Detailing radio frequency heating induced by coronary stents: a 7.0 Tesla magnetic resonance study.

PloS one · 2012 · Mixed · Low evidence

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MixedLow evidencePaper 4488

Study snapshot

PublicationPloS one · 2012

Study typeengineering

Reported directionMixed

Evidence ratingLow

Abstract

The sensitivity gain of ultrahigh field Magnetic Resonance (UHF-MR) holds the promise to enhance spatial and temporal resolution. Such improvements could be beneficial for cardiovascular MR. However, intracoronary stents used for treatment of coronary artery disease are currently considered to be contra-indications for UHF-MR. The antenna effect induced by a stent together with RF wavelength shortening could increase local radiofrequency (RF) power deposition at 7.0 T and bears the potential to induce local heating, which might cause tissue damage. Realizing these constraints, this work examines RF heating effects of stents using electro-magnetic field (EMF) simulations and phantoms with properties that mimic myocardium. For this purpose, RF power deposition that exceeds the clinical limits was induced by a dedicated birdcage coil. Fiber optic probes and MR thermometry were applied for temperature monitoring using agarose phantoms containing copper tubes or coronary stents. The results demonstrate an agreement between RF heating induced temperature changes derived from EMF simulations versus MR thermometry. The birdcage coil tailored for RF heating was capable of irradiating power exceeding the specific-absorption rate (SAR) limits defined by the IEC guidelines by a factor of three. This setup afforded RF induced temperature changes up to +27 K in a reference phantom. The maximum extra temperature increase, induced by a copper tube or a coronary stent was less than 3 K. The coronary stents examined showed an RF heating behavior similar to a copper tube. Our results suggest that, if IEC guidelines for local/global SAR are followed, the extra RF heating induced in myocardial tissue by stents may not be significant versus the baseline heating induced by the energy deposited by a tailored cardiac transmit RF coil at 7.0 T, and may be smaller if not insignificant than the extra RF heating observed under the circumstances used in this study.

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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 directionmixed

PopulationNot supplied

Sample sizeNot supplied

ExposureRF

Evidence strengthLowConfidence: 74% · Peer reviewed: yes

Main findings

Using EMF simulations and myocardium-mimicking agarose phantoms, RF heating-induced temperature changes from simulations agreed with MR thermometry. A dedicated birdcage coil produced power exceeding IEC SAR limits by a factor of three, yielding up to +27 K in a reference phantom, while the maximum extra temperature increase induced by a copper tube or coronary stent was <3 K; stents showed heating behavior similar to a copper tube. The authors suggest that if IEC local/global SAR guidelines are followed, extra RF heating induced by stents in myocardial tissue may not be significant versus baseline heating from the transmit RF coil at 7.0 T.

Outcomes measured

RF power deposition (SAR)
Temperature change/heating (K) near coronary stents/copper tubes in phantoms
Agreement between EMF simulations and MR thermometry

Limitations

Phantom-based study (agarose phantoms mimicking myocardium), not in vivo human tissue
RF power deposition intentionally exceeded clinical SAR limits using a dedicated birdcage coil, which may not reflect typical clinical conditions
No sample size for number/types of stents reported in the abstract

View raw extracted JSON

{
  "study_type": "engineering",
  "exposure": {
    "band": "RF",
    "source": "MRI (7.0 Tesla)",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": null,
  "sample_size": null,
  "outcomes": [
    "RF power deposition (SAR)",
    "Temperature change/heating (K) near coronary stents/copper tubes in phantoms",
    "Agreement between EMF simulations and MR thermometry"
  ],
  "main_findings": "Using EMF simulations and myocardium-mimicking agarose phantoms, RF heating-induced temperature changes from simulations agreed with MR thermometry. A dedicated birdcage coil produced power exceeding IEC SAR limits by a factor of three, yielding up to +27 K in a reference phantom, while the maximum extra temperature increase induced by a copper tube or coronary stent was <3 K; stents showed heating behavior similar to a copper tube. The authors suggest that if IEC local/global SAR guidelines are followed, extra RF heating induced by stents in myocardial tissue may not be significant versus baseline heating from the transmit RF coil at 7.0 T.",
  "effect_direction": "mixed",
  "limitations": [
    "Phantom-based study (agarose phantoms mimicking myocardium), not in vivo human tissue",
    "RF power deposition intentionally exceeded clinical SAR limits using a dedicated birdcage coil, which may not reflect typical clinical conditions",
    "No sample size for number/types of stents reported in the abstract"
  ],
  "evidence_strength": "low",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "7.0 T",
    "ultrahigh field MRI",
    "radiofrequency heating",
    "coronary stents",
    "antenna effect",
    "SAR",
    "IEC guidelines",
    "birdcage coil",
    "phantom",
    "MR thermometry",
    "EMF simulations"
  ],
  "suggested_hubs": [
    {
      "slug": "who-icnirp",
      "weight": 0.2,
      "reason": "Mentions IEC SAR guideline limits relevant to RF exposure standards (not ICNIRP/WHO directly)."
    }
  ]
}

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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: 10.1371/journal.pone.0049963
PubMed: 23185498

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