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Year : 2015  |  Volume : 2  |  Issue : 1  |  Page : 1-6

Review of limb volume measurement techniques in assessing fetal weight by ultrasound with special reference to ImageJ package

Department of Obstetrics and Gynaecology, Kasturba Medical College, Manipal University, Udupi, Karnataka, India

Date of Web Publication4-Jun-2015

Correspondence Address:
Dr. Shripad Hebbar
Kasturba Medical College, Manipal University, Madhavanagar, Manipal - 576 104, District Udupi, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2394-2010.158121

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Traditionally intrauterine nutritional status of the growing fetus is evaluated using ultrasound estimated weight, which is then compared with standardized prenatal growth chart for that particular gestational age. The fetuses belonging to less than 10 th centile groups are considered to have reduced growth, whereas those who are more than 90 th centile belong to macrosomia group. Both these extreme groups have their own characteristic obstetric problems and may have poorer outcome. The conventional fetal weight formulae incorporated in regular ultrasound machines are largely dependent on head size, abdominal circumference, and femur length and are prone to random errors as high as 15% of actual birth weight. The margin of error further increases with very small and very large fetuses, and also, these measurements are not valid when the fetus has anterior abdominal wall defects. Malnourishment and obesity studies in pediatric subjects have shown us that subcutaneous fat significantly contributes to actual weight, and mid arm circumference can be used as screening tool for nutritional disorders. The errors in fetal weight estimation can be minimized if fetal soft tissues such as arm and thigh volumes are included for nutritional assessment of the fetus. The recent advances in three-dimensional (3D) ultrasonography has made limb volume estimation simple, easy, and birth weight models using limb volume measurements have higher accuracy, least systematic and random errors compared with the usual two-dimensional biometry of head, trunk, and limb length alone. However, these machines incur significant cost and procurement may not be feasible for resource poor organizations. The present review discusses developments in 3D analysis of fetal limb volulmetry, the methodologies, and affordable solutions using alternative image processing tools such as ImageJ in regular sonographic practice. We have also searched various databases (PUBMED, MEDLINE, SCOPUS, GOOGLE SCHOLAR AND SCIENCE DIRECT, J-Gate Plus and ProQuest) for birth weight models using limb volume measurements and have provided 13 different birth weight equations based on arm and/or thigh volumes.

Keywords: 3D Ultrasound, fractional limb volume, ImageJ, ultrasound weight estimation

How to cite this article:
Malaviya S, Hebbar S, Rai L. Review of limb volume measurement techniques in assessing fetal weight by ultrasound with special reference to ImageJ package. J Health Res Rev 2015;2:1-6

How to cite this URL:
Malaviya S, Hebbar S, Rai L. Review of limb volume measurement techniques in assessing fetal weight by ultrasound with special reference to ImageJ package. J Health Res Rev [serial online] 2015 [cited 2021 Apr 19];2:1-6. Available from: https://www.jhrr.org/text.asp?2015/2/1/1/158121

  Introduction Top

Fetal growth is a complex biological process, depending on fetal, placental, and maternal factors. [1] For providers of specialized antenatal care, fetal growth and fetal size assessment are of great interest, as fetal growth aberration is associated with adverse perinatal outcome. [2],[3] Alterations in fetal size outside the normal range are associated with increased morbidity and mortality, not only to the neonate, but also to the mother because of increased operative interference. [4] Poor outcomes can result from perinatal asphyxia in growth-restricted fetuses and shoulder dystocia in macrosomic fetuses. [5],[6] Ultrasound plays a major role in prediction of expected birth weight, but most of the ultrasound machines use inbuilt formulae using conventional two-dimensional (2D) parameters such as biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) and are widely subjected to errors as great as 15% from actual birth weight (BW). [7] The majority of the formulae tend to overestimate smaller fetuses and underestimate larger fetuses and thereby create confusions while deciding the route of delivery in obstetric practice. [8]

Experience from body weight estimation in pediatric age group suggests that soft tissue assessments, especially subcutaneous limb fat are greatly diminished in malnourished babies. [9] Inclusion of these parameters in fetal weight estimation formulae greatly improves the accuracy and minimizes errors. [10] Soft tissue abnormalities are usually the earliest manifestation of pathological growth and so unless ultrasound measures are sensitive to subtle changes in muscle or fat, such aberrations will be detected late. Quantification of soft tissue parameters helps the obstetrician in differentiating growth-restricted babies from constitutionally small babies. [11] The differences in actual birth weights in two fetuses with the same BPD, HC, AC, and FL parameters may be in fact due to variations in body fat distributions. [12] However, soft tissue characterization is poorly addressed in 2D imaging. [13] Volume measurements by conventional sonography can be technically difficult because of irregularity in subcutaneous fat distribution.

