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Specific visualization of neuromelanin-iron complex and ferric iron in the human post-mortem substantia nigra using MR relaxometry at 7T. Neuroimage 2018; 172:874-885. [DOI: 10.1016/j.neuroimage.2017.11.035] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 10/19/2017] [Accepted: 11/17/2017] [Indexed: 11/22/2022] Open
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Turkmen E, Yildirim T, Yilmaz R, Hazirolan T, Eldem G, Yilmaz E, Aybal Kutlugun A, Altindal M, Altun B. HFE gene mutation is a risk factor for tissue iron accumulation in hemodialysis patients. Hemodial Int 2017; 21:359-366. [DOI: 10.1111/hdi.12537] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- Ercan Turkmen
- Department of Nephrology; Hacettepe University Medical Faculty; Ankara Turkey
| | - Tolga Yildirim
- Department of Nephrology; Hacettepe University Medical Faculty; Ankara Turkey
| | - Rahmi Yilmaz
- Department of Nephrology; Hacettepe University Medical Faculty; Ankara Turkey
| | - Tuncay Hazirolan
- Department of Radiology; Hacettepe University Medical Faculty; Ankara Turkey
| | - Gonca Eldem
- Department of Radiology; Hacettepe University Medical Faculty; Ankara Turkey
| | - Engin Yilmaz
- Department of Medical Biology; Hacettepe University Medical Faculty; Ankara Turkey
| | | | - Mahmut Altindal
- Department of Nephrology; Hacettepe University Medical Faculty; Ankara Turkey
| | - Bulent Altun
- Department of Nephrology; Hacettepe University Medical Faculty; Ankara Turkey
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3
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Taylor BA, Loeffler RB, Song R, McCarville MB, Hankins JS, Hillenbrand CM. Simultaneous field and R2 mapping to quantify liver iron content using autoregressive moving average modeling. J Magn Reson Imaging 2011; 35:1125-32. [PMID: 22180325 DOI: 10.1002/jmri.23545] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2011] [Accepted: 11/29/2011] [Indexed: 12/14/2022] Open
Abstract
PURPOSE To investigate the use of a complex multigradient echo (mGRE) acquisition and an autoregressive moving average (ARMA) model for simultaneous susceptibility and R 2 measurements for the assessment of liver iron content (LIC) in patients with iron overload. MATERIALS AND METHODS Fifty magnetic resonance imaging (MRI) exams with magnitude and phase mGRE images were processed using the ARMA model, which provides fat-separated field maps, R 2 maps, and T(1) -W imaging. The LIC was calculated by measuring the susceptibility between the liver and the right transverse abdominal muscle from the field maps. The relationship between LIC derived from susceptibility measurements and LIC from R 2 measurements was determined using linear least-squares regression analysis. RESULTS LIC measured from R 2 is highly correlated to the LIC with the susceptibility method (mg/g dry = 8.99 ± 0.15 × [mg Fe/mL of wet liver] -2.38 ± 0.29, R(2) = 0.94). The field inhomogeneity in the liver is correlated with R 2 (R(2) = 0.85). CONCLUSION By using the ARMA model on complex mGRE images, both susceptibility and R 2-based LIC measurements can be made simultaneously. The susceptibility measurement can be used to help verify R 2 measurements in the assessment of iron overload.
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Affiliation(s)
- Brian A Taylor
- Department of Radiological Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee, USA
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4
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Kirk P, Smith GC, Roughton M, He T, Pennell DJ. Myocardial T2* is not affected by ageing, myocardial fibrosis, or impaired left ventricular function. J Magn Reson Imaging 2011; 32:1095-8. [PMID: 21031513 DOI: 10.1002/jmri.22348] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
PURPOSE To evaluate the influence of alterations in myocardial structure and function from increasing age, myocardial fibrosis, or impaired left ventricular function on myocardial T2*. MATERIALS AND METHODS Myocardial T2* was measured in 126 subjects without cardiac iron loading, of whom 63 were normals of varying ages, 39 were patients with impaired left ventricular function from various nonsiderotic cardiac causes, and 24 were patients with chronic myocardial infarction affecting the interventricular septum (where myocardial T2* measurements are normally made). RESULTS The median (Q1, Q3) of myocardial T2* in the normals was 36.3 ms (31.6, 45.4). There was no significant correlation between myocardial T2* and age (R(2) = 0.04; P = 0.11). In the patients with impaired left ventricular function, the median myocardial T2* was 35.5 ms (31, 42.2) (P = 0.34 versus normals). There was no significant correlation between ejection fraction and T2* in patients with left ventricular impairment (R(2) = 0.03; P = 0.33). In the patients with septal infarction, the median septal myocardial T2* was 35.4 ms (32.7, 43) (P = 0.81 vs normals). CONCLUSION There was no significant change in myocardial T2* associated with any alterations of myocardial structure and function occurring with increasing age, impairment of left ventricular function or septal fibrosis from chronic myocardial infarction. These results indicate that myocardial T2* measurements are robust to these potential confounding parameters.
