Marvin Nelson
580 California St., Suite 400
San Francisco, CA, 94104
Mechanisms of tissue–iron relaxivity: Nuclear magnetic resonance studies of human liver biopsy specimens
2005, Magnetic Resonance in Medicine
https://doi.org/10.1002/MRM.20697visibility
…
description
18 pages
link
1 file
Sign up for access to the world's latest research
checkGet notified about relevant papers
checkSave papers to use in your research
checkJoin the discussion with peers
checkTrack your impact
Abstract
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 p...
Related papers
Noninvasive measurement and imaging of liver iron concentrations using proton magnetic resonance
Blood, 2005
Measurement of liver iron concentration (LIC) is necessary for a range of iron-loading disorders such as hereditary hemochromatosis, thalassemia, sickle cell disease, aplastic anemia, and myelodysplasia. Currently, chemical analysis of needle biopsy specimens is the most common accepted method of measurement. This study presents a readily available noninvasive method of measuring and imaging LICs in vivo using clinical 1.5-T magnetic resonance imaging units. Mean liver proton transverse relaxation rates (R2) were measured for 105 humans. A value for the LIC for each subject was obtained by chemical assay of a needle biopsy specimen. High degrees of sensitivity and specificity of R2 to biopsy LICs were found at the clinically significant LIC thresholds of 1.8, 3.2, 7.0, and 15.0 mg Fe/g dry tissue. A calibration curve relating liver R2 to LIC has been deduced from the data covering the range of LICs from 0.3 to 42.7 mg Fe/g dry tissue. Proton transverse relaxation rates in aqueous pa...
Effect of magnetic field and iron content on NMR proton relaxation of liver, spleen and brain tissues
Contrast Media & Molecular Imaging, 2014
Iron accumulation is observed in liver and spleen during hemochromatosis and important neurodegenerative diseases involve iron overload in brain. Storage of iron is ensured by ferritin, which contains a magnetic core. It causes a darkening on T 2 -weighted MR images. This work aims at improving the understanding of the NMR relaxation of iron-loaded human tissues, which is necessary to develop protocols of iron content measurements by MRI. Relaxation times measurements on brain, liver and spleen samples were realized at different magnetic fields. Iron content was determined by atomic emission spectroscopy. For all samples, the longitudinal relaxation rate (1/T 1 ) of tissue protons decreases with the magnetic field up to 1 T, independently of iron content, while their transverse relaxation rate (1/T 2 ) strongly increases with the field, either linearly or quadratically, or a combination thereof. The extent of the inter-echo time dependence of 1/T 2 also varies according to the sample. A combination of theoretical models is necessary to describe the relaxation of iron-containing tissues. This can be due to the presence, inside tissues, of ferritin clusters of different sizes and densities. When considering all samples, a correlation (r 2 = 0.6) between 1/T 1 and iron concentration is observed at 7.0 T. In contrast the correlation between 1/T 2 and iron content is poor, even at high field (r 2 = 0.14 at 7.0 T). Our results show that MRI methods based on T 1 or T 2 measurements will easily detect an iron overloading at high magnetic field, but will not provide an accurate quantification of tissue iron content at low iron concentrations.
Measurement of liver iron overload: Noninvasive calibration of MRI-R2* by magnetic iron detector susceptometer
Magnetic Resonance in Medicine, 2011
An accurate assessment of body iron accumulation is essential for the diagnosis and therapy of iron overload in diseases such as thalassemia or hemochromatosis. Magnetic iron detector susceptometry and MRI are noninvasive techniques capable of detecting iron overload in the liver. Although the transverse relaxation rate measured by MRI can be correlated with the presence of iron, a calibration step is needed to obtain the liver iron concentration. Magnetic iron detector provides an evaluation of the iron overload in the whole liver. In this article, we describe a retrospective observational study comparing magnetic iron detector and MRI examinations performed on the same group of 97 patients with transfusional or congenital iron overload. A biopsy-free linear calibration to convert the average transverse relaxation rate in iron overload (R 2 5 0.72), or in liver iron concentration evaluated in wet tissue (R 2 5 0.68), is presented. This article also compares liver iron concentrations calculated in dry tissue using MRI and the existing biopsy calibration with liver iron concentrations evaluated in wet tissue by magnetic iron detector to obtain an estimate of the wet-to-dry conversion factor of 6.7 6 0.8 (95% confidence level). Magn Reson Med 000:000-000, 2011.
