RTSAR

Real Time SAR is only available with 3.0T systems. When you enter the prescription for the first scan in an exam, the system predicts an estimated SAR. At the end of the first scan, a (RTSAR) correction factor is estimated. This correction factor is the ratio between the measured SAR and the estimated SAR of the first scan. For the second series onwards, the estimated SAR is multiplied with the RTSAR correction factor and hence should result in fewer power monitor trips.

Since RTSAR correction factor is based on the first scan, it is highly recommended to prescribe a reasonably SAR intensive first scan lasting at least approximately 15 seconds (for example a 3-plane SSFSE localizer).

For optimal RTSAR functionality for a spine exam, it is highly recommended to center the first scan at or superior to the xyphoid process if the intended exam includes thoracic spine scans. Otherwise, the first scan is recommended to be centered on the intended anatomy.

If the SAR measured during the first scan is greater than the estimated SAR, the system automatically makes changes to the subsequent RTSAR-enabled sequences (Spin Echo, Single Shot Spin Echo and 2D Fast Spin Echo) in the Workflow Manager. For those sequences:

• The number of slices per acquisition may be less.
• The SAR limited TR is increased. If the prescribed TR is less than the SAR limited TR, the series acquisition may be changed from one to two acquisitions in order to acquire the prescribed number of slices.
• It Auto TR is ON, the TR is automatically adjusted; it is increased to accommodate the prescribed number of slices. You have two choices:
  • keep the increased TR, which may affect image contrast.
  • decrease the TR to the protocol TR and accept the increased scan time due to two rather than one acquisition.