Review
Doppler ultrasonography in the middle cerebral artery and
the umbilical artery of piglets: an exploratory study
Drs. M. van Dullemen, Faculty of Veterinary Medicine, Utrecht University, 2011
Abstract
Objective: Intrauterine growth restriction (IUGR) is a common complication in
human pregnancy. It is often caused by placental-insufficiency and can be diagnosed
with Doppler velocimetry measurements in the umbilical and middle cerebral arteries.
To study the effects, diagnosis and treatment of IUGR a animal model is necessary. In
this study the possibility of using Doppler ultrasound in pig fetuses is examined.
Methods: Twelve 3-5th parity sows between 55-110 days of gestation were scanned.
In each sow two fetuses were recorded for 2-5 minutes. These recordings were
observed and the percentage of fetal movement was calculated. Five 3-5th parity sows
between 70-94 days of gestation were scanned 1-2 times a week for 3 weeks. With
color flow Doppler the arteries were located in two fetuses per sow.
Results: The percentage of fetal movement decreases with advanced gestation.
However, no Doppler flow velocimetry measurements could be done due to constant
fetal movement.
Discussion: During the study it became clear that measuring Doppler velocimetry in
pig fetuses is quite a challenge. To determine if the pig fetus is an accurate animal
model which we can use to diagnose and treat intrauterine growth restriction in human
fetuses, more research has to be done.
Introduction
Since Doppler Ultrasonography was first used for measurements in the fetal
circulation in 1977, this technique has become an established method of antenatal
monitoring [1]. Especially in high-risk pregnancies the use of Doppler can predict
several clinical complications of pregnancy, e.g. intrauterine growth restriction
(IUGR), fetal anemia because of red blood cell alloimmunization, multiple gestation,
and can help to plan the time and method of delivery when necessary [2]. With
Doppler the blood flow velocitymetry can be measured in different fetal vessels and
with these outcomes the blood supply and distribution in the fetal body can be
followed. In fetuses who do not reach their growth potential Doppler can help to
identify if such a fetus is small but normal or if the fetus has a problem with the blood
supply from the placenta. If placental-insufficiency is the cause of the growth
retardation, the fetal body can redistribute his blood to the brain (brain-sparing).
Hereby the diastolic flow to the cerebral vessels often increases and abnormal
waveforms could be detected in the umbilical arteries [3]. The measurements of blood
velocimetry in these vessels are therefore an often used technique in the prediction of
perinatal outcome. Although many studies of the fetal development has been done, it
is still not clear how we can diagnose or treat fetuses with IUGR or other circulatory
problems. For this reason more studies have to be done and the use of animal-models
may come at hand. Because of the many similarities between pigs and humans, they
are commonly used animals for human research. To use the pig as an animal-model
for obstetrical research in human, models for comparison have to be created. In earlier
research bone growth-rates of fetal pigs were made, which can be used to detect
1
growth retardation in the future. In this research we want to find out whether it is
possible to measure the blood flow velocimetry in the arteria umbilicalis and the
middle cerebral artery in pigs with the use of Doppler Ultrasonography and if so,
where in the gestation these measurements can be done best.
Doppler
Principles
Doppler ultrasound is a method for detecting the direction and velocity of moving
blood in vessels. With the use of reflected sound waves, send into the body by a
transducer, the bloodstream can be followed. The sound waves are hitting the red
blood cells, which are sending the waves back to the transducer. The time between
sending and receiving the sound waves is called
the ‘frequency shift’ and it is determined by the
velocity at which the red blood cells are moving.
If the angle between the transduced sound and
the moving blood, which should be as close as
possible to zero degrees, is known, the velocity
of the bloodstream can be measured with the
help of the frequency shift [4]. In 1842 the
Australian Johann Christian Doppler first
described the phenomenon as a ship moving out
to sea, who would meet the incoming waves with
Fig. 1. Doppler effect.
a higher frequency than a ship who is moving
toward the shore. Although J.C. Doppler never referred to sound waves, his findings
are known as the Doppler effect: the change in frequency of a wave for an observer
moving relative to the source of the wave [5, 6].