Relaxivity-iron calibration in hepatic iron overload: Probing underlying biophysical mechanisms using a Monte Carlo model
Magnetic Resonance in Medicine, 2011
Iron overload is a serious condition for patients with b-thalassemia, transfusion-dependent sickle cell anemia, and inherited disorders of iron metabolism. MRI is becoming increasingly important in noninvasive quantification of tissue iron, overcoming the drawbacks of traditional techniques (liver biopsy). Effective transverse relaxation rate (1/effective transverse relaxation time) rises linearly with iron while transverse relaxation rate (1/T 2 ) has a curvilinear relationship in human liver. Although recent work has demonstrated clinically valid estimates of human liver iron, the calibration varies with MRI sequence, field strength, iron chelation therapy, and organ imaged, forcing recalibration in patients. To understand and correct these limitations, a thorough understanding of the underlying biophysics is of critical importance. Toward this end, a Monte Carlo-based approach, using human liver as a ''model'' tissue system, was used to determine the contribution of particle size and distribution on MRI signal relaxation. Relaxivities were determined for hepatic iron concentrations ranging from 0.5 to 40 mg iron per gram dry tissue weight. Model predictions captured the linear and curvilinear relationship of effective transverse relaxation rate and transverse relaxation rate with hepatic iron concentrations, respectively, and were within in vivo confidence bounds; contact or chemical exchange mechanisms were not necessary. A validated and optimized model will aid understanding and quantification of iron-mediated relaxivity in tissues where biopsy is not feasible (heart and spleen). Magn Reson Med 65:837-847,
Measurement of Liver Iron Concentration by MRI Is Reproducible
BioMed Research International, 2015
properly cited.
MRI for the measurement of liver iron content, and for the diagnosis and follow-up of iron overload disorders
Presse Medicale, 2017
Liver iron content determination by magnetic resonance imaging
World Journal of Gastroenterology, 2010
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.
Relaxation induced by ferritin: a better understanding for an improved MRI iron quantification
NMR in Biomedicine, 2004
Ferritin, the iron storing protein, is known to darken T 2 -weighted MRI. This darkening can be used to noninvasively measure iron content. However, ferritin's behavior is not the same in tissue as in solution, a discrepancy that remains unexplained by the recently developed theory matching the NMR properties of ferritin solutions. A better understanding of the relaxation induced by ferritin in tissue could help for the development of new MRI protocols of iron quantification. In this short review, the main relaxation properties of ferritin in solution and in tissue are presented together with a discussion of the possible reasons for the faster transverse relaxation observed in tissues.
Evaluation of iron overload by single voxel MRS measurement of liver T2
Journal of Magnetic Resonance Imaging, 2002
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.
