Transcript Doppler echocardiography & tissue doppler Dolly mathew Properties of blood • Hemodynamics- physical principles of blood flow & circulation • Density – mass per unit volume(g/ml) Resistance.

Doppler echocardiography &
tissue doppler
Dolly mathew
Properties of blood
• Hemodynamics- physical principles of blood
flow & circulation
• Density – mass per unit volume(g/ml)
Resistance to acceleration
• Viscosity – ability of molecules to move past
one another by overcoming frictional forces
0.035 poise at 37◦c
• Flow occurs from high pressure to low
pressure end
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R= 8Lv/ ∏r2
V viscosity of blood
R radius of lumen
L length of the vessel
Q= ∆P/R poiseuille’s law
Q= ∆P∏r2/ 8Lv
Q= ∆P∏r2
Types of flow
Laminar flow
• Acceleration of flow- flat flow profile / plug flow
• Converging flow- flat profile parabolic profile
• Diverging flow - multiple flow patterns(uniform
high velocity flow, stagnant flow, eddy flow)
• Vessel curvature – high velocity in the inner part
of curve in the ascending limb, outer part of the
curve in descending limb
Turbulant flow
• Valve obstruction, regurgitation,septal defects
• Increased velocities , flow vortices
• Predicted by reynold’s number Re= ᵨcd/v
• Laminar flow
– narrow spectral envelope-most cells travel over a
narrow range of velocities
– Large spectral window-echo free area under
spectral doppler trace
• Turbulant flow
– Spectral widening-direction and range of velocities
increase-greater range of doppler shift
frequencies
– Spectral window diminished
Continuity principle fig
• Doppler echocardiography utilizes ultrasound
to record -direction,velocity and pattern of
blood flow
• based upon the changes in frequency of the
backscatter signal from small moving
structures, ie, red blood cells, intercepted by
the ultrasound beam
Comparison of 2-D echo and doppler
• 2-D echocardiography
• target is tissue
• Type of information is
structural
• Optimal alignment is
perpendicular
• Preferred transducer
frequency is high
• Doppler imaging
• Blood is target
• Obtain information on
physiology
• Parallel alignment
between beam and
target
• Low transducer
frequency is preferred
• BASIC PRINCIPLES
• A moving target will backscatter an ultrasound
beam to the transducer
• the frequency observed when the target is
moving toward the transducer is higher
• the frequency observed when the target is
moving away from the transducer is lower
than the original transmitter frequency
• Doppler shift (F[d]) = F[r] - F[t]
• F[d] = 2 x F[t] x [(V x cos ø)] ÷ C
Blood flow velocity (V)
speed of sound in blood (C)
ø, the intercept angle between the ultrasound beam
A factor of 2 is used to correct for the "round-trip"
transit time to and from the transducer.
• This equation can be solved for V, by substituting (F[r] - F[t]) for F[d]:
• V = [(F[r] -F[t]) x C] ÷ (2 x F[t] x cos ø)
• the angle of the ultrasound beam and the direction of blood flow are
critically important in the calculation
• ø of 0º and 180º (parallel with blood flow), cosine ø = 1
• ø of 90º (perpendicular to blood flow), cosine ø = 0 , the Doppler shift is 0
• ø up to 20º, cos ø results in a <10 percent change in the Doppler shift
• ø of 60º, cosine ø = 0.50
Angle of doppler beam in relationship
to direction of blood flow
Doppler effect
Spectral analysis —
• the difference between the transmitted and
backscattered signal is determined by
comparing the two waveforms with the
frequency content analyzed by fast Fourier
transform (FFT). The display generated by this
frequency analysis is termed spectral analysis.
• By convention, time is displayed on the x axis
and frequency shift on the y axis.
Spectral display
• Intensity/amplitude -proportional to the number
of blood cells with that velocity-represented by
brightness of the signal.
