RF Safe

Thermal magnetic resonance: physics considerations and electromagnetic field simulations up to 23.5 Tesla (1GHz).

Radiation oncology (London, England) · 2015 · Unclear · Insufficient evidence

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UnclearInsufficient evidencePaper 4746

An integrated RF hyperthermia and MR imaging system (“thermal MR”) was demonstrated as feasible at 7.0 T. In a head-sized phantom, temperature increased by ~11°C in 3 minutes and RF phase modification enabled steering of the temperature hotspot. Simulations i…

Study snapshot

PublicationRadiation oncology (London, England) · 2015
Study typeengineering
Reported directionUnclear
Evidence ratingInsufficient

Abstract

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.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typeengineering
Effect directionunclear
PopulationNot supplied
Sample sizeNot supplied
ExposureRF · ~3 min RF heating (reported in phantom and simulations)
Evidence strengthInsufficientConfidence: 74% · Peer reviewed: yes

Main findings

An integrated RF hyperthermia and MR imaging system (“thermal MR”) was demonstrated as feasible at 7.0 T. In a head-sized phantom, temperature increased by ~11°C in 3 minutes and RF phase modification enabled steering of the temperature hotspot. Simulations in human voxel models suggested a maximum central brain temperature of 46.8°C after 3 minutes while surface temperatures remained below 41°C, and higher RF frequencies reduced hotspot size.

Outcomes measured

  • Feasibility of integrated RF hyperthermia with MR imaging/thermometry (thermal MR)
  • Temperature increase and hotspot steering in head-sized phantom
  • Simulated brain and surface temperatures in human voxel models
  • Effect of RF frequency on hotspot size

Limitations

  • No clinical outcomes or patient data reported (focus on simulations and phantom experiments)
  • Key exposure metrics such as SAR were not reported in the abstract
  • Frequencies investigated are listed, but the specific frequency corresponding to the 7.0 T demonstration is not explicitly stated in the abstract
View raw extracted JSON
{
  "study_type": "engineering",
  "exposure": {
    "band": "RF",
    "source": "magnetic resonance (thermal MR) RF hyperthermia applicator",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": "~3 min RF heating (reported in phantom and simulations)"
  },
  "population": null,
  "sample_size": null,
  "outcomes": [
    "Feasibility of integrated RF hyperthermia with MR imaging/thermometry (thermal MR)",
    "Temperature increase and hotspot steering in head-sized phantom",
    "Simulated brain and surface temperatures in human voxel models",
    "Effect of RF frequency on hotspot size"
  ],
  "main_findings": "An integrated RF hyperthermia and MR imaging system (“thermal MR”) was demonstrated as feasible at 7.0 T. In a head-sized phantom, temperature increased by ~11°C in 3 minutes and RF phase modification enabled steering of the temperature hotspot. Simulations in human voxel models suggested a maximum central brain temperature of 46.8°C after 3 minutes while surface temperatures remained below 41°C, and higher RF frequencies reduced hotspot size.",
  "effect_direction": "unclear",
  "limitations": [
    "No clinical outcomes or patient data reported (focus on simulations and phantom experiments)",
    "Key exposure metrics such as SAR were not reported in the abstract",
    "Frequencies investigated are listed, but the specific frequency corresponding to the 7.0 T demonstration is not explicitly stated in the abstract"
  ],
  "evidence_strength": "insufficient",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "glioblastoma multiforme",
    "hyperthermia",
    "radiofrequency",
    "thermal magnetic resonance",
    "MR thermometry",
    "electromagnetic field simulations",
    "human voxel models",
    "phantom heating",
    "7.0 T",
    "300 MHz",
    "500 MHz",
    "1 GHz"
  ],
  "suggested_hubs": [
    {
      "slug": "who-icnirp",
      "weight": 0.2,
      "reason": "Involves RF exposure and EMF simulations, potentially relevant to RF safety context, though primarily a therapeutic engineering study."
    }
  ]
}
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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1186/s13014-015-0510-9
PubMed: 26391138

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