Quantification of liver iron overload by T2 quantitative magnetic resonance imaging in thalassemia: impact of chronic hepatitis C on measurements

Correlation of Transient Elastography with Liver Iron Concentration and Serum Ferritin Levels in Patients with Transfusion-Dependent Thalassemia Major from Oman

Aims

In a longitudinal study, we aimed to assess the correlation between ultrasound transient elastography (TE), serum ferritin (SF), liver iron content (LIC) by magnetic resonance imaging (MRI) T2* along with the fibrosis-4 (FIB-4) score as a screening tool to detect significant liver fibrosis among chronically transfusion-dependent beta-thalassemia (TDT) patients.

Methods

The study was conducted at a tertiary health center treating TDT patients. Transient elastography was performed within 3 months of Liver MRI T2* examinations at the radiology department over a median of one-year duration. T-test for independent data or Mann-Whitney U test was used to analyze group differences. Spearman correlation with linear regression analysis was used to evaluate the correlation between TE liver stiffness measurements, Liver MRI T2* values, and SF levels.

Results

In this study on 91 patients, the median age (IQR) of the subjects was 33 (9) years, and the median (IQR) body mass index was 23.8 (6.1) kg/m2. Median (IQR) TE by fibroscan, MRI T2*(3T), Liver iron concentration (LIC) by MRI Liver T2*, and SF levels were 6.38 (2.6) kPa, 32.4 (18) milliseconds, 7(9) g/dry wt., and 1881 (2969) ng/mL, respectively. TE measurements correlated with LIC g/dry wt. (rS =0.39, p=0.0001) and with SF level (rS =0.43, P=0.001) but not with MRI T2* values (rS =-0.24; P=0.98).

Conclusion

In TDT patients, liver stiffness measured as TE decreased significantly with improved iron overload measured as LIC by MRI and SF levels. However, there was no correlation of TE with the fibrosis-4 (FIB-4) score.

Diagnostic value of T2 relaxation time for hepatic iron grading in rat model of fatty and fibrotic liver

The objective of this study was to assess the quantitative diagnostic value of T2 relaxation time for determining liver iron grades in the presence of fat and fibrosis. Sixty Sprague-Dawley (SD) male rats were randomly divided into control (10 rats) and model (50 rats) groups. The model group of coexisting iron, steatosis, and liver fibrosis was induced by intraperitoneal injection of carbon tetrachloride (CCl4) dissolved in edible vegetable oil (40% v/v). The control group received an intraperitoneal injection of 0.9% saline. All rats underwent multi-echo gradient and spin echo (M-GRASE) magnetic resonance imaging, and the T2 relaxation time of the liver was measured. The rats were killed immediately after imaging, and liver specimens were extracted for histological evaluation of steatosis, iron, and fibrosis. The relationship and differences between T2 relaxation time and liver fibrosis stage, as well as the pathological grade of hepatic steatosis, were assessed by Spearman's rank correlation coefficient, non-parametric Mann-Whitney test, and the Kruskal-Wallis test. The area under the receiver operating characteristic curve and interaction analysis were used to quantify the diagnostic performance of T2 relaxation time for detecting different degrees of liver iron grades. Six normal control rats and 34 model rats were included in this study. Fibrosis stages were F0 (n = 6), F1 (n = 6), F2 (n = 8), F3 (n = 10), and F4 (n = 10). Steatosis grades were S0 (n = 5), S1 (n = 8), S2 (n = 12), and S3 (n = 15). Hepatocyte or Kupffer cell iron grades were 0 (n = 7), 1 (n = 9), 2 (n = 12), 3 (n = 10), and 4 (n = 2). The liver fibrosis stages were positively correlated with the iron grades (P < 0.01), and the iron grades and fibrosis stages were negatively correlated with the T2 relaxation time (P < 0.01). The T2 relaxation times exhibited strongly significant differences among rats with different histologically determined iron grades (P < 0.01). Pairwise comparisons between each grade of liver iron indicated significant differences between all iron grades, except between grades 0 and 1, and between grades 1 and 2 (P > 0.05). The T2 relaxation time of the liver had an area under the receiving operating characteristic curve (AUC) of 0.965 (95% CI 0.908-0.100, P < 0.001) for distinguishing rats with a pathological grade of hepatic iron (grade ≥ 1) from those without, an AUC of 0.871 (95% CI 0.757-0.985, P < 0.001) for distinguishing rats with no iron overload (grade ≤ 1) from rats with moderate or severe iron overload (grade ≥ 2), and an AUC of 0.939 (95% CI 0.865-1.000, P < 0.001) for distinguishing rats with no to moderate iron overload (grade ≤ 2) from rats with severe iron overload (grade 3). The interaction of different pathological grades of iron, steatosis, and fibrosis has a negligible influence on the T2 relaxation time (P > 0.05). In conclusion, T2 relaxation time can assess histologically determined liver iron grades, regardless of coexisting liver steatosis or fibrosis; therefore, it is suitable for distinguishing between the presence and absence of iron deposition and it is more accurate for higher iron grading.

