A single volume element (voxel) in a medical image may be composed of a mixture of multiple tissue types. The authors call voxels which contain multiple tissue classes mixels. A statistical mixel image model based on Markov random field (MRF) theory and an algorithm for the classification of mixels are presented. The authors concentrate on the classification of multichannel magnetic resonance (MR) images of the brain although the algorithm has other applications. The authors also present a method for compensating for the gray-level variation of MR images between different slices, which is primarily caused by the inhomogeneity of the RF field produced by the imaging coil.

We studied via computer simulation the effects of electrode diameter, electrode length, interelectrode spacing, and tissue size on the accuracy of measured tissue resistivities and anisotropy ratios obtained with the widely used four-electrode technique. Such measurements commonly assume an ideal situation in which the four electrodes are infinitesimally small and the tissue is semi-infinite. Our study shows that these geometric factors can significantly affect measured resistivities, particularly for anisotropic tissues. The measured anisotropy ratio is decreased by either 1) increasing the electrode diameter or length relative to the interelectrode spacing of the probe or 2) decreasing tissue size. We have provided an equation for estimating errors in the measured anisotropy ratio from the parameters of electrode and tissue geometries. The simulation findings are supported by our in vitro experimental results.

Magnetic nanoparticles (MNPs) possessing low Curie temperatures (TC’s) offer the possibility for self-regulated heating of cancer cells, where the TC acts as an upper limit to heating to prevent damage to neighboring healthy tissue. We report the synthesis of monodisperse metastable fcc γ-phase Fe–Ni MNPs possessing tunable TC’s, whose stoichiometries have been predicted from metastable extensions to an equilibrium Fe–Ni phase diagram. Metastable alloys have been predicted within the constructs of the T0 construction in the Fe–Ni eutectoid phase diagram. Fe–Ni MNPs have been synthesized via chemical reduction in Fe- and Ni-precursors with stoichiometries ranging from Fe90Ni10 to Fe70Ni30. Mn-precursors have been added to further reduce the alloy’s TC. MNP morphology and structure have been confirmed by x-ray diffraction and transmission electron microscopy while magnetic properties were investigated using vibrating sample magnetometry. Fe70Ni30 MNPs were found to have a TC of 82 °C and specific magnetization of 66 emu/g. Addition of 1 wt % Mn to Fe75Ni25 reduced the TC to 78 °C, which is the lowest reported for fcc Fe–Ni alloys. We also report a model for radio frequency self-regulated heating, in which the maximum achievable temperature of water-MNP suspensions (TC<100 °C) or octyl ether-MNP suspensions (TC>100 °C) is approximately the TC of the MNPs suspended in the solution.

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