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24
2 Indices for the Evaluation of Doppler Sonograms
Introduction
The Doppler sonogram of a vessel represents the time
course of the blood flow in that vessel. Erythrocytes
moving at different speeds in the vessel generate a
spectrum of frequency shifts, F. This Doppler spectrum
corresponds to the distribution of erythrocyte velocities in the vessel. The greatest shifts of Doppler
frequencies F
cytes. The time course of these maximal frequency
shifts, derived from the instant of fastest blood flow,
can be displayed by plotting frequency against time in
a two-dimensional image, the flow velocity waveform
(t) (Gonser 1989).
F
max
The immediate goal of a Doppler ultrasound examination is to record, analyze, and quantify the pulsatility
of flow in the interrogated artery by analyzing its
waveform.
In most examinations performed in gynecology the
waveform is the center of attention. The pulsatile flow
in an artery provides, among others, information about
the conditions of the area supplied by the vessel. For
instance, the waveform of the flow in the umbilical a.
provides information on the condition of the placental
vascular bed.
If the insonation angle of the Doppler beam is known,
the waveform also provides information about abso-
lute velocities, such as the highest velocity at the systolic peak and the highest velocity at the lowest diastolic ebb, or, when flow is reversed, the maximum
negative flow. The mean maximal velocity in the interrogated vessel over time can also be determined, being
as it were the mean value of the waveform.
The area under the waveform or the whole Doppler
sonogram contains information about the flow or
velocity profile and flow volume.
The Doppler spectrum is equivalent to the flow or
velocity profile, and so among other things it provides
information about the properties of the flow of blood.
Blood viscosity is a crucial factor. Other factors include
vascular diameter, absolute flow velocity, and factors
that change laminar flow, such as turbulence.
The total of all Doppler signals corresponds to the
number of erythrocytes recorded. Hence it can be considered to be an indicator of flow volume.
The use of wall or high pass filters plays a role in such
analyses, for their insertion masks part of the spectrum. The insertion of a filter can also make a decisive
correspond to the fastest erythro-
max
difference in the evaluation of very low or absent diastolic flow.
Quantitative Measurements
Originally interest in Doppler ultrasound centered on
quantitative measurements of volume flow. However,
the results, especially of quantities of flow in the arteries, varied by 20−30 % and hence were not reproducible. Flow volumes Q (mL × min
of average flow velocity V (cm × s
diameter (π ×r
determination of the vascular diameter, which is difficult to measure in the first place, will be squared in the
results. Moreover, the f indings in obstetrics must be related to estimated fetal weight, and this introduces
another considerable element of uncertainty. For all
these reasons qualitative analyses of the waveform are
preferred.
2
)(Q=V× π ×r2). Hence any error in the
−1
) are the product
−1
) and vascular
Qualitative Measurements
The goal of qualitative measurements is to obtain a reproducible mathematical correlative for the evaluation
of pulsatile Doppler waveforms. A display of the velocities of arterial flow over the course of a complete cardiac cycle in the fetus typically displays maximal flow
velocities as a biphasic curve. A steep upswing to a systolic maximum (A) is followed by a diastolic decline to
the maximal end-diastolic reading (B) of the
waveform. Clinical interpretation of the curve may be
simplified by assuming that the systolic rise of the
waveform is due to cardiac output and stroke volume,
the diastolic decline to the compliance of the interrogated vascular region and the total peripheral resistance of the vascular bed it supplies. For instance,
the waveform of the umbilical cord provides information about the state of the placental vascular bed.
Angle Problems
To calculate the absolute velocity of the flow of erythrocytes the insonation angle α and its cosine (cos
Basic Concepts
25
Indices for the Evaluation of Doppler Sonograms
1
α), which is used in the Doppler formula, must be
known.
