8th Interventional MRI Symposium Book of Abstracts - Otto-von ...

V-14
MR-guided radiofrequency ablation
P. L. Pereira 1,2 , H. Rempp 2 , S. Clasen 2 , D. Schmidt 2 , A. Boss 2 , C. Schraml 2 ,
C. D. Claussen 2
1
Department of Radiology, Minimally-Invasive Therapies and Nuclearmedicine,
SLK-Kliniken, Heilbronn, Germany
2
Department of Diagnostic and Interventional Radiology, Eberhard-Karls University,
Tübingen, Germany
Introduction
Image guided radiofrequency (RF) ablation is a minimally invasive therapy option in
the treatment of primary and secondary hepatic, pulmonal malignancies and renal cancer.
Magnetic resonance (MR) imaging offers an excellent pre-interventional imaging having
important impact on patient selection and planning of the thermoablation procedure. Periinterventional
imaging is used for planning, targeting, monitoring, and controlling of the
ablation procedure. Due to a high soft-tissue contrast offering delineation of tumor tissue and
the surrounding anatomy, coupled with multiplanar capabilities, MR imaging has indiscutable
advantages compared with ultrasonography (US) or computed tomography (CT).
Furthermore, a near-online imaging is feasible at interventional MR units facilitating a fast
and precise placement of the instrument inside the target tissue. MR imaging is sensitive to
thermal effects enabling a monitoring of ablation therapy. Moreover, MR imaging fulfils the
conditions for overlapping ablations gnizing the extent of coagulation as well as by enabling a
precise repositioning of the MR compatible RF applicator if required. MR imaging can be
utilized to define the end point of RF ablation after complete coverage of the target tissue is
verified. Thus, the probability of achieving complete coagulation in larger tumors within a
single therapy session is supposedly increased. A monitoring of thermal effects is moreover
essential in order to prevent unintended tissue damage from critical structures in the
surroundings of the target tissue. Subsequently, the possibility to monitor and control RF
ablation by MR imaging has an important impact on the safety and effectiveness of RF
ablation procedure.
During the last decade, various minimally invasive alternative treatment options for
non resectable tumors specially for liver tumors have emerged. About 90 % of all hepatic
malignancies are metastasis, most of them descending from gastrointestinal tumors, lung
cancer and breast cancer [1]. The fact that 20 % of the patients dying from colon cancer do
not have other than liver metastases shows its prognostic relevance [2-4]. Among other,
highly focused ultrasound, laser induced thermotherapy, microwave and radiofrequency (RF-)
ablation use locally applied heat, aimed to destroy the tumor. The most widely available and
used technique is RF. RF ablation applies an alternating electric current between two electric
poles at a tip of a needle. In the tissue, the heat is produced by the movement of ions under the
influence of a focused electric field at the tip of the probe. In practice, tumors are often larger
than the zone that can be produced by a single needle or a single RF application. Therefore,
overlapping applications have to be performed with the probe being repositioned between the
individual application steps. By this strategy, several overlapping zones may form a larger,
continuous necrotic area including the former tumor and a safety margin at the periphery. It is
obvious that imaging has a key function in optimal planning, performing, monitoring and
controlling percutaneous RF ablation. RF can be used to treat solid tumors in the lung, the
liver and the kidneys or for symptomatic treatments in bones tumors.
For percutaneous treatment of hepatic and renal tumors, different imaging modalities
are used in clinical practice. US is a cheap, easily available, flexible and fast imaging
53