Cited by
Relaxivity-iron calibration in hepatic iron overload: Probing underlying biophysical mechanisms using a Monte Carlo model
Magnetic Resonance in Medicine, 2011
Iron overload is a serious condition for patients with b-thalassemia, transfusion-dependent sickle cell anemia, and inherited disorders of iron metabolism. MRI is becoming increasingly important in noninvasive quantification of tissue iron, overcoming the drawbacks of traditional techniques (liver biopsy). Effective transverse relaxation rate (1/effective transverse relaxation time) rises linearly with iron while transverse relaxation rate (1/T 2 ) has a curvilinear relationship in human liver. Although recent work has demonstrated clinically valid estimates of human liver iron, the calibration varies with MRI sequence, field strength, iron chelation therapy, and organ imaged, forcing recalibration in patients. To understand and correct these limitations, a thorough understanding of the underlying biophysics is of critical importance. Toward this end, a Monte Carlo-based approach, using human liver as a ''model'' tissue system, was used to determine the contribution of particle size and distribution on MRI signal relaxation. Relaxivities were determined for hepatic iron concentrations ranging from 0.5 to 40 mg iron per gram dry tissue weight. Model predictions captured the linear and curvilinear relationship of effective transverse relaxation rate and transverse relaxation rate with hepatic iron concentrations, respectively, and were within in vivo confidence bounds; contact or chemical exchange mechanisms were not necessary. A validated and optimized model will aid understanding and quantification of iron-mediated relaxivity in tissues where biopsy is not feasible (heart and spleen). Magn Reson Med 65:837-847,
Cardiac R2* values are independent of the image analysis approach employed
Magnetic Resonance in Medicine, 2013
Quantitative T2* Magnetic Resonance Imaging for Evaluation of Iron Deposition in the Brain of β-Thalassemia Patients
Clinical Neuroradiology, 2011
Purpose: Few studies of renal iron content have been performed with multiecho gradient-echo (ME-GRE) T2* magnetic resonance imaging (MRI). We assessed the feasibility and reproducibility of ME-GRE T2* MRI for measuring regional and global renal T2* values, and established the lower limits of normal in healthy subjects, also correlating the measured values with age and sex. Methods: Twenty consecutive healthy subjects (13 men and 7 women, mean age 29.1 ± 7.2 years, range 19-42 years) underwent MRI examinations using a 1.5 T magnet and an ME-GRE T2* sequence. For each kidney, T2* was measured in anterior, posterolateral, and posteromedial renal parenchymal regions. The mean T2* value was calculated as the average of the two kidneys T2* values. Results: For the mean kidney T2* value, the coefficients of variation for intra-and inter-operator reproducibility were 1.76% and 6.23%, respectively. The lower limit of normal for the mean kidney T2* value was 31 ms (median 51.39 ± 10.09). There was no significant difference between left and right kidney T2* values (p = 0.578). No significant correlation was found between T2* values and subjects' age or sex. Conclusions: Renal ME-GRE T2* appears to be a feasible and reproducible technique. The renal T2* values showed no dependence on sex or age.
Practical medical applications of quantitative MR relaxometry
Journal of Magnetic Resonance Imaging, 2012
ISMRM workshop on fat-water separation: Insights, applications and progress in MRI
Magnetic Resonance in Medicine, 2012
Approximately 130 attendees convened on February 19-22, 2012 for the first ISMRM-sponsored workshop on water-fat imaging. The motivation to host this meeting was driven by the increasing number of research publications on this topic over the past decade. The scientific program included an historical perspective and a discussion of the clinical relevance of water-fat MRI, a technical description of multiecho pulse sequences, a review of data acquisition and reconstruction algorithms, a summary of the confounding factors that influence quantitative fat measurements and the importance of MRI-based biomarkers, a description of applications in the heart, liver, pancreas, abdomen, spine, pelvis, and muscles, an overview of the implications of fat in diabetes and obesity, a discussion on MR spectroscopy, a review of childhood obesity, the efficacy of lifestyle interventional studies, and the role of brown adipose tissue, and an outlook on federal funding
Separate MRI quantification of dispersed (ferritin-like) and aggregated (hemosiderin-like) storage iron
Magnetic Resonance in Medicine, 2010
A new MRI method is proposed for separately quantifying the two principal forms of tissue storage (nonheme) iron: ferritin iron, a dispersed, soluble fraction that can be rapidly mobilized, and hemosiderin iron, an aggregated, insoluble fraction that serves as a long-term reserve. The method utilizes multiple spin echo sequences, exploiting the fact that aggregated iron can induce nonmonoexponential signal decay for multiple spin echo sequences. The method is validated in vitro for agarose phantoms, simulating dispersed iron with manganese chloride, and aggregated iron with iron oxide microspheres. To demonstrate feasibility for human studies, preliminary in vivo data from two healthy controls and six patients with transfusional iron overload are presented. For both phantoms and human subjects, conventional R 2 and R 2 * relaxation rates are also measured in order to contrast the proposed method with established MRI iron quantification techniques. Quantification of dispersed (ferritin-like) iron may provide a new means of monitoring the risk of iron-induced toxicity in patients with iron overload and, together with quantification of aggregated (hemosiderin-like) iron, improve the accuracy of estimates for total storage iron.
