Medical applications of EPR
Selected applications of continuous-wave EPR in medicine are reviewed. This includes detection of reactive oxygen and nitrogen species, pH measurements and oxymetry. Applications of EPR imaging are demonstrated on selected examples and future developments to faster imaging methods are discussed.
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
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irk-123456789-1220212017-06-26T03:02:56Z Medical applications of EPR Eichhoff, U. Höfer, P. Актуальные проблемы магнитного резонанса и его приложений: Анатоль Абрагам, Евгений Завойский, Казань Selected applications of continuous-wave EPR in medicine are reviewed. This includes detection of reactive oxygen and nitrogen species, pH measurements and oxymetry. Applications of EPR imaging are demonstrated on selected examples and future developments to faster imaging methods are discussed. 2015 Article Medical applications of EPR / U. Eichhoff, P. Höfer // Физика низких температур. — 2015. — Т. 41, № 1. — С. 81-85. — Бібліогр.: 37 назв. — англ. 0132-6414 PACS: 87.53.–j, 87.64.kh http://dspace.nbuv.gov.ua/handle/123456789/122021 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Актуальные проблемы магнитного резонанса и его приложений: Анатоль Абрагам, Евгений Завойский, Казань Актуальные проблемы магнитного резонанса и его приложений: Анатоль Абрагам, Евгений Завойский, Казань |
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Актуальные проблемы магнитного резонанса и его приложений: Анатоль Абрагам, Евгений Завойский, Казань Актуальные проблемы магнитного резонанса и его приложений: Анатоль Абрагам, Евгений Завойский, Казань Eichhoff, U. Höfer, P. Medical applications of EPR Физика низких температур |
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Selected applications of continuous-wave EPR in medicine are reviewed. This includes detection of reactive oxygen and nitrogen species, pH measurements and oxymetry. Applications of EPR imaging are demonstrated on selected examples and future developments to faster imaging methods are discussed. |
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Eichhoff, U. Höfer, P. |
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Eichhoff, U. |
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Medical applications of EPR |
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Medical applications of EPR |
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Medical applications of EPR |
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Medical applications of EPR |
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Medical applications of EPR |
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medical applications of epr |
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Актуальные проблемы магнитного резонанса и его приложений: Анатоль Абрагам, Евгений Завойский, Казань |
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Medical applications of EPR / U. Eichhoff, P. Höfer // Физика низких температур. — 2015. — Т. 41, № 1. — С. 81-85. — Бібліогр.: 37 назв. — англ. |
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Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 1, pp. 81–85
Medical applications of EPR
Uwe Eichhoff and Peter Höfer
Bruker BioSpin GmbH, Silberstreifen, D-76287 Rheinstetten/Germany
E-mail: Uwe.Eichhoff@bruker-biospin.de
Received September 16, 2014, published online November 24, 2014
Selected applications of continuous-wave EPR in medicine are reviewed. This includes detection of reactive
oxygen and nitrogen species, pH measurements and oxymetry. Applications of EPR imaging are demonstrated
on selected examples and future developments to faster imaging methods are discussed.
PACS: 87.53.–j Effects of ionizing radiation on biological systems;
87.64.kh EPR.
Keywords: EPR, reactive oxygen and nitrogen species, EPR dosimetry, oxymetry, EPR imaging.
Introduction
Electron paramagnetic resonance (EPR) was discovered
70 years ago by Zavoisky [1,2]. It relies on the resonance
of an unpaired electron spin in the magnetic field, which
limits its application to free radicals and transition metals.
In contrary nuclear magnetic resonance (NMR) can be
applied to all isotopes of chemical elements with a nuclear
magnetic moment, that means to almost all elements of the
periodic table [3]. Disregarding the limited objects of inves-
tigation EPR has found a large field of applications in al-
most any field of natural science and technology, especially
in physics, chemistry, biology and medicine. A very good
overview can be found in the book of K.M. Salikhov [4,5].
The opening of EPR to new applications was due to three
main developments: transient and pulse EPR [6], high-field
EPR [7–9] and the introduction of spin labels [10] and spin
traps [11]. Most applications in biology, biochemistry are
based on these compounds.
