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Optimization of fat suppression in the head and neck area

Application Tip
van Loon, Lars, R.T. Philips Healthcare

Obtaining good fat suppression is not always easy in the area of the head and neck. This has various reasons, including the sharp angles in the anatomy of head and neck, and also the presence of many different tissues within the area, such as muscle, air, fat, fluid, arteries and veins.

 Sharp angles in the head and neck anatomy are marked with red lines. These cause a B0 disturbance within the field of view., making fat suppression  difficult. Sharp angles in the head and neck anatomy are marked with red lines.
Sharp angles in the head and neck anatomy are marked with red lines. These cause a B0 disturbance within the field of view., making fat suppression difficult.
Sharp angles in the head and neck anatomy are marked with red lines.

 

To obtain the best possible fat suppression, it is very important to choose the correct shimming technique and to properly position the shim volume.

 Bad fat suppression of the posterior triangle due to incorrect shim selection. No fat suppression at the mandibula with auto shim.
Bad fat suppression of the posterior triangle due to incorrect shim selection.
No fat suppression at the mandibula with auto shim.
 

Autoshim / Volume shim / Pencil beam shim

The first decision is the kind of shim method to use.

At 1.5T the available options are volume- and autoshim. Volume shim is the best option for 1.5T.

At 3.0T the available options are volume-, pencil beam (PB) and autoshim. Best results were obtained with PB shim.

 

Size and position of shim volume for bilateral posterior triangle

It is important to carefully set the size and the position of the shim volume. Because fat suppression is difficult in this area, the shim volume must be carefully tailored to the area of interest.

 

When imaging the posterior triangle with a large field of view (shoulder-to-shoulder), use a well-tailored volume shim. The head/neck-thorax junction is the most difficult area to get good suppression. The best way for achieving this is to position a small shim volume at the head/neck-thorax junction (approximately 10x10 cm), centered at the junction, with half the volume in the thorax and half in the neck.

 

Do not position the shim volume too high or too low.

When the shim volume is positioned too high, only the neck is fat suppressed. When the shim volume is too low, it will be in the lungs.

 Correctly positioned small shim volume at the head/neck-thorax junction as described above. Good fat suppression of the head/neck-thorax junction because of the tailored shim volume.
Correctly positioned small shim volume at the head/neck-thorax junction as described above.
Good fat suppression of the head/neck-thorax junction because of the tailored shim volume.
 

Size and position of shim volume for soft tissue neck

In the soft tissue neck, fat suppression is most difficult in the area around the chin and the back of the skull base. The advice is to use volume shim (instead of autoshim) with the complete anatomy inside the shim volume. This approach usually provides improved fat suppression over the whole field of view.

 Left: Good fat suppression over entire field of view. Volume shim is used with complete anatomy inside the volume.<br>
Right: Autoshim is used.
Left: Good fat suppression over entire field of view. Volume shim is used with complete anatomy inside the volume.
Right: Autoshim is used.
 

Size and position of shim volume for unilateral posterior triangle

Again, tailor the shim volume to the area of interest. So, to suppress fat in the head/neck-thorax curve adjust the shim volume to that area.

 

Place an angulated shim volume at the head/neck-thorax junction. Keep the shim volume partly in the neck and partly in the thorax. Try to exclude the lungs.

 Shim volume correctly placed in the curve of the head/neck-thorax junction. Poor fat suppression if shim volume improperly placed. Good fat suppression with proper shim volume placement.
Shim volume correctly placed in the curve of the head/neck-thorax junction.
Poor fat suppression if shim volume improperly placed.
Good fat suppression with proper shim volume placement.


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Aug 6, 2009

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Application Tip
Achieva 1.5T, Achieva 3.0T, Ambition, Elition, Ingenia 1.5T, Ingenia 3.0T, Multiva 1.5T
brachial, Neck, Neuro, Posterior triangle, suppression
 

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