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Thermal magnetic resonance: physics considerations and electromagnetic field
simulations up to 23 5 Tesla (1GHz)
#MMPMID26391138
Winter L
; Oezerdem C
; Hoffmann W
; van de Lindt T
; Periquito J
; Ji Y
; Ghadjar P
; Budach V
; Wust P
; Niendorf T
Radiat Oncol
2015[Sep]; 10
(?): 201
PMID26391138
show ga
BACKGROUND: Glioblastoma multiforme is the most common and most aggressive malign
brain tumor. The 5-year survival rate after tumor resection and adjuvant
chemoradiation is only 10 %, with almost all recurrences occurring in the
initially treated site. Attempts to improve local control using a higher
radiation dose were not successful so that alternative additive treatments are
urgently needed. Given the strong rationale for hyperthermia as part of a
multimodal treatment for patients with glioblastoma, non-invasive radio frequency
(RF) hyperthermia might significantly improve treatment results. METHODS: A
non-invasive applicator was constructed utilizing the magnetic resonance (MR)
spin excitation frequency for controlled RF hyperthermia and MR imaging in an
integrated system, which we refer to as thermal MR. Applicator designs at RF
frequencies 300 MHz, 500 MHz and 1GHz were investigated and examined for absolute
applicable thermal dose and temperature hotspot size. Electromagnetic field (EMF)
and temperature simulations were performed in human voxel models. RF heating
experiments were conducted at 300 MHz and 500 MHz to characterize the applicator
performance and validate the simulations. RESULTS: The feasibility of thermal MR
was demonstrated at 7.0 T. The temperature could be increased by ~11 °C in 3 min
in the center of a head sized phantom. Modification of the RF phases allowed
steering of a temperature hotspot to a deliberately selected location. RF heating
was monitored using the integrated system for MR thermometry and high spatial
resolution MRI. EMF and thermal simulations demonstrated that local RF
hyperthermia using the integrated system is feasible to reach a maximum
temperature in the center of the human brain of 46.8 °C after 3 min of RF heating
while surface temperatures stayed below 41 °C. Using higher RF frequencies
reduces the size of the temperature hotspot significantly. CONCLUSION: The
opportunities and capabilities of thermal magnetic resonance for RF hyperthermia
interventions of intracranial lesions are intriguing. Employing such systems as
an alternative additive treatment for glioblastoma multiforme might be able to
improve local control by "fighting fire with fire". Interventions are not limited
to the human brain and might include temperature driven targeted drug and MR
contrast agent delivery and help to understand temperature dependent bio- and
physiological processes in-vivo.
|*Models, Theoretical
[MESH]
|Electromagnetic Fields
[MESH]
|Humans
[MESH]
|Hyperthermia, Induced/*methods
[MESH]
|Magnetic Resonance Imaging
[MESH]
|Magnetic Resonance Spectroscopy/instrumentation/*methods/therapeutic use
[MESH]
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