Introduction

MRI is a useful tool for lung tumor detection, because it can provide multiple contrast in arbitrary orientation without the release of radiation. For lung region, the image quality of DWI is affected by the commonly used EPI trajectory induced susceptibility artifacts. Further, the inhomogeneous fat saturation in abdominal area also leads to DW image distortions. Recently, individual shimming (iShim) technique was integrated to DW imaging to provide better B0 homogeneity so that to optimize the image quality in regions with strong susceptibility. Previous studies reported that iShim DWI can increase the image SNR and reduce image distorsion in neck and whole body DWI without sacrificing the scan time (1,2). Further, advanced diffusion model, such as intravoxel incoherent motion (IVIM), was proved helpful in identifying benign and malignant tumors in liver and sinus area (3, 4). However, there is no study combining IVIM and ishim for detecting lung tumors. Therefore, the aim of this study is to evaluate the diagnostic value of intravoxel incoherent motion (IVIM) diffusion weighted (DWI) using iShim technique to help diagnose indeterminate the lung lesions.

Methods

A total number of 32 patients (33 lesions) were included in our study, and all the patients were divided into 4 groups, which are Adenocarcinoma, Squamous carcinoma, SCLC and benign lesions, according to the pathological results. All MR exams were performed on a 3 T MRI scanner (MAGNETOM Vida, Siemens Healthcare, Erlangen, Germany) with a 18-channel body coil. The conventional axial T1W1 and coronal and axial TSE T2W images were acquired before contrast injection. The GRASP VIBE was performed for DCE information. The parameters of the DWI sequences with individual shimming was: TR/TE =4200/44ms, slice thickness = 6mm, slices = 20, bandwidth = 2488Hz/Px, FOV =380x306mm2, b = 0, 50, 100, 150, 200, 400, 600, 800 sec/mm2, acquisition time =3min54sec. The ADC value were calculated using the b values of 0 and 800 sec/mm2, the IVIM parameters were obtained using the b value of 0, 50, 100, 150, 200, 400, 600, 800 sec/mm2. The data were processed by a prototype software, body diffusion toolbox, (Siemens Healthcare, Erlangen, Germany) to obtain the following quantitative parameters: 1) apparent diffusion coefficient (ADC), 2) perfusion fraction (IVIM-FP), 3) molecular diffusion coefficient (IVIM-D), 4) pseudo-diffusion coefficient, IVIM-DP). Pearson correlation coefficients were calculated to evaluate the repeatability in the diffusion measurements. The one-way analysis of variance (ANOVA) followed by the least significant difference (LSD)-t method of multiple comparisons were used to compare the quantitative diffusion results across different histologic types.

Results

There were 32 patients (10 females, mean age, 64.6 years, years range from 42-80) with a total of 4 benign SPL and 29 LCs: 6 small cell carcinomas (SCLC), 7 squamous cell carcinomas (SCC), and 16 adenocarcinomas (Adeno-Ca). For the conventional diffusion model, the ADC show significantly higher value in Adeno-Ca group (1.262±0.317×10-3mm2/s), SCC group (1.220±0.270×10-3mm2/s) and SCLC group (1.230±0.286×10-3mm2/s) than that in the benign group(1.846±0.403×10-3 mm2/s). For the IVIM model, the IVIM-D showed significantly lower value in the Adeno-Ca (D: 1.155±0.380×10-3mm2/s) than benign lesions(1.757±0.498×10-3mm2/s); the IVIM-f of Adeno-Ca (0.272±0.188×10-3 mm2/s) and SCC（0.251±0.195×10-3mm2 /s）are lower than that in the benign group (0.588±0.104×10-3 mm2 /s) (figure 1). The area under the ROC curve of the mean ADCs is 0.893, and the optimal cutoff point is 1.940×10-3 mm2/s (figure 2). The processed quantitative IVIM parameters images of representative patient were illustrated in Figure 3.

Discussion & Conclusions

This study successfully performed IVIM acquisition using individual shimming strategy for all the patients to improve DW image quality. ADC, IVIM-derived f, D values are three promising parameters for differentiating LC from benignity. ADC as a quantitative imaging biomarker for DWI in routine clinical practice is an excellent approach for lung lesions assessment of the diffusivity of water molecules within tissue in terms of cellularity, perfusion, tissue disorganization, extracellular space, and other aspects. Water flowing in perfused capillaries within a voxel is representing as volume fraction f value, and quantitative parameters of diffusion coefficient (D), which reflects tissue diffusivity, because of using only higher b values(> 200 s/mm2). In conclusion, both ADC and IVIM model have the potential in clinical practice for the differentiation of benign and malignant lung tumors.

Acknowledgements

The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article. The authors state that this work has not received any funding. No complex statistical methods were necessary for this paper. This prospective study was approved by the Institutional Review Board (NO:2020ZDSYLL178-P01).No study subjects or cohorts have been previously reported.

References

1.Zhang H, Xue H, Alto S, et al. Integrated shimming improves lesion detection in whole-body diffusion-weighted examinations of patients with plasma disorder at 3 T. Invest Radiol 2016;51:297e305. 2. Walter SS, Liu W, Stemmer A, et al. Combination of integrated dynamic shimming and readout-segmented echo planar imaging for diffusion weighted MRI of the head and neck region at 3 Tesla. Magn Reson Imaging 2017;42:32e6. 3. Huan Zhang, Wenhua Li, Caixia Fu, ea al. Comparison of intravoxel incoherent motion imaging, diffusion kurtosis imaging, and conventional DWI in predicting the chemotherapeutic response of colorectal liver metastases[J]. Eur J Radiol, 2020, 130: 109149. 4. Zebin Xiao, Yufeng Zhong, Zuohua Tang, et al. Standard diffusion-weighted, diffusion kurtosis and intravoxel incoherent motion MR imaging of sinonasal malignancies: correlations with Ki-67 proliferation status[J]. Eur Radiol, 2018 28(7):2923-2933.