An non-invasive method for quantifying the lesions of the liver of a subject suspected of suffering from a non-alcoholic fatty liver disease addressing as diagnostic target steatohepatitis, which comprises: a. performing a T2-weighted single shot fast spin echo magnetic resonance imaging (SSFSE-T2 MRI) and a Dynamic contrast-enhanced magnetic resonance imaging (DYNAMIC MRI) and a fast spin-echo short inversion time inversion-recovery (STIR MRI) magnetic resonance imaging (FAST-STIR MRI), on whole or part of the liver of the subject, b. measuring a harmonic mean from the whole set of pixel values of an image generated with said SSFSE-T2 MRI, an order contrast from an image generated with said DYNAMIC MRI and the averaged main curvature from an image generated with said FAST-STIR MRI; and c. using said measurements in a mathematical function useful as a predictive equation to obtain the probability of suffering from steatohepatitis; wherein the mathematical function useful as a predictive equation is as follows: NASH-MRI = 1 / 1 + e 1.654 − 0.079 * E 3 _ T 2 − 0.127 * E 57 _ DYN * E 73 _ FAST wherein: E3_T2 = harmonic mean from the image generated with the T2-weighted single shot fast spin-echo magnetic resonance imaging (SSFSE-T2 MRI). E57_DYN = order contrast from the image generated with the dynamic contrast-enhanced magnetic resonance imaging (DYNAMIC MRI) E73_FAST = averaged mean curvature from the image generated with the fast spin-echo short inversion time inversion-recovery (FAST-STIR MRI); and wherein the MRIs images are each acquired by using a General Electric 1,5-Tesla whole-body system. a. performing a T2-weighted single shot fast spin echo magnetic resonance imaging (SSFSE-T2 MRI) and a Dynamic contrast-enhanced magnetic resonance imaging (DYNAMIC MRI) and a fast spin-echo short inversion time inversion-recovery (STIR MRI) magnetic resonance imaging (FAST-STIR MRI), on whole or part of the liver of the subject, b. measuring a harmonic mean from the whole set of pixel values of an image generated with said SSFSE-T2 MRI, an order contrast from an image generated with said DYNAMIC MRI and the averaged main curvature from an image generated with said FAST-STIR MRI; and c. using said measurements in a mathematical function useful as a predictive equation to obtain the probability of suffering from steatohepatitis; wherein the mathematical function useful as a predictive equation is as follows: NASH-MRI = 1 / 1 + e 1.654 − 0.079 * E 3 _ T 2 − 0.127 * E 57 _ DYN * E 73 _ FAST wherein: E3_T2 = harmonic mean from the image generated with the T2-weighted single shot fast spin-echo magnetic resonance imaging (SSFSE-T2 MRI). E57_DYN = order contrast from the image generated with the dynamic contrast-enhanced magnetic resonance imaging (DYNAMIC MRI) E73_FAST = averaged mean curvature from the image generated with the fast spin-echo short inversion time inversion-recovery (FAST-STIR MRI); and wherein the MRIs images are each acquired by using a General Electric 1,5-Tesla whole-body system. E3_T2 = harmonic mean from the image generated with the T2-weighted single shot fast spin-echo magnetic resonance imaging (SSFSE-T2 MRI). E57_DYN = order contrast from the image generated with the dynamic contrast-enhanced magnetic resonance imaging (DYNAMIC MRI) E73_FAST = averaged mean curvature from the image generated with the fast spin-echo short inversion time inversion-recovery (FAST-STIR MRI);