Effect of magnetic field and iron content on NMR proton relaxation of liver, spleen and brain tissues
Contrast Media & Molecular Imaging, 2014
Iron accumulation is observed in liver and spleen during hemochromatosis and important neurodegenerative diseases involve iron overload in brain. Storage of iron is ensured by ferritin, which contains a magnetic core. It causes a darkening on T 2 -weighted MR images. This work aims at improving the understanding of the NMR relaxation of iron-loaded human tissues, which is necessary to develop protocols of iron content measurements by MRI. Relaxation times measurements on brain, liver and spleen samples were realized at different magnetic fields. Iron content was determined by atomic emission spectroscopy. For all samples, the longitudinal relaxation rate (1/T 1 ) of tissue protons decreases with the magnetic field up to 1 T, independently of iron content, while their transverse relaxation rate (1/T 2 ) strongly increases with the field, either linearly or quadratically, or a combination thereof. The extent of the inter-echo time dependence of 1/T 2 also varies according to the sample. A combination of theoretical models is necessary to describe the relaxation of iron-containing tissues. This can be due to the presence, inside tissues, of ferritin clusters of different sizes and densities. When considering all samples, a correlation (r 2 = 0.6) between 1/T 1 and iron concentration is observed at 7.0 T. In contrast the correlation between 1/T 2 and iron content is poor, even at high field (r 2 = 0.14 at 7.0 T). Our results show that MRI methods based on T 1 or T 2 measurements will easily detect an iron overloading at high magnetic field, but will not provide an accurate quantification of tissue iron content at low iron concentrations.
Mapping tissue water T 1 in the liver using the MOLLI T 1 method in the presence of fat, iron and B 0 inhomogeneity
NMR in Biomedicine
Modified Look-Locker inversion recovery (MOLLI) T 1 mapping sequences can be useful in cardiac and liver tissue characterization, but determining underlying water T 1 is confounded by iron, fat and frequency offsets. This article proposes an algorithm that provides an independent water MOLLI T 1 (referred to as on-resonance water T 1) that would have been measured if a subject had no fat and normal iron, and imaging had been done on resonance. Fifteen NiCl 2-doped agar phantoms with different peanut oil concentrations and 30 adults with various liver diseases, nineteen (63.3%) with liver steatosis, were scanned at 3 T using the shortened MOLLI (shMOLLI) T 1 mapping, multiple-echo spoiled gradient-recalled echo and 1 H MR spectroscopy sequences. An algorithm based on Bloch equations was built in MATLAB, and water shMOLLI T 1 values of both phantoms and human participants were determined. The quality of the algorithm's result was assessed by Pearson's correlation coefficient between shMOLLI T 1 values and spectroscopically determined T 1 values of the water, and by linear regression analysis.
Current and future applications of in vitro magnetic resonance spectroscopy in hepatobiliary disease
World Journal of Gastroenterology, 2006
Nuclear magnetic resonance spectroscopy allows the study of cellular biochemistry and metabolism, both in the whole body in vivo and at higher magnetic field strengths in vitro . Since the technique is non-invasive and non-selective, magnetic resonance spectroscopy methodologies have been widely applied in biochemistry and medicine. In vitro magnetic resonance spectroscopy studies of cells, body fluids and tissues have been used in medical biochemistry to investigate pathophysiological processes and more recently, the technique has been used by physicians to determine disease abnormalities in vivo . This highlighted topic illustrates the potential of in vitro magnetic resonance spectroscopy in studying the hepatobiliary system. The role of in vitro proton and phosphorus magnetic resonance spectroscopy in the study of malignant and non-malignant liver disease and bile composition studies are discussed, particularly with reference to correlative in vivo whole-body magnetic resonance spectroscopy applications. In summary, magnetic resonance spectroscopy techniques can provide non-invasive biochemical information on disease severity and pointers to underlying pathophysiological processes. Magnetic resonance spectroscopy holds potential promise as a screening tool for disease biomarkers, as well as assessing therapeutic response.
