Three- and 4-Dimensional Ultrasound in Obstetrics and Gynecology

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1 Special Report Three- and 4-Dimensional Ultrasound in Obstetrics and Gynecology Proceedings of the American Institute of Ultrasound in Medicine Consensus Conference Beryl R. Benacerraf, MD, Carol B. Benson, MD, Alfred Z. Abuhamad, MD, Joshua A. Copel, MD, Jacques S. Abramowicz, MD, Greggory R. DeVore, MD, Peter M. Doubilet, MD, PhD, Wesley Lee, MD, Anna S. Lev-Toaff, MD, Eberhard Merz, MD, Thomas R. Nelson, PhD, Mary Jane O Neill, MD, Anna K. Parsons, MD, Lawrence D. Platt, MD, Dolores H. Pretorius, MD, Ilan E. Timor-Tritsch, MD Abbreviations ACOG, American College of Obstetricians and Gynecologists; ACR, American College of Radiology; AIUM, American Institute of Ultrasound in Medicine; CT, computed tomography; DICOM, Digital Imaging and Communications in Medicine; 4D, 4-dimensional; MRI, magnetic resonance imaging; PACS, picture archiving and communications system; 3D, 3-dimensional; 2D, 2-dimensional Received September 6, 2005, from the Departments of Radiology and Obstetrics and Gynecology, Harvard Medical School, Brigham and Women s Hospital, Boston, Massachusetts USA (B.R.B., C.B.B., P.M.D.); Department of Obstetrics and Gynecology, Eastern Virginia Medical School, Norfolk, Virginia USA (A.A.); Department of Obstetrics, Gynecology, and Reproductive Sciences, Yale University School of Medicine, New Haven, Connecticut USA (J.C.); Department of Obstetrics and Gynecology, Rush University, Chicago, Illinois USA (J.A.); Fetal Diagnostic Center, Pasadena, California USA (G.R.D.); Department of Obstetrics and Gynecology, William Beaumont Hospital, Royal Oak, Michigan USA (W.L.); Department of Radiology, Thomas Jefferson Medical Center, Philadelphia, Pennsylvania USA (A.L.-T.); Department of Obstetrics and Gynecology, Krankenhaus Nordwest, Frankfurt am Main, Germany (E.M.); Department of Radiology, University of California, San Diego, San Diego, California USA (T.N., D.P.); Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts USA (M.J.O.); Department of Obstetrics and Gynecology, University of South Florida, Tampa, Florida USA (A.P.); Center for Fetal Medicine and Women s Ultrasound, Los Angeles, California USA (L.P.); and Department of Obstetrics and Gynecology, New York University, New York, New York USA (I.E.T.T.). Manuscript accepted for publication September 8, Address correspondence to Beryl R. Benacerraf, MD, 333 Longwood Ave, Suite 400, Boston, MA USA. The American Institute of Ultrasound in Medicine convened a panel of physicians and scientists with interest and expertise in 3-dimensional (3D) ultrasound in obstetrics and gynecology to discuss the current diagnostic benefits and technical limitations in obstetrics and gynecology and consider the utility and role of this type of imaging in clinical practice now and in the future. This conference was held in Orlando, Florida, June 16 and 17, Discussions considered state-of-the-art applications of 3D ultrasound, specific clinical situations in which it has been found to be helpful, the role of 3D volume acquisition for improving diagnostic efficiency and patient throughput, and recommendations for future investigations related to the utility of volume sonography in obstetrics and gynecology. Key words: fetal ultrasound; gynecologic ultrasound; obstetric ultrasound; 3-dimensional ultrasound; ultrasound technology. Three-dimensional (3D) ultrasound has the potential to be a considerable advance in the armamentarium of medical sonography. The qualitative and quantitative assessment of sonographic volume data is now possible with the use of several analysis tools, such as multiplanar imaging, surface and volume rendering, and semiautomated volume calculation using a technique known as virtual organ computer-aided analysis (VOCAL). Conceptually, the acquisition of sonographic volumes rather than single tomographic slices provides the ability to display information in any plane and in any orientation. This ability to image in any plane, not just the acquisition plane, in real time or simultaneously in several different planes has enormous potential for medical diagnosis with ultrasound. Until recently, ultrasound has lacked the capability to reconstruct images rapidly and with high resolution, which other types of cross-sectional 2005 by the American Institute of Ultrasound in Medicine J Ultrasound Med 2005; 24: /05/$3.50