V=
fd×c
2fo × cos α
Where
fo = transmitted ultrasound frequency
α = angle between the incident ultrasound beam and
the longitudinal axis of the direction of flow
c = velocity of ultrasound waves in the tissues
(1540 cm × s
−1
)
fd = Doppler frequency shift =
2fo×V×cosα
c
As the angle of incidence approaches 90° (cos 90° = 0)
the velocity vector in the direction of flow becomes
very small or zero. If the angle approaches 0 (cos 0 = 1),
the recorded Doppler signal becomes optimal. Hence
measurements should be made with as small an angle
as possible. Ideally measurements are made exclusively using tracings obtained with small angles
(쏝 60°).
When the angle of insonation of the Doppler beam is
known, conclusions about absolute flow velocities,
such as maximal velocities at systolic peak, can be
drawn from the waveform. The waveform provides information about the properties of flow, the crucial factor being viscosity. Thus, an elevated maximal flow
velocity may lead to the conclusion that viscosity is
diminished, suggesting, for example, anemia.
Wall Filter
Oscillations due to pulsations of vascular walls create
low frequency Doppler signals of high intensity. These
distort the recording of frequency shifts due to blood
flow. Such distorted signals can be eliminated by the
insertion of a wall filter integrated into the measuring
system. A wall filter of 울100 Hz is used to avoid the
elimination of low frequencies that are important in
diagnostic work.
26
Indices Used to Evaluate Two-Dimensional Doppler Sonograms
Indices used in evaluating two-dimensional Doppler
sonograms using time and velocity axes are usually
classified according to their basic units, including
velocity, acceleration, time course, and area under the
curve (AUC) (
G
Fig. 2.1 Indices for the analysis of a Doppler sonogram with
pulsatile blood flow.
A = temporal peak of maximum frequency waveform,
B = end-diastolic maximum frequency, F
B‘ = temporal minimum of maximum frequency waveform,
C = instantaneous maximum frequency, F
D = temporal average of maximum frequencies F
E = instantaneous spatial average frequency F
(TP)
F
max
(TM)
F
max
Table
2.1).
Doppler frequency
A
C
D
E
F
0T
(T)
max
(t)
max
mean
max
(TA)
(t)
Indices of Velocity
Velocity indices comprise the 2-point indices (Fig. 2.1)
such as the resistance index (RI) of Pourcelot, the B/A
ratio (B/A) or the A/B ratio (A/B) of Stuart (often also
called the S/D ratio). All three ratios are based on the
H
B
F = temporal average of spatial average frequencies F
G = spectral window
H = rising slope
Indices:
1 RI: (A−B)/A
2 A/B ratio: A/B
3 B/A ratio: B/A
4 PI: (A−B)/D
After Vetter (1991)
t
(TA)
mean
Indices Used to Evaluate Two-Dimensional Doppler Sonograms
Tabelle 2.1 Indices used in the analysis of Doppler sonograms of pulsatile blood flows
Doppler frequencies (F=F
RI Resistance Index F(TP)−F(T)/F(TP)
PI Pulsatily index F(TP)−F(T)/F(TA)
A/B A/B ratio F(TP)/F(T)
B/A B/A ratio F(T)/F(TP)
AA Constant flow ratio F(T)/F(TA)
ImI Impedance index F(T) · F(TP)/[F(T)]
SBI Spectrum broadening index (F
SBR Spectrum broadening ratio F
Acceleration
RS Rising slope y = a+bx
DS Descending slope y = ae
ARS Average rising slope [F
Time intervals
RAT Relative acceleration time F
SDTI Systolic decay time index [TP−T
HWI Height width index PI ·T/[T
rMIT Relative mean inflow time MIT/T
twPI Time-weighted PI MIT/(1-MRT)
Wavef orm
PLI Path length index Hk/t =
Areas
Ro Relative flow index AUC(0,TP)/AUC(TP,T)
R Relative flow rate index AUC(0,TP)/AUC(TP,T) : TP/(T−TP)
RSA Relative spectral area AUC(0,T)/T · F
, when not otherwise defined)
max
2
)/F
max−Fmean
(TP)/F
med
bx
(TP)−F
max
(TP)/T
max
(3/4)]/TP/[Td(3/4)−TP]/(T−TP)
r
(1/2)−Tr(1/2)]
d
max
(TP)
max
(T)]/TP · F
max
max
or (F
(TP)
max−Fmin
(TA)
max
)/F
max+Fmin
)
Basic Concepts
same initial values, and are therefore interchangeable.
