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Accuracy in estimating fetal urinary bladder volume using a modified ultrasound technique
Author(s) -
Fägerquist M. A.,
Fägerquist U. O.,
Steyskal H.,
Odén A.,
Blomberg S. G.
Publication year - 2001
Publication title -
ultrasound in obstetrics and gynecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.202
H-Index - 141
eISSN - 1469-0705
pISSN - 0960-7692
DOI - 10.1046/j.1469-0705.2001.abs25-5.x
Subject(s) - medicine , ultrasound , 3d ultrasound , volume (thermodynamics) , standard deviation , urinary bladder , biomedical engineering , surgery , radiology , mathematics , statistics , physics , quantum mechanics
Purpose: The fetal urine production rate can be used as non‐invasive test of fetal well‐being. However, the accuracy of measuring urine production rate by ultrasound depends on the accuracy of volume estimation of the certain bladder image. The aim of this study was to assess the accuracy of measurement of volumes of the bladder using a modified ultrasound technique and digitising the bladder images. Also, it was possible to compare these results with the corresponding findings assessed by conventional ultrasound technique. Methods: A swaying movement of the ultrasound transducer causes characteristic changes on the screen, which can be utilized for identifying whether or not the ellipsoid configuration of fetal bladder is correctly sectioned along its midline. In this study, 34 unselected pregnant women participated and the gestational ages of the fetuses were between 24 and 40 weeks. The assumption was made of a circular appearance of the bladder in the transversal plane and then the calculation of volume was simplified. We distinguished between different kinds of errors, i.e. technical limitations due to the particular ultrasound machine, errors due to the operators measurement in the selected image of the bladder and errors due to the selection procedure of appropriate image. Results: The technical limitations and intraoperators errors measuring the volume of the selected bladder image (the ‘frozen’ error) occupied only a minor part of the total variability, whereas the major part consisted of errors was owing to the selection of scan, the ‘freezing’ procedure. Concerning this dominating part the standard deviation of the measurement errors of volume estimation using the modified technique was SD = 0.37892 + 0.04119 × volume, e.g. for 5–40 mL was 11.7–5.1%, respectively. Corresponding standard deviation without this modified technique was SD = 0.36516 + 0.09978 × volume, e.g. SD for 5–40 mL was 17.3–10.9%, respectively. Conclusion: When estimating the volume of fetal urinary bladder the major part of measurement errors due to the selection of appropriate bladder image. Using a modified technique this error can be reduced.