Diffusion Weighted 3D UTE in the Posterior Cruciate Ligament
Michael Carl1, Yajun Ma2, Graeme M Bydder2, and Jiang Du2

1Global MR Applications & Workflow, General Electric, San Diego, CA, United States, 2University of California San Diego, San Diego, CA, United States

Synopsis

In this work, we used a stimulated echo prepared diffusion 3DUTE sequence to image the posterior cruciate ligament. Volunteer scans in the knee were performed. We found that stimulated echo based diffusion weighted 3DUTE MR imaging can be used effectively to achieve useful b-values in short T2 MSK tissues. This initial proof-of-principle study shows good quantitative agreement with clinical EPI diffusion sequences.

Introduction

Diffusion weighting is a valuable source of contrast in MRI applications throughout the body. However the conventional spin-echo based approach results in moderate to long echo times (TEs) which creates a problem when imaging tissues with short or ultrashort T2s. It is possible to achieve diffusion weighting with steady state sequences allowing access to tissues with short T2s (1-4), but a problem remains with short or ultrashort T2 tissues. One approach is to use the magic angle effect to prolong the T2s of tissues but this has a limited range of applicability (5). A third approach is the use of ultrashort TE sequences with stimulated echo diffusion preparation. This potentially allows acquisition of signals from ultrashort T2 as well as sufficient diffusion weighting mainly during the mixing time between the second and third 90º pulses (see Fig.1) while the magnetization is stored along the z-axis. In this work, we used a stimulated echo prepared diffusion weighted UTE sequence and tested this in-vivo.

Methods

Scans of a normal volunteer knee were performed using an 8-channel knee coil with a center out 3D Cones (3D UTE) acquisition on a 3T GE HDxt clinical MR scanner. To facilitate quantitative comparison, additional scans were performed with a clinical diffusion sequence. Diffusion weighting was applied perpendicular to the imaging slice with b-values ranging from 0-250 s/mm2. ROI measurements were performed in muscle, fat, and the posterior crucial ligament (PCL). In addition, clinical fat suppressed EPI diffusion weighted scans were performed with similar scan parameters.

Results

Fig.2 shows several 3DUTE images at various b-values. The corresponding ROI decay curves are shown in Fig.3 and show good agreement between the clinical EPI and 3DUTE sequences for muscle. Additionally, ROI data was obtained for the UTE sequence in the fat signals and in the PCL. The measured diffusion coefficient for muscle using the EPI based clinical sequence was D* = 1.3*10-3 mm2/s, while the values for the UTE sequence for muscle, fat, and PCL were D* = 1.2*10-3 mm2/s, D* = 0.45*10-3 mm2/s, and D* = 0.21*10-3 mm2/s respectively.

Conclusion

Stimulated echo based diffusion weighted 3DUTE MR imaging can be used effectively to achieve useful b-values in short T2 MSK tissues. This initial proof-of-principle study shows good quantitative agreement with clinical EPI diffusion sequences.

Acknowledgements

No acknowledgement found.

References

[1] Le Bihan D et al, Magn Reson Med 1988 Jul;7(3):346-51, [2] Bieri O et al, Magn Reson Med 2012 Sep;68(3):720-9, [3] Cheung MM et al, Conf Proc IEEE Eng Med Biol Soc 2012:90-3, [4] Granlund KL et al Magn Res Imag 2014 May;32(4):330-41, [5] Bydder M et al, J Magn Reson Imag 2007 Feb;25(2):290:300

Figures

Fig.1: Schematic diagram of DWI preparation used with the 3DUTE pulse sequence. Following the stimulated echo diffusion preparation, several UTE k-space spokes are acquired.

Fig.2: Diffusion weighted 3DUTE images of the knee.

Fig.3: ROI signal curves measured in the knee as a function of b-value. Curves for muscle, fat, and the PCL are shown. The diffusion weighted 3D UTE and EPI data for muscle agree well.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
4496