Advanced Topics on Three-dimensional Ultrasound in Obstetrics and Gynaecology

It is important to know how three-dimensional ultrasound (3DUS) works and its functions for making the best use of 3DUS. 3DUS shows various kinds of images through following processes: 1. Acquisition of 3D data (3D scanning) - A large number of consecutive tomographic (2D) images are obtained through 3D scanning with a 3D probe; 2. Construction of a 3D data set - A 3D data set is constructed from the acquired 2D images. A gated technique called STIC (spatiotemporal image correlation) is used for construction of 3D data sets of the fetal heart; 3. Volume visualization - A computer constructs 2D and 3D images from the 3D data set. 3DUS shows multiplanar images, such as a multi-parallel-plane image and a three-orthogonal-plane image. Each plane can be selected arbitrarily by translation and rotation of the 3D data set. Most of 3D images are constructed by volume rendering. Proper settings of ROI (region of interest) and threshold are important for obtaining a clear surface rendered image. Electrical scalpel (or “MagiCut”) is used to eliminate unfavorable structures around the object. Various kinds of 3D images as well as a surface rendered image can be obtained by volume rendering. Surface rendering is also used for 3D image construction. Boundaries of the object should be outlined strictly and it takes a lot of time to get a 3D image in surface rendering. But once the object is extracted, the volume of the object can be calculated.

Three-dimensional ultrasonography been increasingly used by health care professionals as it provides some improvements, particularly regarding acquisition, training, and display modes. Considering the latter, tridimensional cine (3D cine) improves better depth perception; teal time three-dimensional ultrasound (4D) provides three-dimensional movement view at real time; tomography ultrasound image (TUI) permits displaying several parallel planes in only one image; volume contrasting imaging (VCI) improves image contrast and decreases artifacts between tissues; Omniview rectifies curvilinear structures to be viewed at the same plane; Sonographybased Volume Computer Aided Display (SonoVCAD) minimizes operator dependence by standardization of image acquisition; and spatio-temporal image correlation (STIC) allows 3D acquisition of moving structures through a post processing volume set. In this chapter we will briefly summarize all these imaging modalities.

One of the first applications of three-dimensional ultrasonography (3DUS) in gynaecology and obstetrics was for measuring volume. Previously, volume was measured by two-dimensional ultrasonography (2DUS) assuming that the scanned object was a regular structure like an ellipsoid. With the advent of 3DUS at the beginning of the 1990s, volumetric measurement became more reliable because 3DUS permitted the outer surface of the structure to be assessed, unlike 2DUS, which used mathematical formulas. The first technique available was the multiplanar method or planimetry, which consisted of volume assessment using the three orthogonal planes (x, y, and z). Later came virtual organ computer-aided analysis (VOCAL), a method that assesses volume by rotating the object in question around an axis. More recently, two new techniques have been introduced: extended imaging virtual organ computer-aided analysis (XI VOCAL) and sonography-based automated volume count (SonoAVC). The former consists of defining pre-established areas on the device screen, while the latter measures the volume of liquid structures. In this chapter, we shall discuss the main techniques of volumetric assessment using 3DUS in gynaecology and obstetrics.

Three-dimensional (3D) ultrasonography has been found to be a clinically useful adjunct to two-dimensional (2D) ultrasonography in assessing a variety of fetal anomalies of certain organ systems. 3D/four-dimensional (4D) ultrasonography has great potential for application in telemedicine. Although currently in its early stages, when fully developed it should permit the acquisition of a volume of imaging data by an unskilled operator for image processing and skilled interpretation at a remote site. This chapter will explore the applications of 3D/4D ultrasonography in telemedicine. The equipment and technologies applied and current barriers to implementation are subsequently discussed.

The aim of this review was to determine whether three-dimensional (3D) and four-dimensional (4D) ultrasonography adds diagnostic information to what is currently provided by two-dimensional (2D) ultrasound (US) in the diagnosis of the most common congenital structural defects, namely congenital heart disease. Recent studies suggested that 3D/4D US allows to decrease operator dependency in the visualization of standard diagnostic planes, thus reducing the examination time required for the ultrasound screening examination, with minimal consequences on the imaging quality of the anatomical structures. Furthermore, sonographers with lack of experience may acquire cardiac volumes that can be successfully reviewed offline locally or sent by internet to referral centers for remote review by an observer with more experience. As a consequence 3D/4D US promises to become the method of choice for the diagnosis of congenital structural defects.

