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Intravoxel incoherent motion diffusion-weighted Imaging of lung: comparison between turbo spin-echo and echo-planar imaging
Qi Wan1, Xinchun Li1, Qiang Lei1, Tianjing Zhang2, and Zhongping Zhang2

1The first affiliated hospital of Guangzhou Medical University, Guangzhou, China, 2Philips Healthcare, Guangzhou, China

Synopsis

The image quality of single-shot echo-planar imaging (EPI)-DWI (SS-EPI-DWI) is usually deteriorated by susceptibility artefacts, especially in lung, because EPI sequence is vulnerable to magnetic inhomogeneity and phase error accumulation. This could lead to inabilities of diagnosis or inaccuracy of measurements. In this study, lung DWI were acquired using both single-shot turbo spin-echo (SS-TSE) and SS-EPI techniques. Significantly changes were observed in distortion ratio (DR) between both techniques. SS-TSE-DWI has better image quality and almost zero distortion compared to SS-EPI-DWI.

Introduction

Lung cancer is one of the most common malignancies accompanying with the highest mortality. Diagnosis and characterization of solitary pulmonary lesions (SPLs) are significant for clinical management. In addition, IVIM or DWI, serving as promising imaging tools, have performed well in aspects of tumor characterization[1-3] and treatment response assessment[4] etc. in lung. To date, the majority of studies on the basis of lung DWI studies were conducted using single-shot echo planar imaging (EPI) technique[5] mainly due to its short scan time. However, EPI-DWI suffers from susceptibility distortion that may reduce reproducibility[6] and diagnostic efficiency[7]. By contrast, turbo spin-echo (TSE)-DWI is a robust method against distortion and artifacts due to the usage of radio frequency (RF) refocusing pulses. In this study, intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) was used and compared using TSE and EPI for the purpose of pulmonary lesion evaluation.

Material and Methods

A total of 10 consecutive patients with solid SPLs confirmed by computed tomography findings were referred to MR imaging. DWI data was acquired using both single-shot(SS) TSE sequence and SS-EPI sequence with free breathing. Both sequences were scanned twice. Five b values from 0 - 800 s/mm2 were used (0, 20, 50, 200 and 800 s/mm2). The EPI sequence parameters were as follows: field of view (FOV) 375×305 mm, repetition time (TR)/ echo time (TE) 1195ms/54ms, thickness 5 mm, acquisition voxel size 3×3×5 mm, NSA 3, EPI factor 51 and scanning time 1 min. The TSE sequence parameters were also as follows: FOV 375×305 mm, TR/TE 6197ms/60ms, thickness 5 mm, acquisition voxel size 3×3×5 mm, NSA 2, TSE factor 56, scanning time 3 min 18 sec. Region of interests (ROIs) were delineated by two experienced readers independently and placed in the lesions, thoracic muscle and background for the measurement of signal-to-noise ratio (SNR) and contrast-to-noise (CNR). For the evaluation of distortion, fusion images were created by superimposing DWI on T2WI using RadiAnt DICOM Viewer (Version 4.6.5.18450, https://www.radiantviewer.com/). Multiple b-value DWI images were postprocessed using IVIM biexponential model in IMAgenGINE MRI Diffusion Toolbox (Beta V2.0.3, Vusion Tech, China). Short-term test-retest repeatability was assessed with mean coefficient of variation (CV) averaged for both readers.

Results

Figure 1 shows that distortion ratio (DR) of SS-TSE-DWI was significantly smaller than that of SS-EPI-DWI (P<0.001). In addition, the values of SNR and CNR were similar on the basis of SS-TSE-DWI and SS-EPI-DWI techniques (P>0.05). The comparison of different diffusion parameters between two groups is displayed in figure 2. ADC and IVIM-derived D of TSE-DWI showed significant higher values than those of EPI-DWI (P=0.028 and 0.021 respectively). However, D* and f showed a huge overlapping between the two groups (P>0.05). Comparing two representative cases using two techniques were shown in figure 3 and 4. Test-retest repeatability of IVIM parameters was satisfactory for ADC and D (EPI-DWI mean CV 0.12 and 0.15, TSE-DWI mean CV 0.16 and 0.14), but relatively poor for f and D*(EPI-DWI mean CV 0.23 and 0.50, TSE-DWI mean CV 0.36 and 0.51).