A model for hepatic fibrosis: the competing effects of cell loss and iron on shortened modified Look-Locker inversion recovery T1 (shMOLLI-T1 ) in the liver
Journal of magnetic resonance imaging : JMRI, 2016
To propose a simple multicompartment model of the liver and use Bloch-McConnell simulations to demonstrate the effects of iron and fibrosis on shortened-MOLLI (shMOLLI) T1 measurements. Liver T1 values have shown sensitivity to inflammation and fibrosis, but are also affected by hepatic iron content. Modified Look-Locker inversion recovery (MOLLI) T1 measurements are biased by the lower T2 associated with high iron. A tissue model was generated consisting of liver cells and extracellular fluid (ECF), with iron-dependent relaxation rates. Fibrosis was imitated by increasing the ECF proportion. Simulations of the shMOLLI sequence produced a look-up table (LUT) of shMOLLI-T1 for a given ECF fraction and iron content. The LUT was used to calculate ECF(shMOLLI-T1 ), assuming normal hepatic iron content (HIC), and ECF(shMOLLI- T1,T2*), accounting for HIC determined by T2*, for 77 patients and compared to fibrosis assessed by liver biopsy. Simulations showed that increasing HIC decreases s...
Improved MRIR2* relaxometry of iron-loaded liver with noise correction
Magnetic Resonance in Medicine, 2013
Accurate and reproducible MRI R 2 * relaxometry for tissue iron quantification is important in managing transfusion-dependent patients. MRI data are often acquired using array coils and reconstructed by the root-sum-square algorithm, and as such, measured signals follow the noncentral chi distribution. In this study, two noise-corrected models were proposed for the liver R 2 * quantification: fitting the signal to the first moment and fitting the squared signal to the second moment in the presence of the noncentral chi noise. These two models were compared with the widely implemented offset and truncation models on both simulation and in vivo data. The results demonstrated that the "slow decay component" of the liver R 2 * was mainly caused by the noise. The offset model considerably overestimated R 2 * values by incorrectly adding a constant to account for the slow decay component. The truncation model generally produced accurate R 2 * measurements by only fitting the initial data well above the noise level to remove the major source of errors, but underestimated very high R 2 * values due to the sequence limit of obtaining very short echo time images. Both the first and second-moment noisecorrected models constantly produced accurate and precise R 2 * measurements by correctly addressing the noise problem.
Assessment of liver iron overload by 3 T MRI
Abdominal Imaging, 2017
Purpose: To evaluate the performance and limitations of the signal intensity ratio method for quantifying liver iron overload at 3 T. Methods: Institutional review board approval and written informed consent from all participants were obtained. One hundred and five patients were included prospectively. All patients underwent a liver biopsy with biochemical assessment of hepatic iron concentration and a 3 T MRI scan with 5 breath-hold single-echo gradient-echo sequences. Linear correlation between liver-to-muscle signal intensity ratio and liver iron concentration was calculated. The algorithm for calculating magnetic resonance hepatic iron concentration was adapted from the method described by Gandon et al. with echo times divided by 2. Sensitivity and specificity were calculated. Results: Five patients were excluded (coil selection failure or missing sequence) and 100 patients were analyzed, 64 men and 36 women, 52 ± 13.3 years old, with a biochemical hepatic iron concentration range of 0-630 lmol/g. Linear correlation between biochemical hepatic iron concentration and MR-hepatic iron concentration was excellent with a correlation coefficient = 0.96, p < 0.0001. Sensitivity and specificity were, respectively, 83% (0.70-0.92) and 96% (0.85-0.99), with a pathological threshold of 36 lmol/g. Conclusion: Signal intensity ratio method for quantifying liver iron overload can be used at 3 T with echo times divided by 2.
