MEDT8002 Ultralyd bildediagnostikk

Faglærer: Hans Torp

Institutt for sirkulasjon og bildediagnostikk

Hans TorpNTNU, Norway

New development in color New development in color DopplerDoppler

“Blood motion imaging” “Blood motion imaging”

Arteria bracialisConventionalColor Doppler

Arteria bracialisBlood motion imaging

Carotis communisBlood motion imaging

Hans TorpNTNU, Norway

University(NTNU) - Industry(Vingmed)University(NTNU) - Industry(Vingmed)

1986 CFM 700 First color Dopplerwith mechanical scanning

Beam-adder

442

BFx

1995 System Five Digital beam former>Higher framerate>RF-data for research>Tissue Doppler

2000 Vivid 7 Real-time processingwith PC technology

Data acquistion in Data acquistion in color flow imagingcolor flow imaging

Beam k-1 Beam k Beam k+1

Number of pulses in each direction

3 – 15

Frame rate reduction compared to B-mode

2D Color flow imaging2D Color flow imaging

1. Limited information content in the signal, i.e. short observation time, low signal-to-noise ratio, and low Nyquist velocity limit.

 2. Insufficient signal processing/display.

Full spectrum analysis in each point of the sector is difficult to visualize.

Color mapping typesColor mapping types

Hans TorpNTNU, Norway

Power Doppler (Angio)

Brightnes ~ signal power

Color flow

Brightnes ~ signal powerHue ~ Velocity

Color flow ”Variance map”

Hue & Brightnes ~ VelocityGreen ~ signal bandwidth

Color scale for velocity and - spreadColor scale for velocity and - spread

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Ao

LV

LA

Power

Bandwidth

Aortic insufficiency

Hans TorpNTNU, Norway

Color flow imaging Color flow imaging Mitral valve blood flowMitral valve blood flow

Normal mitral valve Stenotic mitral valve

Hans TorpNTNU, Norway

Autocorrelation methodAutocorrelation methodSensitive to clutter noiseSensitive to clutter noise

)exp(i )G(

)exp(i )G( d i m { R ( 1 ) }

r e { R ( 1 ) }π

- πG (ω )

πω- π

Phase angle of R(1) substantially reduced due to low frequency clutter signalClutter filter stopband much more critical than for spectral Doppler

How to perform clutter filter in How to perform clutter filter in color flow imaging?color flow imaging?

Beam k-1 Beam k Beam k+1

Signal discontinuity causes ringing in high-pass filters

Raw signal from beam k

Signal after high-pass filter

Lost settling time

How to perform clutter filter in How to perform clutter filter in color flow imaging?color flow imaging?

Beam k-1 Beam k Beam k+1

Signal discontinuity causes ringing in high-pass filters

Raw signal from beam k

Signal after high-pass filter

Lost settling time

Color flow scanning strategiesColor flow scanning strategies

B-mode scanning

Mechanical scanning

+ No settling time clutter filter- low frame rate

Electronic scanning Packet acquisition- Settling time clutter filter+flexible PRF without loss in frame rate

Electronic scanning continuous acquisition+ no settling time clutter filter+ High frame rate- low PRF (=frame rate)

scanning directiontim

e

Color flow imaging with a Color flow imaging with a mechanical probemechanical probe

v = W*FR

Image width WFrame rate FRSweep velocity v= W*FR

Virtual axial velocity: vr= v*cotan()

vr

v

Example:Image width W = 5 cmFrame rate FR =20 fr/secAngle with beam = 45 deg.Sweep velocity v= 1 m/s

Virtual axial velocity: vr= 1 m/s

vr > max normal blood flow velocities!

Color flow imaging with a Color flow imaging with a mechanical probemechanical probe

W= N*b

v = W*FR

Beamwidth (Rayleigh criterion): bEffective number of beams: N =W/bFrame Rate: FR

Signal from stationary scatterer

N*Fr*t

Clutter signal bandwidth: 2*N*FR

Power spectrum

Clutter filter cutoff frequency: fc > N*FR Frequency components < fc removed

Minimum detectable Doppler shiftMinimum detectable Doppler shift

Frame rate Frame rate FR =1 Hz FR =1 Hz FR = 10 Hz FR=20 Hz FR = 10 Hz FR=20 HzWidth (# beams)Width (# beams)N=30N=30 30 Hz30 Hz 300 Hz300 Hz 600 Hz 600 HzN=70N=70 70 Hz70 Hz 700 Hz700 Hz1400 Hz1400 Hz

Clutter filter cutoff frequency: fc > N*FR(transit time effect mechanical scan)

Cardiac flow imaging: fo= 2 MHz, 15 mm aperture, beamwidth 3 mm30 beams covers the left ventriclefc = 600 Hz ~ 0.21 m/sec. lower velocity limit

Color flow imaging with a Color flow imaging with a mechanical probemechanical probe

v = W*FR

Reflected wavedoes not hit the transducer

Max Dopplershift 600 Hz~ 0.21 m/sec

Atlanta, GA april 1986Atlanta, GA april 1986

Vingmed, introduced Vingmed, introduced CFMCFM The first commercial The first commercial

colorflow imaging scanner colorflow imaging scanner with mechanical probewith mechanical probe

Horten, Norway Horten, Norway september 2001september 2001

GE-Vingmed closed down GE-Vingmed closed down production line for production line for CFMCFM

after 15 years of continuous after 15 years of continuous productionproduction

Minimum detectable Doppler shiftMinimum detectable Doppler shiftClutter filter cutoff frequency: fc > N*FR

Frame rate Frame rate FR =1 Hz FR =1 Hz FR = 10 Hz FR = 10 Hz FR=20 Hz FR=20 HzWidth (# beams)Width (# beams)N=30N=30 30 Hz30 Hz 300 Hz300 Hz 600 Hz 600 HzN=70N=70 70 Hz70 Hz 700 Hz700 Hz1400 Hz1400 Hz

Periferal vessel imaging with fo= 10 MHzMechanical scanning: fc = 1400 Hz ~ 108 mm/sec. Electronic scanning: fc = 30 Hz ~ 2.3 mm/sec.

Packet acquisition (P=10): Frame rate = 35 frames/secContinuous acquisition: Frame rate = 350 frames/sec

Combining tissue and flowCombining tissue and flowContinuous sweep acquisitionContinuous sweep acquisition

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Brachial artery

Temporal averaging for mean Temporal averaging for mean frequency estimatorfrequency estimator

Example:

Effect of averaging R1 :

Variance of angle(R1)reduced by factor 24!

Effect of averaging angle(R1):

Variance reduction factor=4

)1(*)()1(ˆ1

nxnxR kk

N

nk k=1 : 4, uncorrelated signal packets