Fetal three-dimensional ultrasound: quantitative assessment

Ultrasound in Med. & Biol., Vol. 29, No. 5S, pp. S1–S225, 2003 Copyright © 2003 World Federation for Ultrasound in Medicine & Biology Printed in the USA. All rights reserved 0301-5629/03/$–see front matter

Monday, June 2, 2003 (8:15 am–10:00 am) PLENARY SESSIONS

time. This gives the examiner a direct access to the movements of the fetal face. In a study comparing 2D and 3D ultrasound findings in 67 facial anomalies, 3D ultrasound showed an advantage in 73% of the fetuses. Conclusions: 3D ultrasound enables a detailed tomographic survey of the normal fetal face and permits a precise demonstration or exclusion of subtle malformations.

THREE-DIMENSIONAL/FOUR-DIMENSIONAL ULTRASOUND Three-dimensional/four-dimensional ultrasound—the patient perspective Pretorius DH, Radiology, 7756, University of California, San Diego, La Jolla, CA

Birthweight prediction by three-dimensional ultrasonography Lee W, Division of Fetal Imaging, William Beaumont Hospital, Royal Oak, MI, and Perinatology Research Branch, National Institutes of Child Health and Human Development, Detroit, MI

New developments in ultrasound technology include both 3-dimensional and 4-dimensional (addition of time, allowing for observation of movement) imaging. The surface pictures and movement of the fetus have allowed patients to become an integral part of the obstetrical ultrasound examination. Patients benefit by “seeing” their fetus, whether it is normal or abnormal. The clear images provide reassurance to many families that are concerned about the welfare of the fetus, and they provide additional understanding to parents carrying fetuses with congenital anomalies such as facial anomalies (cleft lip/palate), abdominal wall defects, skeletal dysplasias, and club feet. Much controversy exists regarding the benefit of 3D– 4D studies being performed for reassurance. Preliminary studies suggest that there may be some benefit, particularly in high-risk pregnancies such as families with prior anomalies or a history of anomalies, infertility patients, intended parents with surrogate pregnancies, and hospice patients carrying fetuses with fatal anomalies. As patients become consumers and desire 3D– 4D images of their healthy fetuses, physicians must perform research studies to determine the benefit and risk. The technology is advancing rapidly and will soon be available in inexpensive, hand-held devices.

Prenatal measurements, including abdominal circumference and femoral diaphysis length, have been traditionally used to estimate birth weight. These sonographic parameters, however, do not emphasize the contribution of soft-tissue mass for this assessment. Three-dimensional ultrasonography (3D US) can provide accurate fetal volume measurements as an index of soft tissue mass. This overview will summarize key articles that have examined the accuracy, precision, and reproducibility of fetal weight prediction by this method. For example, standardized mid-limb circumferences, obtained by 3D multi-planar imaging, have been used to predict birth weight. Other investigators have measured volumes of the entire arm or thigh during the late second and third trimesters. Birth weight prediction by 3D US, however, has been somewhat limited for clinical practice because soft tissue borders are not always well visualized from a transverse view at either end of the limb. Furthermore, additional time is required to manually trace soft tissue borders along the entire limb (up to 10 minutes each). A new soft tissue parameter, fractional limb volume, minimizes these limitations by allowing one to analyze a smaller portion of limb. This sub-volume is centered around the arm or thigh mid-point, and its boundaries are defined by 50% of the diaphyseal bone shaft length. Soft tissue borders are more clearly delineated in this region of interest, and this measurement only requires approximately 2 minutes to complete. Prospective studies are evaluating the utility of fractional limb volume for fetal weight prediction throughout pregnancy as well as growth assessment by the Rossavik model.

