Planning and Navigation for Minimally Invasive Radiofrequency Ablation

Minimally invasive procedures for cancer diagnosis and therapy are increasingly replacing open procedures in the clinical routine because of their protective character. Therapeutic thermal procedures such as laser-induced thermotherapy (LITT), radiofrequency ablation (RFA) and cryotherapy are, for example, increasingly being used in the minimally invasive treatment of hepatic tumors. The common underlying principle of these procedures is tissue destruction by means of local temperature changes. The success of the intervention crucially depends on the precision of the instrument insertion and thus the experience of the physician. After computer-assisted navigation on rigid structures has become an established practice in the clinical routine, the use of computer support in soft tissues has become limited to non-invasive diagnostics and operation planning. This especially can be attributed to the absent compensation of intra-interventional organ movement. The objective of this project is to develop, implement and evaluate new concepts for computer-assisted biopsies in soft tissues.

Access planning

To achieve a complication-free and rapid implementation of the intervention by means of a well-chosen needle trajectory, a constraint concept was developed for automatic access planning. First, possible insertion zones on the skin are calculated which exclude those needle trajectories to the target that violate at least one of the specified conditions (hard constraints, Figure 1). For example, the needle must not pass through any critical structures and the selected path must be shorter than the needle which is to be inserted. In a second step, the quality of the remaining possible access pathways is evaluated by means of soft constraints which, for example, require a large distance to critical structures and as short a trajectory as possible.

Navigation

To guarantee an accurate and rapid needle insertion in light of the individual anatomy of each patient, a concept was developed in which the pose of an anatomical structure is continuously calculated from the position of automatically tracked fiducial needles or navigation aids [Maier-Hein08a, b]. These are inserted into the target organ before the intervention and are localized relative to the target structure in a preinterventional planning CT. During the intervention, the current target position is calculated from the current position of the fiducial needles by using a suitable deformation model [Maier-Hein08a]. The needle insertion is then performed in a computer-assisted manner with a real time display of the instruments relative to the individual patient anatomy [Seitel07] (Figure 2).
As the liver is one of the most common sites for metastatic disease and is additionally subject to especially large intra-interventional displacements and deformations, the presented concept was implemented and evaluated by using the example of a navigation system for percutaneous liver interventions [Maier-Hein07, Maier-Hein08b, Müller10].

Respiratory motion simulator

To minimize the number of animal experiments required while evaluating the presented methods, a respiratory motion simulator was developed which facilitates conducting experiments in the moving livers of pigs and humans. It essentially consists of a simplified model of the body which provides for the attachment of a liver to an artificial diaphragm. Connecting a ventilator to the model causes a periodic movement of the liver according to a freely selectable pattern of respiration (respiration rate, inspiration and expiration pressure, etc.). An in-vitro study with explanted pig and human livers was able to show that the movement of these livers in the body model caused by the simulator is comparable to the movement of a human liver in vivo [Müller07].

Awards

04/2010 Ingrid zu Solms-Preis for natural sciences 2009/2010 for an outstanding dissertation granted by the Ingrid zu Solms Foundation
05/2009 Waltraud-Lewenz-Preis 2008 for outstanding scientific work granted by the German Cancer Research Center (DKFZ)
04/2008 BVM Award 2008 for best scientific speech on the congress Bildverarbeitung für die Medizin 2008
12/2007 Best Graduate Award 2007 granted by the Graduiertenkolleg 1126: Intelligente Chirurgie
03/2007 BVM Preis 2007 for best poster presentation on the congress Bildverarbeitung für die Medizin 2007

Selected publications

• [P21-07] Maier-Hein L, Pianka F, Seitel A, Müler SA, Tekbas A, Wolf I, Schmied BM, Meinzer HP. Precision targeting of liver lesions with a needle-based soft tissue navigation system. In N. Ayache, S. Ourselin, and A. Maeder, editors, Proceedings of the 10th International Conference on Medical Image Computing and Computer-Assisted Intervention - MICCAI 2007 (2), volume 4792, pages 42-49, Brisbane, Australia, October 2007. Springer.
• [J11-07] Müller SA, Maier-Hein L, Mehrabi A, Gutt CN, Schmidt J, Meinzer HP, Schmied BM. Creation and establishment of a respiratory liver motion simulator for liver interventions. Med Phys 34(12) 2007;4605-4608.
• [P14-07] Seitel A, Maier-Hein L, Schawo S, Radeleff BA, Mueller SA, Pianka F, Schmied BM, Wolf I, Meinzer HP. In-vitro evaluation of different visualization approaches for computer assisted targeting in soft tissue. Int J CARS (2007) 2 (Suppl 1):S188-S190.
• [J03-08] Maier-Hein L, Müller SA, Pianka F, Wörz S, Seitel A, Müller-Stich BP, Rohr K, Schmied BM, Meinzer HP, Wolf I. Respiratory motion compensation for CT-guided interventions in the liver. Computer Aided Surgery 13(3) 2008;125-138.
• [J11-08] Maier-Hein L, Tekbas A, Seitel A, Müller SA, Satzl S, Schawo S, Radeleff B, Tetzlaff R, Franz AM, Müller-Stich BP, Wolf I, Kauczor HU, Schmied BM, Meinzer HP. In-vivo accuracy assessment of a needle-based navigation system for CT-guided radiofrequency ablation of the liver. Med Phys 35(12) 2008;5385-5396.
• [Müller10] Müller, S. A., Maier-Hein, L., Tekbas, A., Seitel, A., Ramsauer, S., Radeleff B., Franz, A. M., Tetzlaff, R., Mehrabi, A., Wolf, I. Kauczor, H.-U., Meinzer, H.-P., Schmied, B. M., „Navigated Liver Biopsy Using a Novel Soft Tissue Navigation System versus CT-guided Liver Biopsy in a Porcine Model: A Prospective Randomized Trial.“, to appear in Academic Radiology

Project team