Methods for comparison of abdominal organ location and shape in the supine and upright positions

The location and shape variation of the liver due to postural changes has implications in the prediction of blunt abdominal trauma via computational models or other human surrogates. Although abdominal injuries make up only 3-5% of injuries in car crashes, they are often seen in serious crashes with AIS=4 injuries. This study reviews the methods used to quantify variation in the location of the liver relative to surrounding bony structures for two different postures, supine and seated. Methods to investigate shape variation in the liver between these postures are also detailed. Magnetic resonance imaging (MRI) scans of individuals representing the 50th percentile male (M50) and 5th percentile female (F05) in terms of height (M50: 175cm, F05: 150cm) and weight (M50: 78.6kg, F05: 48.1kg) were obtained in the two postures using a GE Twin Speed and a Fonar Upright MRI respectively. Images were acquired using a Fast Spoiled Gradient Recalled pulse sequence. The liver was segmented manually. Vertebral bodies and ribs from CT scans of the same individuals were placed in the MRI space using a semi-automated approach. The center of gravity (CG) was identified for the liver and vertebral bodies. Liver volume in each scan was calculated. The location of the liver was then investigated by examining distances between the center of gravity of the liver and various vertebral bodies. The average volume of the liver for M50 and F05 was found to be 1400 and 1036 cm3, with the coefficient of variance (COV) of .76% and .40% respectively. In the case of M50 and F05 liver movement from the supine to upright positions, the M50 liver was found to move 11.5mm and the F05 liver was found to move 19.7mm in the superior to inferior direction. In addition, the liver in the MRI supine scans was found to have a greater area of rib coverage where as less coverage of the liver was seen in the UMRI seated scans. Regarding shape change, the M50 and F05 liver were found to be compressed 11.36% and 8.13% in the Anterior-Posterior direction when comparing the supine to seated position. The study’s results indicate that postural changes do affect liver location and shape, a finding that may influence computational human body modeling efforts and the development of physical human surrogates.