A new generation SQUID biosusceptometer

Iron overload from genetic disorders and/or regular blood transfusions is a serious health problem in many regions of the world. As liver and spleen iron stores account for more than 70 % of total body iron stores, the precise quantification and the continuous monitoring of these stores is of particular importance in the diagnosis and treatment of these disorders. During the last two decades several noninvasive methods have been explored for the assessment of elevated liver iron stores in patients with primary (genetic hemochromatosis) or with iron loading anemias (e.g., ß-thalassemia major, leukemia after bone marrow transplantation). Of these different methods only quantitative magnetic resonance imaging (qMRI) [1] and SQUID biomagnetic liver susceptometry (BLS) [2] have achieved a broader clinical acceptance. The noninvasive determination of liver iron concentration (LIC) by BLS has become now a routine method in iron overload monitoring. While serum ferritin has been shown to be only a poor predictor of iron overload [3, 4] many European thalassemia centers in Italy, Greece, Switzerland and Germany are using BLS now as part of their regular follow-up programme. From the experience of two decades with SQUID susceptometers [4, 5] we have developed a novel low temperature 3-channel SQUID biosusceptometer system (SQUID BioSusceptometer, model 5700, Tristan) for the Centro Microcitemie at the hospital O.I.R.M. / S. Anna in Turin. The system was especially optimized for 1. improved spatial resolution: below liver iron concentrations of 1000 μg Fe/gliver and in obese patients, the approximate estimation of the magnetic susceptibility of the thorax tissue layer above the liver was the main limiting factor in the precision of the determination of LIC by SQUID-BLS. 2. pediatric measurements: as many of the patients are children with small sized livers and spleens, certain system components such as the waterbag reference, the sensor assembly and the dewar tail had to be optimized in order to allow measurements in pediatric patients <= 3 years old. 3. clinical practicability: as the quality of the data depend largely on the individual positioning of the subjects, many components, such as laser cross alignment used for positioning and the evacuable patient mattress, had to be integrated into the system.