The Effects of Posture and Subject-to-Subject Variations on the Position, Shape and Volume of Abdominal and Thoracic Organs

In this study, the thorax and the abdomen of nine subjects were imaged in four postures using a positional MRI scanner. The four postures were seated, standing, forward-flexed and supine. They were selected to represent car occupants, pedestrians, cyclists and a typical position for medical imaging, respectively. Geometrical models of key anatomical structures were registered from the imaging dataset using a custom registration toolbox. The analysis of the images and models allowed the quantification of the respective effects of posture and subject-to-subject variation on the position, shape and volume of the abdominal organs, skeletal components and thoracic cavity. In summary, except for the supine posture, the organ volumes and their positions in the spinal frame were mostly unaffected by the posture. The supine posture was associated with a motion of all solid organs of up to 39 mm (interpostural maximum for the liver, n=9), and a reduction of the thoracic cavity volume of up to 1300 cm³. Subject-to-subject variations were especially large for the volume of the spleen (variations between 120 and 400 cm³) and the position of the kidneys. As a result, subject-to-subject variations were larger than most postural effects. Other results include values of parameters that can help positioning human models such as positions, volumes and inertial properties of organs as well as skeletal parameters. Overall, this study suggests that subject-to-subject variations and the use of supine geometrical data can be problematic for finite element modeling of the abdomen for injury prediction.