3D Ultrasound in Gynecology and Reproductive Medicine

Abstract

With advances occurring in medicine on a daily basis, it was only a matter of time before essential gynecological investigations, such as ultrasound, were modified. Many clinicians remain unconvinced by its reputed advantages and 3D ultrasound is not without disadvantages. These mainly relate to the cost implications and training requirements. 3D ultrasound imaging is still at a relatively early stage in terms of its role as a day-to-day imaging modality in gynecology and reproductive medicine. 3D imaging has several obvious benefits that relate to an improved spatial orientation and the demonstration of multiplanar views, of which the coronal plane is particularly useful. It offers a more objective and reproducible measurement of volume and vascularity of the region of interest, and an improved assessment of normal and pathological pelvic organs through further postprocessing modalities, including tomographic ultrasound imaging and various rendering modalities. It also has the benefit of offering reduced scanning time, the option of teleconsultation and storage of images for re-evaluation. However, other than its application in the assessment and differentiation of uterine anomalies, there is very little evidence demonstrating that 3D ultrasound results in a clinically relevant benefit or negates the need for further investigation. Future work should ensure that 3D ultrasound is compared with conventional imaging in randomized trials where the observer is blind to the outcome, only after which will we truly be able to evaluate its role in an evidence-based manner.

With advances occurring in medicine on a daily basis, it was only a matter of time before essential gynecological investigations, such as ultrasound, were modified. 2D ultrasound has been one of the key modes of investigation for years, but recent developments have seen the introduction of 3D ultrasound. This review focuses on the current role of 3D imaging in the field of gynecology and reproductive medicine, and outlines how our practice may change in the future as a result. However, very few studies have truly compared conventional ultrasound with 3D ultrasound and the following article appraises the current evidence, which is often derived from observational studies.

What is 3D ultrasound?

Conventional (2D) ultrasound is the most widely available modality at present. 2D ultrasound essentially provides us with 2D images of 3D structures, which appear as real-time cross-sectional slices through the organ/structures being examined. The views can, at times, be restricted owing to limited scan planes. By contrast, 3D ultrasound techniques rely upon the production of a composite of multiple 2D scan images. Computing software is then used to fill in the gaps or ‘interpolate’ between these images to produce a solid volume. The acquired 3D ultrasound volume can then be displayed collectively in a variety of imaging modalities. Several viewing modalities are available to maximize the display of the acquired 3D images. The render mode shows a single image representative of the whole block of 3D data and enhances the contrast between any two areas by recreating an impression of depth (Figure 1), whilst the multiplanar view allows the simultaneous assessment of individual sectional planes (Figure 2) [1,2]. Uniquely, 3D ultrasound allows demonstration of the coronal plane perpendicular to the transducer face facilitating the identification of surface irregularities, which can then be accounted for during volume measurement [3].

Figure 1.

Rendered view of a normal uterus.

Figure 2.

A multiplanar view of the uterus.

2D ultrasound is routinely used to assess the female pelvis and, specifically, the uterus and ovaries. 3D ultrasound should be used as an adjunct to this and performed after a baseline assessment has been concluded. Datasets of these organs are typically acquired and then analyzed after the patient has gone. The acquisition is usually carried out in duplicate, with the first acquisition obtaining grey-scale information and the second obtaining Doppler data to allow the assessment of blood flow within the organs. 3D ultrasound scanning consists of four basic steps:

• Data acquisition

• Volume analysis and processing

• Image animation

• Archiving of volumes [4,5]

Data acquisition can be either manual or automated. The manual acquisition of data involves the observer moving the probe over the organ of interest to generate images. The probe remains stationary in automated acquisition, and the transducer elements automatically sweep over the area of interest generating images. Stored volumes can be viewed and displayed in many ways following the ultrasound scan. This is particularly useful when there is a question regarding the pathology involved, and allows for a ‘virtual review’ of the images once the patient has left if necessary.