2 AIUM Conference: 3D and 4D Ultrasound in Obstetrics and Gynecology imaging, such as computed tomography (CT) and magnetic resonance imaging (MRI), have enjoyed. With current clinically available equipment, 3D sonographic reconstruction is fast with high resolution, giving ultrasound the ability not only to image in real time, which MRI and CT cannot do, but also to be displayed in standardized uniform protocols as in MRI and CT. The American Institute of Ultrasound in Medicine (AIUM) convened a panel of physicians and scientists with interest and expertise in 3D ultrasound in obstetrics and gynecology to discuss the current state of the art for 3D ultrasound and to evaluate the clinical potential of these new capabilities. Setting and Conference Participants The day and a half conference was held immediately before the 2005 Annual Convention of the AIUM, in Orlando, Florida, June 16 and 17. Four program directors (B.R.B., C.B.B., A.Z.A., and J.A.C.) and 10 discussants constituted the panel. Also in attendance in the audience were representatives from invited professional societies, including the AIUM, American College of Obstetricians and Gynecologists (ACOG), Society for Maternal-Fetal Medicine, American College of Radiology (ACR), Society of Diagnostic Medical Sonography, Society of Radiologists in Ultrasound, World Federation for Ultrasound in Medicine and Biology, and American Board of Obstetrics and Gynecology, and from commercial companies, including GE Healthcare, Medison America, Siemens Medical Solutions, Philips Medical Systems, and SonoSite. The first day of the conference was devoted to scheduled presentations from panelists about a variety of state-of-the-art applications of 3D ultrasound in obstetric and gynecologic ultrasound. Discussion periods were interspersed. During the evening between the first and second days, the panelists drafted a summary of the first day s discussion and outlined areas for further discussion. During the second day, the summary was discussed, and statements were modified on the basis of the consensus of the panelists. Where Are We Today? State-of-the-Art 3- and 4-Dimensional Ultrasound: Reports From the Panelists The literature contains many articles addressing the use of 3D ultrasound in obstetrics and gynecology Some articles have shown that, in certain situations, volume sonography adds diagnostic value to standard 2-dimensional (2D) ultrasound. 4 9,16 41,64 66,79,83 Three-dimensional ultrasound can also provide accurate measurements in 3 planes with acceptable interobserver reliability ,42 50 Still other articles have focused on acquiring volumes for subsequent review and interpretation, in addition to improving practice efficiency and patient throughput. 14,15 Most articles, however, are descriptive of new techniques for acquiring and reconstructing 3D volumes or are presentations of the appearances of a variety of conditions with 3D multiplanar reconstruction and surface and volume rendering Although more scientific studies are in progress, it remains difficult to compare 2D and 3D ultrasound because 2D imaging, by necessity, always precedes the 3D volume acquisition. Furthermore, sonography is an operator-dependent imaging modality. Consequently, it may be difficult to generalize some of the results obtained by experts or researchers to other health care providers who use 3D diagnostic ultrasound in their clinical practices. To date, studies focusing on the added value of 3D capabilities to 2D ultrasound have shown that 3D volume sonography provides important diagnostic information for gynecologic evaluation of uterine duplication anomalies 4,9 and for optimal evaluation of the uterine cavity. 5 In the assessment of fetal anomalies, 3D ultrasound can enhance the prenatal characterization of congenital defects, such as facial and skeletal anomalies. 7,22,23,33,79,83 These rendered images may be especially helpful for assisting health care providers who counsel parents about the nature, prognosis, and postnatal management of congenital abnormalities. Three-dimensional imaging of the fetal face, either with multiplanar reconstruction or surface rendering, is a complementary technique to 2D sonography. For example, a single volume acquisition of the fetal face can be used to reconstruct a true midline sagittal plane, often not possible with 2D ultrasound alone. This particular view is important for optimal evaluation of the fetal nasal bone or for suspected cases of micrognathia. Multiplanar and surface-rendered views from volume data of the fetal face can help further delineate a suspected cleft lip and palate or possible orbital and mental abnormalities J Ultrasound Med 2005; 24:

