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(Radiology. 1999;211:441-446.)
© RSNA, 1999

Obstetric Imaging

Fetal Abnormalities: Evaluation with Real-time–Processible Three-dimensional US—Preliminary Report1

Kazunori Baba, MD, PhD, Takashi Okai, MD, PhD, Shiro Kozuma, MD, PhD and Yuji Taketani, MD, PhD

1 From the Departments of Biomedical Engineering (K.B.) and Obstetrics and Gynecology (S.K., Y.T.), Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; and the Department of Obstetrics and Gynecology, Aiiku Hospital, Tokyo, Japan (T.O.). Received August 28, 1997; revision requested October 17; final revision received July 24, 1998; accepted October 14. Address reprint requests to K.B.


   Abstract
TOP
 Abstract
Introduction
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
PURPOSE: To assess the usefulness of real-time–processible three-dimensional (3D) ultrasonography (US) in the evaluation of fetal abnormalities.

MATERIALS AND METHODS: The apparatus comprised a conventional US scanner with a specially designed unit for real-time–processible 3D US and a transabdominal 3D probe. A 3D US examination was performed in 19 women with abnormalities of the fetus (13–35 weeks gestation) that had been detected at two-dimensional (2D) US.

RESULTS: Thirty-six abnormalities were detected with conventional 2D US, real-time–processible 3D US, or both in 19 fetuses with abnormalities. Seventeen (47%) of the 36 abnormalities were demonstrated and confirmed clearly with real-time–processible 3D US, and nine of these had been seen with 2D US. Eighteen intrafetal abnormalities had been demonstrated clearly with 2D US, but 14 of these could not be demonstrated with real-time–processible 3D US.

CONCLUSION: Real-time–processible 3D US is useful for evaluating fetal abnormalities as a supplement to 2D US, particularly for abnormalities of the face, ears, fingers, and anatomic axis, but real-time–processible 3D US is unlikely to be helpful for detecting intrafetal abnormalities except for skeletal abnormalities and some pathologic changes with fluid accumulation.

Index terms: Fetus, abnormalities, 856.87 • Fetus, US, 856.87 • Ultrasound (US), three-dimensional, 856.12989, 856.87


   Introduction
TOP
 Abstract
 Introduction
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Three-dimensional (3D) fetal images obtained with 3D ultrasonography (US) have been shown to facilitate the diagnosis of fetal abnormalities (1–16). In conventional 3D US, however, 3D images cannot be obtained immediately after scanning, because all 3D space data must be entered into a computer, and a 3D data set must be constructed, followed by complex and time-consuming procedures (selections of region of interest and of viewing direction and threshold setting).

In real-time–processible 3D US performed with the volume-rendering technique, the ultrasound beam itself is regarded as a projection ray, and volume ray tracing is conducted in each case in real time; this technique generates a 3D image immediately after several seconds of scanning with simple settings (starting depth and opacity) (17). Real-time–processible 3D US provides not only surface-rendered but also transparent images with selection of an appropriate opacity level. This method would not be applicable to all fetuses because the viewing direction is limited to that of the probe (17). In the present study, real-time–processible 3D US, in combination with two-dimensional (2D) US, was assessed for its usefulness in evaluating fetal abnormalities.


   MATERIALS AND METHODS
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
The apparatus comprised a conventional US scanner (model SSD-1700; Aloka, Tokyo, Japan) with a specially designed unit for real-time–processible 3D US and a transabdominal 3D probe. The 3D probe has a built-in electronic-scanning convex probe (3.5-MHz) that is swung by means of a motor to the direction of the section width. In 5.5 seconds, an area 7 x 7 cm on the abdominal wall of the subject can be scanned with a 60° angle of divergence.

A real-time–processible 3D US examination was performed in 19 women with abnormalities of the fetus that had been detected with conventional 2D US (including two cases of a twin with fetal abnormalities [case 5 and case 19]) (Table 1). Gestational ages at examination were 13–35 weeks. The women had been referred to one of the authors (K.B., T.O., S.K.), who had more than 15 years of experience in obstetric and gynecologic US.


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  		TABLE 1. Fetuses Examined with Real-time–Processible 3D US
 
All fetuses with abnormalities confirmed with 2D US were included in this study. After the diagnosis with conventional 2D US, the same examiner performed real-time–processible 3D US. The depth at which volume ray tracing for volume rendering was started was set first on a 2D US image obtained with the 3D probe without the use of mechanical scanning, so as to eliminate any unnecessary images of overlying structures such as the abdominal and uterine walls (17). The 3D probe was then held manually on the abdominal wall, and fanlike mechanical scanning was performed to obtain 3D fetal images. Informed consent was obtained from each pregnant mother, and the principles of the Declaration of Helsinki were followed.

