Three-dimensional (3D) sonography is regarded as a further development of ultrasound imaging technology and its application has greatly increased in recent years. This thesis summarizes the original research findings of the application of 3D ultrasonography for biometry measurement, morphology screening, prenatal diagnosis of abnormalities, ultrasound training and the application of 3D volumetry in the early diagnosis of homozygous α-thalassemia and birth weight prediction in term pregnancy. In a study involving 50 singleton pregnancies at 17-34 weeks' gestation, fetal biometric measurements obtained by an inexperienced operator using both two-dimensional (2D) and 3D ultrasound were reproducible and showed good agreement with those obtained by an experienced operator (all intraclass correlation coefficients were ≥ 0.991). The use of 3D ultrasound by an inexperienced operator allowed faster measurement of fetal biometric parameters than the use of 2D ultrasound, and also seemed to facilitate the acquisition of higher-quality images for the measurement of abdominal circumference. In basic central nervous system and cardiac screening examination, for the inexperienced operator, 3D/four-dimensional(4D) volume acquisition yielded a quicker but less optimal anatomic examination of the fetal central nervous system and heart structures compared to 2D. The diagnostic accuracy of 3D ultrasonography in central nervous system abnormalities was also investigated. The results illustrated that 3D agreed with 2D ultrasonography in the prenatal diagnosis of intracranial malformations. Homozygous α0-thalassemia is very common in South-east Asia and its prenatal diagnosis is essential due to increased fetal and maternal mortality and morbidity. Placental volume/CRL quotient measured by 3D volumetry was significantly higher in pregnancies with α0-thalassemia major cases, and 1.49 may be regarded as a cut-off for early prediction of α0-thalassemia major. In a cross-sectional study of 290 Hong Kong Chinese women with a singleton pregnancy at 37-42 weeks of gestation, the birth weight prediction models based on 3D thigh volume and conventional 2D biometric measurements were developed. It was found that with 3D thigh model, the precision of birth weight prediction to within 5 and 10% of actual birth weight in a Chinese population at term gestation could be achieved. Previous studies have shown that there is a difference in the learning curve of fetal biometry measurement by 2D ultrasound among trainees. Whether there is any difference in the learning curve between 2D and 3D ultrasound is unknown. The study included three trainees and each of them performed 90 scans in biometry measurements. By using cumulative sum analysis graphs, it could be shown that there was no difference in the learning curve between 2D and 3D ultrasound. In conclusion, the above studies have demonstrated that the use of 3D ultrasound has diversified and provided much additional information in selected indications. / published_or_final_version / Obstetrics and Gynaecology / Doctoral / Doctor of Philosophy

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With advances in imaging and communication systems, there is increased use of multi-dimensional images. Examples include multi-view image/video, hyperspectral image/video and dynamic volume imaging in CT/MRI/Ultrasound. These datasets consume even larger amounts of resources for transmission or storage compared to 2-D images. Hence, it is vital to have efficient compression methods for multi-dimensional images. In this dissertation, first, a JPEG2000 Part-2 compliant scheme is proposed for compressing multi-dimensional datasets for any dimension N>=3. Secondly, a novel view-compensated compression method is investigated for remote visualization of volumetric data. Experimental results indicate superior compression performance compared to state-of-the-art compression standards. Thirdly, a new scalable low complexity coder is designed that sacrifices some compression efficiency to get substantial gain in throughput. Potential use of the scalable low complexity coder is illustrated for two applications: Airborne video transmission and remote volume visualization.

Simulation modelling was used to quantify the accuracy of positions estimated in a three dimensional underwater environment. Time of arrival differences combined with multilateration methods were used to make positional estimates of a signal source (acoustic tag). The network studied was used to examine position estimates of aquatic organisms within a sensor (hydrophone) array. Hydrophone position uncertainty (distribution and variance), background noise converted to a measurement of signal strength in the form of a signal to noise ratio, a signal to noise ratio threshold and geometry of the hydrophone array were considered. Each of these factors was studied at two levels by way of a 2 to the power of 5 factorial design and analyzed with an ANOVA analysis to determine their influence on three dimensional positioning error. The level of background noise and hydrophone geometry were the two most influential factors in position accuracy. When a high level of background noise was present, it was essential that hydrophone geometry was as close to ideal as possible to ensure accurate position estimates.

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