There has been a great deal of research into the potential of 3D ultrasound imaging in obstetrics, and we are now gradually starting to recognize and investigate the potential uses in gynecology. Given the fact that gynecological images tend to be static, as opposed to the constant movement experienced when imaging the fetus in an obstetric setting, the quality of the images are generally better in gynecology since there is less artifact to contend with. The images may not be quite as visually impressive as those of the fetal facial profile in utero, but they do allow us to view the structure in 3D as opposed to building an image in our minds based on 2D images. Advocates of 3D ultrasound [6] suggest that these features offer the user several advantages in comparison with 2D ultrasound (Box 1). Many clinicians remain unconvinced by its reputed advantages and 3D ultrasound is not without disadvantages (Box 2). These mainly relate to the cost implications and training requirements. 3D ultrasound does require specific equipment, but this is becoming widely available and is incorporated in most new systems. It is the additional training that has probably most limited its development, although there are many courses available offering theoretical and hands-on training.

3D in general gynecology Uterus

Normal uterus

When visualized in the coronal plane, the uterine fundus appears to be flat or slightly upwardly convex (Figure 1). The endometrial appearance varies according to the stage of the menstrual cycle, but generally has a homogenous echo-texture and an increased echogenicity when compared with the myometrium. It is important that the uterus is visualized in the midcoronal plane and that the fundus is clearly visualized to ensure that uterine anomalies are not missed and that an entirely normal uterus is not mistaken for an abnormal one. The cervix, which appears as a tubular echogenic structure, is also best visualized in the coronal view. However, it is important to remember that the view through the center of the cervical canal may require the demonstration of a different coronal plane to that providing the midcoronal view of the uterus, according to the degree of version and flexion of the uterus.

Congenital uterine anomalies

Congenital uterine anomalies are associated with an increased risk of abnormal pregnancy outcome [7], which is improved after hysteroscopic septoplasty [8]. This is undoubtedly the area where 3D ultrasound has contributed the most and has become the investigation of choice in units where available. Jurkovic et al. compared the use of 3D ultrasound to detect congenital uterine anomalies against hysterosalpingography and 2D ultrasound in 61 patients with a history of infertility and recurrent miscarriage [2]. They identified that whilst 3D ultrasound and hysterosalpingography, which was considered the gold-standard tool for the investigation of uterine anomalies at the time, resulted in identifying the normality of the uterus, 2D ultrasound was less specific and resulted in more false-positive findings. Raga et al. and Wu et al. reported similar results shortly afterwards, suggesting that 3D ultrasound offered a 100% specificity for the exclusion of uterine anomalies and was able to differentiate between the different anomalies [9,10]. The main benefit of 3D ultrasound for the assessment of uterine anomalies is that it allows us to image the uterine fundus and serosal outline simultaneously in the coronal plane, which is difficult and frequently impossible to obtain with conventional 2D ultrasound. This view allows the user to easily identify an abnormal uterus and then classify the abnormality (Figure 3). 3D ultrasound is now the gold-standard tool for the assessment of uterine anomalies as it is noninvasive and does not require exposure to radiation, in contrast with hysterosalpingography, but is just as sensitive and facilitates the differentiation of the type of anomaly.

Figure 3.

Uterine anomalies.

3D ultrasound has since been used to determine the prevalence of uterine anomalies in various patient groups and to characterize outcome on the basis of the anomaly. As many as 24% of women with recurrent pregnancy loss may have uterine anomalies [2], which is roughly four-times that observed in low-risk women, where the prevalence is in the order of 5–6% [2]. In terms of the type of anomaly, a similar distribution is observed between different groups, with arcuate uteri being the most common followed by subseptate then bicornuate uteri, with the more complex anomalies, such as uterus didelphys and single uterine horns, being the least prevalent. Women with a subseptate uterus have a significantly higher proportion of first-trimester loss. Women with an arcuate uterus have a significantly greater proportion of second-trimester loss (p < 0.01) and preterm labor (p < 0.01) compared with women with a normal uterus [2].

Box 1.

Potential advantages of 3D ultrasound.

• Accurate measurement of organ dimensions and volumes

• Improved anatomic and blood-flow information

• Improved assessment of complex anatomic anomalies

• A better specificity with regard to the confirmation of normality

• Standardization of the ultrasound examination procedure

• Reduced scanning times with cost-effective use of equipment and sonographer time

• Telemedicine and tertiary consultation

Fibroids

3D ultrasound has recently been used to map the exact location of fibroids in relation to the endometrial cavity and surrounding structures (Figure 4). This is extremely important in triaging patients for surgery, which is dependent on the exact position of the fibroid and the extent of its endometrial involvement [11]. It also has the potential to be of use in monitoring the reduction in the size of fibroids in patients receiving gonadotrophin-releasing hormone analogs or following uterine artery embolization.