3 Benacerraf et al Fetal echocardiography, using 3D ultrasound, is practiced by some experts in fetal imaging. These experts have used volume acquisitions to reconstruct images of the fetal heart to show normal cardiac structures From a sonographic volume of the fetal heart, standardized planes of reconstruction can be displayed. In addition, automation can be used to display these standardized planes, diminishing operator dependence. Fetal heart volumes can also be acquired in real time and, with the use of gated technology, can be stored as a cine loop of the cardiac cycle. Thus, any reconstructed plane or surfacerendered image can be displayed as a cine loop of the cardiac cycle. Automated sequences are now being developed to reduce operator dependence for achieving these standardized cardiac views Three-dimensional color and power Doppler sonography can also be used for the assessment of extracardiac vasculature. 43 These techniques can provide images of the placental cord insertion site, vascular anastomoses involving fetuses with twinto-twin transfusion, abnormal vessels from pulmonary sequestration, and aberrations of the central venous system such as an interrupted inferior vena cava with azygous venous return. Another important role of 3D ultrasound relates to the ability to store volume data that can be manipulated long after the patient has left the examination room. 78 The acquisition of sonographic volumes rather than single tomographic or 2D images allows for storage of information that can be reconstructed in any plane or orientation for interpretation. Storage of a single volume of data is quick, yet the stored volume permits interpretation of the scanned region in multiple planes. This obviates the need to take multiple images of an organ in 2 different planes. Rather, a single volume of that organ can be saved and later reviewed in any plane at any level, leading to improved patient throughput and a more efficient ultrasound practice. 15 Sonographic volumes can also be transmitted electronically from a remote site for full interpretation and evaluation elsewhere, making teleradiology ultrasound image interpretation easier and less operator-dependent. 14,15 This capability has the potential to increase the use of ultrasound in remote locations where an ultrasound expert is not present. Furthermore, volume scanning may permit standardization of image display planes in a way similar to other types of cross-sectional imaging modalities, such as CT and MRI. The model of volume scanning with subsequent review has been tested in 2 centers. In the first, obstetric scans were performed using volume acquisitions for the fetal structural survey. In less than 2 minutes, 5 volumes of the fetus were obtained. Subsequent review of the volumes yielded complete fetal surveys in 90% of cases. 15 Another site replaced static 2D image acquisition with volume scanning, reducing scanning time from an average of 15 minutes to 4 minutes, improving efficiency such that 20% more patients could be scanned in a day. In addition, less hands-on scanning was required of interpreting physicians because the physicians had full volumes of information, allowing them to do virtual sweeps through the entire volume, if needed (M. O Neill, personal communication). Three-dimensional ultrasound can improve the accuracy of length, area, and volume measurements. 43 Various strategies have been used, from full manual outlining of structures to semiautomatic and fully automatic algorithms that segment organs and structures for analysis. Currently, there is still a need for improved automated segmentation algorithms for such measurements to be clinically useful. Ultrasound poses challenges in developing robust algorithms; however, advances in image processing should improve the situation in the future. Three-dimensional ultrasound has been used to measure bladder volume, 44,45 the endometrium, and masses and to estimate the weight of fetal organs (eg, brain, lungs, and liver). Some studies suggest that patients who are undergoing volume sonography and viewing the 3D and 4-dimensional (4D) images report enhanced bonding with their fetuses and more positive feelings about the experience than do patients having 2D sonography, although the overall satisfaction from the ultrasound examination remains high with both 2D and 3D/4D imaging. 53 In some nonmedical settings, 3D ultrasound is used to provide keepsake images of the developing fetus for the parents. Bioeffects must also be considered for volume sonography. Ultrasound is a form of energy. It has 2 major effects in tissues it traverses: heating and mechanical bioeffects. Such effects have been shown in vitro and in animals at intensities equivalent to those used in clinical situations. J Ultrasound Med 2005; 24:

