MEDT8002

Blood flow measurement by Doppler technique

Hans Torp

Institutt for sirkulasjon og medisinsk bildediagnostikk

Hans TorpNTNU, Norway

Ultrasound Doppler

• Dopplershift from moving scatterers• Clutter filtering• Spectrum analysis• PW versus CW Doppler• Aliasing• Range ambiguity• Transit time broadning

Red blood cells are hardly visible in the ultrasound image

Carotid artery with calcified plaque

Red blood cell

1.5-

2µm

7.5µm

Probe developmentHigh-frequency

transducer imaging

Examples: Imaging of venous flow using a 16 MHz linear array transducer prototype.

1cm

Cristoph Ballot demonstrated the Doppler effect for sound waves (1845)

Doppler shift: fd = fo v/c

The Doppler effect

Christian Andreas Doppler (1803 - 1853)Described the Dopplereffect to light waves

k

bkj

Lyden forandrer frekvens ved bevegelseo o

Bilens hastighet: 70 km/time ~ 6% av lyd-hastighet

Ét halvtone-trinn i 12-toneskalaen: 2 = 5.94 %

Endring i frekvens (turtall): 6% + 6% = 12 %

1/12

Hans TorpNTNU, Norway

Fartskontroll på E6 ved Heggstadmoen

0 50 100 150 200 250 3000

50

100

150

200

250

300

frekvens [Hz]Motorsykkelens turtall 0.5*(f1+f2) = 140.3 HzDopplerskift: +/- 9.55 Hz ~ +/- 6.8 %Motorsykkelens fart: 340 * 6.8/100 *3.6 = 83.3 km/h

Fartsgrense = 80 km/h

Frekvensspekter før passeringFrekvensspekter etter passering

Ultralyd Doppler

Ultralyd probe

Ultralyd Doppler

Ultralyd probe

Dopplerskift fd = fo v/cDopplerskift fd = fo v/c

+ fo v/c= 2 fo v/c

Signal processing for CW Doppler

fofrequency

fo+fd0 frequencyfd0

Hans TorpNTNU, Norway

Matlab: cwdoppler.m

Blood velocity calculated from measured Doppler-shift

fd = 2 fo v cos(θ) / c

v = c/2fo/cos(θ) fd

fd : Dopplershiftfo : Transmitted frequencyv : blood velocity θ : beam anglec : speed of sound (1540 m/s )Hans Torp

NTNU, Norway

time

Velocity

CW/PW Doppler blood flow meter

PEDOF developed in Trondheim 1976

Blood velocity Mitral inflow

Normal relaxation

Delayed relaxation

Hans TorpNTNU, Norway

Angelsen & Kristoffersen PW&CW Dopper PEDOF - 1976

HolenVelocity -> Pressure gradientLiv Hatle: Clinical practice

Cardiac Doppler in Trondheim

Continous Wave Doppler

ø

Single transducerPW

Double transducerCW

ø

transmit

recieve

Velocity profile, v

Artery

Range cell

Observation region in overlap of beams

Signal from all scattererswithin the ultrasound beam

Pulsed Wave Doppler

Signal from a limited sample volume

ø

Single transducerPW

Double transducerCW

ø

transmit

recieve

Velocity profile, v

Artery

Range cell

Observation region in overlap of beams

Hans TorpNTNU, Norway

Matlab: pwdoppl

a)

b)

10-08/ 12pt

Hans TorpNTNU, Norway

Signal from a large number of red blood cellsadd up to a Gaussian random process

ω

G (ω)e

10-11/ 12pt

Hans TorpNTNU, Norway

Power spectrum of the Doppler signal represents the distribution of velocities

Variable Highpass filter

Signal from tissue

Pow

er

Frequency

Noise

Signal from blood

Lowpass filter

Gaussian noise floor

2-49/12pt

Hans TorpNTNU, Norway

Doppler spektrum

frequ

ency

time

spec

tral a

mpl

itude

Hans TorpNTNU, Norway

Tidsvindu-lengde ved spektralanalyse

Performance of the spectrum sonogram as a function of window length. Upper left: 150 points, upper right: 64 points, lower left: 32 points, and lower right: 16 points. The window type is Hamming and the degree of overlap is 75% in all pictures.

Resolution in Doppler spectrum analysis

50

Δ T

Δ v

Δv *ΔT = λ / 2

Minimum dot area in the spectrum display: Δv *ΔT

Ultrasound wavelength: λ

Doppler spectrumVelocity resolution

Blood flow velocityfo=2 MHz ~ λ = 0.76mmΔT = 10 msecΔv = 3.6 cm/sec ~ 0.7 % of peak syst. velocity

Myocardial velocityfo=3.5 MHz ~ λ = 0.4 mmΔT = 20 msecΔv = 2 cm/sec ~ 25 % of peak syst. velocity

Δv *ΔT = λ / 2

5 m/sec

10cm/sec

Sound packet

Transducer

Sound packet

2-52/12pt

4 8 120

2

4

6

8

Range , R (cm)

Transducer

35

7,5

10

12,5

15

4,062,43

1,621,22

0,970,81

1 MHz

25

10

Nyq

uist

vel

ocity

, m/s

2-53/12pt

PRF < c /2R

fd < PRF/2

fd= 2*f0 *v/c

v < c^2 / (8*f0*R)

Doppler spectrum analysis:Different velocities separated in frequency

Nyquist limit in Pulsed wave Doppler

Nyquist-limit

Doppler spectrumSubclavian Artery

Velocity waveform restoredby stacking