Abstract

Aims

Magnetic resonance (MR) imaging is widely used for diagnostic imaging in medicine as it is considered a safe alternative to ionizing radiation-based techniques. Recent reports on potential genotoxic effects of strong and fast switching electromagnetic gradients such as used in cardiac MR (CMR) have raised safety concerns. The aim of this study was to analyse DNA double-strand breaks (DSBs) in human blood lymphocytes before and after CMR examination.

Methods and results

In 20 prospectively enrolled patients, peripheral venous blood was drawn before and after 1.5 T CMR scanning. After density gradient cell separation of blood samples, DNA DSBs in lymphocytes were quantified using immunofluorescence microscopy and flow cytometric analysis. Wilcoxon signed-rank testing was used for statistical analysis. Immunofluorescence microscopic and flow cytometric analysis revealed a significant increase in median numbers of DNA DSBs in lymphocytes induced by routine 1.5 T CMR examination.

Conclusion

The present findings indicate that CMR should be used with caution and that similar restrictions may apply as for X-ray-based and nuclear imaging techniques in order to avoid unnecessary damage of DNA integrity with potential carcinogenic effect.

See page 2337 for the editorial comment on this article (doi:10.1093/eurheartj/eht214)

Introduction

Magnetic resonance (MR) imaging is a widely used and well-established non-invasive medical diagnostic imaging tool. By using a static and a gradient magnetic field in combination with a radiofrequency field (RF), MR provides excellent contrast among different tissues of the body including the brain, musculoskeletal system, and the heart. Although long-term effects on human health from exposure to strong static magnetic fields seem unlikely,1 acute effects such as vertigo, nausea, change in blood pressure, reversible arrhythmia,2 and neurobehavioural effects have been documented from occupational exposition to 1.5 T.3 Cardiac MR (CMR) imaging requires some of the strongest and fastest switching electromagnetic gradients available in MR exposing the patients to the highest administered energy levels accepted by the controlling authorities.4 Studies focusing on experimental teratogenic5–9 or carcinogenic10–12 effects of MR revealed conflicting results. Since CMR is emerging as one of the fastest growing new fields of broad MR application,13 it is of particular concern that a recent in vitro study with CMR sequences has reported on CMR-induced DNA damages in white blood cells up to 24 h after exposure to 1.5 T CMR.4 It is in this context that the European Parliament,14 the International Commission on Non-Ionizing Radiation Protection (ICNIRP),15,16 and the World Health Organization (WHO)17 have urgently called for an action in order to evaluate adverse biological effects of clinical MR scanning.

The aim of the present study was to assess the impact of routine CMR scanning on DNA double-strand breaks (DSBs) of peripheral blood mononuclear cells (PBMCs) as a measure of the carcinogenic potential of this examination.

Methods

Twenty consecutive patients referred for cardiac evaluation were included. After obtaining written informed consent, 10 mL of peripheral blood was drawn before and after undergoing routine contrast (gadobutrolum, Gadovist, Bayer Schering Pharma, Germany) enhanced CMR examination18 on a 1.5 T MR scanner (Philips Achieva, Best, NL, USA) as approved by the local ethics committee (KEK-Nr. 849). PBMCs were obtained using density gradient separation (Histopaque 1077, Sigma-Aldrich) as previously established.19

The clinical CMR protocol used in our daily routine has been recently reported in detail.20 In brief, a commercially available MR scanner (Philips 1.5 T, Achieva, software release 3.2.1) equipped with a maximum gradient strength of 42 mT/m and a maximum gradient speed of 180 mT/m/ms was used. The following standard pulse sequences to generate images were used: gradient echo, steady-state free precession, FastSE, T2-weighted double-inversion black-blood spin-echo sequence for oedema imaging, balanced SSFP sequence for perfusion and inversion recovery segmented gradient echo sequence for late gadolinium enhancement.

DSBs were detected by immunofluorescence microscopy using a rabbit-anti-human phospho-histone γ-H2AX and a goat-anti-rabbit-AlexaFluor-488 antibody (CST Cell Signalling Technology, adapted from May et al.21). Cell nuclei were counterstained with 4′,6-diamidino-2-phenylindole (DAPI, Vector Laboratories) and the γ-H2AX foci per lymphocyte were visualized on an inverse confocal microscope (CLSM-Model SP5, Leica Microsystems) and quantified by a blinded observer.

With flow cytometry (FACScanto, BD Bioscience), DSBs were additionally quantified in T-lymphocytes22,23 previously identified by a mouse-anti-human CD3-APC antibody (Life Technologies). Based on forward and side light scattering, PBMCs were gated for viable single-cell events and proper compensation controls were used in flow cytometric analyses to correct for spectral overlap. Data from flow cytometric quantification (MFI, geometric mean of fluorescence intensity of γ-H2AXpositive T-lymphocytes) was evaluated using FlowJo software (V10.0.2, Tree Star, Inc.).

Based on a variation of γ-H2AX assessment at 20% as reported by Muslimovic et al.,22 an average difference in γ-H2AX findings reported in ex vivo experiments,4 aiming at alpha = 0.05 and a power (1 − β) of 0.8, the number of patients necessary was calculated between 10 and 15.

SPSS 20.0 (SPSS, Chicago, IL, USA) was used for all statistical analysis. The Shapiro–Wilk test was applied to exclude normal distribution of data sets. This was followed by testing for significant differences between DSBs before and after CMR examination by using the Wilcoxon signed-rank test. P-values of <0.05 (two-tailed) were considered statistically significant.

Results

Mean age of patients was 53 ± 13 years and 16 (80%) were males. Ten patients were referred for evaluation of cardiomyopathy and 10 for the assessment of myocardial ischaemia. The mean CMR scan duration was 68 ± 22 min with an average contrast media bolus of 15 ± 4 mL. The patient baseline characteristics are given in Table 1.

Table 1

Patient baseline characteristics (n = 20)

Age (years ± SD) 53 ± 13 
BMI (kg/m2 ± SD) 25 ± 4 
Male, n (%) 16 (80) 

 
Cardiovascular risk factors, n (%) 
 Arterial hypertension 6 (30) 
 Diabetes mellitus 4 (20) 
 Dyslipidaemia 4 (20) 
 Smoking 2 (10) 
 Positive family history 1 (5) 

 
Medications, n (%) 
 Aspirin 7 (35) 
 Beta-blocker 9 (45) 
 ACE/angiotensin II inhibitor 8 (40) 
 Statin 7 (35) 
Age (years ± SD) 53 ± 13 
BMI (kg/m2 ± SD) 25 ± 4 
Male, n (%) 16 (80) 

 
Cardiovascular risk factors, n (%) 
 Arterial hypertension 6 (30) 
 Diabetes mellitus 4 (20) 
 Dyslipidaemia 4 (20) 
 Smoking 2 (10) 
 Positive family history 1 (5) 

 
Medications, n (%) 
 Aspirin 7 (35) 
 Beta-blocker 9 (45) 
 ACE/angiotensin II inhibitor 8 (40) 
 Statin 7 (35) 

SD, standard deviation; BMI, body mass index.

