2011 International Conference on Instrumentation, Communication, Information Technology and Biomedical Engineering

8-9 November 2011, Bandung, Indonesia

Comparison Studies of 2D and 3D Ultrasound

Biparietal Diameter for Gestational Age Estimation

Lai Khin Wee1, 2

, Lee Mee Yun2, Tan Lee See

2 and Eko Supriyanto

2

1Institute of Biomedical Engineering and Informatics, Technische Universität Ilmenau, Ilmenau, Germany

(Tel: +4915774853251; E-mail: khin-wee.lai@tu-ilmenau.de) 2Department of Clinical Science and Engineering, Universiti Teknologi Malaysia, Skudai 81310, Johor, Malaysia

(Tel: +60167763004; E-mail: eko@utm.my)

Abstract — Accurate determination of gestational age is

fundamental to fetal growth assessment, either clinically or by

ultrasound evaluation. The antenatal measurement of the fetal

biparietal diameter (BPD) by ultrasound has been used to predict

fetal gestational age. The performance of conventional two-

dimensional (2D) ultrasonograhpy (US) measurement and

proposed Visualization toolkit, VTK programmable interactive

three-dimensional (3D) for gestational age prediction is

investigated in this paper. Data has been acquired in the form of

video clip and DICOM file. Three-dimensional BPD

reconstructions were visualized using open-source object-

oriented Visualization toolkit, VTK. Ten trial measurements

were taken for each method. Descriptive analysis of both UTV

380 and DICOM were calculated. Computed mean and standard

deviation for both measurements are 47.326±0.643345mm (UTV

380) and 47.099±0.377343mm (DICOM). Computed mean and

standard deviation for 2D measurement is 46.290±0.455705mm.

Using 3D volume acquisition, it is feasible to perform and

interpret a structural survey with higher accuracy in which a 2D

survey is performed. Further research is necessary to standardize

the acquisition of volumes to minimize artifacts and produce

uniform images.

Keywords - Gestational age, biparietal diameter,

ultrasonography, Visualization toolkit, reconstruction

I. INTRODUCTION

Monitoring fetal growth and assessing its predictors have important place in antenatal care management. Accurate prediction of gestational age is clinically important. In the second and third trimesters, fetal head, body, and extremity measurements have been commonly used to assess gestational age. Those parameters most commonly measured include biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL). The biparietal diameter is among the most accurate second trimester measures of gestational age as fetal head grows continually and at specific rates throughout gestation. BPD had been used as a predictor of gestational age and also accurately predicts the date on which the baby will be born [1]. If the gestational age is already known, then the BPD can be used to evaluate fetal growth. In cases of symmetrical growth retardation, the fetal BPD will fall below the 10th percentile.

BPD was obtained before the procedures. The BPD was measured in the transaxial plane, from the outer edge of the skull to the inner edge of the other side of the skull using the

thalami, cavum septum pellucidum, and the atrial level of the lateral ventricles as internal reference landmarks. BPD measurement is most accurate in assessing gestational age when the head shape is appropriately ovoid. If the head is rounded (brachycephalic) or elongated (dolicocephalic), BPD measurements would overestimate or underestimate gestational age, respectively. Between 12 and 26 weeks the BPD is accurate ±10 to 11 days. After 26 weeks the accuracy of BPD measurement progressively decreases and is ±3 weeks near term. Biologic variation, occur because of differences in maternal age, parity, pre-pregnancy weight, geographic location, and specific population characteristics contribute to inaccuracy in the BPD measurement.

Ultrasound medical imaging is widely used in clinical application due to its intuitive, convenience, safety, non-invasive, and low cost [3-6]. It has proved to be a useful and accurate method for determining the gestational age of the fetus [7-10]. Trans-abdominal sonographic examinations are widely used to show the transaxial view of the fetal head at the level of the thalami to measure the BPD. In present study, we have implemented the generic computing for 3D volumetric ultrasound reconstruction using open-source visualization toolkits, VTK. In order to analyze the significance of proposed method in terms of consistency and accuracy, conventional 2D and proposed computerized 3D program results were evaluated and comparison were done.

