Validity and Reliability of an Offline Ultrasound Measurement of Bladder Base Displacement in Women

Abstract

The effect of different exercises on the position of pelvic organs in women has not been sufficiently assessed. The objective was to analyze the validity and reliability of a new two-dimensional ultrasound algorithm to measure offline the displacement of the bladder base during abdominal exercises. This algorithm could be a useful method to future studies in determine the most appropriate exercises in sports and in rehabilitative program for the pelvic floor in women. All subjects were tested by transverse transabdominal ultrasound. The measurements were conducted offline using a customized code written in MATLAB (Ecolab) for image-processing, and manually on the ultrasound monitor using electronic calipers. The agreement was assessed with a paired t-test, Pearson's linear correlation coefficient (r), the Lin's concordance correlation coefficient (CCC), the intraclass correlation coefficient ICC (A,2) and a Bland-Altman plot. The reliability was confirmed by the interdays intra-rater ICC coefficient. The results were that Ecolab and ultrasound transducer measures did not differ statistically (p = 0.246). Furthermore, both methods showed a very strong relationship, and the Ecolab demonstrated to be a valid and reliable method. We concluded that Ecolab seemed to be a valid and reliable tool to assess the effect of abdominal contractions in the female pelvic floor.

Keywords: MATLAB; pelvic floor muscles; physiotherapy; reliability; ultrasound; validity.

Figure 1

Placement of the marker in the middle of the bladder base. Displacement δ of the bladder base between the resting position (left) and the position during the contraction (right).

Figure 2

Graphical user interface.

Figure 3

The value of $P_f\left(i,j,k\right)$ represents the color intensity of channel $k$of the pixel located in row i and column j of frame $f$.

Figure 4

(a) Collage of frames. (b) Visualization of results.

Figure 5

Scatterplot and correlation values for the measures given by Ecolab on the y-axis and by ultrasound transducer on the x-axis, with the linear regression fit (solid line) and the identity y = x line (dashed 45° line).

Figure 6

Bland–Altman plot (n = 27 volunteers). Differences in the measurements estimated with the Ecolab and the ultrasound transducers on the y-axis are plotted against the mean of the measurements with both methods on the x-axis. The mean difference ($\overline{d}=0.037$) and the relevant 95% confidence limits ($\overline{d}-1.96SD, \overline{d}+1.96SD)=\left(-0.353, 0.279\right)$ are indicated by the horizontal dashed lines.