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3D – 4D Ultrasound in Obstetrics and Gynecology

J Obstet Gynecol India Vol. 56, No. 1 : January/February 2006 Pg 22-24

EDITORIAL The Journal ofObstetrics and Gynecology

of India

Three dimensional (3D) ultrasound (USG) and 4D i.e. realtime 3D are a natural development of the imaging technologyand were first demonstrated nearly 15 years ago, but arebecoming a clinical reality only now. Methods for 3Dreconstruction of CT and MRI images have achieved anadvanced state of development. 3D applications in ultrasoundhave lagged behind CT and MRI, because ultrasound data ismuch more difficult to render in 3D. Only in the past fewyears has the computing power of ultrasound equipmentreached a level adequate enough for the complex signalprocessing tasks needed to render ultrasound data in threedimensions. The clinical application of 3D ultrasound is likelyto advance rapidly, as improved 3D rendering technologybecomes more widely available 1.

The advantages of 3D and 4D ultrasound in certain areasare unequivocal. Most centres already apply its use in theworkup of fetal anomalies involving the face, limbs,thorax, spine and the central nervous system. The use ofthis technology in applying color doppler, in guiding needlesfor different puncture procedures as well in evaluatingthe fetal heart are currently under close research scrutiny.3D ultrasound helps the bonding between the parents andtheir future offspring, and consultants understand fetalpathology better and can plan postnatal interventions better.The multiplanar presentation and niche mode are quiteuseful to determine the extension –inside or outside theorgans, of nodules, cysts or tumors. The volumemeasurement is better assessed with 3D and we canperform studies that follow growth in order to decidemedical or surgical treatment. The VOCAL(R) makes itpossible to obtain a proper after-treatment follow-up offocal disorders in these small organs. Neovascularizationis clearly viewed with 3D USG and probably can suggestmalignant origin of a neoplasm. 3D USG offers a morecomprehensive image of anatomical structures andpathological conditions and also permits observation ofthe exact spatial relationships 1,2.

More studies are needed to demonstrate specificity andsensitivity of 3D and 4D USG. There are limitations toadequate visualization of fetal anatomy with 3D/4Dtechnology. If there is inadequate amniotic fluid surroundingthe fetus, or if the fetus has its face in the posterior position

in the uterus, there will be difficulty visualizing structuresand the face. 3D allows a simultaneous display of multiplesequential parallel planes of the fetal structures, but there issome uncertainty if an isolated image in one of the multi-slice images represents the exact level of a fetal structure.Another problem is the creation of false expectations andoverall the medical value is limited. Pregnant women willask for a picture of their fetus like those they have seen inadvertisements and put pressure on the scanning centres.Such is the demand in the United States that technicianoperated 4D ultrasounds are readily available in scanningbooths in shopping malls, enabling parents to purchase avideo of their moving fetus. This creates problems later onwhen women, having already had such USG, do not realisethat they need a targeted anomaly scan 3-5.

Endometrial thickness, endometrial pattern, pulsatility index(PI) and resistance index (RI) of uterine vessels, endometrialvolume, vascularization index (VI), flow index (FI) andvascularization flow index (VFI) of endometrial and sub-endometrial regions have been studied by 3D with powerdopplers on the day of oocyte retrieval in patients undergoingthe first IVF cycle. Uterine RI, endometrial VI and VFI weresignificantly lower in the pregnant group than in the non-pregnant group. There was a nonsignificant trend of higherimplantation and pregnancy rates in patients with absentendometrial or subendometrial blood flow. The number ofembryos replaced and endometrial VI were the only twopredictive factors for pregnancy. Endometrial and sub-endometrial blood flows measured by 3D power dopplerultrasound were not good predictors of pregnancy if theywere measured at one time-point during IVF treatment 6,7. Asimilar study noted that endometrial volume decreasedsignificantly after hCG injection in women who conceived,but not in those who did not.

Along with crown-rump length (CRL), the size (diameter)of embryonic structures such as gestational sac (GS) andyolk sac (YS) may have prognostic value for embryonicdevelopment. First trimester volume calculations of thesestructures using transvaginal 3D USG technic have beendone. Volumetry of GS proved to be a sensitive predictorfor pregnancy outcome and can be a good supplement toCRL measurements. However, no statistically significant

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difference was found when YS volumes of normal andabnormal pregnancies were compared. Specificity, sensitivity,positive and negative predictive values of GS volumes andCRL were similar. Mean YS/GS ratios also had goodpredictive values (P <0.05) 8.

