Reduced Transverse Relaxation Rate (RR2) for
Improved Sensitivity in Monitoring Myocardial Iron
Jerry S. Cheung, PhD,1–3Wing-Yan Au, MD,4Shau-Yin Ha, MD,5Daniel Kim, PhD,6
Jens H. Jensen, PhD,6Iris Y. Zhou, BEng,1,2Matthew M. Cheung, BEng,1,2
Yin Wu, PhD,1,2Hua Guo, PhD,1,2,7Pek-Lan Khong, MD,8Truman R. Brown, PhD,9
Gary M. Brittenham, MD,10and Ed X. Wu, PhD1,2*
Purpose: To evaluate the reduced transverse relaxation
rate (RR2), a new relaxation index which has been shown
recently to be primarily sensitive to intracellular ferritin
iron, as a means of detecting short-term changes in myo-
cardial storage iron produced by iron-chelating therapy in
transfusion-dependent thalassemia patients.
Materials and Methods: A single-breathhold multi-echo
fast spin-echo sequence was implemented at 3 Tesla (T)
to estimate RR2 by acquiring signal decays with interecho
times of 5, 9 and 13 ms. Transfusion-dependent thalasse-
mia patients (N ¼ 8) were examined immediately before
suspending iron-chelating therapy for 1 week (Day 0), af-
ter a 1-week suspension of chelation (Day 7), and after a
1-week resumption of chelation (Day 14).
Results: The mean percent changes in RR2, R2, and R2*
off chelation (between Day 0 and 7) were 11.9 6 8.9%,
5.4 6 7.7% and ?4.4 6 25.0%; and, after resuming chela-
tion (between Day 7 and 14), ?10.6 6 13.9%, ?8.9 6
8.0% and ?8.5 6 24.3%, respectively. Significant differen-
ces in R2 and RR2 were observed between Day 0 and 7,
and between Day 7 and 14, with the greatest proportional
changes in RR2. No significant differences in R2* were
Conclusion: These initial results demonstrate that signifi-
cant differences in RR2 are detectable after a single week
of changes in iron-chelating therapy, likely as a result of
superior sensitivity to soluble ferritin iron, which is in
close equilibrium with the chelatable cytosolic iron pool.
RR2 measurement may provide a new means of monitor-
ing the short-term effectiveness of iron-chelating agents
in patients with myocardial iron overload.
Key Words: MRI; cardiac MR; heart; RR2; thalassemia;
iron overload; chelation therapy; ferritin; hemosiderin
J. Magn. Reson. Imaging 2011;33:1510–1516.
C 2011 Wiley-Liss, Inc.
THALASSEMIA, THE MOST common human mono-
genic disease, is caused by impaired and imbalanced
production of globin, the protein component of hemo-
globin (1,2). In severely affected individuals, treatment
of the resultant anemia requires regular red blood cell
transfusion beginning in infancy. Because the body is
unable to effectively excrete excess iron, the iron
within transfused red blood cells progressively accu-
mulates, eventually injuring the heart, liver, pancreas,
and other organs (3). Overall, two-thirds or more of
patients with thalassemia major die of iron-induced
In thalassemia patients with transfusional iron
overload, iron-chelation to remove the excess iron is
1Laboratory of Biomedical Imaging and Signal Processing, The
University of Hong Kong, Pokfulam, Hong Kong SAR, China.
2Department of Electrical and Electronic Engineering, The University
of Hong Kong, Pokfulam, Hong Kong SAR, China.
3Athinoula A. Martinos Center for Biomedical Imaging, Department of
Radiology, Massachusetts General Hospital and Harvard Medical
School, Charlestown, Massachusetts, USA.
4Department of Medicine, The University of Hong Kong, Pokfulam,
Hong Kong SAR, China.
5Department of Pediatrics and Adolescent Medicine, The University of
Hong Kong, Pokfulam, Hong Kong SAR, China.
