Calibration of myocardial T2 and T1 against iron concentration.

BACKGROUND: The assessment of myocardial iron using T2* cardiovascular magnetic resonance (CMR) has been validated and calibrated, and is in clinical use. However, there is very limited data assessing the relaxation parameters T1 and T2 for measurement of human myocardial iron. METHODS: Twelve hearts were examined from transfusion-dependent patients: 11 with end-stage heart failure, either following death (n=7) or cardiac transplantation (n=4), and 1 heart from a patient who died from a stroke with no cardiac iron loading. Ex-vivo R1 and R2 measurements (R1=1/T1 and R2=1/T2) at 1.5 Tesla were compared with myocardial iron concentration measured using inductively coupled plasma atomic emission spectroscopy. RESULTS: From a single myocardial slice in formalin which was repeatedly examined, a modest decrease in T2 was observed with time, from mean (± SD) 23.7 ± 0.93 ms at baseline (13 days after death and formalin fixation) to 18.5 ± 1.41 ms at day 566 (p<0.001). Raw T2 values were therefore adjusted to correct for this fall over time. Myocardial R2 was correlated with iron concentration [Fe] (R2 0.566, p<0.001), but the correlation was stronger between LnR2 and Ln[Fe] (R2 0.790, p<0.001). The relation was [Fe] = 5081•(T2)-2.22 between T2 (ms) and myocardial iron (mg/g dry weight). Analysis of T1 proved challenging with a dichotomous distribution of T1, with very short T1 (mean 72.3 ± 25.8 ms) that was independent of iron concentration in all hearts stored in formalin for greater than 12 months. In the remaining hearts stored for <10 weeks prior to scanning, LnR1 and iron concentration were correlated but with marked scatter (R2 0.517, p<0.001). A linear relationship was present between T1 and T2 in the hearts stored for a short period (R2 0.657, p<0.001). CONCLUSION: Myocardial T2 correlates well with myocardial iron concentration, which raises the possibility that T2 may provide additive information to T2* for patients with myocardial siderosis. However, ex-vivo T1 measurements are less reliable due to the severe chemical effects of formalin on T1 shortening, and therefore T1 calibration may only be practical from in-vivo human studies

Iron oxide deposits in iron overload diseases

Iron overload diseases such as thalassaemia are a major public health problem in many parts of the world. Excess iron deposited in such tissues occurs in the form of ultrafine particles of iron oxyhydroxide. At low levels of iron loading, the iron(III) oxyhydroxide particles are mostly found in the iron storage protein, ferritin. At higher levels of loading, iron(III) oxyhydroxide particles are found in insoluble aggregates known as haemosiderin. Three different structures of these iron deposits are known: (i) ferrihydrite (5Fe203.9H20), (ii) poorly crystalline goethite (α-FeOOH), and (iii) non-crystalline hydrated iron(III) oxyhydroxide. In this thesis, Mössbauer spectroscopy has been used to study the form of iron oxyhydroxide present in the tissues of thalassaemic patients who had undergone regular blood transfusion and chelation therapy as well as those receiving little, if any, such treatment. The data show a higher fraction of non-haem iron occurs as the goethite-like form in patients undergoing regular transfusion and chelation treatment. The poorly crystalline goethite form was not found in normal human tissues. To define further some of the factors involved in the deposition of these different iron oxides, an iron-loaded rat system was established. Two routes of administration were chosen. The first involved regular administration of red blood cells injected intraperitoneally for up to one year. The second involved the oral administration of carbonyl-iron as a dietary supplement for nearly two years. Mössbauer spectra of livers and spleens at 78 K consisted of a relatively intense central doublet with spectral parameters indicative of paramagnetic or superparamagnetic high-spin iron(III). Many spectra obtained from parenterally iron-loaded spleens and dietary iron-loaded livers also showed a clear sextet at 78 K, which is indicative of the presence of the goethite-like form of iron oxyhydroxide. The relative intensity of this sextet spectral component in the livers from the dietary iron-loaded rats increased significantly with the age of rats. In order to distinguish iron present in the parenchymal versus non-parenchymal cells in the livers, an indirect quantitative assessment of the iron concentration was performed from liver histological sections using computer-assisted morphometric analysis. The goethite-like form increased significantly as the fraction of iron in non-parenchymal cells increased (r = 0.71, p < 0.005), suggesting that its formation may be associated with the nonparenchymal cells. The ultrastructure of the iron oxide deposits and associated organic components was studied using a combination of scanning probe microscopy and transmission electron microscopy. Liver samples with ferrihydrite or goethite-like haemosiderin were studied as well as aggregated ferritin in the form of ferritin crystals, ferrihydrite-like form of haemosiderin shows topographies of iron aggregation similar to In contrast, liver with goethite-like form of Liver tissue with the that found in the ferritin crystals, haemosiderin showed a different topography. Haemosiderin was isolated from a selection of tissues. Crude haemosiderin from patients who had undergone regular blood transfusion and chelation therapy showed a high fraction of goethite-like form of iron oxyhydroxide with a wide range of particle size. Infrared spectroscopy indicated that the iron oxyhydroxide in haemosiderins is associated with organic components. The availability of the different forms of iron oxyhydroxide present in different haemosiderins was assessed using the iron chelator desferrioxamine. The percentage of iron released showed a negative correlation (r = 0.82, p < 0.001) with the percentage of goethite-like iron oxyhydroxide present in these haemosiderins. In summary, these studies indicate that the chemical forms of iron oxyhydroxide deposits are related to their deposition, toxicity and relative ease of removal. The study has implications for the clinical management of different groups of thalassaemic patients