4D was successfully used to perform amniocentesis, CVS,cordocentesis, and intrauterine transfusion. Using 4D USGguidance, most procedures were performed within 5 minutesand with a 100% success rate, even in cases involving severeoligohydramnios, thin placenta and narrow umbilical veins.Moreover, there were no serious complications during orafter any procedure. This appeared to contribute to theaccuracy of needle placement by eliminating the lateralizationphenomenon when a fixed needle guide attachment was used.Needle tip visualization was seen in each orthogonal plane inmost freehand 4D amniocentesis cases 9,10.

Presently, both 2D and 4D methods are required for theassessment of early fetal motor development and motorbehaviour. Several movement patterns, such as sidewaybending, hiccup, breathing movements, mouth opening andfacial movements could be observed only by 2D USG 11.Isolated hand movement and subtypes of hand movementswere easily recognized by 4D USG. All subtypes of hand tohead movement can be seen from 13 weeks of gestationwith fluctuating incidence. Facial activities and differentforms of expression are easily recognized. 4D USG is superiorover real time 2D USG for qualitative, but inferior forquantitative analysis of hand movements. 4D USG makes itpossible to determine the exact direction of the fetal hand,but the exact number of each type of hand movements canstill not be determined.4D USG is superior to 2D USG in theevaluation of complex facial activity and expression. Amongfacial activities observed by 4D USG, simultaneous eyelidand mouth movements dominate between 30 and 33 weeksof gestation. Pure mouth movements such as mouth opening,tongue expulsion, yawning and pouting are present, but at asignificantly lower incidence. Facial expressions such assmiling and scowling can be precisely observed using 4DUSG 12. There were no movements observed in fetal life thatwere not present in neonatal life; the Moro reflex was presentonly in neonates 13.

Inclusion of 3D and 4D ultrasound imaging in the examinationof cleft lip and/or palate, allows easier and more rapidscreening and more precise evaluation of the different cleftconstituents 14. 3D USG can be a reliable technic forvisualizing most fetal cranial sutures and fontanels. Byperforming a sagittal and a transverse scan, most of thesutures and fontanels can be made visible during the secondhalf of pregnancy. Visualization depends on gestational age15. Gray-scale and color doppler dynamic 3D displays and

multiplanar views used to assess cardiac gating and cardiacmorphology demonstrate clinically useful 4D images of thefetal heart. The reconstruction of 3D and multiplanar viewsprovided additional views not obtainable by 2D imaging 16.3D echocardiography can provide estimates of ventricularvolume and function and may in future be used for evaluationof fetuses with congenital heart disease and cardiacdysfunction 17. Spatio-temporal image correlation incombination with color doppler USG is a promising newtool for multiplanar and 3D/4D rendering of the fetal heart.Limitations may be found later in gestation in fetuses withlarge hearts and early in gestation as a result of lowdiscrimination of signals. In addition, insonation perpendicularto the structure of interest does not image color dopplersignals and should be avoided during acquisition 18. There isa potential value of 3D power doppler in prenatal diagnosisand monitoring of pregnancies complicated by large,vascularized placental chorioangioma 19. No significantdifferences are shown between 2D and 4D ultrasoundplacental scanning 20.

3D power doppler ultrasound provides a useful tool toinvestigate intratumor vascularization and volume of cervicalcancer 21. Alterations of 3D USG derived vascular indiceswere found in patients with cervical cancer and somevascular indices proved to be associated with tumor size 22.In a small group of pelvic masses that appear malignant onB-mode USG, the use of 3D quantification of tumorvascularity yields a diagnostic accuracy that is similar tothat of subjective evaluation of vascularity 23. 3D power-doppler imaging does not have a better diagnosticperformance than 2D power doppler imaging in thediscrimination of benign from malignant complex adnexalmasses 24. Endometrial volume and thickness measurementsby 3D and 2D USG, in patients with postmenopausalbleeding, show good reproducibility but the reproducibilityof 3D ultrasound is better 25. Rectovaginal septal defects arereadily identified on translabial 3D USG as a herniation ofrectal wall and its contents into the vagina. Approximatelyone third of clinical rectoceles do not show a sonographicdefect, and the presence of a defect is associated with age,not parity 26. While 3D pelvic floor imaging is a field that isstill in its infancy, it is already clear that the method hasopened up entirely new opportunities for the observation offunctional anatomy.

The exact applicability of 3D and 4D USG is yet to beascertained. The American Institute of Ultrasound in Medicinehas convened a panel of physicians and scientists with interestand expertise in 3D USG to discuss the current diagnosticbenefits and technical limitations in obstetrics and gynecologyand to consider the utility and role of this type of imaging inclinical practice now and in the future 27.

Editorial

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27. Benacerraf BR, Benson CB, Abuhamad AZ et al. Three- and 4-dimensional ultrasound in obstetrics and gynecology: proceedings ofthe american institute of ultrasound in medicine consensusconference. J Ultrasound Med 2005;24:1587-97.

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