**4. Diffusion of MNPs in a biological tissue for mono and multi-site injection for irregular tumors**

Golneshan and Lahonian (2011a) studied diffusion of MNPs in a biological tissue for irregular tumors. A 2 � 2��� tissue with an irregular tumor inside, was chosen as the domain of the analysis (Figures 13a).

They considered multi-site injection as shown in Figure 13d and divided the irregular tumor almost into four equal sections. In each injection site, one fourth the amount of 0�2��� ferrofluid was injected. Figure 14 shows the concentration of ferrofluid for infusion flow rate of �� � 20� �� ��� ⁄ , at the end of ferrofluid injection [Golneshan and Lahonian (2011a)].

the injection, the maximum concentration of ferrofluid happens at the injection sites, decreasing rapidly with increasing the distance from the injection sites. At this stage, nearly clear boundaries are seen between diffused ferrofluid for each injection regions. As ferrofluid diffuses more and more, these boundaries are disappeared. Thirty minutes after the injection, the ferrofluid is spread all over the tomour [Golneshan and Lahonian (2011a)].

Diffusion of Magnetic Nanoparticles Within a Biological Tissue During Magnetic Fluid Hyperthermia 143

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Comparison between mono-site and multi-site injections in Figures 15 show that diffusion of ferrofluid in the tissue for a multi-site injection is much more uniform and covers all points inside the tumor 30 minutes after the end of injection process. Furthermore, no substantial concentration gradient is seen between the center and the boundary of the tumor at this time for the multi-site injection case [Golneshan and Lahonian (2011a)].
