Evaluation of Iron Overload by Non-Invasive Measurement Techniques

Abstract

In recent years there has been increasing interest in non-invasive iron assessment techniques, especially of the liver, heart, and brain, in patients with iron overload and neurodegenerative diseases. This review is focussing on major development reports since 2000 unless references to former publications are required. Biochemical properties of the iron storage molecular compounds, haemosiderin and ferritin, are presented and all available iron specific magnetic susceptibilities are tabulated. The basics of quantitative iron assessment methods such as magnetic resonance imaging (MRI) techniques such as relaxometry (R1, R2, R2* = 1/T2*), biomagnetic susceptometry based on electronic and nuclear magnetism, and nuclear methods using X-rays are outlined. The central role of dia- or paramagnetic magnetic susceptibility in the magnetization of tissue, which can either be probed by magnetometers (SQUID) or 1H-MR sensors (phase), is discussed. Assessment of in vivo tissue iron concentrations by non-iron specific methods (1H-MRI, biosusceptometry, X-ray CT) need a calibration by physico-chemical iron measurements in biopsy or autopsy tissue at least for validation. Results from different reference methods for liver (MRI-R2) and heart (MRI-R2*), showing their agreement, are compared. Finally, representative in vivo iron assessment studies in different tissues, organs, and glands are presented.