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Affiliation(s)
- Paul Kirk
- Cardiovascular Magnetic Resonance Unit, Royal Brompton Hospital and Imperial College, London, United Kingdom
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McAuley G, Schrag M, Barnes S, Obenaus A, Dickson A, Holshouser B, Kirsch W. Iron quantification of microbleeds in postmortem brain. Magn Reson Med 2010; 65:1592-601. [PMID: 21590801 DOI: 10.1002/mrm.22745] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2010] [Revised: 10/26/2010] [Accepted: 11/07/2010] [Indexed: 12/27/2022]
Abstract
Brain microbleeds (BMB) are associated with chronic and acute cerebrovascular disease and present a source of pathologic iron to the brain proportional to extravasated blood. Therefore, BMB iron content is potentially a valuable biomarker. We tested noninvasive phase image methods to quantify iron content and estimate true source diameter (i.e., unobscured by the blooming effect) of BMB in postmortem human tissue. Tissue slices containing BMB were imaged using a susceptibility weighted imaging protocol at 11.7T. BMB lesions were assayed for iron content using atomic absorption spectrometry. Measurements of geometric features in phase images were related to lesion iron content and source diameter using a mathematical model. BMB diameter was estimated by image feature geometry alone without explicit relation to the magnetic susceptibility. A strong linear relationship (R(2) = 0.984, P < 0.001) predicted by theory was observed in the experimental data, presenting a tentative standardization curve where BMB iron content in similar tissues could be calculated. In addition, we report BMB iron mass measurements, as well as upper bound diameter and lower bound iron concentration estimates. Our methods potentially allows the calculation of brain iron load indices based on BMB iron content and classification of BMB by size unobscured by the blooming effect.
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Affiliation(s)
- Grant McAuley
- Neurosurgery Center for Research, Training and Education, Loma Linda University, Loma Linda, California 92354, USA
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Marinelli M, Gianesin B, Balocco M, Beruto P, Bruzzone C, Carrara P, Gallusi P, Macco A, Musso M, Oliveri E, Pelucchi S, Sobrero G, Villa R, Forni GL. Total Iron-Overload Measurement in the Human Liver Region by the Magnetic Iron Detector. IEEE Trans Biomed Eng 2010; 57:2295-303. [DOI: 10.1109/tbme.2010.2053204] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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7
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McAuley G, Schrag M, Sipos P, Sun SW, Obenaus A, Neelavalli J, Haacke EM, Holshouser B, Madácsi R, Kirsch W. Quantification of punctate iron sources using magnetic resonance phase. Magn Reson Med 2010; 63:106-15. [PMID: 19953510 DOI: 10.1002/mrm.22185] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Iron-mediated tissue damage is present in cerebrovascular and neurodegenerative diseases and neurotrauma. Brain microbleeds are often present in these maladies and are assuming increasing clinical importance. Because brain microbleeds present a source of pathologic iron to the brain, the noninvasive quantification of this iron pool is potentially valuable. Past efforts to quantify brain iron have focused on content estimation within distributed brain regions. In addition, conventional approaches using "magnitude" images have met significant limitations. In this study, a technique is presented to quantify the iron content of punctate samples using phase images. Samples are modeled as magnetic dipoles and phase shifts due to local dipole field perturbations are mathematically related to sample iron content and radius using easily recognized geometric features in phase images. Phantoms containing samples of a chitosan-ferric oxyhydroxide composite (which serves as a mimic for hemosiderin) were scanned with a susceptibility-weighted imaging sequence at 11.7 T. Plots relating sample iron content and radius to phase image features were compared to theoretical predictions. The primary result is the validation of the technique by the excellent agreement between theory and the iron content plot. This research is a potential first step toward quantification of punctate brain iron sources such as brain microbleeds.
