P10.41: Loss of agreement with higher angle correction in Doppler velocimetry. A mathematical demonstration
Year: 2005
Type: conference-abstract
Abstract: Angle correction has been introduced in all ultrasound equipments for real velocity measurements, which is needed in many obstetrical and vascular parameters. The objective is to demonstrate mathematically that the observer's visual error may become clinically significant, producing measures that disagree when the angle correction is higher. The exact angle between the measured vessel and the insonation line is not known and this is estimated visually by the operator. Therefore, the operator's error in the appreciation of the angle will never be measured but is possible to be present in different degrees. In order to simulate this error, two sets of 100 random integer numbers, normally distributed with 0 and 3 mean and SD were used as observer's error at angle correction. Making the assumption that the vessel was at 10°, the observer corrected 11° (one degree of error). The formula applied to introduce the error factor was cos(10°)/cos(10° + e). These sets of errors were applied at 0°, 10° and 20° from the insonation line. Data from each set of randomly distributed errors were paired simulating two measurements and the agreement was evaluated using the Bland and Altman method. 7%, 68% and 82% of the paired measurements disagree when the same sets of errors were applied to vessels at 0°, 10° and 20° respectively. Visual error of angle correction is not possible to be measured. This error may generate increasing disagreement when the vessel is out of the vertical line (0°), with 68% and 82% of disagreement when the real angle of the vessel is at 10° and 20° respectively. We propose that from now the velocity should be measured with the vessel in the most vertical position in the screen, so that the angle correction is minimal. Because the angle correction may affect the repeatability, velocity measurements should always inform the angle correction used.
DOI: 10.1002/uog.2504
Authors: M. Yamamoto, J. Carrillo, A. Insunza, G. Mari, Y. Ville
Language: English
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2043290265