Doty Scientific, Inc.

Other

Medical University of South Carolina

F David Doty

Jonathan B Spitzmesser

Siddarth Shevgoor

David G Wilson

James K Wilcher

Gregory S Hosford

George Entzminger, Jr

Yungan Yang

Brian L Miller

Lester G Hacker

R J Cameron

J B Spitzmesser

An NMR probe for insertion into an NMR magnet from below is disclosed that includes multiple counterflow heat exchangers to enable a wide range of NMR methods at ultra low temperatures, including MAS DNP at temperatures below 15 K. Coolant fluid is ducted from the bottom of the probe through a vacuum insulated transfer line up into the probehead, the region containing the sample and sample coil, where it splits into first and second coolant streams for cooling first and second spin-gas streams, each through a cold counterflow exchanger and at least one cool counterflow exchanger contained within the probe. The cold exchangers would each preferably comprise two straight continuously joined tubes inside a dewared tube that extends from a vacuum chamber in the base of the probe up into the probehead. These cold exchangers are denoted as Dual Inner Tube Exchangers (DITEs). The cool exchanger is preferably a coil of two parallel continuously thermally joined tubes, and it is denoted as a Parallel Tube Recuperator (PTR). The first coolant-stream in the probehead feeds into the top of DITE-1, through which the first coolant stream flows downward, providing final cooling to the first spin gas stream which is flowing upward past it into the probehead. The first coolant stream leaving the bottom end of DITE-1 then enters the cooler end of a first PTR in an evacuated chamber in the base of the probe and proceeds through the first PTR to its warmer end in counter-current to the first spin gas stream which had entered at the warmer end of first PTR, exited at its cooler end, and proceeded into the bottom end of DITE-1. An additional PTR may be series connected to the first PTR to further improve the overall effectiveness of heat transfer from first spin gas stream to the first coolant stream. In like manner, the second coolant stream cools a second spin gas stream. The exchangers are designed to permit fast MAS at temperatures below 15 K when the probe is supplied with room-temperature helium spin gas streams at commonly used pressures and a helium coolant stream at less than 170 kPa from a standard portable helium cryostat. Liquid helium usage rate is typically in the 2-12 L/hr range, depending on the spinning rate and sample temperature. Both the spin gases and the coolant fluid are fully recoverable without contamination for recycling using the standard helium recycling methods and equipment (with minor upgrades) commonly found in many NMR laboratories.

NMR probe for efficient MAS-DNP operation at ultra-low temperatures

An overmoded dielectric-lined waveguide, particularly for the 0.03 to 3 terahertz frequency range, is disclosed with performance advantages relative to prior dielectric-lined waveguides, cost and size advantages relative to corrugated waveguides, and with coupling, bandwidth, and cost advantages relative to micro-structured-fiber waveguides. The waveguide comprises a single-clad flexible microwave laminate rolled into a cylinder with said copper surface on an outside of said guide tube and said dielectric surface on an inside of said guide tube. The rolled laminate is supported inside a metal tube. The same method of achieving the structure needed for efficient guiding of HEmode may be applied to a conical tube to make a low-cost efficient overmoded tapered waveguide transition for the 0.03-3 THz range.

Terahertz waveguide comprising an outer copper layer laminated with an inner dielectric layer to form a rolled guide tube which is encased by a support tube

An improved method of supplying pressurized cold gas consistently of predominately Nand He at low flow rate (typically under 1 g/s) with a desired Nliquid fraction to an instrument requiring such is disclosed. Pressurized ultra-dry nitrogen gas of a controlled mass-flow rate is cooled inside fine coils bathed in liquid nitrogen to condense it to a vapor fraction less than about 20% and typically under 3%. A second gas stream consisting of predominately nitrogen plus helium, supplied from a controlled pressure, is cooled in a separate set of coils to an exit mean temperature significantly above the temperature of saturated nitrogen vapor in this mixture. The fluid from the first (condensed) mixture is injected into the cooled gas from the second mixture and transferred through a thermally insulated line to the input of the instrument needing a supply of cold gas of a target vapor fraction.

