Optimal caliper placement: manual vs automated methods.

OBJECTIVE: To examine the inter- and intra-operator repeatability of manual placement of callipers in the assessment of basic biometric measurements and to compare the results to an automated calliper placement system. METHODS: Stored ultrasound images of 95 normal fetuses between 19 and 25 weeks' gestation were used. Five operators (two experts, one resident and two students) were asked to measure the BPD, OFD and FL two times manually and automatically. For each operator, intra-operator repeatability of the manual and automated measurements was assessed by within operator standard deviation. For the assessment of the interoperator repeatability, the mean of the four manual measurements by the two experts was used as the gold standard.The relative bias of the manual measurement of the three non-expert operators and the operator-independent automated measurement were compared with the gold standard measurement by means and 95% confidence interval. RESULTS: In 88.4% of the 95 cases, the automated measurement algorithm was able to obtain appropriate measurements of the BPD, OFD, AC and FL. Within operator standard deviations of the manual measurements ranged between 0.15 and 1.56, irrespective of the experience of the operator.Using the automated biometric measurement system, there was no difference between the measurements of each operator. As far as the inter-operator repeatability is concerned, the difference between the manual measurements of the two students, the resident, and the gold standard was between -0.10 and 2.53 mm. The automated measurements tended to be closer to the gold standard but did not reach statistical significance. CONCLUSION: In about 90% of the cases, it was possible to obtain basic biometric measurements with an automated system. The use of automated measurements resulted in a significant improvement of the intra-operator but not of the inter-operator repeatability, but measurements were not significantly closer to the gold standard of expert examiners.

Intra- and interoperator reliability of manual and semi-automated measurement of fetal nuchal translucency by sonographers with different levels of experience.

OBJECTIVE: To compare the intra- and interoperator reliability of manual and semi-automated nuchal translucency thickness (NT) measurement by sonographers with different levels of experience. METHODS: From our digital database we selected retrospectively 70 NT images without measurements and of highest quality according to the guidelines of The Fetal Medicine Foundation (FMF). Four operators (two experts who were consultants in fetal medicine, one general consultant in obstetrics and gynecology with average knowledge in obstetric ultrasound and one final-year medical student with no experience in ultrasound), having first attended the FMF's online NT measurement course, measured the fetal NT manually according to FMF guidelines and semi-automatically from the inner to inner borders of the two echogenic lines delineating the NT and from the inner border to the middle of the lower NT line. The semi-automatic measurement algorithm identifies the two NT lines within a manually chosen region of interest and standardizes the caliper placement process. Each operator was blinded to any pre-existing measurements. Each measurement was performed twice by each operator. Intraoperator repeatability was assessed by the within-operator SD and intraclass correlation coefficients (ICC). Interoperator reliability was assessed by comparison with the mean manual measurement of the experts, which was considered as the gold standard. RESULTS: The mean NT measurement of the four sonographers was between 1.9 and 2.0 mm with both the manual and the semi-automated inner-inner NT measurement and it was between 2.2 and 2.3 mm with the semi-automated inner-middle method. The within-operator SDs of the manual measurement for both experts were similar and significantly lower than those of the non-experts, and all four sonographers performed similarly with the semi-automated measurement. Concerning the interoperator biases relative to the manual measurements of the experts taken as the gold standard, the manual measurements of the student and the general consultant were significantly lower, by 0.18 mm and 0.12 mm. The semi-automated inner-inner measurements of all four sonographers were much closer to the gold standard, although there was still a significant underestimation (mean differences from gold standard between 0.04 and 0.06 mm). With the semi-automated inner-middle measurement there was a significant and more pronounced overestimation of fetal NT compared with the gold standard, relative biases ranging from 0.08 to 0.23 mm above it. CONCLUSION: Semi-automation of NT measurement leads to improved standardization of the NT assessment process. In particular, non-expert operators improve as the variability in their caliper placement can be reduced to the level of experts. However, the most important contributor to the inter- and intraoperator variability of NT assessment is that of image acquisition, which is not affected by semi-automation of NT measurement.

Semi-automated system for measurement of nuchal translucency thickness.

OBJECTIVE: To estimate intersonographer and intrasonographer variance components of fetal nuchal translucency (NT) thickness measurement using the traditional manual approach and a new semi-automated system. METHODS: A semi-automated method was developed for measurement of the NT. In this method, the operator places an adjustable box over the relevant area at the back of the fetal neck. The system draws a line through the center of the nuchal membrane and another line at the edge of the soft tissue overlying the cervical spine. The system then identifies the largest vertical distance between the two lines. The images of 12 fetuses at 11-13 weeks of gestation satisfying the guidelines of The Fetal Medicine Foundation for measurement of NT were selected. They were exported in DICOM format from the ultrasound system, and four versions of each image were stored under different names. The resulting 48 images were presented in random order for electronic assessment. A total of 20 sonographers measured the NT in each set of 48 pictures, twice using the semi-automated system and twice using the manual system, according to a randomized block design. Within- and between-operator variance components were estimated. Relative biases were assessed by comparing the means from the two methods. RESULTS: The estimated between-operator SD using the semi-automated method was 0.0149 mm compared with 0.109 mm for the manual method. The respective within-operator SD values were 0.05 mm and 0.126 mm. The intraclass correlation coefficients for different sonographers measuring the same images were 0.98 and 0.85 for the semi-automated method and the manual method, respectively. CONCLUSION: The measurement of fetal NT is more reliable when a semi-automatic approach is used rather than the traditional manual method.