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4D Ultrasound-A Delightful Experience for Moms-to-be
4D takes 3D US images and adds the element of time to the
process.
Natasha Nanda
For over 35 years, radiologists and obstetricians
have used 2D ultrasound (US) technology to evaluate the unborn fetus.
There is no time more precious and cherished than the time the mother-to-be
gets to spend looking at her baby through the miracle of ultrasound.
Today, an ultrasound examination seems incomplete without a 3D,
more popularly known as 4D US (the fourth dimension being time).
In brief, 2D US works by directing ultrasonic sound waves down to
the area being scanned. These waves are reflected back and recorded,
providing the viewer with a 2D, black and white picture of the fetus.
3D US works in a similar fashion except that the ultrasound waves
are directed from multiple angles. The waves are reflected back
and captured, and together provide enough information to construct
a 3-D image in much the same way as 3D movies. It's like watching
a video rather than a still photograph. 4D takes 3D US images and
adds the element of time to the process. This allows you to see
your unborn baby in amazing real time detail.
This technology is becoming increasingly popular and easily available across
hospitals as well as high-end diagnostic centres.
The Working
The first time one sees her baby's face and her heartbeat, is a breathtaking
moment! The new vivid state-of-the-art 4D technology can transform these images
and bring them to life! With 4D scanning, the foetus can now be seen to yawn,
grimace, swallow, open its eyes and perform intricate hand and finger movements.
These activities can be seen through mid and late pregnancy. You can determine
the age and weight of the baby, whether single or multiple. Volumetric images
can be constructed in real time to reveal the smallest details with stunning
clarity and apply sophisticated analytical tools to answer virtually any clinical
questions.
The greatest advantage is in viewing structural abnormalities, such as evaluation
of upper lip for cleft lip and palate, limb deformities like club feet or other
skeletal dysplasias and fetal spine for neural tube defects. The optimal time
for a 'prenatal peek' with 4D US depends on how one would like to see the baby.
Before 24 weeks, babies are small with more skeletal appearance, but one is
able to see more of the baby at once. From 28-36 weeks, babies are developing
the fat layer that fills in their features so one will see more facial detail
at this time. Factors that control optimal images are the baby's position, size
and movement, maternal tissue and amount of amniotic fluid. Several manuscripts
have reported on techniques to examine the fetal heart using this technology.
Outflow tracts can be systematically examined with the use of multi-planar display
techniques. There is better correlation between valves, chambers and vessels
as well as volume calculation of heart cavities.
Vital Role
An important role of 4D US relates to the ability to store volume data that
can be manipulated long after the patient has left the examination room. The
acquisition of sonographic volumes allows for storage of information that can
be reconstructed in any plane or orientation for interpretation. This obviates
the need to take multiple images in different planes. Furthermore, volume scanning
may permit standardisation of image display planes in a way similar to other
types of cross-sectional imaging modalities, such as CT and MRI. Refinements
in 4D US technology, such as improved multi-planar resolution have made this
approach to invasive procedures desirable. Real-time 4D needle guidance technique
has been successfully used to perform invasive obstetric procedures, such as
amniocentesis, cordocentesis, and intrauterine transfusion. The ability to view
the needle tip in two planes simultaneously and in real time provides a sense
of security and accuracy during the procedures.
Traditionally, 3D/4D US has been used as an adjunctive imaging modality to 2D
US. Thus, the current paradigm consists of performing 4D US as part of a target
scan after an initial diagnostic impression has been established by 2D US. 4D
US examinations have a positive impact on both mothers and fathers, and strengthens
the bonding toward the fetus and result in an increase in positive feelings
toward the fetus, leading to changes in behaviour and lifestyle that promote
maternal and fetal health.
The Downside
The downside is the ease of sex determination,
which in our country spells doom, considering statistical increase
in female foeticide. That perhaps is the only 'relative' disadvantage
of this technology, in our milieu. In the West, sex is easily disclosed
with no legal ramifications. Under pressure from women's rights
activists and human rights groups, the Central Government brought
forward the Pre-Natal Diagnostic Techniques (Regulation and Prevention
of Misuse) Act in 1994. The Act, which required ratification by
individual state, bans the use of pre-natal diagnostic techniques
for sex determination purposes and provides for a three-year imprisonment
and a fine of Rs 10,000 for offenders. The law makes it illegal
for the procedure to be used for sex determination purposes.
The writer is Consultant Radiologist Dr LH Hiranandani
Hospital Mumbai E-mail: natasha.nanda@hiranandanihospital.org
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