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Update on Imaging: Detection of Iron in Liver and Heart

Update on Imaging: Detection of Iron in Liver and Heart. Tim St. Pierre, BSc, PhD Professor School of Physics The University of Western Australia Crawley, Australia. Iron Loading Is Different in Different Organs. Why Is Measurement of Liver Iron Concentration Important?.

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Update on Imaging: Detection of Iron in Liver and Heart

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  1. Update on Imaging: Detection of Iron in Liver and Heart Tim St. Pierre, BSc, PhD Professor School of Physics The University of Western Australia Crawley, Australia

  2. Iron Loading Is Different in Different Organs

  3. Why Is Measurement of Liver Iron Concentration Important? • A patient’s liver iron concentration (LIC) value is the best measure of total body iron stores • A patient’s LIC value enables better informed decisions on when to • Initiate chelation therapy • Increase chelation dose • Decrease chelation dose • Change mode of chelator delivery (eg, IV mode)

  4. LIC Is a Reliable Measure of Total Body Iron Stores in Patients with Thalassaemia Major There is a very strong correlation between LIC and total body iron stores in thalassaemia major patients Abbreviation: LIC, liver iron concentration. With permission from Angelucci E, et al. N Engl J Med. 2000;343:327-331.

  5. LIC Thresholds and Associated Risks 1. Olivieri NF, Brittenham GM. Blood. 1997;89:739-761.

  6. LIC and Long-Term Prognosis 32 thalassaemia major patients followed for median period of 13.6 years after single biopsy LIC measurement Telfer PT, et al. Br J Haematol. 2000;110:971-977.

  7. Why Is Measurement of Heart Iron Important? • Heart iron measurements (by cardiac MRI) have been shown to have a high sensitivity and specificity for predicting cardiac failure within 12 months for thalassaemia major patients • In a study of 652 thalassaemia major patients • 83% of patients who developed arrhythmia had a cardiac T2* of <20 ms • 98% of patients who developed heart failure had a cardiac T2* of <10 ms Kirk P, et al. Circulation. 2009;120: in press.

  8. Relationship Between Liver and Heart Iron

  9. Heart Iron Changes Generally Lag Behind Liver Iron Changes With permission from Noetzli LJ, et al. Blood. 2008;112:2973-2978.

  10. Strengths and Weaknesses of Various Imaging Methods

  11. Methods of Monitoring Iron Loading Serum ferritin Liver biopsy Biomagnetic susceptometry MRI

  12. Methods of Monitoring Body Iron Stores

  13. Is Serum Ferritin a Reliable Indicator of LIC? • Cross-sectional study of 37 patients with sickle cell anaemia and 74 patients with thalassaemia major • Only 57% of the variability in plasma ferritin concentration could be explained by the variation in hepatic iron stores • The 95% prediction intervals for hepatic iron concentration, given the plasma ferritin, were so broad as to make a single determination of plasma ferritin an unreliable predictor of body iron stores • Eg, given a plasma ferritin of 1000 ng/mL, the 95% prediction interval for hepatic storage iron was 0–6.948 mg Fe/g liver, wet weight Brittenham GM, et al. Am J Hematol. 1993;42:81-85.

  14. Serum Ferritin in Thalassaemia Major and Intermedia Abbreviations: TI, Thalassaemia intermedia; TM, Thalassaemia major. With permission from: Origa R, et al. Haematologica. 2007;92:583-588. With permission from: Taher A, et al. Haematologica. 2008;93:1584-1585. Serum ferritin has almost no sensitivity or specificity for iron stores in thalassaemia intermedia

  15. Serum Ferritin Serum ferritin can be used for monitoring trends in patient transfusional iron loading Serum ferritin does not give reliable information on degree of patient iron loading

  16. Measuring Liver Iron Concentration by Biopsy • Methods • Percutaneous • Laparoscopic • Transjugular • Risk of Complications • Death 1:10,000–1:12,000 • Bile leak 1:1,000 • Bleeding 1:100 • Any pain 1:4 • Significant pain 1:10–1:20 Siegel CA, et al. Cleve Clin J Med. 2005;72:199-224.

  17. Heterogeneity of Iron Concentration Throughout the Liver Abbreviations: CV, coefficient of variation; dw, dry weight; LIC, liver iron concentration. Ambu R, et al. J Hepatol. 1995;23:544-549. Barry M, Sherlock S. Lancet.1971;1:100-103. Clark PR, et al. Magn Reson Med. 2003;49:572-575. Emond MJ, et al. Clin Chem.1999;45:340-346. Kreeftenberg HG, et al. Clin Chim Acta. 1984;144:255-262.

  18. Noninvasive Methods of Tissue Iron Measurement Biomagnetic Liver Susceptometry (SQUID)

  19. Biomagnetic Liver Susceptometry Liquid helium Cryogenic package Bellows Liver Liver Fischer R. In: Magnetism In Medicine: A Handbook. Wiley-VCH;1998:286-301.

  20. Needle Biopsy LIC vs Biomagnetic Liver Susceptometry • There is a good correlation between LIC by biopsy and LIC by SQUID up to 3.5 mg Fe/g wet tissue • Above 3.5 mg Fe/g wet tissue, correlation decreases, most likely because of increased sampling error on biopsy Fischer R. In: Magnetism In Medicine: A Handbook. Wiley-VCH;1998:286-301.