6Department of Radiology, Center for Biomedical Imaging, New York
University School of Medicine, New York, New York, USA.
7Department of Biomedical Engineering, Tsinghua University, Beijing,
8Department of Diagnostic Radiology, The University of Hong Kong,
Pokfulam, Hong Kong SAR, China.
9Department of Radiology and Biomedical Engineering, Columbia
University, New York, New York, USA.
10Department of Pediatrics and Medicine, Columbia University College
of Physicians and Surgeons, New York, New York, USA.
This work was presented at the 2010 Annual Meeting of International
Society of Magnetic Resonance in Medicine.
Contract grant number: GRF7794/07M; Contract grant sponsor:
HongKong Children Thalassaemia
number: 2007/02; Contract grant sponsor: National Institutes of
Health; Contract grant numbers: R01-DK069373, R01-DK066251,
R37-DK049108, R01-DK049108; Contract grant sponsor: American
Heart Association; Contract grant number: 0730143N.
*Address reprint requests to: E.X.W., Laboratory of Biomedical Imag-
ing and Signal Processing, Departments of Electrical and Electronic
Engineering, Medicine and Anatomy, The University of Hong Kong,
Hong Kong SAR, China. E-mail: email@example.com
Received August 27, 2010; Accepted February 9, 2011.
View this article online at wileyonlinelibrary.com.
Kong ResearchGrant Council;
JOURNAL OF MAGNETIC RESONANCE IMAGING 33:1510–1516 (2011)
C 2011 Wiley-Liss, Inc.
the most direct therapeutic approach (5,6). To prevent
iron toxicity from inadequate chelation therapy and
avoid the adverse effects of excessive chelator admin-
istration, a quantitative means of measuring myocar-
dial iron that is sensitive, safe, and noninvasive is
needed to improve the management of iron-chelating
therapy in transfusion-dependent thalassemia (7).
The use of MRI methods to detect cardiac iron deposi-
tion in the heart has been a crucial advance in the
care of patients with transfusional iron overload
(3,8,9). In particular, measurement of the myocardial
effective transverse relaxation time (T2* ¼ 1/R2*) is a
strong predictor of the risk over one year of cardiac
failure and arrhythmia in patients with thalassemia
major (10). Nonetheless, changes in myocardial R2*
occur at a slow pace, over periods of several months,
even with continuous intravenous therapy with the
iron chelator, deferoxamine, while cardiac function
improves over periods of weeks (11).
The delayed response of myocardial R2* to the
effects of iron-chelating therapy results from differen-
ces in the effects of the major forms of tissue storage
iron on this relaxation rate. In patients with iron over-
load, almost all the excess iron is sequestered within
cells as short-term storage iron in ferritin (soluble
nanometer-sized particles, dispersed, and relatively
uniformly distributed) and as long-term storage iron
in hemosiderin (insoluble and aggregated as irregular
micron-sized clusters within siderosomes) (12,13).
The differences in solubility and intracellular distribu-
tion between ferritin and hemosiderin iron produce
distinct effects on MR signal decay. Dispersed, soluble
ferritin iron affects signal decay principally through
molecular spin-spin relaxation mechanisms (14,15),
while aggregated, insoluble hemosiderin iron primar-
ily induces magnetic field inhomogeneities and causes
spin dephasing through susceptibility effects (16,17).
Because the microscopic magnetic field inhomogene-
ities produced by aggregated iron are very efficient in
causing spin dephasing at field levels of 1.5 Tesla (T)
and above, such conventional relaxation rates, in par-
ticular R2*, are predominately determined by hemo-
siderin iron and will not, in general, accurately reflect
the ferritin iron level.