Discussion

To the best of our knowledge, this is the first study comparing SS-EPI-DWI with SS-TSE-DWI sequences for the evaluation of pulmonary nodules in terms of image quality and IVIM parameters. Our results showed that TSE-DWI possesses excellent image quality for its lack of image distortion resulting from susceptibility effects and eddy currents as compared to EPI-DWI on a 3T MR system. In addition, ADC and D values of TSE-DWI showed significant higher values than those of EPI-DWI suggestting that the established criterion in EPI-DWI, such as cutoff value for differentiation of SPLs, could not be generalized to TSE-DWI. Therefore, there is a need of exploring new cutoff value in a large cohort study for evaluation of SPLs using TSE-DWI. However, higher test-retest repeatabilities were found for ADC and D than for f and D* parameters in both EPI and TSE sequences, which suggests TSE-DWI could not improve the robustness of perfusion parameters f and D* despite possessing significantly lower image distortion.

Conclusion

Lung DWI or IVIM using TSE have almost zero geometric distortion and displacement compared with EPI technique. TSE-DWI could be a good alternative to EPI-DWI and have great potential of application for evaluating pulmonary disease.

Acknowledgements

No acknowledgement found.

References

1. Wan Q, Deng YS, Lei Q, et al. Differentiating between malignant and benign solid solitary pulmonary lesions: are intravoxel incoherent motion and diffusion kurtosis imaging superior to conventional diffusion-weighted imaging? European radiology 2018.

2. Yan C, Xu J, Xiong W, et al. Use of intravoxel incoherent motion diffusion-weighted MR imaging for assessment of treatment response to invasive fungal infection in the lung. European radiology 2017;27(1):212-221.

3. Yuan M, Zhang YD, Zhu C, et al. Comparison of intravoxel incoherent motion diffusion-weighted MR imaging with dynamic contrast-enhanced MRI for differentiating lung cancer from benign solitary pulmonary lesions. Journal of magnetic resonance imaging 2016;43(3):669-679.

4. Shi C, Liu D, Xiao Z, et al. Monitoring Tumor Response to Antivascular Therapy Using Non-Contrast Intravoxel Incoherent Motion Diffusion-Weighted MRII. Cancer research 2017;77(13):3491-3501.

5. Shen G, Hu S, Deng H, Kuang A. Performance of DWI in the Nodal Characterization and Assessment of Lung Cancer: A Meta-Analysis. AJR Am J Roentgenol. 2016;206(2):283-90.

6. Verhappen MH, Pouwels PJ, Ljumanovic R, et al. Diffusion-weighted MR imaging in head and neck cancer: comparison between half-fourier acquired single-shot turbo spin-echo and EPI techniques. AJNR Am J Neuroradiol. 2012;33(7):1239-46.

7. Ohno Y, Koyama H, Yoshikawa T, et al. Diffusion-weighted MR imaging using FASE sequence for 3T MR system: Preliminary comparison of capability for N-stage assessment by means of diffusion-weighted MR imaging using EPI sequence, STIR FASE imaging and FDG PET/CT for non-small cell lung cancer patients. Eur J Radiol. 2015;84(11):2321-31.

Figures

Figure 1.Comparison of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and Distortion ratio (DR) between SS-EPI-DWI and SS-TSE-DWI. Significant differences in DR were evaluated with a Wilcoxon signed-rank test (** denotes p<0.001).

Figure 2. Comparison of different diffusion parameters between SS-EPI-DWI and SS-TSE-DWI. Comparisons were performed with a Wilcoxon signed-rank test (* denotes p<0.05).

Figure 3. A nodular lesion (arrow) in right lower lobe. A. T2WI-SPIR, B. EPI-DWI (b=800 s/mm2), C. TSE-DWI(b=800 s/mm2). D. T2WI fused with EPI-DWI, E. T2WI fused with TSE-DWI. The distortion of lesion as well as spinal displacement (double fine arrow) were showed on EPI-DWI, while lesion on TSE-DWI show almost zero distortion compared to T2WI.

Figure 4. A nodular lesion (arrow) in right upper lobe. A. T2WI-SPIR, B. EPI-DWI (b = 800 s/mm2), C. TSE-DWI (b = 800 s/mm2). D. T2WI fused with EPI-DWI, E. T2WI fused with TSE-DWI. The distortion and displacement of lesion were showed on EPI-DWI. On TSE-DWI, lesion as well as the air bronchus within it can be clearly showed. Fused images showed that TSE-DWI matched perfectly with T2WI.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)
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