Matthias Thorn

Computerized planning of liver surgery - An overview

Abstract Liver surgery is a field in which computer-based operation planning has an enormous impact on the selection of therapeutic strategy. Based on pre-operative analysis of image data, liver operation planning provides a individual impression of tumor location, the exact structure of the vascular system and an identification of liver segments and sub-segments. In this paper we present an operation planning system that is based on an object-oriented framework. This framework offers extensive automation of the integration process for software modules developed for medical software systems. The operation planning system can calculate the operation proposal results using two different approaches. The first method is based on the Couinauds classification system, which uses the main stems of the portal and venous trees. The second approach is a portal vein based method. These two approaches were compared using 23 liver CT scans. The volumetric data for individual segments demonstrates differences between the two segment classification methods.

Branching patterns and drainage territories of the middle hepatic vein in computer-simulated right living-donor hepatectomies.

Full right hepatic grafts are most frequently used for adult‐to‐adult living donor liver transplantation (LDLT). One of the major problems is venous drainage of segments 5 and 8. Thus, this study was designed to provide information on venous drainage of right liver lobes for operation‐planning. Fifty‐six CT data sets from routine clinical imaging were evaluated retrospectively using a liver operation‐planning system. We defined and analyzed venous drainage segments and the impact of anatomic variations of the middle hepatic vein (MHV) on venous outflow from segments 5 and 8. MHV variations led to significant shifts of segment 5 drainage between the middle and right hepatic vein. In cases with the most frequent MHV branching pattern (n = 33), a virtual hepatectomy closely right to the MHV intersected drainage vessels that provided drainage for 30% of the potential graft, not taking into account potential veno‐venous shunts. In individuals with inferior MHV branches that extend far into segments 5 and 6 (n = 10), the overall graft volume at risk of impaired venous drainage increased by 5% (p < 0.001). If this is confirmed in clinical trials and correlated with intraoperative findings, the use of liver operation‐planning systems would be beneficial to improve overall outcome after right lobe LDLT.

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.

An interactive system for volume segmentation in computer-assisted surgery

Computer-assisted surgery aims at a decreased surgical risk and a reduced recovery time of patients. However, its use is still limited to complex cases because of the high effort. It is often caused by the extensive medical image analysis. Especially, image segmentation requires a lot of manual work. Surgeons and radiologists are suffering from usability problems of many workstations. In this work, we present a dedicated workplace for interactive segmentation integratd within the CHILI (tele-)radiology system. The software comes with a lot of improvements with respect to its graphical user interface, the segmentation process and the segmentatin methods. We point out important software requirements and give insight into the concepts which were implemented. Further examples and applications illustrate the software system.

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.

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

Abstract: 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.

Medical imaging: examples of clinical applications

Clinical routine is currently producing a multitude of diagnostic digital images but only a few are used in therapy planning and treatment. Medical imaging is involved in both diagnosis and therapy. Using a computer, existing 2D images can be transformed into interactive 3D volumes and results from different modalities can be merged. Furthermore, it is possible to calculate functional areas that were not visible in the primary images. This paper presents examples of clinical applications that are integrated into clinical routine and are based on medical imaging fundamentals. In liver surgery, the importance of virtual planning is increasing because surgery is still the only possible curative procedure. Visualisation and analysis of heart defects are also gaining in significance due to improved surgery techniques. Finally, an outlook is provided on future developments in medical imaging using navigation to support the surgeons work. The paper intends to give an impression of the wide range of medical imaging that goes beyond the mere calculation of medical images.

Empirische Vergleichsmaße für die Evaluation von Segmentierungsergebnissen

In diesem Beitrag entwickeln wir eine Methodik zum umfassenden und objektiven Vergleich von Segmentierungsergebnissen. Dazu wurde zuerst die Verwendung bestehender Gutemase in der Literatur analysiert. Die unterschiedlichen empirischen Mase wurden kategorisiert und auf ihre Einsatzfahigkeit in der medizinischen Bildverarbeitung uberpruft. Die erfolgversprechendsten Methoden wurden in einer klinischen Studie auf ihre Korrelation miteinander untersucht, um die kleinstmogliche Menge von komplementaren Maszahlen zu erhalten.

Generation of attributed relational vessel graphs from three-dimensional freehand ultrasound for intraoperative registration in image-guided liver surgery

We propose a procedure for the intraoperative generation of attributed relational vessel graphs. It builds the prerequisite for a vessel-based registration of a virtual, patient-individual, preoperative, three-dimensional liver model with the intraopeatively deformed liver by graph matching. An image processing pipeline is proposed to extract an abstract representation of the vascular anatomy from intraoperatively acquired three-dimensional ultrasound. The procedure is transferable to other vascularized soft tissues like the brain or the kidneys. We believe that our approach is suitable for intraoperative application as basis for efficient vessel-based registration of the surgical volume of interest. By reducing the problem of intraoperative registration in visceral surgery to the mapping of corresponding attributed relational vessel graphs a fast and reliable registration seems feasible even in the depth of deformed vascularized soft tissues like in human livers.

Robuste Analyse von Gefäßstrukturen auf Basis einer 3D-Skelettierung

In dieser Arbeit wird ein Verfahren vorgestellt, welches es erlaubt, eine symbolische Beschreibung aus segmentierten Blutgefasen zu erzeugen. Im resultierenden Graphen ist der Verlauf der Gefasaste, deren Durchmesser und die Lage von Verzweigungen gespeichert. Der Algorithmus wurde auf Basis eines existierenden Ansatzes entwickelt, der in Bezug auf die Rotationsinvarianz verbessert und um ein neues Grapherzeugungsverfahren erweitert wurde. Zusatzlich werden Methoden bereitgestellt, die es erlauben, die Enstehung von fehlerhaften Asten zu vermeiden, oder sie im nachhinein ausschlieslich auf Basis der Information im Gefasgraphen zu identifizieren und zu loschen.