Improving CPMG liver iron estimates with a T 1 -corrected proton density estimator

PURPOSE

CPMG spin echo acquisitions are attractive for diagnosing and monitoring liver iron concentration in iron overload disorders due to their time efficiency and potential to reveal unique information about tissue iron distribution. Clinical adoption remains low due to the insensitivity of CPMG-based R 2 estimates to liver iron concentration (LIC) when common fitting techniques are applied. In this work, we demonstrate that the inclusion of a proton density estimator (PDE) derived from the CPMG acquisition increase the sensitivity of CPMG R 2 estimates to LIC in both simulated and in-vivo human data.

THEORY AND METHODS

CPMG R 2 acquisitions from 50 clinically indicated MRI studies in patients with iron overload were analyzed with and without PDE constraints. Liver regions of interest were fit to monoexpontial and nonexponential signal decay equations. LIC by R 2 ∗ served as the reference standard. The observed calibration between CPMG R 2 values and LIC were compared to results predicted from a previously validated Monte Carlo model.

RESULTS

The sensitivity of CPMG-derived R 2 triples when a proton density constraint is applied. When compared with R 2 ∗ -LIC estimates, both monoexponential and nonexponential models were unbiased but demonstrated broad 95% confidence intervals particularly for LIC values below 12 mg/g. Absolute error did not increase with LIC.

CONCLUSION

A proton density constraint can increase the sensitivity of CPMG-based models to iron. CPMG acquisitions are time-efficient and could potentially improve the dynamic range of single spin echo techniques as well as providing insight into tissue iron distribution.

R2 relaxometry based MR imaging for estimation of liver iron content: A comparison between two methods

PURPOSE

To compare the reproducibility and accuracy of R2-relaxometry MRI for estimation of liver iron concentration (LIC) between in-house analysis and FDA-approved commercially available third party results.

METHODS

All MR studies were performed on a 1.5T scanner. Multi-echo spin-echo scans with a fixed TR and increasing TE values of 6 ms, 9 ms, 12 ms, 15 ms, and 18 ms (spaced at 3 ms intervals) were used. Post-processing of the images to calculate mean relaxivity, R2, included drawing of regions of interest to include the whole liver on mid-slice. The relationship between liver R2 values and estimated LIC calculated with in-house analysis and values reported by an external company (FerriScan^®, Resonance Health, Australia) were assessed with correlation coefficients and Bland-Altman difference plots. Continuous variables are presented as mean ± standard deviation. Significance was set at p value < 0.05.

RESULTS

474 studies from 175 patients were included in the study (mean age 10.4 ± 4.2 years (range 1-18 years); 254 studies from girls, 220 studies from boys). LIC ranged from 0.6 to 43 mg/g dry tissue, covering a broad range from normal levels to extremely high iron levels. Linearity between proprietary and in-house methods was excellent across the observed range for R2 (31.5 to 334.8 s^-1); showing a correlation coefficient of r = 0.87, p < 0.001. Bland-Altman R2 difference plot between the two methods shows a mean bias of + 21.5 s^-1 (range - 47.0 to + 90.0 s^-1 between two standard deviations). LIC reported by FerriScan^® compared with LIC estimated in-house with R2 as reported by FerriScan^® agreed strongly, (r = 1.0, p < 0.001).

CONCLUSION

R2 relaxometry MR imaging for liver iron concentration estimation is reproducible between proprietary FDA-approved commercial software and in-house analysis methods.

Assessment of MR-based R2* and quantitative susceptibility mapping for the quantification of liver iron concentration in a mouse model at 7T

PURPOSE

To assess the feasibility of quantifying liver iron concentration (LIC) using R2* and quantitative susceptibility mapping (QSM) at a high field strength of 7 Tesla (T).

METHODS

Five different concentrations of Fe-dextran were injected into 12 mice to produce various degrees of liver iron overload. After mice were sacrificed, blood and liver samples were harvested. Ferritin enzyme-linked immunosorbent assay (ELISA) and inductively coupled plasma mass spectrometry were performed to quantify serum ferritin concentration and LIC. Multiecho gradient echo MRI was conducted to estimate R2* and the magnetic susceptibility of each liver sample through complex nonlinear least squares fitting and a morphology enabled dipole inversion method, respectively.

RESULTS

Average estimates of serum ferritin concentration, LIC, R2*, and susceptibility all show good linear correlations with injected Fe-dextran concentration; however, the standard deviations in the estimates of R2* and susceptibility increase with injected Fe-dextran concentration. Both R2* and susceptibility measurements also show good linear correlations with LIC (R2  = 0.78 and R2  = 0.91, respectively), and a susceptibility-to-LIC conversion factor of 0.829 ppm/(mg/g wet) is derived.

