Improving image quality of mid-trimester fetal sonography in obese women: role of ultrasound propagation velocity.

Objective: The quality of ultrasound images is impaired in obese patients. All ultrasound scanners are calibrated for an ultrasound propagation velocity of 1540 m/s, but the propagation in fatty tissue is slower (in the order of 1450 m/s). The main objective of this study was to evaluate the quality of images obtained with different ultrasound propagation velocity settings during the mid-trimester fetal ultrasound examination in obese patients.

Methods: This was a cross-sectional study using image sets of four recommended scanning planes collected from 32 obese pregnant women during their mid-trimester fetal scan. Each image set comprised three images obtained successively at three different propagation velocity settings (1540 m/s, 1480 m/s and 1420 m/s). A panel of 114 experts assessed the quality of 100 image sets, grading them from A (most acceptable) to C (least acceptable). Scanning-plane-specific indicators of adiposity (fatty layer thickness, probe-to-organ distance) were analyzed for each scanning plane.

Results: The experts had a mean of 18.1 ± 10.2 years of experience. The grade distribution (A, B, C) differed significantly (P < 0.0001) between the three propagation velocity settings tested; at the lower speed of 1480 m/s, images were most often graded A, while at the conventional speed of 1540 m/s, they were most often graded C. Regardless of the scanning plane, the thicker the fatty layer of the abdominal wall in a given plane, the lower the preferred speed (P < 0.0001).

Conclusion: The construction of images taking into account ultrasound propagation velocities lower than 1540 m/s can improve significantly the quality of images obtained during mid-trimester fetal ultrasonography in obese women. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.