Image Presentation Three-Dimensional Inversion Rendering New Sonographic Technique and Its Use in Gynecology Ilan E. Timor-Tritsch, MD, RDMS, na Monteagudo, MD, RDMS, Tanya Tsymbal,, RDMS, Irina Strok, RDMS Objective. The purpose of this presentation is to describe the use of the 3-dimensional (3D) sonographic inversion rendering mode in displaying fluid-filled structures using dedicated hardware and software in gynecology. Methods. The 3D software used inverts anechoic into echogenic voxels, which, against the black background of the monitor screen, display the fluid-filled structure as a cast of it. The technique of the rendering process is described. Three-dimensional sonographic volumes of the adnexal area in 3 patients thought to have adnexal or ovarian masses were stored and rendered with the use of the laptop version of the inversion software. The same process was used in an additional 12 women for various indications: 7 with suspected uterine malformations and 5 with uterine bleeding. Of these 12 women, 11 underwent saline infusion sonohysterography. Results. Rendering the inverted fluid-filled adnexal structures revealed that, in all 3 cases, they were tubal, not ovarian, in origin (chronic hydrosalpinges). Of the 7 uterine cavities suspected of malformation, 3 were normal and 4 had uterine malformations: 2 arcuate uteri and 2 incomplete septate uteri. Of the 4 woman with dysfunctional uterine bleeding, 3 had endometrial cavities with polyps and 1 had an irregular surface of the cast. One woman with postmenopausal spotting had an enlarged but otherwise normal cavity. Conclusions. fter a relatively short learning curve to master the inversion rendering technique, it is possible to use it in a selected number of gynecologic cases with fluid-filled structures. In resolving the correct diagnosis of the adnexal masses, the inversion images performed better than the 2- dimensional (2D) and 3D orthogonal planes. For diagnosis of uterine disease, the inversion pictures presented marginal value over the 2D and 3D images. The 3D inversion rendering technique may have added value in selected gynecologic cases, establishing a more accurate diagnosis somewhat faster than only 2D sonography or even the 3D orthogonal planes. Key words: gynecology; inversion rendering; 3-dimensional sonography. bbreviations DU, dysfunctional uterine bleeding; SIS, saline infusion sonohysterography; 3D, 3-dimensional; 2D, 2-dimensional Received December 15, 2004, from the Department of Obstetrics and Gynecology, New York University School of Medicine, New York, New York US. Revision requested December 20, 2004. Revised manuscript accepted for publication January 20, 2005. ddress correspondence to Ilan E. Timor-Tritsch, MD, New York University School of Medicine, 550 First ve, NV-9N26, New York, NY 10016 US. Video online at www.jultrasoundmed.org. Three-dimensional (3D) sonographic applications in obstetrics and gynecology opened new avenues in enhancing our diagnostic abilities. mple literature is available on obstetric imaging with 3D as well as 4-dimensional sonography. s opposed to this, to our knowledge, relatively few articles deal with its gynecologic use. The volumes acquired can be digitally manipulated with the use of a variety of display modalities such as the multiplanar (orthogonal) views and various surface, transparency, and x-ray modes. Recently, a new display modality was added to the existing ones: the 3D inversion mode. 2005 by the merican Institute of Ultrasound in Medicine J Ultrasound Med 2005; 24:681 688 0278-4297/05/$3.50
Three-Dimensional Inversion Rendering Materials and Methods This new technology, the inversion rendering mode, is available on the Voluson 730 Expert sonography machine (GE Medical Systems, Kretztechnik, Zipf, ustria). Volumes obtained by this system can also be analyzed on a laptop computer using 4DView 2000 version 2.1 computer software (GE Medical Systems, Kretztechnik). The essence of the inversion technique is that the software inverts the fluid-filled structures from anechoic to echogenic voxels. Structures that were anechoic will be transformed into echoic structures, and echogenic structures will become anechoic. t the same time, the gray scale content of the image (volume) is removed to allow this particular display. On the