Rapid and Distortion-Free Diffusion Tensor Imaging for Evaluation of Lumbar Nerve Roots Using Direct Coronal Single-Shot Turbo Spin-Echo Diffusion Sequence
Takayuki Sakai1, Atsuya Watanabe2,3, Kiichi Nose1, Daichi Murayama1, Shigehiro Ochi1, Masami Yoneyama4, and Noriyuki Yanagawa1

1Eastern Chiba Medical Center, Chiba, Japan, 2Chiba university graduate school of medicine, Chiba, Japan, 3Orthopaedic surgery, Eastern Chiba Medical Center, Chiba, Japan, 4Philips Electronics Japan, Tokyo, Japan

Synopsis

The purpose of this study was to visualize the lumbar nerve roots and to measure their FA values in healthy volunteers and in patients with neurological symptom of leg by using TSE-DTI. Tractography of the patients with symptomatic side of lumbar nerve roots indicated abnormalities such as narrowing, deformation, and disruption. The FA values of the symptomatic side of lumbar nerve roots were significantly lower than those of the asymptomatic side. TSE-DTI might more accurately evaluate compressed lumbar nerve roots compared to conventional EPI-DTI. Additionally, tractography of TSE-DTI enables visualization of abnormal nerve tracts and has a lower geometric distortion for diagnosing lumbar nerve compression than EPI-DTI.

PURPOSE

Diffusion Tensor Imaging (DTI) based on single-shot Echo Planner Imaging sequence (EPI-DTI) is established method to evaluate lumbar nerve roots compression in the extraforaminal area, because several studies have shown that DTI and tractography of human lumbar nerves can visualize and quantitatively evaluate lumbar nerves by fractional anisotropy (FA)1,2. Although EPI-DTI might be helpful for evaluating lumbar nerve compression, it has several problems such as long acquisition time and geometric distortion. To solve these problems, we attempt to apply DTI based on single-shot Turbo Spin Echo3 sequence (TSE-DTI). TSE-DWI has been reported to significantly reduce the image distortion and it therefore was useful for diagnosis of middle ear cholesteatoma4. Additionally, to reduce the total acquisition time, we applied to set direct coronal acquisition. The purpose of this study was to measure the FA values of lumbar nerve roots in healthy volunteers and in patients with neurological symptom of legs, by using TSE-DTI. Moreover we also investigated whether tractography is useful for visualizing lumbar foraminal nerve roots entrapment by using TSE-DTI.

METHODS

All subjects were examined with 1.5T whole-body clinical system (Ingenia, Philips Healthcare). The study was approved by the local IRB, and written informed consent was obtained from all subjects.

(1) Parameter optimization of TSE-DTI: A total of six healthy volunteers of lumbar nerve roots (L4 to S1) were examined. We compared b-values (200, 400, 800 s/mm2) and MPG directions (6, 15, 32 axes) by depictabilitty of tractography and the FA values.

(2) Comparison of optimized TSE-DTI and EPI-DTI: We compared depictabilitty of tractography and the FA values between TSE-DTI and EPI-DTI in six healthy volunteers and six patients who have lower back pain with neurological symptom of leg. To quantitatively evaluate tractography and the FA values, the regions of interest (ROIs) were placed at two levels of the L4 to S1 nerve root proximal and distal to the lumbar foraminal zone (Fig.1). The FA values were calculated at the level of the symptomatic nerve root (L4 or L5 or S1) in patients.

Imaging parameters of TSE-DTI were; MPG=32 directions, b-value=400s/mm2, TR/TE=2000/49ms, coronal section orientation, section thickness/gap=4/0.4-mm, FOV=350mm×350mm, actual voxel size=3.98mm×3.98mm×4.0mm, 3 excitations, and total acquisition time of 6m36s.

RESULTS and DISCUSSION

In parameter optimization, tractography of b-value of 400s/mm2 depicted well lumbar nerve roots more distally to extraforaminal area compared to other b-values because background signal was well suppressed while lumbar nerve roots are keeping sufficiently high signal. Furthermore, increasing MPG directions improved the continuity of lumbar nerve roots on the tractography because increasing the MPG directions was able to describe accurate diffusion anisotropy and thus visualize a complicated trajectory of fiber. Therefore we applied the b-value of 400s/mm2 and 32 MPG directions as optimal parameters. The FA value of TSE-DTI was slightly lower than that of EPI-DTI. Fig.2 shows comparison of tractography between TSE-DTI and EPI-DTI. In EPI-DTI, the fusion image, which was consists by tractography and three-dimension T2-weighted TSE, was misaligned in the direction of phase encode due to the geometric distortion of EPI-DTI. On the other hand, TSE-DTI could improve the reliability of tractography due to its less distortion sensitivity. Fig.3 shows tractography of 6 patients by TSE-DTI. Tractography of the patients with symptomatic side of lumbar nerve roots indicated abnormalities such as narrowing, deformation, and disruption. Additionally, colored presentation of tractography, which reflected the diffusion anisotropy, was able to clearly visualize the transversely-oriented nerve roots. The FA values of symptomatic side of lumbar nerve roots were significantly lower than those of asymptomatic side at the proximal and distal levels (p < 0.05) (Fig.4). Intraneural edema, which was caused after compression injury, was encouraged decreasing the FA values because of decreased diffusion anisotropy of the nerves5-7. TSE-DTI was able to capture the feature of that degree of the nerves disability was varied in inverse proportion to the FA values.

CONCLUSION

TSE-DTI might more accurately evaluate compressed lumbar nerve roots compared to conventional EPI-DTI. Additionally, tractography of TSE-DTI enables visualization of abnormal nerve tracts and has a lower geometric distortion for diagnosing lumbar nerve compression than EPI-DTI.

Acknowledgements

No acknowledgement found.

References

1. BalbiV, et al. Tractography of lumbar nerve roots: initial results. Eur Radiol 2011;21(6):1153–9.

2. Eguchi Y, et al. Quantitative evaluation and visualization of lumbar foraminal nerve root entrapment by using diffusion tensor imaging: preliminary results. Am J Neuroradiol 2011;32(10):1824–9.

3. Alsop DC. Phase insensitive preparation of single-shot RARE: applications to diffusion imaging in humans. Magn Reson Med 1997;38:527-5331

4. B. De Foer, et al. Single-Shot, Turbo Spin-Echo, Diffusion-Weighted Imaging versus Spin-Echo-Planar, Diffusion-Weighted Imaging in the Detection of Acquired Middle Ear Cholesteatoma. Am J Neuroradiol 2006;27: 1480–82.

5. Khalil C, et al. Tractography of peripheral nerves and skeletal muscles. Eur J Radiol 2010;76(3):391–7.

6. Andreisek G, et al. Evaluation of diffusion tensor imaging and fiber tractography of the median nerve: preliminary results on intrasubject variability and precision of measurements. Am J Roentgenol 2010;194(1):W65–72.

7. Olmarker K, et al. Edema formation in spinal nerve roots induced by experimental, graded compression. An experimenta study on the pig cauda equina with special reference to differences in effects between rapid and slow onset of compression. Spine 1989(14):569-573.

Figures

Fig.1 ROIs setting to calculate the FA values and tractography.

Fig.2 Comparison of tractography between TSE-DTI and EPI-DTI.

Fig.3 Tractography of 6 patients in TSE-DTI.

Fig.4 Comparison of the FA values of 6 patients between symptomatic and asymptomatic side in TSE-DTI.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
4477