Stabilizing control of a saturated cold gas stream

In a dual-source organic Rankine cycle (DORC), the condensed and slightly sub-cooled working fluid at near ambient temperature (&#x2dc;300 K) and at low-side pressure (0.1 to 0.7 MPa) is (1) pumped to high-side pressure (0.5-5 MPa), (2) pre-heated in a low-temperature (LT) recuperator, (3) boiled using a low-grade heat source, (4) super-heated in a high-temperature (HT) recuperator to a temperature close to the expander turbine exhaust temperature using this exhaust vapor enthalpy, (5) further super-heated to the turbine inlet temperature (TIT) using a mid-grade heat source, (6) expanded through a turbine expander to the low-side pressure, (7) cooled through the HT recuperator, (8) cooled through the LT recuperator, (9) mostly liquefied and slightly subcooled in a condenser, and (10) the condensed portion is returned to the pump to repeat this cycle.

High-temperature dual-source organic Rankine cycle with gas separations

All critical circuit components, including the sample coils, are located along with the spinner assembly in a region that may be evacuated to high vacuum for thermal insulation and high-voltage operation. A hermetically sealed spinner assembly simultaneously satisfies the requirements of hermeticity, low total emissivity, rf compatibility, spinning performance, magnetic compatibility, and high filling factor by utilizing metal construction except for the central region near the rf sample coils. Hence, it is possible to maintain high vacuum in the region external to the MAS spinner assembly even over a broad range of bearing and drive gas temperatures. A bundle of optical fibers is provided for tachometry for spin rates up to 60 kHz. The use of alumina disc capacitors allows the noise contributions from the most critical capacitors to be reduced to a minor fraction of the total and simplifies high voltage operation.

NMR CryoMAS probe for high-field wide-bore magnets

An NMR probe contains a metallic dewar for use in a high field magnet, the dewar characterized as having a major fraction of its inner wall made from an alloy whose weight composition includes at least 70% copper, less than 20% zinc, less than 10% nickel, less than 8% Cr, less than 4% Pb, less than 0.15% iron, less than 0.15% cobalt, and at least 3% from the set comprised of tin, silicon, aluminum, and chromium, and said inner wall further characterized as being plated with a pure metal on at least one surface.

NMR MAS probe with cryogenically cooled critical circuit components

The MRI rf coil known as the balanced high-pass-weighted hybrid birdcage is modified to obtain two homogeneous degenerate resonances, capable of generating circular polarization at widely separated frequencies, by including inductors in parallel with the ring (high-pass) tuning capacitors such that their isolated parallel resonant frequency is greater than the desired low-frequency (LF) homogeneous resonance and not greater than 10% more than the desired high-frequency (HF) homogeneous resonance. The coil is advantageous for the frequency-diameter product range of 10 to 60 MHz-m. The coil is preferably balanced at both frequencies such that the electric potentials vanish on the central axial plane at both the LF and HF homogeneous modes. Additional parasitic-mode-shifting reactive elements, either capacitors or inductors, may be added between adjacent rungs near their ends, and the rungs may each consist of two parallel bands shorted together at their ends, as in the Crozier birdcage. Note that a high-pass-weighted hybrid birdcage is defined as a hybrid birdcage in which the reactance of the rung series capacitors is significantly less than the reactance of the ring series capacitors.

Double-balanced double-tuned CP birdcage with similar field profiles

'An MAS probe is disclosed for obtaining a substantial improvement in signal to noise (S/N) in triple-resonance high-resolution (HR) magic-angle-spinning (MAS) NMR of samples near room temperature (RT) in high-field magnets where the magnet's RT shim bore is greater than 60 mm. All critical circuit components, including the sample coils, are located along with the spinner assembly in a thermally insulated cold zone pressurized with helium gas. The spinner assembly attaches to a sealed, curved, rotor-loading tube to permit automatic sample change, and it is surrounded by a partially insulated jacket cooled with a cryogenic fluid, generally nitrogen gas. The MAS probe is also compatible with magic angle gradients, variable temperature operation, field locking, and commonly available closed-cycle cold fingers.'

A material having a permanent external diametrical electric field is included within an NMR MAS spinner. Such materials include ferroelectret porous films, in which the electric polarization arises from opposite mono-polar charges on separated surfaces within a structured material containing voids. Rotation of electrically polarized material produces a time-dependent electric field, modulated at the rotational frequency, so that a simple antenna achieves high sensitivity and phase stability in spin rate detection. The electrically polarized material is also of sufficiently high resistivity that modulation of the external NMR polarizing magnetic field Bis negligible.