The two most frequently used types of Doppler are the continuous and pulsed wave
Doppler. A continuous wave (CW) system sends and receives a continuous flow of
ultrasound which is produced and collected by a two crystal transducer. With CW
Doppler high blood velocities are precisely
measured, but it cannot produce color flow
images and the beam is not able to identify
specific locations of velocities. The pulsed wave
(PW) system is often used in general and
obstetric research. It uses a transducer which
alternately sends and receipts ultrasound. PW
Doppler can be used for color flow images and
allows measurements of the depth of the flow
site. When blood flow velocities are high
Fig. 2. Aliasing.
however, no accurate measurements can be done.
The maximum velocities that can be measured
are 1.5 to 2 m/sec and these technical limitations are called “aliasing”. When aliasing
occurs, it shows on the spectral trace as a cut-off of a velocity with the placement of
the cut-off section in de opposite channel or reverse flow direction[5, 6].
To use Doppler ultrasound it is important to understand the different controls on the
panel of the machine, which play an important role in the quality of the Doppler
2
recordings. The Doppler gain, gray scale and wall filter are the controls that influence
the quality of the Doppler recordings. The scale factor and baseline position change
the appearance of the graphic display and the last group, the cursor, sample depth and
angle, are related to sample volume and are only used for PW Doppler.
There are different measurements that can be done with Doppler ultrasound. The
pulsatility index (PI) and resistance index (RI) are important indices for the evaluation
of the quality of placental blood flow exchange [7]. The PI was designed by Gosling
in 1974 and is defined as the difference of peak systolic and lowest diastolic flow
velocities, referenced to time-averaged flow velocity[8].
PI = (Vs - Vd) / Vo
The RI, also known as the Pourcelot index, is the resistance of the pulsatile blood flow
caused by the microvascular bed distal to the site of measurement. A RI of zero
corresponds to continuous flow, a resistive index of one corresponds to systolic but no
diastolic flow and a resistive index greater than one corresponds to reversed diastolic
flow [9].
RI =(Vs – Vd) / Vs
Vs = peak systolic blood flow velocity; Vd = lowest diastolic velocity; Vo = time
averaged mean velocity [8, 9].
The use of Doppler in human medicine and obstetrics
The use of Doppler ultrasound in medical diagnosis started in Japan with the work of
Shigeo Satomura at the Osaka University in 1956. He and his associates used Doppler
to detect hart wall motion using 3MHz ultrasound signals. Not long after that
Satomura used Doppler to study heart movement, pulsatility of the eyeball and flow in
peripheral vessels and in 1966 a Doppler flow meter was developed by Kato. The new
findings where especially used in the study of extracranial cerebral arteries in patients
with atherosclerosis. When the availability of continuous wave devices that where
simple to use increased, the interest for clinical application grew and more discoveries
were done [11].
In 1966, Bishop first described the early detection of fetal heart sounds and at the end
of the 1970s the use of Doppler ultrasound to provide a record of blood flow in
pregnancy was first described. Especially to define and understand the concept
placental insufficiency, which was a widely used diagnosis, Doppler and its
measurement of the blood flow and flow velocity waveforms was a useful
development in diagnostics. In 1982 B. Trudinger presented the first study of blood
flow velocity waveforms in the umbilical artery in late pregnancy and the association
of a high resistance pattern with reduced, absent or reversed diastolic flow velocities
and negative fetal outcome [10]. Many more studies concerning this subject followed.
When the placenta works insufficiently and the fetus becomes growth restricted, the
level of placental vascular dysfunction can be measured with Doppler. The
fetoplacental vascular resistance rises and especially the changes that occur in the
velocimetry of the umbilical arteries are important for fetal health [7]. Because the
3
flow velocity waveform of the umbilical artery changes with advancing gestation, the
gestation is a critical factor in interpreting Doppler velocimetry [4]. When one third or
more of the fetal villous vessels are badly perfused, the end-diastolic velocity in the
umbilical arteries decreases. When two third of the villous vascular three is damaged,
absent or reversed end-diastolic velocimetry can even occur [18]. With the exception
of the first trimester of the pregnancy, where the end-diastolic velocity is often absent
[4], these findings make the health of the fetus of serious concern and frequent
monitoring and the timing of delivery become important issues [18].
