The NPL Doppler fetal heart beat detector test facility

Area of Science:

• Biomedical Engineering
• Medical Ultrasound
• Metrology

Background:

• Thousands of Doppler fetal heart beat detectors are in use globally.
• A lack of standardized quantitative methods previously hindered performance comparisons.
• Existing methods did not allow for direct technical performance evaluation under standardized conditions.

Purpose of the Study:

• To develop a reference test facility for measuring Doppler fetal heart beat detector sensitivity.
• To meet manufacturer needs and comply with international standards (IEC 1995).
• To enable direct, standardized comparison of detector technical performance.

Main Methods:

• Developed a reference test facility at NPL for detectors operating at 2 MHz with Doppler shifts up to 1 kHz.
• Tested detectors using an ultrasound beam directed at a small, constant-velocity moving target.
• Determined sensitivity by measuring signal output relative to noise level, incorporating attenuator insertion loss and target reflection loss.

Main Results:

• Established a quantitative method for measuring fetal heart beat detector sensitivity.
• The test facility provides standardized conditions for performance evaluation.
• Uncertainties in measurement have been assessed, and encountered problems have been addressed.

Conclusions:

• The developed NPL test facility provides a standardized method for assessing Doppler fetal heart beat detector sensitivity.
• This enables reliable technical performance comparisons between different devices.
• Compliance with IEC 1995 standards is facilitated, improving fetal monitoring equipment quality.