The limitations of our study include the inability to evaluate fetal activity and behavior without real-time scanning. The goal of our approach is to produce US images that can allow us to perform the anatomic survey. In addition to the time required to acquire several 3D volumes, it might be necessary to perform a short, real-time scan. Another limitation is that BPD measurement was disregards the shape of the cranium. i.e. two heads of equal widths but different lengths will have the same BPD's, but the longer head will have a greater corrected BPD or HC than the shorter head. The shape corrected BPD can be calculated using Equation (1). Another limitation is the rational choice of proper plane of section for sonographic measurement. This must be done to confirm that the chosen section passes through the widest BPD plane to obtain the best image.

Shape corrected BPD = BPD x FOD/1.265 (1)

978-1-4577-1166-4/11/$26.00 ©2011 IEEE

2011 International Conference on Instrumentation, Communication, Information Technology and Biomedical Engineering

8-9 November 2011, Bandung, Indonesia

The paper is organized as follows. In Section II, we

describe the proposed open-source visualization toolkit, VTK and its implementation on 3D ultrasonography reconstruction and visualization. Section III shows the result comparison and analysis for conventional 2D B-mode ultrasound and proposed 3D measurement method. Finally, we summarize with discussions and conclusion.

II. MATERIALS AND METHODS

In this study, we use Fetal Ultrasound Training Phantom model CIRS 065-20 with 20 gestational weeks. The fetal phantom had been chosen as scanning target because it provides a realistic high quality imaging model for 2D and 3D ultrasound applications. The measured ultrasonic parameter is biparietal diameter, or simply BPD using conventional 2D B-mode prenatal ultrasound scan protocol. The type of transducer implemented in current examination is abdominal probe, with beam form 1.54 MHz frequencies. Data were obtained with 10 trials 2D and 3D fetal screening. In the proposed study, multi frames of DICOM ultrasound data and video clips were collected for 3D volume reconstructions. The collected DICOM files are stored in 8 bit, and digital unsigned characteristic with the grey scale value between 0 and 255. The 2D and 3D images were subsequently compared in relation to the accuracy and consistency of biparietal diameter measurements of fetal phantom.

Visualization Toolkit (VTK) is an object-oriented, powerful visualization and graphics, image processing toolkit, providing more than 300 C++ classes [2]. VTK consists of C++ class library and several interpreted interface layers including Tcl/Tk, Java and Python. In this study, we use VTK for 3D reconstruction to display the overall 3D volumetric model which provides comprehensive information on internal 3D features. In our case, we stored the data source in the form of video clips and DICOM files. We extracted the video clips and DICOM files into multiple slices of 2D ultrasound images using Matlab. Lastly, we reconstructed the 2D images into 3D voxel form and made measurement using 3D Euclidean approach. The selected two Cartesian points will be converted into 3 dimension spaces for Euclidean distance computation. Voxel spacing in mm scale for the re-sampled images must be defined in advanced before 3D computing measurement. In this study, we also improved the 3D volumetric using 3D anisotropic diffusion. Fig. 1 shows the BPD measurement on the conventional 2D B-mode ultrasound machine. The computed measurement is 46.5mm.

The deviation measurement can be larger, as the operator changes the position of coronal view during fetal screening. Selecting the correct coronal plane is crucial, which is very subjective and relies on personal experiences and technical skills. Fig. 2 below shows part of the simulated three dimensional volumetric model using ultrasound fetal training phantom for BPD measurement.

Fig. 1 Standard fetal biometry: sonographic measurements of the biparietal diameter

(a) (b)

(c) (d)

Fig. 2 Simulation of DICOM files into 3D using VTK reconstructions (a) 3D volumetric rendering (b) Improved volumetric rendering using 3D anisotropic diffusion (c) Slicing view to get the widest plane for BPD measurement (d) BPD measurement using 3D Euclidean approach

Fig. 3 below shows 3D volumetric reconstruction of video clip. The reconstructed image quality is found to be blurred as compared to 3D DICOM images. There were artifacts in the images produced.

III. RESULTS AND ANALYSIS

All analyses were performed by using SPSS 19 software (IBM SPSS Statistics). The chosen reference standards of BDP measurement is 47mm and its corresponding gestational age is 20 weeks and 0±7 days as indicated in Table 1. The 20 gestational weeks has been selected as reference standard because fetal ultrasound training phantom with 20 weeks gestational age is used during this study.