RI = (Vs - Vd↓) / Vs → RI ↑
PI = (Vs - Vd↓) / Vo → PI ↑
So when the end diastolic flow decreases, the RI and PI increase.
The use of Doppler in veterinary science
Doppler ultrasound has been used in veterinary science since the 70s and has become
a frequently used method nowadays [12]. Doppler is used for the identification and
diagnostics of a wide variety of things. In farm animals Doppler is often used in
research. In cows investigation of the blood flow of the ovary in different stages,
mammary blood flow and in fatty livers have been done. Pigs are frequently used as a
animal-model for human research of organ transplantation and research of the blood
flow of different organs. Especially in small animals veterinary Doppler is used to
diagnose and monitor pregnancy and diagnose heart diseases. In cats and dogs with a
pedigree screening of the heart for hereditary diseases is required, but Doppler is also
used for investigation of blood flow to different organs.
Arteries of interest
Umbilical artery (UA)
Fig. 3. First; Site of insonation of the
umbilical artery Doppler. Progressive
waveform patterns with advancing
severity were: Second; normal umbilical
artery waveform, Third; increased
impedance to flow, Fourth; absent enddiastolic flow, and Fifth; reversed enddiastolic flow [13]
The umbilical artery is a paired artery which supplies
deoxygenated blood from the fetus to the placenta
through the umbilical cord. It is used for Doppler
investigation because it is easy to identify and it
provides information about the fetoplacental
circulation. In combination with the findings of the
middle cerebral or common carotid artery,
information about the brain-sparing effect can also be
given [4]. The umbilical arteries are lying in the
umbilical cord and inside the fetal body they are
surrounding the urinary bladder. Each half of the fetal
body has its own artery. In humans it is possible to
locate and measure the arteries in the umbilical cord,
but due to the great length and number of umbilical
cords it is not possible to do so in pigs. Evaluating the
functionality of the placenta by monitoring the
umbilical artery can distinguish whether a fetus is
small for its gestational age (SGA) or if it is growth
4
restricted [13]. During the pregnancy the pulsatily index in the umbilical artery
reduces because the vascular resistance in the placenta decreases [3]. If the placenta is
working insufficiently, which is the case in 60% of pregnancies with fetal growth
restriction, the vascular resistance in the placenta is increased and the diastolic
component of the umbilical artery is increased [4]. Absent or reversed end-diastolic
velocities will appear. The pulsatily index will be above normal range and the
umbilical waveforms are abnormal. These changes are detectable with Doppler.
RI = (Vs ↑ - Vd) / Vs → RI ↑
PI = (Vs ↑ - Vd) / Vo → PI ↑
So when the diastolic velocity is increased, the PI and RI are increased.
Middle cerebral artery (MCA)
The middle cerebral artery arises from the internal
carotid artery and is one of the three major pared
arteries that supplies blood to the cerebrum, temporal
lobes and insular cortices. It is easy to sample and
therefore it is a often studied cerebral artery [3]. When
a fetus is growth restricted it can redistribute its blood
flow in which case the blood flow to the brain
increases detrimental to the fetal periphery (brainsparing). The increased blood flow to the brain is
caused by an increased diastolic velocity and a
decreased PI. With a low PI there is a greater
incidence of adverse perinatal outcome [4].
Fig. 4. First; Color Doppler assessment of the MCA at the level of the circle of
Willis. Second; Normal and abnormal (high diastolic velocities and decreased
pulsatility index) Third; waveforms are shown. ACA, anterior cerebral artery;
MCA, middle cerebral artery; PCA, posterior cerebral artery [13].
MCA/UA ratio
To predict adverse perinatal outcome and to diagnose growth retardation, both the
pulsatility index of the middle cerebral (MCA PI) and umbilical artery (UA PI) can be
used. Although the UA PI alone is enough to detect intrauterine growth restriction
(IUGR), the MCA PI alone is not a reliable indicator. For the best prediction of IUGR
and adverse perinatal outcome, the MCA/UA ratio is used [15].
