MRI measurement of hepatic magnetic susceptibility - Phantom validation and normal subject studies

A magnetic resonance (MR) imaging method with the potential for assessing hepatic iron overload from measurements of hepatic magnetic susceptibility in vivo is described. Using the blood in the portal and hepatic veins as an internal reference, this technique uses the orientation dependence of signal phase to measure the susceptibility of the liver parenchyma. Computer simulations were done to investigate the requirements on spatial resolution and contrast ratio between the vessels and the background liver tissue for data acquisition. Validation studies were conducted using tubeembedded gel phantoms doped with iron-dextran from 0 to 10 mg Fe/mL to mimic healthy and iron-overloaded livers. The phantom measurements were conducted without motion and flow, under respiration-like oscillatory motion, and with flow. Studies on six normal human subjects demonstrated excellent reproducibility and precision. All images were collected at 1.5 T using a 3D T1-weighted turbo field echo sequence for inflow MR angiographies with full flow compensation and capable of cardiac synchronization, navigator gating, and motion correction. Magn Reson Med 52:1318 –1327, 2004. © 2004 Wiley-Liss, Inc. Reliable measurement of magnetic susceptibility of the liver has an important application in the assessment of iron overload (1), which occurs in patients with thalassemia, sickle cell disease, and other diseases requiring longterm transfusion therapy, as well as hereditary hemochromatosis (2). The excess iron leads to oxidative injury to tissues and in severe cases can be life threatening. The iron can be removed effectively by regular chelation therapy, but this treatment often has undesirable side effects and poor compliance is common. Currently, reliable measurement of the liver iron concentration plays a central role in managing patients with iron overload (3). The degree of hepatic iron storage accurately reflects the whole-body iron excess in systemic iron overload (4,5). Hepatic iron concentration can be evaluated chemically from the hepatic tissue obtained by invasive needle biopsy (6,7). Un