Magnetic resonance spin–spin relaxation time estimation in a rat model of fatty liver disease

Purpose: To compare mono- and bi-exponential relaxation model equations to discriminate between normal and fatty liver disease. Materials and Methods: Six rats on a choline deficient amino acid modified (CDAA) diet and six on normal chow were studied. Multiple spin echo images with increasing echo times (TEs) were collected at 9.4T. Pixel-wise T ₂ maps were generated using mono-exponential decay function to calculate T _2M , and a bi-exponential to calculate, short T ₂ component (T _2S ), long T ₂ component (T _2L ), and fractions of these components (ρ _S , ρ _L ), respectively. Statistical F-tests and Akaike's information criterion (AIC) were used to assess the relative performance of the two models. Results: F-test and AIC showed that in the CDAA group, T ₂ bi-exponential model described the signal of T ₂ weighted imaging of the liver better than the mono-exponential model. Controls were best described by the mono-exponential model. Mean values for T _2M , T _2L , T _2S , ρ _S , ρ _L were 31.2 ± 0.7 ms, 72.8 ± 3.3 ms, 8.2 ± 0.6 ms,71.2 ± 2.1%, 30.4 ± 1.3%, respectively, in CDAA rats, compared with 18.8 ± 0.5 ms, 32.3 ± 0.7 ms, 9.2 ± 1.8 ms, 79 ± 2%, 21.0 ± 1.1% in controls. Conclusion: In the fatty liver of CDAA rats we have shown that T ₂ weighted images fit the bi-exponential model better than mono-exponential decays thus providing a better description of the data. Level of Evidence: 1. Technical Efficacy: Stage 2. J. Magn. Reson. Imaging 2018;47:468–476.