# Magnetic Nanoparticles as Mediators for Magnetic Hyperthermia Therapy Applications: A Status Review
## 3 Results and Discussion
### Calorimetric Measurements  
Figures 25-27 show the calorimetric measurements of maghemite MNPs coated with CM-dextran, (Mg, Ti)-ferrite MNPs, NiCu MNPs synthesized by microemulsion technique and sol-gel method, and ball-milled NiCu and NiCr MNPs. Magnetic heating effect measurements were performed in a conventionally built calorimetric system that generates an AMF with a nominal field strength of 2 kA/m up to 42 kA/m in the frequency range from 80 kHz to 800 kHz and equipped with a fiber optic temperature probe to measure the temperature required to determine the specific absorption rate (SAR). Figure 24: Magnetization vs. magnetic field of Cu\({}_{1-x}\)Ni\({}_{x}\) alloy particles, samples (A–F) ball-milled for 20 h.  
In Figure 25, left graph, a time dependence of the heating of maghemite nanoparticles coated with CM-dextran (sample B) under the influence of different AMF intensities at 104 kHz [27] can be seen. The values of SAR were calculated based on the calorimetric response at a frequency of 104 kHz and in the range of 1.5 to 3 kA/m. The SAR was estimated as:  
\[\text{SAR}=\left(\frac{C_{\text{solvent}}}{x_{\text{iron oxide}}}\right)\left( \frac{\Delta T}{\Delta t}\right), \tag{2}\]  
Figure 27: Time function of self-heating temperature under the influence of a magnetic field of varying strength for Cu\({}_{27.5}\)Ni\({}_{72.5}\) (sample C) at AMF m1- \(H\) = 3.83 kA/m; m2- \(H\) = 3.13 kA/m; m3- \(H\) = 2.41 kA/m—(**left graph**)—and time function of self-heating temperature under the influence of a magnetic field of varying strength for Cr\({}_{28}\)Ni\({}_{72}\) at AMF (a) \(H\) = 9.20 kA/m; (b) \(H\) = 12.52 kA/m; (c) \(H\) = 16.18 kA/m—(**right graph**). Figure 25: Time dependence of the heating of maghemite nanoparticles coated with CM-dextran (sample B) under the influence of different AMF intensities—(**left graph**)—and the calorimetric measurements of a sample (Mg. Ti)-ferrite (x = 0.37, sample B), at different magnitudes of AFM—(**right graph**) (a) 8.4 kA/m; (b) 12,7 kA/m; (c) 16.9 kA/m; (d) 21.7 kA/m; (e) 25.4 kA/m; (f) 29.6 kA/m). where \(c_{\text{solvent}}\) is the heat capacity of the solvent (\(c\) = 4.18 J/Kg for water); \(x_{\text{iron oxide}}\) is the weight fraction of iron oxide; and \((\Delta T/\Delta t)\) is the initial slope of the time dependence of the self-heating temperature. After a certain period of self-heating, the steady state was achieved when generated heat at a constant temperature was equal to that lost to the environment due to thermal convection. The maximum temperature of this steady state is important when iron oxide-based magnetic fluids (MFs) with a high \(T_{\text{C}}\) are used for in vivo applications, as this is the only way to use such an MF without damaging the surrounding tissue during MH. Figure 25, right graph, shows tested MNPs and the corresponding MF for the SAR [26]. From the course, the SAR was estimated as:  
\[\text{SAR}=\left(\frac{C_{solvent}}{x_{(Mg,\,\,Ti)-ferite}}\right)\left(\frac{ \Delta T}{\Delta t}\right), \tag{3}\]  
where \(c_{solvent}\) equals \(c_{\text{water}}\) 4.18 J/kg; \(x_{(Mg,\,\,Ti)-ferite}\) is the weight fraction of (\(Mg\), \(Ti\))-ferrite; and \((\Delta T/\Delta t)\) is the initial heating slope as a function of time. SAR values were estimated between 1.2 and 3.9 W/g (8.4 kA and 29.6 kA/m). The result of calorimetric measurements shows that the stationary temperature is higher than the planned \(T_{\text{C}}\) (sample B, \(x\) = 0.37). In Figure 26, left graph, a calorimetric measurements for the Ni\({}_{0.725}\)Cu\({}_{0.725}\) sample performed under the influence of AMF with an amplitude between 16.9 and 42.0 kA/m and a frequency of 104 kHz [41] can be seen. The SAR was estimated as:  
\[\text{SAR}=(c_{\text{Ni}})\left(\frac{\Delta T}{\Delta t}\right), \tag{4}\]  
where \(c_{\text{Ni}}\) represents the heat capacity of nickel and is 0.444 J/kg. \(\Delta T/\Delta t\) represents the initial slope of the time dependence of the self-regulating temperature.