MR characterization of hepatic storage iron in transfusional iron overload

Abstract

Purpose To quantify the two principal forms of hepatic storage iron, diffuse, soluble iron (primarily ferritin), and aggregated, insoluble iron (primarily hemosiderin) using a new MRI method in patients with transfusional iron overload. Materials and Methods Six healthy volunteers and twenty patients with transfusion-dependent thalassemia syndromes and iron overload were examined. Ferritin- and hemosiderin-like iron were determined based on the measurement of two distinct relaxation parameters: the “reduced” transverse relaxation rate, RR2 and the “aggregation index,” A, using three sets of Carr-Purcell-Meiboom-Gill (CPMG) datasets with different interecho spacings. Agarose phantoms, simulating the relaxation and susceptibility properties of tissue with different concentrations of dispersed (ferritin-like) and aggregated (hemosiderin-like) iron, were employed for validation. Results Both phantom and in vivo human data confirmed that transverse relaxation components associated with the dispersed and aggregated iron could be separated using the two-parameter (RR2, A) method. The MRI-determined total hepatic storage iron was highly correlated (r = 0.95) with measurements derived from biopsy or biosusceptometry. As total hepatic storage iron increased, the proportion stored as aggregated iron became greater. Conclusion This method provides a new means for non-invasive MRI determination of the partition of hepatic storage iron between ferritin and hemosiderin in iron overload disorders.

A model for hepatic fibrosis: the competing effects of cell loss and iron on shortened modified Look-Locker inversion recoveryT1(shMOLLI-T1) in the liver

“…The other possible issue with using R2 calibration of St Pierre et al is that R2 was measured using a single spin echo sequence. In patients with high levels of iron, particularly high levels of hemosiderin (which aggregates into larger particles), R2 measured using a fast spin echo sequence is dependent on echo spacing . However, the maximum iron level for the patients included in our study was less than 2.5 mg/g.…”

“…However, the maximum iron level for the patients included in our study was less than 2.5 mg/g. The contribution of aggregate, hemosiderin‐like iron at this relatively low level is minimal, much less than 10% . We thus chose not to incorporate any echo‐spacing dependence of R2 into the model reported here.…”

Quantification of liver fat in the presence of iron overload

“…R2* is often used as a proxy measure of iron overload, but may also be affected by factors such as fibrosis . However, the dephasing effects of iron dominate R2* in vivo, particularly at higher iron levels …”

Biexponential R2* relaxometry for estimation of liver iron concentration in children: A better fit for high liver iron states

“…Recent studies showed it is feasible to measure ferritin and hemosiderin iron separately based on non‐monoexponential signal decay models . However, while histologic studies demonstrate that hemosiderin in states of high iron overload accounts for up to 75% of the total iron storage, the mean slow component in our sample was only around 5%, reaching up to 15% in some patients.…”