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?
• 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)

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 Eng J Med . 2000;343:327-331.

LIC Thresholds and Associated Risks
LIC Threshold
(mg Fe/g dry weight)
1.8
3.2
7.0
15.0
Clinical Relevance
Upper 95% of normal
Suggested lower limit of optimal range for LICs for chelation therapy in transfusional iron overload 1
Suggested upper limit of optimal range for LICs for transfusional iron overload and threshold for increased risk of iron-induced complications 1
Threshold for greatly increased risk for cardiac disease and early death in patients with transfusional iron overload 1
1. Olivieri NF, Brittenham GM. Blood . 1997;89:739-761.

LIC and Long-Term Prognosis
Initial LIC
(mg Fe/g dw)
<7
7 –15
>15
13-Year Cardiac
Disease –Free
Survival
93.3% (SE 6.4)
71.4% (SE 17.1)
50.0% (SE 15.8)
Patients (n)
15
7
10
Group
(i)
(ii)
(iii)
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.

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.

Relationship Between
Liver and Heart Iron

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

Strengths and Weaknesses of
Various Imaging Methods

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

Methods of Monitoring
Body Iron Stores

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.

Serum Ferritin in Thalassaemia
Major and Intermedia
Serum ferritin has almost no sensitivity or specificity for iron stores in thalassaemia 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
• 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

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

Heterogeneity of Iron Concentration
Throughout the Liver
Sample Size and Type
Needle biopsy
(<4 mg dw)
Needle biopsy
(<4 mg dw)
Needle biopsy
(9 mg dw)
“Cubes”
(200 –300 mg wet weight)
“Cubes”
(1000 –3000 mg wet weight)
CV of LIC
19%
>40%
9%
17%
24%
19%
Pathology
Normal
End-stage liver disease
Normal

-thalassaemia
Noncirrhotic

-thalassaemia
Part-cirrhotic
Source
Emond, et al. 1999
Kreeftenberg, et al. 1984
Emond, et al. 1999
Kreeftenberg, et al. 1984
Barry, Sherlock. 1971
Ambu, et al. 1995
Clark, et al. 2003
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.

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

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

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.

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

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.

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

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

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.

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.

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

Relationship Between R2 and
Needle Biopsy LIC (dw)
Biopsy Iron Concentration (mg/g dry tissue)
With permission from St. Pierre TG, et al. Blood.
2005;105:855-861.

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.

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

Methods of Monitoring Heart Iron

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.

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

Relationship Between R2* and
Cardiac Function
With permission from Anderson, LJ, et al.
Eur Heart J.
2001;22:2171-2179.
Abbreviation: LVEF, left ventricular ejection fraction.
Transform using R2* = 1/T2*
100
80
60
40
20
0
0 50 100 150
R2* (s
-1
)
200 250
Graphic courtesy of Dr. Tim St. Pierre

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.

Implementing These Methods at
Your Institution

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

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

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

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