TTK 4165

Signalbehandlingsteknikker i

medisinsk bildediagnostikk

Signal Processing in Medical Imaging

Faglærer: Hans TorpInstitutt for sirkulasjon og bildediagnostikk

Hans TorpNTNU, Norway

Introduksjon Introduksjon

• Litt ultralydfysikk og historisk tilbakeblikkLitt ultralydfysikk og historisk tilbakeblikk

• Ultralyd avbildningUltralyd avbildning

• Ultralyd Doppler for måling/avbildning av hastighetUltralyd Doppler for måling/avbildning av hastighet

• Oversikt over faget TTK4165Oversikt over faget TTK4165

Hans TorpNTNU, Norway

lecture overview

• Physical principles of ultrasoundPhysical principles of ultrasound

• Ultrasound imagingUltrasound imaging

• Ultrasound Doppler and flow imagingUltrasound Doppler and flow imaging

• Overview TTK4165Overview TTK4165

Hans TorpNTNU, Norway

Sound field depends on source size and Sound field depends on source size and wavelengthwavelength

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Ultrasonic M-Mode (Motion Mode)Ultrasonic M-Mode (Motion Mode)

Hans TorpNTNU, Norway

Echoes from tissue structures are received and displayed

First Cardiac trials by Edler and Hertz in 1953

Real-time Ultrasound B-mode Real-time Ultrasound B-mode 19741974

N. Bom & al. “Multiscan EchoCardiograph” Ultrasound in Medicine aug. 74

Hans TorpNTNU, Norway

Vis film

Doppler blood flow meter Pedof 1976Doppler blood flow meter Pedof 1976Blood velocity Mitral inflow

Normal relaxation

Delayed relaxation

• Fourier transform - measure bloodflowFourier transform - measure bloodflow

• Gaussian Random process Gaussian Random process - ultrasound signal- ultrasound signal

• Analog computer diff. equation solverAnalog computer diff. equation solver- model of the cardiovascular system - model of the cardiovascular system

• Bernouli equationBernouli equation- from blood velocity to pressure- from blood velocity to pressure

Ultrasound probeUltrasound probe

Fokus

Focusing Steering and Focusing

50-200 elements 50-200 elements

Received Echoes Received Echoes from close objectsfrom close objects

probeelements

Objects

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2

Digital Beam FormerDigital Beam Former

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#Channels:128

# samples per channel: 10.000

•Data per scanline: 2*10.000*128 = 2.5 Mb •Data per image: 2.5*100 = 250 Mb•Data per second: 40* 250 Mb = 10 Gb

1986CFM 700 5 channelsMekanisk scanning

1996System Five 128 channelsElektronic scanningMekanisk scanning

2000Vivid 7 128 kanalerElektronisk scanning

Real-time 2D B-modeReal-time 2D B-modeWall motion assessmentWall motion assessment

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Hans TorpNTNU, Norway

Ultrasound ProbesUltrasound Probes

Linear arrayHigh resolutionLimited width

Curve-linear arrayLarge image widthLarge near field

Phased arraySmall footprint90 deg. sector format

Hans TorpNTNU, Norway

Ultrasound imaging can be applied Ultrasound imaging can be applied to almost all human organsto almost all human organs

Liver Fetus 3 ½ mnd

Kidney

Twin fetus

Ultrasound imaging:Measure dimensions, areas, volumesStudy anatomical detailsAssessment of muscle contractionHeart-valve function

Heart, 4 chamber view

Image resolutionImage resolution

Daperture

F:

Foc

al d

epth

F-number f# = F/D

Wavelength: L

”Dot-size”: f# L

Camera exampleL = 0.9 e-3 mmf# = 5.6Resolution: 0.005 mm ~ 50000 dpiInfrared camera gives lower resolution

Ultrasound exampleL = 0.5 mm (3 MHz)f# = 8cm/2cm= 4 Resolution: 2 mm ~ 125 dpi

Larger probe -> improved resolutionHigher frequency -> improved resolution

Probe-diameterD

F:

Foc

al d

epth

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•Computer-simulated ultrasound image•Higher frequency -> better resolution

Embryo 7 weeks. Ca 13 mm length

3D Transvaginal ultrasound3D Transvaginal ultrasoundThe Lancet:

In-vivo three-dimensional ultrasound reconstructions in the embryonic and early fetal period

Harm-Gerd Blaas 1, Sturla H. Eik-Nes 1, Sevald Berg 2, Hans Torp 2;

Limb development in Norway 20Limb development in Norway 20thth century century

12 weeks 18 weeks

Color Doppler velocity imagingColor Doppler velocity imaging

PW Doppler: Velocity from one point

Color flow imaging:Velocities in the whole image

Color M-mode: Velocities along a line

Tissue Velocity ImagingTissue Velocity Imaging

Moving upwardMoving downward

SystoleEarlyrelax.

Atrialsystole

Curved M-mode

Hans TorpNTNU, Norway

Strain rateStrain rate

Lvv

SR 12

Lv1v2

Tissue velocity Strain rate

SR

Adapted from J-U. Voigt and A. Heimdal

ShorteningNo changeElongation

Wall motion quantification

SystoleEarlyrelax.

Atrialsystole

Curved M-mode

Real-time 3D imagingReal-time 3D imaging2D matrix array2D matrix array

• 32-192 elements in a 1D 32-192 elements in a 1D arrayarray

• 32*32 ... 96*96 elements 32*32 ... 96*96 elements in a 2D arrayin a 2D array

• 1000 - 10000 elements1000 - 10000 elements

• CableCable

• ElectronicsElectronics

• BeamformerBeamformer

50 x 1elements

50 x 50=2500elements

Sanntid 3DSanntid 3D

Azimuth

Elevation

4D Volume Imaging4D Volume Imaging

• No ECG gatingNo ECG gating

• Volume rendering / orthogonal Volume rendering / orthogonal slicingslicing

• Volume size: Volume size: ~20 x 80º / ~35 x 45º~20 x 80º / ~35 x 45º

• Volume rate: 17-25Volume rate: 17-25

Standard setup Increased elevation width

4D Color Imaging (ECG Gated)4D Color Imaging (ECG Gated)

• Gated from 7 heart Gated from 7 heart beatsbeats

• High frame rates High frame rates (17-35 frames / (17-35 frames / second)second)

• High Color sensitivityHigh Color sensitivity

• High Color resolutionHigh Color resolution

TTK4165 OverviewTTK4165 Overview

• Pulse Echo principlePulse Echo principle

• Ultrasound beamformingUltrasound beamforming

• General imaging system General imaging system

• Ultrasound imaging system Ultrasound imaging system

• Doppler – blood velocity measurement and imagingDoppler – blood velocity measurement and imaging

• Patient safety issuesPatient safety issues

• Ultrasound contrast imagingUltrasound contrast imaging

• 3D imaging3D imaging