Acw Radiologica 41 (2000) 348-351
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`ACTA RADIOLOGICA
`ISSN 0284-1851
`
`NON-INVASIVE MYOCARDIAL IRON ASSESSMENT IN
`THALASSAEMIC PATIENTS
`
`T2 relaxometry and magnetization transfer ratio measurements
`
`N. PAPANlKOLAOU 1, A. GHIATAS2, A. K ATTAM1s3, C. L ADIS3, N. KRmKos2 and C. KATTAMIS3
`1 Philips Greece Medical Systems_ Department of MR Clinical Science. 1Iaso Hospital and 3Department of Radiology, Agia
`Sophia Childrens Hospital, Athens. Greece.
`
`Abstract
`Key ll'ords: Thalassaemia, MR T2
`Purpose: To compa re T2 relaxometry and magnetization transfer ratio
`(MTR) measurements of myocardial tissue in normal voluntee
`and thalassa- -
`relaxometry; iron; magnetization
`transfe r ratio.
`emic patients fo r assessment of the myocardial iron levels. ~
`Material a11d Merliods: All examinatio ns were done o a I T MR sys m
`using a multi-echo spin-echo sequence with 8 echoes for 2 measurements a d
`ic cardiac tri cr
`ng
`a gradient echo sequence for MTR measurements. Diast
`was used in both sequences. Ten patients a nd I 0 normal SUDJ
`e mcluded
`in the study. T2 a nd MTR measurements were correlated with serum ferriti n
`levels.
`Results: Regression ana lysis between T2 and MTR measurements and ferritin
`demonstrated a reversed linear relationship. (r=-0.932, p < 0.05) a nd (r=
`- 0.824, p < 0.05). respectively. Mean T2 relaxa tion time a nd mean MTR of the
`norma l subjects (57.95±4.9 ms and 43.70±3.3%) was significantly higher than
`that of the thalassaemic paii~nts (38.8 ± 6.2 ms a nd 26.40± 6. 1%) (p< 0.01), re-
`. , }
`spectively.
`Co11c/11sio11: MTR measurements can be used to complement T2 measure(cid:173)
`ments for non-invasive myocardial iron assessment.
`
`Correspo11de11ce: Nicko las
`Papanikolaou , Philips Greece
`Medical Systems, leroloxiton 12 1,
`Heraklion. G RE-71 305 Crete.
`Greece. FAX + 30 8 1 237652.
`
`Accepted for p11blicario11 25 January
`2000.
`
`Iron deposits in various tissues have been well cor(cid:173)
`related with l/T2 relaxation rate. Liver l/T2 values
`were fo und to be linearly dependent on iron tissue
`concentration in patients with haemosiderosis (7,
`10, 14). Brain iro n deposits were also correlated
`with 1/T2 values in basal ganglia in normal sub(cid:173)
`jects (I, 18). Despite the technical difficulties to es(cid:173)
`timate the T2 constant with high accuracy, several
`groups have proved the clinical potential of MR
`relaxometry in the evaluation of iron deposits in
`several tissues.
`Magnetization transfer ratio (MTR) measure(cid:173)
`ments were used in several clinical applications like
`differentiation between active and chronic multiple
`sclerosis lesions (5), brain and hepatic tumour
`
`348
`
`characterisation ( 11, 13 ). Magnetization transfer
`(MT) effect is most prominent in tissues with mac(cid:173)
`romolecular biochemical compositio n, including
`muscle, myocardium, liver, white and grey matter
`(17).
`In thalassemic patients, iron deposits are more
`pronounced in liver and myocardial tissue. Serum
`ferritin test has'been used to monitor iron levels in
`such patients but it suffers from high inaccuracy
`especially when an inflammation is present. An(cid:173)
`other approach to quantify the iron in liver is by
`biopsy which is an accurate, but invasive, tech(cid:173)
`mque.
`Since one of the major complications in thalas-
`saemic patients is cardi
`·
`· nc due to ex-
`EXHIBIT
`'
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`1 bx , D 5to
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`1 of 4
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`Taro Pharmaceuticals, Ltd.