A or S here correspond to the highest point of the
waveform, i. e., the systolic peak, B or D the lowest
point. A or S can also be written F
(TP), which stands
max
for maximal Doppler shift frequency at the temporal
peak. Similarly B can be written F
(T), standing for
max
maximal Doppler shift frequency at the end of the cardiac cycle T, or F
(TM) when the minimum does not
max
occur at the end of the cardiac cycle (temporal minimum, TM).
For the RI the dif ference between A and B is divided
by the maximal value of A, for B/A the minimal value B
is divided by the maximal value A, while A/B is the in-
verse, A divided by B. Clearly all three indices will present problems if B is immeasurably small. The value of
RI then becomes 1, the ratio B/A 0, and the ratio A/B infinity. Up to that point the values for the B/A ratio and
the RI change in a linear manner, while the A/B ratio
changes exponentially.If the flow reverses, i. e., when B
is negative, the value of RI exceeds 1. In this case the
amount after the decimal point represents the reverse
portion of the flow. The corresponding values of the
B/A are more difficult to interpret, since it can range
from 0 to −1, while the A/B ratio is even more difficult,
ranging from −infinity to −1. Which 2-point ratio is
used is a matter of personal preference, the choice
being between linear values with a limited range from
0 to 2 in the RI or between 1 and −1 for the B/A ratio,
and the exponential values of the A/B ratio, ranging be-
Fig.
tween 1 and infinity or −infinity and −1 (
2.2).
The best-known 3-point index of impedance is the
pulsatility index (PI) of Gosling and King, which, in addition to A (F
(TP)) and B (F
max
poral average of the mean frequencies D (F
(TM), uses the tem-
max
(TA)) as a
max
reference point. This is a rough way of expressing additional changes in the waveform mean D (F
(TA)) be-
max
tween the waveform’s systolic peak and temporal min-
5
4
A/B
3
2
RI
1
0
–1
DI
–2
–3
–4
–5
–1
0
1
Fig. 2.2 Progression of changes in the three transposable 2point indices: RI, A/B ratio (A/B), and diastolic index (DI). Forward flow is represented on the right, reverse flow on the left.
The progressions begin on the right, with continuous flow
without difference between systole and diastole. At point zero,
diastolic flow is absent. Points on the left of zero flow show increasing diastolic flow reversal.
27
Indices for the Evaluation of Doppler Sonograms
1
imum. Moreover, the PI has the advantage over the 2point indices in that, when it is used, absent or retrograde flows do not pose a problem. Basically F
replaced in the index by F
(TM), the lowest point of
max
max
(T) is
the waveform, which does not necessarily occur at the
end of diastole. The temporal minimum is used in contrast to the temporal maximum.
The impedance index (ImI) (Gill 1979) has achieved
little significance. It is calculated using the same values
as the PI: The product of maximal and minimal value is
divided into the square of the minimal value (A × B/B
2
This calculation, too, cannot be performed if the value
for end-diastolic flow is zero.
A little-used 2-point value is the constant flow ratio
(AA) (Thompson et al. 1985). It also, in addition to B
(T)), rests on the temporal mean D (F
(F
max
(TA)) of
max
the maximal frequencies. AA = B/D. Hence AA is not a
pure measure of pulsatility, but rather identifies the
part played by end-diastolic maximal frequencies in
the mean maximal frequencies.
F
(t)
max
F
(t)
min
HPF
The spectrum broadening index (SBI) does not define
the waveform, but in its two best-known variations it
captures the instantaneous Doppler spectrum itself at
specific points in the cardiac cycle, since the Doppler
spectrum changes during the cardiac cycle with the
velocity and acceleration of blood flow. One variation
(Kassam et al. 1982) takes into account the instant
mean frequency F
mean
. SBI=(F
max−Fmean
)/F
other variation uses the instant minimal frequency F
(cf. Fig. 2.3). SBI = (F
).