Although two-dimensional (2D) ultrasound represents the standard approach to the study of the brain anatomy in the fetus, the technical advancement offered by three-dimensional (3D) ultrasound, as well as the increased equipment availability and operator skill, is such that integrating 2D with 3D ultrasound may be considered the “gold standard” of care in the current diagnostic investigation of central nervous system anatomy. 3D ultrasound of the fetal brain or neuroscan may be performed using the standard multiplanar mode or 3D software techniques such as tomographic ultrasound imaging, Omniview or other commercially available reconstructing technique. 3D neuroscan offers the advantage to insonate planes that are usually difficult to image using 2D ultrasound, even when a transvaginal approach is considered. In addition, volume of the cerebral structures can be calculated using virtual organ computer-aided analysis (VOCAL) methodology. Notwithstanding, 3D volumes may be filed and reconstructed accurately by offline “navigation”. Moreover, volume can be sent at remote site for expert consultation using telemedicine or submitted using low cost streaming Internet channel for real-time counseling at tertiary center with expertise in 3D/four-dimensional (4D) ultrasound. The digital technology of 3D/4D ultrasound may be used in teaching and training setting as volume can freely be sectioned on demand on three orthogonal planes. Finally, 3D volume data sets can be incorporated with fetal magnetic resonance imaging (MRI) 3D data and converted to create physical models of the congenital anomalies, thus enhancing parents understanding of the pathologic conditions and aiding both the prenatal counseling and the perinatal management.

Three-dimensional (3D) ultrasound provides a major diagnostic tool in the examination of fetal face abnormalities. 3D ultrasound enables spatial orientation, which is crucial for the evaluation of fetuses with facial malformations, especially ones with cleft palate. This chapter summarizes the different modalities currently undertaken to examine fetal face with special emphasis on the palate, ears and eyes, providing practical tools for manipulation of volumes.

The assessment of fetal limb volume as a marker of nutritional status began in the mid 1980’s using the two-dimensional ultrasound. However, with the advent of three-dimensional ultrasound in the beginning of 1990s’ research into using the fetal thigh and upper-arm volumes for predicting birth weight began. These studies suggested that fetal limb volumes were more accurate than two-dimensional biometric parameters in the prediction actual weight after delivery. Multiplanar or planimetric method was first used to assess the whole fetal limb volume, including the volume around of epiphysis, followed by use of the 3D extended imaging VOCAL technique. Reference ranges for total fetal limb volume were established for specific populations. By the end of 1990’s a new concept, the fractional limb volume, was introduced. This measurement was limited to the volume of central region of fetal limb and assesses the region with the great amount of soft tissue. It has been studied as a marker of intrauterine status nutrition and used to detect early fetal growth disturbances. Continued research has established the importance of fractional limb volume in predicting birth weight and its usefulness in the evaluation of intrauterine development in the second half of pregnancy.

The present chapter reviews the main technical aspects, indications and results of clinical use of three-dimensional ultrasonographic lung volumes. There are two methods to measure fetal lung volumes using three-dimensional ultrasonography: the technique of parallel slices and the rotational technique. Nowadays, the rotational technique is the method of choice because of reproducibility and less time consuming. Clinical indications for assessing fetal lung volumes are congenital anomalies or situations where there is an increased risk for severe pulmonary hypoplasia. Fetal lung volume is useful tool to diagnose pulmonary hypoplasia, but more important to predict the severity of this complication. Clinical situations that may benefit from fetal lung volume assessment are: congenital diaphragmatic hernia, fetal hyperechogenic lung lesions, omphalocele, premature rupture of the membranes and prolonged oligohydramnios (fetal renal/urological problems).

