Background and Purpose

In recent years, single-shot echo-planar-imaging (SS-EPI) diffusion-weighted imaging (DWI) has been widely used in bladder, prostate, breast, and thyroid cancers. But its known geometric distortion and T2* blurring have limited DWI applications in rectal cancer imaging. Recently, iShim-DWI was introduced to improve image quality and lesion detection. This study aimed to compare iShim-DWI with conventional 3D-Shimming SS-EPI DWI looking at image quality and the pathologic characterizations of rectal cancer.

Materials and Methods

One hundred and ninety-three consecutive patients with rectal tumors were enrolled for a retrospective analysis. Among these patients, 101 underwent prototype iShim DWI (b=0, 800, and 1600 s/mm2), and 92 underwent conventional 3D-Shimming SS-EPI DWI (b=0 and 1000 s/mm2) on a 1.5T MR system (MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany) with an 18-channel body coil and a 32-channel spine coil.Qualitative analysis of the DWI images was performed by two independent readers, including assessments of adequate fat suppression, the presence of image artifacts, and image quality. The assessments were performed in a Likert-type manner:
1) Adequate fat suppression in the DWI images. Score 1: fat suppression failure Score 2: regional fat-water failure but still interpretable Score 3: minimal failures at the image periphery Score 4: perfect fat-water separation2) The presence of artifacts on both the DWI images and ADC maps. Score 1: non-diagnostic Score 2: artifacts but diagnostic Score 3: no artifacts 3) Image quality for both the DWI images and ADC maps: Score 1: non-diagnostic image quality with serious artifacts, image distortion, or poor signal intensities Score 2: poor diagnostic image quality and reader diagnostic confidence, with serious artifacts, pronounced image distortions, or relatively poor signal intensities Score 3: moderate image quality and reader confidence with some artifacts and moderate image distortionsScore 4: good diagnostic image quality and reader confidence with few artifacts, slight image distortions, and well-delineated anatomic structures (e.g., rectal wall) Score 5: excellent image quality and strong reader confidence in diagnosing rectal cancer with almost no artifacts or imaging distortionsQuantitative analyses were performed by calculating standard deviations (SDs) of the gluteus maximus, signal intensities (SIs) of the lesion and residual normal rectal wall tissue, apparent diffusion coefficient (ADC) values, and image quality parameters, such as signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) of primary rectal tumors. For patients with primary rectal cancer, two pathologic groups were formed according to the pathologic results: Group 1 (well-differentiated) and Group 2 (poorly differentiated). Statistical analyses were performed with a p <0.05 considered significantly different.

Results

Compared with conventional 3D-Shimming SS-EPI DWI, significantly higher scores of image quality were obtained in iShim DWI images (P<0.001). The SDbackground was significantly reduced in b1600 images and ADC maps of iShim DWI. Both SNR and CNR of b=800 s/mm2 and b=1600 s/mm2 images in iShim DWI were higher than that of b=1000 s/mm2 images in conventional 3D-Shimming SS-EPI DWI. In primary rectal cancer of the iShim cohort, SIlesion was significantly higher than SIrectum in both b=800 s/mm2 and b=1600 s/mm2 images. ADC values were significantly lower in Group 2 (732±85) mm2/s) than that in Group 1 ((912±207) mm2/s). ROC analyses showed the significance of ADC and SIlesion values between the two groups.

Conclusion

DWI of iShim with b values of 800 and 1600 s/mm2 is a promising rectal tumor imaging technique and has the potential ability to differentiate rectal cancer from normal wall architecture and predict pathologic characterizations in rectal cancer patients.

Acknowledgements

No acknowledgement found.

References

[1] Gatidis S, Graf H, Weiß J, Stemmer A, Kiefer B, Nikolaou K, Notohamiprodjo M, Martirosian P. Diffusionweighted echo planar MR imaging of the neck at 3 T using integrated shimming: comparison of MR sequence techniques for reducing artifacts caused by magnetic-field inhomogeneities. MAGMA. 2017; 30:57–63.[2] Zhang H, Xue H, Alto S, Hui L, Kannengiesser S, Berthold K, Jin Z. Integrated Shimming Improves Lesion Detection in Whole-Body Diffusion-Weighted Examinations of Patients With Plasma Disorder at 3 T. Invest Radiol. 2016; 51:297–305.[3] Chen L, Sun P, Hao Q, Yin W, Xu B, Ma C, Stemmer A, Fu C, Wang M, Lu J. Diffusion-weighted MRI in the evaluation of the thyroid nodule: Comparison between integrated-shimming EPI and conventional 3D-shimming EPI techniques. Oncotarget 2018;9(40):26209-26216. doi:10.18632/oncotarget.25279.[4] Li H, Liu L, Shi Q, Stemmer A, Zeng H, Li Y, Zhang M. Bladder cancer: detection and image quality compared among iShim, RESOLVE, and ss-EPI diffusion-weighted MR imaging with high b value at 3.0 T MRI. Medicine (Baltimore) 2017;96(50):e9292. doi:10.1097/MD.0000000000009292.[5] Gatidis S, Graf H, Weiß J, Alto Stemmer A, Kiefer B, Nikolaou K, Notohamiprodjo M, Martirosian P. Diffusion-weighted echo planar MR imaging of the neck at 3 T using integrated shimming: comparison of MR sequence techniques for reducing artifacts caused by magnetic-field inhomogeneities. MAGMA 2017;30(1):57–63. doi: 10.1007/s10334-016-0582-z.[6] Lee SK, Tan ET, Govenkar A, Hancu I. Dynamic slice-dependent shim and center frequency update in 3 T breast diffusion weighted imaging. Magn Reson Med 2014;71(5):1813–1818. doi: 10.1002/mrm.24824.[7] Naranjo ID, Gullo RL, Morris EA, Larowin T, Fung MM, Guidon A, Pinker K, Thakur SB. High-Spatial-Resolution Multishot Multiplexed Sensitivity- encoding Diffusion-weighted Imaging for Improved Quality of Breast Images and Differentiation of Breast Lesions: A Feasibility Study. Radiology 2020; 2(3):e190076. doi:10.1148/rycan.2020190076.[8] Zhang H, Xue H, Alto S, Hui L, Kannengiesser S, Berthold K, Jin Z. Integrated shimming improves lesion detection in whole-body diffusion-weighted examinations of patients with plasma disorder at 3 T. Invest Radiol 2016;51:297–305. doi: 10.1097/RLI.0000000000000238.