Exact CT-based liver volume calculation including nonmetabolic liver tissue in three-dimensional liver reconstruction.

Exact preoperative determination of the liver volume is of great importance prior to hepatobiliary surgery, especially in living donated liver transplantation (LDLT) and extended hepatic resections. Modern surgery-planning systems estimate these volumes from segmented image data. In an experimental porcine study, our aim was (1) to analyze and compare three volume measurement algorithms to predict total liver volume, and (2) to determine vessel tree volumes equivalent to nonmetabolic liver tissue. Twelve porcine livers were examined using a standardized three-phase computed tomography (CT) scan and liver volume was calculated computer-assisted with the three different algorithms. After hepatectomy, livers were weighed and their vascular system plasticized followed by CT scan, CT reconstruction and re-evaluation of total liver and vessel volumes with the three different algorithms. Blood volume determined by the plasticized model was at least 1.89 times higher than calculated by multislice CT scans (9.7% versus 21.36%, P=0.028). Analysis of 3D-CT-volumetry showed good correlation between the actual and the calculated liver volume in all tested algorithms with a high significant difference in estimating the liver volume between Heymsfield versus Heidelberg (P=0.0005) and literature versus Heidelberg (P=0.0060). The Heidelberg algorithm reduced the measuring error with deviations of only 1.2%. The present results suggest a safe and highly predictable use of 3D-volumetry in liver surgery for evaluating liver volumes. With a precise algorithm, the volume of remaining liver or single segments can be evaluated exactly and potential operative risks can therefore be better calculated. To our knowledge, this study implies for the first time a blood pool, which corresponds to nonmetabolic liver tissue, of more than 20% of the whole liver volume.

The segments of the hepatic veins-is there a spatial correlation to the Couinaud liver segments?

PURPOSE: To investigate and describe the volume, position and shape of venous segments within the human liver and define their spatial correlation to the Couinaud segments (CS) and to the portal vein segments (PVS). MATERIAL AND METHODS: This study was based on 64 routinely acquired CT scans of patients undergoing hepatic surgery. The final analysis included 19 patients. All 19 CT data sets were transformed into 3D liver models. Three venous segments were postulated reflecting the left, middle, and right hepatic vein. Each venous segment was furthermore divided in two venous subsegments. Volume, position and shape of these venous segments/subsegments were calculated and, finally, compared with the volume, position and shape of the Couinaud segments and the portal vein segments. RESULTS: The right hepatic vein covers with 539.8 +/- 119.5 ml (47.1%) the largest part of total liver volume followed by the middle hepatic vein 372.7 +/- 151.1 ml (32.5%) and the left hepatic vein 248 +/- 75.9 ml (20.4%). The Couinaud liver segments and portal vein segments 2, 3, 5, 7, and 8 have consistent positional assignments within the three venous segments. Only the CS 4a, 4b, and 6 showed significantly different positions compared to the PVS 4a, 4b, and 6 (P < 0.03). The venous subsegments have a broad volumetric distribution reaching from 79 to 337 ml. There is no positional correlation of venous subsegments compared to Couinaud segments or portal vein segments at all (kappa < 0.75). In contrast, the venous segments/subsegments which can be assigned to either liver halve and either liver lobe have an identical volume, shape and position compared to the corresponding Couinaud liver segments (kappa > 0.75). CONCLUSION: The venous segments distinguish liver areas divided by the left and middle hepatic vein in exactly the same pattern as Couinaud segments and portal vein segments do. However, the comparison of shape and position of venous subsegments showed no correlation with both liver segmental approaches.

Visualization and attributation of vascular structures for diagnostics and therapy planning.

In various medical fields vascular structures have to be examined with usually two-dimensional views which present imaging techniques produce. The interpretation of the data can be supported by 3-dimensional visualization techniques. The further analysis requires often the attributation of the particular functional or anatomical entities. To attribute these interactively we developed two different visualization strategies. In the first one the shape of the structures is modelled with OpenGL achieving very fast response times, most notably during the navigation. The second strategy, the direct rendering of the volume, benefits from the accurate reproduction of the vascular structures. Although the rendering needs much more time, the strategy provides similar response times for the attributation. Thus, the strategies complement one another.