black background of the monitor screen, the inverted rendered fluid-filled structures appear as white casts of the cavity they represent. The threshold and levels of transparency were changed (threshold level of 41 and transparency level 44) until the structure was adequately displayed. The gradient light mode was applied. With the use of the electronic scalpel tool, the unnecessary echoes were removed to enable an unobstructed view of the structure. The final image can be colorized to appear in 1 of 5 colors. This process is shown in Figure 1. This inversion technique does not distinguish between various kinds of fluids such as blood and water; therefore, it can be used to display any fluid-containing structure. In obstetrics, the inversion technique has a wide range of uses depicting the heart, great vessels, and other fluidcontaining fetal structures. 1 Figure 1. Major steps in the 3D inversion rendering process., cquisition in the 3 orthogonal planes and the rendered volume in the bottom right box., With activation of the invert button, the inverted volume appears in the bottom right box. C, Eliminating the surrounding nonpertinent structures with the electronic scalpel leaves the central structure of interest (bottom right box). D, Final inverted and rendered volume. Diagnosis: hydrosalpinx. C D 682 J Ultrasound Med 2005; 24:681 688
Timor-Tritsch et al Fifteen women were scanned. Three patients were thought to have ovarian masses on the basis of bimanual pelvic examination. Twelve women had sonographic examinations for various indications: 7 with suspected uterine malformations, 4 with dysfunctional uterine bleeding (DU), and 1 with postmenopausal spotting. Of the 12 women with vaginal bleeding, 11 underwent saline infusion sonohysterography (SIS) to further define the uterine cavity and the endometrial lining. The 3D sonographic volumes were stored, transferred to a CD, and rendered with the use of the above-mentioned laptop version of the inversion software. Results Table 1 summarizes the results. The diagnosis of the 3 adnexal masses after the 2-dimensional (2D) and 3D scans (without rendering) was ovarian cysts. Scrolling through the 3D volume shifted the suspicion from an ovarian mass toward tubal abnormalities. fter the inversion rendering, all 3 appeared as chronic hydrosalpinges. Figures 1 and 2 are 3D sonographic renderings of the left adnexa of a patient (case 1) referred for an adnexal mass to rule out ovarian disease. Two additional adnexal masses were subjected to the same algorithm. They too were consistent with chronic distended hydrosalpinges (Figures 2 and 3). One of them (case 2) revealed in addition a 3-cm simple cyst behind the fluid-filled tube (Figure 2). The 2D and 3D inversion rendering in the second group of 7 patients with suspected uterine malformations revealed the following: 3 had normal-shaped cavities and fundal contours; 2 had arcuate uteri; and 2 had incomplete septate uteri. Figure 4 represents the cavity of 1 of the 3 normal uteri. Examples of an arcuate uterus and an incomplete septate uterus are shown in Figures 5 and 6. The inversion rendering mode enabled a clear visual inspection of the shape of the uterine cavity; however, it contributed only marginal addition to the information already obtained by the orthogonal planes. The importance of the rendered uterine shape was its better understanding by the referring provider (specifically praising the images sent) and by the patient herself. The third group of 4 patients with DU had the following findings: In a patient with 3 months of menometrorrhagia, the 2D and 3D sonography with SIS showed an 8-mm thick, irregular endometrium. The inversion image visualized a rugged surface of the cast covered with indentations caused by the grossly irregular endometrium (Figure 7). Three patients had endometrial polyps shown by SIS on 2D and 3D sonography. The inversion reinforced the diagnoses. The polyps, as expected, appeared as spherical dropout areas representing the imprints of the polyps (Figures 8 and 9). In the only patient with postmenopausal spotting with cervical stenosis and some trapped endocavitary fluid, there was no notable difference between the diagnosis after the 2D and 3D sonographic examinations. The cavity of this uterus was somewhat distended