Three-dimensional (3D) sonoembryology allows the analysis of embryonic surface structures (rendering mode), with enhanced detail, and offers the possibility of performing a volumetric study of the gestational sac, embryo, yolk sac, amniotic fluid and placenta during the first trimester of pregnancy. Furthermore, the identification of abnormalities in these structures can also predict early pregnancy failure and determine new predictors of pregnancy outcome. Therefore, the main aspects of sonoembryology and the structure volumes observed during the first trimester of pregnancy using 3DUS were being decrypted in this chapter.

The study of fetal neurological function in order to better predict in utero which fetuses are at risk of adverse neurological function after delivery and even later in life, has remained on of the most difficult and unanswered dilemmas in perinatal medicine. It has been proven that fetal behavioral patterns are directly related with the level of fetal brain maturation. Studies have shown that fetuses have specific behavioral patents during certain periods of gestation that correspond to the expected level of brain development. Knowing these patents having standarised the method of assessment of fetal neurobehavior can make possible the distinction between normal and abnormal in utero brain development. This was made possible firstly due to the evolution of ultrasound technology and mainly four-dimensional (4D) ultrasonography, which made possible the detailed depiction of fetal movements, and details that could not be viewed with 2D ultrasound such as facial expressions, mouth opening and grimacing, finger movements etc. A new scoring system for the assessment of fetal neurobehavior based on prenatal assessment of the fetus with 4D sonography has been developed based on the same technique that neonatologists assess newborns during the first days of their postnatal life. This overview aims to offer an insight on fetal behavior and assessment of fetal neurology with the assistance of four-dimensional ultrasound.

Three-dimensional (3D) power Doppler ultrasound facilitates the evaluation of fetal cardiac blood flow and peripheral vascular trees, fetal organ blood flow, placental vasculature and blood flow, and maturation of the uterine cervix. With the recent advances in 3D power Doppler ultrasound as well as quantitative 3D power Doppler histogram analysis, quantitative and qualitative assessments of the vascularization and blood flow of fetal organs, the placenta, and uterine cervix have become feasible. This technique may assist in evaluation of the fetal cardiovascular system and feto-placental function, and offer potential advantages relative to conventional two-dimensional power Doppler ultrasound assessments. In this chapter, we discuss the present and future applicability of 3D power Doppler ultrasound in obstetrics. 3D power Doppler ultrasound may become an important modality in future research on fetal and placental blood flow, and assist in prenatal diagnosis of the fetal and placental vascular abnormalities.

Since the introduction of three-dimensional ultrasonography (3DUS) in clinical practice, much has been published about the capabilities of this technology to evaluate the fetal anatomy in multiple planes, obtain rendered images of the fetal face, exquisite images of the fetal skeletal system and, more recently, volumetric images of the fetal heart, using spatiotemporal image correlation (STIC) technology. While 3DUS helps in the diagnosis of certain anomalies, such as facial clefts, skeletal dysplasias and spinal abnormalities, besides being an invaluable tool in a telemedicine setting, there are still limitations, inherent to ultrasonography, such as susceptibility to motion artifacts and shadowing. In this chapter, we review the diagnostic capabilities of 3DUS for the diagnosis of a variety of fetal anomalies as well as its limitations.

Caesarean sections in the second stage of labour are on the rise globally and a significant proportion is due to the inadequacy of clinical assessment of the relationship between the fetal head and the maternal pelvis structures and the influence this has on the selection of the mode of delivery. Ultrasound technology has rapidly advanced over the last 40 years, so much so that the application of the three-dimensional (3D) ultrasound can now be considered in the management of the second stage of labour. Extensive work has been done to establish criteria for the assessment of the fetal head descent and the relationship it has to the maternal pelvic structures in the second stage. The development of intrapartum translabial ultrasound (ITU) measurements such as the "angle of progression" measurement has been proven to help in the selection of patients who will benefit from a trial of spontaneous delivery or operative instrumental delivery while on the other hand identifying those patients who may benefit from a caesarean section when the measurements are not favourable. It is in this regard, where the clinical application of the ITU is playing an emerging role in influencing the clinical outcomes of patients in the second stage of labour. Further to this, the use of new advanced computer software using multiplanar mode acquisition techniques can generate 3D images and volume measurements from two-dimensional parameters to assess the progress in labour and the second stage of delivery. There are several benefits to this. Firstly, an objective assessment of the fetal head relationships can be documented, detailing not only descent but also flexion, rotation and aspects asynclytism which are all important, especially, where an operative delivery is being considered. Secondly, the risk of ascending intrapartal infection may be reduced as internal examinations are less frequent. Finally, the ITU is not as invasive a procedure as an internal examination.

