Ultrasound

Recent advances in prenatal diagnosis and therapy has been made possible with the invention of newer imaging modalities including 3D and 4D ultrasound. Two dimensional ultrasound remains the method by which most fetal structural abnormalities are screened and diagnosed, however 3D and 4D are being used increasingly for the examination of the human fetus. Two dimensional scanning allows visualisation of static images while 3D and 4D imaging adds a further dimension to fetal study by allowing interaction with volume data sets to examine anatomic structures of interest in planes of section.

The examination of fetal face by 3D ultrasound has generated a great deal of intereest by both the medical fraternity and prospective parents. The "photographic-like" images are easily recognized by both the layperson and expert alike. Facial expressions such as mouth-opening, tongue protursion and yawning may be studied in detail using 4D ultrasound. This has lead several  investigators to hypothesise that the adjuctive use of 3D/4D ultrasound would improve the diagnostic accuracy of 2D ultrasound. The advantage of 3D ultrasound was an improvement  in the diagnostic accuracy to detect clefts of the palate and decrease in the number of false positive diagnoses.

The benefits of 3D ultrasound in fetal  central nervous system include:

• The ability to determine the severity, location and extent of central nervous system abnormalities
• The possibility of reconstructing and visualising the corpus callosum in the sagital plane from volume data sets
• The ability to visualise  the  3 horns of the ventricular system in a single plane

The ability to visualise the level of defect in cases of spina bifida using 3D imaging is important in counselling regarding prognosis and treatment.
Conditions such as diapraghmatic hernia, skeletal dysplasias and preterm premature rupture of membranes are associated with risk of pulmonary hypoplasia. Prognosis is dependent on the residual size of the affected lung.
The fetal heart should be examined in motion but with standard 3D the spatio and temporal resolution of the image is limited. It is further complicated by motion artefacts.