CONCLUSION

The feasibility of quantifying LIC using MR-based  R2* and QSM at a high field strength of 7T is demonstrated. Susceptibility quantification, which is an intrinsic property of tissues and benefits from being field-strength independent, is more robust than R2* quantification in this ex vivo study. A susceptibility-to-LIC conversion factor is presented that agrees relatively well with previously published QSM derived results obtained at 1.5T and 3T.

Magnetic Resonance Elastography and Other Magnetic Resonance Imaging Techniques in Chronic Liver Disease: Current Status and Future Directions

Recent advances in the noninvasive imaging of chronic liver disease have led to improvements in diagnosis, particularly with magnetic resonance imaging (MRI). A comprehensive evaluation of the liver may be performed with the quantification of the degree of hepatic steatosis, liver iron concentration, and liver fibrosis. In addition, MRI of the liver may be used to identify complications of cirrhosis, including portal hypertension, ascites, and the development of hepatocellular carcinoma. In this review article, we discuss the state of the art techniques in liver MRI, namely, magnetic resonance elastography, hepatobiliary phase MRI, and liver fat and iron quantification MRI. The use of these advanced techniques in the management of chronic liver diseases, including non-alcoholic fatty liver disease, will be elaborated.

Comparison of Tissue Elastography With Magnetic Resonance Imaging T2* and Serum Ferritin Quantification in Detecting Liver Iron Overload in Patients With Thalassemia Major

BACKGROUND & AIMS

We investigated whether tissue elastography (TE) can be used as an alternative to magnetic resonance imaging (MRI) T2* analysis to determine the degree of iron overload in patients with thalassemia major.

METHODS

We conducted a prospective study of 154 patients (99 male; mean age, 12 ± 3.6 years) with thalassemia major requiring chronic blood transfusion and on iron chelator therapy. The study was performed at a tertiary hospital in India from January 2015 through June 2015. We performed routine blood sample analyses, measurements of serum levels of ferritin, and TE within 1 month of MRI T2* analysis of the liver. The Spearman correlation test and linear regression analysis were used to evaluate the correlation between TE liver stiffness measurements and R2* MRI results or serum ferritin levels.

RESULTS

The subjects' mean total serum levels of bilirubin, alanine aminotransferase, aspartate aminotransferase, and albumin were 1.4 ± 0.6 mg/dL, 65.0 ± 51.8 IU/L, 62.9 ± 44 IU/L, and 4.2 ± 0.2 g/d, respectively. Mean liver stiffness measurement, MRI T2* (3 T), corresponding MRI R2* (3 T), and ferritin values were 8.2 ± 4.4 kPa, 3.18 ± 2.6 milliseconds, 617.3 ± 549 Hz, and 4712 ± 3301 ng/mL, respectively. On the basis of MRI analysis, 67 patients (43.5%) had mild iron overload, 49 patients (31.8%) had moderate iron overload, and 22 patients (14.3%) had severe iron overload. Fibroscan liver stiffness measurements correlated with MRI R2* values (r = 0.85; P < .001). TE results identified the patients with severe, moderate, and mild iron overload with area under the receiver operating characteristic curve values of 94.8%, 84.5%, and 84.7%, respectively. Liver stiffness measurements greater than 13.5, 7.8, and 5.5 kPa identified patients with severe, moderate, and mild iron overload, respectively; the sensitivity and specificity values were 92% and 93% for severe overload, 82% and 82% for moderate overload, and 73% and 75% for mild overload. No correlation was found between TE results and serum level of ferritin (r = 0.19; P = .11).

CONCLUSIONS

Results of TE correlate with those from MRI T2* analysis. TE is cheaper and more available than MRI and might be used to estimate hepatic iron overload, especially moderate to severe overload in patients with thalassemia major who require chronic transfusion.

Quantification of liver iron with MRI: state of the art and remaining challenges

Liver iron overload is the histological hallmark of hereditary hemochromatosis and transfusional hemosiderosis, and can also occur in chronic hepatopathies. Iron overload can result in liver damage, with the eventual development of cirrhosis, liver failure, and hepatocellular carcinoma. Assessment of liver iron levels is necessary for detection and quantitative staging of iron overload and monitoring of iron-reducing treatments. This article discusses the need for noninvasive assessment of liver iron and reviews qualitative and quantitative methods with a particular emphasis on magnetic resonance imaging (MRI). Specific MRI methods for liver iron quantification include signal intensity ratio as well as R2 and R2* relaxometry techniques. Methods that are in clinical use, as well as their limitations, are described. Remaining challenges, unsolved problems, and emerging techniques to provide improved characterization of liver iron deposition are discussed.

Quantification of iron concentration in the liver by MRI

OBJECTIVE

Measurement of liver iron concentration is a key parameter for the management of patients with primary and secondary haemochromatosis. Magnetic resonance imaging (MRI) has already demonstrated high accuracy to quantify liver iron content. To be able to improve the current management of patients that are found to have iron overload, we need a reproducible, standardised method that is, or can easily be made, widely available.

METHODS

This article discusses the different MRI techniques and models to quantify liver iron concentration that are currently available and envisaged for the near future from a realistic perspective.