Cellular ferritin iron is in close equilibrium with the
low-molecular-weight cytosolic iron pool (18,19) that
is involved in cellular injury and eventually organ fail-
ure (20) and is accessible to iron chelators (19). Con-
sequently, measurement of myocardial ferritin iron
may be valuable in assessing the risk of iron toxicity
in the heart and in monitoring the effects of iron-che-
lating agents. Recently, a new MRI approach has been
developed (21) and validated (22–25) for separately
method exploits the property that aggregated hemo-
siderin iron can induce non-monoexponential multi-
echo spin-echo signal decay (17,26). To evaluate the
sensitivity of this new approach, we examined and
compared RR2 with R2* and R2 in detecting myocar-
dial iron changes associated with a brief suspension
and resumption of iron-chelating therapy in transfu-
sion-dependent thalassemia patients. We carried out
cardiac MR examinations at 3T immediately before
discontinuing iron chelation for 1 week, after a 1-
week suspension of chelation, and after a 1-week
resumption of iron chelation. We found that RR2
could detect differences in myocardial ferritin iron af-
ter as little as 1 week of changes in iron-chelating
MATERIALS AND METHODS
In brief, non-monoexponential signal decay in the
presence of dispersed ferritin iron and aggregated he-
mosiderin iron is predicted to approximately follow
SðTEÞ ¼ S0? expð?RR2 ? TEÞ
? expð?A3=4? ðDtÞ3=4? TE3=8Þ;
where S(TE) is the signal amplitude at echo time TE,
S0is the initial signal amplitude, 2 Dt is the interecho
time, RR2 is the reduced transverse relaxation rate,
and A is the aggregation index. In tissues loaded with
both ferritin and hemosiderin iron, RR2 is primarily
sensitive to ferritin iron while A is predominately sen-
sitive to hemosiderin iron (21,22). It is worth nothing
that, in the absence of hemosiderin iron (A ¼ 0), the
signal decay is monoexponential and independent on
the interecho time, and RR2 is simply equal to the
conventional transverse relaxation rate, R2. This
approach could provide an improved characterization
of tissue storage iron and potentially lead to more
accurate estimates of the total storage iron concentra-
Patients and 1-Week Suspension of Iron Chelation
This study was performed in accordance with proto-
cols approved by the Institutional Review Board.
Patients with transfusion-dependent thalassemia (N ¼
8, four males and four females; mean age ¼ 29.3 6
8.6 years) receivingregular
recruited, based on prior measurement of T2* (¼ 21.9
6 3.1 ms) at 1.5T. T2* of 20 6 5 ms was chosen to be
the selection criterion to ensure accurate measure-
ment of RR2, R2, and R2* with sufficient signal-to-
noise ratio and curve-fitting quality at 3T. Note that
the clinical definition of cardiac iron overload is T2* <
20 ms at 1.5T (8). Six patients were being treated with
combination chelation therapy consisting of deferoxa-
mine, 30 to 50 mg/kg for 2 to 5 days weekly and
deferiprone, 55 to 95 mg/kg daily; two were being
treated with deferiprone alone. Left ventricular ejec-
tion fraction measured at 1.5T was 65.1 6 2.9%,
while serum ferritin level was 4475 6 3100 rmol/L in
obtained from all subjects. Cardiac MR was performed
immediately before discontinuing iron chelation for 1
week (Day 0), after a 1-week suspension of chelation
(Day 7), and after a 1-week resumption of iron-chelat-
ing therapy (Day 14). This brief interruption of chela-
tion therapy would likely lead to an increase of ferritin
iron in myocardium due to its close equilibrium with
informed consent was
Monitoring Iron Chelation Effect in Thalassemia Patients 1511
the cytosolic iron pool, which would be expected to
increase during the 1-week suspension of chelation.
With resumption of iron-chelating therapy, the myo-
cardial cytosolic iron pool, and, in turn, the ferritin
iron, would be expected to decrease back to levels
near those observed on Day 0.
