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AVAILABLE
TECHNOLOGIES |
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SQUID-Detected
NMR and MRI at Ultralow Magnetic Fields
IB-1729
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APPLICATIONS:
- Magnetic resonance imaging (MRI) in low field
- Imaging of joints, peripheral regions of the body
- Screening for tumors
- Obtaining
direct stereochemical information using J (scalar)coupling
spectroscopy in low magnetic field
- Spectroscopy
of heterogeneous samples which are subject to spatial variation
in magnetic susceptibility, e.g. oil well logging, in
vivo spectroscopy, living organisms
- Multinuclear
nuclear magnetic resonance (NMR) studies
- NMR
spectroscopy of metals
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ADVANTAGES:
- Removes major technical barriers to developing lower cost
MRI scanners and NMR
spectrometers
- Open system
- Uses magnetic fields 10,000 times weaker than conventional
MRI
- Lower field homogeneity requirements (only 10,000 ppm
to achieve 1 mm resolution)
- Excellent T1-contrast
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Fig.1
MRI images at 0.13mT and 0.1mT/m: (a) image of a sliced
pepper, (b) slice-selected image of a whole pepper.
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ABSTRACT:
John Clarke, Alexander Pines, and colleagues have pioneered
systems for Nuclear Magnetic Resonance (NMR) and Magnetic
Resonance Imaging (MRI) that work in extremely low magnetic
fields, typically 1-100 microtesla. They achieved this breakthrough
by combining sample prepolarization with ultrasensitive magnetic
field detection by Superconducting QUantum Interference Devices
(SQUIDs).
Since low magnetic fields are easier and less costly to generate
than the high fields necessary for conventional high-field
MRI (1.5 tesla), this technique paves the way for developing
MRI scanners for certain applications that are less expensive
than current commercial systems. Furthermore, the demands
on magnetic field homogeneity are greatly reduced at low fields.
The Berkeley Lab researchers achieved narrow (~ 1 Hz) NMR
lines from protons in liquids in fields of about 100 microtesla
even though the homogeneity was only about 1 part in 10,000.
In the context of MRI, the linewidth of the NMR signal determines
the spatial resolution of the image for a given strength of
magnetic field gradient. The researchers exploit this narrow
linewidth to acquire MRIs with 1-mm resolution using a static
field of 132 microtesla and field gradients of the order of
100 microtesla/meter three orders of magnitude smaller
than the gradients used in conventional high-field MRI. Clarke,
Pines, and colleagues prepolarize the sample in a field of
100-300 millitesla. This field is removed before the image
is acquired in the much lower field. This technique differs
from the standard method in which the protons are polarized
and the signal is detected in the same high field. The low-field
operation is made possible because a SQUID magnetometer has
a magnetic field sensitivity that is independent of frequency.
In contrast, the sensitivity of conventional NMR detectors,
which rely on Faradays Law, scales linearly with frequency
and thus with the magnetic field.
Figure 1 shows two images acquired at 5.6 kHz. Figure 1(a)
is a magnetic resonance image of a sliced pepper, while Fig.
1(b) is an MRI slice of an intact pepper obtained by means
of a slice-selecting gradient.
Studies of phantoms with a paramagnetic salt dissolved in
water to reduce the longitudinal relaxation time T1 show that
excellent T1-contrast images can be obtained see Fig.
2. This technique offers the possibility of low-cost screening
for tumors.
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Fig
2 T1-contrast
images of phantom consisting of four columns of water.
The upper left (a) and lower right (d) columns were
doped with a paramagnetic salt to reduce T1.
Times (td) refer to delay time between polarizing pulse
and image acquisition. At longer delay times, the relative
intensity of the doped columns diminished as a result
of T1
relaxation.
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STATUS:
U.S. Patent #6,885,192. Available for licensing or collaborative
research for stand-alone MRI systems and certain other fields
of use.
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FOR
MORE INFORMATION PLEASE SEE:
- McDermott R.,
Trabesinger A.H., Mück M., Hahn, E., Pines, A., Clarke,
J., "Liquid-State NMR and Scalar Couplings in Microtesla
Magnetic Fields," Science 2002, 295, 2247-49
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REFERENCE
NUMBER: IB-1729
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SEE
THESE OTHER BERKELEY LAB TECHNOLOGIES IN THIS FIELD:
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CONTACT:
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Technology
Transfer Department
E.O. Lawrence Berkeley National Laboratory
MS 90-1070
Berkeley, CA 94720
(510) 486-6467 FAX: (510) 486-6457
TTD@lbl.gov |
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