A multichannel, real-time MRI RF power monitor for independent SAR determination

Abdel Monem M. El-Sharkawy, Di Qian, Paul A. Bottomley, William A. Edelstein

Research output: Contribution to journalArticlepeer-review


Purpose: Accurate measurements of the RF power delivered during clinical MRI are essential for safety and regulatory compliance, avoiding inappropriate restrictions on clinical MRI sequences, and for testing the MRI safety of peripheral and interventional devices at known RF exposure levels. The goal is to make independent RF power measurements to test the accuracy of scanner-reported specific absorption rate (SAR) over the extraordinary range of operating conditions routinely encountered in MRI. Methods: A six channel, high dynamic range, real-time power profiling system was designed and built for monitoring power delivery during MRI up to 440 MHz. The system was calibrated and used in two 3 T scanners to measure power applied to human subjects during MRI scans. The results were compared with the scanner-reported SAR. Results: The new power measurement system has highly linear performance over a 90 dB dynamic range and a wide range of MRI duty cycles. It has about 0.1 dB insertion loss that does not interfere with scanner operation. The measurements of whole-body SAR in volunteers showed that scanner-reported SAR was significantly overestimated by up to about 2.2 fold. Conclusions: The new power monitor system can accurately and independently measure RF power deposition over the wide range of conditions routinely encountered during MRI. Scanner-reported SAR values are not appropriate for setting exposure limits during device or pulse sequence testing.

Original languageEnglish (US)
Pages (from-to)2334-2341
Number of pages8
JournalMedical physics
Issue number5
StatePublished - May 2012


  • RF safety
  • SAR
  • heating
  • power monitoring

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

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