Reactive oxygen (ROS) and nitrogen species
EPR in medical and pharmaceutical investigations is
based on the quantitative determination of free radicals in
the organism, mainly of reactive oxygen species (ROS)
and reactive nitrogen species (RNS) [12–14]. Reactive oxy-
gen species like superoxide and hydroxide are formed by
radiation or by malfunctions of some enzymes. They are
often an indication of a pathological state. ROS normally
have low concentration and short lifetime. Spin labels al-
low to add a paramagnetic center to the EPR-silent mole-
cules and allow detection by EPR. Short-lived radicals can
be caught by spin traps and form long living radicals,
which then become also accessible to EPR. Antioxidant ac-
tivity can be monitored through the reaction with diphenyl-
picrylhydrazine (DPPH) (Fig. 1(a)) and spin trapping with
butyl-phenyl-nitron (PBN) (Fig. 1(d)). ROS are involved in
aging [15], diabetes [16], hypertension [17], cardiovascular
diseases [18], infections and inflammations [19], Alz-
heimer disease [20], lung disease [21] and cancer. Their
concentration in blood plasma is increased by stress but
can be diminished by physical exercise [22] (Fig. 2). For
instance, players of Bavaria Munich EPR showed an in-
crease of ROS by 40% after a soccer game.
The NO-radical, which is involved in many processes in
the organism, can be detected directly. Peroxynitrite gives
Fig. 1. (Color online) EPR measurements of reactive oxygen and
reactive nitrogen species: (a) DDPH assay. DDPH is attacked by
ROS. DPPH signal is inversely proportional to ROS concentra-
tion; (b) Oxidation leads to ascorbyl radical. Ascorbyl signal is
proportional to ROS concentration; (c) NO bound to hemoglobin
at 77 °C (finger dewar); (d) Spin trapping of ROS by PBN.
© Uwe Eichhoff and Peter Höfer, 2015
Uwe Eichhoff and Peter Höfer
no EPR signal, but forms with the reactive oxygen species
EPR active long living nitroxyl radicals. Nitric oxide binds
to hemoglobin forming a long living spin-labeled adduct
with is detectable at low temperature and allows to deter-
mine the NO concentration in blood plasma (Fig. 1(d)).
Measurements of ROS and RNS must be performed
at clearly defined temperature and oxygen partial pressure.
pH measurements
One of the key biological parameters in the mainte-
nance of physiological homeostasis is pH. The EPR spectra
of some radicals are sensitive to pH. The hyperfine coup-
ling (hfc) is altered by pH of the local environment. By
acquiring hfc measurements across a range of known pH
samples, a calibration curve (hfc vs known pH) can be con-
structed. The pH can be even used as an imaging parame-
ter. In cancer research extracellular pH (pHe) may provide
a useful biomarker for tumor cell metabolism. The hfc of
a pH-sensitive nitroxide (R-SG) was measured in a mouse
cancer model before and after x-ray irradiation. During
growth the tumor tissue becomes more acidid. After irradi-
ation the tumor growth is stopped and the pH goes back to
its initial value (Fig. 3).
Effects of ionizing radiation, EPR dosimetry
Ionizing radiation leads to disruption of chemical bonds
and formation of free radicals. The amplitude of the corre-
sponding EPR signal is over a wide range proportional to
the radiation dose [24–26]. In the regions, which suffered
from the Chernobyl accident in Russia, Belorussia and
Ukraine, EPR spectrometry is used for tooth enamel
dosimetry [27–29]. The EPR signal of tooth enamel re-
flects the total radiation dose, which a person has accumu-
lated during its life (Fig. 4). EPR spectrometers for these
investigations need a very high sensitivity and stability.
EPR imaging
Any EPR spectrometer can be extended to EPR imag-
ing by adding gradient coils with a special power supply
and appropriate software. For medical applications the
strong absorption by water in the X-band is an additional
obstacle. Biological objects due to their greater size and high
water content are therefore better investigated in the L- and
S-bands with a special large bore magnet and gradient as-
sembly. For material science X- and Q-bands are prefer-
able due to higher sensitivity. A standard universal EPRI
system includes two magnet systems for X- and L-bands.
Human whole-body EPR imaging like with NMR is in prin-
ciple possible, but only with very low sensitivity and extre-
mely long imaging times at very low frequencies in the
MHz range. This fact additionally to the low radical con-
centration in the organism prevents its clinical application.
Additionally, in contrary to MRI, EPR imaging relies
mainly on continuous wave (cw) methods. The short relax-
ation times in EPR (nsec–µsec), further shortened by
the strong imaging gradients, do not allow to apply pulse
sequences and Fourier imaging, which are standard in
start 2 4 6 8 weeks
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0R
O
S
pr
od
uc
tio
n,
m
M
/m
in
49 +/– years old group
22 +/– years old group
Fig. 2. (Color online) ROS production profile in human volun-
teers during moderate daily exercise for 8 weeks. Elder people
have higher ROS blood level then young ones, but they can
decrease it by exercise, whereas for younger people the low level
remains almost constant.