An even better indicator of spectral breadth, the
max−Fmin
)/(F
max+Fmin
).
spectrum broadening ratio (SBR) (Favre et al. 1989), is
the ratio of instant median frequency F
frequency F
(Fig. 2.4). SBR = F
max
med
(TP)/F
to maximal
med
(TP). In this
max
index the median velocity is preferred to the mean
velocity, as it is less subject to distortions due to incidental scatter.
Indices of Acceleration
Indices of acceleration may be derived from the slope of
a tangent to the systolic rise (rising slope [RS]) (Stuart
et al. 1980) or from a nonlinear approximation to the
curve such as the velocity of systolic descent (de-
scending slope [DS]) (Lingman and Maršál 1986). Indices can also be determined from a combination of
measures of velocity and time, such as the average rising slope (ARS). ARS= (F
(TA). The difference between the maximal and
F
max
minimal point on the waveform is divided by the product of the time to systolic peak and mean maximal
velocity.
(TP) − F
max
max
. The
max
min
(TM))/TP ×
28
Fig. 2.3 Derivation of the SBI from maximal frequency F
and minimal frequency F
frequency. F
frequency, HPF (after Vetter 1991).
(T) maximal frequency, F
max
(T), with consideration of the filter
min
(T) minimal
min
0
82
P:150
A :
V1/2 :
V2/3 :
B :
TAMV :
RI :
P I :
RMRT :
VCL :
Maxim
91.00
40.00
29.50
14.00
46.92
0.85
1.64
0.39
66.00
Median
60.50
22.00
18.50
8.50
27.25
0.86
1.91
0.39
34.00
Med/Max
0.66
0.55
0.63
0.61
0.58
1.02
1.16
1.00
0.52
max
(T)
6
561
Fig 2.4 Doppler sonogram. The
relations of spectral broadening
are displayed on a printout of a
computerized evaluation of Doppler sonograms. A typical
waveform with its concomitant
median intensity curve has been
derived from six cardiac cycles
characterized by waveforms
(above). The relation of median
to maximum was calculated for
each data point. In the figure this
value has been calculated for the
systolic peak (A).
Indices Used to Evaluate Two-Dimensional Doppler Sonograms
All three acceleration indices characterize the
waveformin the systolic part of the cardiac cycle, using
the descending slope of systole to take into account the
diastolic course of the waveform.
Path Length Index
A special waveform index is derived from the length of
the waveform in relation to duration of the cycle,
known as the path length index (PLI) (Johnston et al.
1984). The more curves there are in the waveform, i.e.,
the greater the flow pulsatility, the longer is the
waveform tracing and the greater the PLI.
Temporal Indices
Some of the temporal indices are again measures of acceleration, such as the relative acceleration time (RAT).
RAT = F
divided by cycle duration. For the systolic decay time
index (SDTI) (Thompson et al. 1985) especial attention
is paid to the upper quarter of the waveform (
It is derived from relations of time course before and
after the systolic peak. The ratio of the time taken from
three quarters of peak velocity to reach the peak (A) to
total systolic rise (C) is divided by the ratio of the time
from peak to three quarters of peak velocity (B) to total
time of decay (D).
By contrast the height width index (HWI) (Johnston
et al. 1984) uses the upper half of the systolic sonogram
Fig. 2.7). Hence it can only be used in vessels in which
(
the end-diastolic maximal velocity is less than half of
peak velocity. It is derived from the PI, total cycle duration (T), and the time from achieving half peak velocity
to the time of decay below peak velocity (S). HWI = PI ×
T/S, or = PI × T/T
Indices can also be derived from the center of gravity
line (CL) (Gonser 1986, Gonser et al. 1987) Fig. 2.8. This
calculation involves a complex comparison of two
paths. The CL divides the area of the sonogram
functionally, comparing two areas instead of two lines.
The central column of blood flows with maximal velocity. The CL divides the temporal axis of the maximal
axial flow velocity into two parts: One part represents
the mean time during which the column remains in a
defined segment of the vessel, while a second part defines the mean time required for the column to enter
the next segment. The CL cuts the time axis at its center
of gravity (CG). The two indices represent the relative
mean inflow time (rMIT) and its complement, the time-
weighted pulsatility index (twPI).
