Changes in Liver Morphology
Deformation of the liver from before to after the death is large and might not be accounted for by an SSM trained on in vivo livers. Figure 4.28 shows the typical shapes of an in vivo liver and that of a postmortem liver . Diaphragmatic elevation is caused by respiratory arrest, and enlargement of the right ventricle is caused by circulatory arrest. Such deformation results in the right lobe of the liver
Fig. 4.28 Typical examples from an in vivo liver (left) and a postmortem liver (right). The red regions indicate the true liver regions. In the postmortem liver, the right lobe was elevated owing to respiratory arrest, and cardiac arrest caused enlargement of the right ventricle, resulting in a downward deformation of left lobe migrating cephalad and the left lobe migrating caudad. The growth of gas-forming bacteria can form an abdominal gas reservoir which pushes the liver cephalad and deforms it.
These are some reasons why a conventional SSM learnt from in vivo liver labels [177-179] may not delineate the postmortem liver shape accurately. One possible solution to the problem would be to collect more postmortem liver labels to construct an SSM. However, because of the shortage of liver labels of postmortem CT volumes used in construction of an SSM and the large diversity of postmortem liver shapes, an SSM learnt only from a small number of postmortem liver labels may display limited ability.