NMR MAS electret spin rate detection

An improved axial gas bearing for a gas-driven NMR MAS sample rotor is disclosed that utilizes inward flow with a low rotational component over a rotor conical end. A conical flow region is formed between the rotor conical end and a conical stator bearing surface such that the included angle defining the stator surface is not less than the included angle defining the rotor conical end. Gas is injected radially inward with a significant axial rearward component from a number of small holes at high velocity from the periphery into the conical flow region. Compared to the radial velocity components, the tangential flow components of the injected gas are small and preferably opposed to the direction of the rotor rotation. The high and accelerating negative radial velocities may result in significant Bernoulli effect, such that the mean axial pressure over the conical rotor end may be less than atmospheric pressure for a given axial clearance, but as the clearance decreases, the hydrostatic effects exceed the Bernoulli effects and the mean axial pressure over the conical rotor end may then exceed atmospheric pressure by a substantial amount. Thus, a self-stabilizing axial bearing is formed with improved stability and stiffness for rotor surface speeds up to at least 80% of the speed of sound. Motive power required to spin the rotor may be provided by a radial-inflow microturbine at the opposite end of the rotor in a way that is readily compatible with automatic sample change.

NMR MAS inflow bernoulli bearing

A MAS probe offers a substantial improvement in signal to noise (S/N) in triple-resonance high-resolution (HR) magic-angle-spinning (MAS) NMR of samples near room temperature (RT) in high field magnets, especially where the RT shim bore is less than 55 mm. Critical circuit components other than the sample coils, including both high-power capacitors and inductors for one or more channels are located in a small, thermally insulated, cold zone immediately below the sample spinner assembly. Cooling these components to 100 K allows their thermal noise power to be conveniently reduced by a factor of three or more. Variable capacitors for fine tuning are located in an RT tuning zone below the cold zone. The circuit is designed such that the currents, voltages, and standing wave ratio (SWR) in circuit tuning elements in the RT tuning zone are relatively low, so rf losses and noise contributions below the cold zone may be only a few percent. The MAS probe is also compatible with magic angle gradients, automatic sample change, multi-nuclear tuning, variable temperature operation, field locking, and optical spin rate detection.

A flexible, low-loss, low-capacitance, high-voltage, high-current, moderate-impedance, unshielded, balanced, rf-pulse transmission twinline is produced by etching parallel copper traces on opposite sides of a flexible substrate, spaced apart such that the distance between the conductors is greater than four times the substrate thickness and at least one of the conductors has a width greater than half of the separation between the conductors. A second, similar twinline may be etched on the same substrate beside the first twinline and paralleled at both ends with the first twinline to form a lower-impedance quadline such that alternate conductors in the quadline are on alternate sides of the substrate and have opposite current phases. Both surfaces may be coated with a thin, flexible dielectric to increase the voltage rating for a given conductor separation with minimal affect on propagation factor, attenuation constant, or flexibility. A second, similar quadline on a separate laminate displaced along the normal from the first may be paralleled with the first quadline forming a lower-impedance dual-quadline such that the two laminates have mean spacing comparable to or greater than the spacing between conductors within a twinline. The two quadlines are paralleled such that the phases in the conductors in one quadline are the same as the phases in the adjacent conductors in the adjacent quadline. The concepts may be extended in like manner for further reduction in characteristic impedance without sacrifice in propagation factor, attenuation constant, or flexibility.

High power flexible leads for DAS NMR

The two halves of a conventional RF saddle coil, such as spirals or other related structures for use in high resolution NMR or MRI, are disposed on opposite sides of a cylindrical coilform, and rotated from the conventional orientation 90 degrees about the B1 axis, so that the leads are paralleled near the axial center of the RF coil.

Center-fed paralleled coils for MRI

HR MAS NMR coils with magic angle capacitors

An edge-wound NMR solenoidal sample coil is made by winding at least two turns of flattened wire around a cylindrical coilform such that the major cross-sectional axis of the flat wire is perpendicular to the axis of the solenoid. The space between turns near the center is greater than the space between turns at the ends but less than the major cross-sectional dimension of the flat wire. The flattened wire is magnetically compensated by forming copper tubing around paramagnetic wires. The resulting solenoid has considerably higher .eta..sub.F Q and B.sub.1 homogeneity than prior-art solenoids of comparable size and transverse transparency. Similar principles may be used to improve the segmented, transparent, loop-gap resonator for breast and other imaging applications by using segmented planar ring resonators, tightly coupled by means of balanced transmission lines at the magic angle, with outermost conductive surfaces oriented more in the radial than axial direction. Similar principles may also be used to produce an improved, segmented, conical surface coil.

Growing community of inventors

Columbia, SC, United States of America

F David Doty