(TP)/T. In this index systolic peak flow is
max
Fig.
1
/2)−T
1
(
/2).
r
(
d
2.6).
y = ae
bx
cm s
–1
.
y = a+bx
150
100
V
peak
50
V
0
Fig. 2.5 Doppler sonogram. Graphic representation of the RS
and DS (after Lingman and Maršál 1986).
ACC
Time
Total time
min
ms
1
3/4
A
C
B
D
0
0TT (3/4) T (3/4)TP
rd
Fig. 2.6 Intervals to calculate systolic decay. The essential
values are the time of the systolic peak and its height (= 1).
Based on this reading the ascent and descent of the waveform is
intersected at three quarters of the height of the peak. The projections of these points to the time axis—points T
(3/4)—define the distances A = TP−Tr(3/4), B=Td(3/4)−TP,
T
d
C = TP, D = T−TP (after Vetter 1991).
(3/4) and
r
1
1/2
S
0
0TT (1/2) T (1/2)TP
rd
Fig. 2.7 Intervals to calculate the HWI (= PI × T/s). The height
of the systolic peak is the essential factor. The waveform is intersected in its ascent and descent at the halfway point to this
peak. The distance between these intersections (S = T
(1/2)) is a core factor in this index (after Vetter 1991)
(T
r
T
(1/2)−
d
Basic Concepts
29
Indices for the Evaluation of Doppler Sonograms
Relative Flow Index
30
1
F (MRT)
max
Finally, indices derived by comparing descriptive areas
measure divisions of the area under the waveform at
the time of the systolic maximum velocity (V
2.9), such as the relative flow index (R
CL
(Fig.
pson et al. 1985). For this index the AUC before the systolic peak (L) is divided by the remaining area (R).
Ro = L/R, or = AUC (0,TP)/AUC (TP,T).
MRT MIT T
Fig. 2.8 CL and derived parameters. The CL divides the time
axis of the waveform into a part that represents the mean residence time (MRT) in a segment of the vessel, and another that
defines the mean inflow time (MIT) into the next segment.
CL = center of gravity line
(MRT) = maximal velocity at the center of gravity line,
F
max
MRT = mean residence time
MIT = (T-MRT) mean inflow time
rMRT = relative mean residence time (MRT/T)
twPI = time-weighted pulsatility index (MIT/MRT)
(after Vetter 1991).
The relative flow rate index (R
1985) comprises additionally the ratio of the corresponding temporal paths l and r. R = L/R : l/r, or
AUC(0,TP)/AUC(TP,T).
The total area of a sonogram can also be defined by a
rectangle formed by the duration of the cardiac cycle
(T) and peak velocity (A) or V
area covered by the sonogram in this rectangle is the
relative spectral area (RSA) (Marhold 1987, personal
communication). This measure is a simple way of detecting a loss of area in instances where the waveform
shows subtle changes.
In the literature the same designations are essentially used for the indices of pulsatile flow waveforms.
In fact, though, these values are in part determined,
processed, and eventually calculated in a variety of
ways. The least affected by these problems are the 2point indices such as the A/B and B/A ratio or the RI. In
LR
these cases any systematic error in the calculation of
the peak in comparable flow waveforms affects both
points similarly. By contrast segments of the velocity
profile lost by the use of a high pass filter (HPF) can
10TTP r
Fig. 2.9 Intervals and areas used to calculate relative flow. The
essential point is the systolic peak. It marks the division of the
area under the waveform as well as the intervals of the cardiac
cycle. (1. relative flow index R
1/r: R = L/R; 1 = TP, r = T−TP, L = AUC (0,TP), R = AUC (TP,T))
(after Vetter 1991).
= L/R, 2. relative flow rate index
o
only be reconstructed inconsistently if at all. As previously noted, the same applies to systematic losses
due to an unfavorable insonating angle, where the
deficit can be magnified disproportionately in the part
of the curve showing low frequency shifts.
