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Improvement of distortion-free diffusion tensor imaging for evaluation of lumbar nerve roots: Utility of direct coronal single-shot turbo spin-echo diffusion sequence with a split acquisition.Takayuki Sakai1,2, Masami Yoneyama3, Atsuya Watanabe4,5, Daichi Murayama1, Shigehiro Ochi1, and Tosiaki Miyati6
1Radiology, Eastern Chiba Medical Center, Chiba, Japan, 2Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan, 3Philips Japan, Tokyo, Japan, 4Orthopaedic Surgery, Eastern Chiba Medical Center, Chiba, Japan, 5General Medical Services, Chiba University Graduate School of Medicine, Chiba, Japan, 6Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Japan
Synopsis
This study was to investigate the availability of SPLICE-DTI (a split acquisition of fast spin-echo signals for diffusion imaging) with high spatial resolution for evaluation of lumbar nerve roots.
PURPOSE
Diffusion tensor imaging (DTI) based on single-shot echo planner imaging sequence (EPI-DTI) is established method to evaluate lumbar nerve roots compression, 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. However, EPI-DTI has several problems such as long acquisition time and high geometric distortion. To solve these problems, we attempted to apply DTI based on single-shot Turbo Spin Echo sequence (TSE-DTI). Additionally, to reduce the total acquisition time, we applied TSE-DTI to set direct coronal acquisition. In previous study, we reported that TSE-DTI has a lower geometric distortion and it might more accurately evaluate compressed lumbar nerve roots compared to conventional EPI-DTI3. However, since the actual voxel size of TSE-DTI in previous study was 4.0mm3, the quantitative values such as the FA values might be inaccurate due to partial volume effect. In this study, we aimed at improving the quantitative performance. To reduce partial volume effect, higher spatial resolution in needed. We tried to apply a split acquisition of fast spin-echo signals for diffusion imaging (SPLICE) instead of conventional Mx-eliminated TSE-DTI3. SPLICE is shown to be insensitive to the phase of the magnetization4. The purpose of this study was to investigate the feasibility of SPLICE-DTI with high spatial resolution in evaluation of lumbar nerve roots.METHODS
All subjects were examined with 3.0T whole-body clinical system (Ingenia CX, Philips Healthcare). The study was approved by the local IRB, and written informed consent was obtained from all subjects. We compared SNR (lumbar nerve root and vertebral body) and FA values between TSE-DTI and SPLICE-DTI in lumbar nerve roots of 6 healthy volunteers. Additionally, lumbar nerve roots of 6 patients who have unilateral neurological symptom were examined using SPLICE-DTI. We evaluated the relationship of average FA values between bilateral nerve roots at normal levels and at symptomatic levels. Imaging parameters for SPLICE-DTI were; Coronal, voxel
size=3.0mm3, FOV=350×350mm2, b-value=400s/mm2, MPG=32 directions, TR=4000ms, TE=52ms, and total acquisition time=6m50s.RESULTS AND DISCUSSION
SNR in SPLICE-DTI were higher than those of TSE-DTI. FA values in SPLICE-DTI were lower than those of TSE-DTI (Fig.1). However, there was no difference in the FA values of bilateral nerve roots in TSE-DTI and SPLICE-DTI. In addition, isotropic diffusion image of SPLICE-DTI depicted well lumbar nerve roots more distally compared to TSE-DTI because lumbar nerve roots are keeping sufficiently high signal (Fig.2). At the symptomatic level, the FA values in SPLICE-DTI of symptomatic side were significantly lower than those of asymptomatic side (Fig.3). In addition, since tractography of patient with low back pain using SPLICE-DTI were enabled to visualize the lumbar nerve roots without distortion, it would be useful for the preoperative information (Fig.4). Intraneural edema and demyelination caused by compression injury indicated decreasing the FA values because of decreased diffusion anisotropy of the nerves5. Therefore, measurement accuracy of the FA values is very important for evaluation of nerve injury. SPLICE-DTI with high spatial resolution might achieve higher measurement accuracy and reproducibility of FA values due to low distortion, high SNR and low partial volume effect.CONCLUSION
SPLICE-DTI with high spatial resolution might be improve measurement accuracy and reproducibility of FA values for evaluation of lumbar nerve roots.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] Sakai T, et al. Distortion-free diffusion tensor imaging for evaluation of lumbar nerve roots: Utility of direct coronal single-shot turbo spin-echo diffusion sequence. Magnetic Resonance Imaging 49 (2018) 78–85
[4] Schick F. SPLICE: sub-second diffusion-sensitive MR imaging using a modified fast spin-echo acquisition mode. Magn Reson Med. 1997 Oct;38(4):638-44.
[5] Olmarker K, et al. Edema formation in spinal nerve roots induced by experimental, graded compression. An experimental study on the pig cauda equina with special reference to differences in effects between rapid and slow onset of compression. Spine 1989 Jun;14(6):569-73.
Figures
Fig.1 Comparison of SNR and FA values between TSE-DTI with SPLICE-DTI
in 6 healthy volunteers
Fig.2 Comparison of isotropic diffusion image
(partial MIP)
between TSE-DTI (A) with SPLICE-DTI (B)
Fig.3 Comparison of the average FA values of lumbar nerve roots at
symptomatic level in six patients
Fig.4 Tractography in SPLICE-DTI of patients with
low back pain