All images were videotaped and viewed later by all four authors together in a group. The results of real-time–processible 3D US scanning for each abnormality were scored as follows: grade 1, detected with real-time–processible 3D US but not with 2D US; grade 2, suspected at 2D US and confirmed with real-time–processible 3D US; grade 3, detected with 2D US, with further information provided at real-time–processible 3D US; grade 4, detected with 2D US but only suspected at real-time–processible 3D US; or grade 5, detected with 2D US but not with real-time–processible 3D US.


   RESULTS
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Thirty-six abnormalities were disclosed with 2D US, real-time–processible 3D US, or both in 19 fetuses with abnormalities (Table 2). Of the 36 fetal abnormalities, eight (22%) that had not been identified adequately at 2D US were disclosed with real-time–processible 3D US (scored 1 or 2). For nine abnormalities (25%) diagnosed at 2D US, real-time–processible 3D US gave further information (scored 3). Nineteen abnormalities (53%) were diagnosed only with 2D US (scored 4 or 5). The authors were unanimous in the scoring for each abnormality.


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  		TABLE 2. Results of Real-time–Processible 3D US Scanning
 
In those fetuses with hydramnios, realistic 3D surface images were obtained with real-time–processible 3D US (Figs 1–5). In the fetus in case 1, real-time–processible 3D US showed a flat nose and slanted palpebral fissures, which suggested Down syndrome and which had been overlooked at 2D US. In the fetus in case 4, 2D US disclosed polydactyly of the foot, but real-time–processible 3D US could not depict it because of the limited viewing direction.



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  		Figure 1a. Case 2. (a) A 2D US image shows opening of the mouth and micrognathia (arrow) in a fetus at 34 weeks gestation. (b) Real-time–processible 3D US image of the same fetus shows these findings more clearly and also shows dysplastic ear (arrow).

 


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  		Figure 1b. Case 2. (a) A 2D US image shows opening of the mouth and micrognathia (arrow) in a fetus at 34 weeks gestation. (b) Real-time–processible 3D US image of the same fetus shows these findings more clearly and also shows dysplastic ear (arrow).

 


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  		Figure 2a. Case 4. (a) Longitudinal view of the profile of the fetus with holoprosencephaly shows proboscis (arrow) at 29 weeks gestation. (b) Real-time–processible 3D US facial image of the same fetus shows proboscis (arrow) and cyclopia (arrowhead) more clearly.

 


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  		Figure 2b. Case 4. (a) Longitudinal view of the profile of the fetus with holoprosencephaly shows proboscis (arrow) at 29 weeks gestation. (b) Real-time–processible 3D US facial image of the same fetus shows proboscis (arrow) and cyclopia (arrowhead) more clearly.

 


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  		Figure 3. Case 3. Real-time–processible 3D US image obtained at 32 weeks gestation in a fetus suspected of having a chromosomal abnormality shows overlapping index finger (arrow) and severe flexion of the right wrist (arrowhead). Although these abnormalities could be detected or suspected at 2D US, real-time–processible 3D US showed the abnormalities more clearly.

 


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  		Figure 4. Case 8. Real-time–processible 3D US image of a fetus with short-limb dysplasia at 28 weeks gestation shows clubfoot (arrow). Clubfoot, which was virtually undetectable with 2D US, was detected only with real-time–processible 3D US. A = fetal abdomen, C = umbilical cord.

 


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  		Figure 5. Case 4. Real-time–processible 3D US image of omphalocele (arrow) clearly shows the extent of herniation.

 
In five fetuses with oligohydramnios, surface-rendered images were difficult to obtain; however, on real-time–processible 3D US images with low opacity (17), bones and the skin surface were silhouetted. Massive subcutaneous edema was evident in the fetus in case 6 (Fig 6), and a short and curved femur could been seen in the fetus in case 9 (Fig 7).



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  		Figure 6. Case 6. Real-time–processible 3D US image of head and forearm of the fetus with massive subcutaneous edema at 22 weeks gestation. Arrows indicate skin surface over scalp.

 


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  		Figure 7. Case 9. Real-time–processible 3D US image of a fetus with short-limb dysplasia at 25 weeks gestation was obtained by setting the opacity level low and shows short and curved femur (F). V = vertebrae.

