Evaluation of tubal status is one of the initial steps in the diagnostic work-up of infertile women. Hysterosalpingo-contrast sonography (HyCoSy), currently performed as part of the infertility work-up to assess tubal patency by transvaginal ultrasound (TVS)1, is based on the introduction of fluid into the uterine cavity and Fallopian tubes.
To evaluate the Fallopian tubes, a sonographic enhancing positive-contrast medium may be used. Air, albumin with micro air bubbles, and galactose with micro air bubbles have been studied. These positive-contrast agents outline the course of the Fallopian tubes, producing a hyperechoic appearance. The most simple and inexpensive positive-contrast medium is saline solution mixed with air. When this solution is shaken, it generates a suspension of air bubbles that is easily identified sonographically when injected into the uterine cavity and Fallopian tubes2–4 with spillage around the ovaries. However, while two-dimensional (2D) TVS HyCoSy with saline solution mixed with air appears to be an accurate and inexpensive screening tool to assess tubal patency, it is highly observer-dependent and is accurate only in the hands of experienced investigators2–5. In addition, unlike hysterosalpingography (HSG), 2D HyCoSy does not provide an image of the entire tube and its course.
While ultrasound-enhancing contrast media may improve the evaluation of tubal occlusion6–8 and visualization of the tubal course, sometimes there are difficulties. Occasionally tubal spasm causes temporary tubal obstruction or the tubal course, being irregular, is difficult to identify. Furthermore, the similar echogenicity of contrast medium and certain tissues (or air in the bowels) causes difficulties differentiating the medium from surrounding organs (such as bowel and ovaries). As a result, it is not always possible to visualize the entire tube with these ultrasound-dedicated hyperechoic positive-contrast media (albumin, or galactose micro air bubbles), and the false-positive rate for tubal occlusion is still about 5–10%. The two most commonly used contrast media (Echovist and Levovist, Schering AG, Berlin, Germany) create a contrast response consisting of an overlapping of the tissue and the medium.
The limitations and difficulties encountered with conventional 2D HyCoSy, therefore, are:
- 1.The Fallopian tube cannot be seen completely in any scanning plane due to its tortuosity and visualization of the entire tube happens only on rare occasions.
- 2.Spill of the echo-positive contrast medium from the fimbrial end of the tube is difficult to distinguish from bowel surrounding the tube because of their similar echogenicity.
- 3.There is a requirement of an experienced sonographer who is able to quickly manipulate the TVS probe and detect contrast medium echoes in order to visualize the different parts of the tubes.
To overcome these problems of conventional 2D HyCoSy, two ultrasound technologies have been combined, the first to better evaluate the signals coming from the contrast medium and the second to acquire a three-dimensional (3D) sonographic volume of the Fallopian tube.
In an attempt to enhance the signal from the contrast medium, dedicated software has been developed which is able to exclude the fundamental image, and the contrast medium is identified distinctly without interference from other pelvic organs. This special software has been used with a new second-generation contrast medium (SonoVue, Bracco International BV, Amsterdam, The Netherlands)9. This ultrasound technology (using the combination of ultrasound-dedicated software and second-generation contrast medium) emits an ultrasound beam at a selected frequency and receives a narrow band of harmonic signal, avoiding the overlapping between the tissue and the contrast response. The earlier generations of contrast agents have microbubbles with quite rigid membranes and are thus unable to respond with harmonic signals at low acoustic pressure. The second-generation agents such as SonoVue provide a substantial harmonic response at low acoustic pressure. Primarily it is used intravenously to study microcirculation of the liver, breast lesions and various gynecological lesions but it has also been studied extensively in the assessment of myocardial perfusion. Recently, it was introduced for sonographic tubal patency evaluation6, 9, 10, 11.