Related papers
Quantification of iron concentration in the liver by MRI
Insights into Imaging, 2011
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.
Liver iron concentration evaluated by two magnetic methods: Magnetic resonance imaging and magnetic susceptometry
Magnetic Resonance in Medicine, 2005
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 (R 2) 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 ؋ 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. Magn Reson Med 54:122-128, 2005.
Improved MRIR2* relaxometry of iron-loaded liver with noise correction
Magnetic Resonance in Medicine, 2013
Accurate and reproducible MRI R 2 * relaxometry for tissue iron quantification is important in managing transfusion-dependent patients. MRI data are often acquired using array coils and reconstructed by the root-sum-square algorithm, and as such, measured signals follow the noncentral chi distribution. In this study, two noise-corrected models were proposed for the liver R 2 * quantification: fitting the signal to the first moment and fitting the squared signal to the second moment in the presence of the noncentral chi noise. These two models were compared with the widely implemented offset and truncation models on both simulation and in vivo data. The results demonstrated that the "slow decay component" of the liver R 2 * was mainly caused by the noise. The offset model considerably overestimated R 2 * values by incorrectly adding a constant to account for the slow decay component. The truncation model generally produced accurate R 2 * measurements by only fitting the initial data well above the noise level to remove the major source of errors, but underestimated very high R 2 * values due to the sequence limit of obtaining very short echo time images. Both the first and second-moment noisecorrected models constantly produced accurate and precise R 2 * measurements by correctly addressing the noise problem.
MR characterization of hepatic storage iron in transfusional iron overload
Journal of Magnetic Resonance Imaging, 2014
Purpose: To quantify the two principal forms of hepatic storage iron, diffuse, soluble iron (primarily ferritin), and aggregated, insoluble iron (primarily hemosiderin) using a new MRI method in patients with transfusional iron overload.
R2 relaxometry with MRI for the quantification of tissue iron overload in beta-thalassemic patients
Journal of magnetic resonance imaging : JMRI, 2006
To evaluate the usefulness of a time-efficient MRI method for the quantitative determination of tissue iron in the liver and heart of beta-thalassemic patients using spin-spin relaxation rate, R2, measurements.
R2 relaxometry with MRI for the quantification of tissue iron overload in β-thalassemic patients
2006
Purpose: To evaluate the usefulness of a time-efficient MRI method for the quantitative determination of tissue iron in the liver and heart of -thalassemic patients using spinspin relaxation rate, R2, measurements.
Assessment of liver iron overload by 3 T MRI
Abdominal Imaging, 2017
Purpose: To evaluate the performance and limitations of the signal intensity ratio method for quantifying liver iron overload at 3 T. Methods: Institutional review board approval and written informed consent from all participants were obtained. One hundred and five patients were included prospectively. All patients underwent a liver biopsy with biochemical assessment of hepatic iron concentration and a 3 T MRI scan with 5 breath-hold single-echo gradient-echo sequences. Linear correlation between liver-to-muscle signal intensity ratio and liver iron concentration was calculated. The algorithm for calculating magnetic resonance hepatic iron concentration was adapted from the method described by Gandon et al. with echo times divided by 2. Sensitivity and specificity were calculated. Results: Five patients were excluded (coil selection failure or missing sequence) and 100 patients were analyzed, 64 men and 36 women, 52 ± 13.3 years old, with a biochemical hepatic iron concentration range of 0-630 lmol/g. Linear correlation between biochemical hepatic iron concentration and MR-hepatic iron concentration was excellent with a correlation coefficient = 0.96, p < 0.0001. Sensitivity and specificity were, respectively, 83% (0.70-0.92) and 96% (0.85-0.99), with a pathological threshold of 36 lmol/g. Conclusion: Signal intensity ratio method for quantifying liver iron overload can be used at 3 T with echo times divided by 2.
