Measurement of liver iron overload: noninvasive calibration of MRI-R2* by magnetic iron detector susceptometer.

An accurate assessment of body iron accumulation is essential for the diagnosis and therapy of iron overload in diseases such as thalassemia or hemochromatosis. Magnetic iron detector susceptometry and MRI are noninvasive techniques capable of detecting iron overload in the liver. Although the transverse relaxation rate measured by MRI can be correlated with the presence of iron, a calibration step is needed to obtain the liver iron concentration. Magnetic iron detector provides an evaluation of the iron overload in the whole liver. In this article, we describe a retrospective observational study comparing magnetic iron detector and MRI examinations performed on the same group of 97 patients with transfusional or congenital iron overload. A biopsy-free linear calibration to convert the average transverse relaxation rate in iron overload (R(2) = 0.72), or in liver iron concentration evaluated in wet tissue (R(2) = 0.68), is presented. This article also compares liver iron concentrations calculated in dry tissue using MRI and the existing biopsy calibration with liver iron concentrations evaluated in wet tissue by magnetic iron detector to obtain an estimate of the wet-to-dry conversion factor of 6.7 ± 0.8 (95% confidence level).

Total iron-overload measurement in the human liver region by the magnetic iron detector.

An accurate assessment of body iron accumulation is essential for the diagnosis and therapy of iron overload in diseases, such as hemochromatosis, thalassemia and other forms of severe anemias. The magnetic iron detector (MID) is a room-temperature susceptometer, which measures the total iron overload in the liver. Since February 2005, about 600 patients have been assessed using this device. The iron overload is obtained by calculating the difference between the measured magnetization signal of the patient and the patient's background signal. The latter is the magnetization signal that the patient would generate with normal iron content. This study presents the method for calculating the background signal of healthy volunteers and the application of the same method to patients with iron burden in order to evaluate their overload. The present MID sensitivity is 0.8 g and the reproducibility of the iron overload measurement of the same patients is lower than 0.5 g. The MID does not require calibration with liver biopsies. We correlated the MID measurements with the results of 26 biopsies (R = 0.62), 64 superconducting quantum interference device susceptometer measurements (R = 0.79), 666 serum ferritin concentration measurements (R = 0.72), and 41 MRI- R2* measurements (R = 0.71).

Iron overload detection in rats by means of a susceptometer operating at room temperature.

Biosusceptometry is a non-invasive procedure for determination of iron overload in a human body; it is essentially an assessment of the diamagnetic (water) and paramagnetic (iron) properties of tissues. We measured in vivo iron overload in the liver region of 12 rats by a room temperature susceptometer. The rats had been injected with sub-toxic doses of iron dextran. A quantitative relationship has been observed between the measurements and the number of treatments. The assessment of iron overload requires evaluating the magnetic signal corresponding to the same rat ideally without the overload. This background value was extrapolated on the basis of the signal measured in control rats versus body weight (R(2) = 0.73). The mean iron overload values for the treated rats, obtained after each iron injection, were significantly different from the means of the corresponding control rats (p < 0.01). The in vivo measurements have been complemented by chemical analysis on excised livers and other organs (R(2) = 0.89). The magnetic moment of iron atoms in liver tissues was measured to be 3.6 Bohr magneton. Evaluation of the background signal is the limit to the measure; the error corresponds to about 30 mg (1 SD) of iron while the instrument sensitivity is more than a factor of 10 better.