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Affiliation(s)
- Grant McAuley
- Neurosurgery Center for Research, Training and Education, Loma Linda University, Loma Linda, California 92354, USA
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8
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Wang ZJ, Fischer R, Chu Z, Mahoney DH, Mueller BU, Muthupillai R, James EB, Krishnamurthy R, Chung T, Padua E, Vichinsky E, Harmatz P. Assessment of cardiac iron by MRI susceptometry and R2* in patients with thalassemia. Magn Reson Imaging 2010; 28:363-71. [PMID: 20061110 DOI: 10.1016/j.mri.2009.12.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2009] [Revised: 07/07/2009] [Accepted: 12/06/2009] [Indexed: 10/20/2022]
Abstract
A magnetic resonance imaging cardiac magnetic susceptometry (MRI-CS) technique for assessing cardiac tissue iron concentration based on phase mapping was developed. Normal control subjects (n=9) and thalassemia patients (n=13) receiving long-term blood transfusion therapy underwent MRI-CS and MRI measurements of the cardiac relaxation rate R2*. Using MRI-CS, subepicardium and subendocardium iron concentrations were quantified exploiting the hemosiderin/ferritin iron specific magnetic susceptibility. The average of subepicardium and subendocardium iron concentrations and R2* of the septum were found to be strongly correlated (r=0.96, P<.0001), and linear regression analysis yielded CIC (microg Fe/g(wet tissue))=(6.4+/-0.4).R2* (septum) (s(-1)) - (120+/-40). The results demonstrated that septal R2* indeed measures cardiac iron level.
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Guo H, Au WY, Cheung JS, Kim D, Jensen JH, Khong PL, Chan Q, Chan KC, Tosti C, Tang H, Brown TR, Lam WWM, Ha SY, Brittenham GM, Wu EX. Myocardial T2 quantitation in patients with iron overload at 3 Tesla. J Magn Reson Imaging 2009; 30:394-400. [PMID: 19629983 DOI: 10.1002/jmri.21851] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
PURPOSE To investigate the feasibility of measuring myocardial T2 at 3 Tesla for assessment of tissue iron in thalassemia major and other iron overloaded patients. MATERIALS AND METHODS A single-breathhold electrocardiogram-triggered black-blood multi-echo spin-echo (MESE) sequence with a turbo factor of 2 was implemented at 3 Tesla (T). Myocardial and liver T2 values were measured with three repeated breathholds in 8 normal subjects and 24 patients. Their values, together with the T2 values measured using a breathhold multi-echo gradient-echo sequence, were compared with those at 1.5T in the same patients. RESULTS At 3T, myocardial T2 was found to be 39.6 +/- 7.4 ms in normal subjects. In patients, it ranged from 12.9 to 50.1 ms. "T2 and T2(*) [corrected] were observed to correlate in heart (rho = 0.93, P [corrected] < 0.0001) and liver (rho = 0.95, P < 0.0001). Myocardial T2 and T2 at 3T were also highly correlated with the 1.5T measurements. Preliminary results indicated that myocardial T2 quantitation was relatively insensitive to B1 variation, and reproducible with 3.2% intra-exam and 3.8% inter-exam variations. CONCLUSION Myocardial T2 quantitation is feasible at 3T. Given the substantially decreased T2 and increased B0 inhomogeneity, the rapid myocardial T2 measurement protocol demonstrated here may present a robust alternative to study cardiac iron overload at 3T.
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Affiliation(s)
- Hua Guo
- Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
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Fischer R, Harmatz PR. Non-invasive assessment of tissue iron overload. HEMATOLOGY. AMERICAN SOCIETY OF HEMATOLOGY. EDUCATION PROGRAM 2009; 2009:215-221. [PMID: 20008201 DOI: 10.1182/asheducation-2009.1.215] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
In recent years, there has been increasing interest in non-invasive iron measurement, especially of the liver and heart, in patients with iron overload. Serum ferritin still remains an essential monitoring parameter in intervals between liver iron measurements; however, confounding factors such as inflammation, chelation treatment changes and the specific disease have to be taken into account. Liver iron measurements can now routinely be performed in clinical applications either by quantitative magnetic resonance imaging (MRI) using the transverse magnetic relaxation rate R(2) or R(2)* (1/T(2)*) or by biomagnetic liver susceptometry. For iron measurements in the heart, the single-breathhold multi-echo MRI-R(2)* method has become a standard modality and is now applied in clinical settings beyond research studies. In other tissues like the pancreas, pituitary, and brain, different MRI methods are employed, but their clinical benefit has yet to be proven.
