Synopsis

There was moderate positive correlation between fibrosis stage and T1ρ values (r=0.566; 95% CI 0.291-0.754; P<0.0001), and LS value (r=0.726; 95% CI 0.521-0.851; P=0.003). T1ρ values showed moderate positive correlations with LS values (r=0.693; 95% confidence interval [CI]: 0.472-0.832; P<0.0001). Areas Under ROC (AUROCs) were 0.861 (95% CI: 0.705-0.953) for SWE and 0.856 (95% CI: 0.698-0.950) for T1ρ (P = 0.940), 0.906 (95% CI: 0.762-0.978) for SWE and 0.849 (95% CI: 0.691-0.946) for T1ρ (P = 0.414), 0.870 (95% CI: 0.716-0.958) for SWE and 0.799 (95% CI: 0.632-0.913) for T1ρ (P = 0.422), and 0.846 (95% CI: 0.687-0.944) for SWE and 0.692 (95% CI: 0.517-0.835) for T1ρ (P = 0.137), when diagnosing liver fibrosis with ≥F1, ≥F2, ≥F3 and F4, respectively. There was moderate positive correlation between inflammatory activity and T1ρ values (r=0.520; 95% CI 0.158-0.807; P=0.013).

Introduction

Noninvasive methods, especially imaging technique, have been an intense field of research for liver fibrosis assessment. Elastography techniques has been now widely recognized as a reliable method to assess liver fibrosis. Recent studies have shown a correlation between the liver shear modulus measured by using 2D shear-wave elastography (SWE) and the degree of fibrosis obtained through liver biopsy.

Spin-lattice relaxation time in the rotating frame (T1ρ) can reflect biologic processes associated with alterations in macromolecular composition and proton exchange in tissues. Nowadays, liver T1ρ imaging has potential for fibrosis staging, liver function test and hepatocyte regeneration evaluation [25-29]. However, conflicting results were reported in several studies about liver fibrosis. Therefore, further studies are needed to clarify the value of T1ρ imaging for liver fibrosis staging.

Purpose

Methods

Twenty-nine rabbit models of CCl4-induced liver fibrosis were established and six untreated rabbits served as controls. MRI was performed using a clinical 3T scanner (Ingenia, Philips Healthcare, Best, the Netherlands) with an eight-channel animal radiofrequency coil (Chenguang Medical Healthcare).

For T1ρ imaging, a rotary echo spin-lock pulse was implemented in a 3D turbo field echo (TFE) sequence. Spin-lock frequency was set to 500 Hz, and the spin-lock times (TSL) of 1, 10, 20, 40, and 50 ms were used for T1ρ mapping. Parameters were as follows: TR/TE=3.8/1.8 ms, flip angle, 40º;slice thickness, 2mm; voxel size, 1.2×1.2×2mm3; FOV=120×120×10 mm2, matrix=100×79, SENSE acceleration factor =2, TFE factor=64, NSA=4, and spectral presaturation inversion recovery fat suppression (SPIR). Five axial slices were selected to cover the central areas of the liver. T1ρ mapping was conducted using Philips Research Integrated Development Environment (PRIDE) software written in IDL 6.3 (ITT, CO, USA). T1ρ maps were computed on a pixel- by-pixel basis by using a monoexponential decay model, as described by the following equation: M (TSL) = M0 · exp (-TSL/T1ρ) M is signal intensity in the T1rho relaxation preparation images with a certain spin lock time, and TSL is time of spin-lock pulse. Image quantification analyses were conducted using ImageJ software (NIH, Bethesda, MD). T1ρ measurements were performed on the largest section of the liver by a radiologist. Regions of interest (ROIs) conforming to the liver margins but excluding major blood vessels were manually drawn on T1ρ maps to measure T1ρ value .

2D real-time SWE examination was performed using the Aixplorer US system (Resona 7，mindray, China) with a linear array probe (L15-4) and a frequency of 4-15 MHz by a radiologist. Liver stiffness (LS) measurements were acquired at least 1 cm below the liver capsule in the right liver lobe on 2D quantitative SWE image. The mean value of six consecutive measurements was used for statistical analyses.

Fibrosis was staged according to the METAVIR scoring system. Correlation between LS values, T1ρ values, and liver fibrosis stage were assessed using Spearman’s non-parametric rank correlation coefficient. Pearson correlation test was used to evaluate the correlation of T1ρ values and LS values. Receiver operating characteristic (ROC) analysis was performed for assessing diagnostic performance of T1ρ and SWE in detection and grading fibrosis.

Results

Conclusion

Acknowledgements

References

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