial spaces)

• 5 L in blood volume

– 2 L of RBCs

– 3 L of plasma

Ultrasound and Tissue Water Ultrasound and Tissue Water Ultrasound and Tissue Water Ultrasound and Tissue Water

1540m/sec1540m/sec1540m/sec1540m/sec6.56.56.56.5µµµµsec/cmsec/cmsec/cmsec/cmStill the law!Still the law!Still the law!Still the law!

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Partition of Ultrasonic Imaging EventsPartition of Ultrasonic Imaging EventsPartition of Ultrasonic Imaging EventsPartition of Ultrasonic Imaging Events

TissueTissueTissueTissue----ultrasoundultrasoundultrasoundultrasound

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22

Doppler Doppler Doppler Doppler Doppler Doppler Doppler Doppler Image Image Image Image Image Image Image Image

ProcessingProcessingProcessingProcessingProcessingProcessingProcessingProcessing

Gray Scale Gray Scale Gray Scale Gray Scale Gray Scale Gray Scale Gray Scale Gray Scale ImageImageImageImageImageImageImageImage

ProcessingProcessingProcessingProcessingProcessingProcessingProcessingProcessing33

The scanhead orThe scanhead orThe scanhead orThe scanhead orTransducerTransducerTransducerTransducer

Specialized Signal Specialized Signal Specialized Signal Specialized Signal ProcessingProcessingProcessingProcessing

44

Color/Gray scale Color/Gray scale Color/Gray scale Color/Gray scale displaydisplaydisplaydisplayMass Storage:Mass Storage:Mass Storage:Mass Storage:

VCRVCRVCRVCRCDCDCDCDPACSPACSPACSPACSLANLANLANLAN

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Transmit signal out Transmit signal out Transmit signal out Transmit signal out Echo signal returnEcho signal returnEcho signal returnEcho signal return

History of Modern Diagnostic Ultrasound

•A-Mode•M-Mode•B-Scan•Mechanically Steered Real-time•Linear Array Real-time•Zero-crossing Doppler•Spectral Doppler (FFT)•Phased Array Real-time•CW Doppler in Probe – Bernoulli Equation•Color Flow Doppler•Triplex modes of Operation•Pseudo-Color•Color “Angio” & Power Doppler•Harmonic Imaging & Variants•Contrast Media Imaging•Spatial Compounding•3D Imaging – Volumetric•4D Imaging – Steered Curved Array•Phase Aberration Correction

≅≅≅≅ t∆ In complexity

1979

1985 1997

2009

3D Volumetric cardiac imagederived from 2D Matrix Array

with 2,500 elementspseudo Color display identifies

proximal and distal echoes

Some 3D Clinical AdvantagesSome 3D Clinical AdvantagesSome 3D Clinical AdvantagesSome 3D Clinical Advantages:

No geometric assumptionsNo mental interpolations(cognitive reconstruction)

Provides pre-surgical perspectiveProvides post-surgical perspective

Pyramidal volume of ultrasonic dataPyramidal volume of ultrasonic dataPyramidal volume of ultrasonic dataPyramidal volume of ultrasonic data

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Evolution of Ultrasound System Architecture + =

Proprietary Hardware

Centric Design

Proprietary Software Centric Design

Specialized Front EndGeneralized Back End

Single Platform

Microsoft XP Embedded Software Platform

Change of System Technologies Since 1990Change of System Technologies Since 1990Change of System Technologies Since 1990Change of System Technologies Since 1990

Proprietary Hardware CentricHybrid CentricProprietary Software CentricSoftware + Generalized Backend Centric

Shift from analog to digital beamformers

PA = Pre amplifierPA = Pre amplifierPA = Pre amplifierPA = Pre amplifierADC = Analog to digital converterADC = Analog to digital converterADC = Analog to digital converterADC = Analog to digital converter

TGC Application

PAPA

PAPA

PAPA

PAPA

PAPA

PAPA

PAPA

PAPA

PAPA

ADCADC

ADCADC

ADCADC

ADCADC

ADCADC

ADCADC

ADCADC

ADCADC

ADCADC

Dyn

amic

Tim

e D

ela

ys

ΣΣΣΣ

128 ElementTransducer

10 bits 36 MHz10 bits 36 MHz10 bits 36 MHz10 bits 36 MHz1024 Values1024 Values1024 Values1024 Values60 dB Dynamic Range60 dB Dynamic Range60 dB Dynamic Range60 dB Dynamic Range

The digital beamformer The digital beamformer The digital beamformer The digital beamformer function has historically function has historically function has historically function has historically

resided in the main console resided in the main console resided in the main console resided in the main console of the ultrasound systemof the ultrasound systemof the ultrasound systemof the ultrasound system

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Digital beamforming 2009Digital beamforming 2009Digital beamforming 2009Digital beamforming 2009

Higher element counts were once restricted by the need to have a

single wire in the probe cable for each element in the array. Multiplexing the elements allowed for transducers with

higher element counts and a lower number of transmit channels in the

beamformer. Current 2D matrix arrays with element counts of 2,500 necessitated a different approach to

beamforming, and where the beamforming, or at least parts of it

would take place.

