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Comparative Study
. 2017 Jan 10;16(1):73-77.
doi: 10.2463/mrms.mp.2016-0047. Epub 2016 Oct 11.

Preliminary Comparison of Multi-scale and Multi-model Direct Inversion Algorithms for 3T MR Elastography

Kengo Yoshimitsu  1 , Yoshinobu Shinagawa, Toshimichi Mitsufuji, Emi Mutoh, Hiroshi Urakawa, Keiko Sakamoto, Ritsuko Fujimitsu, Koichi Takano
Affiliations
Comparative Study

Preliminary Comparison of Multi-scale and Multi-model Direct Inversion Algorithms for 3T MR Elastography

Kengo Yoshimitsu et al. Magn Reson Med Sci. .

Abstract

Purpose: To elucidate whether any differences are present in the stiffness map obtained with a multiscale direct inversion algorithm (MSDI) vs that with a multimodel direct inversion algorithm (MMDI), both qualitatively and quantitatively.

Materials and methods: The MR elastography (MRE) data of 37 consecutive patients who underwent liver MR elastography between September and October 2014 were retrospectively analyzed by using both MSDI and MMDI. Two radiologists qualitatively assessed the stiffness maps for the image quality in consensus, and the measured liver stiffness and measurable areas were quantitatively compared between MSDI and MMDI.

Results: MMDI provided a stiffness map of better image quality, with comparable or slightly less artifacts. Measurable areas by MMDI (43.7 ± 17.8 cm2) was larger than that by MSDI (37.5 ± 14.7 cm2) (P < 0.05). Liver stiffness measured by MMDI (4.51 ± 2.32 kPa) was slightly (7%), but significantly less than that by MSDI (4.86 ± 2.44 kPa) (P < 0.05).

Conclusion: MMDI can provide stiffness map of better image quality, and slightly lower stiffness values as compared to MSDI at 3T MRE, which radiologists should be aware of.

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Figures

Fig 1.
Fig 1.
Relationship between the liver stiffness calculated with multiscale direct inversion (MSDI) and multimodel direct inversion (MMDI) algorithms. (A) Bland-Altman analysis. Most of the data are scattered outside of the 95% confidence interval (between 0.28 and 0.41 kPa). The dispersion of the data along y-axis is larger as the value along x-axis becomes larger. Namely, the difference between MSDI and MMDI stiffness is large, when the stiffness is large. (B) Regression analysis for Y, which is the MMDI stiffness, and X, which represents the MSDI stiffness. An equation, Y = −0.05 + 0.94 * X (R2 = 0.98, P <0.0001) was obtained, suggesting a strong and significant correlation between MSDI and MMDI stiffness.
Fig 2.
Fig 2.
Regression analysis for Y, which is the difference in the liver stiffness calculated with multiscale direct inversion (MSDI) and multimodel direct inversion (MMDI) algorithms, and X, which represents the MSDI stiffness values. An equation, Y = 0.03 + 0.06*X (R2 = 0.1, P <0.0001), was obtained, suggesting a weak but significant correlation between MSDI stiffness and MSDI-MMDI difference in stiffness.
Fig 3.
Fig 3.
39 year-old woman with no known liver disease. (A) Magnitude echo-planar image. A free-hand region-of-interest (ROI) was drawn within the contour of the right lobe, avoiding major vessels and focal lesions (B) Wave image. Relatively good wave propagation is noted within the area of ROI (C) Stiffness map calculated from multiscale direct inversion algorithm. Note more cross-hatching marks, prominent “hot spots” (*), and inhomogeneity in the areas within the contour of the liver, as compared to 3D. Because of the presence of cross-hatching marks, the size of ROI needed to be made smaller than those on other images (3A–D). Stiffness value was measured to be 2.3 kPa, and subclassified as grade 1 stiffness (D) Stiffness map calculated from multimodel direct inversion algorithm. Note less cross-hatching marks and homogeneity in the areas within the contour of the liver, as compared to 3C. Overall image quality was assessed as better than 3C. An ROI of the same size as 3A and 3B was able to be placed. Stiffness value was measured to be 2.1 kPa, and subclassified as grade 1 stiffness.
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