RESULTS

T2 relaxometry methods are more accurate than signal intensity ratio (SIR) methods and they are reproducible but are not yet standardised or widely available. SIR methods, on the other hand, are very specific for all levels of iron overload and, what is more, they are also reproducible, standardised and already widely available.

CONCLUSIONS

For these reasons, today, both methods remain necessary while progress is made towards universal standardisation of the relaxometry technique.

MRI quantification of splenic iron concentration in mouse

PURPOSE

To quantify hepatic and splenic iron load, which is a critical issue for iron overload disease diagnosis. MRI is useful to noninvasively determine liver iron concentration, but not proven to be adequate for robust evaluation of splenic iron load. We evaluated the usefulness of MRI-derived parameters to determine splenic iron concentration in mice.

MATERIALS AND METHODS

A mouse model of experimental iron load was used. Multi-echo spin-echo images of liver and spleen were acquired at 4.7 Tesla. The parameters were tested at all echoes with and without an external reference. Splenic and hepatic iron concentrations were determined using biochemical assay as the gold standard.

RESULTS

Our results show that (i) use of an internal or external reference is essential; (ii) optimal echo times were TE = 19.5 ms and TE = 32.5 ms for the liver and spleen, respectively; (iii) in the liver, the relationship between biochemical and MRI iron concentration determinations is logarithmic; (iv) in the spleen, the best relationship is an inverse function.

CONCLUSION

A single spin-echo sequence allows robust estimation of hepatic and splenic iron content. Parameters classically used for hepatic iron concentration cannot be applied to splenic iron determination, which requires both the specific sequence and the adapted fitting function.

Liver iron content determination by magnetic resonance imaging

Accurate evaluation of iron overload is necessary to establish the diagnosis of hemochromatosis and guide chelation treatment in transfusion-dependent anemia. The liver is the primary site for iron storage in patients with hemochromatosis or transfusion-dependent anemia, therefore, liver iron concentration (LIC) accurately reflects total body iron stores. In the past 20 years, magnetic resonance imaging (MRI) has emerged as a promising method for measuring LIC in a variety of diseases. We review the potential role of MRI in LIC determination in the most important disorders that are characterized by iron overload, that is, thalassemia major, other hemoglobinopathies, acquired anemia, and hemochromatosis. Most studies have been performed in thalassemia major and MRI is currently a widely accepted method for guiding chelation treatment in these patients. However, the lack of correlation between liver and cardiac iron stores suggests that both organs should be evaluated with MRI, since cardiac disease is the leading cause of death in this population. It is also unclear which MRI method is the most accurate since there are no large studies that have directly compared the different available techniques. The role of MRI in the era of genetic diagnosis of hemochromatosis is also debated, whereas data on the accuracy of the method in other hematological and liver diseases are rather limited. However, MRI is a fast, non-invasive and relatively accurate diagnostic tool for assessing LIC, and its use is expected to increase as the role of iron in the pathogenesis of liver disease becomes clearer.

Accurate liver T2 measurement of iron overload: a simulations investigation and in vivo study

PURPOSE

To investigate the accuracy of T 2 liver iron quantification using different curve-fitting models under varying acquisition conditions, and to compare in iron-overloaded patients the reliability of rapid T 2 measurements against approved and slower T(2) protocols.

MATERIALS AND METHODS

Simulations were conducted to assess the influence of various factors on the accuracy of T 2 measurement: curve-fitting model, signal-to-noise ratio (SNR), and echo time (TE) spacing. Fifty-four iron-overloaded pediatric patients were assessed using a standard T(2) and two variations of T 2 acquisitions. In both simulations and in vivo data, three analysis models were evaluated: monoexponential, constant offset, and truncated.

RESULTS

Simulations show the truncated model provides the best accuracy but is susceptible to underestimating high iron species under low SNR or high minimum TE. In contrast, the offset model tends to overestimate but maintains the most reliable measurements across the relevant range of iron levels. Furthermore, a much lower SNR can be tolerated if the acquisition uses a low minimum TE. In vivo results confirm theoretical findings and show that T 2 measurements can be as reliable as those from approved and slower T(2) protocols.

CONCLUSION

Guidelines are provided on choosing an appropriate model under specific noise conditions and acquisition schemes to ensure accurate and rapid T2 liver iron quantification.

MRI evaluation of tissue iron burden in patients with beta-thalassaemia major

beta-Thalassaemia major is a hereditary haemolytic anaemia that is treated with multiple blood transfusions. A major complication of this treatment is iron overload, which leads to cell death and organ dysfunction. Chelation therapy, used for iron elimination, requires effective monitoring of the body burden of iron, for which serum ferritin levels and liver iron content measured in liver biopsies are used as markers, but are not reliable. MRI based on iron-induced T2 relaxation enhancement can be used for the evaluation of tissue siderosis. Various MR protocols using signal intensity ratio and mainstream relaxometry methods have been used, sometimes with discrepant results. Relaxometry methods using multiple echoes achieve better sampling of the time domain in which relaxation mechanisms take place and lead to more precise results. In several studies the MRI parameters of liver siderosis have failed to correlate with those of other affected organs, underlining the necessity for MRI iron evaluation in individual organs. Most studies have included children in the evaluated population, but MRI data on very young children are lacking. Wider application of relaxometry methods is indicated, with the establishment of universally accepted MRI protocols, and further studies, including young children, are needed.

