Philips mDIXON provides images with and without fat suppression in a time efficient manner. The patented 2-echo implementation, versus conventional 3-point techniques, is key to delivering superb fat suppression at routine scan times.
The fast and robust fat suppression provided by mDIXON TSE makes the method well suited for enhancing routine musculoskeletal (MSK) MR imaging. These tips are intended to help you implement mDIXON TSE in your MSK protocols and ExamCards.
Use a fat suppressed protocol as starting point. Choose a protocol in which SNR,
resolution and scan time are already well balanced for your purpose.
mDIXON TSE is compatible with all common profile orders, however protocol optimization is easiest with an asymmetric profile order as it gives full control over TE, TR, BW and echo spacing.
On the Contrast tab, set ‘profile order’ to asymmetric. TE and TR may be adjusted according to your preference. Use a TR range for convenience. The table provides some recommended settings.
Click on picture to enlarge
On the Contrast tab:
- Set ‘Fat suppression’ to No to switch off SPIR or SPAIR.
- Set ‘mDIXON’ to yes.
- If volume shim is present, set to Auto to reduce workflow steps.
- Set ‘WFS’ to user defined, select 1.3 (pixels).
Scan time first increases by switching on mDIXON
mDIXON uses 2 echoes (2-point mDIXON) to calculate the inphase (IP) and water (W) images. This effectively doubles scan time but also increases the signal-to-noise ratio, similar to doubling NSA which doubles scan time and increases SNR by 41% (factor √2).
After switching to mDIXON, the easiest way to revert to the original scan time is by reducing NSA on the Motion tab to use less averages. If a scan has only 1 NSA, use SENSE to reduce scan time
Scan time reduces again by changing NSA
Specifically in MSK imaging, some radiologists prefer a partial fat suppression. This is easy to obtain with mDIXON.
To achieve this, also the fat (F) images need to be reconstructed. On the Postproc tab, expand the parameter ‘mDIXON images’ and add the fat image
When the mDIXON scan is finished:
Load the scan into the ‘Image Algebra’ post processing package.
- In viewport A (lower left) scroll to the fat (F) image using the left and right arrow keys.
- Viewport B (lower right) should contain the water (W) image.
- Use the ratio slider to adjust the amount of fat added. In general, a ratio of 0.05 to 0.10 is advised for MSK. The upper right viewport displays a preview, helping the user to fine-tune the level of fat suppression interactively.
- Create the series by clicking the ‘Generate’ button.
- After performing this once, this postprocessing step will be saved in the ExamCard as a SmartLine step. It can be copied to other mDIXON scans.
Viewport A, fat image (F) Viewport B, water image (W)
ExamCards without mDIXON TSE
mDIXON TSE can help to simplify an ExamCard by replacing two or more separate sequences. This can reduce redundancy and support standardization.
Why not take advantage of mDIXON for each
TSE scan to double the information in the same scan?