Advances in image-scanning technology have led to vast improvements in fetal evaluation. Ultrasound is the primary method of fetal assessment because it is patient-friendly, useful, cost effective, and considered to be safe. Three-dimensional (3D) ultrasound can be used as an important tool for diagnostic and prognostic evaluation. Magnetic resonance imaging (MRI) is generally used when ultrasound cannot provide sufficiently high-quality images. It offers high-resolution fetal images with excellent contrast that allow the visualization of internal tissues. 3D MRI can be an important tool in the reconstruction of virtual and physical fetal models.

Müllerian anomalies are congenital defects of the female reproductive tract resulting from failure in the development of the Müllerian ducts and their associated structures. Uterine anomalies are uncommon and are discovered during the investigation of infertility or premature delivery. The most common müllerian anomaly is the septate uterus. Identification of the septate uterus depends on the identification of a flat, rounded, or minimally (<1 cm) concave uterine fundus. Hysterosalpingography identifies two uterine cavities but is inaccurate for diagnosis of septate versus bicornuate uterus. Hematocolpos is often caused by an obstructing vaginal septum, usually in association with uterus didelphys. Three-dimensional ultrasound and magnetic resonance imaging (MRI) are both highly accurate tests for the diagnosis of a Müllerian anomaly. MRI is the preferred test because the large field of view demonstrates renal anomalies.

Innovations in contraceptive methods have emerged in large numbers in recent decades. Intrauterine devices are a commonly used form of contraception worldwide. Another contraceptive method recently developed is Essure, which is a permanent sterilization intratubal device that can be introduced by hysteroscopy. When it comes to intrauterine devices, the ultrasound is the gold standard method to identify problems related to their position; additionally ultrasound can be reliably used to assess the position of intratubal devices, although the gold standard is still the hysterosalpingography. In this chapter we will report the main applications described for ultrasound when evaluating these devices and summarize the evidences comparing the diagnostic accuracy of two-dimensional and three-dimensional ultrasound.

Though computed tomography (CT) and magnetic resonance imaging (MRI) have been reaping the benefits of three-dimensional reconstruction for many years, threedimensional sonography is a relatively recent advancement and valuable tool for gynecologic imaging. The most useful clinical three-dimensional applications in the pelvis have evolved from the ability to reconstruct and obtain the coronal plane of the uterus. Ambiguity that arises in the evaluation of masses and adhesions associated with the endometrial cavity and adjacent myometrium may be resolved using this technique. The coronal plane is most beneficial for examination of fibroids, polyps, and adhesions. Retrospective volume manipulation with or without sonohysterography creates reconstructions that aid in precise localization, measurement, and characterization of such abnormalities. The approach for therapeutic intervention can be reliably guided by threedimensional sonography, thus promoting greater patient comfort, safety, and preservation of fertility.

Endometrial cancer is the most common gynecological malignancy in developed countries. On the other hand, endometrial polyps constitute the most common endometrial pathology both in pre- and postmenopausal women. Ultrasound has been extensively used for evaluating women with suspected or already known endometrial cancer and for diagnosing endometrial polyps. Three-dimensional ultrasound (3DUS) was introduced into clinical practice 15 years ago. This technology allows unique ways for assessing the uterus and the endometrium, such as uterine and endometrial volume, calculation virtual navigation, multiplanar display, tomographic ultrasound imaging (TUI) and volume contrast imaging (VCI), as well as for assessing endometrial vascularization, namely 3D power Doppler vascular assessment using 3D vascular network reconstruction and the so-called 3D derived vascular indices. Additionally, three-dimensional sonohysterography has been proposed to be used for a better assessment of the uterine cavity. Some studies have evaluated the role of 3DUS for assessing endometrial cancer, either as a diagnostic method in women with postmenopausal bleeding or for assessing myometrial infiltration. In this chapter we shall review current evidence and data about the use of 3DUS for diagnosing endometrial cancer and polyps, its use for assessing myometrial infiltration and also the correlation of 3DUS parameters with tumor characteristics.

