Intra- and inter-rater reliability in a comparative study of cross-sectional and spiral computed tomography pelvimetry methods

Abstract

Background: Different low-dose computed tomography (CT) pelvimetry methods can be used to evaluate the size of birth canal before delivery. CT pelvimetry might generate an acceptable low fetal radiation dose but its measurement accuracy is unknown.

Purpose: To investigate intra- and inter-rater measurement reliability of cross-sectional and two spiral CT pelvimetry methods: standard spiral and short spiral.

Material and methods: Ten individuals (age ≥60 years, body mass index ≥30 kg/m²) having a CT scan of the abdomen also had CT pelvimetry scans. Three radiologists made independent measurements of each pelvimetry method on two occasions and also in consensus for a reference pelvimetry computed from the standard-dose CT scan of the abdomen. Inter- and intra-rater reliability was analyzed by intraclass correlation coefficient.

Results: Measurements in the short spiral pelvimetry demonstrated excellent intra- and inter-rater reliability, intraclass correlation coefficient ≥0.93, and good to excellent 95% confidence interval 0.87-0.99. Corresponding results of the standard spiral and cross-sectional pelvimetry showed good to excellent intraclass correlation coefficient ≥0.85 and ≥0.76, and 95% confidence interval was least good and moderate 0.73-0.98 and 0.59-0.97, respectively. Intraclass correlation coefficient between reference pelvimetry and other CT methods showed analogous results.

Conclusion: The short spiral pelvimetry demonstrated high and best reliability in comparison to other methods. Standard spiral method showed also good measurement reliability but the short spiral pelvimetry generates lower fetal radiation dose. This method might be suitable for measurements at narrow pelvis. Patient acceptance and attitude to CT pelvimetry should be investigated.

Keywords: Pelvimetry; computed tomography spiral; inter-rater reliability; intra-rater reliability.

Fig. 1.

Additional scans for the study purpose: (a, b) a posteroanterior (PA) (a) and lateral (b) pre-view image; (c) a cross-sectional single-slice image centered at fovea caput femur; and (d) a standard spiral scan of the pelvis.

Fig. 2.

Measurement distance (a–d) needed for pelvimetry. Projections with intertuberous (a) and interspinous distance (b) measured on a PA projection to the left and anteroposterior (AP) pelvic inlet diameter (c) and the AP pelvic outlet distance (d) measured on a lateral projection to the right. Intertuberous distance (a) is the widest distance between the ischial tuberosities, interspinous distance (b) is the shortest distance between both ischial spines, AP pelvic inlet (c) is the shortest distance between promontory and symphysis while the AP pelvic outlet distance (d) is the distance between the inferior inner aspect of the symphysis and the distal end (the joint) of the sacrum.

Fig. 3.

Measurements in the cross-sectional method: (a) PA image for measurement of the intertuberous distance; (b) LAT for measurement of the AP pelvic inlet and outlet distance; (c) a cross-sectional single-slice image for measurement of the interspinous distance. The white lines in the figure are the measurement distance/s performed in the image. The black dashed line in (a) represents the location for the single-slice cross-sectional image.

Fig. 4.

Measurements in the standard spiral method: (a, b) the intertuberous and the interspinous distances were measured from the spiral scan and/or transverse reconstruction images; (c) and the AP inlet and outlet diameters were measured in sagittal reconstructions. An oblique reconstructed image of 150-mm thickness (d) was also included for the measurement of the intertuberous distance. The white lines represent the measurement distances in the images.

Fig. 5.

Measurements in the short spiral method: LAT image (a) of the pelvis for measurement of the AP pelvic inlet diameter (b, c) From the spiral scan and/or transverse reconstruction images, the intertuberous and the interspinous distances were measured. The AP pelvic outlet diameter, was measured in sagittal reconstructions (d). An oblique reconstructed image of 150-mm thickness (e) was also included for measurement of the intertuberous distance. The dark dashed lines mark the area of a short spiral. The white lines represent the measurement distances in the images.