Nuchal translucency thickness measurement: repeatability using a virtual ultrasound scanner.

AIM: To use a PC-based virtual ultrasound scanner (VirUS) in the investigation of inter- and intraoperator nuchal translucency (NT) thickness measurement repeatability of experienced ultrasound operators. METHODS: Realistic fetal ultrasound images of defined NT thickness were simulated with VirUS with emulation of scanner gain and time-gain compensation and gain-dependent echo size changes. A set of 50 images was generated with uniformly distributed NT thickness (range, 1-5 mm at 1-mm intervals) and translucency angle (mean +/- standard deviation of +/- 2.52 degrees +/- 1.85 degrees about the horizontal). Operators (n = 13) measured NT thickness in the image set on three occasions separated by at least 1 day, giving 150 measurements per operator (total measurements, 1950). RESULTS: Inter- and intraoperator repeatabilities were +/- 0.41 mm and +/- 0.22 mm, respectively (at the 95% confidence level). There were significant correlations between repeatability and mean measured NT thickness (r = - 0.72, P = 0.005 at 4-mm interval), between gain and mean measured NT thickness (P

A rapid and reproducible on line automated technique to determine endothelial function.

OBJECTIVE: To evaluate clinically a new on line, automated technique to measure flow mediated dilatation (FMD) as a marker of endothelial function. DESIGN: Prospective study. PATIENTS: 12 healthy volunteers and 12 patients with significant, angiographically documented coronary artery disease. INTERVENTIONS: Brachial arteries were imaged using a standard vascular ultrasound system with a 5-12 MHz linear transducer. Arterial diameter was measured on line (in real time) by connecting the ultrasound system to a personal computer equipped with a frame grabber and artery wall detection software (VIA) specially developed by the authors' group. By using this new technique, FMD was measured following 4.5 minutes of ischaemia of the proximal forearm in all subjects on two separate days. RESULTS: The mean (SD) day to day variability in FMD measurements was 0.90 (0.48)%,which compares very favourably with current methods. The FMD measurement was available within seconds of completing the scan. CONCLUSIONS: Personal computer based automated techniques to assess FMD involve image acquisition and recording after which a second (off line) image interpretation session is required. The need for off line analysis makes current methods time consuming and increases the variability of measurement. This on line, automated analysis technique for FMD assessment reduces the variability and greatly increases the speed of measurement. Using this system may mean that fewer patients will be required in clinical trials assessing the effects of interventions on endothelial function. Adopting this method may also facilitate the screening of larger numbers of subjects for endothelial dysfunction.

Online artery diameter measurement in ultrasound images using artificial neural networks.

An automated online technique is described for measurement of artery diameter in flow-mediated dilation (FMD) ultrasound (US) images, using artificial neural networks to identify and track artery walls. This allows FMD results to be calculated without the inherent delay of current retrospective methods. Two networks were trained to identify artery anterior and posterior walls using over 3200 examples from carotid artery images. Both networks correctly classified approximately 97% of the randomly selected test samples. The technique was verified using a physical model with absolute measurement error of -1.16% +/- 1.04% (mean +/- SD) over the diameter range 2 to 8 mm. Advantages of the technique include: online analysis; wall tracking optimisation before the study proper; measurement of diameter changes over the cardiac cycle; low FMD measurement variance; minimal image degradation; and no unwieldy image store. Measurement of artery diameter changes over the cardiac cycle was explored using simulated image sequences generated with a virtual US scanner.