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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004 
  
structure, the user can set another starting point or new ran 
values. 
The calculation of the resection strategy is currently based on 
the portal system structure but both parts of the venous system 
are enhanced. Because of noise and low resolution, pseudo- 
connections may occur between the portal and hepatic systems 
and, therefore, parts of the hepatic system may be included in 
the segmentation result. Usually, an editing step becomes 
necessary to separate portal from hepatic veins (Thorn, 2001a). 
The same extraction strategy takes place for the extraction of 
the arteries and bilary duct from the registered volume images. 
oc 
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2.4 Separating vessel systems 
The main component of this module is the three-dimensional 
reconstruction created from the preceding module. In this 
module the user can edit the vessel system. The segmentation 
process may have generated invalid connections between the 
two venous systems but these can be severed interactively. 
  
Visualisation of the liver and vessels after separation 
(portal vein in light-grey and hepatica in dark-grey) 
The location of the invalid connections can be detected by 
calculating the path from the portal stem to a part of the hepatic 
system that belongs to the segmentation result. In this display 
the location where the segmentation result must be severed is 
easily detected. Each branch can be chosen interactively and 
tagged as a "stop branch". This tag severs the pseudo- 
connection. Only those parts of the vessel tree that are still 
connected to the portal stem will be brightly displayed. This is 
done until all parts of the hepatic system are removed from the 
segmentation result (Thorn, 2001a). Also the vessels that are 
represented in the other CT-phases — arterial and bile duct — are 
segmented and preprocessed in the same way. 
2.5 Resection Planning and Visualisation 
The next step of the planning procedure is the presentation of 
the results. This step includes a visualisation that shows the 
specific relation between the different vessel systems. 
Operation planning will visualise the proposed resection lines 
on the surface of the liver with the help of the OrgaNicer 
(Thorn, 2004a). 
After segmentation and vessel extraction, vessel dependent 
tissue is calculated. To evaluate the volumetric results a study 
was performed that leads to an highly valid prognosis of the 
real liver volume (Thorn, 2004b). The quantitative results 
include total liver volume, graft size and remaining liver tissue. 
  
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Screenshot of the OrgaNicer-tool showing a liver including the 
portal system (light-grey), the arteries (grey) and 
bile duct (dark-grey) 
2.6 Volumetric analysis 
In addition to the anatomical visualisation for the estimation of 
the complexity of the surgical intervention a volumetric 
examination is done. A crucial factor for a successful LDLT is 
the ratio between the liver mass and the body weight as well for 
the donor as for the recipient. As a rule the liver graft should be 
1% of the body weight of the recipient and 0.8% of the body 
weight should be the remaining liver in the donor (Marcos, 
2000b: Hess, 2002). For that reason the volume of thc whole 
liver 1s calculated on the basis of the segmentation result 
(Thorn, 2004b). Afterwards the both liver halves are calculated 
and analysed in dependency of the portal vein structure. 
2.7 Intraoperative presentation 
The whole planning procedure take less than 1.5 hours. After 
the planning the results are presented during the preliminary 
discussion. In that meeting they are used to find the final 
decision if the potential donor will be able to spend one part of 
his liver. The volumetric results lead to a decision if the volume 
is sufficient for both patients. Afterwards the visualisation are 
examined concerning the feasibility of the surgical intervention. 
    
      
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Presentation of the planning results 1 
n the operation room 
Some days after the final decision is made the surgical 
intervention takes place. During the surgery the visualisations 
arc presented with a monitor which is placed directly over the 
situs of the patient (Thorn, 2001b). The software can either be 
used with the help of a touch-screen monitor or by an additional