Cyclical, hormone-driven molecular and morphological changes within the endometrium lead to a state of endometrial receptivity, when the embryo entering the uterine cavity is most likely to result in a successful pregnancy. Endometrial receptivity can be assessed directly by sampling the tissue, or indirectly by ultrasound. Direct sampling prior to embryo replacement in an in vitro fertilization cycle may decrease the chances of pregnancy; so indirect assessment is the only way to ascertain the optimum timing for embryo replacement. In a natural menstrual cycle, the endometrial thickness and volume increase, and the echo pattern changes form iso-echoic to hyperechoic in the luteal phase of the cycle. Endometrium in the assisted reproductive treatment cycles undergoes similar changes. Based on the currently available evidence, no single sonographic marker of endometrial receptivity exists. A combination of endometrial thickness in excess of 6 mm with a triple pattern appearance, an endometrial volume of over 2cm3, with present Doppler signal within the endo and sub-endometrium seem to be the most promising sonographic markers of endometrial receptivity. As the sonographic equipment continues to advance allowing for more detailed assessment of the endometrium, continuous search for sonographic endometrial receptivity markers is warranted.

Transvaginal Ultrasound (TVUS) is widely used to assess the number and the size of the follicles in clinical practice, particularly for women undergoing assisted reproductive techniques (ART). The antral follicle count (AFC) is defined by the number of follicles considering both ovaries by TVUS and it is mainly used to assess woman´s functional ovarian reserve, which is useful to predict the ovarian responsiveness to controlled ovarian stimulation (COS) with gonadotropins. During COS, monitoring of follicle growth helps on: cancelation of cycles, appropriate time to trigger final follicular maturation and assessment of the risk of OHSS (ovarian hyperstimulation syndrome). Traditionally, follicle counting and measuring are performed by two-dimensional TVUS, but the use of three-dimensional TVUS allows faster acquisition time and standardized evaluation; additionally it provides additional features as the multiplanar view, volume contract imaging (VCI) and Sono-Automatic Volume Calculation (SonoAVC), which might help improving the reliability of follicle count and measurement.

The emergence of new ultrasound machines and hence the possibility of a more detailed view from the female reproductive system, has incorporated some changes in the gynecologist routine and in some previously defined concepts for diagnostics. The hyperandrogenic anovulation, also called polycystic ovary syndrome (PCOS), is frequently associated with a large follicle number per ovary (FNPO); which is being used as a diagnostic criterion for more than one decade. In this chapter we will review the need for updating the cut-off value when using FNPO to diagnose hyper androgenic anovulation and the current knowledge about the use of three-dimensional ultrasound (3DUS) machines when assessing ovarian volume, ovarian follicle count and ovarian blood flow.

Adnexal masses constitute a common clinical practice. Accurate diagnosis is essential for optimal management. Ultrasound is considered as first-line imaging technique for differential diagnosis between benign and malignant adnexal tumors. However, limitations still exist. New technologies may provide additional information. Three-dimensional ultrasound is a relatively new technique that is being increasingly used in gynecological sonography. In this chapter current knowledge about using threedimensional ultrasound for discriminating benign from malignant adnexal tumors will be reviewed and discussed.

The pelvic floor is a fundamental structure not only for the support of abdominopelvic structures during elevation of intra-abdominal pressure, but also for urinary and fecal continence, micturition, evacuation, and childbirth, among others. Several methods have been described in the literature for the assessment of the pelvic floor, but most of them only provide indirect, and therefore limited, information. Over the last few years, strategies for the analsis of pelvic floor morphology have been proposed, such as ultrasound scanning, computed tomography and magnetic resonance imaging. This chapter will deal in particular with mechanical three-dimensional ultrasound, with eventual brief reference to the other modalities or their comparison. The benefits inherent to the technique and the possibility of dynamic assessment cause this method to be a promising innovation for pelvic floor assessment.