Spatio-Temporal Image Correlation; the Key to fetal EchocaRdiography
Part I Examination of the cardiac anatomy of the normal fetus.

The cardiovascular system is one of the first systems to develop in the human
fetus. The fetal cardiovascular system plays an important role during
intrauterine life and undergoes major anatomical and functional transition
following delivery. Congenital heart defects (CHD) are the most common
congenital anatomic malformations, affecting approximately 0,6-5% of live born
children. In neonates with congenital malformations, CHD cause 20% of neonatal
deaths and up to 50% of infant mortality and morbidity in the first year of
life. Therefore the fetal heart is the subject of major screening programs
aiming to detect cardiac defects in an early stage of pregnancy. Prenatal
diagnosis of congenital heart disease is associated with improvement in
neonatal morbidity and mortality.
The accuracy of prenatal diagnosis of CHD ranges from 31 to 96%. The difference
in detection rate is mainly explained by different levels of training of
ultrasonographers. In individual cases, scanning conditions like maternal
adipositas , oligohydramnion or an unfavourable fetal position can play a role.
Other problems are that the interpretation must be done in real time, so the
whole procedure might be rather time-consuming. An accurate and reproducible
method to investigate cardiac anatomy/morphology could be very valuable for the
obstetrician who has to make decisions about a fetus with a suspected cardiac
anomaly.

Spatio-temporal image correlation (STIC) is the latest ultrasonographic
approach to clinical assessment of the fetal heart. STIC is an automated volume
acquisition, recording one single 3D volume dataset. STIC technology allows
visualisation of cardiac structures as a 4D cine sequence, containing
information of one full cardiac cycle. STIC has the potential to increase the
accuracy of the examination, because the investigator can rotate and reslice
all cardiac planes within the 3D volume. By using STIC technology with
post-processing rendering capabilities, an unlimited number of *virtual planes*
of the fetal heart can be obtained. Another advantage of STIC is shortening of
the examination time, because the recording of a STIC volume takes only 12,5
seconds. Finally STIC offers the possibility of navigating through the volume
dataset off-line so that the fetal heart can be examined in absence of the
patient.

We will investigate the feasibility of using STIC technology to evaluate the
normal fetal cardiac anatomy and morphology in different stages of gestation.
Further we aim at making normograms of different intracardiac parameters in
relation to gestational age and estimated fetal weight.

In this prospective longitudinal study STIC volume datasets will sequentially
be collected every four weeks from healthy fetuses with gestational age ranging
from 12 to 36 weeks. At first, a conventional 2D echocardiography will be made
using a check list. After the 2D echocardiographic analysis, a STIC acquisition
will be made and systematically examined using the same check list. To evaluate
the ability of both methods in assessing the normal fetal cardiac anatomy and
morphological identification hallmarks at different stages of pregnancy, scores
from conventional 2D fetal echocardiography will be compared to scores from
STIC. Furthermore, normograms for the area of the aortic and pulmonary valve,
mitral and tricuspid valve and the foramen ovale will be created and related to
estimated fetal weight and gestational age.

Spatio-Temporal Image Correlation (STIC)

Ultrasound has been used in obstetrics since the 1970's. There are no proven
adverse effects of ultrasound investigations on foetus or mother.