The role of MRI to estimate liver iron concentration (LIC) for identifying patients with iron overload and guiding the titration of chelation therapy is increasingly established for routine clinical practice. However, the existence of multiple MRI-based LIC quantification techniques limits standardization and widespread clinical adoption. In this article, we review the existing and widely accepted MRI-based LIC estimation methods at 1.5 T and 3 T: signal intensity ratio (SIR) and relaxometry (R2 and R2*) and discuss the basic principles, acquisition and analysis protocols, and MRI-LIC calibrations for each technique. Further, we provide an up-to-date information on MRI vendor implementations and available offline commercial and free software for each MRI-based LIC quantification approach. We also briefly review the emerging and advanced MRI techniques for LIC estimation and their current limitations for clinical use. Lastly, we discuss the implications of MRI-based LIC measurements on clinical use and decision-making in the management of patients with iron overload. Some of the key highlights from this review are as follows: 1) Both R2 and R2* can estimate accurate and reproducible LIC, when validated acquisition parameters and analysis protocols are applied, 2) Although the Ferriscan R2 method has been widely used, recent consensus and guidelines endorse R2*-MRI as the most accurate and reproducible method for LIC estimation, 3) Ongoing efforts aim to establish R2*-MRI as the standard approach for quantifying LIC, and 4) Emerging R2*-MRI techniques employ radial sampling strategies and offer improved motion compensation and broader dynamic range for LIC estimation. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 2.

Quantitative abdominal magnetic resonance imaging (MRI) offers non-invasive, objective assessment of diseases in the liver, pancreas, and other organs and is increasingly being used in the pediatric population. Certain quantitative MRI techniques, such as liver proton density fat fraction (PDFF), R2* mapping, and MR elastography, are already in wide clinical use. Other techniques, such as liver T1 mapping and pancreas quantitative imaging methods, are emerging and show promise for enhancing diagnostic sensitivity and treatment monitoring. Quantitative imaging techniques have historically required a breath-hold, making them more difficult to implement in the pediatric population. However, technological advances, including free-breathing techniques and compressed sensing imaging, are making these techniques easier to implement. The purpose of this article is to review current liver and pancreas quantitative techniques and to provide a practical guide for implementing these techniques in pediatric practice. Future directions of liver and pancreas quantitative imaging will be briefly discussed.

Traditionally, liver disease diagnosis relied heavily on invasive liver biopsies, considered the gold standard for direct liver assessment. However, the emergence of less invasive alternatives, such as magnetic resonance elastography (MRE) and magnetic resonance imaging (MRI), has transformed the field. In this study, a wide array of novel biomarkers, including stiffness, corrected longitudinal relaxation time (cT1), longitudinal relaxation time (T1), and apparent diffusion coefficient (ADC), were employed to assess liver fibrosis. Proton density fat fraction (PDFF) was determined using the Dixon technique for steatosis evaluation, and transversal relaxation time (T2*) was utilized to gauge iron overload. A comprehensive imaging protocol, including calibration with an albumin phantom, encompassed five sequences performed on 27 patients suspected of non-alcoholic steatohepatitis (NASH). The MRI data were acquired using a 3 Tesla GE Medical Systems SIGNA Architect MRI scanner. This study calibrated T1 maps with an albumin phantom and assessed the reliability of elastography by magnetic resonance (MRE) for fibrosis analysis. Significant correlations were observed between biomarkers and liver health indicators: cT1 correlated with stiffness (r=0.4272, p=0.0331) and PDFF (r=0.6699, p=0.0002), ADC correlated with stiffness (r=0.6278, p=0.0008), and PDFF demonstrated a strong association with the IDEAL technique (r=0.9792, p=0.0001), confirming its reliability for steatosis assessment.Clinical Relevance- The current study presents a novel and innovative approach to the non-invasive diagnosis of liver diseases, including conditions like iron overload, steatosis, and fibrosis. This groundbreaking approach involves a multiparametric and multimodal analysis of biomarkers, enabling a higher degree of non-invasive diagnostic accuracy.

Quantitative magnetic resonance imaging (MRI) techniques are emerging as non-invasive alternatives to biopsy for assessment of diffuse liver diseases of iron overload, steatosis and fibrosis. For testing and validating the accuracy of these techniques, phantoms are often used as stand-ins to human tissue to mimic diffuse liver pathologies. However, currently, there is no standardization in the preparation of MRI-based liver phantoms for mimicking iron overload, steatosis, fibrosis or a combination of these pathologies as various sizes and types of materials are used to mimic the same liver disease. Liver phantoms that mimic specific MR features of diffuse liver diseases observed in vivo are important for testing and calibrating new MRI techniques and for evaluating signal models to accurately quantify these features. In this study, we review the liver morphology associated with these diffuse diseases, discuss the quantitative MR techniques for assessing these liver pathologies, and comprehensively examine published liver phantom studies and discuss their benefits and limitations.