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AAPM 2005

The Ultrasound Research Interface: A New Tool for Biomedical Investigations

The Ultrasound Research Interface: A New Tool for Biomedical Investigations

Shelby Brunke1, Laurent Pelissier2, Kris Dickie2, Jim Zagzebski3, Tim Hall3, Thaddeus Wilson4

1Siemens Medical Systems, Issaquah WA2Ultrasonix Medical Corporation, Vancouver, BC

3Department of Med. Physics, University of Wisconsin4Department of Radiology, University of Tennessee

AAPM 2005

IntroductionIntroductionIntroductionDigitally controlled ultrasound scanners offer extensive levels of programmability, which enable manufacturers to explore and to readily incorporate alternative beam formation, signal and image processing, networking, and interfacing capabilities.

Recent efforts have led manufacturers to share these tools for innovation with academic and clinical researchers. This discussion will present capabilities of two such machines and present examples of research uses.

AAPM 2005

The Ultrasound Research Interface: A New Tool for Biomedical Investigations

Examples of Use

The Ultrasound Research Interface: A New Tool for Biomedical Investigations

Examples of Use

Jim Zagzebski, Tim Hall, Thaddeus Wilson*

Department of Med. Physics, University of Wisconsin*Department of Radiology, University of Tennessee

AAPM 2005

Parametric ImagingParametricParametric ImagingImaging

• Except for Doppler, ultrasound imaging is based entirely on echo amplitudes

• Parametric images•Acoustic attenuation•Scatterer size •Speed of sound•Elasticity (many forms)

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Ultrasound Attenuation Ultrasound Attenuation Ultrasound Attenuation

• Attenuation is used diagnostically in the liver, breast, etc.

• However, only qualitative estimates are made– “mass exhibits shadowing”– “mass exhibits good through transmission”

• Goals: incorporate methods for determining attenuation locally, and in the form of images.

AAPM 2005

Measuring AttenuationMeasuring AttenuationMeasuring Attenuation

• Record RF echo data from ROI• Filter, measure reduction of rf signal

with depth• In a clinical machine, signal amplitude

changes with depth are also affected by:– Beam focusing, beam shapes– TGC settings set by operator– Internal TGC set by the manufacturer– Nonlinear processing in scanners

• Reference phantom techniques have been developed that effectively account for instrumentation effects.

Depth

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Human liverHuman liverHuman liver

• ROI outlined from B-mode image (blue line)

• Areas of inhomogeneityeliminated (red line)

• Algorithm retrieves RF echo data from ROI, computes attenuation

• Results in normal liver agree with many previous reports (0.5 dB/cm-MHz)

Attenuation in liver vs. frequency

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Tu et al

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Attenuation ImagingSiemens SONOLINE Antares

Attenuation ImagingAttenuation ImagingSiemens SONOLINE AntaresSiemens SONOLINE Antares0.3 dB/cm/MHz contrast, 1 cm diameter

Spatial and Frequency Compounding

•Acquire RF data from multiple angles

•Compute α from ROI’s at each angle

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AAPM 2005

Attenuation ImagingSiemens SONOLINE Antares

Attenuation ImagingAttenuation ImagingSiemens SONOLINE AntaresSiemens SONOLINE Antares0.3 dB/cm/MHz contrast, 1 cm diameter

Spatial and Frequency Compounding

•Acquire RF data from multiple angles

•Compute α from ROI’s at each angleAAPM 2005

“Scatterer Size” Imaging““ScattererScatterer SizeSize”” ImagingImaging

• RF data can be processed to yield the “backscatter coefficient” at frequencies throughout the signal bandwidth

• Values of backscatter vs. frequency reflect the size of scatterers contributing to the signal.

• By applying scatterer size dependent correlation models to the backscatter vs. data, possible to estimate size.

AAPM 2005

Mouse tumor model (Oelze and O’Brien, IEEE UFFC, 2004)Mouse tumor model Mouse tumor model ((OelzeOelze and Oand O’’Brien, IEEE UFFC, 2004)Brien, IEEE UFFC, 2004)

Carcinoma

Fibroadenoma

Scatterer size

Use single element transducer, 20 MHz

Reflects histological structure

AAPM 2005

Overlaid B-mode and Scatterer sizeOverlaid BOverlaid B--mode and Scatterer sizemode and Scatterer size

• Acquire RF echo data from normal human thyroid

• Siemens Antares, 6-13 MHz• Histology book: 100-200 µm

lobules• Scatterer size image data

appears to correlate with anatomy.

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AAPM 2005

Patient with thyroid nodule (Wilson et al)Patient with thyroid nodule Patient with thyroid nodule (Wilson et al)(Wilson et al)

Near real-time scatterer size imaging mode on UltrasonixRP500

AAPM 2005

Elasticity ImagingElasticity Imaging

• Improve on manual palpation • Use a clinical ultrasound imaging system as

a sensor of anatomic deformation• Relative deformation quantifies the bulk

mechanical properties of tissue• Provides new diagnostic information

Estimation of Strain (Uses RF data frames)Estimation of Strain (Uses RF data frames)

Pre-compression RF line

Post-compression RF line

2τ

1τ T∆

TStrain

∆−= 12

ττ(Gradient of the axial displacement)

Array Transducer

AAPM 2005

Implementation on Machine with URIImplementation on Machine with URIImplementation on Machine with URI

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Relative Size of LesionsRelative Size of LesionsRelative Size of Lesions

Invasive Ductal Carcinoma

Fibroadenoma

AAPM 2005

169 Breast Lesions; 1 Observer169 Breast Lesions; 1 Observer169 Breast Lesions; 1 Observer

AAPM 2005

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Spatial Angular Compounded Elastograms(Ultrasonix 500 RP)

AAPM 2005Compounded ElastogramsCompounded ElastogramsCompounded Elastograms

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AAPM 2005

Speed of soundSpeed of soundSpeed of sound

Hayashi et al, A new method for measuring in vivo speed of sound speed in the reflection mode, J. Clin Ultrasound 16: 87-93, 1988.

Can you measure SOS in pulse-echo mode?

AAPM 2005

Speed of soundSpeed of soundSpeed of sound

• Beam former adds time delays to echo data picked up from elements in an array. Assumes SOS = 1540 m/s.

• Some URI’s allow assumed speed of sound to be programmed.

• Proper focusing is obtained only when the assumed speed of sound matches the speed of sound in the subject. Affects image intensity, for example.

AAPM 2005

Speed of soundSpeed of soundSpeed of sound• Generate images of phantoms for different assumed

SOS in the beamformer

• Measure image brightness vs assumed SOS

• Peak occurs near SOS of phantom

RMI 403C=1540 m/s

ATS 539C=1460m/s

AAPM 2005

ConclusionsConclusionsConclusions• Parametric imaging adds new information to

improve diagnostic accuracy• The ‘research interface’ on high-end systems are

somewhat limiting in what the user can control Extended control and system programming available through close working relationship with manufacturer

• The ‘research interface’ on lower-end systems provide greater access to system resources and system parameters

• These research interfaces provide an opportunity to investigate imaging algorithms that were impractical with laboratory data acquisition systems