Liver, bone marrow, pancreas and pituitary gland iron overload in young and adult thalassemic patients: a T2 relaxometry study

Thirty-seven patients with beta-thalassemia major, including 14 adolescents (15.2 +/- 3.0 years) and 23 adults (26.4 +/- 6.9 years), were studied. T2 relaxation time (T2) of the liver, bone marrow, pancreas and pituitary gland was measured in a 1.5-Tesla magnetic resonance (MR) imager, using a multiecho spin-echo sequence (TR/TE 2,000/20, 40, 60, 80, 100, 120, 140, 160 ms). Pituitary gland height was evaluated in a midline sagittal scan of a spin-echo sequence (TR/TE, 500/20 ms). The T2 of the pituitary gland was higher in adolescents (59.4 +/- 15 ms) than in adults (45.3 +/- 10.4 ms), P < 0.05. The T2 of the pancreas was lower in adolescents (43.6 +/- 10.3 ms) than in adults (54.4 +/- 10.4 ms). No difference among groups was found in the T2 of the liver and bone marrow. There was no significant correlation of the T2 among the liver, pancreas, pituitary gland and bone marrow. There was no significant correlation between serum ferritin and T2 of the liver, pancreas and bone marrow. Pituitary T2 showed a significant correlation with pituitary gland height (adolescents: R = 0.63, adults: R = 0.62, P < 0.05) and serum ferritin (adolescents: R = -0.60, adults: R = -0.50, P < 0.05). In conclusion, iron overload evaluated by T2 is organ specific. After adolescence, age-related T2 changes are predominantly associated with pituitary siderosis and fatty degeneration of the pancreas. Pituitary size decreases with progressing siderosis.

Iron overload in the liver diagnostic and quantification

Hereditary Hemochromatosis is the most frequent modality of iron overload. Since 1996 genetic tests have facilitated significantly the non-invasive diagnosis of the disease. There are however many cases of negative genetic tests that require confirmation by hepatic iron quantification which is traditionally performed by hepatic biopsy. There are many studies that have demonstrated the possibility of performing hepatic iron quantification with Magnetic Resonance. However, a consensus has not been reached yet regarding the technique or the possibility to reproduce the same method of calculus in different machines. This article reviews the state of the art of the question and delineates possible future lines to standardise this non-invasive method of hepatic iron quantification.

The pancreas in beta-thalassemia major: MR imaging features and correlation with iron stores and glucose disturbances

The study aims at describing the MR features of pancreas in beta-thalassemia major, investigating the relations between MR findings and glucose disturbances and between hepatic and pancreatic siderosis. Signal intensity ratios of the pancreas and liver to right paraspinous muscle (P/M, L/M) were retrospectively assessed on abdominal MR imaging studies of 31 transfusion-dependent patients with beta-thalassemia major undergoing quantification of hepatic siderosis and 10 healthy controls, using T1- (120/4/90), intermediate in and out of phase - (120/2.7, 4/20), and T2*-(120/15/20) weighted GRE sequences. Using the signal drop of the liver and pancreas on opposed phase images, we recorded serum ferritin and results of oral glucose tolerance test (OGTT). Decreased L/M and P/M on at least the T2* sequence were noticed in 31/31 and 30/31 patients, respectively, but no correlation between P/M and L/M was found. Patients with pathologic OGTT displayed a higher degree of hepatic siderosis (p < 0.04) and signal drop of pancreas on opposed phase imaging (p < 0.025), implying fatty replacement of pancreas. P/M was neither correlated with glucose disturbances nor serum ferritin. Iron deposition in the pancreas cannot be predicted by the degree of hepatic siderosis in beta-thalassemia major. Fatty replacement of the pancreas is common and may be associated with glucose disturbances.

Mechanisms of tissue-iron relaxivity: nuclear magnetic resonance studies of human liver biopsy specimens

MRI is becoming an increasingly important tool to assess iron overload disorders, but the complex nature of proton-iron interactions has troubled noninvasive iron quantification. Intersite and intersequence variability as well as methodological inaccuracies have been limiting factors to its widespread clinical use. It is important to understand the underlying proton relaxation mechanisms within the (human) tissue environment to address these differences. In this respect, NMR relaxometry was performed on 10 fresh human liver biopsy specimens taken from patients with transfusion-dependent anemia. T1 (1/R1) inversion recovery, T2 (1/R2) single echo, and multiecho T2 CPMG measurements were performed on a 60-MHz Bruker Minispectrometer. NMR parameters were compared to quantitative iron levels and tissue histology. Relaxivities R1 and R2 both increased linearly with hepatic iron content, with R2 being more sensitive to iron. CPMG data were well described by a chemical-exchange model and predicted effective iron center dimensions consistent with hemosiderin-filled lysosomes. Nonexponential relaxation was evident at short refocusing intervals with R2 and amplitude behavior suggestive of magnetic susceptibility-based compartmentalization rather than anatomic subdivisions. NMR relaxometry of human liver biopsy specimens yields unique insights into the mechanisms of tissue-iron relaxivity.