Figure 4.

Fibroids.

An improvement in the diagnostic specificity of ultrasound with 3D imaging has been demonstrated by Sylvestre et al. in their study of 209 subfertile patients thought to have an intrauterine lesion on transvaginal 2D ultrasound or hysterosalpingography [12]. Using saline infusion sonography with 2D and then 3D ultrasound, 92 patients were subsequently identified as having a variety of intrauterine lesions suggesting a sensitivity and specificity of 97 and 11%, respectively, for 2D ultrasound, 87 and 45%, respectively, for 3D ultrasound and 98 and 100%, respectively, for 2D saline-infusion sonography. Of the 59 patients that had undergone hysteroscopy, the sensitivity and positive predictive value of saline-infusion sonography were 98 and 95%, respectively, when performed in combination with 2D ultrasound, and 100 and 92%, respectively, with 3D ultrasound. The study clearly demonstrates how simple contrast media potentially increase the specificity of 2D ultrasound since 55% (116 of 209) of patients were found to have normal cavities following the infusion of saline. This was largely owing to the correct localization of leiomyomas as intramural rather than submucosal (54 of 101 patients).

Box 2.

Disadvantages of 3D ultrasound.

• Definite learning curve

• Cost implications in purchasing equipment

• Attenuation of 2D ultrasound means that image quality differs with depth within any 3D volume

Adenomyosis

The diagnosis of adenomyosis is often made retrospectively following histopathological examination of the uterus after hysterectomy. However, ultrasound is useful and shows disruption of the myometrial–endometrial border and an irregular, thickened junctional zone in many cases. MRI appears to have a higher sensitivity and specificity (70–82 and 84–92%, respectively) than 3D ultrasound (53–70 and 65–97%, respectively) [13].

Endometrial polyps

An accurate diagnosis as to whether or not a patient has an endometrial polyp is crucial when planning further management, and may determine whether outpatient or inpatient hysteroscopy is more appropriate, depending on the size of the polyp and its pedicle. This has the potential to improve the use of resources and could be cost effective. Some studies have demonstrated that by using 3D ultrasound, with or without the instillation of saline, the accuracy of diagnosis is greater than that of 2D ultrasound. La-Torre et al. studied the specificity of 2D against 3D ultrasound in 23 women with endometrial polyps [14]. They concluded that 2D ultrasound had a specificity of 69%, 3D had a specificity of 88% and 3D sonohysterography a specificity of 100%. However, Ayida et al., who performed a similar study, found that 2D and 3D ultrasound were comparable when used in conjunction with saline sonohysterography [15].

Studies have demonstrated that the uterine cavity, endometrial lining and myometrium are best visualized using sonohysterography [16], and that these images are further improved by the use of 3D ultrasound [17,18]. 3D ultrasound allows the images to be captured as the saline is introduced and these can then be reviewed after the procedure even if the saline leaks out quickly afterwards (Figure 5). One such study investigated 36 women with postmenopausal bleeding who underwent 3D sonohysterography [18]. The results were compared against 2D ultrasound alone, 2D sonohysterography and hysteroscopy with histological correlation. The results revealed that 3D sonohysterography provided the most useful images of the uterine cavity and endometrial thickness, and that these correlated well with the hysteroscopic findings. However, hysteroscopy remains the gold-standard investigation for visualization of the uterine cavity until proven otherwise in future randomized, controlled trials.

Figure 5.

3D saline-infusion sonohysterography.

Location of intrauterine contraceptive devices

Displacement of intrauterine contraceptive devices can reduce their effectiveness. In addition to this, if the threads of the device are not visible on speculum examination, it can be difficult to be sure of their exact location, and it may be difficult to retrieve the device. Lee et al. carried out a study using 3D ultrasound to identify the position of intrauterine devices in 96 women and were able to confirm the location of the device, which could be seen in its entirety in a single 3D image in 95% of cases [19]. The coronal plane images provide views of both the arms and shaft of the device and the relation of these to the endometrial cavity (Figure 6).

