**1. Introduction**

Hyperthermia is one of many techniques used in oncology. It uses the physical methods to heat certain organ or tissue delivering an adequate temperature in an appropriate period of time (thermal dose), to the entire tumor volume for achieving optimal therapeutic results. Thermal dose has been identified as one of the most important factors which, influences the efficacy of hyperthermia [Perez and Sapareto (1984)]. Although there are definite prescriptions for temperature (generally 43 ℃) and time (usually �� ���), variations in the temperature and time of delivery are frequent throughout the treatment sessions [Perez and Sapareto (1984), Jordan *et al.* (1999), Jordan *et al.* (2001), Overgaard *et al.* (2009)].

The effectiveness of hyperthermia treatment is related to the temperature achieved during the treatment. An ideal hyperthermia treatment should selectively destroy the tumor cells without damaging the surrounding healthy tissue. [Andrä *et al.* (1999), Lagendijk (2000), Moroz *et al.* (2002), Maenosono and Saita (2006), Lin and Liu (2009)]. Therefore, the ability to predict the temperature distribution inside as well as outside the target region as a function of the exposure time, possesses a high degree of importance.

In the past fifteen years, MFH has drawn greater attention due to the potential advantages for cancer hyperthermia therapy. In MFH, a nanofluid containing the MNPs is injected directly into the tumor. An alternating magnetic field is then applied to the target region, and then MNPs generate heat according to Néel relaxation and Brownian rotation losses as localized heat sources [Jordan *et al.* (1999), Jordan *et al.* (2001), Thiesen and Jordan (2008)]. The heat generated increases the temperature of the tumor. In general, the cancerous cells possess a higher chance to die when the temperature is above 43 ℃ whereas healthy cells will be safe at this temperature [Andrä *et al.* (1999), Moroz *et al.* (2002)].

© 2013 Lahonian, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Two techniques are currently used to deliver the MNPs to the tumor. The first is to deliver particles to the tumor vasculature [Matsuki and Yanada (1994)] through its supplying artery; however, this method is not effective for poorly perfused tumors. Furthermore, for a tumor with an irregular shape, inadequate MNPs distribution may cause under-dosage of heating in the tumor or overheating of the normal tissue. The second approach, is to directly inject MNPs into the extracellular space in the tumors. The MNPs diffuse inside the tissue after injection of nanofluid. If the tumor has an irregular shape, multi-site injection can be exploited to cover the entire target region [Salloum *et al.* (2008a)].

Diffusion of Magnetic Nanoparticles Within a Biological Tissue During Magnetic Fluid Hyperthermia 131

S

**Figure 1.** Schematic of magnetic fluid hyperthermia process.

Heat Healthy Tissue

Tumor

Injection of Magnetic

Fluid

component in a given suspending medium [Nedelcu (2008)].

(2002), Nedelcu (2008)]:

movement of the magnetic moment in an external field that results in heat generation. In the Brownian mode, the whole particle oscillates towards the field with the moment locked along the crystal axis under the effect of a thermal force against a viscous drag in a suspending medium. This mechanism essentially represents the mechanical friction

N

**Figure 2.** Relaxation mechanisms of MNPs in Magnetic Fluid. a) Brownian relaxation, entire particle rotates in fluid; b) Néel relaxation, direction of magnetization rotates in core. The structure of MNP: core (inner), shell (outer). The arrow inside the core represents the direction of magnetization.

a b

Power dissipation of MNPs in an alternating magnetic field is expressed as [Rosensweig

�� ����

1 + (����)� (1)

Nanoparticles

� � �������

The nanofluid injection volume as well as infusion flow rate of nanofluid are important factors in dispersion and concentration of the MNPs, within the tissue. A successful MFH treatment is substantially dependent on the MNPs distribution in the tissue [Bagaria and Johnson (2005), Salloum *et al.* (2008a), Salloum *et al.* (2008b), Lin and Liu (2009), Bellizzi and Bucci (2010), Golneshan and Lahonian (2011a)].