Sub-beamformingperformed in the

probe

100 Channels feeding & receiving

2,500 elements

Would be normally whata “standard” front endwould expect to see

High speed serial interface that provides control signals for the sub-beamformere.g., defining delays for each unique element

x (f)x(f)

Time sampling is digital, all else is analog

x

x(f)

Beamformation Analysis Beamformation Analysis Beamformation Analysis Beamformation Analysis TextTextTextText----fixture and setfixture and setfixture and setfixture and set----upupupup

Commercially availableultrasound probe and system testing device

using a single crystal toboth receive signals from

the probe and transmitsignals into the system

via the probe.

5

+

-

ComparatorTransducer

Amplifier

Red LEDGreen LED

Threshold Level

Threshold timer 10 mSec

ON OFF

Power On Timer 200 mSec

Target Generator

3-5 cm 10 MHz

5-7 cm 5 MHz

7-9 cm 2.5 MHz

Target Transmitter

Test Device – Block Diagram

26µsec = 2cm 26µsec = 2cm 26µsec = 2cm

10MHz 3-5cm 5MHz 5-7cm 2.5MHz 7-9cm

Fundamental Imagingsample rate gaps inphased array sector

display

2nd Harmonic Imaging

Harmonic ImageFundamental Image

An example of expanding aperture focusing used to maintain spatial resolutionthroughout depth of field

Active aperture changes as a function of depth

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Old imaging problems, new imaging approachesOld imaging problems, new imaging approachesOld imaging problems, new imaging approachesOld imaging problems, new imaging approaches

1540m/sec1540m/sec1540m/sec1540m/sec6.56.56.56.5µµµµsec/cmsec/cmsec/cmsec/cmStill the law!Still the law!Still the law!Still the law!

Transducer

Shadow

Scanning Field

ShadowingObject

Shadowing in Propagation EventsShadowing in Propagation EventsShadowing in Propagation EventsShadowing in Propagation Events

Objects that are very reflective or very attenuating remove

ultrasound from the image area behind the mass producing

shadows. These events mark a specific interaction between

ultrasound and tissues, and a property of the shadowing

tissues.

Transducer

Scanning Field

RefractiveShadow

RefractiveSurface

Ultrasound Refraction at the Edge of a Circular ObjectUltrasound Refraction at the Edge of a Circular ObjectUltrasound Refraction at the Edge of a Circular ObjectUltrasound Refraction at the Edge of a Circular Object

Circular or cystic structures can produce refraction at the edge of the structure, bending the beam

into the object, producing shadows extending from the edge of the object. This happens with a change in propagation velocity, but does not happen if there are

no velocity changes.

Probe

Breast

Lesion

Normal Scan Lines

SonoCTScan Lines

Spatial CompoundingSpatial CompoundingSpatial CompoundingSpatial Compounding

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Spatial Spatial Spatial Spatial CompoundingCompoundingCompoundingCompoundingUsing MultipleUsing MultipleUsing MultipleUsing MultipleApertures andApertures andApertures andApertures andAnglesAnglesAnglesAngles

Limited Fields of ViewLimited Fields of ViewLimited Fields of ViewLimited Fields of View

With a structure identifying algorithm, the system locates and positions major structures, calculating the structure location in the continuous slicing scan of the transducer. This technique is equivalent to compound

B-scanning without a scanning arm.

SliceMotion

SieScapeSieScapeSieScapeSieScape by Siemensby Siemensby Siemensby Siemens

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Complex Beamforming in 4D SystemsComplex Beamforming in 4D SystemsComplex Beamforming in 4D SystemsComplex Beamforming in 4D Systems

60 Degree Angle

20 Degree Angle TextTextTextText----fixture and setfixture and setfixture and setfixture and set----up for 4D Image Formation Analysisup for 4D Image Formation Analysisup for 4D Image Formation Analysisup for 4D Image Formation AnalysisUsing a Philips iE33 Ultrasound System and X7Using a Philips iE33 Ultrasound System and X7Using a Philips iE33 Ultrasound System and X7Using a Philips iE33 Ultrasound System and X7----2t probe2t probe2t probe2t probe

In order to create “real-time” 4D ultrasound images (i.e., three spatial dimensions plus motion), volume

datasets must be acquired, processed and displayed at a rate higher than the capacity of the

human eye to retain a visual impression

2D Matrix Array 2,500 elements

Frame rate paces random access to the array

Bench SetBench SetBench SetBench Set----upupupup

Nickel (PVDF)Nickel (PVDF)Nickel (PVDF)Nickel (PVDF)Tektronix ScopeTektronix ScopeTektronix ScopeTektronix Scope