Purpose of the study
In this research we are investigating whether it is possible to measure Doppler
velocimetry in the arteries of interest despite fetal movement. If so, what is the
outcome and where in the gestation are the best chances for success?
5
Material and methods
Sow housing and handling
The animals were housed in a group of 200 pregnant sows, had outdoor access and
large lying places with straw. A standard diet was fed twice a day and there was
unlimited roughage. The sows had free access to water. For the measurements the
sows where led to a service crate, where
they had to lay down voluntarily on their
right side. To let the sows get used to the
observers
presence,
handling,
the
manipulation of the transducer and
because the observer was inexperienced
with using ultrasound, there was a two
week training period in advance of the
measurements. In these two weeks each
sow was trained four times and the
observer got experienced with using the
ultrasound equipment in a three day training in the Wilhelmina children’s hospital.
With the use of a Doppler ultrasound scanner with a 3.75 MHz transducer and
lubrication jelly a fetus was located and observed.
Fetal movement
Fetal movement often disturbs Doppler ultrasound measurements. Decreased fetal
movement towards birth have been reported in several species, such as the rat, horse,
cow, and sheep. In pigs, researchers have also found a decrease in fetal movement
towards birth [16, 19].
Twelve 3-5th parity sows were divided into six groups with different gestation lengths
between 55-110 days. Two fetuses per sow were selected and observed for 2-5
minutes. These sessions were recorded and evaluated. The seconds that a fetus was
moving, so that an Doppler measurement was impossible to do, were counted and a
percentage was calculated.
Movement % = (Duration of movements (sec.) / Total time (sec.)) * 100%
Table 1. Sow grouping using parity and gestational age.
Group
1
2
3
4
5
6
Median parity (range)
4,5 (4-5)
3,5 (3-5)
5
5
4,5 (4-5)
5
6
Median days (range)
59,5 (59-60)
65,5 (65-66)
80
86
98,5 (98-99)
108,5 (108-109)
Measuring Doppler velocitimetry
In humans the middle cerebral and umbilical artery are easy to locate in a fetus. In
pigs however the ossification of the fetal skull makes it impossible to find the middle
cerebral artery and measure its velocimetry. Therefore the common carotid artery is,
in consultation with a experienced gynecologist, used to measure the blood flow to the
brain. In humans the umbilical artery is detectable in the umbilical cord, but in pigs
we use the artery around the fetal bladder.
The common carotid artery is a paired structure whereby the left and right artery
originates from different places. The left artery is a direct branch of the aorta while
the right artery arises from the brachiocephalic artery, which originates from the aorta.
Both common carotid arteries divides in internal and external carotid branches which
supply blood to the neck and head of the body. In human the common carotid artery is
often used for measuring pulse [14].
Five sows between 70-94 days of gestation and 3-5th parity were used for this study.
For finding and observing the same piglets in different sessions, the location and dept
of each piglet was noted and a drawing of the piglet was made. Each sow was
scanned 1-2 times a week and two piglets per sow were followed. With the help of
color flow Doppler the vessels of interest were located.
Results
The percentage of fetal movement decreases with advanced gestation. However, no
measurements could be done due to constant fetal movement.
120
Movement %
100
80
60
Fetal movement %
40
20
0
60
80
100
Days of gestation
Fig. 6. Percentage of fetal movement during gestation.