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Affiliation(s)
- Roland Fischer
- University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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11
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Abstract
High hepatic iron concentration (HIC) is associated with cardiac iron overload. However, simultaneous measurements of heart and liver iron often demonstrate no significant linear association. We postulated that slower rates of cardiac iron accumulation and clearance could reconcile these differences. To test this hypothesis, we examined the longitudinal evolution of cardiac and liver iron in 38 thalassemia major patients, using previously validated magnetic resonance imaging (MRI) techniques. On cross-sectional evaluation, cardiac iron was uncorrelated with liver iron, similar to previous studies. However, relative changes in heart and liver iron were compared with one another using a metric representing the temporal delay between them. Cardiac iron significantly lagged liver iron changes in almost half of the patients, implying a functional but delayed association. The degree of time lag correlated with initial HIC (r = 0.47, P < .003) and initial cardiac R2* (r = 0.57, P < .001), but not with patient age. Thus, longitudinal analysis confirms a lag in the loading and unloading of cardiac iron with respect to liver iron, and partially explains the weak cross-sectional association between these parameters. These data reconcile several prior studies and provide both mechanical and clinical insight into cardiac iron accumulation.
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Abstract
High hepatic iron concentration (HIC) is associated with cardiac iron overload. However, simultaneous measurements of heart and liver iron often demonstrate no significant linear association. We postulated that slower rates of cardiac iron accumulation and clearance could reconcile these differences. To test this hypothesis, we examined the longitudinal evolution of cardiac and liver iron in 38 thalassemia major patients, using previously validated magnetic resonance imaging (MRI) techniques. On cross-sectional evaluation, cardiac iron was uncorrelated with liver iron, similar to previous studies. However, relative changes in heart and liver iron were compared with one another using a metric representing the temporal delay between them. Cardiac iron significantly lagged liver iron changes in almost half of the patients, implying a functional but delayed association. The degree of time lag correlated with initial HIC (r = 0.47, P < .003) and initial cardiac R2* (r = 0.57, P < .001), but not with patient age. Thus, longitudinal analysis confirms a lag in the loading and unloading of cardiac iron with respect to liver iron, and partially explains the weak cross-sectional association between these parameters. These data reconcile several prior studies and provide both mechanical and clinical insight into cardiac iron accumulation.
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Abstract
PURPOSE OF REVIEW To highlight recent advances in magnetic resonance imaging estimation of somatic iron overload. This review will discuss the need and principles of magnetic resonance imaging-based iron measurements, the validation of liver and cardiac iron measurements, and the key institutional requirements for implementation. RECENT FINDINGS Magnetic resonance imaging assessment of liver and cardiac iron has achieved critical levels of availability, utility, and validity to serve as the primary endpoint of clinical trials. Calibration curves for the magnetic resonance imaging parameters R2 and R2* (or their reciprocals, T2 and T2*) have been developed for the liver and the heart. Interscanner variability for these techniques has proven to be on the order of 5-7%. SUMMARY Magnetic resonance imaging assessment of tissue iron is becoming increasingly important in the management of transfusional iron load because it is noninvasive, relatively widely available and offers a window into presymptomatic organ dysfunction. The techniques are highly reproducible within and across machines and have been chemically validated in the liver and the heart. These techniques will become the standard of care as industry begins to support the acquisition and postprocessing software.
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Affiliation(s)
- John C Wood
- Divisions of Pediatric Cardiology and Radiology, Children's Hospital Los Angeles, Los Angeles, CA 90027, USA.