Figure 6.

Well-placed intrauterine contraceptive device.

Multiplanar view of an intramural fibroid situated at the fundus.

Ovary

Normal ovary

Normal ovaries appear lateral to the uterus and vary in their relative position within the pelvis. They can be visualized in 95% of premenopausal women and in 85% of postmenopausal women using transvaginal ultrasound [3].

Polycystic ovarian syndrome

The criteria used to define polycystic ovaries are the presence of twelve or more follicles measuring 2–9 mm or an increased ovarian volume (>10 cm³) [20]. Stromal vascularity and blood-flow velocities are higher in women with polycystic ovaries [21,22], and it has been suggested that this may be one of the reasons why women with polycystic ovarian syndrome have a tendency towards ovarian hyperstimulation. Kyei-Mensah et al. used 3D ultrasound to compare polycystic ovaries against normal ovaries and demonstrated that there was an increased stromal volume in women with polycystic ovaries [23]. However, using a similar approach, Nardo et al. were unable to demonstrate any relationship between serum follicle-stimulating hormone, luteinizing hormone or testosterone and ovarian stromal volume in 23 infertile women with clomiphene citrate-resistant polycystic ovarian syndrome at the same stage of the menstrual cycle [24]. 3D imaging can calculate ovarian volumes more accurately than measurements based on 2D estimations [25], and facilitates detailed follicle counts; this should arguably mean that it becomes the ultrasound technique of choice for diagnosis in the future.

Ovarian cysts

Ovarian cysts are commonly diagnosed with transvaginal ultrasound, which offers a sensitivity of 88–100% and specificity of 62–96% to discriminate between benign and malignant adnexal masses [13]. The commonly encountered benign ovarian cysts are confidently diagnosed using ultrasound as they demonstrate characteristic sonographic appearance [26].

Functional or simple ovarian cysts are usually smaller with a diameter of 6 cm or less and are sonolucent. They are usually follicular cysts, unilocular with a thin, smooth outer and inner wall. Emorrhagic cysts (FIGURE 7A) typically contain spider web-like material that represents layers of fibrin. Blood clots may be seen and can be confused with papillary projections. The most consistent ultrasonographic feature of endometrioma (FIGURE 7B) has been the typical ‘ground glass’ appearance, characterized by diffuse low-level internal echoes within the cyst. They have thick walls, and some of them show septations. One or more ‘solid masses’ are occasionally seen to protrude from the cyst wall into the cyst lumen, which is described as ‘wall nodularity’. Ultrasound characteristics of a dermoid cyst (FIGURE 7C) are highly variable, ranging from predominantly cystic to uniformly dense. Most dermoid cysts are easily identifiable sonographically owing to their fat and hair content. The distinctive feature is the presence of a discrete, highly echogenic focus, with posterior shadowing (Rokitansky protuberance). Other characteristics considered pathognomonic are fine, echogenic bands representing hair within the cystic area and the presence of a fat–fluid level. Although 3D techniques have the potential to improve the diagnostic accuracy of ultrasound for differentiating these benign ovarian cysts, since they offer an improved spatial orientation through the provision of different image displays, such as multiplanar view, tomographic ultrasound imaging and different rendering modalities, they still need to be tested in prospective studies.

Figure 7.

Ovarian cysts.