 
Defects of vertebral arches (spina bifida) in a fetus at 35 weeks gestation were apparent on a real-time–processible 3D US image obtained by setting the starting depth (17) under the skin to eliminate any image of the skin (Fig 8). For the fetus with ascites (case 12), surface-rendered images of the liver and bowel were obtained by setting the starting depth in the ascites to eliminate the unnecessary image of the fetal abdominal wall (Fig 9).



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  		Figure 8. Case 10. Real-time–processible 3D US image of the spine of a fetus at 35 weeks gestation shows spina bifida (arrow and below).

 


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  		Figure 9. Case 12. Real-time–processible 3D US intraabdominal image obtained in the fetus with ascites (arrows) at 30 weeks gestation. A = abdominal wall, B = bowel, L = liver, U = urinary bladder.

 
On the basis of a popular definition in Japan (18), intrauterine growth retardation was diagnosed with fetal biometry at 2D US in four fetuses, including one twin; the fetal weights were estimated to be below the mean -1.5 SD value of the Japanese fetal growth standard curve (19). This diagnosis was not possible with real-time–processible 3D US, which demonstrated only discordant growth between discordant twins.

Except for the small stomach in the fetus in case 1, the US findings were confirmed with postnatal or postmortem follow-up in cases 1–4, 8–13, and 19. The US finding of a small stomach might be a temporary finding in utero. Except for case 1, no chromosome tests were performed because of patient refusal. Spondyloepiphyseal dysplasia was diagnosed in the fetus in case 8 after birth. A regular autopsy was performed on the fetus in case 9, but the type of short-limb dysplasia was unclear. In case 4, after birth of the neonate, an imperforate anus was found that had been missed at conventional 2D US and real-time–processible 3D US. Postnatal follow-up examinations were not possible in the neonates in cases 5–7 and 14–18; consequently, the US findings were not confirmed after birth.


   DISCUSSION
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
Compared with conventional 3D US, real-time–processible 3D US more easily generates realistic 3D fetal images in a shorter time for fetuses surrounded by adequate amniotic fluid. Although the viewing direction is limited to that of the probe, the desired viewing direction for fetuses with hydramnios is possible in most cases by selecting the proper position and direction of the probe on the abdominal wall.

In particular, the face, ears, and fingers, which are difficult to discern on 2D US images, can be seen realistically with real-time–processible 3D US. Abnormal severe flexion, distortion of the anatomic axis, such as clubfoot, and abnormal limb curvature may be diagnosed more easily and accurately with real-time–processible 3D US than with 2D US. It is necessary to distinguish real abnormal findings, such as overlapping fingers and severe flexion of the limb, from temporary findings by observing the fetus repeatedly. The 3D fetal images can be obtained in succession at 3-second intervals with real-time–processible 3D US, thus ensuring correct diagnosis.

Surface-rendered images of the fetus with oligohydramnios and the fetus with thin skin or thin subcutaneous tissue were difficult to obtain with real-time–processible 3D US. Real-time–processible 3D US essentially failed to depict intrafetal abnormalities except those of the skeleton and some pathologic changes with fluid accumulation. Fetal growth could not be evaluated, except in cases such as discordant twins and fetuses with severe short-limb dysplasia, because fetal biometry is not possible with real-time–processible 3D US.

Merz et al (9) examined 204 patients with fetal malformation by using conventional 3D US scanners that were capable of arbitrary section display, simultaneous display of three orthogonal sections, and 3D image display. The 3D US technique was found to effectively demonstrate fetal defects in 62% (127 of 204 patients), compared with 2D US.

In our experience with a limited number of fetal abnormalities, real-time–processible 3D US was useful for detecting, confirming, and clearly depicting 17 (47%) of 36 fetal abnormalities (scored 1, 2, or 3) when the technique was applied to fetuses suspected of having abnormalities on the basis of 2D US findings. These results were obtained despite the limited viewing direction with the technique and despite the absence of functions such as arbitrary section display.

The 3D US diagnosis could have been influenced by the 2D US results in our study because both the 2D US examination and the real-time–processible 3D US examination were performed by the same individual. However, performing 2D US before real-time–processible 3D US scanning is essential to determine the proper position for 3D scanning and the proper starting depth (17); consequently, real-time–processible 3D US examination is impossible to perform without the 2D images.

The results of our study demonstrate that real-time–processible 3D US is useful for evaluating fetal abnormalities as a supplement to 2D US, particularly for abnormalities of the face, ears, fingers, and anatomic axis. It is easy to switch back and forth between 2D US and 3D images with real-time–processible 3D US. By using real-time–processible 3D US in conjunction with 2D US, a perinatal diagnosis may be determined speedily and accurately. Real-time–processible 3D US surface-rendered images easily provide good visual perception not only to physicians but also to parents and thus may provide assurance that the parents see the abnormality.


