MRI assessment of the influence of body position on the shape and position of the urinary bladder.

Abstract

Continuous surveillance of patients' bladder volume may be of benefit during the treatment of various urologic disorders. In order to design optimal bladder volume monitoring equipment, information about the shape and position of the bladder, not at least in relation to posture, is crucial. The purpose of this study was consequently to evaluate the influence of body position on the change in shape and position of the bladder. MRI was performed in three young volunteers during posture changes. MRI scans in the transverse, frontal and sagittal planes were recorded in bladders of various sizes. The position of the bladder midpoint in the three planes was determined. Moreover, to account for its shape, the compactness of the cross-section of the bladder was calculated on the basis of its perimeter and area. For the medial-lateral and cranial-caudal positions, the maximal displacements were 4 and 5 mm, respectively. In the ventral-dorsal direction the displacement varied, but was <18 mm. The compactness changed maximally by 11%, indicating a minimal change in shape. In young subjects, the position and shape of the bladder only change modestly for different body positions, thus eliminating the need for special correction measures when designing bladder volume monitoring equipment.