Routine three-dimensional ultrasound examination of the fetal face Merz E, Obstetrics and Gynecology, Krankenhaus Nordwest, Frankfurt/Main, Germany Objective: In contrast to conventional 2D ultrasound, which provides only one imaging mode to demonstrate the fetal face, 3D technology offers the ability to review the face in three different display modes: 1) the multiplanar mode, 2) the surface mode, and 3) the transparent mode. Methods: All routine 3D ultrasound examinations were performed using a Voluson 530 MT or 730 from GE-Kretztechnik, Austria. In every fetus, a volume of the face was acquired and stored on an optical disk (540 MB). Results: The simultaneous display of all three orthogonal sectional planes can accurately define the true facial profile, especially in severe oligohydramnions. The surface view opens up entirely new possibilities in the evaluation of surface anomalies such as facial dysplasia, cleft lip and palate, and cyclopia. The translucency mode provides a complete survey view of the fetal skull and the facial bones, similar to the appearance of an x-ray film. With the latest 4D ultrasound technology of Voluson 730, the fetus can be visualized three-dimensionally in real

Fetal three-dimensional ultrasound: Quantitative assessment Chang F, OB/GYN, National Cheng Kung University Medical Center, Tainan, Taiwan In this communication, we report our studies on the clinical use of quantitative 3D ultrasound (US) in assessing fetal organ volume and circulation. In brief, our studies can be divided into three phases as follows. Phase I: Fetal organ volumetry. Conventional 2D US has the limitation in assessing fetal organ volume, especially for the fetal organs with unique shapes. In other words, 2D US volumetry has to assume fetal organs have ideal geometric shapes, which is not correct. With the advent of 3D US, fetal organ volumetry can be assessed. We have reported a series of fetal organ volume assessments using 3D US, such as fetal liver, lungs, brain, cerebellum, and renal volumes, and

*Presenter of scientific paper with more than one author. S1

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proved that 3D US can achieve high reproducibility and accuracy in assessing fetal organ volumes. With these normal data of 3D fetal organ volumetry, fetal organ growth can be assessed more precisely, and thus abnormal conditions in fetal growth may be revealed. Phase II: Fetal weight prediction. To date, the accuracy of fetal weight prediction by 2D US remains to be improved. Using 3D US in assessing fetal upper arm volume and fetal thigh volume, we obtained better results in predicting fetal weight than using conventional 2D weight-predicting formulae. Other investigators have also confirmed our studies that fetal weight prediction may be improved by using 3D volumetry. Phase III: Vascularization and flow of fetal organs. The vascularization and blood flow of fetal organs cannot be assessed directly by 2D US. With the quantitative 3D power Doppler, the vascularization and flow of fetal organs can be evaluated directly in utero. The quantitative 3D power Doppler flow indexes, i.e., vascularization index (VI), flow index (FI), and vascularization-flow index (VFI), of fetal kidney, liver, brain, and placenta all significantly correlated with gestational age. In fetal growth restriction, abnormal VI, FI, and VFI may be detected. In conclusion, we believe that quantitative 3D US will be of help in assessing fetal well-being, either in organ growth or in fetal hemodynamics. Further studies of quantitative fetal 3D US are warranted.

IN HONOR OF DR. EUGENE STRANDNESS, LECTURES IN VASCULAR ULTRASOUND The work of D. Eugene Strandness, Jr., MD Zierler RE, Surgery, University of Washington, Seattle, WA D. Eugene Strandness, Jr., MD, died on January 7, 2002. At this 10th Congress of the WFUMB, it is appropriate to reflect on the many contributions Dr. Strandness made to the field of medical ultrasound. His initial work was based on the use of strain gauge plethysmography for the evaluation of arterial and venous disease, and it established physiologic testing as a valid and important clinical tool. The use of Doppler ultrasound for the transcutaneous assessment of vascular disease was pioneered by Dr. Strandness at the University of Washington in the 1960s. Based on this early work, the noninvasive vascular laboratory gradually became established as an indispensable resource for patient care and research. In the 1970s, Dr. Strandness and the bioengineering group at the University of Washington investigated the use of real-time B-mode scanning in the evaluation of the carotid artery bifurcation. An early case in which the internal carotid appeared patent on the B-mode image but occluded by arteriography led to the “duplex” concept of combining B-mode imaging and Doppler flow detection in a single instrument. The prototype duplex scanner built at the University of Washington gave rise to modern commercial duplex systems. Dr. Strandness also participated in the early efforts to credential vascular technologists and accredit vascular laboratories, which continue today. On the personal side, Dr. Strandness was both inspiring and challenging. He seemed to have an unlimited supply of enthusiasm and ideas. Those who worked closely with him will remember him as a strong friend and advocate, with a broad smile and a generous sense of humor. At the end of his life, Dr. Strandness was still actively engaged in his work and looking toward the future. Ongoing projects in his laboratory included the development of 3-dimensional ultrasound imaging, refining methods for vein graft surveillance, and the natural history of venous thromboembolism. In this era of large multicenter trials and program projects, it is exceedingly rare for one person to make a real difference in a medical field. Dr. Strandness is one of these rare people. His work will be remembered, and his presence among us will be missed.

