Figure 4. Measured SAR values for samples dispersed in Isopar M
(top), Isopar V (centre) and wax (bottom). Solid lines are guides to
the eye.
very low value of SAR observed. For a complete agreement to
be achieved it will be necessary for the distribution of particle
elongation and hence the distribution ofKs to be included in the
model. An attempt at this challenging measurement is being
undertaken.
In conclusion, heating arising in magnetic nanoparticles
dispersed in solvents of different viscosity can be understood
when the distributions of physical and hydrodynamic sizes
are known to high accuracy. For the materials described here
the contribution of susceptibility loss to the SAR is small at
111.5 kHz and hysteresis heating is dominant. Measurements
of samples dispersed in wax show that the contribution of
stirring is about 43% of the heating effect. These effects are
uncontrollable and will not occur in vivo. Meaningful SAR
values should be obtained from measurements of samples in a
solid form.