[Magnetic resonance and hepatic siderosis]

Abstract

The principles of generation of magnetic resonance imaging (MRI) are resumed by briefly explaining the effects of an external magnetic field (EMF) on hydrogen nuclei and of pulses of radiofrequency (RF) radiation. The latter creates a resonant effect, and the same nuclei, moved from the external field axis, when RF pulse is stopped, will "relax" to their original alignment in the magnetic field and in so doing radiate the absorbed energy to their surroundings. This energy provides a signal that can be detected and spatially resolved by the receiver coil wrapped around the patient, through a computerized system. After briefly explaining also the distinctive parameters T2 and T1, the author presents his experience in the MRI detection of different degrees of siderosis of the liver--ranging from idiopathic and secondary haemochromatosis to milder siderosis of alcoholic liver disease and porphyria cutanea tarda. The results were accomplished by employing an equipment operating at an enhanced field strength (1.5 Tesla). Previous reports have validated this technique in order to distinguish idiopathic from secondary haemochromatosis. Furthermore, the present study shows that even low to moderate degrees of liver iron deposition can be appreciated and roughly quantitated by the decrease of the transverse relaxation time (T2), which resulted proportional to the amount of liver iron, under these operating conditions. Thus, MRI is proposed as an useful and non-invasive way to detect iron deposition and to follow up iron depletion treatments.