In the PI, which depends on 3 points, the variations
due to different methods of calculation become clearer
because of the additional calculated values. In this case
the outcome is influenced by the way the individual
points in the waveform are determined. Thus, it makes a
F (TP)
max
difference whether calculations are based on the actual peak velocity, or on the 15/16 or 7/8 quantile of the
power spectrum, for depending on the density distribution such a peak value materially differs from the
actual value both absolutely and relatively. All values
depending on this quantity suffer from corresponding
errors that are difficult to assess (
and spectrum analyzers incorporate qualitative differences that influence the sharpness of the edges of Dop-
0T
Fig. 2.10 Areas used to calculate RSA. The calculation is of the
portion of the area of the waveform relative to the area of the
rectangle, which is defined by the duration of the cardiac cycle
and the height of the systolic peak. (RSA = AUC [0,T]/T ·
(TP)) (after Vetter 1991).
F
max
pler spectra, and these are of importance in this type of
waveform analysis.
In extreme cases, when calculation of the total
waveformis not feasible, substitute values may be use d.
These are calculated quite differently, for example,
weighted mean flow velocity V
o
) (Thompson et al.
o
(TP) (Fig. 2.10). The
max
Fig. 2.11). Doppler
(TA) in lieu of mean
mean
(TP))
max
) (Thom-
Indices Used to Evaluate Two-Dimensional Doppler Sonograms
maximal velocity V
(TA). Such a calculation may give
max
an index, but this, too, is problematic, since its components include not only the changes in maximal
velocity but also the rather delicate density distribu-
tion of the spectrum.
Gonser tested the sensitivity of various measures of
the waveform. He showed in a theoretical model that 2point indices reach a limit as soon as end-diastolic flow
velocities can no longer be demonstrated and how this
limit is reached. In such cases Gosling’s (Gosling et al.
1971, Gosling and King 1975, Gosling 1976) 3-point PI
2.12). Since the PI is not very
still registers changes (
Fig. 2.11 Graphic representation of the effect of a waveform
calculation using a 7/8 quantile intensity distribution. The 7/8
quantile differs from the actual maximal value depending on
the intensity distribution. This may result in disproportionately
high errors in the estimate, which can affect the calculation of
waveform indices (after Vetter 1991).
Fig.
ABCDE
(22222) (32221) (33211) (42211) (43111)
Intensity
Time
7/8 8/8
Frequency
Basic Concepts
Fig. 2.12 Schematic represen-
tation of the functions of
waveform assessment indices
resulting from a series of
selected test signals. (a)
Sequence of test signals (including code numbers), arrangement by increasing pulsatility.
(b) Functions of the selected
waveform assessment indices
resulting from the tests. The
index values have been plotted
against the sequence of test
signals (after Gonser 1986).
FGH I J
(52111) (43210) (52210) (53110) (53200)
KLMN
(62200) (63100) (64000) (73000)
a
5
1
ABCDEFGHIJKLMN
0,8
0,7
0,6
0,5
ABCDEFGHIJKLMN ABCDEFGHIJKLMN
b
A/B RI PI
rMIT
1
0,5
00
ABCDEFGHIJKLMN ABCDEFGHIJKLMN
5
4
3
2
1
twPI
3
2
1
31
1
Indices for the Evaluation of Doppler Sonograms
0 Max 1/2 2/3 Min
1
RI: 1/2 1/3 1/4 2/3 3/4 2/4
RAT: 2/4 2/3 3/4
Fig. 2.13 The 4-point model. Four points of the waveform can
be linked to each other. The relations between these points provide a picture of the changes of the waveform in the six recordable time segments. Additionally the numerical values of
the relationships (here RAT) derived from the peak (in this case
RI) can be compared (after Vetter 1991).
23
4
specific in these situations, Gonser (1986) suggested
the twPI, the basic idea of which is the centroidal axis
of a tracing of the maximal velocities of one cardiac
cycle. This index clearly registers not only all conceivable gradations, but in this respect it is more specific
than the PI. On the other hand, in contrast to the other
commonly used indices, it cannot be calculated
without a computer.