Fig. 3. (Color online) Relationship between tumor volume and pHe during normal tumor growth. An inverse relationship between tumor
volume and pHe was observed in all mice from Day 3. Significant difference in pHe between Day 0 and Day N is shown “*” (Fig. 3(b))
tumour regrowth and pHe in irradiated mice.
2000 2000
1500 1500
1000 1000
500
500
0
0
7.6 7.6
7.5 7.5
7.4 7.4
7.3 7.3
7.2 7.2
7.1 7.1
7.0 7.0
6.9 6.9
pH pH
Tu
m
ou
r v
ol
um
e,
m
m
Tu
m
ou
r v
ol
um
e,
m
m
0 2 4 6 8 10
Days
(a) (b)
0 1 2 3 4 5 6 7
Days after irradiation
82 Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 1
Medical applications of EPR
MRI [30]. Therefore at present the EPR cw spectrum is
measured in the presence of a gradient, which is stepped in
two or three coordinate directions and the image is ob-
tained by back-projection like in x-ray tomography and in
the very early days of MRI.
In EPR imaging the relationships between field of view
(FOV), spatial resolution, pixel bandwidth and gradient
strength are the same as for MRI. In practice, however,
there is a large difference regarding the pixel bandwidth. In
low and medium field MRI the gradient strength is often
large enough to ensure that no chemical shift distortion
appears in the image. In EPRI suppression of hyperfine
interaction in any image would require enormous gradi-
ents. Instead, the distortion of the spectral features by the
gradient is removed using deconvolution with the original
EPR spectrum yielding the integral EPR signal amplitude.
For an EPR line width of 100 mG a resolution of 25 µ can
be achieved.
One of the most promising applications of EPR imaging
is oximetry [31,32]. The width of the EPR line depends on
the partial oxygen pressure. The line width in blood can be
calibrated against the partial oxygen pressure and then the
partial oxygen pressure can be calculated from the EPR
line width and displayed in a colour code. The image there-
fore reflects the oxygen concentration in the sample and
ischemic conditions can be easily detected with EPR
oximetry. An overlay on an MRI image relates the ischem-
ic area to the anatomy (Fig. 5).
In malignant tumors like melanoma [33] radicals are
created, which allow the imaging of core tumor and metas-
tases. Melanin is an indogenous free radical responsible for
the black pigments in melanoma. Ex vivo samples of mela-
noma have been imaged in the X-band with cw imaging
(1024 points in 32.5 min). The comparison with the EPR
images and the stained histological samples show a strong
correlation between pigmentation and the EPR signal of
melanin [34]. Unpigmented samples exhibit no EPR signal.
EPR imaging of biopsies may evaluate stage and aggres-
siveness of melanoma. Figure 6 shows the melanin spec-
trum, 2D and 3D EPR images of melanoma in relation to
histology and images of corresponding lung metastases.
Fig. 4. (Color online) Irradiation-induced defects in teeth. Human upper 3rd molar (wisdom tooth) after x-ray irradiation: EPR signal at
g = 2 line width ≈ 0.2 mT. The EPR image shows radiation-induced radicals mainly on the surface in the tooth-enamel. This is the basis
of tooth-enamel dosimetry, which allows to determine the total radiation a person has received during his life-time. (Data courtesy of Dr.
Graham Timmins, University of Wales College of Medicine, Cardiff, UK.)
Fig. 5. (Color online) Ischemic stroke in rat brain: (a) MR diffusion image; (b) EPR line width image; (c) MRI/EPRI overlay; (d) his-
tology.
(c) (d)
ischemic core
(a) (b)
ischemic
side
normal
side
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 1 83
Uwe Eichhoff and Peter Höfer
Pulse EPR, FT-EPR imaging
Pulse EPR, not only in imaging, meets many challenges.
Relaxation times are in the range of nano- to microseconds
(NMR: micro- to milliseconds). This necessitates fast digi-
tizers and signal avaragers to detect the signals. This prob-
lem has been solved meanwhile with dwell times of 1 ns
and even below. The signal to noise ratio (S/N) is propor-
tional to the square root of the Q-factor and decays expo-
nentially with the dead time td: 2– / 1/2S/N e dt T Q≈ . For sen-
sitivity reasons it is desirable to have a high Q. But high Q
leads to a small bandwidth and long dead time, during
which the EPR signal may be significantly reduced or even
vanish. The length of the exciting π/2 pulse is inversely
proportional to the microwave power P: t(π/2) ~ P–1/2 and
must be in the order of the reciprocal line width to excite
the broad EPR line. Therefore a compromise has to be
made between the Q of the resonator and the dead time. As
a rule of thumb the optimal Q is in the order of the relaxa-
tion time in nanoseconds (e.g., Q = 100 for T2 = 100 ns).