By immunofluorescence microscopy (Figure 1), the median number of DSBs (foci, Table 2) per lymphocyte in baseline samples was 0.066 (range: 0–0.661) and increased significantly (P < 0.05) after CMR exposure to 0.190 (range: 0–1.065, Figure 2).

Table 2

Increase in double-strand breaks after cardiac magnetic resonance assessed by immunofluorescence

  Microscopy foci per lymphocyte
 
Flow cytometry MFI
 
Before After Before After 
Mean 0.143 0.270* 2989 3395* 
SD 0.191 0.227 850 906 
Median 0.066 0.190* 2758 3232* 
MAD 0.137 0.199 640 696 
IQR 0.169 0.257 1133 1198 
  Microscopy foci per lymphocyte
 
Flow cytometry MFI
 
Before After Before After 
Mean 0.143 0.270* 2989 3395* 
SD 0.191 0.227 850 906 
Median 0.066 0.190* 2758 3232* 
MAD 0.137 0.199 640 696 
IQR 0.169 0.257 1133 1198 

IF, immunofluorescence (units are foci per lymphocyte); MFI, geometric mean of T-lymphocyte fluorescence intensity (arbitrary units); γ-H2AX, marker of DSBs; SD, standard deviation; MAD, median absolute deviation; IQR, interquartile range.

*Indicates P < 0.05 vs. before.

Figure 1

Visualization of double-strand breaks (DSBs) in nuclei (arrow heads) of human lymphocytes of two patients before and after cardiac magnetic resonance scans by immunofluorescence microscopy. DSBs (foci, white arrows) are detected by γ-H2AX staining (green).

Figure 1

Visualization of double-strand breaks (DSBs) in nuclei (arrow heads) of human lymphocytes of two patients before and after cardiac magnetic resonance scans by immunofluorescence microscopy. DSBs (foci, white arrows) are detected by γ-H2AX staining (green).

Figure 2

Amount of double-strand breaks before and after cardiac magnetic resonance (CMR) scan by immunofluorescence microscopy. After CMR scanning, there was a significant increase (*P < 0.05) in γ-H2AX foci per lymphocyte by immunofluorescence microscopy. Bars indicate median values with median absolute deviation (left panel) and individual values are interconnected with a line (right panel).

Figure 2

Amount of double-strand breaks before and after cardiac magnetic resonance (CMR) scan by immunofluorescence microscopy. After CMR scanning, there was a significant increase (*P < 0.05) in γ-H2AX foci per lymphocyte by immunofluorescence microscopy. Bars indicate median values with median absolute deviation (left panel) and individual values are interconnected with a line (right panel).

In T-lymphocytes, flow cytometry (Figure 3) revealed a median MFI (arbitrary units) of 2758 (range: 1907–5109) before and 3232 (range: 2413–5484) after CMR (P < 0.005, Table 2 and Figure 4).

Figure 3

Flow cytometric analysis of double-strand breaks (γ-H2AXpositive T-lymphocytes) before and after cardiac magnetic resonance (CMR) scan. T-lymphocytes were readily identified by representative dot plots and histograms (lymphocytes, DAPI, and CD3). The shift of the left curve (red, before CMR) to the right curve (blue, after CMR) in the presented overlay indicates an increase in double-strand breaks (γ-H2AXpositive T-lymphocytes). SSC-A: side scatter channel area. FSC-A: forward scatter channel area. DAPI: 4′,6-diamidino-2-phenylindole, counterstaining cell nuclei. CD3: mouse-anti-human CD3-APC antibody counterstaining specifically the T-lymphocytes.

Figure 3

Flow cytometric analysis of double-strand breaks (γ-H2AXpositive T-lymphocytes) before and after cardiac magnetic resonance (CMR) scan. T-lymphocytes were readily identified by representative dot plots and histograms (lymphocytes, DAPI, and CD3). The shift of the left curve (red, before CMR) to the right curve (blue, after CMR) in the presented overlay indicates an increase in double-strand breaks (γ-H2AXpositive T-lymphocytes). SSC-A: side scatter channel area. FSC-A: forward scatter channel area. DAPI: 4′,6-diamidino-2-phenylindole, counterstaining cell nuclei. CD3: mouse-anti-human CD3-APC antibody counterstaining specifically the T-lymphocytes.

Figure 4

Amount of double-strand breaks before and after cardiac magnetic resonance scan by flow cytometry of γ-H2AXpositive T-lymphocytes using geometric mean fluorescence intensity (MFI). The median MFI increased significantly after cardiac magnetic resonance scanning (*P < 0.005, left panel). Individual values are interconnected with a line (right panel).

Figure 4

Amount of double-strand breaks before and after cardiac magnetic resonance scan by flow cytometry of γ-H2AXpositive T-lymphocytes using geometric mean fluorescence intensity (MFI). The median MFI increased significantly after cardiac magnetic resonance scanning (*P < 0.005, left panel). Individual values are interconnected with a line (right panel).

Discussion

We show here that clinical routine CMR scanning exerts genotoxic effects. Although many experimental in vitro studies have suggested DNA damage after exposure to MR imaging, we present the first in vivo results documenting that contrast CMR scanning in daily clinical routine is associated with increased lymphocyte DNA damage.

The different components of the magnetic field during CMR may have contributed to the observed DNA damage. The gradient field generated during MR scanning includes extremely low frequencies (ELF), which have been classified by the International Agency for Research on Cancer (IARC) as possible human carcinogen (group 2B)24 based on a large body of literature on the genotoxic effects of ELF magnetic fields.25–28 The latter seem to be involved directly and indirectly in DNA and chromosomal damage by inducing reactive oxygen species.29 Similarly, DNA damage and chromosome alterations have been discussed after exposure to RF.