3D & gynecological malignancy

Endometrium

Endometrial thickness measurements taken using sagittal plane images are currently used to evaluate the need for further investigation in cases of postmenopausal bleeding and to assess the likelihood of implantation following assisted reproduction treatment. Granberg et al. identified that endometrial thickness measurements below 5 mm had a 96% specificity for excluding endometrial disease in women with postmenopausal bleeding [27]. 3D ultrasound imaging provides us with an assessment of endometrial volume in contrast with endometrial thickness measurements produced by 2D ultrasound. Gruboeck et al. compared endometrial thickness measurements against endometrial volume measurements in 103 women who presented with postmenopausal bleeding [28]. Using a cutoff volume of 13 ml, endometrial cancer was diagnosed with a sensitivity of 100% and a specificity of 98% using 3D ultrasound, compared with a sensitivity of 83% and a specificity of 88% for endometrial thickness measurements with optimum cutoff levels of 15 mm. However, the cutoff levels reported in this study were high. A recent study has suggested that endometrial vascular indices measured using 3D power Doppler in addition to endometrial thickness and endometrial volume are increased in women with endometrial hyperplasia or carcinoma [29]. Of all these variables compared using receiver operative characteristics curve analysis, endometrial volume demonstrates the best discriminative potential for diagnosing endometrial cancer with an area under the curve (AUC) of 0.73 compared with the corresponding values of 0.70, 0.62, 0.63 and 0.63 for endometrial thickness, vascular index, flow index and vascular flow index, respectively. Since Merce et al. noted a significantly higher blood flow in cases of myometrial invasion greater than 50% [30], endometrial vascular indices may play a role in predicting the extension of the disease.

Cervix

Ultrasound scanning is not routinely used, at present, in the management of suspected cervical cancer. Following colposcopy and biopsy, the imaging of choice would be computed tomography or MRI. However, there may be a role for ultrasound and for 3D ultrasound as the transvaginal probe allows close approximation to the cervix and facilitates the use of high-frequency ultrasound, which, therefore, improves resolution and image quality. Suren et al. performed a study using 3D power Doppler to assess the vascular architecture of benign and malignant cervical changes [31]. Although they reported differences, allowing determination between benign and malignant changes, the study was small, involving only eight patients and no valid conclusions can be drawn. Despite recent reports of the role on 3D power Doppler ultrasound in assessing the tumoral volume and vascularization, particularly in early-stage cancer [32], it still remains as a research tool in current clinical practice.

Ovary

Several groups have used 3D ultrasound to investigate adnexal masses and differentiate benign and malignant disease. This remains a problem for conventional ultrasound, largely owing to the wide range of histological types of ovarian tumors and the fact that certain tumors, particularly those of low malignant potential, may exhibit features of both benign and malignant tumors. Various methods have been used in an attempt to improve the predictive power of ultrasound, including mathematical models, neural networks and, now, 3D ultrasound [33,34]. These authors claim that 3D ultrasound is superior to 2D imaging as it facilitates a more detailed analysis of the components of the tumor. 3D imaging allows a clearer view of features, such as papillary projections from the cyst wall, the extent of capsular infiltration of the tumor and the characteristics of the cyst walls [5]. However, the experience of the sonographer must play a large part in the detection of such features, and it remains to be determined whether or not these results are reproducible. A recent multicenter study investigating 181 women with an adnexal mass evaluated the addition of 3D ultrasound features to a diagnostic model, which included patient characteristics, cancer antigen (CA) 125 level and 2D ultrasound features, to determine whether this improves the discriminative capacity of the model to predict the probability of malignancy of an ovarian mass [35]. The use of 3D ultrasound significantly improved (p < 0.05) the diagnostic power of the diagnostic model to differentiate malignant ovarian tumor from benign lesions, as demonstrated by an increased AUC of 0.92 from 0.82. 3D power Doppler has also been suggested to provide additional diagnostic information to discriminate between benign and malignant ovarian masses. Whilst the subjectively assessed morphology of the vessel tree (e.g., density of vessels, branching, caliber changes and tortuosity) differs significantly between benign and malignant tumors, the addition of vascular features to the logistic regression model containing three gray-scale ultrasound variables did not significantly improve the diagnostic accuracy [36]. The objective quantitation of the color content of the tumor scan using 3D power Doppler ultrasound adds only marginal value to gray-scale imaging for the diagnosis of malignant tumor [37]. Further large, randomized, controlled trials are warranted to determine whether or not 3D ultrasound offers significant advantages over other imaging modalities in cases of suspected gynecological malignancy.

3D & reproductive medicine

Reproductive medicine involves the assessment and treatment of couples with subfertility. A baseline ultrasound assessment of the pelvis is an essential part of the female investigations and many of the pathologies outlined previously are known to have a negative effect on fertility and early pregnancy. Assisted reproduction technology (ART) refers to the more advanced therapies used to help couples conceive, such as IVF treatment. There are two key areas where ultrasound can be used: to predict the woman's response to ovarian stimulation (ovarian reserve) and to evaluate the chance of successful implantation of an embryo (endometrial receptivity).

