c Original Contribution
THREE-DIMENSIONAL ULTRASOUND IN THE ASSESSMENT OF FETALCEREBELLAR TRANSVERSE AND ANTERO-POSTERIOR DIAMETERS
CHIUNG-HSIN CHANG,* FONG-MING CHANG,* CHEN-HSIANG YU,* HUEI-CHEN KO, andHSI-YAO CHEN
*Department of Obstetrics and Gynecology and Research Institute of Behavior Medicine, National Cheng KungUniversity Medical College, Tainan, Taiwan; and Department of Obstetrics and Gynecology, National Taiwan
University Medical College, Taipei, Taiwan
(Received 11 May 1999; in final form 9 August 1999)AbstractFetal cerebellum scanning by prenatal ultrasound (US) is very important for early detection of fetalcentral-nervoussystem anomaly, as well as for the determination of gestational age (GA). Due to the small organsize and the unique shape of the fetal cerebellum (CL), accurate measurement of the dimensions of CL bytwo-dimensional (2-D) US is not easy if the appropriate plane cannot be reached. With the advent of three-dimensional (3-D) US, the disadvantages of 2-D US in assessing the fetal CL dimensions can be avoided. Thepurpose of this study was to assess the fetal cerebellar transverse diameter (CTD) and cerebellar antero-posteriordiameter (CAD) using 3-D US. First, we compared the reproducibility of 2-D and 3-D US on the assessment offetal cerebellar dimensions. Second, we prospectively measured CTD and CAD in 223 healthy fetuses using across-sectional design with an attempt to establish the normal growth charts of fetal CL. Our results showed 3-DUS is superior to 2-D US in the reproducibility test of fetal cerebellar dimensions. In addition, with GA as thedependent variable, polynomial regression analysis showed that the best-fit equations for both CTD vs. GA andCAD vs. GA were the first-order. The best-fit predictive equation of GA by CTD was GA (week) 5 9.0281 10.58533 3 CTD (mm) (r 5 0.95, n 5 223, SE 5 1.82 weeks, p < 0.0001), and the best-fit predictive equation ofGA by CAD was GA (week) 5 10.855 1 1.1672 3 CAD (mm) (r 5 0.82, n 5 223, SE 5 3.41 weeks, p < 0.0001).Furthermore, all the correlation coefficients of CTD or CAD vs. the common fetal growth indexes were alsohighly significant (all p < 0.0001). In conclusion, our data of fetal CL dimensions assessed by 3-D US may serveas a useful reference in assessing fetal CL growth, dating GA or detecting fetal CL anomalies. 2000 WorldFederation for Ultrasound in Medicine & Biology.
Key Words: Three-dimensional ultrasound, Fetus, Cerebellar transverse diameter, Cerebellar antero-posteriordiameter.
Accurate assessment of the fetal organ dimensions byprenatal ultrasound (US) is very crucial in the evaluationof fetal growth and maturation (Chitty et al. 1994a,1994b, 1994c). However, using two-dimensional (2-D)US to precisely assess the growth of small organs, suchas cerebellum (CL), is not an easy task. Although thefetal CL is scanned now for screening the central-ner-voussystem (CNS) anomaly (Benacerraf et al. 1989;
Persutte et al. 1997; Robins et al. 1998) and for deter-mining the gestational age (GA) (Goldstein et al. 1987).In fact, to measure the accurate largest diameters offetal CL in an attempt to determine the cerebellar trans-verse diameter (CTD) (Goldstein et al. 1987) or cerebel-lar antero-posterior diameter (CAD) (Smith et al. 1986)in utero is relatively difficult by 2-D US. Because thefetal CL is a small organ with a unique shape, to measurethe largest diameters of CL by 2-D US is prone tosubstantial errors if the accurate plane for the measure-ment of CTD and CAD is not reached.
With the advent of three-dimensional (3-D) US, itbecomes an easy technique to access any possible viewsand planes whenever the scanned 3-D volume is obtained(Kelly et al. 1992; Kuo et al. 1992; Lee et al. 1994; Merzet al. 1995; Riccabona et al. 1996). Moreover, precise
Address correspondence to: Dr. Fong-Ming Chang, Departmentof Obstetrics and Gynecology, National Cheng Kung University Med-ical College, 138 Victory Road, Tainan 70428 Taiwan. E-mail:firstname.lastname@example.org
This paper has been reported in part as a poster in the 1998Annual Meeting of American Institute of Ultrasound in Medicine(AIUM) in Boston, MA, March 1998.
Ultrasound in Med. & Biol., Vol. 26, No. 2, pp. 175182, 2000Copyright 2000 World Federation for Ultrasound in Medicine & Biology
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quantitative measurement of fetal organ dimensions be-comes feasible when the 3-D volume is retrieved (Lee etal. 1994; Merz et al. 1995; Riccabona et al. 1996). Inaddition to our primary application of 3-D US in obstet-rics (Kuo et al. 1992), we have recently reported a seriesof fetal organ assessments using 3-D US; for example,fetal liver, heart, upper arm and thigh, from early secondtrimester to third trimester, and obtained more accurateresults (Chang et al. 1997a, 1997b, 1997c; Liang et al.1997).
