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3D & 4D ultrasound comparatives
Several studies have compared 3D to 2D ultrasonography for the diagnosis of congenital anomalies, yielding conflicting results.
While some have reported that 3D ultrasonography would be advantageous for the diagnosis of congenital anomalies, others have suggested that this method does not provide significant additional information over what is provided by 2D ultrasonography.
In this study, we deliberately inverted the order that 3D/4D examinations are normally performed in clinical practice to ask the question of whether the examination of volume datasets alone could provide reliable diagnostic information when compared to 2D ultrasonography or neonatal outcome. A single examiner, who was blinded to study indications, performed all studies. In 90% of the cases, there was complete agreement between the findings of 3D/4D and 2D ultrasonography.
When diagnoses established by 3D/4D and 2D ultrasonography were compared to postnatal diagnoses, there was no statistical difference in the detection rates of the two diagnostic modalities, despite the potential bias of this study favoring 2D ultrasonography. A hemivertebra and a small occipital encephalocele were missed, in the same fetus, by both 3D/4D and 2D ultrasonography. Two-dimensional ultrasonography, in contrast, correctly diagnosed a horseshoe kidney and a VSD, which were detected after delivery. Most false-positive diagnoses, either by 3D/4D or 2D ultrasonography, were VSDs not identified after birth. However, between 32.7% and 46.1% of VSDs diagnosed during the prenatal period underwent spontaneous closure in utero.33,34
Knowledge of whether or not the examination of 3D volume datasets can provide accurate diagnostic information is important if this technology is to be used as the primary modality to establish a diagnosis.
Regarding the potential application of 3D/4D ultrasonography in telemedicine, we investigated the possibility of performing virtual 3D ultrasound examinations at remote clinical sites. One hundred patients underwent 2D and 3D ultrasonography at the University of California in San Diego and the volume datasets were sent over computer networks or magnetic media for review at Thomas Jefferson University in Philadelphia, PA. Differences between measurements obtained by 2D and 3D ultrasound methods were, in general, less than 5% for individual measurements. 3D performed better than 2D for the visualization of first trimester fetal structures and organs (e.g., stomach, kidneys, cord insertion, lateral ventricles, and extremities) and the visualization rate was equivalent during the second trimester.
We conclude that the evaluation of fetal anatomy and diagnosis of congenital anomalies is possible by the examination of 3D/4D volume datasets alone. Discordance between 3D/4D and 2D diagnoses generally occurred for volume datasets of poor diagnostic quality and, in two cases, anomalies that were initially overlooked by the examiner could be retrospectively identified by review of the volume datasets. The design employed in this study could be used to validate sonographic tomography in diagnostic units considering a more extensive application of this technology in clinical practice.
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