Discussion
During the study it became clear that measuring Doppler velocimetry in pig fetuses is
quite a challenge. To locate fetal vessels with color Doppler the fetus has to lay in the
right angle to the transducer, since an angle as close as possible to zero degrees gives
the best measurements. In human the pregnant abdomen is round and can be
approached from frontal, lateral and also from caudal an cranial sides while in sows
7
only the left lateral side of the abdomen can be approached. This makes it difficult to
access a vessel in the right angle for a Doppler measurement. When a fetus is found in
the right position and the vessel is located, the constant fetal movement makes it
impossible to measure the blood flow velocity. Because a fetus has to lay still and the
frame cannot be paused, it was not possible to measure any PIs in sows up to 94 days
of gestation. Closer to birth the fetuses move less, but still they move too much for
Doppler measurement. In human pregnancies, there is also an decrease in fetal
activity towards labor. The constant fetal movements change into rest-activity cycles
because the nervous system matures and since moving costs energy, the increasing
periods of rest may save nutrients and oxygen. Near term human fetuses have periods
of quiet sleep for up to 50 minutes in which no movements has been seen and in
which the heart rate is low. Although pig fetuses also have periods in which a low
heart rate is measured, periods without any movement hardly occur [19]. To use pig
fetuses as an animal model for unborn babies, several comparisons between the two
species are necessary. Since human fetuses are monitored by parameters like
biparietal diameter, abdominal circumference, femur length and Doppler blood flow
velocimetry in the UA and MCA, these growth curves have to be developed for pig
fetuses [20]. In previous research the femur length of pig fetuses up to 100 days of
ages was measured. After 100 days the pig uterus became to crowded to distinguish
different fetuses. Since measuring the pulsatility index with Doppler ultrasound is not
possible in fetuses up to 94 days, there is only a small period of time in which
Doppler velocimetry could be measured. Also, the middle cerebral artery is not
approachable due to the early ossification of the piglets skull. This means that another
artery (the common carotid artery) is measured. To determine if the pig fetus is an
accurate animal model which we can use to diagnose and treat intrauterine growth
restriction in human fetuses, more study has to be done.
8
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
Fitzgerald DE, Drumm JE. Non-invasive measurement of human fetal circulation
using ultrasound: a new method. British Medical Journal, 1977; 2; 1450-1451.
Dubiel M, Breborowicz GH, Marshal K, Gudmundsson S. Fetal adrenal and middle
cerebral artery Doppler velocimetry in high-risk pregnancy. Ultrasound Obstet
Gynecol, 2000;16;414-418.
Mari G, Hanif F. Fetal Doppler: Umbilical Artery, Middle Cerebral Artery, and
Venous system. Seminars in Perinatology, 2008; 32; 253-257.
Detti L, Mari G, Cheng CC, O R, Singh B. Fetal Doppler velocimetry. Obstetrics and
Gynecology Clinics of North America, 2004; 31; 201-214.
Nicolaides K, Rizzo G, Hecher K, Ximenes R. Doppler in Obstetrics. The Fetal
Medicine Foundation, 2002.
Kisslo JA, Adams DB. Principles of Doppler echocardiography and the Doppler
examination.
Gerber S, Hohlfeld P, Viquerat F, Tolsa JF, Vial Y. Intrauterine growth restriction
and absent or reverse end-diastolic blood flow in umbilical artery (Doppler class II or
III): A retrospective study of short- and long-term fetal morbidity and mortality.
European Journal of Obstetrics & Gynecology and Reproductive Biology, 2006, 126;
20-26.
Michel E, Zernikow B. Gosling’s Doppler Pulsatilty Index revisited. Ultrasound in
Medicine & Biology, 1998; 24; 597-599.
Bude RO, Rubin JM. Relationship between the Resistive Index and the Vascular
Compliance and Resistance. Radiology, 1999; 211; 411-417.
Trudinger B. Editorial, Doppler: more or less? Ulrasound Obstet Gynecol, 207; 29;
243-246.
Sigel B. A brief history of Doppler Ultrasound in the diagnosis of peripheral vascular
disease. Ultrasound in Obstetrics & Biology, 1998; 24; 169-176.
Blanco PG, Arias DO, Gobello C. Doppler Ultrasound in Canine Pregnancy. Journal
Ultrasound Med, 2008; 27; 1745-1750.
Figueras F, Gardosi J. Intrauterine growth restriction: new concept in antenatal
surveillance, diagnostics, and management. American Journal of Obstetrics &
Gynecology, 2011; april; 289-299.
Dyce, Sack, Wensing. Textbook of Veterinary Anatomy, third edition. Saunders.
Bano S, Chaudhary V, Pande S, Mehta VL, Sharma AK. Color Doppler evaluation of
cerebral-umbilical pulsatility ratio and its usefulness in the diagnosis of intrauterine
growth retardation and prediction of adverse perinatal outcome. Indian Journal of
Radiology and Imaging, 2010; 20(1): 20-25.
