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Tips for breast imaging

Application Tip
Rijckaert, Yvonne Philips Healthcare Philips Global

Patient positioning

Patient positioning is key in fat suppressed breast imaging. Make sure the breasts of the patient 'hang loose' in the coil. Folds in the breast(s) may disturb shimming and thus disturb fat suppression.

 

In the image below the left breast is positioned correctly and homogeneous fat suppression is achieved. The right breast is folded, which negatively affects fat suppression.

THRIVE Incorrect positioning of right breast negatively affects fat suppression.
THRIVE
Incorrect positioning of right breast negatively affects fat suppression.

 

 

F0 determination during scan preparation

F0 determination is performed during scan preparation to determine the resonance frequency of water. At 3.0T,  F0 determination is performed before every scan. At lower field strengths, this preparation phase may be skipped by changing the 'preparation phases' parameter (on the postproc page) to 'auto'. However, we advise to always use 'full' preparation phases for fat suppressed breast imaging.

 

F0 determination is based on peak finding. The system will take the highest peak found in the spectrum as the water peak. Most tissues will show a broad fat peak with low amplitude and a narrow water peak with high amplitude at a higher frequency. In such cases, the water frequency is easy to identify.

 

In some patients breast tissue may have a very high fat content, so that a relatively high fat peak is found. In rare cases the fat peak may be much higher than the water peak, and the system may identify the fat peak as water. Consequently, fat suppression will not work. If this occurs, it usually is either:

  • a patient with large breasts (larger fat content of the breast)
  • an older patient (post menstrual cycle, relatively more fat than parenchyma in the breast)

 

In such a case, a solution is to position a small volume shim box between both breasts to minimize the amount of fat tissue in the volume shim box.

 

Robust F0 determination in R1.5.4

Previously, one channel of a multi-element receive coil was used for F0 determination. This was typically the channel receiving the highest signal.

 

From R1.5.4 onwards, F0 determination has become more robust by averaging signals of all channels of a multi-element receive coil. So, effectively F0 determination is performed closer to the center of the coil. Even with non-perfect shimming, fat suppression will be equal on both breasts.

 

The images below compare the old (one channel ) and new (all channels) implementation of F0 determination.

 

Also, in R1.5.4 also adiabatic pulses are used for F0 determination and shimming to make images insensitive for B1 variations at 3.0T.

 One channel used for F0 determination. All channels used for F0 determination (R1.5.4)
One channel used for F0 determination.
All channels used for F0 determination (R1.5.4)

 

 

Shimming for best fat suppression

Auto shim or a large volume shim box (covering two breasts) can be chosen. Best fat suppression is achieved when a large shim box is used. In R1.5.4 and higher a large shim box should always be used.

 

The example images below compare imperfect fat suppression on the top part of both breasts when the volume shim box is (too) small, and excellent fat suppression achieved in both breasts when a large shim box is used.

 

NOTE: In releases before R1.5.4, fat suppression may not work in rare cases, if an extremely high fat peak confuses F0 determination. In such a case, position a small volume shim box between both breasts to decrease the amount of fat tissue in the volume shim box.

Positioning small shim box Result when shim box is too small
Positioning small shim box
Result when shim box is too small
Positioning large shim box Result with large shim box Excellent result if large shim box is used. Click to enlarge image.
Positioning large shim box
Result with large shim box
Excellent result if large shim box is used. Click to enlarge image.

 

 

Frequency offset to refine fat suppression

Adjusting the frequency offset of the fat suppression pulse enables further optimization of fat suppression. Increasing the frequency offset parameter will move the fat suppression pulse closer to the water peak, which may lead to reduced water signal in some areas in the image. To avoid this local water suppression, lower the frequency offset value to increase the space between the fat suppression pulse and the water peak. Excessive lowering of the frequency offset value may result in areas of incomplete fat suppression.

 

The best frequency offset value varies per anatomy and per patient. To determine the best frequency offset for a patient, some quick scans (10 sec. each) can be inserted before the first fat suppression sequence in the ExamCard. These (low resolution) images can be used to select the best frequency offset value for this particular patient. See example below.

Frequency offset 135 Frequency offset 180 Frequency offset 225
Frequency offset 135
Frequency offset 180
Frequency offset 225

 

 

Optimizing signal homogeneity

Especially at higher field strengths signal intensity differences between the two breasts may be seen, particularly in fat suppressed images. This effect is related to the patient's position inside the bore: when using the 7ch breast coil or the 4ch breast coil, the patient is prone and lifted, instead of close to the tabletop as usual. If this effect occurs, avoid use of CLEAR to minimize signal intensity differences. In Release 2 and higher CLEAR may be switched off in the parameter editor, even when SENSE is used.

 

In this example of axial fat suppressed THRIVE, the signal intensity differences are reduced by switching off CLEAR.

 

To optimize contrast between lesions and breast parenchyma in T1-weighted images at 3.0T, we strongly recommend to use 3D sequences only (not 2D). In addition, slightly increase the flip angle of the THRIVE sequence to 12-15ยบ.

CLEAR No CLEAR
CLEAR
No CLEAR

 

 

Silicon imaging and silicon suppression

Silicon imaging can be achieved by suppressing both fat and water, leaving the silicon signal only. Since the difference between the frequencies of fat and silicon is small, frequency selective fat suppression is difficult without also suppressing some silicon. However, the relaxation times of fat and silicon are very different. So, fat suppression is performed by using Inversion Recovery TSE. This sequence is combined with SPAIR for frequency selective suppression of water. See image below.

 

Suppression of silicon can be achieved by using a frequency selective pre-pulse (SPAIR). Because the difference between frequencies of fat and silicon is small, fat may also be (partially) suppressed. See images below.

 

Note that in release 2 the implementation of inversion based TSE sequences is further optimized. This particularly benefits its feasibility and reliability at higher field strengths (3.0T).

Silicon imaging Silicon suppression
Silicon imaging
Silicon suppression

 

 

SENSE Flex coils for breast imaging

Apart from dedicated breast coils, also surface coils can be used for breast imaging. For 1.5T a dedicated breast mattress is designed for use in combination with the 1.5T SENSE Body coil. With Release 2 the same mattress may also be ordered for 3.0T to use in combination with the SENSE Flex coils. The SENSE Flex L coil fits exactly into the breast mattress as shown in the photographs below. Signal-to-noise ratio of the SENSE Flex L coil images is comparable to the images made with dedicated breast coils.

 

Note that Release 2 enables scanning with a combination of two SENSE Flex coils in dual mode.

 

From R2.1.3 onwards the reference scans of the SENSE Flex L and M coils are enlarged to allow foldover suppression in combination with SENSE /CLEAR.

 

See examples below of breast images made with the SENSE Flex L coil.

 

T2w TSE THRIVE
T2w TSE
THRIVE

 

 

Related information:






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Application Tip
Achieva 1.5T, Achieva 3.0T
Release 1, Release 2
Nova, Nova Dual, Pulsar, Quasar, Quasar Dual
Body, Breast, fatsat, Women's health
 

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