Semi‐automated measurement of nuchal translucency thickness: blasphemy or oblation to quality?

摘要

The quality of nuchal translucency (NT) measurement is widely regarded as the cornerstone of ultrasound screening in the first trimester. It can also be seen as the lowest common denominator that ultrasonologists should be able to achieve. The Fetal Medicine Foundation (FMF) certification for NT measurement was a breakthrough in the practice of obstetric ultrasound. The litany of requirements for an appropriate measurement are recited as the 11th commandment by several thousands of FMF believers and non-believers alike. NT measurement has also become an undisputed genetic test, for which pre- and post- procedure counseling are required, potentially being a matter of life and death for the fetus, either through disclosure of an underlying severe abnormality or through fetal loss related to an invasive procedure triggered by a combination of risk factors, of which NT is the most powerful. ‘Automation’ describes the execution by a machine, usually a computer, of a function that was previously carried out by a human. The aim of replacing the human operator is generally to increase efficiency, reliability, accuracy and/or cost1. The use of automation in medicine is not new and its application to ultrasound seems both logical and feasible, since more challenging pattern and image recognition processes, including cytogenetic and malignancy screening as well as computer-aided and robotic surgery, have been successfully implemented for years. Automation is rarely all-or-nothing, and interaction with human experience and judgement are required for appropriate control1. Two articles published in this issue of the Journal2, 3 and one published ahead of print4 suggest that there might be a benefit from semi-automated measurement of NT. Although the senior author of one of the papers is Kypros Nicolaides, I would like to raise some concerns, acting as a guardian of the Temple but hopefully not as the Pythia of Delphi. Table 1 summarizes the steps and requirements for obtaining an optimal NT measurement, of which the measurement itself is only one, and including the possibility for semi-automated measurement as an alternative to manual measurement5. The success of semi-automated measurement of NT is based on the operator's selection of an appropriate image and manual placement of a region-of-interest (ROI) box over a limited part of the nuchal area, comprising both distal and proximal echogenic lines defining the translucency. It allows for inner-to-inner (calipers placed on the edge of the echogenicity of the NT area—equivalent to manual ‘on-to-on’ measurement) and inner-to-middle (lower caliper placed at the geometrical middle of NT echogenic margin) caliper placement options. The software then allows for the largest, mean or shortest of these measurements to be chosen within the measurement box. Thus, the choice of the best placement of the calipers, while performed automatically by the semi-automated measurement software, is limited by the operator's decision as to placement of the ROI box and the type of measurement to be performed2-4. This human–machine interaction is exposed to two main types of drift from the expected clinical and economic benefits, which can be designated as misuse and abuse of automation. Abuse occurs when the design of automated function does not fit with the clinical expectation and the operator's role becomes a by-product of the automation. This can lead to misuse, i.e. overreliance on automation1. Automated measurements may well be systematically larger than the corresponding manual measurements of NT by an average of 0.2 mm3. Inner-to-inner caliper placement satisfies The FMF requirement to show the whole translucency and nothing but the translucency. However, ultrasound image resolution has improved dramatically over the last 5–10 years and both pre- and post-processing tools are responsible for a sharper image and possibly thicker echogenic margins of the structures under examination, including NT6. The high