SAR

1. SAR Specific Absorption Rate

2. SAR Defined..What Factors Impact SAR? The SAR Power Monitor Preventing Monitor Trips Tips for Optimizing Protocols Agenda

3. SAR: A measure of RF absorption and the patient’s ability to dissipate excess heat (measured in watts/kg). Patient Weight Coil being used (local T/R vs. body coil T/R) Number slices Saturation pulses (spatial and spectral) ETL Flip angle TR Pulse sequence Amplitude of pulses Tissue specific heating 3.0T Physics: What Affects SAR? Q. Which of these factors can the technologist directly impact?

4. As field strength increases, more power is needed to flip the protons, especially in the body coil. Management Techniques: Power Monitor Modify protocols and workflow to use less power or decrease SAR Apply imaging options that reduce SAR Use localized transmit/receive coils Always use the patient alert device 3.0T Physics: SAR Considerations

5. 3.0T Physics: SAR Management Real Time Power Monitor • Use it for your initial protocol set-up to improve work-flow efficiency • On HD monitor “Pops-up” at 50% and 85% of the regulatory limit On HDx..this monitor stays on at all times!

6. Do not use the auto scan feature on thin patients 3.0T systems are more sensitive to patient positioning than 1.5T…keep body coil loading considerations in mind. Ensure that predicted SAR does not exceed 2.5W/Kg Do not use the Auto Scan feature with thin patients Always use first level operating mode Consider applying SAR reducing imaging options as appropriate (ASSET, VERSE, MART, Tailored RF) Consider interleaving high SAR series, such as FSE, FLAIR and SSFSE or use lower SAR series such as GRE to prevent “tripping” of the power monitor. Preventing SAR Monitor Trips Workflow Considerations:

7. If regulatory limits for six minutes are reached, the scan pauses. You must wait until regulatory limits are satisfied before re-launching the scan. No data is lost. If the 10 second average is reached, the scan pauses. You must wait until regulatory limits are satisfied before re-launching the scan. No data is lost. . SAR Management Cont….

8. 3.0T Physics: SAR Management Tips For Protocol Optimization • Increasing TR decreases SAR • Keeping the same amount of energy (# of slices, ETL, etc.) but extending time (TR) reduces SAR • Example: • Double the TR= ½ the SAR! Increased TR

9. MART VERSE ASSET 3.0T Physics: SAR Management Tips For Protocol Optimization

10. MART- Modulated Angle Refocusing Train Decreases SAR by modifying the RF pulse A “pseudo” steady-state is reached Uses a constant FA for the center of K-space Considerable reduction in SAR, without large SNR loss Use for SSFSE on 3.0T 3.0T Physics: SAR Management Tips For Protocol Optimization

11. VERSE- Variable Rate Selective Excitation Decreases SAR by modifying the RF pulse through a reduced power technique Re-shaping of the RF pulses Gradient scaling proportionate with RF amplitude Use on all FSE sequences, except SSFSE 3.0T Physics: SAR Management Tips For Protocol Optimization

12. 3.0T Physics: SAR Management Tips For Protocol Optimization Parallel Imaging • Related Terms and Techniques: • ASSET = GE • SENSE = Philips • iPAT = Siemens

13. 3.0T Physics: SAR Management Tips For Protocol Optimization • 2D Fast Recovery Fast Spin Echo – 2DFRFSE • 2D Fast Recovery Fast Spin Echo-XL – 2DFRFSE-XL • 2D Fast Spin Echo Inversion Recovery – 2DFSEIR • 2D T1 Fluid Attenuated Inversion Recovery- 2D T1 FLAIR • 3D Fluid Attenuated Inversion Recovery- 3D FLAIR • Single Shot Fast Spin Echo – SSFSE • Echo Planar Imaging-EPI • Diffusion Weighted EPI - DWEPI • Diffusion Tensor EPI – DTI • 2D Fast Gradient Echo – 2DFGRE • 2D Fast Spoiled Gradient Echo – 2DFSPGR • 3D Fast Gradient Echo – 3DFGRE • 3D Fast Spoiled Gradient Echo – 3DFSPGR • 3D Time of Flight Spoiled Gradient Echo – 3DTOFSPGR • 3D Time of Flight Gradient Echo – 3DTOFGRE • 2D Fast Spin Echo– 2DFSE • 2D Fast Spin Echo-XL – 2DFSE-XL • LAVA ASSET Across All Applications

14. 3.0T Physics: SAR Management Tips For Protocol Optimization • ASSET(Array Spatial Sensitivity Encoding Technique) is the GE implementation of SENSE (SENSitivity Encoding). Sensitivity = receive coil B1 • Purpose: • Decrease acquisition time while maintaining resolution. • . • Increase resolution within a fixed scan time. • Increase scan volume with a fixed scan time. • Decrease echo train length within a fixed scan time (reducing SAR and susceptibility/motion artifacts!) • Concept: • Use information in the spatial sensitivity profiles of multiple receive coil elements to scan faster.

15. 3.0T Physics: SAR Management Tips For Protocol Optimization ASSET reduces scan time by collecting every other line of k-space. This reduces the phase FOV while keeping the same resolution.

16. 3.0T Physics: SAR Management 3.0T Physics: SAR Management Tips For Protocol Optimization ASSET reduces susceptibility artifacts and geometric distortion by reducing the length of the echo train (ETL). Diffusion imaging with ASSET x 2 Diffusion imaging without ASSET

17. Thank You