Elemental analysis of dugong organs

Fe, Zn, Cu, Pb, Mn, Ni, Co, Al, P and S have been analyzed by ICP-AES. The concentrations of Fe in all dugong livers are extremely high (13000-71000 μg g-1 dry wt.). The levels of Zn are also high (1500-2800 μg g-1 dry wt.). The level of Fe in spleen (7600 μg g-1 dry wt.), heart (340 μg g-1 dry wt.) and kidney (1200 μg g-1 dry wt.) are considerably high. Cd is mostly concentrated in kidney (60 μg g-1 dry wt.). Concentrations of P and S in liver, spleen, kidney and heart are considerably high

Iron overload diseases: the chemical speciation of non-heme iron deposits in iron loaded mammalian tissues

57Fe Mössbauer spectra of iron overloaded human spleen, rat spleen and rat liver tissue samples at 78 K were found to consist of a quadrupole doublet (major component) with magnetic sextet (minor component with fractional spectral area Fs). The distributions of Fs for spleen tissue from two different clinically identifiable groups (n = 7 and n = 12) of thalassemic patients were found to be significantly different. The value of Fs for dietary-iron loaded rat liver was found to rise significantly with age/duration (up to 24 months) of iron loading

Magnetic energy-barrier distributions for ferrihydrite nanoparticles formed by reconstituting ferritin

The spherical cage-like protein ferritin was reconstituted with varying numbers of iron atoms perprotein shell ranging from approximately 20 to 1100 at temperatures of both 25 and 50 C toproduce ironIII oxyhydroxide ferrihydrite particles with different average particle sizes anddegrees of crystallinity. After characterization of the structural properties of the resultingiron-oxyhydroxide nanoparticles with transmission electron microscopy and M?auerspectroscopy, magnetic viscosity measurements were made in zero applied magnetic field and theresulting data were used to calculate the apparent magnetic-moment-weighted energy barrierdistributions for the samples. The distributions measured were typically comprised of both alognormal distribution and an exponential decay of barrier frequency with increasing barrier height.Evidence that the lognormal component of this distribution arises from the distribution of particlevolumes and moments within the ensemble is strongly supported by the increase in the mode of theenergy barrier distribution with increasing particle size. The exponentially decaying distribution hasa relatively higher contribution to the overall distribution for the more crystalline reconstitutedferritin samples suggesting that it may be associated predominantly with uncompensated spins atparticle surfaces

Reductive changes to polynuclear iron (III) clusters in iron-loaded human spleen tissue

Mössbauer spectroscopy was used to monitor, over a period of three days, the form of iron in iron-loaded spleen tissue following splenectomy from a patient with β-thalassemia. The tissue was stored at room temperature for a three day period in order to allow degradation and autolytic processes to take place. The majority of the iron in the fresh spleen tissue was found to be in the form of inorganic polynuclear iron (III) oxyhydroxide clusters associated with ferritin and hemosiderin. After three days, some of the iron had been reduced to high-spin iron (II)

Characterization of dugong liver ferritin

Dugong liver contains very high levels of iron (up to 71 000μgg-1 dry wt). Generally, iron is stored in the protein ferritin and the insoluble material hemosiderin. Histological studies indicated dense deposit of iron in the tissue, without evidence of the tissue damage normally associated with very high iron levels. The speciation studies on iron were carried out by Mossbauer spectroscopy. The size distribution and iron core crystallinity of the ferritin were also determined using a transmission electron microscope. Mossbauer spectra of purified ferritin at 78K indicated the presence of ferrihydrite (5Fe2O3.9H2O) rather than geothite-like (α-FeOOH) iron oxide. The Mossbauer spectra of a sample of dugong liver tissue indicated the presence of a goethite-like iron phase related to that found in transfused human thalassemic patients. The iron core study indicated that purified dugong ferritin had a limited crystallinity. The characteristics of purified dugong ferritin are similar to other mammalian ferritins, based on amino acids determination of the ferritin protein cage. The naturally high level of iron in its food is reflected in the high liver iron values. The ability of the liver tissue to withstand the high concentration of iron in the tissue without apparently damaging the tissue deserves further study