Christian Schumann, Jennifer Bieberstein, Christoph Trumm, Diethard Schmidt, Philipp Bruners, Matthias Niethammer, Ralf Hoffmann, Andreas Mahnken, Philippe Pereira, Heinz-Otto Peitgen
Percutaneous image-guided interventions, such as radiofrequency ablation (RFA), biopsy, seed implantation, and
several types of drainage, employ needle shaped instruments which have to be inserted into the patient's body.
Precise planning of needle placement is a key to a successful intervention. The planning of the access path has
to be carried out with respect to a variety of criteria for all possible trajectories to the selected target. Since
the planning is performed in 2D slices, it demands considerable experience and constitutes a significant mental
task. To support the process of finding a suitable path for hepatic interventions, we propose a fast automatic
method that computes a list of path proposals for a given target point inside the liver with respect to multiple
criteria that affect safety and practicability. Prerequisites include segmentation masks of the liver, of all relevant
risk structures and, depending on the kind of procedure, of the tumor. The path proposals are computed
based on a weighted combination of cylindrical projections. Each projection represents one path criterion and
is generated using the graphics hardware of the workstation. The list of path proposals is generated in less
than one second. Hence, updates of the proposals upon changes of the target point and other relevant input
parameters can be carried out interactively. The results of a preliminary evaluation indicate that the proposed
paths are comparable to those chosen by experienced radiologists and therefore are suited to support planning
in the clinical environment. Our implementation focuses on RFA and biopsy in the liver but may be adapted to
other types of interventions.
J. Bieberstein, C. Schumann, A. Weihusen, T. Boehler, S. Wirtz, P. Bruners, D. Schmidt, C. Trumm, M. Niethammer, G. Haras, R.-T. Hoffmann, A. Mahnken, P. Pereira, H.-O. Peitgen
Radiofrequency (RF) ablation is an image-guided minimally invasive therapy which destroys a tumor by locally
inducing electrical energy into the malignant tissue through a radiofrequency applicator. Treatment success is essentially
dependent on the accurate placement of the RF applicator. In the case of CT-guided RF ablation of liver tumors, a central
problem during monitoring is the reduced quality and information content in the peri-interventional images compared to
the images used for planning. Therefore, the question of how to effectively transfer information from the planning scan
into the peri-interventional scan in order to support the interventionalist is of high interest. Key to such an enhancement
of peri-interventional scans is an adequate registration of the pre- and peri-interventional image, which also needs to be
fast since intervention duration is still a challenge. We present an approach for the fast and automatic registration of a
high quality CT volume scan of the liver to a spiral CT scan of lower quality. Our method combines an approximate pre-registration
to compensate large displacements and a rigid registration of a liver subvolume for further refinement. The
method focuses on the position of the tumor to be ablated and the corresponding access path. Thereby, it achieves both
fast and precise results in the region of interest. A preliminary evaluation, on 37 data sets from 20 different patients,
shows that the registration is performed within a maximum of 18 seconds, while obtaining high accuracy in the relevant
region of the liver comprising tumor and the planned access path.
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