MRI R2 and R2* mapping accurately estimates hepatic iron concentration in transfusion-dependent thalassemia and sickle cell disease patients

Measurements of hepatic iron concentration (HIC) are important predictors of transfusional iron burden and long-term outcome in patients with transfusion-dependent anemias. The goal of this work was to develop a readily available, noninvasive method for clinical HIC measurement. The relaxation rates R2 (1/T2) and R2* (1/T2*) measured by magnetic resonance imaging (MRI) have different advantages for HIC estimation. This article compares noninvasive iron estimates using both optimized R2 and R2* methods in 102 patients with iron overload and 13 controls. In the iron-overloaded group, 22 patients had concurrent liver biopsy. R2 and R2* correlated closely with HIC (r2 > or = .95) for HICs between 1.33 and 32.9 mg/g, but R2 had a curvilinear relationship to HIC. Of importance, the R2 calibration curve was similar to the curve generated by other researchers, despite significant differences in technique and instrumentation. Combined R2 and R2* measurements did not yield more accurate results than either alone. Both R2 and R2* can accurately measure hepatic iron concentration throughout the clinically relevant range of HIC with appropriate MRI acquisition techniques.

Liver iron concentration evaluated by two magnetic methods: magnetic resonance imaging and magnetic susceptometry

Quantification of liver iron concentration (LIC) is crucial in the management of patients suffering from certain pathologies that can produce iron overload, such as Cooley's anemia and hemochromatosis. All of these patients must control the level of iron deposits in their organs to avoid the toxicity of high LIC, which is potentially lethal. This paper describes experimental protocols for LIC measurement using two magnetic techniques: magnetic resonance imaging (MRI) and biomagnetic liver susceptometry (BLS). MRI proton transverse relaxation rate (R2) and image intensity, evaluated pixel by pixel, were used as indicators of iron load in the tissue. LIC measurement by BLS was performed using an AC superconducting susceptometer system. A group of 23 patients with a large range of iron overload (0.9 to 34.5 mgFe/g(dry tissue)) was evaluated with both techniques (MRI x BLS). A significant linear correlation (r = 0.89-0.95) was found between the LIC by MRI and by BLS. These results show the feasibility of using two noninvasive methodologies to evaluate liver iron store in a large concentration range. Both methodologies represent an equivalent precision.

Single spin-echo proton transverse relaxometry of iron-loaded liver

A single-spin-echo methodology is described for the measurement and imaging of proton transverse relaxation rates (R2) in iron-loaded and normal human liver tissue in vivo. The methodology brings together previously reported techniques dealing with (i) the changes in gain between each spin-echo acquisition, (ii) signal level offset due to background noise, (iii) estimation of signal intensities in decay curves at time zero to enable reliable extraction of relaxation times from tissues with very short T2 values, (iv) bi-exponential modelling of decay curves with a small number of data points, and (v) reduction of respiratory motion artefacts. The accuracy of the technique is tested on aqueous manganese chloride solutions yielding a relaxivity of 74.1+/-0.3 s-1 (mM)-1, consistent with previous reports. The precision of the in vivo measurement of mean liver R2 values is tested through duplicate measurements on 10 human subjects with mean liver R2 values ranging from 26 to 220 s-1. The random uncertainty on the measurement of mean liver R2 was found to be 7.7%.

Comparison between signal-to-noise ratio, liver-to-muscle ratio, and 1/T2 for the noninvasive assessment of liver iron content by MRI

PURPOSE

To compare different MRI-derived parameters, i.e., liver signal-to-noise ratio (LSNR), liver-to-muscle ratio (LMR) and liver transversal relaxation rate (R2), in terms of their correlation with the ex vivo determined iron content in an experimental model of liver iron overload.

MATERIALS AND METHODS

Multi-echo spin echo (SE) images of the liver were acquired at 4.7 T from a group of 33 male wistar rats subjected to a high iron content diet for feeding periods ranging from 2 to 50 days. Liver transversal relaxation time, liver signal-to-noise ratio, and liver-to-muscle ratio were measured over the same region of interest in order to get a direct comparison between these parameters. After MRI experiments, the rats were sacrificed and the liver iron content was measured ex vivo by atomic absorption spectroscopy.

RESULTS

The iron content is better correlated to the LSNR than to the other parameters (LMR, R2).

