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PURPOSE: The aim of this study was to develop microspheres with an ultra high holmium content which can be neutron activated for radioablation of malignancies. These microspheres are proposed to be delivered selectively through either intratumoral injections into solid tumors or administered via an intravascularly placed catheter.METHODS: Microspheres were prepared by solvent evaporation, using holmium acetylacetonate (HoAcAc) crystals as the sole ingredient. Microspheres were characterized using light and scanning electron microscopy, coulter counter, titrimetry, infrared and Raman spectroscopy, differential scanning calorimetry, X-ray powder diffraction, magnetic resonance imaging (MRI), and X-ray computed tomography (CT).RESULTS: Microspheres, thus prepared displayed a smooth surface. The holmium content of the HoAcAc microspheres (44% (w/w)) was higher than the holmium content of the starting material, HoAcAc crystals (33% (w/w)). This was attributed to the loss of acetylacetonate from the HoAcAc complex, during rearrangement of acetylacetonate around the holmium ion. The increase of the holmium content allows for the detection of (sub)microgram amounts of microspheres using MRI and CT.CONCLUSIONS: HoAcAc microspheres with an ultra-high holmium content were prepared. These microspheres are suitable for radioablation of tumors by intratumoral injections or treatment of liver tumors through transcatheter administration.

Object Proton resonance frequency shift (PRFS)-based MR thermometry (MRT) is hampered by heat-induced susceptibility changes when applied in tissues containing fat, e.g., the human breast. In order to assess the impact of fat susceptibility changes on PRFS-based MRT during thermal therapy in the human breast, reliable knowledge of the temperature dependence of the magnetic volume susceptibility of fat, dχfat/dT , is a prerequisite. In this work we have measured dχfat/dT of human breast fat tissue, using a double-reference method to ensure invariance to temperature-induced changes in the proton electron screening constant. Materials and methods Ex vivo measurements were taken on a 14.1 T five mm narrow bore NMR spectrometer. Breast fat tissue samples were collected from six subjects, directly postmortem. The susceptibility was measured over a temperature range from 24 ◦ Ct o 65 ◦ C. Results A linear behavior of the susceptibility over temperature was observed for all samples. The resulting dχfat/dT of human breast fat ranged between 0.0039 and 0.0076 ppm/ ◦ C. Conclusion It is concluded that the impact of heat-induced susceptibility changes of fat during thermal therapy in the breast may not be neglected.