Pressure determination
• ∆P pressure difference
between 2 points
• V1 proximal,v2 distal velocity
• ᵨ density of liquid
• dv change in velocity over
the time period
• ds distance over which
pressure decrease
• R viscous resistance in the
vessel
• v velocity of blood flow
• Simplified ∆P = 4(V2²-V1²)
=4V²
Doppler formats
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Continous wave doppler
Pulse wave doppler
Colour flow imaging
Tissue doppler
Continous wave doppler
• Continuous transmission of doppler signal
towards the moving RBCs & continuous
reception of reflected signals
• Blood flow along the entire beam is observed
• Range resolution not possible
• High velocities can be recorded
• Aliasing does not occur
Pulse wave doppler
• Short intermittent bursts of ultrasound emitted
• Listens only at a fixed and brief time interval to receive
signals from a specific distance
• Select doppler information from a particular location
using sample volume
• PRF-number of pulses transmitted from transducer
each second,determines the sampling rate
• PRF limits the max.velocity detectable-Nyquist limit
:PRF/2
• PRF/2= ±∆f = 2 f○ v cosø/C
• V = C PRF/ 4 f○ v cosø
Sample volume
• three-dimensional,
teardrop shaped portion
of the ultrasound beam
• width is determined by
the width of the
ultrasound beam at the
selected depth.
• length determines the
length of time that the
transducer is activated to
receive information from
sv location
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main disadvantage of PW inability to accurately measure
high blood flow velocities ,
limitation technically known
as "aliasing"
• inability of pulsed Doppler to
faithfully record velocities
above 1.5 to 2 m/sec when the
sample volume is located at
standard ranges in the heart
• Aliasing is represented on the
spectral trace as a cut-off of a
given velocity with placement
of the cut section in the
opposite channel or reverse
flow direction.
Aliasing
Control of aliasing
V = C PRF/4f◦cosø
◦
• Increasing the PRF
D = c t /2 ; c propagation speed thro’tissue
t time taken for us signal to return to the
transducer
2 pulse must travel to the structure & then back
again
T= 2D/C
PRF = 1/T = C/2D
• Decreasing the transmitted frequency
• Baseline shift ("zero
shift" or "zero off-set" )
Repositioning of zero
baseline effectively
increases the maximum
velocity in one direction,
at the expense of other
direction
• Changing from PW to CW
• Utilising high PRF mode: transmission of any
given pulse occurs before the reception of all
the echoes from the previous pulse
• Use multiple sample gates at various locations
• Signals received at different depths
simultaneously
• Disadvg- exact location of doppler shift is not
known
The spectral outputs from PW and CW
appear differently
• When there is no
turbulence, a laminar
(narrow band) spectral
output- PW
• CW - all the various
velocities encountered
by the ultrasound
beams are detected by
CW
Comparison between CW & PW
cw
pw
Depth resolution
no
yes
Sample volume
large
small
Detection of high velocities yes
no
Aliasing
no
yes
Spectral content
Wide
narrow
Use in duplex instruments
yes
yes
sensitivity
more
less
Transducer power
Lower
Higher
Control Of Sample Volume
Placement
Poor
Good
Doppler audio signal
• audio outputs
– High pitched sounds -large Doppler shifts -high
velocities
– low pitched sounds -lesser Doppler shifts
• Flow direction information
– stereophonic audio output
• Flow
– Laminar flow -smooth, pleasant tone –uniform V.
– Turbulent flow -high-pitched and whistling or harsh
and raspy sound- different velocities
• It can usually be said that when an operator
wants to know where a specific area of
abnormal flow is located that PW Doppler is
indicated.
• When accurate measurement of elevated flow
velocity is required, CW Doppler should be
used
The Use of the Doppler Controls
• Gray Scale : the gray scale control provides a means of
altering the various ranges of gray (from white to black)
on the spectral display and has no effect on the audio
output of the Doppler system.
• Different Doppler instruments have from two to more
than eight different ranges of gray scale display.
• Lighter shades of gray indicate that there are fewer red
cells moving at that velocity in comparison to darker
shades of gray or black where many red cells are
moving at that velocity.
• The use of this control
at eight different gray
scale settings is
demonstrated
• A spectral recording of
normal aortic flow with
properly set gain and
gray scale
• The problem with leaving the gray scale
control at the maximum setting is that a light
level of gray is assigned to low amplitude
background noise in the spectral trace.
• balanced adjustment between the gain
control and the gray scale control ,so that the
cleanest spectral trace with the most shades
of gray is displayed.
