Due to finite size effects, such as the high surface-to-volume ratio and different crystal structures, magnetic nanoparticles are found to exhibit interesting and considerably different magnetic properties than those found in their corresponding bulk materials. These nanoparticles can be synthesized in several ways (e.g., chemical and physical) with controllable sizes enabling their comparison to biological organisms from cells (10–100 μm), viruses, genes, down to proteins (3–50 nm). The optimization of the nanoparticles’ size, size distribution, agglomeration, coating, and shapes along with their unique magnetic properties prompted the application of nanoparticles of this type in diverse fields. Biomedicine is one of these fields where intensive research is currently being conducted. In this review, we will discuss the magnetic properties of nanoparticles which are directly related to their applications in biomedicine. We will focus mainly on surface effects and ferrite nanoparticles, and on one diagnostic application of magnetic nanoparticles as magnetic resonance imaging contrast agents.

Localized magnetic hyperthermia using magnetic nanoparticles (MNPs) under the application of small magnetic fields is a promising tool for treating small or deep-seated tumors. For this method to be applicable, the amount of MNPs used should be minimized. Hence, it is essential to enhance the power dissipation or heating efficiency of MNPs. Several factors influence the heating efficiency of MNPs, such as the amplitude and frequency of the applied magnetic field and the structural and magnetic properties of MNPs. We discuss some of the physics principles for effective heating of MNPs focusing on the role of surface anisotropy, interface exchange anisotropy and dipolar interactions. Basic magnetic properties of MNPs such as their superparamagnetic behavior, are briefly reviewed. The influence of temperature on anisotropy and magnetization of MNPs is discussed. Recent development in self-regulated hyperthermia is briefly discussed. Some physical and practical limitations of using MNPs in magnetic hyperthermia are also briefly discussed.

Purpose: To measure for the first time the apparent diffusion coefficient (ADC) values in anatomical regions of the prostate for normal and patient groups, and to investigate its use as a differentiating parameter between healthy and malignant tissue within the patient group.Materials and Methods: Single‐shot diffusion‐weighted echo‐planar imaging (DW‐EPI) was used to measure the ADC in the prostate in normal (N = 7) and patient (N = 19) groups. The spin‐echo images comprised 96 × 96 pixels (field of view of 16 cm, TR/TE = 4000/120 msec) with six b‐factor values ranging from 64 to 786 seconds/mm².Results: The ADC values averaged over all patients in non‐cancerous and malignant peripheral zone (PZ) tissues were 1.82 ± 0.53 × 10⁻³ (mean ± SD) and 1.38 ± 0.52 × 10⁻³ mm²/second, respectively (P = 0.00045, N = 17, paired t‐test). The ADC values were found to be higher in the non‐cancerous PZ (1.88 ± 0.48 × 10⁻³) than in healthy or benign prostatic hyperplasia central gland (BPH‐CG) region (1.62 ± 0.41 × 10⁻³). For the normal group, the mean values were 1.91 ± 0.46 × 10⁻³ and 1.63 ± 0.30 × 10⁻³ mm²/second for the PZ and CG, respectively (P = 0.011, N = 7). Significant overlap exists between individual values among all tissue types. Furthermore, ADC values for the same tissue type showed no statistically significant difference between the two subject groups.Conclusion: ADC is quantified in the prostate using DW‐EPI. Values are lower in cancerous than in healthy PZ in patients, and in BPH‐CG than PZ in volunteers. J. Magn. Reson. Imaging 2002;16:196–200.

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