Does It Matter? The Effect of Ultrasound Machine Settings on Small Measurements
Objectives: To establish the impact of ultrasound machine settings on small measurements in terms of the distance measured, repeatability and observer error.
Abstract: Image enhancing modalities are widely incorporated into ultrasound machine design, providing improved image quality and artifact reduction. However, little evidence exists analyzing the effect of such techniques on the accuracy of small measurements, particularly nuchal translucency assessments.
This study utilizes an in vitro experimental set-up, mimicking a nuchal translucency measurement. Two membrane layers are separated by a variable metal ring and immersed in a water bath, creating a fluid filled structure of a defined thickness. The effect of multiple machine settings were assessed independently including compound imaging, harmonics, XRes®, gain, dynamic range, magnification and transducer frequency and design. Accredited participants performed multiple blinded measurements of this structure using the standard nuchal translucency protocol.
Our results confirmed minimal intraobserver and interobserver variability of measurements recorded. For an estimated 2.3 mm measurement, the machine settings producing the greatest difference were:
75% image magnification versus 200% magnification - 0.31 mm larger measurement
harmonics off versus on – 0.27 mm larger
low versus high gain – 0.25 mm larger
low versus high dynamic range – 0.15 mm larger
Altering the other variables had minimal impact.
This study confirms that image magnification, harmonics, gain and dynamic range settings have a significant impact upon small measurements and quantifies the impact of these changes in detail. For nuchal translucency measurements this could result in risk assessment alteration and may require standardization of machine settings.