Magnetic resonance imaging of the liver : T1 dynamics : confounders and modelling

Non-alcoholic fatty liver disease (NAFLD) is becoming increasingly prevalent in the world population. The current gold standard for diagnosing NAFLD, however, is still the liver needle biopsy, the evaluation of which can be subjective, lacks good reproducibility, and suffers from sampling bias. Multiparametric MRI exams comprising measurements of proton density fat fraction, hepatic iron concentration and liver T₁ values, with iron- corrected T₁ measurements correlating well with liver fibrosis and inflammation, have been suggested as a good non-invasive candidate to diagnose NAFLD. However, T₁ values and T₁ measurement methods are affected by more than just iron. The work presented in this thesis focussed on characterising the complex dependence of T₁ values on hepatic lipid concentration when using the MOLLI methods. Dependent on field strength, magnetic field inhomogeneities, and sequence parameters (such as echo time and repetition time), the deleterious effects of fat can result in an artificial increase or decrease of measured liver T₁s. An algorithm capable of reversing the effects of fat and frequency offsets was developed and tested in phantoms and in prospectively recruited participants by comparing the outcome of the algorithm to liver water T₁ values measured using MR spectroscopy. Finally, two other influencing factors of liver T₁ were also studied: liver glycogen concentration and body hydration status, both of which are subject to significant diurnal variation and their T₁ effect has been shown earlier. A small study involving healthy vol- unteers undergoing metabolic interventions was conducted to determine the dependence of liver T₁ values on liver glycogen concentration and hydration status.