The purpose of this study was to determine the feasibility and features of low-field MR imaging in performing interstitial laser ablation of osteoid osteomas. Between September 2001 and April 2002, five consecutive patients with clinical and imaging findings suggesting osteoid osteoma and referred for removal of osteoid osteoma were treated with interstitial laser treatment. A low-field open-configuration MRI scanner (0.23 T, Outlook Proview, Philips Medical Systems, Finland) with optical instrument guidance hardware and software was used. Laser device used was of ND-Yag type (Fibertom medilas, Dornier Medizin Technik, Germany). A bare laser fiber (Dornier Medizin Technik, Germany) with a diameter of 400 microm was used. Completely balanced steady-state (CBASS; true fast imaging with steady precession) imaging was used for lesion localization, instrument guidance, and thermal monitoring. A 14-G (Cook Medical, USA) bone biopsy drill was used for initial approach. Laser treatment was conducted through the biopsy canal. All the lesions were successfully localized, targeted, and treated under MRI guidance. All the patients were symptom free 3 weeks and 3 months after the treatment. There was one recurrence reported during follow-up (6 months). The MRI-guided percutaneous interstitial laser ablation of osteoid osteomas seems to be a feasible treatment mode.

Salt segregation and isotopic fractionation during sea-ice formation can be parameterized as a function of the ice growth rate. We performed a study to investigate if the salt segregation models derived for saline sea-ice studies are pertinent during the growth of Baltic Sea ice in brackish water. We used a time series of ice-salinity profiles and modeled growth rates to examine the relationship between effective salt segregation and growth rate. The results show that models derived for saline sea water are not directly applicable for use in the brackish waters of the Baltic Sea. We derived a simple model for the effective salt segregation in relation to ice growth rate, for a wide range of growth rates, pertinent for use in low-salinity Baltic Sea conditions and in the future development of a Baltic Sea ice salinity model.