Sensitivity Enhancement and Fast NMR
BCMB 8190
References
• T. Maly, G.T. Debelouchina, V.S. Bajaj, K-N. Hu, C-G.
Joo, M.L. Mak–Jurkauskas, J.R. Sirigiri, P.C.A. van der
Wel, J. Herzfeld, R.J. Temkin, and R.G. Griffin. (2008).
Dynamic nuclear polarization at high magnetic fields. J.
Chem. Phys. 128:52211-19.
• B.M. Goodson. (2002) Advances in Magnetic
Resonance: Nuclear Magnetic Resonance of LaserPolarized Noble Gases in Molecules, Materials, and
Organisms. J. Mag. Reson. 155:157–216.
• Title: Principles and Progress in Ultrafast
Multidimensional Nuclear Magnetic Resonance
• M. Mishkovsky and L. Frydman. (2000) Principles and
progress in multidimensional NMR. Ann. Rev. Phys.
Chem. 60:429-448
Sensitivity Enhancement:
Where can you Get It?
• Better detection: cryo-probes, SQUIDS,
mechanical oscillators
• Higher magnetic fields: 23.4T (1.0 GHz)
• Higher polarization: low temp, transfer
from systems with higher γ, pumping
For S=1/2 detection with a coil at low polarization:
Signal = γ3B02h2 / (16π2kT)
P = γB0h/(4πkT)
Alkali Metal Spin Exchange
From: B.M. Goodson (2002) J. Mag. Reson. 155:157–216.
Depends on the use of circularly polarized light
and the conservation of angular momentum
Experimental Set-up: Optical Pumping
and Spin Exchange of Alkali Metal
1) 129Xe (or 3He) at low pressure (~ 8 atm) is enclosed in a cylindrical
glass chamber in a low magnetic field (~ 10 G). Trace amounts of Rb
added, heated to 200°C.
2) Circularly
polarized laser light
applied. λ = 794.8
nm, 5s to 5p (D1)
transition of Rb
3) Absorption of the laser light produces a high electronic polarization
in the Rb atoms by means of optical pumping. Polarization transferred
to 129Xe by flip-flop term of Fermi-contact hyperfine interaction. Can
reach 10% polarization – enhancements of 10,000
Lung MRI using HP gases
• First report of a HP gas MR lung image was in 1994
of mouse lungs:
– Albert MS, Cates GD, Driehuys B, et al. Biological magnetic resonance
imaging using laser-polarized 129 Xe. Nature. 1994;370:199–201.
• First human images were reported in 1996:
– Kauczor HU, Hofmann D, Kreitner KF, et al. Normal and abnormal
pulmonary ventilation: visualization at hyperpolarized He-3 MR imaging.
Radiology. 1996;201:564–568.
– MacFall JR, Charles HC, Black RD, et al. Human lung air spaces:
potential for MR imaging with hyperpolarized He-3. Radiology.
1996;200:553–558.
Lungs
•
Coronal HP 3He image of normal healthy volunteer lungs showing
homogeneous signal distribution throughout the pulmonary gas space
• Secondary branching of bronchi is visible as well as some pulmonary
vasculature characterized as low-intensity structures
Moller, H.E., et al., MRI of the lungs using hyperpolarized noble gases. Magn Reson Med, 2002. 47(6): p. 1029-51.
3He
Coronal HP
lung images of
patients with cystic fibrosis
a) patient with mild disease
and normal spirometry (FEV1 =
91% of predicted) shows few
peripheral ventilation defects
b) patient with severe
cystic fibrosis (FEV1 – 41%
of predicted) has extensive
ventilation defects
FEV1 – forced expiratory volume in one second
Moller, H.E., et al., MRI of the lungs using hyperpolarized noble gases. Magn Reson Med, 2002. 47(6): p. 1029-51.
3He
Coronal HP
lung images of
patients with asthma
a) patient with mild disease
and normal spirometry (FEV1 =
98% of predicted) shows few
pleural-based peripheral
ventilation defects
b) patient with severe asthma
(FEV1 – 36% of predicted)
has large number of defects
Moller, H.E., et al., MRI of the lungs using hyperpolarized noble gases. Magn Reson Med, 2002. 47(6): p. 1029-51.
