A two-step risk assessment method for radiofrequency ablations of spine metastases.

BACKGROUND: Spine metastases (MTS) can be treated via Radiofrequency Ablation (RFA) electrodes. To bring these electrodes into vertebral MTS, pathways have to be created. This can be done via transpedicular hammering or drilling. However, this is challenging due to spatial constraints, and because MTS can alter bone density considerably. METHOD: In this work a two-step method is presented that intends to offer cognitive and physical assistance. Step 1 comprises two visualization methods that depict safety margins between and in risk structures. For Step 2, the correlation between Hounsfield Units (HUs) and drilling forces was analyzed to support manual and robot-assisted RFAs. RESULTS: In-depth descriptions of two clinical cases and detailed feedback from the local clinic of neuroradiology are used to present the capabilities of the proposed method. Furthermore, a stiffness criterion is presented to predict drilling force changes from the local distribution and homogeneity of HUs with an inaccuracy of less than 1 mm. CONCLUSIONS: The combination of visualization and drilling force prediction shows potential to support manual and robot-assisted spine RFAs. However, limitations have to be addressed in the future. For example, it has to be carefully evaluated to which extent the proposed method can speed up the planning process and increase intervention safety.

[The hexobarbital sleeping time in a pharmacologico-toxicological experiment with special reference to age and chronobiologically-limited variations in Wistar rat strain WIST/Lppt]. / Untersuchungen zur Hexobarbitalschlafzeit im pharmakologisch-toxikologischen Experiment unter besonderer Berücksichtigung alters- und chronobiologisch bedingter Schwankungen bei Wistarratten Stamm WIST/Lppt.

Investigations were performed to determine the hexobarbital sleeping time (HST) of a strain of Wistar rats (WIST/Lppt). Another aim of the studies was to demonstrate possibilities to use the HST as a method to get additional informations during pharmacological and toxicological experiments. The age--and sex--dependent changes in the hexobarbital sleeping time of the investigated strain of rats are in coincidence with results of other authors, using different rat strains. Additionally, the HST more or less depends on circadian and circannual rhythm. It was stated that the HST as a prescreening-method before starting investigations in detail is of great importance.