Now three-dimensional (3D) ultrasonography can be used for fetal weight estimation by measurement of the upper-arm and thigh volumes. [14] Various soft tissue markers such as arm and thigh volumes (both total and fractional) have been studied extensively in order to increase the accuracy of fetal birth weight prediction, which has been described in the subsequent paragraphs. To obtain birth weight models involving limb volume (either arm or thigh), we searched various databases mainly PUBMED, MEDLINE, SCOPUS, GOOGLE SCHOLAR AND SCIENCE DIRECT, J-Gate Plus, and ProQuest and we could get 13 articles describing birth weight formulae either using arm volume or thigh volume or both [Table 1].
Table 1: Birth weight formulae involving soft tissue measurements

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  Literature review Top

Initially ultrasonic birth weight measurements were based on either linear (BPD and FL) or ellipsoid measurements (HC and AC) and more than 27 formulae have been tested using these parameters. [28] There were considerable variations in birth weight prediction and maximum errors were detected in extremes of weight groups.

Jeanty et al. (1985) were the first researchers who thought limb volume measurements can add to the accuracy of fetal weight. [11] They evaluated fetal growth and nutrition using measurements of the subcutaneous tissues of the arm and leg to calculate limb volume. Limb measurements included anteroposterior and transverse diameters including the subcutaneous tissue thickness along with lengths and thickness of long bones (humerus and femur). Circular and elliptical perimeters were used to calculate both arm and thigh and they found that limb volumes were found to be strongly correlated with gestational age and fetal weight. In another study, thigh circumference was used in addition to conventional parameters to increase the power of birth weight prediction; however, using a single cutting plane and circular approximation may limit the usefulness of such studies, especially with large-sized fetuses. [29],[30]

However, 3D technology has revolutionalized the volume measurements in all aspects of ultrasound practice. Virtually any organ can be three-dimensionally assessed using these advanced techniques. Song et al. (2000) have described diagrammatically limb volume measurement method using 3D ultrasound [Figure 1] and have opined that thigh volume measurements using three cross-sectional images of femur is simple and better than -2D ultrasound methods for predicting fetal weight during the third trimester of pregnancy. [17]
Figure 1: The yellow shaded rod indicates plane of femur length. Perpendicular to this axis, thigh area has been identified at three places; proximal (A), middle (B) and distal (C) in transaxial plane. These areas have been measured and volume data are integrated automatically by a built in processor in ultrasound unit

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Patipanawat et al. (2006) measured limb volumes using Voluson 530 MT 3D ultrasound machine with a 5.0-MHz transabdominal sector transducer. [31] During neutral position of the fetus, humerus, and femur lengths were visualized in traditional planes. When the whole contour of the humerus or femur diaphysis was visualized, three-dimensional scanning was performed. All image information of the scanned volume of the whole limb was stored in machine's hard disk. Measurements of cross-sectional areas of the limb were made at 5-mm intervals and complete analysis could be completed within 10 and 20 min [Figure 2].
Figure 2: Thigh volume analysis. The standard plane of femur length has been used for 3D volume rendering. With focus on sagittal and frontal (superior) view, perimeter of the limb contour has been traced starting from the beginning to the end of femoral diaphysis at regular intervals, mainly whenever the shape of the thigh contour is changed. The built-in computer calculates the total thigh volume

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But both the methods described so far have the technical limitations in the sense that the limb border is not sharp both at the beginning and at the end because of acoustic shadowing caused by the joint and many a times one may not be able to trace the contour because of flexion at hip and knee joint (in case of arm; the elbow joint). Lee et al. (2009) have felt that transverse slices of the mid-limb are more likely to display the sharpest soft tissue borders for manual tracing. [23] They have introduced a new concept, which is known as fractional limb volume. Fractional limb volume is a fetal soft tissue parameter that includes fractional arm volume (AVol) or fractional thigh volume (TVol), and is based on 50% of the long bone diaphysis length [Figure 3]. Such measurements are reproducible among blinded examiners and can be manually calculated from 3D volume datasets within approximately 2 min [Figure 4].
Figure 3: Fractional limb volume. First the center of the long bone is delineated. Two cursers are placed equidistant from the center, so that mid 50% of the long bone is covered in volume measurement

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Figure 4: Measurement of fractional thigh volume. First the screen is focussed in such a way that entire thigh is visualised which included both the end of femur. Curser is placed at beginning and end of femur. The computer automatically selects center 50% of femur length and draws five equidistant sections and corresponding axial sections are displayed side by side. The circumference of the thigh is manually drawn in all five sections. In built computer measures the areas and distance between the slices and calculates the volume

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Recently a new volumetric technique called Virtual Organ Computer-aided AnaLysis (VOCAL) became available as part of the 3D extended imaging in advanced higher end scan machines. Such technique consists of the delimitation of areas of sequential adjacent planes displayed on the apparatus screen (multislice view), and at the end of the process the equipment sums up the areas, automatically providing the volume as well as the distance between initial and end plane and slices thickness. [32] Cavalcante et al. (2010) have done extensive studies on use of this technique in measurements of fetal limb volume and have opined that the volume measurements done by this procedure is very accurate and has good intra- and interobserver reproducibility. [33] However, the cost of the machine is of concern and may not be affordable for resource-poor settings.

In this review, we explain how the fractional limb volumes can be obtained using softwares that are distributed free under GNU General Public License. The steps of volume measurements are follows:

  1. Volume acquisition in Audio Video Interleave (AVI) format
  2. Conversion of AVI to individual frames
  3. Selection of frames for area analysis
  4. Volume measurement using ImageJ software.