2011 International Conference on Instrumentation, Communication, Information Technology and Biomedical Engineering

8-9 November 2011, Bandung, Indonesia

(a) (b)

Fig. 3 Reconstruction of 3D volumetric rendering of video clips using VTK reconstruction (a) before diffusion (b) after diffusion

TABLE I SUMMARY OF GESTATIONAL AGE BY BPD

All measurements were tabulated in Table 2. The range of

the deviation from measurements in VIDEOCLIP_3D are much larger compared to DICOM_3D, varies from minimum values 46.56mm (T2) to maximum values 48.41mm (T5) in VIDEOCLIP_3D, and minimum values 46.54mm (T1) to maximum values 47.76mm (T5) in DICOM_3D respectively.

Descriptive analysis of 3D and 2D measurements were computed. For numerical statistics analyses, Table 3 shows the difference of their means and standard deviations. As indicated in Table 3 above, the computed mean and standard deviation for VIDEOCLIP_3D are much larger as compared to DICOM_3D, which are 47.326±0.643345mm and 47.099±0.377343mm respectively. This revealed that VIDEOCLIP_3D has higher variability than DICOM_3D. In comparison of maximum range, VIDEOCLIP_3D (1.85mm) shows greater value compared to DICOM_3D (1.22mm). Hence, we chose DICOM_3D to be further compared with 2D in term of accuracy and consistency of measurement.

The data distributions for both 3D and 2D cases were illustrated in Fig. 4 and Fig. 5 below. The figures show the histogram of Gaussian bell shape data distribution for conventional 2D and our computerized 3D ultrasonic BPD measurement, which imply that the data follows the General Linear Model (GLM) foundation.

TABLE II

SUMMARY OF 3D AND 2D DATA COLLECTION FOR B-MODE ULTRASONIC BPD

MEASUREMENT IN MM

No. of

trial BPD(mm)

VIDEOCLIP_3D DICOM_3D 2D

T1 48.29 46.54 45.50

T2 46.56 46.99 46.60

T3 46.91 47.15 47.00

T4 46.86 46.64 46.30

T5 48.41 47.76 45.80

T6 47.61 47.53 46.40

T7 47.66 47.11 45.80

T8 46.79 47.19 46.50

T9 46.93 47.27 46.40

T10 47.24 46.81 46.60

TABLE III

SUMMARY OF STATISTICAL ANALYSIS OF 3D AND 2D FOR BPD MEASUREMENT

IN MM

VIDEOCLIP_3D DICOM_3D 2D

Mean, x 47.326 47.099 46.29

Standard Deviation, 0.643345 0.377343 0.455705

Variance, 0.413893 0.142388 0.207667

Maximum Range 1.85 1.22 1.5

It may be apparent from constructing a histogram or

frequency curve that the data follow a normal distribution. However, with small sample sizes (n < 20), it may not be obvious from the graph that the data are drawn from a normally distributed population. To confirm the normal distribution of the analyses data with parametric symmetry, Shapiro-Wilk Test can be used from SPSS, as shown in Table 3 below. Shapiro-Wilk Test is performed in this study because it is not sensitive to the sample size and it shows effectiveness in small sample size. 2D, VIDEOCLIP_3D and DICOM_3D ultrasonic measurements were distributed normally with significant statistic values at 0.894, 0.932 and 0.974 respectively. All three test statistic values show a positive value and being close to one. These data were significant in supporting that the data distributions were normally distributed.

TABLE IV

SHAPIRO-WILK TEST- TEST FOR NORMALITY

Shapiro-Wilk

Statistic df Sig.

VIDEOCLIP_3D .894 10 .187

BPD_2D .932 10 .467

DICOM_3D .974 10 .929

TABLE V

DESCRIPTIVE STATISTICS ANALYSIS FOR 2D AND 3D MEASUREMENT

COMPARISON

N Skewness Kurtosis

Statistic Statistic Std. Error Statistic Std. Error

VIDEOCLIP_3D 10 .725 .687 -.782 1.334

DICOM_3D 10 .201 .687 -.297 1.334

2D 10 -.439 .687 -.394 1.334

Valid N (listwise) 10

S2

BPD

(mm)

Gestational age

(weeks and days)

BPD

(mm)

Gestational age

(weeks and days)