Evaluation of visualization techniques for image-guided navigation in liver surgery.

A substantial component of an image-guided surgery system (IGSS) is the kind of three-dimensional (3D) presentation to the surgeon because the visual depth perception of the complex anatomy is of significant relevance for orientation. Therefore, we examined in this contribution four different visualization techniques, which were evaluated by eight surgeons. The IGSS developed by our group supports the intraoperative orientation of the surgeon by depicting a visualization of the spatially tracked surgical instruments with respect to intrahepatic vessels that have to be conserved vitally, the tumor, and preoperatively calculated resection planes. In the prelimenary trial presented here we examined the human ability to percept an intraoperative virtual scene and to solve given navigation tasks. The focus of the experiments was to measure the ability of eight surgeons to orientate intrahepaticaly and to transfer the percepted spatial relation to movements in real space. An autostereoscopic visualization with a prism-based display yielded that the navigation can be performed faster and more accurately than with the other visualization techniques.

Measurement of tumor volumes improves RECIST-based response assessments in advanced lung cancer.

OBJECTIVE: This study was designed to characterize the reproducibility of measurement for tumor volumes and their longest tumor diameters (LDs) and estimate the potential impact of using changes in tumor volumes instead of LDs as the basis for response assessments. METHODS: We studied patients with advanced lung cancer who have been observed longitudinally with x-ray computed tomography in a multinational trial. A total of 71 time points from 10 patients with 13 morphologically complex target lesions were analyzed. A total of 6461 volume measurements and their corresponding LDs were made by seven independent teams using their own work flows and image analysis tools. Interteam agreement and overall interrater concurrence were characterized. RESULTS: Interteam agreement between volume measurements was better than between LD measurements (i = 0.945 vs 0.734, P = .005). The variability in determining the nadir was lower for volumes than for LDs (P = .005). Use of standard thresholds for the RECIST-based method and use of experimentally determined cutoffs for categorizing responses showed that volume measurements had a significantly greater sensitivity for detecting partial responses and disease progression. Earlier detection of progression would have led to earlier changes in patient management in most cases. CONCLUSIONS: Our findings indicate that measurement of changes in tumor volumes is adequately reproducible. Using tumor volumes as the basis for response assessments could have a positive impact on both patient management and clinical trials. More authoritative work to qualify or discard changes in volume as the basis for response assessments should proceed.

A routine liver transplantation in a patient with situs inversus: a case report and an overview of the literature.

Liver transplantation (LT) in an adult with situs inversus (SI) is extremely rare and requires precise pre-operative management. A 48-yr-old male with SI suffering from alcoholic liver cirrhosis underwent LT at our institution in March 2003. Pre-operatively, liver anatomy was determined by CT scan, three-dimensional liver reconstruction and angiography. LT was performed using the Belghiti technique with side-to-side cavo-caval anastomosis, transplanting a graft from a donor with normal anatomy. Post-operatively, the patient recovered without major complications, except an epileptic event because of a central pontine myelinolysis, and he was discharged on the 25th post-operative day. Three months after surgery, the T-drain placed intra-operatively into the donor bile duct was removed; transplant perfusion and function were stable with an actual follow-up period of 24 months. LT in patients with SI is feasible. Pre-operative imaging with three-dimensional reconstruction is a beneficial tool for operation planning in patients with rare anatomic variations.

Improved correlation of histological data with DCE MRI parameter maps by 3D reconstruction, reslicing and parameterization of the histological images.

