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      ARTICLE - How to set up Saturation Bands

      Activate the Advanced Tab, then return to Geometry to access the new parameters: Sat. Band Number and Sat. Band Thickness. Add and select bands using Selected Sat. Band. Press S to move and angle the saturation band.

       

      For certain types of sequences, you are able to activate, place and angle Saturation Bands.

      Saturation bands (SAT Bands in technical jargon) are extra RF pulses applied to a specific region outside the imaging area to suppress unwanted blood flow signals. Think of them like "signal blockers" that stop blood flowing from the wrong direction from showing up in your image.

      Note: Currently the sequences that support the activation of Saturation Bands are the following:

      1. Balanced GREs: bSSFP, IR-bSSFP
        1. The underlying assumption is that bSSFP train has a short duration, enough to be able to achieve decent saturation by only playing one saturation band at the start. In this case the saturation bands are not part of the repetition, and therefore do not impact the minimum TR calculation. Enabling saturation bands leads to an increase of TIRL and SAR.
      2. Spoiled GREs: DIXON, GRE-OOP, GRE-ME, GRE, GRE-3D, SWI, MPRAGE
        1. The saturation bands are part of the spoiled GRE repetition, and therefore impact the minimum TR calculation. Because of this, only an increase in SAR (but not in TIRL) is expected. When saturation bands are enabled, in order to avoid having a strong SAR increase in case of short TR, a saturation period of 400 ms has been defined. This means that the saturation blocks are periodically muted and are played out with a periodicity of 400 ms.
      3. Fast spin echo: FLAIR, IR-TSE, TSE, TSE-3D, DIR-TSE, SS-FSE, SE, IR-SE
        1. the saturation bands are part of the fast spin echo repetition and are played out before the excitation RF. They therefore impact the minimum TR (and the minimum TI in case of inversion recovery) calculation. Because of this, only an increase in SAR (but not in TIRL) is expected.
      4. EPIs: GRE-EPI, SE-EPI
        1.  the saturation bands are part of EPI repetition and they therefore impact the minimum TR calculation. Since there is no option to set the sequence TR in the UI (the sequence operates at minimum TR), enabling saturation bands is going to impact TIRL and SAR.
      5. Time of Flight (TOF): TOF 2D or 3D

        1. In MR angiography, typically performed using Time of Flight (TOF) sequences, we depend on the bright appearance of fresh, unsaturated blood flowing into the imaging slab. However, blood that flows from incorrect directions—such as venous return or recirculating arterial flow—can introduce artifacts, obscuring the clarity of the arteries. Saturation bands effectively address this issue by nullifying these unwanted blood signals before they enter the imaging area, enhancing the visibility of the arteries in the final image.

        2. A 90° RF pulse is transmitted outside the imaging slab, directed towards a specific area. This pulse saturates the blood in that region, causing the spins to become excited and then dephased. As a result, when this blood enters the imaging slab, it is already in a saturated state, causing it to appear dark on the final image.

          ⚠️ The placement of saturation bands is influenced by the direction of blood flow:

        3. For 2D Time of Flight (TOF) sequences, such as those used for imaging the carotid bifurcation, which typically targets slow-flow vessels, a saturation band is positioned above the slice stack. This placement effectively suppresses venous flow that moves downward.

        4. In contrast, for 3D TOF sequences, like those used to visualise the Circle of Willis, which are intended to capture rapid arterial inflow, the saturation band is generally placed below the imaging slab. This configuration helps eliminate venous contamination that flows from superior to inferior. Additionally, implementing dual saturation bands—one positioned above and another below the imaging area—can further enhance image clarity by suppressing both venous flow and retrograde flow.

      The sequences that should not support saturation bands are:
      1. Cardiac sequences: CINE, Molli, LGE, TI-scout, T2p-SSFP, perfusion-GRE, 3D-bSSFP
      2. Diffusion: trace DWI

      After you select and added the sequence that you want to use a sat. band on:
      • Open the Advanced tab.
      • Enable saturation bands to Yes.
      • Click on the Geometry tab.
      • Select No. sat. bands that you want to use.
      • Select which Selected sat. band you want to move
      • HOLD DOWN the letter S • The sat bands can be rotated and moved by clicking the white box in the middle of the sat. band
      • Sat. bands thickness(mm) for size adjustment of the bands. Both sat. bands will be the same thickness.
      • Work on the Selected sat. band that you have selected. When you are ready to move to the next group, make sure you change the Selected sat. bands that you will be working on.

      *Tip: This is what it will look like when setting up a sat band on a Lumbar Spine Axial T2 Multi Slice scan

      • At this point you can Save the scan and Run the pulse.

      Expected results:
                             Sat Band on Sagittal                                               Sat Band on Axial