A single-breathhold electrocardiography (ECG)-trig-
gered multi-echo fast spin-echo (FSE) sequence (27–
29) was implemented to measure spin-echo signal
decays on a 3T MRI scanner (Achieva, Philips Health-
care, Amsterdam, Netherlands) with maximum gradi-
ent strength of 40 mT/m and slew rate of 200T/m/s,
and a six-channel cardiac coil array for signal recep-
tion. An accelerated multi-echo spin-echo sequence
with a turbo factor of 2, partial Fourier and sensitivity
encoding (SENSE) acquisition, permitted single-slice
multi-echo T2 mapping within a single end-expiratory
acquired per TR (¼ one cardiac cycle) for each effec-
tive TE, with odd echoes occupying the central k-
space lines to minimize the first TE at high field (27).
This multi-echo FSE sequence was previously used to
measure T2 in a group of iron overloaded patients at
3T (27). In brief, one mid-ventricular short-axis slice
with double-inversion black blood preparation was
acquired with acquisition matrix ¼ 128 ? 96, turbo
factor ¼ 2, SENSE factor ¼ 2, partial Fourier factor ¼
0.6, TR ¼ 750–1200 ms, field of view ¼ 370 mm, and
slice thickness ¼ 10 mm for 90?excitation (27,30)
within a single end-expiratory breathhold (?15 car-
diac cycles). Slice thickness of 30 mm was chosen for
180?refocusing to minimize stimulated echo effects
(31). ECG trigger delay was set to the late diastole to
minimize the effect of cardiac wall motion. Spin-echo
signal decays with three different interecho times (5,
9, and 13 ms; six echo images each) were acquired to
estimate RR2. Note that with turbo factor of 2 and
odd echoes occupying the central k-space lines, the
first effective TE was equal to the interecho time while
the subsequent effective interecho spacing of echo
images was twice the interecho time. The minimum
first TE and shortest interecho time (i.e., 5 ms) were
largely limited by the minimum duration of the selec-
tive 180?radiofrequency (RF) pulse, which was in
turn limited by the maximum B1 of 13.5 mT (associ-
ated with 25 kW peak RF power) for body RF trans-
mission. To achieve this minimum TE, a 1.97 ms 90?
self-refocusing excitation pulse was used together
with a 1.52-ms 180?refocusing pulse. The total echo
number (i.e., six effective echoes or echo images for
interecho time of 5 ms) was limited by the maximum
allowable specific absorption rate (SAR) and heart
rates. Gradient crushers were applied around each
refocusing pulse along all three directions with 0.68-
ms duration and intra-voxel phase dispersion of 8.5 p
along each direction. For comparison, R2* measure-
ment was performed in the same slice location using
a single-breathhold ECG-triggered multi-echo gradi-
ent-echo (MEGE) sequence (32) with first TE ¼ 1.55
ms, interecho time ¼ 1 ms, echo number ¼ 25, flip
angle ¼ 20?, turbo field echo factor ¼ 4 and black-
blood preparation (27,30) within a single end-expira-
tory breathhold (?10 cardiac cycles). Before R2 and
R2* scans, B0 shimming was performed in a three-
dimensional volume covering the whole heart region.
To minimize intersubject and intrasubject variation,
all subjectswere trained
breathhold procedure before MRI data acquisition. To
improve measurement accuracy,
described above were repeated five times at the same
slice location during each exam for each subject.