4 AIUM Conference: 3D and 4D Ultrasound in Obstetrics and Gynecology Epidemiologic studies have not shown harmful effects of 2D ultrasound in humans with the use of indicated diagnostic ultrasound. Because 3D and 4D ultrasound uses computer reconstructions of 2D images obtained through sweeps across the organ of interest, the level of energy is not higher than in 2D scanning. Manipulations of the volumes obtained are performed offline or on the ultrasound machine after the patient s scan is completed, therefore resulting in no additional exposure to ultrasound. The studies evaluating volume acquisitions for subsequent interpretation suggest that this new scanning method has the potential to decrease scanning time, which is likely to decrease exposure. Conversely, constant scanning, such as might occur with 4D scanning to observe fetal movement over time, could potentially return exposure to 2D levels or more. As with 2D ultrasound, adherence to the ALARA (as low as reasonably achievable) principle should be respected with 3D and 4D ultrasound. 76 Panel Discussion I. Definitions and Summary Statements The panelists thought it was important to list some definitions and statements related to 3D ultrasound in obstetrics and gynecology. They are as follows: 1. Three-dimensional ultrasound, or volume sonography, is an imaging technology that involves acquisition of a series of 2D images covering a volume from a patient that may be displayed in different orientations after the acquisition. 2. Three-dimensional ultrasound, or volume sonography, may be acquired and displayed over time. This is variously known as 4D ultrasound, real-time 3D ultrasound, and live 3D ultrasound. 3. When used in conjunction with 2D ultrasound, 3D ultrasound has added diagnostic and clinical value for select indications and circumstances in obstetric and gynecologic ultrasound. 4. Volumetric acquisition of sonographic data with subsequent offline review and interpretation has the potential to improve patient throughput, efficiency of clinical practice, and teleimaging interpretation. II. Examples of Clinical Utility of 3D and 4D Ultrasound Panelists agreed that 3D ultrasound is not yet widely used on a routine basis. It has been shown to be a problem-solving tool in selected circumstances and may well become a part of many obstetric and gynecologic ultrasound examinations in the future. The role of 3D ultrasound is still being evaluated in many areas. Panelists thought that it was important to list examples of some areas in which members of the panel have found 3D ultrasound to be helpful ,79,83 This list in no way is intended to be all-inclusive or exclusive, nor is it a current standard of care in the conditions listed: I. Gynecology 1. Assessment for congenital anomalies of the uterus; 2. Evaluation of the endometrium and uterine cavity with or without saline infusion sonohysterography; 3. Mapping of myomata for planning myomectomy; 4. Cornual ectopic pregnancies; 5. Intrauterine device location and type; 6. Imaging of adnexal lesions, to distinguish ovarian from tubal origin and ovarian from uterine origin; 7. Abscess drainage in the pelvis and abdomen; 8. Three-dimensional guidance in interventional procedures for infertility; and 9. Evaluation and monitoring of patients with infertility, including patients with polycystic ovaries and tubal occlusion. II. Obstetrics 1. Facial anomalies (eg, cleft lip and palate, micrognathia, abnormal midline profile, and genetic syndromes); 2. Nasal bone; 3. Ears; 4. Central nervous system (eg, agenesis of the corpus callosum and Dandy-Walker malformation); 5. Cranial sutures; 1590 J Ultrasound Med 2005; 24:

5 Benacerraf et al 6. Thorax (eg, rib evaluation, intrathoracic masses, and lung volumes); 7. Spine (eg, level of neural tube defect and vertebral abnormalities); 8. Extremities (eg, clubfeet, amputation defects, and skeletal dysplasia); 9. Heart (eg, conotruncal anomalies and evaluation of normal anatomy); 10. Placenta (eg, vasa previa) such as to determine the relationship of the vessel to the internal os; 11. Visual depiction for reassurance or demonstration of an abnormality for consulting clinicians and patients; 12. Extent of anomalies, such as cystic hygroma; 13. Multiple gestations (eg, conjoined twins and vascular mapping for twin-twin transfusion); and 14. Umbilical cord (eg, cord insertion sites or cord knots). III. Telemedicine and Offline Image Review 1. Storing of volumes for subsequent review and interpretation; 2. Central monitoring of data for quality and accuracy in remote clinical sites and in multicenter research studies; and 3. Telemedicine and offline image review on an independent workstation. IV. Education 1. Teaching standardized views and postprocessing techniques for training; and 2. Teaching normal and abnormal anatomy using volumes as simulated scans. Where Do We Go Next? Panelists thought that it is important to educate and train the medical community on the utility and functionality of 3D ultrasound as part of working toward general acceptance of 3D ultrasound as a component of the imaging armamentarium in obstetrics and gynecology. How Do We Get There? The panelists outlined key steps toward