Uses
• Doppler echo may offer a valid alternative to
invasive cardiac catheterization for
hemodynamic assessment of patients with
advanced heart failure
• it may assist in monitoring and optimization
of therapy in heart transplant recipients.
Optimisation of doppler signals
• Angle dependency-parallel alignment of blood flow &
ultrasound beam
• Sample volume position-placed where the blood flow
is most parallel to us beam
- increasing the depth of the sample volume;reduces
PRF; lowers the maximum velocity that can be
displayed
• Velocity scale adjusts the maximum velocity that can
be displayed
• Baseline is a horizontal line with zero doppler shift;
velocities towards the transducer above the baseline;
away from transducer below the baseline
• Wall filters- eliminates the low frequency
doppler shifts that typically occurs due to
motion of heart valves or heart walls
• Gain function adjusts the degree of
amplification of received doppler signals
• Should be adjusted to optimally display the
entire doppler spectrum without any
excessive background noise
• Sample volume length- 2-5mm, avoid spectral
broadening
Doppler examination of mitral valve
inflow
• PW sample volume at
the tip of mv leaflets.
• IVRT (Ao valve closure –
m v opening)-can be
measured by displaying
mv inflow signal & LVOT
signal in the same
spectral trace
• E- early rapid filling
• Deceleration slope
• Diastasis- equalisation
of pressures-low
uniform velocities close
to the baseline
• Atrial filling phaseAwave
• Stroke volume thro’ mvsv at mitral annulus
Doppler examination of LVOT &Ao
• Apical 5 chamber view –
LVOT, Ao
• Pw sample vol (3-5mm) just
proximal to the aortic valve
• Ao flow – cw ideal
• Desc Ao- suprasternal long
axis, sv 1cm distal to the
origin of left subclavian
artery
• Below the baseline,v
shaped, steep acceleration
& deceleration
Doppler examination of PV flow
• Apical 4 chamber view
• Sv (3-5mm) placed 12cm into RUPV
• Systolic forward flow
• Diastolic forward flow
• Atrial flow reversal
Doppler examination of TV inflow
• Plax RV inflow tract/apical 4 chamber view
• Positioned centrally between open leaflet tips
on the RV side
Doppler examination of RVOT & PA
• Sv within the outflow tract , 1cm prox to
pulmonary valve leaflets
• PA – centre of PA 1cm below the pulmonary
valve
Doppler examination of hepatic veins
• subcostal long axis view of ivc
• Sv placed 1-2cm into the hepatic vein proximal
to its jn with IVC
• Systolic forward flow
• Diastolic forward flow
• Atrial flow reversal
Doppler examination of svc
• Suprasternal notch or rt supraclavicular fossa
• Sv 5-7 cm into ivc
Doppler artifacts
• Mirror imaging or crosstalk
– Symmetric spectral image on opposite side
– Less intense
– Decrease power output,optimise alignment
• Ghosting
– Brief displays of colour painted over regions of
tissues
– Usually solid colour,occur into tissue area of image
– Produced by motion of strong reflectors
Basic principles of colour doppler
imaging
• Produced by using multiple sample gaits along
multiple scan lines
• Where doppler signals are detected, pixels
representing that areas are designated a
colour
• Colour coding relative to the transducer is
direction sensitive
• Blood flow direction – BART system
• Blood flow velocity- low velocity flow indicated
by colours closest to colour baseline
- Appear in deeper colour hues
- High velocity flow – towards the end of colour
bar, appears brighter
- No angle correction
-Peak velocity estimations are not possibe
-Only mean doppler velocities are depicted
• Frequency aliasing -appears as colour reversal
• Timing of the colour doppler signals- achieved
by observing CFI in relation to ECG
• Laminar vs turbulant flow – smooth
homogenous pattern; RBCs move at about the
same velocity & in the same general direction
• Turbulant flow- disorganised mosaic pattern
containing all colours on the colour bar
Optimisation of colour flow doppler
images
• Frame rate- no of frames produced per second
• Depends upon depth,colour sector width,& line
density
• Velocity scale- djusts the maximum velocity that
can be displayed
• Wall filters
• Gain
• Angle dependency-best doppler signal when
direction of blood parallel to the us beam