Our results do not allow commenting on the persistence of the induced DNA damage, although this is a key issue of genetic risk assessment, because damage can trigger DNA instability and exert tumourigenic effects. Due to the long time delay between DSB induction and resulting cancer development, our study cannot quantify such long-term effects as this was beyond the scope of the present study. This, however, is true in principle for any observation of DSB induction from any diagnostic radiation exposure including ionizing radiation, for which no direct observational proof of its adverse impact on outcome is available due to the small scale of damage and the long delay between exposure and event. In view of the growing use of new generation MR scanners with increasing magnetic field strength (higher Tesla), our results seem to support the suggestions of the ICNIRP for an urgent need of monitoring workers and for epidemiologic studies on subjects with high levels of exposure or particular conditions such as for example pregnant occupational workers.30

Despite activation of repair mechanisms, persistence of DNA damage has been found in human lymphocytes more than 24 h after exposing patients and blood samples to CMR scanning.4 Co-genotoxic effects of MR in combination with the administered gadolinium-based contrast material may further have contributed to DNA damage due to the potentiating effect of gadolinium-based contrast material and MR exposure.31 As in our study all patients underwent contrast enhanced CMR, reflecting widely used clinical practice,32 we cannot differentiate the precise contribution of the known genotoxic effect of the gadolinium-based contrast material from the effects of the magnetic field. However, the use of contrast material is generally an integrated part of CMR scanning and therefore our results may appropriately represent the effect of a routine CMR scan. The absolute amount of DNA damage is certainly larger in our study compared with previous in vitro studies, as the entire blood of each patient rather than a blood sample was exposed during CMR. According to the assumptions used in the field of radiation protection, an increased number of DNA damages confer a linearly increased risk of cancer. Conversely, even a low number of DSBs may represent a carcinogenic risk according to the linear-no threshold theory. Our results compare well to the more than two-fold increase in DSBs induced by CMR and assessed by immunofluorescence microscopy as reported by Simi et al.,4 which was substantially less pronounced than the almost six-fold increase observed after cardiac CT by Kuefner et al.33 Although only a few data are available using FACS analyses for this low scale of signal, the excellent agreement between microscopy and FACS over a large range of signal including the present study strengthens the validity of our results.34

Of note, observations in several subsets of patients seem to suggest increased sensibilities to MRI exposition, as higher susceptibility for DNA damage by MRI has been found for example in lymphocytes of patients with Turner's syndrome.35 Thus, inappropriate examinations should be avoided and CMR should be used with caution and similar restrictions may apply as for X-ray-based and nuclear imaging techniques where the potential harm is carefully weighted against the obvious benefit offered by each examination in order to avoid unnecessary damage of DNA integrity with potential carcinogenic effect.

Funding

Grants from the Swiss National Science Foundation to P.A.K. and to M.F. are gratefully acknowledged.

Acknowledgements

We thank Christiane Koenig, Jose Maria Mateos, PhD, Stefano Ferrari, PhD, and Florian Mair, MSc, from the University of Zurich, Zurich, Switzerland, and Arnold von Eckardstein, MD, Institute for Clinical Chemistry, University Hospital Zurich, Zurich, Switzerland, for their invaluable advice and excellent technical support for the immunofluorescence analysis.

Conflict of interest: none declared.

References

1
Kangarlu
A
Robitaille
P
Biological effects and health implications in magnetic resonance imaging
Concepts Magn Reson
 , 
2000
, vol. 
12
 (pg. 
321
-
359
)
2
Franco
G
Perduri
R
Murolo
A
Health effects of occupational exposure to static magnetic fields used in magnetic resonance imaging: a review
Med Lav
 , 
2008
, vol. 
99
 (pg. 
16
-
28
)
3
de Vocht
F
van-Wendel-de-Joode
B
Engels
H
Kromhout
H
Neurobehavioral effects among subjects exposed to high static and gradient magnetic fields from a 1.5 Tesla magnetic resonance imaging system—a case-crossover pilot study
Magn Reson Med
 , 
2003
, vol. 
50
 (pg. 
670
-
674
)
4
Simi
S
Ballardin
M
Casella
M
De Marchi
D
Hartwig
V
Giovannetti
G
Vanello
N
Gabbriellini
S
Landini
L
Lombardi
M
Is the genotoxic effect of magnetic resonance negligible? Low persistence of micronucleus frequency in lymphocytes of individuals after cardiac scan
Mutat Res
 , 
2008
, vol. 
645
 (pg. 
39
-
43
)
5
Carnes
KI
Magin
RL
Effects of in utero exposure to 4.7 T MR imaging conditions on fetal growth and testicular development in the mouse
Magn Reson Imaging
 , 
1996
, vol. 
14
 (pg. 
263
-
274
)
6
High
WB
Sikora
J
Ugurbil
K
Garwood
M
Subchronic in vivo effects of a high static magnetic field (9.4 T) in rats
J Magn Reson Imaging
 , 
2000
, vol. 
12
 (pg. 
122
-
139
)
7
Rodegerdts
EA
Gronewaller
EF
Kehlbach
R
Roth
P
Wiskirchen
J
Gebert
R
Claussen
CD
Duda
SH
In vitro evaluation of teratogenic effects by time-varying MR gradient fields on fetal human fibroblasts
J Magn Reson Imaging
 , 
2000
, vol. 
12
 (pg. 
150
-
156
)
8
Saito
K
Suzuki
H
Suzuki
K
Teratogenic effects of static magnetic field on mouse fetuses
Reprod Toxicol
 , 
2006
, vol. 
22
 (pg. 
118
-
124
)
9
Schiffer
IB
Schreiber
WG
Graf
R
Schreiber
EM
Jung
D
Rose
DM
Hehn
M
Gebhard
S
Sagemuller
J
Spiess
HW
Oesch
F
Thelen
M
Hengstler
JG
No influence of magnetic fields on cell cycle progression using conditions relevant for patients during MRI
Bioelectromagnetics
 , 
2003
, vol. 
24
 (pg. 
241
-
250
)
10
Greenland
S
Sheppard
AR
Kaune
WT
Poole
C
Kelsh
MA
A pooled analysis of magnetic fields, wire codes, and childhood leukemia. Childhood Leukemia-EMF Study Group
Epidemiology
 , 
2000
, vol. 
11
 (pg. 
624
-
634
)
11
Repacholi
MH
Greenebaum
B
Interaction of static and extremely low frequency electric and magnetic fields with living systems: health effects and research needs
Bioelectromagnetics
 , 
1999
, vol. 
20
 (pg. 
133
-
160
)
12
Vijayalaxmi
OG
Controversial cytogenetic observations in mammalian somatic cells exposed to extremely low frequency electromagnetic radiation: a review and future research recommendations
Bioelectromagnetics
 , 
2005
, vol. 
26
 (pg. 
412
-
430
)
13
Greenwood
JP
Maredia
N
Younger
JF
Brown
JM
Nixon
J
Everett
CC
Bijsterveld
P
Ridgway
JP
Radjenovic
A
Dickinson
CJ
Ball
SG
Plein
S
Cardiovascular magnetic resonance and single-photon emission computed tomography for diagnosis of coronary heart disease (CE-MARC): a prospective trial
Lancet
 , 
2012
, vol. 
379
 (pg. 
453
-
460
)
14
Mattsson
MO
Auvinen
A
Bridges
J
Norppa
H
Schütz
J
European Parliament and the Council. Research needs and methodology to address the remaining knowledge gaps on the potential health effects of EMF
 
Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR)
 
15
Vecchia
P
Hietanen
M
Ahlbom
A
Anderson
LE
Breitbart
E
de Gruijl
FR
Lin
JC
Matthes
R
Peralta
APT
Söderberg
P
Stuck
BE
Swerdlow
AJ
Taki
M
Saunders
R
Veyret
B
International Commission on Non-Ionizing Radiation Protection (ICNIRP). Guidelines on limits of exposure to static magnetic fields
Health Phys
 , 
2009
, vol. 
96
 (pg. 
504
-
514
)
16
Vecchia
P
Hietanen
M
Ahlbom
A
Anderson
LE
Breitbart
E
de Gruijl
FR
Lin
JC
Matthes
R
Peralta
APT
Söderberg
P
Stuck
BE
Swerdlow
AJ
Taki
M
Saunders
R
Veyret
B
International Commission on Non-Ionizing Radiation Protection (ICNIRP). Amendment to the ICNIRP ‘Statement on medical magnetic resonance (MR) procedures: protection of patients’
Health Phys
 , 
2009
, vol. 
97
 (pg. 
259
-
261
)
17
Belyaev
I
Static Fields Environmental Health Criteria No. 232
 
Geneva, Switzerland
World Health Organization, WHO
 
18
Myerson
S
Francis
J
Neubauer
S
Cardiovascular Magnetic Resonance
 , 
2010
2nd ed
Oxford
Oxford University Press
19
Winchester
R
Ross
G
Rose
NR
Friedman
H
Methods for enumerating lymphocyte populations
Manual of Clinical Immunology
 , 
1976
1st ed
Washington, DC
American Society for Microbiology
(pg. 
64
-
76
)
20
Fiechter
M
Fuchs
TA
Gebhard
C
Stehli
J
Klaeser
B
Stahli
BE
Manka
R
Manes
C
Tanner
FC
Gaemperli
O
Kaufmann
PA
Age-related normal structural and functional ventricular values in cardiac function assessed by magnetic resonance
BMC Med Imaging
 , 
2013
, vol. 
13
 pg. 
6
 
21
May
MS
Brand
M
Wuest
W
Anders
K
Kuwert
T
Prante
O
Schmidt
D
Maschauer
S
Semelka
RC
Uder
M
Kuefner
MA
Induction and repair of DNA double-strand breaks in blood lymphocytes of patients undergoing (18)F-FDG PET/CT examinations
Eur J Nucl Med Mol Imaging
 , 
2012
, vol. 
39
 (pg. 
1712
-
1719
)
22
Muslimovic
A
Ismail
IH
Gao
Y
Hammarsten
O
An optimized method for measurement of gamma-H2AX in blood mononuclear and cultured cells
Nat Protoc
 , 
2008
, vol. 
3
 (pg. 
1187
-
1193
)
23
Andrievski
A
Wilkins
RC
The response of gamma-H2AX in human lymphocytes and lymphocytes subsets measured in whole blood cultures
Int J Radiat Biol
 , 
2009
, vol. 
85
 (pg. 
369
-
376
)
24
World Health Organization (WHO), International Agency for Research on Cancer (IARC), Working Group on the Evaluation of Carcinogenic Risks to Humans
Non-ionizing radiation, Part 1: static and extremely low-frequency (ELF) electric and magnetic fields
IARC Monogr Eval Carcinog Risks Hum
 , 
2002
, vol. 
80
 (pg. 
1
-
395
)
25
Jian
W
Wei
Z
Zhiqiang
C
Zheng
F
X-ray-induced apoptosis of BEL-7402 cell line enhanced by extremely low frequency electromagnetic field in vitro
Bioelectromagnetics
 , 
2009
, vol. 
30
 (pg. 
163
-
165
)
26
Juutilainen
J
Do electromagnetic fields enhance the effects of environmental carcinogens?
Radiat Prot Dosimetry
 , 
2008
, vol. 
132
 (pg. 
228
-
231
)
27
Nordenson
I
Mild
KH
Andersson
G
Sandstrom
M
Chromosomal aberrations in human amniotic cells after intermittent exposure to fifty hertz magnetic fields
Bioelectromagnetics
 , 
1994
, vol. 
15
 (pg. 
293
-
301
)
28
Winker
R
Ivancsits
S
Pilger
A
Adlkofer
F
Rudiger
HW
Chromosomal damage in human diploid fibroblasts by intermittent exposure to extremely low-frequency electromagnetic fields
Mutat Res
 , 
2005
, vol. 
585
 (pg. 
43
-
49
)
29
Phillips
JL
Singh
NP
Lai
H
Electromagnetic fields and DNA damage
Pathophysiology
 , 
2009
, vol. 
16
 (pg. 
79
-
88
)
30
Bassen
H
Bernhardt
JH
Brix
G
Lejeune
JJ
Owen
RD
de Seze
R
Saunders
R
Ueno
S
Veyret
B
Zaremba
L
Medical magnetic resonance (MR) procedures: protection of patients
Health Phys
 , 
2004
, vol. 
87
 (pg. 
197
-
216
)
31
Yildiz
S
Cece
H
Kaya
I
Celik
H
Taskin
A
Aksoy
N
Kocyigit
A
Eren
MA
Impact of contrast enhanced MRI on lymphocyte DNA damage and serum visfatin level
Clin Biochem
 , 
2011
, vol. 
44
 (pg. 
975
-
979
)
32
Bruder
O
Schneider
S
Nothnagel
D
Dill
T
Hombach
V
Schulz-Menger
J
Nagel
E
Lombardi
M
van Rossum
AC
Wagner
A
Schwitter
J
Senges
J
Sabin
GV
Sechtem
U
Mahrholdt
H
EuroCMR (European Cardiovascular Magnetic Resonance) registry: results of the German pilot phase
J Am Coll Cardiol
 , 
2009
, vol. 
54
 (pg. 
1457
-
1466
)
33
Kuefner
MA
Hinkmann
FM
Alibek
S
Azoulay
S
Anders
K
Kalender
WA
Achenbach
S
Grudzenski
S
Lobrich
M
Uder
M
Reduction of X-ray induced DNA double-strand breaks in blood lymphocytes during coronary CT angiography using high-pitch spiral data acquisition with prospective ECG-triggering
Invest Radiol
 , 
2010
, vol. 
45
 (pg. 
182
-
187
)
34
MacPhail
SH
Banath
JP
Yu
TY
Chu
EH
Lambur
H
Olive
PL
Expression of phosphorylated histone H2AX in cultured cell lines following exposure to X-rays
Int J Radiat Biol
 , 
2003
, vol. 
79
 (pg. 
351
-
358
)
35
Scarfi
M
Prisco
M
Lioi
M
Zeni
O
Della Noce
M
Di Pietro
R
Franceschi
C
Iafusco
D
Motta
M
Bersani
F
Cytogenetic effects induced by extremely low frequency pulsed magnetic fields in lymphocytes from Turner's syndrome subjects
Bioelectrochem Bioenerg
 , 
1997
, vol. 
43
 (pg. 
221
-
226
)