Therefore for most samples we have no sensitivity gain for
pulsed EPR as compared to continuous wave.
These limitations are even more severe for pulse Fourier
EPR imaging because the gradients cause additional line
broadening. EPR imaging in cw mode is very time con-
suming. Modification of the single point imaging technique
by compressed sensing and partial FT may lead to a signi-
ficant reduction of imaging time (e.g., from 30 to 5 min)
but cannot really access the short imaging times available
in MRI.
Fourier EPR imaging is only possible for long relaxation
times (or very narrow lines) resulting in imaging times well
below one minute (Fig. 7). Rapid scan methods without
field modulation may be a promising alternative [9,35,36]
for broader lines. Scan rates above 13.4 kHz over a range
Fig. 6. (Color online) In vitro EPR spectra and images from melanoma B16 metastases in mice lung [1]: (a) spectrum from a freeze-
dried melanoma; (b) 2D image; (c) 3D image; (d) picture from a fresh melanoma slice; (e) corresponding EPR image; (f) picture of
freeze dried lungs with metastases; (g) 2D transversal EPR image; (h) longitudinal section through a 3D EPR image.
Fig. 7. (Color online) FT-EPR image of 3 trityl sample tubes (line
width 0.3 MHz; left tube inclined, lower tube leaky) obtained
with 32 ns-pulses in 12.7 s acquisition time (total imaging time
including gradient recovery: 45 s).
0.15 mm1.0
0.8
0.8
0.6
0.4
0.4
0.2
0
0
–0.2
–0.4
–0.4
–0.6
–0.8
–0.8
–1.0
Y,
m
m
Z, mm
ZY G/cm FOV 2 mm measurement time 1 15' ''
84 Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 1
Medical applications of EPR
of 155 G, sufficient for almost all radicals of medico-
biological interest, have been achieved in a Bruker Flexline
ER4118-XMD5 dielectric resonator (Q: 9000) over 150 G
line width and increased sensitivity by one order of magni-
tude as compared to cw methods [37]. We believe, that the
application of these methods to EPR imaging is just a mat-
ter of time.
1. E.K. Zavoisky, Zh. Eksp. Teor. Fiz. 15, 344 (1944).
2. E.K. Zavoisky, J. Phys. 9, 211 (1944).
3. R.K. Harris and B.E. Mann, NMR and Periodic Table, Aca-
demic Press (1978).
4. The Treasures of Heureka, Vol. I: Electron Paramagnetic Re-
sonance from Fundamental Research to Pioneering
Applications & Zavoisky Award, K.M. Salikhov (ed.), AXAS
Publishing Ltd., New Zealand (2009).
5. S.S. Eaton, G.R. Eaton, and K.M. Salikhov, Foundations of
Modern EPR, World Scientific, Singapore–New Jersey–
London–Honkong (1998).
6. A. Schweiger and G. Jeschke, Principles of Pulse Electron
Paramagnetic Resonance, Oxford University Press, Oxford,
New York (2001).
7. Ya.S. Lebedev, in: Modern Pulsed and Continuous Wave
Electron Spin Resonance, L. Kevan and M.K. Bowman (eds.),
Chap. 8: High-Frequency Continuous Wave Electron Spin
Resonance, Wiley, New York (1990).
8. K. Möbius, A. Savitsky, and M. Fuchs, in: Very High-Fre-
quency ESR/EPR, O.A. Grinberg and L.J. Berliner (eds.),
Chap. 3: Primary Processes in Photosynthesis. What do we
Learn from High-Field EPR Spectroscopy?, Kuwer, New
York (2004).
9. S.S. Eaton, R.W. Quine, M. Tseitlin, D.G. Mitchell, G.A.
Rinard, and G.R. Eaton, in: Handbook of High-Frequency
EPR, S. Misra (ed.), Wiley, New York (2014).
10. L.J. Berliner, Spin Labeling II: Theory and Applications,
Academic Press, New York (1979).
11. E.G. Janzen, Methods Enzymol. 105, 188 (1984).
12. D.G. Harrison and S. Dikalov, in: Molecular Mechanisms in
Hypertension Abington, D. DiPette, E. Schiffrin, and E. So-
wers (eds.), U.Uk., Taylor & Francis Medical Books (2006),
p. 297.
13. H. Shi, G. Timmins, M. Monske, A. Kalyanamaran, Y. Liu,
J.L. Clement, S. Burchiel, and K.J. Liu Arch, Bichem.
Biophys. 471(1), 437 (2005).
