## 4 Discussion  
The heating mechanism during RFTA using superparamagnetic iron oxide magnetic nanoparticles of 20 nm in size is explained mainly by the Neel and Brownian relaxation depicted in Figure 12. During the Neel relaxation, the magnetic nanoparticles applied to the external electromagnetic moment rotate within the crystal to align with the magnetic moment, while during the Brownian motion, the rotation of particles happens to align the magnetic moment that is enclosed to the crystal axis as depicted in Figure 12[27]. Hence, the superparamagnetic nanoparticles of 20 nm in size produce the increment of heat absorbing the electromagnetic energy when the particle moment tends to return to its equilibrium state [28]. The size of nanoparticles used for the thermal ablation procedure is vital and varied between 10 and 30 nm in order to have single domain superparamagnetic nanoparticles. The other vital parameters of nanoparticles used for the thermal therapy are the concentration of nanoparticles that is in direct proportion to the sum of the generated heat, and the dynamic viscosity that influences the amount of generated heat by Brownian relaxation. The solvents with higher viscosity affect the Brownian rotation phenomena leading to the decrease in heat generation [15]. Moreover, it is preferable to inject the lower concentration of nanoparticles to prevent the negative impact of high concentrations and ease of washing out from the body.  
Figure 11: The maximum temperature reached during the radiofrequency ablation of porcine liver loaded with 20 nm iron oxide nanoparticles dispersed: (**A**) in agarose solvent; and (**B**) in chitosan solvent.  
Figure 12: The schematic representation of the physical mechanism of electromagnetic energy transfer into heat when nanoparticles are used.  
The studies regarding the thermal dosimetry for optimal thermal ablation therapy demonstrated the demand in the achievement of cytotoxicity heat range between 42 \({}^{\circ}\)C and 60 \({}^{\circ}\)C in order to get the protein coagulation and cell damage as can been seen from the scale in Figure 12. However, it is important to prevent the heat of the cells at a temperature higher than 100 \({}^{\circ}\)C because at this range, the vaporization and carbonization of tissue happen which decreases the heating outcome [9]. Therefore, the broad investigation of the impact of nanoparticles during the thermal ablation procedure provides the advanced protocol to optimize the time and concentration of nanoparticles to terminate the process when the desired parameters were obtained. Table 2 provides the extensive results of the maximum temperatures obtained during RFTA along with the maximum ablated diameters (d\({}_{60}\) and d\({}_{42}\)) reached at temperatures of 42 and 60 \({}^{\circ}\)C including the mean value and standard deviations recorded during 10 trials of experimental studies.  
The current research involved 200 experimental trials conducted for 10 concentrations of IONPs dispersed in two solvents among 10 trials in order to evaluate the heating properties of nanomaterials that were measured using the 16-element array FBGs. It is important to note that for all the trials, the single 16-element array FBG sensing system was employed, demonstrating the accurate temperature recording without diminishing its property over the measurements. In addition, the sensing system validated that the temperature increment over 42 \({}^{\circ}\)C occurs only at an area of close proximity to the electrode tip and where the nanoparticles were introduced, which made it possible to prevent the overheating of the surrounding area.  
The estimated results brought to the conclusion that the magnetic nanoparticles dispersed in both solvents behave similarly regarding the increase in the ablation area and reaching the maximum temperature, however, agarose demonstrated better heating features by reaching the cytotoxicity temperature ranges in a shorter time and lower concentrations compared to the IONPS dispersed in chitosan solutions.