Enhancing Sensitivity for Metabolite Observation
Dynamic Nuclear Polarization (DNP)
• Transfers large electron polarization to nucleus (γe / γp = 650)
• Usual detection is 15N or 13C (loss of 32 or 316 in S/N vs 1H)
• Requires addition of a free radical and micro wave irradiation
• Samples are frozen prior to enhancement (2K)
• With low temp enhancements can be 1000 to 10,000
• Data acquired with a single pulse train of small angle pulses
Several mechanisms:
• The Overhauser Effect – liquids and certain solids
• The solid effect – requires hyperfine coupling
• The cross effect – a three spin process (we1 = we2 +wn)
• Thermal mixing - combination of this with CE most probable
Maly et al, (2009) J. Chem. Phys. 128:52211-19
Dynamic Nuclear Polarization (DNP)
the Overhauser Mechanism
• Illustrated for a 13C-electron pair
• Irradiate with micro waves
• Allow relaxation in which W0 is most efficient
βα 0
αα δ
ββ Δ
αβ Δ+δ
}δ
βα Δ/2
αα δ+Δ/2
}δ
βα Δ/2
αα δ
}δ
ββ Δ/2
αβ Δ/2+δ
}δ
ββ Δ
αβ Δ/2+δ
!
}Δ/2
-δ
}Δ/2
-δ
Polarization Instrumentation is Complex
NMR Magnet
Polarizer
Transfer of polarized
sample must be fast.
Lasts only a few tens
of seconds
Courtesy of Oxford Instruments
Ardenkaer-Larsen et al. PNAS 100:10158 (2003)
Direct 15N observe of 50% Deuterated 15NAcetyl Phenylalanine
Enhancement of 5000; 250 DNP, 200 temperature
~4000 μg
50 MHz
Not enhanced
2376 scans
~40 μg
40 MHz
DNP enhanced
One scan
Courtesy, Steve Reynolds, Oxford Instruments
Current In Vivo Applications Utilize 13C Observation
and Pyruvate 13C Labeled at Carbonyl
Monitoring of pyruvate metabolism in TRAMP mouse (prostate model) with highgrade primary tumor – M. J. Albers et al., 2008, Cancer Research, 68:8607-8615
Polarization Storage Limits Experiment Time
Long relaxation times are desirable
T1 for N-D
B0 (Tesla)
T1 for C=O
B0 (Tesla)
Singlet storage in proton pairs can also be explored:
(αβ-βα)/√2
Experimental Effect of Deuterating Glutamine
Sensitivity can be improved by indirect detection
through protons – reintroduce these by H/D exchange
Indirect Detection of Polarized 15N by Amide Proton Exchange
Barb, Hekmatyar, Glushka, & Prestegard. (2011) J Mag Res 212:304-310.
Useful signal up to a minute
Sensitivity enhancement ~100,000 x direct 15N observe
Second Dimension Offers Improved
Resolution of Metabolites – HSQC of Glucose
2nd Dimension Normally Collected a Point at a Time
t1
t1
FT
ν1
ν2
ν2
Ultra-Fast HSQC – 2D in 1s
Mishkovsky and Frydman, ChemPhysChem, 9:2340-2348 (2008)
Chirp
Chirp
RF
Mix
ω1
τ1
ω2
τ2
Gradients
Δ
Observe (echo-planar)
Z
t1
t1
t1
t1
t2
For each chemical shift, ω1 = zGγ + Ω; ω2 = -zGγ + Ω
ω1 = c τ1; ω2 = c τ2; τ1 + τ2 = 2Ω/c; Δ - τ1 + τ2 = n/ Ω
Therefore each element in tube has unique chemical
shift inversion – spatial encoding
t1
t1
t1
t1
1 Sec 2D HSQC Taken with Ultra-Fast Sequence
DNP polarization enhanced
M. Mishkovsky and L. Frydman. (2000) Ann. Rev. Phys. Chem. 60:429-448