   Footnotes
 
Abbreviations: 2D = two-dimensional 3D = three-dimensional

Author contributions: Guarantors of integrity of entire study, K.B., T.O., S.K., Y.T.; study concepts and design, K.B., T.O., S.K., Y.T.; definition of intellectual content, K.B., T.O., S.K., Y.T.; literature research, K.B.; clinical studies, K.B., T.O., S.K., Y.T.; data acquisition and analysis, K.B., T.O., S.K., Y.T.; statistical analysis, K.B.; manuscript preparation, K.B.; manuscript review, K.B., T.O., S.K., Y.T.


   References
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

  1. Baba K, Satoh K, Sakamoto S, Okai T, Ishii S. Non-invasive three-dimensional imaging system for the fetus in utero. In: Maeda K, eds. The fetus as a patient '87. Amsterdam, the Netherlands: Excerpta Medica, 1987; 111-116.
  2. Baba K, Furukawa T, Ishii S, Okai T, Satoh K, Sakamoto S. Ultrasonic three-dimensional imaging system for a fetus in utero. In: Maeda K, Hogaki M, Nakano H, eds. Computers and perinatal medicine. Amsterdam, the Netherlands: Excerpta Medica, 1990; 83-92.
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  4. Lee A, Deutinger J, Bernaschek G. Voluvision: three-dimensional ultrasonography of fetal malformations. Am J Obstet Gynecol 1994; 170:1312-1314.[Medline]
  5. Pretorius DH, Nelson TR. Prenatal visualization of cranial sutures and fontanelles with three-dimensional ultrasonography. J Ultrasound Med 1994; 13:871-876.[Abstract]
  6. Kelly IG, Gardener JE, Brett AD, Richards R, Lees WR. Three-dimensional US of the fetus. Radiology 1994; 192:253-259.[Abstract/Free Full Text]
  7. Hamper UM, Trapanotto V, Sheth S, DeJong MR, Caskey CI. Three-dimensional US: preliminary clinical experience. Radiology 1994; 191:397-401.[Abstract/Free Full Text]
  8. Steiner H, Staudach A, Spitzer D, Schaffer H. Three-dimensional ultrasound in obstetrics and gynaecology: technique, possibilities and limitations. Hum Reprod 1994; 9:1773-1778.[Abstract/Free Full Text]
  9. Merz E, Bahlmann F, Weber G. Volume scanning in the evaluation of fetal malformations: a new dimension in prenatal diagnosis. Ultrasound Obstet Gynecol 1995; 5:222-227.[Medline]
  10. Blaas HG, Eik-Nes SH, Kiserud T, Berg S, Angelsen B, Olstad B. Three-dimensional imaging of the brain cavities in human embryos. Ultrasound Obstet Gynecol 1995; 5:228-232.[Medline]
  11. Lee A, Kratochwil A, Deutinger J, Bernaschek G. Three-dimensional ultrasound in diagnosing phocomelia. Ultrasound Obstet Gynecol 1995; 5:238-240.[Medline]
  12. Pretorius DH, Nelson TR. Fetal face visualization using three-dimensional ultrasonography. J Ultrasound Med 1995; 14:349-356.[Abstract]
  13. Lee A, Deutinger J, Bernaschek G. Three-dimensional ultrasound: abnormalities of the fetal face in surface and volume rendering mode. Br J Obstet Gynaecol 1995; 102:302-306.[Medline]
  14. Budorick NE, Pretorius DH, Nelson TR. Sonography of the fetal spine: technique, imaging, findings and clinical implications. AJR 1995; 164:421-428.[Abstract/Free Full Text]
  15. Nelson TR, Pretorius DH. Visualization of the fetal thoracic skeleton with three-dimensional sonography. AJR 1995; 164:1485-1488.[Abstract/Free Full Text]
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  17. Baba K, Okai T, Kozuma S, Taketani Y, Mochizuki T, Akahane M. Real-time processable three-dimensional US in obstetrics. Radiology 1997; 203:571-574.[Abstract/Free Full Text]
  18. Takeda Y, Muraoka M, Nakabayashi M, Iwashita M. New aspects in the cause and pathophysiology of intrauterine growth retardation. In: Maeda K, eds. The fetus as a patient '87. Amsterdam, the Netherlands: Excerpta Medica, 1987; 231-246.
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