This work examines feasibility, practical advantages, and disadvantages
of a combined MRI/magnetic particle hyperthermia (MPH) system for
cancerous tumor treatment in low perfusion tissue. Although combined
MRI/hyperthermia systems have been proposed and constructed, the current
proposal differs because the hyperthermia system would be specifically
designed to interact with the magnetic nanoparticles injected at the
tumor site. The proposal exploits the physical similarities between the
magnetic nanoparticles currently employed for MPH and those used as
superparamagnetic iron oxide (SPIO) contrast agents in MR imaging. The
proposal involves the addition of a rotating magnetic field RF
hyperthermia source perpendicular to the MRI B0 field which operates in a similar manner to the MRI RF excitation field, B1,
but at significantly higher frequency and field strength such that the
magnetic nanoparticles are forced to rotate in its presence. This
rotation is the source of increases in temperature which are of
therapeutic benefit in cancer therapy. For rotating magnetic fields with
amplitudes much smaller than B0, the nanoparticles' suspension magnetization rapidly saturates with increasing B0.
Therefore, the proposal is best suited to low-field MRI systems when
magnetic saturation is incomplete. In addition, careful design of the RF
hyperthermia source is required to ensure no physical or RF
interference with the B1 field used for MRI
excitation. Notwithstanding these caveats, the authors have shown that
localized steady-state temperature rises in small spherical tumors of up
to 10°C are conceivable with careful selection of the nanoparticle
radius and concentration, RF hyperthermia field amplitude and frequency.