Because 3-D US can overcome the obstacle of 2-DUS in reaching the accurate plane for measuring fetal CLdimensions, this study was undertaken to investigate twopurposes. First, we compared the reproducibility of 2-Dand 3-D US in the assessment of fetal cerebellar dimen-sions. Second, we attempted to establish the normalgrowth charts of fetal cerebellar transverse diameter(CTD) and cerebellar antero-posterior diameter (CAD)during gestation, using the new modality of 3-D US.
MATERIALS AND METHODS
SubjectsThe inclusion criteria of subjects in this study were
as follows: 1. patients with defined last menstrual period(LMP) and confirmed by a dating US examination inearly pregnancy, either by crown-rump length (CRL) orbiparietal diameter (BPD); 2. singleton pregnancies withGA ranging from 20 to 40 weeks; 3. healthy pregnancieswithout maternal or fetal complications; and 4. the USexamination of each fetus being selected only once inthis series (a cross-sectional study). The setting was atthe Ultrasound Unit of the Department of Obstetrics andGynecology, National Cheng Kung University Hospital.All the fetuses scanned in this study were followed todelivery to ensure that they were born healthy.
3-D ultrasonographyWe used the 3.5- or 5-MHz transabdominal Volu-
son transducer of the 3-D US equipment (Combison530D, Kretz-Technik, Zipf, Austria) for fetal cerebellarscanning. The details of the 3-D US scanning were aspreviously described (Chang et al. 1997a, 1997b, 1997c;Liang et al. 1997; Merz et al. 1995). Initially, the high-resolution, real-time 2-D US scanner was applied forscanning of the typical plane for fetal CL described bySmith et al. (1986). Then, we turned on the 3-D trans-abdominal Voluson sector transducer to scan the cere-bellar hemispheres and vermis with the normal velocitymode (which swept 40 automatically within 4 s) whenthe fetus was at rest. The 3-D volume can be evaluatedslice by slice in any arbitrary plane. The built-in 3-Dview software permitted the simultaneous display of the3-D volume in three perpendicular planes on the monitor.
As shown in Fig. 1, when the fetal cerebellum wasrotated to a horizontal position, the cerebellar transversediameter (CTD) was measured at the largest diameter bytracing axially in the cross-sectional planes of 3-D US. Ina similar manner, the cerebellar antero-posterior diame-ter (CAD) was measured at the largest diameter bytracing axially in the cross-sectional planes of 3-D US.The data set was further saved into the built-in computeror in the laser disks for further retrieval and processing,such as volume determination or 3-D image reconstruc-tion.
In addition, we measured the fetal biparietal diam-eter (BPD), occipito-frontal diameter (OFD), head cir-cumference (HC), abdominal circumference (AC) andfemur length (FL) according to the methods described inprevious reports (Chitty et al. 1994a, 1994b, 1994c;Chang et al. 1996, 1998). Estimated fetal weight (EFW)was calculated from the weight-predicting equation com-posed of BPD, AC and FL, reported by Hsieh andcolleagues, derived from a Taiwanese population (Hsiehet al. 1987).
StatisticsAll the data of cerebellar measurements were put
into an IBM-compatible personal computer (PC) for finalanalysis. We used the SPSS-PC statistical package (Chi-cago, IL) to perform statistical calculation. Paired t-tests(with mean, standard deviation, SD, and standard error,SE, of the differences) and correlation coefficients wereused to compare the superiority of reproducibility (Daw-
Fig. 1. 3-D US in the measurement of fetal cerebellar transversediameter (CTD, between the black and white arrow head in theupper-left panel) and cerebellar antero-posterior diameter(CAD, between the white arrows in the upper-left panel). Whenthe 3-D volume was scanned and retrieved, the most appropri-ate plane for measuring the CTD and CAD was reached afterrotating the scans in the three orthogonal planes in the upper-left, upper-right, and lower-left panels. The relative position ofthe plane is displayed simultaneously in the lower-right panel.
176 Ultrasound in Medicine and Biology Volume 26, Number 2, 2000
son-Saunders and Trapp 1994; Sladkevicius and Valen-tin 1995). Linear regression and the correlation analysiswere calculated to test the relationship between the in-dependent and dependent variables. With GA as depen-dent variable, polynomial regression analysis was calcu-lated from the first order to the fourth order to find thebest-fit equations to obtain the predicted values of GAusing CTD and CAD as the independent variables. Sim-ilarly, to compare with previous series (Goldstein et al.1987; Smith et al. 1986) in which GA was used as theindependent variable, polynomial regression analysiswas calculated from the first order to the fourth order tofind the best-fit equations to obtain the predicted valuesof CTD and