Ovarian reserve

Ovarian reserve, defined by the size and quality of the remaining ovarian follicular pool at any given time, reflects the fertility potential of a woman [38]. It is important to assess ovarian reserve accurately prior to commencing ART since it allows specialists to individualize patient treatment. There are essentially three parameters to consider when using ultrasound to assess ovarian reserve:

• Antral follicle count

• Ovarian volume

• Stromal blood flow (Figure 8)

Figure 8.

Quantifying ovarian reserve.

Ovarian volume can be calculated more reliably and accurately using 3D ultrasound data [39]. If the volume is less than 3 cm³ then a poor response is likely, but if it is more than 10 cm³ the ovary can be considered polycystic and the patient is at an increased risk of ovarian hyperstimulation syndrome. However, studies using 3D ultrasound to investigate the relationship between ovarian volume and IVF outcomes have generated different results and suggest volume may not be an important predictor [40,41].

Studies assessing antral follicle counts have been more encouraging than those assessing ovarian volume measurements, since they appear to demonstrate a more positive correlation with IVF outcomes [42–44]. Transvaginal ultrasound can be used to assess the number of antral follicles measuring between 2 and 10 mm in diameter during the early follicular phase of the menstrual cycle. A poor response to ovarian stimulation is likely if there are fewer than seven follicles in total [45], whereas ovarian hyperstimulation syndrome is more prevalent in women with more than twelve follicles in either ovary [46]. Although the reproducibility of antral follicle count measurement is improved with 3D ultrasound when compared with 2D ultrasound [47], the prediction of ovarian response during ART is similar for antral follicle count, regardless of whether the measurements were performed using 2D or 3D techniques [45].

The additional use of power Doppler does not appear to improve the prediction of ovarian response above that of antral follicle counts. Kupesic et al. used quantitative 3D power Doppler angiography to predict ovarian response in 56 women, with normal basal serum follicle-stimulating hormone levels, undergoing their first cycle of IVF [48]. They concluded that antral follicle counts were better predictors of ovarian response than ovarian volume and vascularity. Further studies also supported this conclusion [44,49].

Endometrial receptivity

Successful implantation following embryo transfer primarily depends on the quality and competence of the embryo, but is also affected by the endometrium and its ability to accept the developing blastocyst (endometrial receptivity) and this is unlikely to occur in an endometrium measuring less than 5 mm in diameter [50]. Studies by Schild et al. [41] and Yaman et al. [51] demonstrated no significant differences between endometrial thickness or endometrial volume measurements in patients who conceived compared with those who did not, but the studies did suggest that a minimal volume of 2.0–2.5 cm³ was required for implantation to occur. This concept is supported by Raga et al. [52], who assessed endometrial volume in 72 women on the day of embryo transfer, and noted that no pregnancies occurred in patients with an endometrial volume below 1 cm³ and that implantation rates were significantly lower when the endometrial volume was less than 2 cm³. It is uncertain if volume measurements provide more predictive information than standard 2D measures of endometrial thickness as this has not been thoroughly assessed in randomized, blinded trials.

However, the addition of power Doppler appears to help. Kupesic et al. studied 89 patients undergoing ART and noted significantly higher endometrial blood flow in women who conceived [53]. Wu et al. also found 3D power Doppler angiography to be an important determinant of endometrial receptivity. This was only observed on the day of human chorionic gonadotrophin (hCG) administration in 54 patients undergoing their first IVF cycle [54]. 3D ultrasound may also be used to examine endometrial vascularity and determine endometrial receptivity prior to ovarian stimulation. Schild et al. reported significantly lower (p < 0.05) indices of vascularity at downregulation in 15 patients who subsequently conceived (20%) compared with 60 non-conception cycles [41]. Endometrial measurements were once again not correlated with outcome. This may reflect a more profound pituitary suppression but is more likely to reflect patients' responsiveness to exogenous hormonal therapy.

