MFEL 3010

Ultrasound in Medicine Part 3

Ultrasound blood flow measurements and imaging

Hans Torp

Department of Circulation and Medical Imaging NTNU

Hans Torp NTNU, Norway

Red blood cells are hardly visible in the ultrasound

image

Carotid artery with calcified plaque

Red blood cell

1.5-

2µm

7.5µm

V=80µm

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 Doppler effect to light waves

Doppler speed control

motorsykkel_0001.wmv

0 50 100 150 2000

50

100

150

200

250

300

frekvens [Hz]

Dopplershift: +/- 9.55 Hz ~ +/- 6.8 % Motor bike speed: 340[m/s] * 6.8/100 *3.6 = 83.3 km/h Speed limit = 80 km/h

Frequency before pass by: 150.80 Hz Frequency after pass by: 130.85 Hz

Frequency analysis of sound

Ultrasound Doppler

Ultralyd probe

Ultrasound Doppler

Ultralyd probe

Dopplerskift fd = fo v/c

Dopplerskift fd = fo v/c + fo v/c = 2 fo v/c

Signal processing for CW Doppler

fo frequency

fo+fd 0 frequency fd 0

Hans Torp NTNU, Norway

Matlab: cwdoppler.m

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 scatterers within 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 Torp NTNU, Norway

Matlab: pwdop

Blood velocity calculated from measured Doppler-shift

fd = 2 fo v cos(θ) / c

v = c/2fo/cos(θ) fd fd : Dopplershift fo : Transmitted frequency v : blood velocity θ : beam angle c : speed of sound (1540 m/s )

Hans Torp NTNU, Norway

a)

b)

10-08/12pt

Hans Torp NTNU, Norway

Signal from a large number of red blood cells

add up to a Gaussian random process

time

Velocity

Doppler blood flow meter

PEDOF developed in Trondheim 1976

Blood velocity Mitral inflow

Normal relaxation

Delayed relaxation

Hans Torp NTNU, Norway

Color Doppler velocity imaging

PW Doppler: Velocity from one point

Color M-mode: Velocities along a line Hans Torp NTNU, Norway

Color flow imaging: Velocities in the whole image

Relation blood pressure / blood flow

• Blood pressure = Blood flow * periferal resistance

• periferal resistance increases by narrowing of

capillaries

• Blood flow to an organ may have substantial

variation, with a constant blood pressure

Blood flow – low periferal resistance

Blood pressure

Blood flow

Blood flow – high periferal resistance

Blood pressure

Blood flow

Spill film

Stenosis assessment

V1 V2

A1 A2

V1 * A1 = V2 * A2

% reduksjon A1 - A2 = V2 - V1 A1 V2

Example:

5x velocity corresponds to 80% stenose

Degree of stenosis can be calculatet without angle correction

V1 V2

P1 P2

Bernouli’s equation Pressure gradient: P1 - P3 = 4 V22

P3

Example: 80% aortic-stenosis V1= 1 m/s V2 = 5 m/s ~ pressure gradient of 4*5*5 = 100 mmHg Left ventricular pressure of 220 mmHg is required to achieve 120 mmHg aothic pressure

Hans Torp NTNU, Norway

Pressure gradient in a stenosis

Off-pump bypass surgery(beating heart)

Rune Haaverstad Stein Samstad Hans Torp

Coronary artery

occlusion

bypass

Quality control

Vis film!

Tissue Velocity Imaging

Moving upward Moving downward

Systole Early relax.

Atrial systole

Curved M-mode

Hans Torp NTNU, Norway

Strain rate

LvvSR 12 −=

L v1 v2

Tissue velocity Strain rate

SR

Adapted from J-U. Voigt and A. Heimdal

Shortening No change Elongation

Wall motion quantification

Systole Early relax.

Atrial systole

Curved M-mode

Akutt infarkt

21

Lasse Løvstakken et al, 2010

Real-time 3-D flow imaging with 2-D matrix arrays

64 – 128 array elements

From 1D Array…

to 2D Array…

2000 – 3000 array elements

Example: Mitral valve insufficiency

22

Lasse Løvstakken et al, 2010

Blood Flow Imaging (BFI) Angle-independent flow visualization

Regular Color-Doppler Imaging Blood Flow Imaging = color flow imaging + speckle movement

23

Lasse Løvstakken et al, 2010

New metod for blood flow imaging

Carotis plack

Hans Torp NTNU, Norway

Kidney

24

Lasse Løvstakken et al, 2010

Probe development High-frequency transducer imaging

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

1cm

25

Lasse Løvstakken et al, 2010

Intraoperative imaging in coronary bypass surgery

26

Lasse Løvstakken et al, 2010

Modeling and simulation of flow in a coronary bypass (LIMA-LAD)

High competitive flow due to insignificant stenoses was found to produce unfavourable wall shear stress conditions that may be linked to endothelium dysfunction and subsequent graft narrowing and failure

New hope for tiny hearts Advances in imaging methods to discover heart defects in children and newborns

References: Siri A. Nyrnes, L. Lovstakken et al, Echocardiography. 2007;24:975-981, Echocardiography 2010;27:1113-1119

Quantification of jet flow in shunt between the heart chambers

Ultrasound technology Research opportunities at NTNU

TTK4160 Medical imaging TTK4165 Signal processing in medical imaging TTK4170 Mod. Id. Biolog. Systems Master project and master thesis PhD possibilities www.ntnu.no/ultrasound