improving and promoting the clinical acceptance of 3D ultrasound for diagnostic applications in obstetrics and gynecology. These points are as follows: Encourage those who perform gynecologic ultrasound examinations to incorporate 3D ultrasound into their ultrasound practices. Encourage those who perform obstetric ultrasound examinations to incorporate 3D ultrasound into their ultrasound practices. Achieve acceptance of 3D ultrasound as a valuable tool in medical imaging by providing education, training courses, publications, simulators, online training, and multimedia tools. Optimize ultrasound volume displays and tomographic analysis by using experience gained from CT and MRI and integrate these into picture archiving and communications systems (PACS). Continue to develop quantitative applications for 3D ultrasound. Develop indications and protocols for 3D ultrasound. Standardize terminology for volume sonography so that it is universal and avoids proprietary terminology. Set standardized display algorithms to permit reproducibility and automation. Define the role of the sonographer because some of the offline reconstruction of images may well be performed by sonographers in the future and may replace some hands-on scanning time. Advancement Strategy To advance the use of 3D ultrasound, work is necessary on a number of fronts, including (1) technological advances, (2) standardization, (3) education and training, and (4) research and clinical investigation. J Ultrasound Med 2005; 24:

6 AIUM Conference: 3D and 4D Ultrasound in Obstetrics and Gynecology Technological advances to improve the ease of use of 3D ultrasound are key to general acceptance. Potential obstacles for its widespread clinical use are the time and effort required to learn how to use the new technology. The technology must become easier, faster, and more intuitive, and the user interface must be simple. Otherwise, only power users with special expertise in gynecologic and obstetric ultrasound will learn these new features and incorporate them into their imaging practices. In addition, the image resolution of the 3D volume probes must be improved. Even when the basic resolution of the probe is adequate, resolution is diminished in reconstructed images. In particular, the reconstructed planes are degraded in resolution compared with the acquisition plane. Therefore, 3D images can have image resolution that is inferior to conventional 2D sonography. Standardization is required at multiple levels for 3D ultrasound to gain widespread use. First, the equipment needs to be standardized across manufacturers with respect to terminology of functions and the display on the ultrasound system. This includes the incorporation of anatomic markers into the 3D volumes so that there is no confusion about right versus left or cranial versus caudal for a given patient. These markers must be maintained with the volume data so they are not lost on reconstructed planes. Standardization is also needed for methods of electronic transmission, display, and storage of volume data. This includes adopting or developing Digital Imaging and Communications in Medicine (DICOM) standards for 3D and 4D volume data sets that are compatible with current image storage systems (PACS). The ability to store volume data on PACS and PACS-based basic image reconstruction algorithms is needed to enhance penetration of 3D technology in general practice. This will facilitate multimodality imaging evaluation and comparison. The ability to manipulate the volume from the PACS system is crucial also for evaluating specific types of fetal anomalies. For example, algorithms to view fetal bony structures will permit evaluation of bony anomalies. Image orientation must also be standardized by using algorithms to display anatomic reference points within multiplanar displays and rendered reconstructed images. The practitioners, both sonographers and physicians, need to set protocols for volume acquisitions for various types of 3D ultrasound examinations. After that, there need to be standards for display. In particular, image orientation must be defined. Education and training are required for widespread dissemination of information about when to use 3D ultrasound, as well as how to use and how to interpret 3D sonographic volumes. Practitioners will need to learn the appearances of normal structures, as well as various pathologic conditions. A solid understanding of sonographic artifacts resulting from use of 3D ultrasound will also be essential. Last, research and clinical investigations must be performed to show the utility of 3D ultrasound through peer-reviewed scientific publications. Studies assessing the effect of volume acquisitions on practice efficiency are needed. Because early studies suggested increased