Due to poor correlation of slice thickness and orientation, verification of radiological methods with histology is difficult. Thus, a procedure for three-dimensional reconstruction, reslicing and parameterization of histological data was developed, enabling a proper correlation with radiological data. Two different subcutaneous tumors were examined by MR microangiography and DCE-MRI, the latter being post-processed using a pharmacokinetic two-compartment model. Subsequently, tumors were serially sectioned and vessels stained with immunofluorescence markers. A ray-tracing algorithm performed three-dimensional visualization of the histological data, allowing virtually reslicing to thicker sections analogous to MRI slice geometry. Thick slices were processed as parameter maps color coding the marker density in the depth of the slice. Histological 3D reconstructions displayed the diffuse angioarchitecture of malignant tumors. Resliced histological images enabled specification of high enhancing areas seen on MR microangiography as large single vessels or vessel assemblies. In orthogonally reconstructed histological slices, single vessels were delineated. ROI analysis showed significant correlation between histological parameter maps of vessel density and MR parameter maps (r=0.83, P=0.05). The 3D approach to histology improves correlation of histological and radiological data due to proper matching of slice geometry. This method can be used with any histological stain, thus enabling a multivariable correlation of non-invasive data and histology.

Navigation and image-guided HBP surgery: a review and preview.

Image-guided surgery and navigation have resulted from convergent developments in radiology, teletransmission, and computer science. Patient selection and preoperative planning in hepatobiliary-pancreatic (HBP) surgery rely on preoperative imaging. The operative procedure is finally led by the fusion of additional information gained by the palpating hand and intraoperative ultrasound. Despite advances in reducing morbidity and mortality, decisions are often hardly quantifiable and are restricted to super-specialists in HBP surgery. New developments in computed tomography (CT) and magnetic resonance imaging (MRI) technology have led to the possibility of the volumetric prediction of liver resections. These data can be shared via telemedicine and used for simulation and training. Three-dimensional (3D) reconstructions have led to a better topologic understanding of tumor-vascular tree relations in the individual patient. With the increasing use of ablative procedures and laparoscopy, intraoperative imaging and navigation will hold increasing significance for the HBP surgeon. Flat screen monitors adjacent to the surgical field present computer-generated 3D virtual liver resection proposals which can be transferred into the real liver. The main obstacles in HBP navigation are the flexibility and mobility of the target organ. Intrahepatic and surface markers seem to be mandatory for computer-navigated surgery. The first feasibility studies are promising.

Limits of Couinaud's liver segment classification: a quantitative computer-based three-dimensional analysis.

PURPOSE: Traditionally, liver surgery relies on Couinaud's liver segment classification. As the position and shape of these segments are variable and their borders are hidden within the homogeneous liver mass, the accuracy of segment identification methods needs computer-aided reevaluation. METHOD: The segmental liver anatomy of 23 patients receiving diagnostic helical CT scans because of suspected intrahepatic lesion was analyzed with the aid of a computer-based operation-planning system. We compared the standard Couinaud classification, which depends particularly on the main stems of portal and hepatic veins, with a method that calculates the segment borders by analyzing the complete portal venous tree. Volume, shape, and position of the liver segments found by each method were compared. RESULTS: With reference to the portal vein-based method, segmental volumes were overestimated by the classic Couinaud method by up to 24% and underestimated to 13%. Volumes of Couinaud segments 4a, 7, and 8 were generally larger compared with those obtained by the portal vein-based method, whereas segments 3 and 6 were smaller. Gross variations were found in segments 5, 7, and 8. When shape and position were considered, poor correlation was found for five segments (median kappa = 0.35-0.45). Only segments 2, 7, and 8 had kappa values clearly above 0.45 in the majority of cases. The plane that divides the two hemilivers along the middle hepatic vein and the border between the left sector (segments 2 and 3) and the medial sector (4a and 4b) were found in both methods with very good conformity (kappa > 0.75). CONCLUSION: Couinaud's method of dividing the liver into eight autonomous liver segments has to be accepted as a good approximation. Nevertheless, the volume, position, and shape of these segments and their segmental borders show significant variability.