but otherwise normal (Figure 10). Table 1. Results of 3D Inversion Rendering Case Clinical Diagnosis Diagnosis by 2D Sonography Diagnosis by Inversion 1 dnexal mass Suspected ovarian cyst, left Chronic hydrosalpinx, left 2 dnexal mass Suspected chronic hydrosalpinx, left Chronic hydrosalpinx/simple cyst, left 3 dnexal mass Suspected ovarian cyst, left Chronic hydrosalpinx, left 4 Suspected uterine malformation fter SIS: normal uterus Normal uterus 5 Suspected uterine malformation fter SIS: normal uterus Normal uterus 6 Suspected uterine malformation fter SIS: normal uterus Normal uterus 7 Suspected uterine malformation fter SIS, arcuate uterus rcuate uterus 8 Suspected uterine malformation fter SIS, arcuate uterus rcuate uterus 9 Suspected uterine malformation fter SIS: incomplete septate uterus Incomplete septate uterus 10 Suspected uterine malformation fter SIS: incomplete septate uterus Incomplete septate uterus 11 DU fter SIS: endometrial polyp 1 endometrial polyp 12 DU fter SIS: endometrial polyps 2 endometrial polyps 13 DU fter SIS: endometrial polyps 3 endometrial polyps 14 DU fter SIS: irregular endometrium (8 mm) Irregular surface of the cast 15 Postmenopausal bleeding Nl, endometrium (4 mm), cervical stenosis Mild distension of the cavity J Ultrasound Med 2005; 24:681 688 683
Three-Dimensional Inversion Rendering Figure 2. Three-dimensional inversion rendering of adnexal disease., cquisition in the 3 orthogonal planes and the rendered structure in the bottom right box., Left hydrosalpinx and an ovarian cyst behind the distended tube. The arrows point to the ovarian cyst. Clips of cases presented here are shown in online Videos 1 9. Discussion We live in a 3D world. The introduction of 3D sonography, contrary to all criticism and skepticism leveled at it, created a revolutionary imaging modality. Surface rendering of an organ in 3D imaging (one of the many tools that make up the different display modalities) caters to our binocular vision to better perceive the image. The new 3D inversion rendering software is yet another development complementing the various other software-enabled tools currently available on one sonography system (GE Voluson 730 Expert). Soon, however, it is expected to be introduced by other sonography machine manufacturers too. s with all the other electronic tools to manipulate the acquired volumes in terms of the various known display modes, such as filtering, colorizing, and blood vessel enhancing (3D angiography and -flow), inversion rendering will find its proper place in the right circumstances for the right diagnostic requirements. s shown here, inversion rendering proved useful to us mostly in displaying the fluid-filled fallopian tubes. It clearly helped differentiate an Figure 3. Three-dimensional inversion rendering of adnexal disease., cquisition in the 3 orthogonal planes and the rendered structure in the bottom right box., Left hydrosalpinx. 684 J Ultrasound Med 2005; 24:681 688
Timor-Tritsch et al C D Figure 4. Three-dimensional inversion rendering of a normal uterine cavity obtained by SIS., Display of the uterus in the orthogonal planes and the rendered volume in the bottom right box., The inverted volume appears in the bottom right box. C, Uterine cavity after removal of the unnecessary echoes (bottom right box). D, Final image of the normal-shaped cavity. Figure 5., Display of an arcuate uterus in the orthogonal planes and the rendered volume in the bottom right box., Final image of the cavity of this arcuate uterus. J Ultrasound Med 2005; 24:681 688 685
Three-Dimensional Inversion Rendering Figure 6., Display of an incomplete septate uterus in the orthogonal planes and the rendered volume in the bottom right box., Final image of the cavity in this septate uterus. Figure 7., Display of a uterus in a patient with DU in the orthogonal planes and the rendered volume in the bottom right box., Final image picture of the cavity showing irregular imprints in the surface of the cast in this patient with 3 months of DU. Figure 8., Display of a uterus in a patient with DU in the orthogonal planes and the rendered volume in the bottom right box., Final image of the cavity showing the filling defect in the cast of a small endometrial polyp (arrow) in the lower segment of the cavity. 686 J Ultrasound Med 2005; 24:681 688