Despite the availability of all these indices some
phenomena of the waveformcannot be recorded selectively or specifically, such as a late systolic notch or a
bimodal curve.
For our own analyses we searched for measures that
would be simple to calculate, supplementing the range
of points measured in a waveform with one at the halfway point of the cardiac cycle (T
thirds of the cycle (T
). The four measured points on
2/3
) and one at two
1
/2
the waveform
(1) V
(2) V
(3) V
(4) V
(TP)
max
(T
1
max
max(T2/3
(T)
max
)
/2
)
define the indices of the 4-point model (4 MPM). These
indices allow a number of indices to be derived,
specifically those defining the late systolic and dias-
2.13). The RI was gener-
tolic course of the curve (
Fig.
ally calculated by the method of Pourcelot. Admittedly
the two additional points halfway and two thirds of the
way along the curve are also discontinuous, but for the
time course of velocities they allow much better conclusions than the 2-point indices PI, A/B, or B/A. Thus, it
can capture the characteristic notch seen in a uteroplacental disturbance of placental function.
32
Optical Classification
Even before the development of qualitative numerical
indices derived from the waveform, an examiner will
obtain auditory and visual impressions of the sonogram. Thus, it is possible to classify both normal and
pathological waveforms “at a glance.”
Normally the end-diastolic Doppler shift in the
umbilical a. is about 30−50% of that at the systolic
peak. If the end-diastolic shift is very low or absent, its
pathological import is easy to recognize. After the 24th
week of pregnancy a late systolic notch in the uteroplacental flow curve must always be regarded as a sign
of pathological blood flow. The gray areas between
normal and pathological flow patterns are quite narrow over arteries near the heart such as the aorta or
the middle cerebral aa.. Hence it is particulary in those
areas that measurements should be taken. The recognition of these facts has led to more or less standardized proposals for classifications based on visual impressions. Mention should be made here of Laurin’s
(Laurin 1987) and Maršál’s (Maršál et al. 1987) proposed classification of blood flow into four types for
Fig.
evaluation of blood flow in the fetal aorta (
2.14):
0 Diastolic flow present and PI in the normal range
I Diastolic flow present, but PI abnormal
II End-diastolic block
III Flow absent during a large part of diastole or
reverse flow present
Fig. 2.14 Criteria for assessment of blood flow classifica-
tion (BFC) 0, I, II, and III. Class 0
and I are assigned by the appropriate value of the PI and the
qualitative finding of continuous
diastolic flow, while in class II
and III qualitative findings of absent or reverse diastolic flow are
the determining factors (after
Laurin 1987 and Maršál et al.
1987).
cm s
Clinical Procedure
v
peak
y = a + bx
–1
.
BFC 0 PI < + 2 SD and continuous
diastolic (forward) flow (normal)
BFC I
PI ≥ + 2 SD and continuous
diastolic (forward) flow (normal)
BFC II
0
v– v
peak
PI =
RS =
v
v
min
mean
b
mean
An alternative is given by the Doppler score of Fendel
and Sohn (1989). Here the visual classification of the
flow waveforms of the aorta, umbilical a., and utero-
Points
01 2
Fetal aorta
v
min
0
Time
BFC III
0
0
placental aa. is evaluated using a system of points
(Fig. 2.15).
Basic Concepts
Uterine aa.
Umbilical a.
Fig. 2.15 Doppler score for the evaluation of perinatal risk.
Normal: 0 points
Questionable: 1 point
Abnormal: 2 points
Clinical Procedure
The examiner must first study the acoustic and visual
impressions of the Doppler sonogram. To begin with
measurements must be made of the umbilical aa. to interrogate the fetoplacental circulation and of the
uteroplacental aa. on both sides to interrogate the maternal circulation. The next points of interest are the
fetal vessels (abdominal aorta and middle cerebral a.
[MCA]). Experience has shown that with normal fetoplacental and uteroplacental flow patterns a centralization of the fetal circulation distal to the aorta or a redistribution of flow favoring the brain will hardly ever
be found. Hence the basic examination is that of the fe-
33