Tissue iron quantification in chronic liver diseases using MRI shows a relationship between iron accumulation in liver, spleen, and bone marrow
Clinical radiology, 2017
To investigate iron loading within the liver, pancreas, spleen, and bone marrow using magnetic resonance imaging (MRI) transverse relaxation rate (R2*), in patients with diffuse liver diseases; to evaluate the relationships between iron accumulation in these tissue compartments; and to assess the association between tissue iron overload and the pattern of hepatic cellular iron distribution (hepatocytes versus Kupffer cells). Fifty-six patients with diffuse liver diseases had MRI-derived R2* values, using a multi-echo chemical-shift encoded MRI sequence, of the liver, pancreas, spleen, and vertebral bone marrow. All patients had liver biopsy samples scored for hepatic iron grading (0-4) and iron cellular distribution (within hepatocytes only or within both hepatocytes and Kupffer cells). Liver R2* increased with histological iron grade (RS=0.58, p<0.001) and correlated with spleen (RS=0.71, p<0.001) and bone marrow R2* (RS=0.66, p<0.001), but not with pancreatic R2* (RS=0.22...
Variable-field relaxometry of iron-containing human tissues: a preliminary study
Contrast Media & Molecular Imaging, 2009
Excess iron is found in brain nuclei from neurodegenerative patients (with Parkinson's, Alzheimer's and Huntington's diseases) and also in the liver and spleen of cirrhosis, hemochromatosis and thalassaemia patients. Ferritin, the iron-storing protein of mammals, is known to darken T 2 -weighted MR images. Understanding NMR tissue behavior may make it possible to detect those diseases, to follow their evolution and finally to establish a protocol for non-invasive measurement of an organ's iron content using MRI methods. In this preliminary work, the MR relaxation properties of embalmed iron-containing tissues were studied as well as their potential correlation with the iron content of these tissues. Relaxometric measurements (T 1 and T 2 ) of embalmed samples of brain nuclei (caudate nucleus, dentate nucleus, globus pallidus, putamen, red nucleus and substantia nigra), liver and spleen from six donors were made at different magnetic fields (0.00023-14 T). The influence of the inter-echo time on transverse relaxation was also studied. Moreover, iron content of tissues was determined by inductively coupled plasma atomic emission spectroscopy. In brain nuclei, 1/T 2 increases quadratically with the field and depends on the inter-echo time in CPMG sequences at high fields, both features compatible with an outer sphere relaxation theory. In liver and spleen, 1/T 2 increases linearly with the field and depends on the inter-echo time at all fields. In our study, a correlation between 1/T 2 and iron concentration is observed. Explaining the relaxation mechanism for these tissues is likely to require a combination of several models. The value of 1/T 2 at high field could be used to evaluate iron accumulation in vivo. In the future, confirmation of those features is expected to be achieved from measurements of fresh (not embalmed) human tissues.
Liver iron overload assessment by MRI R2* relaxometry in highly transfused pediatric patients: An agreement and reproducibility study
Diagnostic and interventional imaging, 2015
Perform an agreement and reproducibility study of the estimation of iron overload in highly transfused pediatric patients comparing R2* relaxometry (R2*=1000/T2*) to the reference technique liver/muscle signal intensity ratio (SIR). Ninety-two MRI were performed in 68 children who were mainly transfused for sickle cell disease, mean age 9.9years old. The examination included six sequences for the SIR protocol and a single multiecho T2* sequence. R2* relaxometry was measured by two radiologists independently, either by a region of interest (ROI) in the right liver, or an outline of the whole liver. Hepatic iron load was determined by the Wood formula (Femg/g=R2*×0.0254+0.202). The validity of R2* relaxometry compared to SIR was evaluated by the coefficient of variation and the quadratic weighted Kappa value. The correlation between R2* relaxometry and SIR was very good with a Pearson coefficient of 0.89 and a coefficient of variation of 17.3%. The inter- and intraobserver reproducibi...
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.