Low-Field NMR/MRI Using Rotating-Frame Gradient Fields

APPLICATIONS OF TECHNOLOGY:

Portable MRI of:
- Oil fields at any depth, for MRI devices that can be sent into the borehole
- Joints, brain, prostate, heart, lungs (may be used with hyperpolarized noble gas)
- Water content of soil and its distribution
- Surface measurements (maps) of skin and other biological tissue
Magnetic resonance imaging (MRI) in low field
Screening for tumors
Imaging patients who have metal joint implants, knee plates, dental restorations

ADVANTAGES:

Significantly reduces image distortion when using low-field NMR/MRI, thereby eliminating the need for postcorrections
Optimizes cost- and energy-efficient NMR/MRI systems at low field
Can operate in conjunction with spectroscopy to detect specific chemical species
Enables the selection of specific detection volumes for chemical species
Faster signal detection
Can be paired with SQUID and other magnetometers, low-field detectors, conventional MRIs, remote NMR detectors (e.g., hyperpolarized Xe-gas detectors)

ABSTRACT:

Alexander Pines, Louis-Serge Bouchard, and Vasiliki Demas of Berkeley Lab have created a new low-field NMR/MRI system that overcomes image distortions that typically occur when applying conventional NMR detection and MR imaging methods at low fields. The first NMR/MRI technology to truly overcome the problem of image distortion from concomitant gradients at low fields, this Berkeley Lab invention significantly improves image acquisition and reconstruction for a wide variety of portable MRI applications such as the imaging of soil content (e.g., oil logging, hydrology studies), the organs (such as the brain, heart, and lungs), and the surface of the skin. It also may be effective in imaging the joints of patients who have metal implants.

While low-field NMR/MRI is desirable for making MRI devices that are portable, affordable, and energy-efficient, the strength of magnetic field gradients previously used in low-field NMR/MRI has been limited because of slower image processing, and image distortions that arise from concomitant field gradients. But the Berkeley Lab researchers have discovered a way to significantly reduce image distortions in low-field NMR/MRI by superimposing pairs of rotating-frame gradient fields on a static magnetic field to detect NMR signals.

In this Berkeley Lab NMR/MRI system with rotating gradients, the optimal ratio of gradient field amplitude to static magnetic field strength (i.e., DBmax/B0) may be greater than 0.1 and can even exceed 1; in fact, for a type I gradient, the larger the ratio is, the better the performance. This new rotating-gradient field scheme is especially useful in low field (where the static field is less than 100 mT) and attains a new level of low-field image clarity that was impossible with standard imaging gradients.

The new low-field NMR/MRI system also offers a way to detect the density of specific chemical species within a sample by combining undistorted MRI with spectroscopy techniques. The application of a special class of “soft” AC pulses (a combination of soft and hard pulses) provides undistorted excitation of a selected volume of chemical species, e.g., 1H or 13C, within a specific bandwidth. This type of soft/hard composite pulse reduces the image-distorting concomitant fields to zero, minimizing warping of the selected volume. This is the first time that rotating fields have been used with a static field to significantly reduce low-field NMR/MR imaging distortions, and to eliminate the need for imaging postcorrections.

STATUS:

Published Patent Application WO/2008/154059 available at www.wipo.int. Available for licensing or collaborative research.

To learn more about licensing a technology from LBNL see here.

FOR MORE INFORMATION:

Bouchard, L.S., “Unidirectional magnetic-field gradients and geometric-phase errors during Fourier encoding using orthogonal ac fields,” Phys. Rev. B, 2006, 74: 054103.

REFERENCE NUMBER: IB – 2288

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