`Exhibit 1056
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`

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`NON-INVASIVE MYOCARDIAL TRON ASSESSMENT IN THALASSEMTC PATIENTS
`
`tensive iron deposits in the myocardial tissue, a
`technique capable of monitoring the iron levels
`would be desirable.
`In this study we have made T2 and MTR meas(cid:173)
`urements of the myocardial tissue in normal sub(cid:173)
`jects and thalassacmic patients in order to evaluate
`these techniques for monitoring myocardial iron
`levels.
`
`Material and Methods
`
`Ten patients with thalassaemia and IO normal sub(cid:173)
`jects were investigated. Patients' mean age was 24
`years ( l 9-32 years) while normal subjects' mean
`age was 28 years (24--35 years). Serum ferrit in
`values were recorded in all patients. T2 measure(cid:173)
`ments were obtained by using a multiecho spin(cid:173)
`echo sequence with 8 echoes (20, 40, 60, 80, lOO,
`120, 140 and 160 ms). All measurements were done
`using a 1.0 T MR system (Gyroscan NT-TIO, Phil(cid:173)
`ips Medical Systems). One slice was acquired in
`do uble oblique plane (Fig. l ) and the slice thick(cid:173)
`ness was 10 mm. T he field-of-view was 230X350
`mm2 while the matrix was l28X256. TR ranged
`from 1,800 to 2,500 ms depending on patient
`heartbeat. The MTR measurements were done
`using a dynamic gradient echo sequence (fast field
`echo) with TRs ranging from 700 to l ,000 ms de(cid:173)
`pending on patient heartbeat, TE of 7 ms and flip ·
`angle of 30°. This acquisition consisted of two
`identical dynamic scans. The only difference be(cid:173)
`tween the first and the second scan was that in the
`second an additional on-resonance MT prepulse
`was added. Ten slices were acquired with a slice
`thickness of 6 mm and an interstice gap of 0.6 mm.
`Both sequences were cardiac-synchronized with a
`delay time of 400 ms frQQl the R-pulse, resulting in
`diastolic triggering. We used diastolic triggering in
`order to reduce the motion artefacts from cardiac
`pulsation. Additionally, a
`flow compensation
`gradient scheme was used to reduce ghosting from
`blood pulsation in the left ventricle. Acquisition
`time was 10 to 12 min due to the use of cardiac
`and respirato ry triggering techniques.
`Image analysis, 12 calculation: Signal intensity
`measurements were done using a region-of-interest
`(ROI) placed in myocardial tissue in all 8 echoes.
`The background signal was also measured by pla(cid:173)
`cing a ROI in the air (avoiding ghost artefacts) and
`the noise level was measured using the SD-value
`of the air. The background signal intensities were
`subtracted from the myocardial signal intensities
`and a noise-weighted non-linear least squares fit(cid:173)
`ting algorithm was used to calculate the T2 con(cid:173)
`stant of the myocardial tissue.
`MTR calculation: Signal intensity of the myo-
`
`cardial tissue was recorded by placing a ROI (Fig.
`l) in both dynamic images (with and without MT
`prcpulse). MTR was calculated using the following
`formula:
`
`MTR= 1 OO*(Sla - Sib )/Sia
`
`where Sia represented the myocardial signal inten(cid:173)
`sity without an MT prepulse and Slb represented
`the myocardial signal intensity with an MT pre(cid:173)
`pulse.
`Statistical analysis: Mean T2 and MTR values
`were calculated for patients and normal subjects.
`A Student's t-test was used to compare T2 and
`MTR mean values between patients and normal
`subjects with a p-value less than 0.0 l considered as
`significant. A linear regression analysis with scrum
`ferritin values was performed for both measure(cid:173)
`ments on patients a nd a correlation coefficient was
`recorded. Statistical analysis was do ne on a per(cid:173)
`sonal computer using Instat Software (GraphPad
`Software Inc.).
