Optimisation of the coagulation zone for thermal ablation procedures: a theoretical approach with considerations for practical use.

PURPOSE: This paper outlines a theoretical approach for optimisation of the coagulation zone for thermal ablation procedures and considerations for its practical application. METHODS: The theoretical approach is outlined in the Cartesian coordinate system. Considerations for practical application are implemented. The optimised coagulation zone is defined as the bare coverage of tumour mass plus a safety margin. The eccentricity of coagulation centre (ECC) is defined as the distance between the coagulation centre and the tumour centre. The direction of the applicator shaft is determined based on the x-axis direction. The tumour centre and coagulation centre are defined within the x/y-plane. The distance between coagulation margin (applicator tip) and tumour margin is called parallel offset (PAO). RESULTS: For spherical coagulation shapes, a linear relationship exists between optimised coagulation diameter and ECC. An exponential relationship exists between optimised coagulation volume and ECC. A complex relationship was found between PAO and determinants of ECC, which are ex and ey. PAO is an extremely important parameter, which allows for determination of the optimal applicator tip position in relation to the tumour margin. It can be calculated in such a manner that the optimised coagulation zone is minimised by neutralising dislocation of the coagulation centre in applicator shaft direction. The latter can be realised by withdrawing or further inserting the applicator shaft. CONCLUSIONS: The presented concept can be used to optimise the extent of the coagulation zone for thermal ablation procedures after positioning of the applicator. Its inherent advantage is the simple adjustment of the applicator shaft, which obviates the need for a repuncture.

Effect of tissue perfusion on microwave ablation: experimental in vivo study in porcine kidneys.

PURPOSE: To determine the effect of tissue perfusion on microwave ablation lesions in an experimental in vivo study in porcine kidneys. MATERIALS AND METHODS: Twelve kidneys of six pigs were studied. In each animal, two microwave ablations were created in one kidney without limitation of tissue perfusion (group 1). In the other kidney, two microwave ablations were performed with interruption of blood flow (group 2). All microwave ablations were performed with identical system parameters (eg, temperature control mode, ablation time of 80 s, and temperature of 110°C). The animals were euthanized 3 hours later. The kidneys were harvested and cut into 2-3-mm transverse slices. Microwave ablation zone dimensions (eg, length, width, and volume) and shape (eg, sphericity ratio) and corresponding variability were compared between groups. RESULTS: Microwave ablation areas were significantly longer (41.6 mm ± 4.0 vs 34.2 mm ± 5.9; P < .01) and wider (16.6 mm ± 1.2 vs 12.2 mm ± 2.1; P < .001) in group 2 than in group 1. Similarly, microwave ablation volume was significantly greater in group 2 compared with group 1 (6.7 cm(3) ± 1.0 vs 3.3 cm(3) ± 1.2; P < .001). Ablation area shapes were similar between groups (sphericity ratio, 2.57 ± 0.42 vs 2.39 ± 0.34). Ablation area variabilities were also comparable between groups (volume variance of 1.32 vs 0.93; sphericity ratio variance of 0.18 vs 0.11). CONCLUSIONS: After interruption of blood flow, microwave ablation areas are significantly larger than those achieved without limitation of tissue perfusion. Microwave ablation area shape and variability were comparable between study groups.

Application of a new segmentation tool based on interactive simplex meshes to cardiac images and pulmonary MRI data.

RATIONALE AND OBJECTIVES: Medical image segmentation is still very time consuming and is therefore seldom integrated into clinical routine. Various three-dimensional (3D) segmentation approaches could facilitate the work, but they are rarely used in clinical setups because of complex initialization and parametrization of such models. MATERIALS AND METHODS: We developed a new semiautomatic 3D-segmentation tool based on deformable simplex meshes. The user can define attracting points in the original image data. The new deformation algorithm guarantees that the surface model will pass through these interactively set points. The user can directly influence the evolution of the deformable model and gets direct feedback during the segmentation process. RESULTS: The segmentation tool was evaluated for cardiac image data and magnetic resonance imaging lung images. Comparison with manual segmentation showed high accuracy. Time needed for delineation of the various structures could be reduced in some cases. The model was not sensitive to noise in the input data and model initialization. CONCLUSIONS: The tool is suitable for fast interactive segmentation of any kind of 3D or 3D time-resolved medical image data. It enables the clinician to influence a complex 3D-segmentation algorithm and makes this algorithm controllable. The better the quality of the data, the less interaction is required. The tool still works when the processed images have low quality.

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.