Author notes

Contributed equally to this work.
Guest edited by Jeroen Bax, Professor of Cardiology, Leiden University Medical Centre, Leiden, Netherlands.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com.

Comments

7 Comments
No evidence that MR causes dsDNA damage
21 July 2013
Dudley J. Pennell (with S Neubauer; SA Cook; G McKenna; S Plein; E Nagel; SF Keevil; S Kozerke; J Schwitter; Bucciarelli-Ducci C; H Mahrholdt; M Lombardi; B Gerber; FE Rademakers; JC Moon; F Leyva; A Arai; SC West; MD Schneider)
The publication by Fiechter et al,[1] makes egregious scientific errors that render its results uninterpretable and its far-reaching conclusions untenable. Some of the many scientific failures are:

1. GammaH2AX phosphorylation is not specific for dsDNA breaks and can be seen with immunoglobulin class switching in lymphocytes, at stalled replication forks, with telomere erosion, in ageing and stress. Lesions such as stalled replication forks are not carcinogenic. There is no proof that the DNA damage signaling cascade was activated which is more specific for dsDNA damage.[2]

2. There was no control for patient position and exertion which affects circulating blood mononuclear cells. Patients having been physically active will yield a first sample prior to MR with different circulating cell types compared with a second sample taken after inactivity for the scan. Different PBMCs have very different gammaH2AX levels.[3]

3. There are no control data from patients not undergoing scanning, from patients undergoing x-ray examinations, or from patients who did not receive gadolinium. It is impossible to discount confounders occurring with ex-vivo handling, or compare putative MR induced damage with that seen with x-rays.

4. It is difficult to assess carcinogenic risk because of inadequate dsDNA characterisation. Carcinogenicity depends on the lesion complexity, with ionizing radiation producing clustered lesions. Similar complexity of any putative lesions produced by MR is unlikely, making them less efficient in inducing carcinogenesis.

5. There are no data on whether a dose response relationship can be seen between the duration or intensity of MR and the number of gammaH2AX foci, which would provide additional evidence of an interaction.

6. There is complete disagreement with previous data showing no effect of MR on gammaH2AX foci,[4] or other measures of DNA damage.[5] These data are not cited or discussed.

7. The sample size of 20 is completely inadequate. Just 3 patients are driving the results with a barely significant p-value.

8. It is stated that CMR requires some of the strongest and fastest switching electromagnetic gradients available in MR exposing the patients to the highest administered energy levels accepted by the controlling authorities. However, strong fast gradients are also widely used for neuro-MR. The limits on gradients are nothing to do with energy levels, but are to avoid peripheral nerve stimulation, an uncomfortable but transient effect that is well understood. The RF energy used is far too low to induce ionisation, which is the mechanism by which x-rays cause damage.

9. There remains a gap in understanding linking MR with DNA damage. This does not mean that it is not possible, but that mechanisms that are biologically plausible need to be proposed. The conclusions of the paper that inappropriate examinations should be avoided and CMR should be used with caution are completely unjustified. Patients must not be frightened away from life-saving MR investigations on the basis of this deeply flawed paper. Patient safety is paramount, but safety is a negative finding that is often very difficult to prove. Properly conducted epidemiological studies examining possible harmful effects are required.

References

1 Fiechter M, Stehli J, Fuchs TA, Dougoud S, Gaemperli O, Kaufmann PA. Impact of cardiac magnetic resonance imaging on human lymphocyte DNA integrity. Eur Heart J 2013: Jun 21. [Epub ahead of print] PMID: 23793096

2 Polo SE, Jackson SP. Dynamics of DNA damage response proteins at DNA breaks: a focus on protein modifications. Genes Dev 2011; 25: 409-33.

3 Hedfors E, Holm G, Ohnell B. Variations of blood lymphocytes during work studied by cell surface markers, DNA synthesis and cytotoxicity. Clin Exp Immunol 1976; 24: 328-35.

4 Schwenzer NF, Bantleon R, Maurer B, Kehlbach R, Schraml C, Claussen CD, Rodegerdts E. Detection of DNA double-strand breaks using gammaH2AX after MRI exposure at 3 Tesla: an in vitro study. J Magn Reson Imaging 2007; 26: 1308-14.

5 Szerencsi A, Kubinyi G, Valiczko E, Juhasz P, Rudas G, Mester A, Janossy G, Bakos J, Thuroczy G. DNA integrity of human leukocytes after magnetic resonance imaging. Int J Radiat Biol 2013; Jun 12. [Epub ahead of print] PMID: 23679232

Conflict of Interest:

Some authors work in CMR which involves interacting with industry and guarding patient safety. Some authors work in basic science of DNA, in radiation biology and in basic MR physics.

Submitted on 21/07/2013 8:00 PM GMT
Response of the authors to the letter by Pennell et al.
21 July 2013
Phillipp Kaufmann (with Fichter M, Stehli J, Fuchs TA, Dougoud S, Gaemperli O)

Dear Editor,

We appreciate the opportunity to comment on the letter authored by a highly distinguished panel of experts of whom many are highly subspecialized in cardiac magnetic resonance imaging (MRI). They expressed concerns about our findings on cardiac MRI affecting human lymphocyte DNA integrity and found our conclusions (1) inadequate for applying the precautionary principle to MRI.

1. The assessment of gammaH2AX foci has been proposed as a sensitive quantitative biologically relevant biomarker of low-level radiation exposure (2). Despite potential limitations which can be found for most techniques, this test is currently widely used and established for the assessment of DNA double strand breaks in the field of radioprotection (3) and for radio-sensitivity testing in cancer research (4). It is reassuring that other groups using different methods such as the comet assay have also found an association of MRI and lymphocyte DNA breaks (5). With regard to stress and ageing, we cannot comment on whether the subjective stress experienced during an MRI scan is strong enough to cause DNA damage and by which mechanism this may happen, while we feel that ageing effects within one hour are even less likely to confound the measurements.