patient throughput, further investigations are needed to determine methods for optimizing the efficiency of volume acquisitions and interpretations without compromising the diagnostic yield. Clinical studies are also needed to compare 3D ultrasound with MRI and other imaging modalities. It is understood that these comparisons will be made against a background of rapidly emerging technology as volume probes with improved resolution become available. Recommendations To achieve the goal of widespread acceptance of 3D and 4D ultrasound in obstetrics and gynecology, the panel provided a number of recommendations: Encourage manufacturers, experts, and societies to make it easier to learn how to perform 3D ultrasound examinations with more accessible educational opportunities such as online and hands-on courses. Encourage manufacturers to make 3D ultrasound machines easier to use. Encourage manufacturers to make 3D ultrasound systems faster and completely real time. Encourage manufacturers to include offline software with basic postprocessing tools with 1592 J Ultrasound Med 2005; 24:

7 Benacerraf et al the purchase of an ultrasound system to promote penetration of the technology. Develop innovative software tools to analyze ultrasound volumes quantitatively, for example, fractional volume and cardiac output, including improved automated segmentation algorithms to improve analysis time. Encourage manufacturers to develop new ways to tag volumes as to right/left, anterior/posterior, and cranial/caudal to standardize orientation and minimize confusion. Encourage governmental agencies, professional societies, and industry to support scientific studies and further development of 3D ultrasound. Diagnostic benefits and technical limitations should be compared with other imaging modalities, such as 2D sonography, MRI, and CT. The cost-effectiveness of this emerging technology should also be examined. Integrate 3D sonographic volume assessment into PACS systems, including the development of DICOM standards for 3D ultrasound. Urge the ACR, AIUM, and ACOG to develop collaborative guidelines for performance of 3D ultrasound examinations in gynecologic and obstetric ultrasound. Encourage the ACR, AIUM, and ACOG to discuss the importance of 3D sonography with third-party payers and include it in future reimbursement policies. Set up a task force or committee to define 3D ultrasound terminology and standardization. (This is in process in the AIUM Clinical Standards Committee.) Set up a task force or committee including experts and representatives from manufacturing to evaluate methods for educating health care professionals. Recommend studies to evaluate exposure and potential bioeffects resulting from volume sonography. Encourage manufacturers to ensure that image quality and resolution of the 3D image are comparable with those of 2D imaging in all planes. Summary Three-dimensional ultrasound is becoming an important part of state-of-the-art sonographic imaging in obstetrics and gynecology. It is a problem-solving tool in selected circumstances. It has the potential to improve practice efficiency and patient throughput without jeopardizing diagnostic capabilities. To become widely accepted, however, work must be done by several groups, including manufacturers, to make the 3D ultrasound systems faster and more userfriendly. Additionally, standards must be established for transmission and storage of volume data; educational efforts should be expanded for teaching practitioners how to use and interpret these results; and medical societies and industry need to reach a consensus about how to best standardize imaging protocols and display. The panel proposed several recommendations to encourage the use of 3D ultrasound for clinical care, teaching, and research in obstetric and gynecologic ultrasound. References 1. Nelson TR, Downey DB, Pretorius DH, Fenster A. Three-Dimensional Ultrasound. Philadelphia, PA: Lippincott Williams & Wilkins; Bega G, Lev-Toaff A, Kuhlman K, Kurtz A, Goldberg B, Wapner R. Three-dimensional ultrasonographic imaging in obstetrics: present and future applications. J Ultrasound Med 2001; 20: Bega G, Lev-Toaff AS, O Kane P, Becker E Jr, Kurtz AB. Three-dimensional ultrasonography in gynecology: technical aspects and clinical applications. J Ultrasound Med 2003; 22: Woelfer B, Salim R, Banerjee S, Elson J, Regan L, Jurkovic D. Reproductive outcomes in women with congenital uterine anomalies detected by threedimensional ultrasound screening. Obstet Gynecol 2001; 98: Lev-Toaff AS, Pinheiro LW, Bega G, Kurtz AB, Goldberg BB. Three-dimensional multiplanar sonohysterography: comparison with conventional two-dimensional sonohysterography and X-ray J Ultrasound Med 2005; 24:

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