Biomedical Engineering Reference
In-Depth Information
for screening for chromosomal abnormalities more accurately than 2D ultra-
sound. A 3D image can make complicated fetal abnormalities clear and can
demonstrate all fetuses in multiple pregnancy.
Second and Third Trimesters
Morphological abnormalities of a fetus, and their severity, especially on the
face, ears, extremities and skeleton, can be depicted clearly on 3D images
by transabdominal 3D ultrasound [19,20]. A 3D fetal surface image assures
worrying parents that their fetus is normal, and may aid the parents-fetus
bonding [21]. Three orthogonal sectional displays are useful for analyzing a
complicated structure step by step.
2.2.4
The Advantages and Limitations
of Three-Dimensional Ultrasound
Advantages
It is often dicult to imagine the 3D structure of a fetus from 2D images,
even for an expert on ultrasonography. Three-dimensional fetal images can
make the 3D structure clear and are useful for an accurate diagnosis of fe-
tal abnormalities which may be overlooked by conventional 2D ultrasound.
An appropriate section cannot be always obtained by conventional 2D ul-
trasound, because of the limitation of probe manipulation, especially in the
transvaginal approach. In 3D ultrasound, any desirable section for diagno-
sis or biometry can be obtained by section reconstruction. This results in
accurate diagnosis and shortens examination time.
Reexamination is possible without the presence of the patient by using the
3D data set. This means that reexamination or tele-examination by an expert
is possible by just sending the 3D data set via the Internet, for example.
Volume measurement is another prominent function of 3D ultrasound.
The difference between estimated fetal body weight by 2D ultrasound and
actual weight is sometimes not negligible in critical cases, such as a fetus
with a severe intrauterine growth restriction or a fetus in preterm labor.
Volume measurement by 3D ultrasound is expected to provide more accurate
fetal body weight estimation. Volume measurement by 3D ultrasound is also
applicable to fetal organs such as the lungs and liver.
Limitations
It takes some time to scan a 3D space. A 3D ultrasound scanner generates a
3D image on the assumption that the object (the fetus) does not move during
the scan. When the fetus moves during the scan, motion artifacts will appear
on a 3D image. Even maternal aortic pulsation sometimes causes pulsatile
movements in the uterus and motion artifacts on a 3D fetal image. Although
the fetal heart is an important organ for prenatal diagnosis, it is not a suitable
object for 3D ultrasound because of its beating motion.
