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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