  21. Noninvasive Methods of Tissue Iron Measurement Magnetic Resonance Imaging (MRI)

  22. Principles of MRI • Magnetic field and radio signal pulses • Initial pulse excites protons in tissue • Signal received from tissue decays with time after initial pulse • Rate of decay different for different tissues • Rate of decay highly influenced by presence of iron • Rate known as either R2 or R2* depending on data acquisition technique • Characteristic time of decay known as T2 or T2* depending on data acquisition technique Clark PR, St. Pierre TG. Mag Res Imaging. 2000;18:431-438.

  23. Calculating Tissue Iron from MRI Measurements Typical non–iron-loaded tissue Relaxometry methods, eg R2 or R2* Intensity ratio methods The rate at which signal decays is known as R2 or R2* 100 The characteristic time of decay is known as T2 or T2* 80 60 Signal Strength Effect of increasing iron loading 40 20 0 0 5 10 15 20 Echo Time (ms) St. Pierre TG. Ann N Y Acad Sci. 2005;1054:379-385. Graphic courtesy of Dr. Tim St. Pierre.

  24. Methods of Measurement of Tissue Iron Concentrations with MRI Relaxometry measurement of R2 is the most widespread method for measurement of liver iron concentration Relaxometry measurement of T2* is the most widespread method for assessing iron in the heart

  25. Proton Transverse Relaxation Rate (R2) Image and Distribution LIC = 7.7 mg.g-1 Transverse Relaxation Rate R2 (s-1) R2 (s-1) With permission from St. Pierre TG, et al. Blood. 2005;105:855-861.

  26. Liver R2 Images and Distributions Non–iron-loaded subject 3 iron-loaded subjects R2 distribution shifts to higher values as LIC increases With permission from St. Pierre TG, et al. Blood. 2005;105:855-861.

  27. Dissected Liver Samples Mean R2 vs iron concentration for 32 cubes of liver dissected from a single iron–loaded liver postmortem Mean Transverse Relaxation Rate <R2> (s-1) Iron Concentration (mg/g dw) With permission from Clark PR, et al. Mag Res Med. 2003;49:572–575.

  28. Relationship Between R2 and Needle Biopsy LIC (dw) Mean Transverse Relaxation Rate <R2> (s-1) Biopsy Iron Concentration (mg/g dry tissue) With permission from St. Pierre TG, et al. Blood. 2005;105:855-861.

  29. R2-MRI Is a Reliable Measure of LIC High sensitivity and specificity over entire range of LIC encountered Unaffected by presence of fibrosis/cirrhosis Fibrosis stages: 0–1 =  2–4 =  5–6 =  With permission from St. Pierre TG, et al. Blood. 2005;105:855-861.

  30. Example—R2-MRI Measurements to Monitor Iron Chelation Therapy Low iron High iron LIC map Before chelation therapy intervention Mean LIC = 16.0 After 12 months of chelation therapy intervention Mean LIC = 1.6 Graphic courtesy of Dr. Tim St. Pierre.

  31. Methods of Monitoring Heart Iron

  32. Methods for Heart Iron Assessment T2* methods are used to assess heart iron loading Echo time increasing With permission from Westwood M, et al. J Magn Reson Imaging. 2003;18:33-39.

  33. Relationship Between T2* and Cardiac Function With permission from Anderson LJ, et al. Eur Heart J. 2001;22:2171-2179.

  34. Relationship Between R2* and Cardiac Function Transform using R2* = 1/T2* With permission from Anderson, LJ, et al. Eur Heart J. 2001;22:2171-2179. Abbreviation: LVEF, left ventricular ejection fraction. Graphic courtesy of Dr. Tim St. Pierre

  35. Calibration of Cardiac T2*/R2* Against Tissue Iron Concentration Preliminary calibration over small iron concentration range obtained from a single human heart With permission from Ghugre, et al. Magn Reson Med. 2006;56:681-686.

  36. Implementing These Methods at Your Institution

  37. Implementing These Methods at Your Institution • MRI data acquisition • Relatively simple for liver • More involved for heart • Requires extra hardware and software on scanner • MRI data analysis • Problematic for liver • High risk of erroneous analysis due to low signal to noise ratios; need to account for background noise, etc. • Relatively simple for heart

  38. Implementing These Methods at Your Institution • MRI data acquisition • Liver • No face-to-face training required • Heart • May require expert training of technicians • MRI data analysis • Liver • ISO9001 Quality Assurance should be implemented, or data analysis should be outsourced to quality assured core lab • Heart • Technicians should receive training from experts

  39. When to Measure Iron in the Liver vs the Heart • Patients on regular blood transfusion • Measure liver iron annually • Measure heart iron annually after 20 units have been transfused • Patients with hereditary haemochromatosis • Measure liver iron at diagnosis if >40 years of age and serum ferritin >1000 ng/mL • Patients with thalassaemia intermedia • Measure liver and heart iron annually after age 10 years • If the baseline cardiac T2* in normal range, subsequent cardiac T2* no more frequent than 3–5 years unless there is difficulty controlling the liver iron

  40. Conclusions • It is now possible in most major hospitals to monitor iron in the liver and the heart using magnetic resonance imaging • The ability to measure iron in these 2 organs provides the basis for making better informed decisions concerning the need to adjust patients’ chelation regimens

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