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library:specific_absorption_rate [2025/06/21 18:44] – scottlibrary:specific_absorption_rate [2026/07/20 13:45] (current) – [Reducing SAR] scott
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 On even relatively older scanners, SAR is tracked throughout the scan, typically in 15 minute intervals. If the scanner senses SAR limits being exceeded, scanning will be prohibited and a 'cool down' time will have to elapse before scanning can resume. When scanning veterinary patients, body weights are typically far lower than the SAR model was meant to be used with, leading to inaccurate estimates and SAR errors preventing scanning unnecessarily. Additionally, animals under anesthesia do not have the same thermoregulatory capacity as when they're awake, often leading to patients being too cold despite what the scanner SAR level reads. Generally, the best approach is to maintain adequate patient temperature with blankets and warmers, and mitigate SAR errors so they don't prolong anesthesia time. On even relatively older scanners, SAR is tracked throughout the scan, typically in 15 minute intervals. If the scanner senses SAR limits being exceeded, scanning will be prohibited and a 'cool down' time will have to elapse before scanning can resume. When scanning veterinary patients, body weights are typically far lower than the SAR model was meant to be used with, leading to inaccurate estimates and SAR errors preventing scanning unnecessarily. Additionally, animals under anesthesia do not have the same thermoregulatory capacity as when they're awake, often leading to patients being too cold despite what the scanner SAR level reads. Generally, the best approach is to maintain adequate patient temperature with blankets and warmers, and mitigate SAR errors so they don't prolong anesthesia time.
  
-====Reducing SAR While Scanning====+====Reducing SAR====
  
 The first part of knowing how to reduce SAR errors is knowing where and when they are likely to occur: The first part of knowing how to reduce SAR errors is knowing where and when they are likely to occur:
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   * Large axial stacks of T1's   * Large axial stacks of T1's
   * Post contrast imaging: lots of T1's back to back   * Post contrast imaging: lots of T1's back to back
 +  * Very high bandwidth sequences; results in shorter spacing between RF pulses
  
 SAR reduction strategies are pretty straightforward: reduce the amount, frequency, and strength of RF pulses!  SAR reduction strategies are pretty straightforward: reduce the amount, frequency, and strength of RF pulses! 
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   * Choose Low SAR RF mode   * Choose Low SAR RF mode
   * Space out T1 FSE with T2's or GRE's   * Space out T1 FSE with T2's or GRE's
 +  * Decrease bandwidth
  
-While not explicitly a 'safe' thing to do, it is possible to trick the scanner with very very small patients by inputting a weight of 10kg or above.+While not explicitly a 'safe' thing to do, it is possible to trick the scanner with very very small patients by inputting a weight of 10kg or above. This can be done if needed to prevent the scanner from stopping scanning because the SAR model is inaccurate for very small animals, and SAR becomes overestimated.