CONCLUSION

The finding that liver signal-to-noise ratio is better correlated to the iron content than the liver T2 relaxation rate is relevant for clinical applications of MRI because a T2 determination is more time-consuming, both for acquisition and postprocessing of images, than a simple SNR determination.

Urine biochemical markers of early renal dysfunction are associated with iron overload in beta-thalassaemia

Renal dysfunction in thalassemia patients can be attributed to chronic anemia, and iron overload as well as to desferioxamine (DFO) toxicity. We analyzed the urine of 91 well-maintained homozygous beta-thalassemia patients, with no evidence of renal disease, for early evidence of kidney dysfunction by means of electrophoresis and quantitative biochemical tests. Measurement of liver magnetic resonance imaging (MRI) T2 values and serum ferritin concentration was used to estimate iron overload. In 55 of the 91 patients, urine analysis indicated signs of tubular dysfunction. The urine concentration of albumin and beta 2-microglobulin, as well as the activity of N-acetyl-beta-D-glucosaminidase (NAG), correlated positively with serum ferritin concentration and liver iron deposition, as detected by MRI T2 values. This suggested that the cause of renal dysfunction in homozygous beta-thalassemia is iron overload. On the other hand, the same urine markers did not correlate with age, indicating that chronic anemia or desferrioxamine (DFO) treatment are not related to renal dysfunction in thalassemia.

Detection limits for ferrimagnetic particle concentrations using magnetic resonance imaging based proton transverse relaxation rate measurements

A clinical magnetic resonance imaging (MRI) system was used to measure proton transverse relaxation rates (R2) in agar gels with varying concentrations of ferrimagnetic iron oxide nanoparticles in a field strength of 1.5 T. The nanoparticles were prepared by coprecipitation of ferric and ferrous ions in the presence of either dextran or polyvinyl alcohol. The method of preparation resulted in loosely packed clusters (dextran) or branched chains (polyvinyl alcohol) of particles containing of the order of 600 and 400 particles, respectively. For both methods of particle preparation, concentrations of ferrimagnetic iron in agar gel less than 0.01 mg ml(-1) had no measurable effect on the value of R2 for the gel. The results indicate that MRI-based R2 measurements using 1.5 T clinical scanners are not quite sensitive enough to detect the very low concentrations of nanoparticulate biogenic magnetite reported in human brain tissue.

Proton transverse relaxation rate (R2) images of liver tissue; mapping local tissue iron concentrations with MRI [corrected]

Proton transverse relaxation rate (R(2)) imaging measurements were made on post mortem iron-loaded human liver tissue samples (both intact and dissected into approximately 1-cm cubes) from a single subject. Iron concentrations for the dissected samples as measured by atomic absorption spectrometry varied from 10.8 to 23.3 mg Fe.g(-1) dry tissue. A significant linear correlation between the mean R(2) and iron concentration of each sample was found (r = 0.95). In addition, regions of liver tissue with micronodular cirrhosis exhibited lower R(2) values, corresponding to the displacement of iron by fibrotic septa. The cirrhotic tissue was clearly identified as a separate peak in the R(2) distribution of the tissue. The relaxivity of the iron did not appear to depend on the microarchitecture of the tissue.

Liver density measured by DEXA correlates with serum ferritin in patients with beta-Thalassemia Major

Patients with beta-Thalassemia Major have a requirement for repeated blood transfusion, which ultimately results in liver iron- and whole body iron-overload. These patients are also at risk of reduced bone mineral density (BMD). Seventeen patients (9 female, age 19-32 yr) were referred for bone density estimations of the hip, spine, and whole body. As well as calculating the usual indices of body composition, we superimposed regions of interest over the liver, and expressed the result as "BMD" (g/cm2). This was compared with the serum ferritin as a noninvasive indication of total body iron status. Twelve patients were studied at least twice, more than 18 mo apart. This group showed a significantly below average BMD (T-spine -2.1, T-femoral neck -1.2, T-whole body -1.7, p < 0.001). The group's hepatic density correlated significantly with initial serum ferritin (r = 0.90, p < 0.001). Changes in individual liver density did not correlate significantly with changes in ferritin levels (p = 0.15), possibly due to wide variability in individual results. DEXA may be a useful noninvasive technique for estimating liver-iron concentration.

Evaluation of iron overload by single voxel MRS measurement of liver T2

PURPOSE

To overcome the difficulty of poor signal-to-noise ratio of magnetic resonance imaging (MRI) in evaluating heavy iron overload by using a single voxel magnetic resonance spectroscopy (MRS) technique.

MATERIALS AND METHODS

A single voxel STEAM pulse sequence with a minimum TE of 1.5 msec and a sampling volume of 36.6 cm(3) was developed and applied to 1/T2 measurement of the liver in 14 patients with thalassemia whose liver iron concentration was determined through biopsy.

RESULTS

The iron level ranged from 0.23 to 37.15 mg Fe/g dry tissue with a median value of 18.06. In all cases, strong MR signals were obtained. 1/T2 was strongly correlated with the liver iron concentration (r = 0.95, P < 0.00005).

