Object ID: 00000018WIA3068B770GYZ
Topic ID: id_40024348 Version: 1.5
Date: Aug 14, 2022 6:34:03 PM

Excitation Mode

Select Excitation Mode to modify the type of the excitation RF pulse. Excitation Mode is located on the Scan Parameters Detail screen. The Excitation Mode menu only appears if a compatible application or PSD is currently selected.

There are three options. Only options available with the currently selected Application or PSD appear in the menu. If the menu selection is grayed-out, then it is the only option available and it is automatically applied.

Excitation Modes Selective and Non-Selective replace the old User CV Whole Volume Excitation.

Figure 1. Example of an Excitation Mode menu with 3D Cube T1 . The menu changes based on the selected application or PSD

Whole Volume Excitation On = Non-Selective Excitation Mode.
Whole Volume Excitation Off = Selective Excitation Mode.

Selective

Use Selective for routine scanning, which uses a selective excitation RF pulse. If Non-Selective and Focus are unavailable, the menu only displays a grayed-out Selective.

Non-Selective

Images are annotated: NSL in the lower left corner of the image and on the Series text page.

The User CV Whole Volume Excitation has been replaced with Excitation Mode Non-Selective.

Non-Selective is used with multiple PSDs:

Multiple 3D PSDs and one-click Applications.
3D FSE PSDs such as Cube and Cube T2 FLAIR.

Table 1. Non-selective Excitation Mode
PSD	Description
Non-Selective Excitation Mode is applicable for Sagittal and Coronal scans with many 3D Fast Gradient Echo Applications and PSDs.	Excitation Mode Non-Selective uses a very short duration hard RF pulse without a slab selective gradient pulse. It results in shorter TE/TR and improves signal uniformity at edge slices but introduces wrap in the slice direction. The slab must be large enough to include all anatomy to avoid wrap in the slice direction. It is recommended not to use it when FTMRA is selected. Excitation Mode Selective is typically used when you cannot cover the anatomy that is scanned in the slice direction. An exception is (other than for LAVA-Flex, VIBRANT-Flex or if slice acceleration is used), if the wrap artifact will not fall within the region of interest; in which case you could select Excitation Mode Non-Selective.
Non-Selective Excitation Mode with Cube is used to reduce the shading or banding artifacts observed in some Cube images (acquired or reformatted). The Excitation RF, Readout Dephaser Gradient and Slice Rephaser Gradient are applied in a unique manner that results in reducing shading or banding artifact	Be sure to cover the whole anatomy that is scanned, otherwise aliasing artifacts will be observed. Non-Selective Excitation Mode is not compatible with the Flow Compensation imaging option. Non-Selective Excitation Mode is not compatible with Axial and Oblique Axial planes. Selective Excitation Mode turns off Whole Volume Excitation.

Focus

Use Focus to acquire brain, spine, body and extremity images with the following PSDs:

2D DWI and DTI
3D FSE
3D FRFSE-XL
3D CUBE
3D Cube T2 FLAIR
3D Cube DIR

Focus is an excitation method that can be combined with other MR acquisition techniques to image a reduced FOV. Compared with conventional RF excitation, Focus reduces the FOV in the phase encode direction within the imaging plane and does not cause the conventional phase wrap artifact. Focus is particularly useful in exams where the region of interest is small in the phase encode direction, for example spine, prostate and pancreas. The reduction in phase FOV can be achieved, for example, by 2D spatially selective excitation as in Focus DWI or with outer volume suppression as with Focus CUBE. For more details regarding Focus with Cube, see Cube and Cube T2 FLAIR scan.

The 2D RF pulse used by Focus DWI is sensitive to hardware delays, which can result in image degradation in areas that are far away from isocenter. The image degradation can manifest as poor signal homogeneity and/or dark bands in the image. Care should be taken to image close to iso-center in the phase and slice direction when possible.

Because of the sensitivity of EPI acquisitions to B₀ inhomogeneities, placement of a local shim box around the region of interest is also highly recommended to achieve better image quality.

Figure 2. A example of a scanned phantom demonstrates the signal loss and banding like artifacts when the FOV is centered off iso-center in the phase encoding direction.

Image are annotated: FOC in the lower left corner of the image and on the Series text page.

Other PSD scan parameters, imaging options and saturation techniques are available if they can be selected; if not, they either don't appear or are grayed-out.

Figure 3. Images acquired with Focus Excitation mode

Number	Description
1	DWI spine images with Focus.
2	DWI pancreas images with Focus.
3	DWI prostate images with Focus.

Number	Description
1	DWI images acquired with Excitation Mode: Selective. Note the increased images magnetic susceptibility distortion effect.
2	DWI images acquired with Excitation Mode: Focus. Note the increased resolution due to less magnetic susceptibility distortion effect.