Image and Statistical Analysis
Image analysis was performed using customized anal-
ysis software developed
Natrick, MA). A region of interest (ROI) was placed
within the interventricular septum to minimize the
effect of susceptibility differences from the heart-lung
interface (33–35). Identical ROIs in septum were used
with slight position adjustments to account for motion
among different breathholds (27,30). Spin-echo signal
decays of the three different interecho times were
simultaneously fitted to the non-monoexponential
equation (Eq. ) with floating noise for RR2 measure-
ment, i.e., 18 effective echo signals for estimating four
unknown parameters. Specifically, nonlinear least
square fitting was performed using Levenberg-Mar-
quardt algorithm, with signal intensity for shortest
TE, 10 s?1, 500 s?3/2and signal intensity for longest
TE as initial values for S0, RR2, A and floating noise,
respectively. The fitting performance of the Levenberg-
Marquardt algorithm was tested with different initial
values for RR2 and A, and considered stable because
the estimated parameters converged to the same val-
ues. R2 was calculated using the spin-echo signal
decay with the shortest interecho time (i.e., 5 ms) in
which the magnetic field inhomogeneities and diffu-
sion effects of hemosiderin iron were minimized. Both
R2 and R2* were measured by monoexponential fit-
ting of signal decays with floating noise. Note that the
total acquisition periods of echoes or echo ranges
were different for R2*, R2 and RR2 (26, 55, and 143
ms, respectively). Fitting with floating noise as an
extra parameter was used to account for different
noise levels. The five repeated trials or measurements
were analyzed to obtain the average value for RR2, R2
and R2*. Repeated measures analysis of variance
(ANOVA) with Tukey’s multiple comparison test was
used to compare the RR2, R2, and R2* measurements
among the three time points. Results were expressed
as mean 6 standard deviation (SD). A P-value of less
than 0.05 was considered statistically significant.
Figure 1 illustrates typical septum ROI delineation
and the corresponding multi-echo FSE signal decays
with interecho times of 5, 9, and 13 ms, demonstrat-
ing excellent reproducibility among five trials or
breathhold measurements during a single MRI exam.
The typical ROI size was 214 6 55 mm2in all patients
1512Cheung et al.
at different time points. Note that the zigzag decay of-
ten observed by traditional Carr-Purcell Meiboom-Gill
(CPMG) multi-echo spin-echo sequences was absent
here because both odd echoes and the following even
echoes were combined with the central k-space lines
occupied by odd echoes. Figure 2 shows representa-
tive spin-echo signal decays in the septum ROI of dif-
ferent interecho times (5, 9, and 13 ms), indicating
significant interecho time dependence and non-mono-
exponentiality of the signal decays.
Figure 3 shows the RR2, R2, and R2* changes in
patients before (Day 0), and after chelation suspen-
sion (Day 7) and then 1 week after resuming iron che-
lation (Day 14). As compared with Day 0 (19.8 6 5.6
s?1), RR2 increased significantly (P < 0.01) at Day 7
(22.1 6 5.4 s?1); then decreased significantly (P <
0.01) at Day 14 (20.0 6 5.6 s?1). When compared
with Day 0 (34.5 6 10.7 s?1), R2 increased (P < 0.05)
at Day 7 (37.0 6 12.8 s?1); and then decreased (P <
0.01) at Day 14 (33.5 6 11.1 s?1). No significant dif-
ferences in R2* were found between different time
points (76.5 6 35.9 s?1, 74.1 6 39.0 s?1and 71.9 6
43.3 s?1at Day 0, 7, and 14, respectively). This find-
ing indicates that transverse relaxation rates RR2 and
R2, especially RR2, are more sensitive in detecting
changes in myocardial iron. Between Day 0 and 7, the
mean percent changes in RR2, R2 and R2* were 11.9
6 8.9%, 5.4 6 7.7% and ?4.4 6 25.0%, respectively.
Between Day 7 and 14, the mean percent changes in
RR2, R2 and R2* were ?10.6 6 13.9%, ?8.9 6 8.0%
and ?8.5 6 24.3%, respectively. Note that no signifi-
cant differences were found in R2 computed with
other interecho times (i.e., 9 and 13 ms) as well as the
average of three R2 values computed from three inter-
echo times (data not shown).
