Thus, the B1+RMS value is calibrated by the MR system’s software during the “prep” or “pre-scan” phase or measurements of an MRI exam. The MR scanner measures the B1+ field (the positively rotating RF magnetic field produced by the scanner) needed for an imaging sequence and uses the time averaged B1+ field, or B1+RMS, that will occur due to a particular imaging sequence. B1+RMS is measured in units of micro-Tesla (μT). A number of years ago, the Joint Working Group comprised of scientists and scientists affiliated with MR system and device manufacturers, along with the FDA, recommended that B1+RMS be used as a metric for implant heating as opposed to using SAR.ī1+RMS is the root-mean-square value of the MRI effective component of the RF magnetic (B1) field or, in other words, the time-averaged RF magnetic field component relevant for creating an MR image that is generated by the MR system during a scan. Therefore, it is potentially dangerous to use SAR in these cases, as reported by Baker, et al. When active implants and devices are present in patients, the use of SAR appears to be an unreliable means of characterizing RF-induced heating. As a result, MR system manufacturers rely on numerical models to conservatively estimate the SAR for a particular scan sequence and each manufacturer uses conservative assumptions for their SAR models to ensure that no patient is exposed to RF energy that exceeds the specified SAR limits. Of note is that there is no direct way to measure SAR prior to or during an MRI procedure. SAR is patient dependent and varies depending on the patient’s size and mass (weight). SAR is the rate at which energy is absorbed by the body when exposed to the RF electromagnetic field (B1) and is measured in units of Watts per kilogram (W/kg) of body weight. The metric typically presented in MR Conditional labeling that addresses this matter is the whole body averaged specific absorption rate (SAR). When performing magnetic resonance imaging (MRI) examinations on patients with implants and devices, it is important to be aware of, and to control, the amount of radiofrequency (RF) power that is utilized in order to ensure patient safety. B1+RMS, The root-mean-square value of the MRI Effective Component of the RF Magnetic (B1) Field

Clearview value metric mri