Timor-Tritsch et al Figure 9., Display of a uterus in a patient with DU in the orthogonal planes and the rendered volume in the bottom right box., Final image of the cavity showing the imprint of 3 endometrial polyps (arrows). ovarian from a tubal abnormality. The pathogenesis of a fluid-filled fallopian tube and its 2D sonographic picture were described by us previously. 2 The inversion mode in the case of hydrosalpinges provided further sonographic support of the 2D appearance of this condition. We also arrived at the diagnostic image faster than scrolling through the original volume using only the orthogonal planes. The other possible application of the 3D inversion mode is to highlight the uterine cavity in cases of suspected uterine malformations or endometrial abnormalities in patients with infertility or gynecologic conditions. ecause the technique is based on rendering a relatively echo-free structure to be inverted, saline infusion into the cavity of the uterus was first performed to provide the necessary black cavity. Some patients may already have fluid in the cavity (in cases of cervical stenosis). fter the acquisition of the volume with the fluid in the cavity, the inversion process reveals the shape of the cavity. lthough the 2D as well as the 3D orthogonal display furnishes adequate information to diagnose polyps, submucous fibroids, and irregular Figure 10., Display of a uterus in a postmenopausal patient with vaginal spotting in the orthogonal planes and the rendered volume in the bottom right box., Final image of the cavity showing an enlarged fluid-filled cavity in this 72-year-old patient with cervical stenosis. The endometrial lining was normal; however, note the distended cavity, most probably the result of the increased intracavitary pressure. J Ultrasound Med 2005; 24:681 688 687
Three-Dimensional Inversion Rendering endometrial linings, the inversion rendering is simple enough to add as a further tool to strengthen the diagnosis. With the 3D-cine loop mode, the 3D cast of the cavity (normal or pathologic) can be inspected from all sides, turning it into a desired position. This display modality may prove useful in teaching and patient counseling. Similarly to all the other sonographic technologies, this rendering algorithm too can be fraught with artifacts. These occur if excessive transparency or threshold levels are used. The best rendering is obtained, at first, by trial and error. However, with experience, the values of the different variables contributing to the best representation of the organ can be standardized. The advantage of the 3D inversion rendering mode in gynecology as opposed to its obstetric use is that, in gynecology, a motionless organ is imaged. This enables a slower acquisition speed and, hence, a somewhat higher resolution than imaging the mobile fetus. In conclusion, a new sonographic application of rendering the acquired 3D volume, the inversion mode, was used in patients with gynecologic conditions or infertility. The technique requires the structure of interest to be relatively anechoic. Those who are familiar with 3D imaging will undoubtedly need only a relatively short learning curve to master the technique. In our cases, the inversion mode presented various degrees of information to achieve or strengthen the diagnosis. This new display mode will find its due place for use in selected cases in which it may provide added value in establishing the correct diagnosis. nimating the inverted volume with the use of the 3D cine function further increases its clinical value by allowing the observer to evaluate the structure from different angles. This feature is also useful in teaching. We believe that this new tool further enhances the diagnostic power of 3D sonography in obstetric and gynecologic imaging. References 1. Goncalves LF, Espinoza J, Lee W, Mazor M, Romero R. Three- and four-dimensional reconstruction of the aortic and ductal arches using inversion mode: a new rendering algorithm for visualization of fluidfilled anatomical structures. Ultrasound Obstet Gynecol 2004; 24:696 698. 2. Timor-Tritsch IE, Lerner JP, Monteagudo, Murphy KE, Heller DS. Transvaginal sonographic markers of tubal inflammatory disease. Ultrasound Obstet Gynecol 1998; 12:56 66. 688 J Ultrasound Med 2005; 24:681 688