Impact of Iron Assessment by MRI
The use of magnetic resonance imaging (MRI) to estimate tissue iron was conceived in the 1980s, but has only become a practical reality in the last decade. The technique is most often used to estimate hepatic and cardiac iron in patients with transfusional siderosis and has largely replaced liver biopsy for liver iron quantification. However, the ability of MRI to quantify extrahepatic iron has had a greater impact on patient care and on our understanding of iron overload pathophysiology. Iron cardiomyopathy used to be the leading cause of death in thalassemia major, but is now relatively rare in centers with regular MRI screening of cardiac iron, through earlier recognition of cardiac iron loading. Longitudinal MRI studies have demonstrated differential kinetics of uptake and clearance among the difference organs of the body. Although elevated serum ferritin and liver iron concentration (LIC) increase the risk of cardiac and endocrine toxicities, some patients unequivocally develop extrahepatic iron deposition and toxicity despite having low total body iron stores. These observations, coupled with the advent of increasing options for iron chelation therapy, are allowing clinicians to more appropriately tailor chelation therapy to individual patient needs, producing greater efficacy with fewer toxicities. Future frontiers in MRI monitoring include improved prevention of endocrine toxicities, particularly hypogonadotropic hypogonadism and diabetes.