3D & pelvic floor imaging

3D ultrasound has now increasingly been used to examine pelvic floor anatomy and to detect changes associated with trauma to the pelvic floor following vaginal delivery [55]. It has also been proposed to image the paravaginal supports, prolapse and implants used in pelvic floor reconstruction and anti-incontinence surgery. This modality allows examination in a coronal plane through the urethra and the periurethral tissue, which is inaccessible with 2D ultrasound techniques [56]. Whilst earlier studies used a transrectal approach to acquire a 3D volume [55], recent technical developments enable abdominal transducers to be used for translabial/transperineal imaging [57–59], which is more acceptable to patients. Tomographic ultrasound imaging, possible with 3D ultrasound, has been found to be particularly useful in quantifying the degree of levator ani defects in women presenting with symptoms of pelvic floor dysfunction [57]. Further prospective studies are awaited in order to establish the role of pelvic floor imaging using 3D ultrasound in the clinical application of pelvic floor trauma and surgery.

Executive summary

What is 3D ultrasound?

• 3D ultrasound involves the acquisition of a series of 2D images that can then be displayed collectively in a variety of imaging modalities.

• 3D ultrasound scanning consists of four basic steps: data acquisition, volume analysis and processing, image animation and archiving of volumes.

• Many clinicians remain unconvinced by its reputed advantages and have concerns regarding its cost and training requirements.

3D in general gynecology

• The uterus

• Ovary

3D & gynecological malignancy

• Endometrium

• Cervix

• Ovary

3D & reproductive medicine

• There are two key areas where ultrasound can be used: to predict the woman's response to ovarian stimulation (ovarian reserve) and to evaluate the chance of implantation of an embryo (endometrial receptivity).

• Ovarian reserve

• Endometrial receptivity

3D & pelvic floor imaging

• 3D ultrasound is now increasingly used to examine pelvic floor anatomy, to detect changes associated with trauma to the pelvic floor following vaginal delivery and to image the paravaginal supports, prolapse and implants used in pelvic floor reconstruction and anti-incontinence surgery.

• Further prospective studies are awaited to establish its role in the clinical application of pelvic floor trauma and surgery.

Conclusion

• 3D ultrasound imaging is still at a relatively early stage in terms of its role as a day-to-day imaging modality in gynecology and reproductive medicine.

• Other than its application in the assessment and differentiation of uterine anomalies, there is very little evidence that 3D ultrasound results in a clinically relevant benefit or negates the need for further investigation.

• Future work should ensure that 3D ultrasound is compared with conventional imaging in randomized trials, where the observer is blind to the outcome, after which we will truly be able to evaluate its role in an evidence-based manner.

Future perspective

• One benefit of 3D imaging, which has yet to be fully explored, is its ability to archive and share volume datasets that can be reassessed in a virtual real-time manner.

• This facility may be useful when reviewing cases and for teaching purposes, and lends itself to telemedicine.

Conclusion

3D imaging has several obvious benefits that relate to an improved spatial orientation and the demonstration of additional image planes, such as the coronal plane. Similarities can be drawn with the additional information gained from the use of computerized tomography and MRI. 3D ultrasonography has become a moderately easy technique to learn, but experience in 2D ultrasonography is essential to obtain the images required for 3D visualization. However, other than its application in the assessment and differentiation of uterine anomalies, there is very little evidence that 3D ultrasound results in a clinically relevant benefit or negates the need for further investigation. Future work should ensure that 3D ultrasound is compared with conventional imaging in randomized trials, where the observer is blind to the outcome, only after which we will truly be able to evaluate its role in an evidence-based manner.

Future perspective

One benefit of 3D imaging, which has yet to be fully explored, is its ability to archive and share volume datasets that can be reassessed in a virtual real-time manner. This facility may be useful when reviewing cases as well as for teaching purposes, and lends itself to telemedicine. Developments in software and the continued reduction in the cost of memory and data storage will allow the formation of large databases and volume libraries that can be used for training and even virtual consultation. These possibilities make 3D imaging a most exciting form of ultrasound that cannot be ignored. History has seen ultrasound develop from static A-mode spikes of information, through B-mode grey-scale maps and real-time imaging, to the modern day where we have 3D and images and 4D movies. We do not know what the next technological breakthrough will be, but we know there will be one.