|An R2 image of an iron loaded human liver superimposed on a T2-weighted cross-sectional image of the patient. The bright regions indicate areas of higher iron concentration while the darker areas correspond to regions of lower iron concentration.|
The quantification and monitoring of tissue iron concentrations play important roles in the clinical management of patients with iron overload diseases such as thalassemia and hereditary hemochromatosis. Although blood tests such as serum ferritin and transferrin saturation are used for assessing the degree of iron overload in thalassaemia patients, these tests can be confounded by factors such as the presence of infection or tumours. In order to make a definitive measurement of the degree of iron overload, the currently accepted method is chemical analysis of iron from liver needle biopsy specimens.
However, hepatic iron concentration (HIC) measurements by needle biopsy have several associated problems. Primarily there is a sampling error owing to the large variation in HIC from site to site within the liver. This error increases as iron loading increases. Secondly, liver needle biopsy is an unpleasant procedure for the patient and carries some degree of risk. These latter two factors limit the frequency with which measurements can be made.
The Biomagnetics Group at The University of Western Australia has recently developed a magnetic resonance imaging (MRI)-based method of measuring and imaging water proton transverse relaxation rates (R2) in iron loaded liver in vivo [Clark & St. Pierre, 2000]. Studies on synthetic paramagnetic phantoms, iron loaded animal models, and human patients with a range of hepatic iron concentrations indicate that R2 can be measured accurately in vivo with a spatial resolution of approximately 5mm and that R2 correlates with the local HIC. These observations indicate that the method can measure and image non-invasively tissue iron concentrations in patients with iron overload diseases and hence eliminates the need for needle biopsy for liver iron concentration measurement (data in preparation for publication).
Clark, P.R. and St. Pierre, T.G. (2000) Quantitative 1/T2 mapping of
hepatic iron overload: a single spin echo imaging methodology. Magnetic
Resonance Imaging, 18, 431-438.
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