Noninvasive Quantification of Liver Fat Content by Different Gradient Echo Magnetic Resonance Imaging Sequences in Patients with Nonalcoholic Fatty Liver Disease.

BACKGROUND: Noninvasive quantification of liver fat by gradient echo (GRE) technique is an interesting issue in quantitative magnetic resonance imaging. In this study, the fat content in patients with nonalcoholic fatty liver disease (NAFLD) was quantified with GRE sequences with different T 1 and T 2* weighting. METHODS: This prospective, cross-sectional study was performed on thirty NAFLD patients. Sixteen GRE sequences with different T 1 weighting were performed with four echo times. In each sequence, repetition time (TR) or flip angle was changed and other parameters were fixed. Forty-eight fat indexes (FIs) from 16 sequences were calculated based on three methods. To determine the relationship between FIs and histological findings, Pearson's correlation coefficient was used at the level of 1% significance. RESULTS: Mean FIs which obtained from Eq. 3 have the maximum values in comparison to other FIs. The maximum FI was 23.58%, which related to heavily T 1 weighted sequence obtained with method 3. The minimum FI was -2.49%, which related to the minimal T 1 weighted obtained with method 2. FIs increase with a flip angle, especially at low flip angles. Increase the TR parameter decrease the FIs gradually. Calculated FIs with methods 1 and 3 stronger correlated with histological findings relative to calculated FIs with method 2. CONCLUSION: For fat quantification, T 1 relaxation effects probably more critical than T 2*. Flip angle parameter could be a major factor causing the overestimation of liver fat content. Sequences with low flip angle are more suitable for fat quantification with methods 1 and 3. In fat quantification with GRE techniques, it is possible that the third and fourth echoes are unnecessary.