Cohen S, Mulder EJH, Oord van HA, Jonker FH, Weijden van der GC, Taverne
MAM. Ultrasound observations of fetal movement in the pig: an exploratory study.
Applied Animal Behaviour Science, 1999; 64; 153-158.
Byun YJ, Kim HS, Yang JI, Kim JH, Kim HY, Chang SJ. Umbilical Artery Doppler
Study as a Predictive Marker of Perinatal Outcome in Preterm Small for Gestational
Age Infants. Yonsei Medical Yournal, 2009; 50(1); 39-44.
Vergani P, Roncaglia N, Locatelli A, Andreotti C, Crippa I, Pezullo JC, Ghidini A.
Antenatal predictors of neonatal outcome in growth restriction with absent enddiastolic flow in the umbilical artery. American Journal of Obstetrics and
Gynecology, 2005; 193; 1213-8.
Cohen S, Mulder EJH, Oord van HA, Jonker FH, Parvizi N, Weijden GC, Taverne
MAM. Fetal movements during late gestation in the pig: A longitudinal
ultrasonographic study. Theriogenology 2010; 74; 24-30.
Varol F, Saltik A, Kaplan BP, Kilic T, Yardim T. Evaluation of Gestational Age
Based on Ultrasound Fetal Growth Measurements. Yonsei Medical Journal 2001; 42;
299-303.
9
Leerdoelen.

Inzicht krijgen in het doen van wetenschappelijk onderzoek.
Ik heb geleerd wat het doen van onderzoek in houdt. Wat mij vooral erg
aansprak is de praktische aard van dit onderzoek. Vooraf dacht ik dat het doen
van onderzoek vooral erg theoretisch is, maar juist de combinatie van beide is
erg leuk. Het doen van onderzoek heeft mij positief verrast. Hoewel ik
voorafgaand aan dit onderzoek nooit had nagedacht aan het doen van
onderzoek na mijn studie, is dit nu zeker een optie. Waar ik aan moest wennen
is dat wanneer er geen resultaten uit een onderzoek komen, dat toch een
uitkomst is waarmee verder gewerkt kan worden.

Praktische vaardigheden ontwikkelen, zowel in het omgang met varkens als in
het gebruik van echoscopische apparaten.
Voorafgaand aan het onderzoek had ik, los van was praktische lessen, niet veel
contact gehad met varkens. Ik wist dan ook niet veel wat de omgang met deze
dieren. Door de bijna dagelijkse aanwezigheid in de stal en het directe contact
met de zeugen heb ik een hoop over varkens geleerd wat in de toekomst zeker
van pas gaat komen.
Tijdens de studie wordt er weinig tijd besteed aan het gebruik van
echoscopische apparaten. Toch is deze vaardigheid voor de praktijk van groot
belang. Doordat ik voor het onderzoek veel met het maken van echo’s heb
kunnen oefenen heb ik hiermee een voorsprong gekregen.

Het schrijven van een wetenschappelijk artikel op niveau.
Omdat ik over het algemeen best wat moeite heb met het maken van
verslagen, vond ik het een enorme uitdaging om een wetenschappelijk artikel
te schrijven. Vaak heb ik de feedback gekregen dat ik te kort van stof ben en
daarom was het nu erg fijn om te merken dat dit deze keer als zeer positief
werd ervaren. Ook het schrijven in het Engels viel me heel erg mee.

Zelfstandig werkzaam zijn.
Ik ben graag werkzaam in een team, maar voor dit onderzoek ben ik vooral
zelfstandig bezig geweest. Hierdoor heb ik meer verantwoordelijk genomen
dan dat ik in een groep doe en dat beviel me goed. In een groep ben ik geneigd
me wat op de achtergrond te houden en juist omdat dat deze keer niet mogelijk
was heb ik gemerkt dat ik het ook best zelf kan. Dit geeft vertrouwen en in de
toekomst zal ik proberen ook in een groep wat leiding te nemen.
10