Volume 29, Number 5S, 2003

Deep vein thrombosis (DVT): Lessons learned by duplex scanning Meissner MH, Surgery, University of Washington, Seattle, WA Venography has historically been the gold standard for the diagnosis of acute deep venous thrombosis (DVT). However, it is an invasive study requiring contrast and cannot be easily repeated. The development of duplex ultrasonography has permitted the course of an acute DVT to be followed over time and changes in the venous system to be related to the underlying pathophysiology and long-term clinical manifestations. Rather than being static structures that change little over time, it is now clear that the venous lumen is most often re-established after an episode of acute DVT. Approximately 55% of subjects will show complete recanalization within 6 to 9 months of thrombosis. However, ultrasound-documented recurrent thrombotic events are more common than clinically recognized and may occur in up to 52% of limbs. Thrombus evolution is thus a dynamic process with recanalization and recurrent thrombosis occurring as competing events. These ultrasound-documented processes are related to both the underlying degree of activated coagulation and the level of fibrinolytic inhibitors. Duplex ultrasound has also been critical in identifying those factors that lead to the development of the post-thrombotic syndrome. Although reflux resulting from valvular damage is the most important pathophysiologic feature of the post-thrombotic syndrome, limbs developing skin changes and ulceration are more likely to have a combination of reflux and obstruction than either abnormality alone. Long-term studies employing duplex ultrasound have shown the development of valvular incompetence to be related to the rate of recanalization, the degree of recanalization, and recurrent thrombotic events. Duplex ultrasound has thus become not only the most important diagnostic modality for acute DVT, but has also contributed to an understanding of the natural history that has important implications for treatment.

Surveillance of lower extremity bypass grafts Bandyk DF, Vascular Surgery, University of South Florida, Tampa, FL Duplex ultrasound graft surveillance can prevent graft failure by accurate detection and then repair of lesions prior to graft thrombosis occurring. Lower limb bypass grafts are prone to develop intrinsic lesions after implantation into the arterial circulation, despite careful operative technique. Duplex surveillance after infrainguinal vein bypass grafting should begin in the operating room because 15% of grafts will have lesions identified— conduit stenosis/fibrosis, inadequate valve lysis, anastomotic stenosis, and formation of platelet thrombus. The correction of graft lesions reduces the incidence of early thrombosis and the need for secondary interventions for residual stenosis. Vein bypasses with normal intraoperative duplex studies demonstrate ⬍1% incidence of graft thrombosis within the first 3 months of implantation; by comparison, residual duplex abnormalities result in thrombosis or revision in 15–25% of grafts. Duplex testing should be repeated prior to discharge, as the identification of a low-flow (⬍40 cm/s) graft may indicated need for anticoagulation. Testing at 4 – 6 weeks is recommended if pre-discharge scanning was not complete or a residual stenosis (PSV ⬍ 300 cm/sec, Vr ⬍ 3.5) identified. Repair of all stenoses with a PSV ⬎ 300 cm/s and Vr ⬎ 3.5 is recommended, especially if the lesion has progressed (increasing PSV) on serial scans, or a low (PSV ⬍ 40 cm/s) graft flow velocity is detected. The combination of high- and low-velocity criteria identifies bypasses at the highest risk for thrombosis. These threshold criteria identified all grafts at risk for thrombosis, and ⬍5% of lesions with high-velocity criteria regressed. Most graft stenoses are asymptomatic, and thus appropriate criteria of the “severe” stenosis should be applied when recommending