To define thresholds of safe local temperature increases for MR equipment that exposes patients to radiofrequency fields of high intensities for long duration. These MR systems induce heterogeneous energy absorption patterns inside the body and can create localised hotspots with a risk of overheating.
The MRI + EUREKA research consortium organised a “Thermal Workshop on RF Hotspots”. The available literature on thresholds for thermal damage and the validity of the thermal dose (TD) model were discussed.
The following global TD threshold guidelines for safe use of MR are proposed:
All persons: maximum local temperature of any tissue limited to 39 °C
Persons with compromised thermoregulation AND
Uncontrolled conditions: maximum local temperature limited to 39 °C
Controlled conditions: TD < 2 CEM43°C
Persons with uncompromised thermoregulation AND
Uncontrolled conditions: TD < 2 CEM43°C
Controlled conditions: TD < 9 CEM43°C
The following definitions are applied:
- Controlled conditions:
A medical doctor or a dedicated trained person can respond instantly to heat-induced physiological stress
- Compromised thermoregulation:
All persons with impaired systemic or reduced local thermoregulation
• Standard MRI can cause local heating by radiofrequency absorption.
• Monitoring thermal dose (in units of CEM43°C) can control risk during MRI.
• 9 CEM43°C seems an acceptable thermal dose threshold for most patients.
• For skin, muscle, fat and bone,16 CEM43°C is likely acceptable.
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This workshop was co-sponsored by the Mobile Manufacturers Forum, the GSM Association, and the US Food and Drug Administration. A selection of the presentations are published in the Special Issue entitled “Thermal Aspects of Radio Frequency Exposure on Human Health”; Int. J. Hyperthermia; 4, 2011. Guest Editor: Joseph Morrissey.
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This study was supported by the EUREKA (E4144) and CTI (9193.1) project MRI+. This study was also supported by The Netherlands Organization for Health Research and Development ZonMw project 85400003 and project 85800002.
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van Rhoon, G.C., Samaras, T., Yarmolenko, P.S. et al. CEM43°C thermal dose thresholds: a potential guide for magnetic resonance radiofrequency exposure levels?. Eur Radiol 23, 2215–2227 (2013). https://doi.org/10.1007/s00330-013-2825-y
- Thermal dose
- Thermal threshold
- Safe exposure