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Ghugre NR, Enriquez CM, Gonzalez I, Nelson MD, Coates TD, Wood JC. MRI detects myocardial iron in the human heart. Magn Reson Med 2006; 56:681-6. [PMID: 16888797 PMCID: PMC2887674 DOI: 10.1002/mrm.20981] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2005] [Accepted: 05/03/2006] [Indexed: 12/12/2022]
Abstract
Iron-induced cardiac dysfunction is a leading cause of death in transfusion-dependent anemia. MRI relaxation rates R2(1/T2) and R2*(1/T2*) accurately predict liver iron concentration, but their ability to predict cardiac iron has been challenged by some investigators. Studies in animal models support similar R2 and R2* behavior with heart and liver iron, but human studies are lacking. To determine the relationship between MRI relaxivities and cardiac iron, regional variations in R2 and R2* were compared with iron distribution in one freshly deceased, unfixed, iron-loaded heart. R2 and R2* were proportionally related to regional iron concentrations and highly concordant with one another within the interventricular septum. A comparison of postmortem and in vitro measurements supports the notion that cardiac R2* should be assessed in the septum rather than the whole heart. These data, along with measurements from controls, provide bounds on MRI-iron calibration curves in human heart and further support the clinical use of cardiac MRI in iron-overload syndromes.
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Affiliation(s)
- Nilesh R. Ghugre
- Division of Cardiology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
- Department of Radiology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Cathleen M. Enriquez
- Division of Cardiology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Ignacio Gonzalez
- Department of Pathology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Marvin D. Nelson
- Department of Radiology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Thomas D. Coates
- Division of Hematology-Oncology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - John C. Wood
- Division of Cardiology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
- Department of Radiology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
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Sheth S, Tang H, Jensen JH, Altmann K, Prakash A, Printz BF, Hordof AJ, Tosti CL, Azabagic A, Swaminathan S, Brown TR, Olivieri NF, Brittenham GM. Methods for noninvasive measurement of tissue iron in Cooley's anemia. Ann N Y Acad Sci 2006; 1054:358-72. [PMID: 16339684 DOI: 10.1196/annals.1345.044] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
To examine the relationship between myocardial storage iron and body iron burden, as assessed by hepatic storage iron measurements, we studied 22 patients with transfusion-dependent thalassemia syndromes, all being treated with subcutaneous deferoxamine, and 6 healthy subjects. Study participants were examined with a Philips 1.5-T Intera scanner using three multiecho spin echo sequences with electrocardiographic triggering and respiratory navigator gating. Myocardial and hepatic storage iron concentrations were determined using a new magnetic resonance method that estimates total tissue iron stores by separately measuring the two principal forms of storage iron, ferritin and hemosiderin. In a subset of 10 patients with beta-thalassemia major, the hepatic storage iron concentration had been monitored repeatedly for 12-14 years by chemical analysis of tissue obtained by liver biopsy and by magnetic susceptometry. In this subset, we examine the relationship between hepatic iron concentration over time and our current magnetic resonance estimates of myocardial iron stores. No significant relationship was found between simultaneous estimates of myocardial and hepatic storage iron concentrations. By contrast, in the subset of 10 patients with beta-thalassemia major, the correlation between the 5-year average of hepatic iron concentration and the current myocardial storage iron was significant (R = .67, P = .03). In these patients, myocardial storage iron concentrations seem to reflect the control of body iron over a period of years. Magnetic resonance methods promise to provide more effective monitoring of iron deposition in vulnerable tissues, including the liver, heart, and endocrine organs, and could contribute to the development of iron-chelating regimens that more effectively prevent iron toxicity.
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Affiliation(s)
- Sujit Sheth
- Department of Pediatrics, Columbia University College of Physicians and Surgeons, Harkness Pavilion, Room HP5, 180 Fort Washington Avenue, New York, NY 10032, USA.
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Wood JC, Enriquez C, Ghugre N, Otto-Duessel M, Aguilar M, Nelson MD, Moats R, Coates TD. Physiology and pathophysiology of iron cardiomyopathy in thalassemia. Ann N Y Acad Sci 2006; 1054:386-95. [PMID: 16339687 PMCID: PMC2892916 DOI: 10.1196/annals.1345.047] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Iron cardiomyopathy remains the leading cause of death in patients with thalassemia major. Magnetic resonance imaging (MRI) is ideally suited for monitoring thalassemia patients because it can detect cardiac and liver iron burdens as well as accurately measure left ventricular dimensions and function. However, patients with thalassemia have unique physiology that alters their normative data. In this article, we review the physiology and pathophysiology of thalassemic heart disease as well as the use of MRI to monitor it. Despite regular transfusions, thalassemia major patients have larger ventricular volumes, higher cardiac outputs, and lower total vascular resistances than published data for healthy control subjects; these hemodynamic findings are consistent with chronic anemia. Cardiac iron overload increases the relative risk of further dilation, arrhythmias, and decreased systolic function. However, many patients are asymptomatic despite heavy cardiac burdens. We explore possible mechanisms behind cardiac iron-function relationships and relate these mechanisms to clinical observations.
