Fat and Iron Quantification in the Liver

Abstract

Liver fat, iron, and combined overload are common manifestations of diffuse liver disease and may cause lipotoxicity and iron toxicity via oxidative hepatocellular injury, leading to progressive fibrosis, cirrhosis, and eventually, liver failure. Intracellular fat and iron cause characteristic changes in the tissue magnetic properties in predictable dose-dependent manners. Using dedicated magnetic resonance pulse sequences and postprocessing algorithms, fat and iron can be objectively quantified on a continuous scale. In this article, we will describe the basic physical principles of magnetic resonance fat and iron quantification and review the imaging techniques of the "past, present, and future." Standardized radiological metrics of fat and iron are introduced for numerical reporting of overload severity, which can be used toward objective diagnosis, grading, and longitudinal disease monitoring. These noninvasive imaging techniques serve an alternative or complimentary role to invasive liver biopsy. Commercial solutions are increasingly available, and liver fat and iron quantitative imaging is now within reach for routine clinical use and may soon become standard of care.

Liver MRI: From basic protocol to advanced techniques

“…The T2* estimation is used to correct the effect of T2* in PDFF quantification. Moreover, because liver T2* is related to the amount of iron deposition, it can also be used for simultaneous quantification of iron deposits [36,[40][41][42]. Nevertheless, because large iron content lead to extremely low signal in GRE sequences, PDFF measurements may be corrupted in livers with severe iron overload [41].…”

“…As mentioned above, MECSE-MR sequences, the same as described for fat quantification, can also be used for R2* estimation and LIC quantification (Figs. 9 and 10) [40][41][42]48] while simultaneously assessing the liver fat content (Figs. 9 and 10).…”

“…The first echo should be as short as possible (1 ms or less) and the echo spacing should be short enough (approximately 1 ms or less) [42], to guarantee that the signal decay is captured even in high iron-loaded livers. The LIC (mg Fe/g or μmol Fe/g) can be estimated from the R2*/ T2* measurements, using calibration curves that were pre-validated against liver biopsies [42,48,51,52]. As mentioned above, MECSE-MR sequences, the same as described for fat quantification, can also be used for R2* estimation and LIC quantification (Figs.…”

“…R2 techniques are less sensitive to external magnetic inhomogeneities [48] but require a longer acquisition time than R2* techniques, being more prone to motion artefacts. R2* relaxometry methods are usually performed with SPGR multiecho sequences, during one or two breath-hold acquisitions [42,48,51]. T2* or R2* measurements can be calculated using commercial postprocessing software (CMR Tools ® ) or in-house developed software.…”

Noninvasive MRI-Based Liver Iron Quantification: Methodic Approaches, Practical Applicability and Significance

“…Based on the studies of Alustiza, Gandon and St. Pierre, quantitative determination of liver iron content has been possible for ten years [18 -20]. Yokoo et al provide an overview of this development [21]. Today MRbased methods for determining liver iron content are an essential part of guideline recommendations for managing secondary iron overload [7] (latest version available at: http://www.awmf.org/leitlinien/detail/ll/025 -029.html).…”