2. We agree that heavy physical exercise at a heart rate of 150 beats per minute maintained over 10 minutes may affect circulating cell types (6). However, since our patients were calm, resting, and did not perform any physical exercise - both in the waiting room and during preparation according to standard routine procedure before cardiac MRI for about 1 hour before the scan - this would not appear to be a source of error.

3. We share the concerns raised by this panel of experts about the potential genotoxic effect of gadolinium-based contrast material, which may act as a confounder, particularly at the relatively high doses typically administered for the "off label" use in cardiac MRI (7). Since this impact on lymphocyte DNA damage has been shown to significantly add to the effect of MRI alone (5), we have clearly stated that our study was not designed to evaluate the relative contribution of both components. However, we felt that this is of minor importance since more than 90% of patients undergoing cardiac MRI receive contrast material as reported by several colleagues contributing to the letter (7).

4. We are not aware of data which would lend support to the speculative hypothesis that MRI-induced DNA lesions are less carcinogenic than others. According to the linear no threshold theory (LNT), any DNA damage even on a very low scale has the theoretical potential to be a source of carcinogenesis.

5. It must have escaped the attention of the lead author of this multi-authored letter, that a dose-response relationship has been reported by several groups (8), peculiarly including a group led by one of his undersigning co-authors who has previously reported that, "A dose- dependent increase in micronuclei frequency was observed in vitro" after exposure to cardiac MRI (9). Micronuclei are yet another alternative to gammaH2AX foci for assessing DNA damages and cancer risk (10) which has been used in support of our results.

6. The criticism that our data are in "complete disagreement" with previous data is untenable. We simply agree with those who have found the same, while we disagree with those who have not. This lies in the nature of a controversial and fruitful scientific discussion, which must give a voice to discrepant findings from other scientists, without questioning the scientific credibility of the latter. Accordingly, we have clearly stated that the literature has revealed conflicting results and we have cited studies reporting no influence of MRI on cell cycle progression, e.g. from Schiffer et al. (11) as it would seem injudicious neglecting scientific data just because they are not concordant to own results or interests; a fundamental rule not entirely adopted in the letter. Finally, it seems that all 19 authors have also overlooked the detail that we were unable to cite the excellent article by Szerencsi et al. (12) for the simple reason that it was published online three months after our own submission. We strongly recommend careful reading of the scientifically sound article by Szerencsi et al. (12), which supports a balanced discussion of the large body of literature on DNA damages observed after MRI.

7. Certainly an increase in sample size could allow reaching higher power than indicated in the statistics section, which, however, was approved by the statistical reviewer of the European Heart Journal. For our data with non-normal distribution, we used a non-parametric rank test. This was chosen according to specific expert advice because it lies in the nature of this test that it specifically excludes that a positive result can be driven by a few outliers since the rank rather than the amplitude drives the results. In the FACS analysis, an increase in DNA damage was found in 17 out of 20 individuals, with a p<0.005, significantly beyond any doubt.

8. Our statements on the "strongest and fastest switching" gradients in cardiac MRI are extracted from an appropriately referenced publication of one of the colleagues now criticising us (9). We agree that MRI may cause additional uncomfortable transient effects as mentioned in the letter and referenced in our introduction, but this was beyond the focus of our study. Indeed, patients are exposed to strong and fast gradients also in non-cardiac MRI, underlining the general appropriateness of the call for urgent evaluation of adverse biological effects of clinical MRI scanning by the European Parliament, the International Commission on Non- Ionizing Radiation Protection (ICNIRP), and the World Health Organisation (WHO) (1).

9. Science often starts with new observations, triggering the search for mechanistic explanations. However, as pointed out by the accompanying editorial, our findings are neither new nor singular (13). Therefore, several potential explanations have been published during the last decade, including impairment of repair mechanisms, for example by activation of oxidative stress pathways as pointed out in our discussion, or initiation of transcription by interacting with moving electrons in DNA by generating repulsive (Lorentz) forces causing chain separation at specific DNA sequences (14).

As members of an imaging service also using ionizing radiation, we could not agree more in that safety being a negative finding is difficult to prove - , a burden now also shared by exclusive MRI users. We fully concur with the statement in the letter that "patients must not be frightened away" from any appropriate imaging examination, but we will take Pennell and colleagues at their word that this holds true for all cardiac imaging examinations, irrespective of whether any DNA damage is the result of ionizing or non-ionizing radiation. The general rule to avoid inappropriate examinations should not be questioned. With specific regard to MRI, our conclusions are in perfect line with those published by one of the many esteemed co-signing authors on the letter now criticizing us, who stated that "until a wider knowledge of the potential risk related to diagnostic MRI is available, a prudent attention should be adopted in order to avoid unnecessary examinations, according to the precautionary principle" (15). I do not see a great deal of difference to our conclusions "that CMR should be used with caution to avoid unnecessary damage of DNA integrity". However, after reading the letter to our article, his further statement that ,"it is never too much to draw attention on this, since doctors are insufficiently aware of the risks associated with clinical tests" (9) - really seems to hit the bull's eye.

References

1. Fiechter M, Stehli J, Fuchs TA, Dougoud S, Gaemperli O, Kaufmann PA. Impact of cardiac magnetic resonance imaging on human lymphocyte DNA integrity. Eur Heart J. 2013 Jun 21.

2. Lobrich M, Rief N, Kuhne M, Heckmann M, Fleckenstein J, Rube C, et al. In vivo formation and repair of DNA double-strand breaks after computed tomography examinations. Proc Natl Acad Sci U S A. 2005 Jun 21;102(25):8984-9.

3. Rothkamm K, Balroop S, Shekhdar J, Fernie P, Goh V. Leukocyte DNA damage after multi-detector row CT: a quantitative biomarker of low-level radiation exposure. Radiology. 2007 Jan;242(1):244-51.

4. Rube CE, Grudzenski S, Kuhne M, Dong X, Rief N, Lobrich M, et al. DNA double-strand break repair of blood lymphocytes and normal tissues analysed in a preclinical mouse model: implications for radiosensitivity testing. Clin Cancer Res. 2008 Oct 15;14(20):6546-55.

5. Yildiz S, Cece H, Kaya I, Celik H, Taskin A, Aksoy N, et al. Impact of contrast enhanced MRI on lymphocyte DNA damage and serum visfatin level. Clin Biochem. 2011 Aug;44(12):975-9.