14. S. Dikalov, M. Skatchkov, and E. Basenge, Biochem.
Biophys. Res. Commun. 231, 701 (1997).
15. D.S. Erdincler, A. Seven, F. Inci, T. Beger, and G. Candan,
Clin. Chim. Acta 265, 77 (1997).
16. T.J. Guzik, S. Mussa, D. Gastaldi, J. Sadowski, C. Ratnatunga,
R. Pillai, and K.M. Channon, Circulation 105, 1656 (2002).
17. M.C. Gongora, Z. Quin, K. Laude, H.W. Kim, L. McCann,
J.R. Folz, S. Dikalov, T. Fukai, and D.G. Harrison, Hyper-
tension 48, 473 (2006).
18. S. Dikalov, K.K. Griendling, and D.G. Harrison, Hyperten-
sion 49, 1 (2007).
19. G.M. Rosen, B.E. Britigan, H.J. Halpern, and S. Pou, in:
Free Radicals, Biology and Detection by Spin Trapping,
Oxford Univeristy Press, New York (1999).
20. J. Petrlova, T. Kalai, I. Maezawa, R. Altman, G. Harishand-
ra, H.S. Hong, D.A. Bricarello, A.N. Parikh, G.A. Lorigan,
L.W. Jin, K. Hideg, and J.C. Voss, Plos One 7 (4), e35443
(2012). doi:10.1371/journal.pone.0035443.
21. N.W. Kooy, J.A.A. Royall, Y.Z. Ye, D.R. KJelly, and J.S. Beck-
man, Am. J. Respir. Crit. Care Med. 151, 1250 (1995).
22. M.I. Covas, R. Elosua, M. Fito, M. Alcantara, L. Coca, and
J. Marrugat, Med. Sci. Sports Exerc. 34, 814 (2002).
23. J. Goodwin, K. Yachi, M. Nagane, H. Yasui, Y. Miyake, O. Ina-
nami, A.A. Bobko, V.V. Khramtsov, and H. Hirata, Proc.
Intl. Soc. Mag. Reson. Med. 22, 2932 (2014).
24. D.F. Ragulla and U. Deffner, Appl. Radiat. Isotopes 33, 1101
(1982).
25. H. Ishii and M. Ikeya, Jpn. J. Appl. Phys. 29, No. 5, 871 (1990).
26. M.A. Brilliant et al., Hematologia and Transfusiologia 9, 14
(1990).
27. M. Ikeya, Magn. Reson. Rev. 13, No. 3, 91 (1988).
28. B. Pass and J.E. Aldrich, Med. Phys. 12, No. 3, 305 (1985).
29. V.G. Skvortsov, A.I. Vannikov, and U. Eichhoff, J. Mol.
Struct. 347, 321 (1995).
30. A. Kumar, D. Welti, and R. Ernst, J. Magn. Reson. 18, 69
(1975).
31. M. Elas, B.B. Williams, A. Parasca, C. Mailer, C.A. Peliz-
zari, M.A. Lewis, J.A. River, G.S. Karczmar, E.D. Barth,
and H.J. Halpern, Magn. Reson. Med. 49, 682 (2003).
32. M. Elas, K.-H. Ahn, A. Parasca, E.D. Barth, D. Lee, C. Ha-
ney, and H.J. Halpern, Clin. Cancer Res. 12,4209 (2006).
33. E. Vanea, N. Charlier, J. DeWever, M. Dinguizli, O. Feron,
J.F. Baurain, and B. Gallez, NMR Biomed. 21, 296 (2008).
34. Q. Godechal, G. Ghanem, M. Cook, and B. Gallez, Proc.
Intl. Soc. Mag. Reson. Med. 21, 1988 (2013).
35. D.G. Mitchell, R.W. Quine, M. Tseitlin, S.S. Eaton, and
G.R. Eaton, J. Magn. Reson. 214, 221 (2012).
36. D.G. Mitchell, G.M. Rosen, M. Tseitlin, B. Symmes, S.S.
Eaton, and G.R. Eaton, Biophys. J. 105, 338 (2013).
37. Yu. Zhelin, R.W. Quinn, G.A. Rinard, M.Tseitlin, H. Elajaili,
V. Kathirvelu, L.J. Clouston, P.J. Boratynski, A. Rajca, R. Stein,
H. Mchaourab, S.S. Eaton, and G.R. Eaton, submitted to
J. Magn. Reson. (2014).
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 1 85
Introduction
Reactive oxygen (ROS) and nitrogen species
pH measurements
Effects of ionizing radiation, EPR dosimetry
EPR imaging
Pulse EPR, FT-EPR imaging
|