Magnetic resonance imaging (MRI) is a powerful imaging technology that serves as a noninvasive method to render images of the inside of an object. During an MRI scan, the nuclei of an object’s hydrogen atoms align with the scanner’s powerful, uniform magnetic field. Pulses of radio waves are then sent into the scanner that knock these hydrogen nuclei out of their normal position.After the radio wave pulsing stops, the nuclei realign back into their proper position. During this realignment process, the nuclei send out signals. These signals are captured by the computer system that analyzes and translates them into an image of the object being scanned.
MRI is primarily used in medical imaging to demonstrate pathological or physiological alterations of living tissues. It also has uses outside the medical field, for instance as a nondestructive testing method to characterize the quality of products such as produce and timber. ConventionalMRI usually operates at the scale of millimetres to micrometres—3 mm at best—which is good enough
for the mostly medical diagnostic purposes it is used for. Researchers have now shown that the imaging of nuclear spins using magnetic resonance, the basis for MRI, can be pushed to sub-100 nm resolution, into the nanoscale realm. Theydemonstrated that, using an emerging technique based on force detection, they can image nuclear spins with a sensitivity that is 60 000 times better than MRI.The resolution is about 30 times better than the most advanced conventional
MRI imaging. By improving this technique, researchers will be able to push deeper into the nanorange and approach the capability needed for direct 3-D imaging of individual macromolecules.
As MRI increasingly finds applications in material and biological sciences,scientists are trying to find ways to overcome its sensitivity limitations and push its resolution into the nanorange and, ultimately, the atomic scale. Magnetic resonance force microscopy (MRFM) seems to be the solution.
‘‘Our MRFM method measures a very tiny magnetic force between the nuclei in the sample and a nearby nanomagnet,’’ explains John Mamin. ‘‘Many common types of atoms, including hydrogen, fluorine, phosphorus, copper,and aluminium, have nuclei that are very weakly magnetic. Sometimes this basic magnetic property is referred to as the nuclear ‘spin’. MRI typically uses the magnetism of hydrogen nuclei contained in water. In our work, we use the
How Can You ‘See’, ‘Feel’ or ‘Hear’ Something so Incredibly Tiny?magnetism of fluorine nuclei contained in a small sample of calcium fluoride, though we can also use hydrogen.’’ Mamin is a member of an IBM team at the company’s Almaden Research center in California that succeeded, for the first time, in pushing NMR imaging below the 100nm threshold.
MRFM uses a magnetic tip and an ultrasensitive cantilever to sense the magnetic force generated between the tip and spins in a sample. Unlike the permanent magnet tips previously used for MRFM detection of electron spin resonance, the tips used by the IBM researchers are based on a thin film of magnetic material that has a high magnetic moment, but is magnetically soft.‘‘The tips we developed are compatible with sample-on-cantilever experiments,’’says Mamin. ‘‘In such an experiment, the sample is placed on the distal end of an ultra-sensitive cantilever situated above the magnetic tip. By choosing the sample-on-cantilever configuration, rather than tip-on-cantilever, we eliminated the magnetic damping that occurs when a soft magnetic tip vibrates in the presence of an external magnetic field.’’
The ability to image a single molecule with atomic resolution would have a huge impact in structural biology, in particular the area of protein structure determination—an important and famously difficult problem—and would aid the development of new drugs. It also could revolutionize the study of materials, ranging from pharmaceuticals to integrated circuits,for which a detailed understanding of the atomic structure is essential. Knowing the exact location of specific atoms within nanoelectronic structures,for example, would enhance designers’ insight into manufacture and performance.
The IBM team is motivated by the prospect of developing such a tool—the ‘holy grail’ of molecular imaging—an instrument that is able to perform direct,3-D imaging of complex structures such as molecules with atomic resolution.‘‘Our detection limit of about 1000 nuclear spins is a significant step toward the goal of detecting a single nuclear spin,’’ says Mamin. ‘‘The best conventional MRI today requires at least 100 million nuclear spins to obtain a detectable
signal. If we can achieve single spin detection in the future, this would open up the possibility of taking 3-D MRI images of the atoms in a molecule.Obviously, there is still considerable progress needed to extend our capability to the single spin level.’’
‘‘The main issues are related to the very tiny magnetic forces that must be detected. Better nanomagnetic tips are needed to generate stronger force signals, and noise reduction will also be key. There is still a lot of room for innovation in these areas.’’