RF Power AmplifierRF Power AmplifierRF Power AmplifierRF Power AmplifierProbe/Nickel FixtureProbe/Nickel FixtureProbe/Nickel FixtureProbe/Nickel Fixture

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TEE/Nickel InterfaceTEE/Nickel InterfaceTEE/Nickel InterfaceTEE/Nickel InterfacePosition/PressurePosition/PressurePosition/PressurePosition/Pressure

Control MechanismControl MechanismControl MechanismControl Mechanism

1 2 33

2

2

2

3

3

X7-2t5x5 element sub-aperture

Philips X7-2t probe2500 elements100 channels

Array CarrierArray CarrierArray CarrierArray Carrier

Tip CollarTip CollarTip CollarTip Collar

TransducerTransducerTransducerTransducerArrayArrayArrayArray

Coax toCoax toCoax toCoax toFlex CircuitFlex CircuitFlex CircuitFlex Circuit

InterfaceInterfaceInterfaceInterface

Potted PassivePotted PassivePotted PassivePotted PassiveComponentsComponentsComponentsComponents

Inside the X7Inside the X7Inside the X7Inside the X7----2t2t2t2tFlex to ArrayFlex to ArrayFlex to ArrayFlex to Array

Interface Interface Interface Interface Flex CircuitFlex CircuitFlex CircuitFlex Circuit

BackingBackingBackingBackingMaterialMaterialMaterialMaterial Gold FoilGold FoilGold FoilGold Foil

I/O connection forI/O connection forI/O connection forI/O connection forIntegrated CircuitIntegrated CircuitIntegrated CircuitIntegrated Circuit

NonNonNonNon----insulated insulated insulated insulated µµµµm m m m thick bonding wires* thick bonding wires* thick bonding wires* thick bonding wires*

Inside the X7Inside the X7Inside the X7Inside the X7----2t2t2t2t CCD

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System InterfaceSystem InterfaceSystem InterfaceSystem Interface

Battery poweredBattery poweredBattery poweredBattery poweredDiff PreDiff PreDiff PreDiff Pre----amplifieramplifieramplifieramplifier

good high freqgood high freqgood high freqgood high freqdetection and CMRR*detection and CMRR*detection and CMRR*detection and CMRR*

Detecting xmit, generatestarget, gets amplified by

the RF amp* common mode rejection ratio

Input signal from Nickel4µsec burst @ 5MHz

Noise feed throughfrom RF amp

Acoustic signal onlyReceive out of ultrasound system

Noise + Acoustic

Nickel transmit pulse matches every othersystem transmit creating one line gaps in

sector display shown above

Nickel pulseNickel pulseNickel pulseNickel pulse

Ultrasound system pulseUltrasound system pulseUltrasound system pulseUltrasound system pulse

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3D image Nickel transmit pulse displayed

3D image rotatedNickel transmitpulse displayedacross all slices

½ sector switching

Mixed mode (Color Flow Doppler and Imaging)Reduced frame rate approximately matches every

Nickel pulse thereby “filling in” each sector line

Ni Sys Ni SysSignal In Front

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Signal In Middle Signal In Back

So What is Coming Next?So What is Coming Next?So What is Coming Next?So What is Coming Next? Major innovation in ultrasound willwillwillwill slow, but…

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(1) 2D Matrix Arrays will be developed for broader clinical application

(2) Design and optimization of capacitive micro-machined ultrasonic

transducers – silicon substrates may not be the avenue

(3) Extended sub-beamformer + CMUTs

…………ultrasound still must remain competitive with other ultrasound still must remain competitive with other ultrasound still must remain competitive with other ultrasound still must remain competitive with other advanced imaging modalities such as MR, soadvanced imaging modalities such as MR, soadvanced imaging modalities such as MR, soadvanced imaging modalities such as MR, so…………

Standard Imaging System Connector

Standard Ultrasound Cable

1. Wrist-Mounted Connector

2. Flat Flex Cable

3. Small-profile, finger-mounted array

For example, extensions of ultrasoundFor example, extensions of ultrasoundFor example, extensions of ultrasoundFor example, extensions of ultrasoundapplications based on clinical need applications based on clinical need applications based on clinical need applications based on clinical need andandandand

cost effectivenesscost effectivenesscost effectivenesscost effectiveness

Nobility of Soul Never Kept a Business in the BlackNobility of Soul Never Kept a Business in the BlackNobility of Soul Never Kept a Business in the BlackNobility of Soul Never Kept a Business in the BlackNobility of Soul Never Kept a Business in the BlackNobility of Soul Never Kept a Business in the BlackNobility of Soul Never Kept a Business in the BlackNobility of Soul Never Kept a Business in the Black

END PRESENTATIONEND PRESENTATIONEND PRESENTATIONEND PRESENTATION

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