6. Hedfors E, Holm G, Ohnell B. Variations of blood lymphocytes during work studied by cell surface markers, DNA synthesis and cytotoxicity. Clin Exp Immunol. 1976 May;24(2):328-35.

7. Bruder O, Schneider S, Nothnagel D, Pilz G, Lombardi M, Sinha A, et al. Acute adverse reactions to gadolinium-based contrast agents in CMR: multicenter experience with 17,767 patients from the EuroCMR Registry. JACC Cardiovasc Imaging. 2011 Nov;4(11):1171-6.

8. Ivancsits S, Diem E, Jahn O, Rudiger HW. Intermittent extremely low frequency electromagnetic fields cause DNA damage in a dose-dependent way. Int Arch Occup Environ Health. 2003 Jul;76(6):431-6.

9. Simi S, Ballardin M, Casella M, De Marchi D, Hartwig V, Giovannetti G, et al. Is the genotoxic effect of magnetic resonance negligible? Low persistence of micronucleus frequency in lymphocytes of individuals after cardiac scan. Mutat Res. 2008 Oct 14;645(1-2):39-43.

10. Bonassi S, Znaor A, Ceppi M, Lando C, Chang WP, Holland N, et al. An increased micronucleus frequency in peripheral blood lymphocytes predicts the risk of cancer in humans. Carcinogenesis. 2007 Mar;28(3):625- 31.

11. Schiffer IB, Schreiber WG, Graf R, Schreiber EM, Jung D, Rose DM, et al. No influence of magnetic fields on cell cycle progression using conditions relevant for patients during MRI. Bioelectromagnetics. 2003 May;24(4):241-50.

12. Szerencsi A, Kubinyi G, Valiczko E, Juhasz P, Rudas G, Mester A, et al. DNA integrity of human leukocytes after magnetic resonance imaging. Int J Radiat Biol. 2013 Jun 12.

13. Knuuti J, Saraste A, Kallio M, Minn H. Is cardiac magnetic resonance imaging causing DNA damage? Eur Heart J. 2013 Jul 2.

14. Blank M, Goodman R. Electromagnetic initiation of transcription at specific DNA sites. J Cell Biochem. 2001;81(4):689-92.

15. Hartwig V, Giovannetti G, Vanello N, Lombardi M, Landini L, Simi S. Biological effects and safety in magnetic resonance imaging: a review. Int J Environ Res Public Health. 2009 Jun;6(6):1778-98.

Conflict of Interest:

None declared

Submitted on 21/07/2013 8:00 PM GMT
Re:No evidence that MR causes dsDNA damage
18 August 2013
Massimo Lombardi

The Authors misinterpreted the paper from our group (reference 4) which was much more realistic in several points a) the data were much cleaner (only volunteers, no pharmacologic therapy and no contrast agent), here, as you say, it is difficult to understand the selection criteria if any b) a time course of the healing process was provided which is deeply different from the one detectable with ionizing radiation. This was sharply underlined in the discussion. In this paper risks related to the use of MR seems to be at the same level of CT or NUCLEAR technology. This is not sustainable!!

Conflict of Interest:

None declared

Submitted on 18/08/2013 8:00 PM GMT
Cardiac magnetic resonance imaging and lymphocyte DNA integrity
21 August 2013
Philipp A Kaufmann

Dr. Lombardi points out that in his study (reference 4) the patient selection was different as only healthy volunteers with no pharmacologic stress and no contrast agent were included in his study. This indeed allows to evaluate the effect of MRI alone, without the impact of gadolinium-based contrast agent. Although this has been discussed in the original article and also in our reply to the letter from a panel of experts in cardiac MRI (including Dr. Lombardi) we are grateful for this statement which must be interpreted in support of our results as even with their design (with what he calls a cleaner patient population) they reported a "dose-dependent increase of micronuclei frequency" after exposure to MRI. Finally, we concur that we did not evaluate the time course of repair so that we cannot comment on the healing process. With regard to this question we acknowledge reference 4, where the team of Dr. Lombardi has observed that "after in vivo scan, a significant increase in micronuclei is found till 24h". The phrases in brackets are quotes from the abstract of reference 4; we trust that this definitely excludes any source of misunderstanding.

Conflict of Interest:

None declared

Submitted on 21/08/2013 8:00 PM GMT
Doubt on the DSB-induction after MRI
22 September 2013
Michael Brand (with Matthias Sommer, Stephan Ellmann, Michael Uder)

Erlangen, GERMANY, 14.08.2013

Dear Editor!

With great interest we read the article from Michael Fiechter and colleagues entitled: "Impact of cardiacmagnetic resonance imaging on human lymphocyte DNA integrity" published in the June 2013 issue of the European Heart Journal (doi:10.1093/eurheartj/eht184).

We are certainly aware of the importance and the clinical impact of this study but the results of the study raise some questions:

Since the first publication of Loebrich et al. in 2005 a lot of studies have been published which evaluated DNA double strand breaks in blood lymphocytes using the gamma H2AX-Method. In these investigations normally the baseline DSB-level ranges from 0.05 to 0.15 DSB/cell [1-4]. In contrast in the study of Fiechter et al. there is a group of 5 patients with a DSB baseline-level of more than 0.200 DSB/cell (see figure 2). In the majority of published studies such a high level of DNA damage occurs only after irradiation of about 10 to 50mGy. In general high baseline levels of DSB's can be explained by the misinterpretation of extra nuclear staining like stained intracellular granolas or by previous exposure of the patients to ionizing radiation and/or chemotherapy or by a severe repair deficiency of the patients.

On the other hand there are at least 5 patients with a DSB baseline level of nearly zero (0.00-0.05) DSB/cell (see figure 2), which is also in contradiction to the literature. Some amounts of DSBs are normally present in human blood cells due to metabolic processes and natural radiation. An explanation of the missing background DSB's could be a failing of permeabilization, which prohibits the propagation of antibodies to the DNA during staining. In total only 10 patients out of the study population remain for a statistical analysis.

Furthermore the interindividual course of the DSB is very atypical. In some cases there is a very strong increase of the DSBs and in other cases there is only a small increase of the DSBs (see figure 2). In irradiated cells the induction of DSB depends linearly on the delivered dose [1, 3, 5, 6]. Therefore one can assume that MRI protocols also induce a linear rise of DSB.

It is confusing that the patient with the baseline-level of 0.66 DSB/cell after MRI showed an extreme decline of DSBs. The authors give no explanation for this phenomenon. However it is not possible to explain it by repair of DSB's because according to the literature this should definitely take more time than the one hour between the first and the second blood sample [1, 7, 8] (see figure 2).