`
`ResuJts
`
`Mean myocardial T2 value and SD in patients was
`38.84±6.2 ms while in normal subjects it was
`57.95±4.9 ms (p< 0.01). The mean MTR value and
`Sb in patients was 26.4±6. l while in normal sub(cid:173)
`jects it was 43. 7±3.3 (p<O.O l) (Fig. 2). Mean
`
`Fig. 1. Four images of the multiecho spin-echo acquisition cor(cid:173)
`responding to echo times of 20 ms (upper left). 40 ms (upper
`right). 100 ms (lower left) a nd l-lO ms (lower right).
`
`349
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`Taro Pharmaceuticals, Ltd.
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`N. PAPANIKOLAOU ET AL.
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`60
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`50
`
`40
`
`30
`
`20
`
`10
`oJ.-_ _.
`MTR(+) MTR(-)
`
`T2 (-)
`T2 (+)
`Fig. 2. Mean myocardial MTR, T2 values and SD of the patient
`group ( + ) and the control group (- ).
`
`scrum ferritin level and SD for the patient group
`was 2 128.7±801 µg/1. Linear regression analysis
`showed a very good reversed linear relationship be(cid:173)
`tween serum ferritin levels and T2 value with a cor(cid:173)
`relation coefficient r=-0.932 (p< O.Ol), and serum
`ferritin levels and MTR value also sl1owed a very
`good reversed linear relationship with a correlation
`coefficient r=-0.824 (p<0.05).
`
`Discussion
`
`The presence of iron in myocardium results in T2
`shortening. The effect is caused by dephasing of
`water protons as they diffuse through local field
`gradients induced by iron. This effect depends lin(cid:173)
`early on the amount of iron (9). Several investi(cid:173)
`gators have tried to quantify iron in various tissues
`in vitro by utilizing T2 relaxometry (3, 12, 16) with
`successful results using NMR spectrometers. Other
`groups (7, 10, 14) have utilized whole-body im(cid:173)
`agers to quantify in vivo irpp deposition. The main
`problem of this approach is the low accuracy of
`the measurements.
`The systematic errors include radio frequency
`pulse imperfections, susceptibility artefacts and
`timing errors responsible for low accuracy of T2
`measurements in a whole-body imager (6, 8). An(cid:173)
`other major limitation of T2 relaxometry is the
`fact that human tissues have large intrinsic vari(cid:173)
`ation of the T2 values. The limitations of accurate
`T2 calculations in patients with high-grade haemo(cid:173)
`siderosis performed on a standard whole-body im(cid:173)
`ager compared to a NMR spectrometer were re(cid:173)
`ported by DIXON & STYLES (4). The main draw(cid:173)
`backs of using a whole-body unit are low signal(cid:173)
`to-noise ratios, limited number of echoes (less than
`32) and long inter-echo intervals.
`BOTTOMLEY et al. reported normal myocardial
`T2 to be around 57± 16 ms (2) while the myocar(cid:173)
`dial T2 constant in thalassaemic patients could go
`
`350
`
`down to 10 ms. The prerequisite to accurately
`quantify high iron levels was the use of a large
`number of echoes at the first 50 ms in order to
`sample the exponential T2 decay of the iron-rich
`tissue with better accuracy.
`MTR measurements were made by utilizing a
`gradient recalled sequence with and without an
`magnetic transfer constant on-resonance prepulse.
`This approach proved less susceptible to artefacts
`and more robust than T2 relaxometry, while the
`correlation coefficient with serum ferritin levels in
`thalassaemic patients was comparable to that of
`T2 relaxometry. MTR values in iron-rich tissues
`are reduced ( 15) since iron possibly destroys the
`normal myocardial macromolecules which are sub(cid:173)
`jected to MT effects. The reduction in MTR values
`seems to be linearly dependent on the iron concen(cid:173)
`tration.
`In conclusion, MTR measurements may be used
`instead of or in addition to T2 relaxometry in the
`evaluation of myocardial iron deposition using a
`whole-body unit. However, an extended study is
`necessary to confirm our preliminary findings.
`
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`NON-INVASIVE MYOCARDIAL IRON ASSESSMENT fN THALASSEMIC PAT IENTS
`
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`
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`351
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`4 of 4
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`Taro Pharmaceuticals, Ltd.
`Exhibit 1056
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