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Tips for (3.0T) spine imaging

Application Tip
Rijckaert, Yvonne Philips Healthcare Philips Global

Tip 1: Use CLEAR with the 3.0T CTL Spine coil

For best results (especially in the cervical and lumbar spine) combine the 3.0T CTL Spine coil with CLEAR (Constant Level AppeaRance). Standard homogeneity correction is not optimized for the 3.0T CTL Spine coil with its rather low penetration depth. Standard homogeneity correction compensates for global intensity changes over a distance, leading to noise enhancement, especially when REST is positioned anterior to the spine. CLEAR will calculate the exact signal contribution of each pixel to the image (above a certain threshold). Noise enhancement is absent in the resulting (CLEAR) images. Using CLEAR requires a refscan (21 seconds duration) prior to the first scan. CLEAR can then be enabled in all following sequences of this patient performed with the 3.0T CTL Spine coil.

Homogeneity Correction CLEAR
Homogeneity Correction
CLEAR

 

Note that the Synergy Spine coil (available for 0.5T, 1.0T and 1.5T) has a larger penetration depth. With the Synergy Spine coil the standard homogeneity correction method may give better results (less noise enhancement), especially when REST is positioned anterior to the spine.

Tip 2: Carefully position the refscan for 3.0T thoracic spine imaging

If CLEAR is combined with the 3.0T CTL Spine coil on larger volumes (thoracic spine imaging), make sure the position of the refscan matches the position of the (following) anatomic scans.

 

If the survey for thoracic spine imaging is moved towards the cervical spine region (for counting vertebrae), move the refscan down to the same position as the following anatomic scans.  Positioning the refscan higher than the actual anatomic scans may cause signal loss on the lower part of the thoracic spine (at the edge of the refscan).

 

For ease of use in planning two internal (fiducial) markers are located in the coil base of the 3.0T CTL Spine coil. These markers can be identified as white dots on the survey scan. The lowest marker is positioned between section D and E of the 3.0T CTL Spine coil and indicates the end of the thoracic spine section of the coil.

Refscan positioning too high Refscan positioning OK
Refscan positioning too high
Refscan positioning OK

Tip 3: Optimizing T1w/TSE imaging

Use multiple NSA to minimize FID effects in T1w/TSE imaging. If foldover suppression is used, the number of averages (NSA) should be at least 4 (2 real averages). Increasing NSA will increase SNR, but lengthen scan time. FID effects can also be reduced by enabling flow compensation. Note that SNR may slightly decrease by enabling flow compensation. Check the info page for changes in scan time and/or SNR.

Tip 4: Optimizing the sagittal T1w/TSE lumbar spine sequence at 3.0T

At 3.0T, high signal intensity areas are sometimes seen in the CSF of the lumbar spine on sagittal T1w/TSE sequences with foldover direction FH. Select foldover direction AP to eliminate these high signal intensity areas in the CSF.

Foldover direction FH Foldover direction AP
Foldover direction FH
Foldover direction AP

 

Note that at 3.0T dielectric effects are more pronounced. These dielectric effects are patient dependent (more prominent on thin patients than on heavy patients). Select a higher excitation flip angle to reduce dielectric effects.

Tip 5: 3D T1-weighted isotropic imaging (THRIVE)

THRIVE (T1 weighted High Resolution Isotropic Volume Excitation) can be used for 3D T1-weighted spine imaging. The THRIVE sequence is scanned in the sagittal plane. Multiple MPR reconstructions can be made in the axial plane with dedicated angulations following the curvature of the neck. High spatial resolution is maintained in the reconstructions because the voxels are isotropic.

THRIVE MPR reconstruction
THRIVE
MPR reconstruction

Tip 6: Enhancing CSF signal with DRIVE

Add DRIVE (Driven Equilibrium RF reset pulse) to T2-weighted TSE sequences to enhance the CSF signal. DRIVE sets residual magnetization to the equilibrium state at the end of the TSE echo train. To preserve T2-weighting in the images, choose a TR of at least 1500 ms and a TE of at least 100 ms. Also SNR will benefit from DRIVE. NSA can thus be reduced to decrease scan time.

Tip 7: Optimizing FLAIR imaging

Increase the width of the inversion prepulse to reduce sensitivity for CSF inflow effects in FLAIR sequences. The width of the inversion prepulse is related to the gap between slice excitations. This gap can be controlled by the parameter 'minimum nr. of packages'. Check the info page for the required minimum number of packages. Increasing the number of packages leads to a wider slice profile of the inversion prepulse and thus reduces CSF flow related effects. Note that the scan time will increase if more packages than minimally required are selected. Use a fixed TR to avoid automatic decrease in TR when the number of packages is increased.

 

At 3.0T the SNR is high enough to combine sagittal FLAIR with 1 NSA. Note that a combination of 1 NSA with IR technique, fold over direction FH and foldover suppression is not allowed. Using foldover direction FH requires more NSA, leading to extra scan time. As an alternative, change the foldover direction to AP and switch off foldover suppression. Make sure the anatomy fits within the FOV, especially when RFOV is applied. Add REST and/or randomized shots to reduce ghosting effects from breathing/swallowing.

T1w/FLAIR NSA=1, Foldover direction=APT2w/FLAIR NSA=2, Foldover direction=FH
T1w/FLAIR
T2w/FLAIR
NSA=1, Foldover direction=AP
NSA=2, Foldover direction=FH

Tip 8: Remove REST in sagittal spine imaging to decrease scan time

Removing REST decreases SAR (and thus scan time) and increases contrast between CSF and cord (especially in T1-weighted sequences) due to lower MTC effects. Apply foldover direction FH, so that ghosting effects (due to breathing/swallowing) may only occur anteriorly of the spine, not obscuring the anatomy of interest. 

