B1+rms vs SAR

What is the key difference between SAR and B1+rms as safety metrics?. SAR is based solely on imaging parameters, while B1+rms is based on patient physiology. SAR is an estimate based on patient weight and tissue composition, whereas B1+rms is based strictly on imaging parameters. B1+rms is measured in Watts per kilogram, while SAR is measured in micro-Tesla. There is no difference; the terms are interchangeable.

In the term B1+rms, what does the "+" (plus sign) refer to?. The addition of multiple RF pulses. The positively rotating component of the B1 field that excites nuclear spins. The increase in temperature within the tissue. The electrical charge of the RF transmitter coil.

What does "RMS" stand for in the context of RF safety metrics?. Radiofrequency Magnetic Strength. Relative Magnetic Stability. Real-time Monitoring System. Root Mean Square.

What is the standard unit of measurement for B1+rms?. Watts per kilogram (W/kg). Decibels (dB). Micro Tesla ($\mu T$). Volts per meter (V/m).

According to the pacemaker example in the video, what must be done if a 3T system does not report B1+rms?. Proceed with the scan using standard SAR limits. The patient must be imaged on a 1.5T system using SAR limits described in the labeling. The technologist must manually calculate the B1+rms. The pacemaker must be removed before the scan.

In the clinical example provided, how does the landmark position affect B1+rms limits?. If the landmark is above C7, there are no B1+rms limits; if below C7, it must not exceed 2.8 $\mu T$. There are no limits regardless of the landmark. If the landmark is below the waist, the B1+rms limit is doubled. Landmarks are only used for SAR calculations, not B1+rms.

If you need to reduce the B1+rms for a sequence, what action should you take?. Decrease the TR (Repetition Time). Make changes to the sequence that would also reduce SAR (e.g., increase TR or reduce refocusing angles). Increase the number of slices. Increase the flip angle.

Where is the B1+rms information typically found on the MRI system's user interface?. In the patient registration tab. On a separate physical monitor outside the control room. In the image post-processing menu. In the same area or tab as the SAR information.

When using some MRI systems, when do the B1+rms display the most accurate value for a planned sequence?. Immediately upon loading the protocol. Only after the scan has finished. Only after the scan prep or pre-scan phase has been performed. When the scanner is in standby mode.

Why is it recommended to disable the "automatic start" feature when scanning an implant with B1+rms limits?. To save electrical power. To allow the system to pause so the user can verify the B1+rms value after the prep phase. To prevent the patient from becoming anxious. To allow the magnet to cool down between sequences.