Repeatability and Reproducibility of Multiparametric MRI

As the burden of liver disease reaches epidemic levels, there is a high unmet medical need to develop robust, accurate and reproducible non-invasive methods to quantify liver tissue characteristics for use in clinical development and ultimately in clinical practice. Repeatability and reproducibility validation studies are important in evaluating metrics, such that any changes can be confidently attributed to disease progression or regression, rather than inter-examination variability in the instrument. Magnetic resonance (MR) techniques offer an attractive non-invasive option for liver assessment. Multiparametric MRI is a safe and non-invasive method for quantification of liver tissue characteristics. Images for quantification of hepatic fat from proton density fat fraction (PDFF) maps, T2\*, and iron-corrected T1 (cT1) can be rapidly obtained during abdominal breath-hold acquisitions without the need for contrast agents or additional external hardware. Iron correction of T1 is necessary to address the confounding effects of excess iron, which is common in chronic liver disease. LiverMultiScan™ (LMS, Perspectum Diagnostics, Oxford, UK) is a software application that can be used with supported MR-systems to correct T1 for the effects of excess iron, and thus, to calculate cT1 from T1 and T2\* maps, and standardise to a 3T field strength. This method has been shown to have high diagnostic accuracy for the assessment of liver fibrosis compared to histology, predict clinical outcomes in patients with mixed liver disease aetiology, stratify patients with non-alcoholic steatohepatitis (NASH) and cirrhosis, reliably exclude clinically significant liver disease and is cost-effective in diagnosing NAFLD. In addition to demonstrating accuracy, imaging biomarker validation requires precision and repeatability (US Department of Health and Human Services, 2015). From a clinical perspective, it is essential to ensure that there is good inter-examination repeatability, so that any changes seen can be correctly attributed to disease progression or regression, rather than inter-examination variability. This is tested by examining the closeness of repeated measurements made in different MR examinations (with both subject and coil repositioning) over a time frame in which physiologic conditions are assumed constant. This study aims to systematically test the repeatability and reproducibility of each multiparametric MRI measurement, cT1, T2\* and PDFF, corresponding to hepatic fibro-inflammation, iron and fat respectively, across scanner field strength, manufacturer and model in human participants and phantoms.