Tip 9: Optimizing axial T2w/TSE sequences

Perform a 3D (volume) scan instead of a multi-slice axial T2w/TSE to avoid CSF flow effects, especially in the cervical and upper thoracic spine. If multislice is preferred, using thicker slices (4 mm or even 5 mm) will reduce/eliminate CSF flow effects.

 

In case of thin slices (3 mm) use cardiac triggering via the Peripheral Pulse sensor (PPU), so that the acquisition is performed at defined moments in the cardiac cycle. Note that values of TR, (maximum) TSE factor and scan time will now depend on the entered heart rate. Keep TR long (at least 2000 ms) to maintain T2-weighting. Set the TSE factor to the maximum possible value (minimum echo spacing) to minimize CSF flow effects. Check (and adjust if necessary) the entered heart rate at the (ExamCard) parameter editor.

(multi-slice) T2w/TSE No cardiac triggering applied(multi-slice) T2w/TSE Cardiac triggering applied by PPU
(multi-slice) T2w/TSE
(multi-slice) T2w/TSE
No cardiac triggering applied
Cardiac triggering applied by PPU

Tip 10: Optimizing axial T2w/FFE sequences

Add a (free coronal) REST slab to axial multislice T2w/FFE sequences to enhance contrast between CSF and cord. Adding REST introduces MTC, which saturates bound protons in the cord, and thus enhances contrast between CSF and cord.

 

Without REST, lengthening TE and TR will achieve the same contrast between CSF and cord but leads to longer scan times and more susceptibility related effects.

 

Choose a higher bandwidth to reduce water fat shift (at the cost of SNR) or use SPIR fat suppression (at the cost of a lengthened scan time). Note that SPIR will further enhance contrast between CSF and cord.

T2w/FFE without REST T2w/FFE, REST added
T2w/FFE without REST
T2w/FFE, REST added

Tip 11: Optimizing balanced sequences

In a balanced sequence you want TE and TR as short as possible to minimize susceptibility- related effects, but you also want to avoid out-of-phase TE effects (dark lines at tissue boundaries). To optimize image quality force TE to be in-phase by selecting 'user defined' for 'TE' and manually set it to the shortest possible in-phase value (or close to that). Alternatively, the effects of an out-of-phase TE can be masked by adding fat saturation at the cost of extra scan time.

 

In balanced TFE a shot interval can be defined. By adding a shot interval tissues have more time to relax, which will benefit signal intensities (from muscle) and improve the overall image quality. Select a shot interval of at least 1000 ms longer than the shot acquisition time. The shot acquisition time can be found on the info page.

balanced TFE No shot interval addedbalanced TFE Shot interval of 1000ms added
balanced TFE
balanced TFE
No shot interval added
Shot interval of 1000ms added

Tip 12: Reduce ghosting effects in TSE based sequences

Use 'randomized shots' in TSE spine sequences to reduce ghosting effects due to respiratory motion and swallowing, without affecting profile order and effective TE. This is more effective with a large number of shots (at least 4). Check the info page for the number of shots used.

Tip 13: Reduce SAR by lowering refocusing flip angles

Use refocusing control (reduced refocusing flip angles) to decrease SAR and thus scan times in TSE. The refocusing angles can be freely chosen. A sweep will be used towards the chosen value. Note that  T2-weighted sequences become more sensitive to flow if lower refocusing flip angles are applied. Switch on flow compensation (at the cost of a slight decrease in SNR) or use small echo spacings (by choosing a high TSE factor) to reduce these flow effects. To maintain the same T2-weighted contrast, TE has to be slightly increased, because the effective TE will increase if lower refocusing flip angles are applied.  

Tip 14: Reduce SAR by lowering the B1 amplitude.

Set 'B1 mode' to 'user defined' to alter the maximum allowed B1 transmit field. Reduce the B1 amplitude (using a lower B1 transmit field) to reduce SAR. Side effects are a shorter minimum TR, smaller or larger echo spacing, a longer shortest TE and shorter scan time. Check the info page for actual values of these parameters. It is advised to not use a B1 amplitude below 10 uT.

 

If the 'B1 mode' is set to default, the maximum allowed B1 transmit field is determined by the selected 'SAR mode' (high, moderate or low).

Tip 15: Use flexible matrix to decrease scan time

Matrix sizes can be freely chosen in steps of 16. This allows flexible tailoring of pixel sizes. For axial spine imaging a smaller FOV in combination with a lower matrix can be chosen. Pixel size and SNR will remain unchanged, while scan time is shortened.

Tip 16: Reduce acoustic noise levels

Switch on the parameter 'SofTone' to significantly reduce the acoustic noise of MR sequences. The 'SofTone factor' can be set to values in the range of 1 (no reduction) to 5 (maximum reduction). It controls the gradient slope, leaving the amplitude untouched. Note that a higher SofTone factor achieves more acoustic noise reduction but may lead to an increased minimum TE, echo spacing and TR and a decrease in maximum TSE factor and SNR. Check the info page for actual values of these parameters.

Related application tips:



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Application Tip
Achieva 1.5T, Achieva 3.0T
Cervical spine, Lumbar spine, Neuro, Thoracic spine
 

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