The authors have supplemented the gamma H2AX experiments by FACS analyses. Thereby the MFI increased the measured Levels from 2758 to 3232 which corresponds with an increase from 100% to 117%. In contrast the immunofluorescence microscopy with the gamma H2AX method showed an increase from 0.066 DSB/cell to about 0.190 DSB/cell which corresponds to an increase from 100% to 288%. Even considering the different approaches for measurement this difference is hard to understand and fostered the suspicion of a methodological error (see figure 2 and 4).

Unfortunately the paper gives no explanation of the mechanism of the proposed DNA damage.

In view of the above we think the results of the study of Fiechter et al. should be handled very carefully.

Sincerely yours

Dr. Michael Brand, Dr. Matthias Sommer, Dr. Stephan Ellmann, Professor Dr. Michael Uder

Department of Radiology, University of Erlangen, Maximiliansplatz 1, 91054 Erlangen GERMANY

References:

[1] Lobrich M, Rief N, Kuhne M, et al. In vivo formation and repair of DNA double-strand breaks after computed tomography examinations. Proc Natl Acad Sci U S A 2005;102(25):8984-9.

[2] Kuefner MA, Grudzenski S, Hamann J, et al. Effect of CT scan protocols on x-ray-induced DNA double-strand breaks in blood lymphocytes of patients undergoing coronary CT angiography. Eur Radiol 2010;20(12):2917-24.

[3] Kuefner MA, Grudzenski S, Schwab SA, et al. DNA double-strand breaks and their repair in blood lymphocytes of patients undergoing angiographic procedures. Invest Radiol 2009;44(8):440-6.

[4] Rube CE, Grudzenski S, Kuhne M, et al. DNA double-strand break repair of blood lymphocytes and normal tissues analysed in a preclinical mouse model: implications for radiosensitivity testing. Clin Cancer Res 2008;14(20):6546-55.

[5] Beels L, Bacher K, De Wolf D, Werbrouck J, Thierens H. gamma- H2AX foci as a biomarker for patient X-ray exposure in pediatric cardiac catheterization: are we underestimating radiation risks? Circulation 2009;120(19):1903-9.

[6] Kuefner MA, Hinkmann FM, Alibek S, et al. Reduction of X-ray induced DNA double-strand breaks in blood lymphocytes during coronary CT angiography using high-pitch spiral data acquisition with prospective ECG- triggering. Invest Radiol 2010;45(4):182-7.

[7] Rothkamm K, Lobrich M. Evidence for a lack of DNA double-strand break repair in human cells exposed to very low x-ray doses. Proc Natl Acad Sci U S A 2003;100(9):5057-62.

[8] May MS, Brand M, Wuest W, et al. Induction and repair of DNA double-strand breaks in blood lymphocytes of patients undergoing F-18-FDG PET/CT examinations. Eur J Nucl Med Mol I 2012;39(11):1712-9.

Conflict of Interest:

None declared

Submitted on 22/09/2013 8:00 PM GMT
Cardiac magnetic resonance imaging and DNA damage
22 September 2013
Sohrab Fratz

After reading the intriguing article "Impact of cardiac magnetic resonance imaging on human lymphocyte DNA integrity" by Fiechter and colleagues with great interest in my view one issue needs clarification.

The patients studied where referred to cardiac evaluation including magnetic resonance imaging. Cardiac evaluation is a very broad term and may include other imaging or other potentially DNA damaging procedures besides cardiac magnetic resonance imaging.

Therefore some questions need clarification: What other imaging or other potentially DNA damaging procedures where performed for this cardiac evaluation? Where these other procedures performed before or after cardiac magnetic resonance imaging? Was the blood for this study drawn immediately before and after the cardiac magnetic resonance imaging or was there a time delay possibly introducing a confounding factor?

Conflict of Interest:

None declared

Submitted on 22/09/2013 8:00 PM GMT
Re:Impact of cardiac magnetic resonance imaging on human lymphocyte DNA integrity. Fiechter, et al., 34 (30): 2340-2345 doi:10.1093/eurheartj/eht184
8 October 2013
James A Metcalfe (with Kevin M Brindle, Professor of Biomedical Mgentic Resonance Imaging)

The title of this paper strongly implies a causal effect of the cardiac magnetic resonance (CMR) procedure on the changes observed in lymphocyte DNA double-strand breaks (DSBs). As the authors noted, this effect would be of potential concern if these short term changes translated into an increase risk of leukaemias. Unfortunately a series of essential control experiments were not performed that would be required to demonstrate that the CMR procedure caused the reported changes in DSBs.

1. No data are presented for the variation of DSBs in the patients over similar periods of time when the patients were not scanned. Normal spontaneous variations may well occur as the activity of DSB repair mechanisms fluctuate due to circadian and other transient metabolic mechanisms. Control blood samples taken from the same patients the day before and/or the day after the scans at the same time of day as the scans would be required to establish the extent of spontaneous fluctuations in the group. Furthermore no controls were described for any effects of administering the bolus of contrast agent required for the CMR scans.

3. No controls were performed for any effects of mild stresses associated with the CMR procedure on DSB levels. Substantial transient variations in blood cortisol, the major stress response hormone, occur in normal volunteers subjected to mild stress, for example in the Trier Social Stress Test [1]. Such changes may well affect the activity of DSB repair mechanisms. Further experiments replicating the mild stress associated with CMR scans, but without the associated RF and magnetic field exposures, would be required to determine whether the exposures are responsible for the changes in DBSs.

4. Fourteen of 20 patients showed an increase in DSBs after CMR, two showed little change and four showed a substantial decrease (Fig. 2). Other factors clearly modulate the levels of DSBs that are at the least comparable in magnitude to any putative effect of the CMR exposures. Without knowledge of other modulators it is not possible from the data presented to attribute any part of the changes observed to the exposures in CMR scans.

We conclude the data do not show that clinical routine CMR scanning exerts genotoxic effects, as stated in the discussion, mainly because of the omission of essential and comprehensive controls. We suggest that an adequately designed study should be performed, including the control experiments outlined. Given the importance of the CMR procedure in clinical management and the well-established risks of alternative imaging procedures using ionising radiation, it is highly irresponsible to attribute the reported changes in DSBs to the CMR exposures based on the data presented.

Reference

1. Determinants of the NF-kappaB response to acute psychosocial stress in humans. Wolf JM etal. Brain Behav Immun 2009; 23:742-9.

Conflict of Interest:

KMB has research contracts with GE Healthcare

Submitted on 08/10/2013 8:00 PM GMT