Featured scientist: John Mamin
Organization: IBM Almaden Research Center, San Jose, CA, USA
Relevant publication: H. J. Mamin, M. Poggio, C. L. Degen, D. Rugar:
Nuclear magnetic resonance imaging with 90-nm resolution. Nat.
Nanotechnol., 2, 301–306.
Source
Nano-Society
www.rsc.org/nanoscience
MRI is primarily used in medical imaging to demonstrate pathological or physiological alterations of living tissues. It also has uses outside the medical field, for instance as a nondestructive testing method to characterize the quality of products such as produce and timber. ConventionalMRI usually operates at the scale of millimetres to micrometres—3 mm at best—which is good enough
for the mostly medical diagnostic purposes it is used for. Researchers have now shown that the imaging of nuclear spins using magnetic resonance, the basis for MRI, can be pushed to sub-100 nm resolution, into the nanoscale realm. Theydemonstrated that, using an emerging technique based on force detection, they can image nuclear spins with a sensitivity that is 60 000 times better than MRI.The resolution is about 30 times better than the most advanced conventional
MRI imaging. By improving this technique, researchers will be able to push deeper into the nanorange and approach the capability needed for direct 3-D imaging of individual macromolecules.
As MRI increasingly finds applications in material and biological sciences,scientists are trying to find ways to overcome its sensitivity limitations and push its resolution into the nanorange and, ultimately, the atomic scale. Magnetic resonance force microscopy (MRFM) seems to be the solution.
‘‘Our MRFM method measures a very tiny magnetic force between the nuclei in the sample and a nearby nanomagnet,’’ explains John Mamin. ‘‘Many common types of atoms, including hydrogen, fluorine, phosphorus, copper,and aluminium, have nuclei that are very weakly magnetic. Sometimes this basic magnetic property is referred to as the nuclear ‘spin’. MRI typically uses the magnetism of hydrogen nuclei contained in water. In our work, we use the
How Can You ‘See’, ‘Feel’ or ‘Hear’ Something so Incredibly Tiny?magnetism of fluorine nuclei contained in a small sample of calcium fluoride, though we can also use hydrogen.’’ Mamin is a member of an IBM team at the company’s Almaden Research center in California that succeeded, for the first time, in pushing NMR imaging below the 100nm threshold.
MRFM uses a magnetic tip and an ultrasensitive cantilever to sense the magnetic force generated between the tip and spins in a sample. Unlike the permanent magnet tips previously used for MRFM detection of electron spin resonance, the tips used by the IBM researchers are based on a thin film of magnetic material that has a high magnetic moment, but is magnetically soft.‘‘The tips we developed are compatible with sample-on-cantilever experiments,’’says Mamin. ‘‘In such an experiment, the sample is placed on the distal end of an ultra-sensitive cantilever situated above the magnetic tip. By choosing the sample-on-cantilever configuration, rather than tip-on-cantilever, we eliminated the magnetic damping that occurs when a soft magnetic tip vibrates in the presence of an external magnetic field.’’
The ability to image a single molecule with atomic resolution would have a huge impact in structural biology, in particular the area of protein structure determination—an important and famously difficult problem—and would aid the development of new drugs. It also could revolutionize the study of materials, ranging from pharmaceuticals to integrated circuits,for which a detailed understanding of the atomic structure is essential. Knowing the exact location of specific atoms within nanoelectronic structures,for example, would enhance designers’ insight into manufacture and performance.
The IBM team is motivated by the prospect of developing such a tool—the ‘holy grail’ of molecular imaging—an instrument that is able to perform direct,3-D imaging of complex structures such as molecules with atomic resolution.‘‘Our detection limit of about 1000 nuclear spins is a significant step toward the goal of detecting a single nuclear spin,’’ says Mamin. ‘‘The best conventional MRI today requires at least 100 million nuclear spins to obtain a detectable
signal. If we can achieve single spin detection in the future, this would open up the possibility of taking 3-D MRI images of the atoms in a molecule.Obviously, there is still considerable progress needed to extend our capability to the single spin level.’’
‘‘The main issues are related to the very tiny magnetic forces that must be detected. Better nanomagnetic tips are needed to generate stronger force signals, and noise reduction will also be key. There is still a lot of room for innovation in these areas.’’
Featured scientist: John Mamin
Organization: IBM Almaden Research Center, San Jose, CA, USA
Relevant publication: H. J. Mamin, M. Poggio, C. L. Degen, D. Rugar:
Nuclear magnetic resonance imaging with 90-nm resolution. Nat.
Nanotechnol., 2, 301–306.
Source
Nano-Society
www.rsc.org/nanoscience
No comments:
Post a Comment