Within the cytoplasm of cells, metabolically active iron
is present physiologically in low-molecular-weight
forms destined for incorporation into functional com-
pounds or, if present in amounts exceeding cellular
requirements, for storage (36). Excess iron is normally
first stored within the protein shell of ferritin, which
Figure 1. Typical ROI delineation in interventricular septum
(left) and the corresponding multi-echo fast spin-echo (FSE)
signal decays of repeated scans (right), demonstrating excel-
lent reproducibility among five trials or breathhold measure-
ments during a single MRI exam. Note that, with turbo factor
of 2 and odd echoes occupying the central k-space lines, the
first effective TE was equal the interecho time and while the
subsequent effective interecho spacing of echo images was
twice the actual interecho time. The signal intensities at the
first TE in repeated measurements were normalized to unity
for comparison. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
spin-echo signal decays in the
interventricular septum of dif-
ferent interecho times (5, 9,
and 13 ms; six effective ech-
oes each) in linear scale (a)
and in logarithmic scale (b),
Monitoring Iron Chelation Effect in Thalassemia Patients1513
is soluble and diffusely distributed within cells (12).
As the amount of cellular iron to be stored increases
further, the iron is gathered within insoluble aggre-
gates and clumps of varying sizes identified as hemo-
siderin (13). As the total amount of tissue iron
increases, the proportion stored as hemosiderin rises,
from trace amounts in normal individuals to 90% or
more in patients with severe iron overload (37).
Increases in the amount of cytosolic iron that exceed
the cellular capacity for safe storage are believed to
result in oxidative damage, ultimately leading to cell
death, organ injury and failure (20). Recent studies
have provided compelling evidence that iron entry and
exit from ferritin are the result of an equilibrium
based on the concentration of cytosolic iron (18,19),
suggesting that ferritin iron may serve as indicator of
cellular toxicity. Moreover, all three iron-chelating
agents in clinical use, deferasirox, deferiprone, and
deferoxamine, decrease the intracellular concentration
of ferritin iron, although by different mechanisms.
Therefore, noninvasive measurement of cellular ferri-
tin iron may provide early warning of iron-induced
toxicity, and permit rapid monitoring of the effective-
ness of iron-chelating regimes.
In the presence of both ferritin and hemosiderin
iron, the analytic form of the signal decay, as shown
in Eq. , can be regarded as a product of the mono-
exponential factor and a non-monoexponential factor
that describes the more complex effects of diffusion in
the spatially inhomogeneous field generated by aggre-
gated hemosiderin iron (21,22). Most importantly, the
effects of ferritin and hemosiderin iron on the signal
decay are largely reflected in RR2 and A, respectively.
The findings in the current study demonstrate the
ability of RR2 to detect myocardial iron changes asso-
ciated with a 1-week suspension of iron-chelating
patients. The current results also show that RR2 after
resumption of chelation (Day 14) normalized to the
baseline level (Day 0). Moreover, RR2 is shown to be
more sensitive in detecting changes in myocardial
iron than the commonly used relaxation rates includ-
ing R2* and R2. These initial results suggest the feasi-
bility of better characterization of myocardial storage
iron, particularly ferritin iron, using the new trans-
verse relaxation index RR2. This is likely a result of
its superior sensitivity to soluble ferritin iron, which is
in close equilibrium with the cytosolic iron pool that
is expected to increase during the 1-week suspension
of chelation and then decrease after resumption of
iron-chelating therapy (18,19,38). Furthermore, along
with the hemosiderin iron index A, RR2 approach
may allow more accurate measurements of total tis-
sue storage iron burden (21,22).
Clinically, determination of T2* (¼ 1/R2*) in the
interventricular septum has been used directly as an
index of total myocardial storage iron (8,11,39). How-
ever, Anderson et al showed that myocardial T2*,
Figure 3. Reduced transverse
(using interecho time of 5 ms),
and R2* values at Day 0 (on
regular chelation), Day 7 (off
chelation for 1 week), and Day
14 (on chelation again for 1
ANOVA with Tukey’s multiple
formed with **P < 0.01, *P <
0.05, n.s. for insignificance.