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Affiliation(s)
- John C Wood
- Division of Cardiology, Mailstop 34, Childrens Hospital of Los Angeles, 4650 Sunset Blvd., Los Angeles, CA 90027, USA.
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Abstract
Magnetic resonance T2* values of the myocardium are directly related to tissue iron levels. Minor effects from myocardial oxygenation and fibrosis are overwhelmed by the highly dominant iron effect in clinically relevant levels of myocardial iron overload. Myocardial T2* values less than 20 ms indicate iron overload, and this is considered severe when T2* is less than 10 ms. Decreasing myocardial T2* levels are associated with systolic and diastolic ventricular dysfunction. Most recorded cases of heart failure in thalassemia to date have occurred in patients with very low T2* values (in the severe range). Exceptions to this have occurred in patients with other causes of heart failure such as concomitant congenital heart disease. In patients presenting with heart failure who undergo aggressive chelation with continuous intravenous deferoxamine, longitudinal studies show that myocardial T2* increases, and this is accompanied by increases in ejection fraction and relief of heart failure. In cross-sectional studies, the myocardial T2* and ejection fraction of patients on deferiprone was superior to that of patients on deferoxamine. Randomized controlled prospective trials comparing these two drugs for their action in clearing myocardial iron, as measured by myocardial T2*, are under way and should report in 2005/2006. These trials will clarify the role of different chelators in the management of myocardial iron overload and may be valuable in reducing the toll of death in thalassemia from heart failure.
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Affiliation(s)
- Dudley J Pennell
- CMR Unit, Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK.
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Wood JC, Otto-Duessel M, Aguilar M, Nick H, Nelson MD, Coates TD, Pollack H, Moats R. Cardiac iron determines cardiac T2*, T2, and T1 in the gerbil model of iron cardiomyopathy. Circulation 2005; 112:535-43. [PMID: 16027257 PMCID: PMC2896311 DOI: 10.1161/circulationaha.104.504415] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
BACKGROUND Transfusional therapy for thalassemia major and sickle cell disease can lead to iron deposition and damage to the heart, liver, and endocrine organs. Iron causes the MRI parameters T1, T2, and T2* to shorten in these organs, which creates a potential mechanism for iron quantification. However, because of the danger and variability of cardiac biopsy, tissue validation of cardiac iron estimates by MRI has not been performed. In this study, we demonstrate that iron produces similar T1, T2, and T2* changes in the heart and liver using a gerbil iron-overload model. METHODS AND RESULTS Twelve gerbils underwent iron dextran loading (200 mg . kg(-1) . wk(-1)) from 2 to 14 weeks; 5 age-matched controls were studied as well. Animals had in vivo assessment of cardiac T2* and hepatic T2 and T2* and postmortem assessment of cardiac and hepatic T1 and T2. Relaxation measurements were performed in a clinical 1.5-T magnet and a 60-MHz nuclear magnetic resonance relaxometer. Cardiac and liver iron concentrations rose linearly with administered dose. Cardiac 1/T2*, 1/T2, and 1/T1 rose linearly with cardiac iron concentration. Liver 1/T2*, 1/T2, and 1/T1 also rose linearly, proportional to hepatic iron concentration. Liver and heart calibrations were similar on a dry-weight basis. CONCLUSIONS MRI measurements of cardiac T2 and T2* can be used to quantify cardiac iron. The similarity of liver and cardiac iron calibration curves in the gerbil suggests that extrapolation of human liver calibration curves to heart may be a rational approximation in humans.
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Affiliation(s)
- John C Wood
- Division of Pediatric Cardiology, Department of Pediatrics and Radiology, Children's Hospital of Los Angeles, 4650 Sunset Blvd, Los Angeles, CA 90027, USA.
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Bluemke DA, Liddell RP. Can MR imaging provide a noninvasive "biopsy" of the heart to measure iron levels? Radiology 2005; 234:647-8. [PMID: 15734922 DOI: 10.1148/radiol.2343041670] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- David A Bluemke
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Hospital, 600 N Wolfe St, MRI Room 143, Baltimore, MD 21287, USA.
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