CONCLUSION

The single voxel MRS measurement of T2 in liver iron overload overcomes the difficulty of lack of detectable signals in conventional MRI when the iron level is high. There is an excellent correlation between the iron level and 1/T2.

MR imaging of iron depositional disease

This article discusses the physiology of iron metabolism in humans. The pathophysiology and MR imaging findings of disorders that result in iron deposition in the liver are described. Emphasis is placed on genetic, clinical, and imaging findings of hemochromatosis. Radiologists should familiarize themselves with the patterns of iron deposition on MR images in order to suggest a potential etiology, which may not be known at the time of imaging.

Non-infectious complications of transfusion therapy

Blood transfusion is considered safe when the infused blood is tested using state of the art viral assays developed over the past several decades. Only rarely are known viruses like HIV and hepatitis C transmitted by transfusion when blood donors are screened using these sensitive laboratory tests. However, there are a variety of transfusion risks which still remain that cannot be entirely eliminated, many of which are non-infectious in nature. Predominantly immune-mediated complications include the rapid intravascular or slow extravascular destruction (hemolysis) of transfused red cells or extravascular removal of platelets by pre-formed antibodies carried by the transfusion recipient. Alternatively, red cells can be damaged when exposed to excessive heat or incompatible intravenous fluids before or during the transfusion. Common complications of blood transfusion that at least partly involve the immune system include febrile non-hemolytic and allergic reactions. While these are usually not life-threatening, they can hamper efforts to transfuse a patient. Other complications include circulatory overload, hypothermia and metabolic disturbances. Profound hypotensive episodes have been described in patients on angiotensin-converting enzyme (ACE) inhibitors who receive platelet transfusions through bedside leukoreduction filters. These curious reactions appear to involve dysmetabolism of the vasoactive substance bradykinin. Products contaminated by bacteria during blood collection and transfused can cause life-threatening septic reactions. A long-term complication of blood transfusion therapy unique to chronically transfused patients is iron overload. Less common - but serious - reactions more specific to blood transfusion include transfusion-associated graft-versus-host disease and transfusion-associated acute lung injury. Many of these complications of transfusion therapy can be prevented by adhering to well-established practice guidelines. In addition, individuals who administer blood transfusions should recognize these complications in order to be able to quickly provide appropriate treatment.

In vivo investigation of hepatic iron overload in rats using T2 maps: quantification at high intensity field (4.7-T)

In vivo quantitation of hepatic iron content is useful in diagnosis and staging of several iron related diseases. We used an experimental model of hepatic iron overload to determine the correlation between iron content and T2 relaxation time in rat liver. Experiments were carried out at 4.7T for high signal-to-noise ratio (SNR) using a spin-echo multiecho sequence with six echoes and minimum echo-time of 5.5 msec. The liver iron content was determined ex vivo by atomic absorption spectrophotometry (AAS). T2 maps were calculated in order to evaluate the space distribution of the iron content. We found good linear correlation between the in vivo liver transversal relaxation rate and the iron content within the range explored (106-4538 microg Fe/g liver wet wt.). T2 maps revealed that the decrease in T2 is not homogeneous through the liver parenchyma. This finding represents a physiological limitation to obtaining better correlation between T2 and iron content.

Noninvasive methods for quantitative assessment of transfusional iron overload in sickle cell disease

Because optimal management of iron chelation therapy in patients with sickle cell disease and transfusional iron overload requires accurate determination of the magnitude of iron excess, a variety of techniques for evaluating iron overload are under development, including measurement of serum ferritin iron levels, x-ray fluorescence of iron, magnetic resonance imaging, computed tomography, and measurement of magnetic susceptibility. The most promising methods for noninvasive assessment of body iron stores in patients with sickle cell anemia and transfusional iron overload are based on measurement of hepatic magnetic susceptibility, either using superconducting quantum interference device (SQUID) susceptometry or, potentially, magnetic resonance susceptometry.

The use of skin Fe levels as a surrogate marker for organ Fe levels, to monitor treatment in cases of iron overload

A system based on the detection of K-shell x-ray fluorescence (XRF) has been used to investigate whether a correlation exists between the concentration of iron in the skin and the concentration of iron in the liver, as the degree of iron loading increases. The motivation behind this work is to develop a non-invasive method of determining the extent of the body's iron stores via measurements on the skin, in order to monitor the efficacy of chelation therapy administered to patients with beta-thalassaemia. Sprague-Dawley rats were iron loaded via injections of iron dextran and subsequently treated with the iron chelator CP94. The non-haem iron concentrations of the liver, heart and spleen were determined using bathophenanthroline sulphonate as the chromogen reagent. Samples of abdominal skin were taken and the iron concentrations determined using XRF. A strong correlation between the skin iron concentration and the liver iron concentration has been demonstrated (R2 = 0.86). Similar correlations exist for the heart and the spleen. These results show that this method holds great potential as a tool in the diagnosis and treatment of hereditary haemochromatosis and beta-thalassaemia.