DFO ¼ deferoxamine; L1 ¼
deferiprone. [Color figure can
be viewed in the online issue,
1514 Cheung et al.
which is predominately sensitive to hemosiderin iron,
changed only slowly after months of intensive iron-
chelating therapy, despite significantly improved car-
diac function within weeks (11). In line with this find-
ing, no significant difference in R2* was found after
suspending and resuming chelation therapy in the
current study. Myocardial hemosiderin iron, as esti-
mated by R2*, would be expected to change little dur-
ing the 1-week periods in our study. It should be
noted that methods based on a single metric, such as
R2* or R2, have an associated uncertainty reflecting
variations in the relative amounts of ferritin and he-
mosiderin iron (40). In particular, these methods can-
not accurately quantify ferritin iron levels in patients
with high iron levels, in which ferritin iron can only
be a small fraction of the total iron storage. It is note-
worthy that because myocardial R2* increases promi-
nently at 3T as compared with 1.5T, it is technically
challenging to use R2* as an iron overload index at 3T
where the shortest TE and interecho time can be lim-
ited by the peak RF power and gradient strength.
More importantly, R2* measurement at high magnetic
field (> 1.5T) is more vulnerable to increased B0 inho-
mogeneity likely resulted from the increased suscepti-
bility and shimming related effects.
With recent advances in the development of multi-
echo FSE sequences that permit accurate acquisitions
of multi-echo spin-echo signals in the heart during a
single breathhold (27–29), the RR2 measurement by
acquiring spin-echo signal decays with three or more
different interecho times has become feasible and
practical with a clinically acceptable examination
time. Given the specific interecho time dependence
predicted by Eq. , use of two or more signal decays
with different interecho times for fitting could improve
the accuracy of RR2 measurement (22). Acquiring sig-
nal decays with three different interecho times as
used in this study would be a reasonable compromise
between accuracy and scan time for clinical applica-
tions. In addition, signal-to-noise ratio increase at 3T
can facilitate the acceleration of breathhold acquisi-
tion sequence by use of large SENSE factor and half-
Fourier sampling as demonstrated in the current
study. Such reduction of breathhold time can be a
major advantage in patient study, likely leading to
more patient comfort and reliable measurements at
3T. On the other hand, it should be noted that for
images with long echo times, signal-to-noise ratio
could be compromised by increased R2 at 3T com-
pared with 1.5T (34,41). Because R2* at high field
increases substantially and its quantitation is vulner-
able to increased B0 inhomogeneity, the rapid myo-
cardial R2 and RR2 measurement protocols demon-
stratedin this studymay
alternative to the traditional R2* measurement for
assessment of cardiac iron overload at 3T. Note that
patient recruitment in this study was based on prior
measurements of T2* (¼ 21.9 6 3.1 ms) at 1.5T with
selection criterion (i.e., T2* ¼ 20 6 5 ms) to exclude
patients with severe iron overload. This was to ensure
sufficient signal-to-noise ratio in the signal decays at
3T, consequently improving the data and curve-fitting
consistency and quality for RR2, R2, and R2* meas-
urements. However, this selection criterion could also
be a limitation of the current study because RR2
method could not be verified in patients outside this
range of T2* (20 6 5 ms at 1.5T). In addition, such
selection criterion also limited the number of patients
studied (N ¼ 8) at our institution. Future study with-
out T2* range restriction in a larger number of
patients is warranted to further evaluate and validate
the RR2 technique.
In conclusion, the experimental findings in this
study demonstrate that RR2 measurement can detect
myocardial iron changes associated with brief (1
week) changes in iron-chelating therapy in patients
with transfusion-dependent thalassemia. While fur-
ther studies in larger numbers of patients with wider
ranges of iron loading over longer periods of time are
needed, these initial results suggest that estimation of
myocardial ferritin iron level by measuring RR2 may
serve as a promising new means to rapidly evaluate
the effectiveness of iron-chelating regimes in thalasse-
mia patients. RR2 measurement may also allow moni-
toring the risk of iron-induced toxicity in patients
with iron overload and be helpful in the evaluation of
new candidate iron chelators.
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