A. Volume acquisition in AVI format

We have used regular ultrasound equipment (Philips HD11XE) for acquisition of volume data set. First the entire length of the femur is visualized in sagittal plane and femur length (FL) is measured [Figure 5] using transabdominal probe. The probe is then turned by 90 degrees and a linear sweep is performed starting from the beginning to end of the femoral diaphysis. The machine automatically records the video (at 18 frames per second) and stores it in AVI format (usually less than 20 mb) in its magnetic disc. The entire procedure takes less than 10 s. This data is then transferred to an optical compact disk using machine's CD drive for offline analysis.
Figure 5: Entire length of femur with thigh outline. Cursers are placed at both the ends and femur length (FL) is measured

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B. Conversion of AVI to individual frames

We have used Virtualdub v1.10.4 software (can be downloaded from www.virtualdub.org, which is a free package under GNU General Public License) convert video frames of AVI file to individual sequentially named JPEG files. Typically a 5-s video is converted to 90 individual frames. The image sequence that includes starting and end of femoral diaphysis (seen as boomerang shape) are included for further analysis [Figure 6].
Figure 6: Beginning and end of femoral diaphysis which appear as curved boomerang echogenic structures. The images which appear before the beginning of femur and after end of femur are discarded. The intermediate images are further used for volume analysis

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C. Selection of frames for area analysis

The cross-sectional images that represent the true length of femur are considered for further analysis. It can be seen from [Figure 6] that both the beginning and end images do not have sharp borders and have acoustic shadows. Hence the midportion of femur (which constitutes 50% of femoral diaphysial length) is considered for fractional limb volume estimation. However, even this length is represented by 40+ frames and it is tedious to perform cross-sectional area measurement in all these sections. Hence only five representative frames at equal distances are chosen [Figure 7].
Figure 7: The five equidistant images representing the mid-thigh cross sections. Note the sharp borders

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For example, if "n" represents the total number of slices representing the total length of femur, the middle five equidistant cross-sections (x1, x2, x3, x4, x5) are represented by the slice number [a*n] where in [a] takes the value of 0.25, 0.375, 0.50, 0.625, and 0.75 for x1, x2, x3, x4, x5 (rounded to nearest integer). [Figure 8] gives pictorial explanation of mid-limb volume (arm and thigh) and the five cross-sections that are measured for volume calculation.
Figure 8: The yellow shaded area represents mid limb volume. The five circles represent equidistant transaxial cross sections of the limb. The areas of these sections and the limb bone length are used for volume calculations

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D. Volume measurement using ImageJ software

Once the representative images of mid-thigh are chosen as described previously, the next step is to calculate the areas of cross-sections of the thighs in these images. This can be easily accomplished by ImageJ software. ImageJ is a public domain, Java-based image processing program developed at the National Institutes of Health. [34] The software package for various operating systems can be downloaded free of charge from http://imagej.nih.gov/ij/download.html, which includes documentation, help manual, and example images. The software is user-friendly and has the ability to solve many image processing and analysis problems, from -3D live-cell imaging to radiological image processing. [35] At the time of writing this review, pubmed search revealed 850+ indexed articles using search item for the Medical Subject Headings (meSH) word "ImageJ".

Actually the software measures the number of pixels within the given boundary. To convert it into square centimeters one has to set scale, which can be easily accomplished as all ultrasound images have scale bar on the right edge of the picture. The scale can be set for 10 cm for easy visualization [Figure 9] and later on the limb cross-section can be traced manually using free hand trace tool. Once the borders are defined, the software immediately returns the area value. The cross-sectional areas are measured in all five representative images [Figure 10].
Figure 9: Image J interphase to set scale for distance measurements

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Figure 10: Limb circumference tracing and area measurement

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Once five measurements are obtained, then the fractional thigh volume can be calculated using the formula: Volume (mL) = Avg (A1 + A2 + A3 + A4 + A5) × FL/2 (A = Area, Avg = Average of all areas calculated on five slices).

Actually this formula can be entered into an excel sheet, which automatically calculates the volume. Similarly, fractional arm volume can be calculated using the same guidelines. One can also calculate the entire limb volume as some of the older birth weight formulae still make use of total limb volume. [Table 1] gives details of some of the fetal birth weight estimation models using either total limb volume (or only one volume such as arm volume or thigh volume) or fractional limb volume (either both arm and thigh fractional volume or one of them).

  Conclusions Top

The advances in ultrasound techniques have allowed more accurate volumetric analysis of upper and lower limbs for estimation of fetal weight for earlier, accurate, and precise diagnosis of fetal growth aberrations such as intrauterine growth restriction and macrosomia. It may be ideal to do volume related weight estimation using higher end ultrasound machines with 3D/4D imaging modality with built-in volumetric software such as VOCAL system, but these facilities may not be available to all obstetric ultrasound units because of cost constraints. In this article, we have demonstrated that volume-based ultrasound fetal weight estimation is still possible in an existing setup using ImageJ software provided by the National Institutes of Health, USA. We recommend extended use of this gadget in all 3D volumetric analyses using ultrasound.

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]

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