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Experiences in orthopedic MRI at 3.0T

Case Study
Shnier, Ron, M.D. Symbion Research Clinical Imaging Center • Australia
Hughes, Kathleen Mayne Clinical Research Imaging • Australia

 

Orthopedic imaging at 3.0T presents a new and exciting opportunity to supplement and advance cartilage and joint imaging over a wide range of sports injuries. The SNR increase alone at 3.0T enables increases in resolution where our standard protocols use 2.0 to 2.5 mm slices in all joints, including T2-weighted SPIR and STIR techniques.

 

Challenges at 3.0T include increased respiration and flow artifacts, which can be overcome with simple protocol adjustments. Several new user interface parameters allow users to adjust TR/TE and TSE factors for better resolution and contrast.

 

This article reviews our experiences in protocol optimization, the use of SENSE, and our clinical results, all with the SENSE Flex M coil.

Ron Shnier, MD Kathy Hughes, RT
Ron Shnier, MD
Kathy Hughes, RT

PD-weighted orthopedic scanning at 3.0T

There are several ways to create a proton-density-weighted protocol. One method uses long TR / short TE and low-high or linear profile order. Another method uses long TR / long TE and linear profile order, which results in brighter fluid and better contrast at the fluid/cartilage interface.

 

Preliminary experience shows that increasing the TSE factor reduces blurring. Using a high TSE factor (13-16) results in shorter echo spacing and therefore less blurring and better overall contrast. This would be an unfamiliar choice for 1.5T users and those with non-Philips MRI systems. We have also found that very high TSE factors, which result in echo spacing of 5-6 ms, reduce fluid brightness and therefore contrast.

 

Initial findings suggest that halfscan is very useful in PD-weighting in all joints except shoulders, where respiratory motion impairs image quality. Halfscan combined with RF refocusing control allows you to select the optimal TR in a relatively short scan time. Most of our knee protocols use FOV 130-140 mm, 28-32 slices, 2.5 mm slice thickness and run just over 3 minutes. Small knees need only 24 slices or less, with a scan time of about 2:30 minutes.

 

Spatial resolution requirements raise the usual dilemma of using either a combination of thin slice / small FOV / lower matrix, versus larger slice thickness / larger FOV / higher matrix. For axial shoulders we tend to choose smaller FOV / lower matrix, but larger FOV / higher matrix for coronal.

 

The 3.0T parameter refocusing control angle enables SAR reduction and simultaneously allows easy reduction of the shortest TR. We normally use 100-120 degrees to optimize for a high TR > 4000 ms and the lowest number of packages. Higher TR contributes to stronger PD-weighting and better SNR.  TR > 5000 ms is used only for T2-weighted SPIR imaging in combination with TE 70 ms.

 

The system handles SAR issues very well within the range of programmable factors, so for us SAR is not an issue. In addition, you have several options of RF refocusing control and B1 mode to enable a very "hands-on" manipulation to customize protocols.


Shoulder

Long TR / short TE (8.8 ms) Long TR / long TE without halfscan Long TR / long TE, halfscan
Long TR / short TE (8.8 ms)
Long TR / long TE without halfscan
Long TR / long TE, halfscan

Combining long TR (2500-3000 ms) and long TE (35-40 ms) (middle image) results in brighter fluid signal and better contrast at the fluid/cartilage interface than the long TR / short TE combination (left image). High TSE factors of 14-16 (8 ms echo spacing) give the brightest signal. Using halfscan in the shoulder improves contrast, but respiratory motion impairs image quality.

 

Long TR / long TE and larger FOV 170 mm
Long TR / long TE and larger FOV 170 mm

The larger FOV of 150-170 mm at higher scan matrix (1024) works well for coronal coverage of the supra-spinatus muscle and good overall SNR. Slice thickness 3 mm.

 

For axial and sagittal images, smaller FOVs and thinner slices, provide excellent detail.

 

SPIR
SPIR

We use a high-resolution SPIR scan to complement our PD-weighted protocols, FOV 150 mm, matrix 512, slice thickness 2.5 mm.


Knee

 Also in the knee, a long TR > 4000 ms and a long TE 35 ms provide excellent PD-weighted contrast. TSE factor 14, halfscan, matrix 1024, scan time 4:35 min.
 SENSE reduces scan time to 3:00 min. and maintains contrast and diagnostic quality. PD-weighted image with SPIR fat suppression.This is an excellent intermediate. The good SNR helps visualize the meniscal tear.
Also in the knee, a long TR > 4000 ms and a long TE 35 ms provide excellent PD-weighted contrast. TSE factor 14, halfscan, matrix 1024, scan time 4:35 min.
SENSE reduces scan time to 3:00 min. and maintains contrast and diagnostic quality.
PD-weighted image with SPIR fat suppression.This is an excellent intermediate. The good SNR helps visualize the meniscal tear.
.
 FS22
FS22
Without SENSE, scan time 4:01 min.                         With SENSE, scan time 2:56 min.

 

Both images are made with long TR / long TE, FOV 130 mm, matrix 1024, halfscan. Also in these coronal images, SENSE reduces scan time and maintains diagnostic quality.

 

 

 FS22
FS22
Long TR / long TE, TSE factor 8                           Long TR / long TE,TSE factor 10   

 

Small increases in TSE factor will fine tune the protocol for sharper detail along the cartilage surface.


Ankle

 fs22
fs22

Both have excellent SNR, good fluid/cartilage contrast, but the higher TSE factor (left is TSE factor 12, right is TSE factor 14) results in a slight SNR increase, much better resolution and sharper margins due to the shorter echo spacing. Compare for instance the trabeculae distal tibia and post subtalar joint. FOV 150 mm, matrix 1024, 2 mm slices, TR 4000 ms, TE 35 ms.

 

SPAIR SPIR
SPAIR
SPIR
SPIR achieves good fat suppression and T2 weighting, but SPAIR fat suppression shows excellent SNR and significantly less blurring at the fluid/cartilage interface than SPIR, compare for instance the post subtalar joint. SPAIR enables partial fat saturation by manipulating inversion time.


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Case Study
Achieva 3.0T
Release 1, Release 10, Release 11, Release 9
Knee, Musculoskeletal
 

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