13 10 w 1 d ± 4 d 33 15 w 5 d ± 5 d

14 10 w 3 d ± 4 d 34 16 w 0 d ± 5 d

15 10 w 5 d ± 4 d 35 16 w 2 d ± 5 d

16 11 w 0 d ± 4 d 36 16 w 4 d ± 5 d

17 11 w 2 d ± 4 d 37 16 w 6 d ± 6 d

18 11 w 4 d ± 4 d 38 17 w 1 d ± 6 d

19 11 w 6 d ± 4 d 39 17 w 4 d ± 6 d

20 12 w 1 d ± 4 d 40 17 w 6 d ± 6 d

21 12 w 3 d ± 4 d 41 18 w 1 d ± 6 d

22 12 w 6 d ± 4 d 42 18 w 3 d ± 6 d

23 13 w 1 d ± 5 d 43 18 w 5 d ± 6 d

24 13 w 3 d ± 5 d 44 19 w 0 d ± 6 d

25 13 w 5 d ± 5 d 45 19 w 0 d ± 6 d

26 13 w 5 d ± 5 d 46 19 w 4 d ± 6 d

27 14 w 0 d ± 5 d 47 20 w 0 d ± 7 d

28 14 w 2 d ± 5 d 48 20 w 2 d ± 7 d

29 14 w 4 d ± 5 d 49 20 w 4 d ± 7 d

30 14 w 6 d ± 5 d 50 20 w 6 d ± 7 d

31 15 w 1 d ± 5 d 51 21 w 1 d ± 7 d

32 15 w 3 d ± 5 d

2011 International Conference on Instrumentation, Communication, Information Technology and Biomedical Engineering

8-9 November 2011, Bandung, Indonesia

Referring to Table 5, VIDEOCLIP_3D and DICOM_3D

measurements show a positive value of skewness, with values 0.725 and 0.201 respectively. This indicates that both distributions have an asymmetric tail extending out to the right which is referred to as “positively skewed” or “skewed to the right. On the other hand, 2D measurement shows a negative value of skewness which implies that the distribution has an asymmetric tail extending out to the left and is referred to as “negatively skewed” or “skewed to the left.

(a)

(b)

Fig. 4 Histogram of three-dimensional ultrasonography biparietal diameter distributions with different data acquiring methods (a) in video clips (b) in DICOM files

Fig. 5 Histogram of two-dimensional ultrasonography biparietal diameter distributions

Kurtosis test is then conducted to examine the measurements of the thinness of tails or “peakedness” of a probability distribution. Both 2D and 3D measurements show negative kurtosis which indicates a “flat” distribution or known as platykurtic distribution. DICOM_3D and 2D measurements have a higher kurtosis compared to VIDEOCLIP_3D. This implies that high kurtosis tends to have a distinct peak near the mean, decline rather rapidly with heavy tails while low kurtosis tend to have a flat top near mean.

Fig. 6 illustrates the relationship of data distribution for the sample’s range, mean, variability, and skewness. From Figure 6(a), it can be seen that VIDEOCLIP_3D has higher variability compared to DICOM_3D. The mean value of DICOM_3D is observed to be nearly the same as the standard reference value. Hence, we chose DICOM_3D to be further compared with 2D to assess their accuracy. The computed mean for 2D is largely differing from reference standard value while DICOM_3D has mean value nearly close to reference standard value. Compared with complete fetal surveys performed with 2D ultrasonographic, BPD measurements were identified less accuracy than using 3D US.

IV. CONCLUSION

Our study demonstrates that, in a sample size N=10, both 2D and 3D ultrasonography data distributions were found to be normally distributed with Shapiro-Wilk Test. BDP measurement of 47mm and its corresponding gestational age of 20 weeks and 0±7 days were used as reference standard. 3D measurement has higher accuracy compared to 2D. Hence, it can be observed that the proposed three-dimensional simulation having great advantage compare to conventional two-dimensional B mode ultrasound images, in terms of its visualization, measurement accuracy, flexibility and consistency.

2011 International Conference on Instrumentation, Communication, Information Technology and Biomedical Engineering

8-9 November 2011, Bandung, Indonesia

(a)

(b)

Fig. 6 Error bar of biparietal diameter (mm) (a) in relation to DICOM_3D and VIDEOCLIP_3D compared to standard reference value (b) in relation to 3D and 2D measurement compared to standard reference value (Sample size N=10)

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