Coded contrast imaging (CCI) with coded phase inversion technology (GE Healthcare, Zipf, Austria) is a new software that optimizes the use of ultrasound contrast medium by means of low acoustic pressure and enhances the visualization of the Fallopian tube by enabling the clinician to differentiate between the harmonic response of the contrast medium microbubbles and the signals from pelvic organs. The image displayed is based only on harmonic signals produced by contrast medium microspheres; broadband ultrasonic signals from surrounding tissue are filtered out completely. CCI with second-generation ultrasound contrast medium (SonoVue) is able to emit an ultrasound beam at a selected frequency and to receive a narrow band of harmonic responses, preventing overlap of tissue and contrast responses.
Using CCI technology during HyCoSy, the intrauterine injection of ultrasound contrast medium (1.5 mL SonoVue diluted with 2.5 mL saline solution) in a completely anechoic pelvis is visualized as hyperechoic fluid, seen first in the uterus and then in the tube if it is patent proximally; finally, it spills into the abdominal cavity if the tube is totally patent distally. Because the contrast medium is highly hyperechogenic and can be visualized for several minutes, the tubal course and shape can be studied and 3D volume acquisition can be performed.
3D HyCoSy without CCI has been reported in previous studies12–14 using a saline-air solution and Echovist as the contrast media. Color and power Doppler flow imaging were used to detect tubal flow, but the resulting image was not always sufficiently clear as to draw a conclusion about tubal patency.
Automated 3D sonographic tubal patency evaluation requires volume acquisition of the uterus and tubes with CCI during injection of second-generation contrast medium. The TVS probe is positioned in such a way as to visualize the transverse section of the uterus and, if possible, both ovaries laterally. The CCI mode is then introduced and the view of the pelvis becomes completely anechoic. 3D volume acquisition is then performed with the region of interest set as wide as possible, so that uterus, both ovaries and the whole length of the Fallopian tube can be seen. The angles of the 2D scan and the volume 3D scan are set at 180° and 90°, respectively. The multiplanar view of the contrast medium in the uterus and tubes is obtained during injection of the medium (Figure 1) and special software automatically provides the volume image produced by the medium. The result is a view of the uterine cavity in coronal section with both tubes laterally and of the contrast medium that spills around the ovaries (Figure 2). The possibility to rotate this volume shows better the tubal course in 3D space (Videoclips 1a and b, online).
Many of the disadvantages associated with 2D HyCoSy are overcome by means of the 3D CCI mode:
- 1.Automated 3D volume acquisition of the entire Fallopian tube easily shows the course of the tube.
- 2.CCI allows distinction of contrast medium in the tubes and around the ovaries from surrounding tissue and organs due to the clearly detectable difference between the harmonic response of the contrast medium microbubbles and the broadband ultrasonic signals from surrounding tissue.
- 3.3D volume acquisition during HyCoSy is static and avoids difficult probe movements, so it is less dependent on the experience and skill of the operator.
Other advantages of automated 3D CCI HyCoSy are that the volume, which includes the uterus and tubes, can be stored and analyzed later, reducing the examination time for patients. Furthermore, because both tubes are visualized during volume acquisition, less contrast agent is required compared with 2D HyCoSy, which, because of the difficulty in visualizing each tube separately, may require an excessive amount of contrast to achieve diagnosis. Another major advantage is that TVS HyCoSy with automated 3D CCI produces images of the tubes similar to those from HSG and the pictures can be seen and evaluated by other clinicians, whereas 2D HyCoSy is dynamic so spillage is seen only by the sonographer and images are more difficult to interpret.
We believe that, after diagnostic feasibility and accuracy studies, this novel technique will find a place in the early investigation of subfertile women.
SUPPORTING INFORMATION ON THE INTERNET
The following supporting information may be found in the online version of this article:
Videoclips S1a and b Automated three-dimensional coded contrast imaging during hysterosalpingo-contrast sonography: view of the automated reconstructed volume of contrast medium in the uterus and patent tubes. Note the tubal course in the space with spillage of the contrast around the ovaries. The uterine cavity is distorted by the balloon of the catheter.