Richard R Rzedzian

US Patent:

52432866, Sep 7, 1993

Filed:

Jun 29, 1990

Appl. No.:

7/546503

Inventors:

Richard Rzedzian - Lexington MA
Charles Martin - Arlington MA

Assignee:

Advanced NMR Systems, Inc. - Wilmington MA

International Classification:

G01Y 300

US Classification:

324318

Abstract:

Narrower conductive strips are provided in a segmented RF shield to reduce the gradient coil power loss attributable to the shield. Narrower conductive strips reduce the eddy current losses experienced by the gradient coil, thereby reducing the power required to operate the gradient coil, especially in high speed imaging where high frequencies up to 10 KHz are used. The conductive strips can be made sufficiently narrow to substantially reduce the gradient coil power loss attributable to the shield. When these strips are made in this manner, a third conductive layer may be placed over a transition region where there is a substantial change in the direction of the conductive strips. In such a transition region, RF current tends to travel in curved paths across the pattern of conductive strips instead of along the lengths of the strips, with resulting decrease in coil quality factor, Q. The third conductive layer provides a lower impedance path for RF currents in the transition region, to reduce RF power loss. An ancillary conductor is connected to the RF shield in such a manner as to be insulated from the shield at the lower frequencies at which the gradient coil operates but capacitively connected at RF frequencies.

US Patent:

46282645, Dec 9, 1986

Filed:

Mar 14, 1984

Appl. No.:

6/589539

Inventors:

Richard R. Rzedzian - Lexington MA

Assignee:

Advanced NMR Systems, Inc. - Woburn MA

International Classification:

G01R 0000

US Classification:

324322

Abstract:

A circuit and method are disclosed for providing high, constant amplitude sinusoidally modulated NMR gradient fields. A capacitor is connected in parallel with the gradient coil, but separated by a switch. A pre-determined amount of energy is stored in the capacitor and then the switch is closed to permit a sinusoidal oscillation of energy between the capacitor and gradient coil. By precharging appropriately, sine wave or cosine wave oscillation can be obtained for the NMR system. The oscillation is terminated by opening the switch at a time when all of the oscillating energy is in the capacitor. In a preferred embodiment of the invention, the switch is a bridge circuit, each of whose sides is a back-to-back thyristor pair, so that the gradient field may be modulated either as a full wave, half-wave rectified or non-rectified sinusoidal oscillation. In one embodiment, a full-wave rectified sine wave is used, and all the oscillating energy is caught in the capacitor during intervals in which 180. degree. RF pulses are applied to generate echoes.

US Patent:

49409417, Jul 10, 1990

Filed:

Apr 3, 1989

Appl. No.:

7/331806

Inventors:

Richard R. Rzedzian - Lexington MA

Assignee:

Advanced NMR Systems, Inc. - Woburn MA

International Classification:

G01R 3320

US Classification:

324312

Abstract:

A method of high-speed magnetic resonance imaging in which the object to be imaged is placed in a high static magnetic field. Nuclear spins are excited in an image area by applying a pulse of radio frequency magnetic field. Optionally, a first gradient field, termed a slice selection gradient, may be applied in conjunction with the RF excitation pulse such that spins are excited only in a selected plane of the object. Following an encoding pulse sequence and rephasing of the nuclear spins by the application of a 180. degree. radio frequency pulse, mutually orthogonal phase-encoding and readout gradients are alternatively applied in the image plane to effect a traversal through spatial frequency domain (k-space). In a preferred embodiment of the invention, the readout gradient is applied as a continuous sinusoidal wave, resulting in a slight overlap between the phase-encoding and readout gradients. If phase errors vary slowly in time, only a partial k-space trajectory is required.

US Patent:

52851613, Feb 8, 1994

Filed:

Jun 1, 1993

Appl. No.:

8/070639

Inventors:

Richard Rzedzian - Lexington MA
Stephen Crump - Newton Center MA

Assignee:

Advanced NMR Systems, Inc. - Wilmington MA

International Classification:

G01R 3320

US Classification:

324322

Abstract:

A series topology is provided for the magnetic-field-generating coil and storage capacitor in the circuitry driving the coil of an MRI system. The coil and capacitor thus form a series resonant circuit that can deliver a sinusoidal current through the coil at a resonant frequency. A power source and switch are connected in series with the coil and capacitor, and current flow to the coil is initiated and interrupted by closing and opening the switch.

US Patent:

55721311, Nov 5, 1996

Filed:

May 30, 1995

Appl. No.:

8/452540

Inventors:

Richard Rzedzian - Lexington MA

Assignee:

Advanced NMR Systems, Inc. - Wilmington MA

International Classification:

G01V 300

US Classification:

324318

Abstract:

A unitary, generally cylindrical member supports both the primary and shielding coils. By supporting both coils on a unitary member it is possible to take advantage of the antiphase relationship between the primary and shielding coils and thereby reduce the acoustic noise generated by the gradient coil assembly. The unitary member can be formed by starting with a mandrel to which the primary coil is applied, and then successively adding layers each having a cylindrical outer surface aligned with the same longitudinal axis. Each new cylindrical surface is formed by adding material and then removing some of the material while rotating the member about the longitudinal axis (e. g. , turning on a lathe, or passing a blade past a still liquid skim coat). Additional primary and shielding coils are applied after each new aligned, cylindrical surface is formed. One or more correction coils are located outside of the shielding coils to cancel any gradient field present there as the result of misalignment between the primary and shielding coils.

US Patent:

54811910, Jan 2, 1996

Filed:

May 13, 1994

Appl. No.:

8/242706

Inventors:

Richard Rzedzian - Lexington MA

Assignee:

Advanced NMR Systems, Inc. - Wilmington MA

International Classification:

G01V 300

US Classification:

324318

Abstract:

A unitary, generally cylindrical member supports both the primary and shielding coils. By supporting both coils on a unitary member it is possible to take advantage of the antiphase relationship between the primary and shielding coils and thereby reduce the acoustic noise generated by the gradient coil assembly. The unitary member can be formed by starting with a mandrel to which the primary coil is applied, and then successively adding layers each having a cylindrical outer surface aligned with the same longitudinal axis. Each new cylindrical surface is formed by adding material and then removing some of the material while rotating the member about the longitudinal axis (e. g. , turning on a lathe, or passing a blade past a still liquid skim coat). Additional primary and shielding coils are applied after each new aligned, cylindrical surface is formed. One or more correction coils are located outside of the shielding coils to cancel any gradient field present there as the result of misalignment between the primary and shielding coils.

US Patent:

47679913, Aug 30, 1988

Filed:

Aug 17, 1987

Appl. No.:

7/085568

Inventors:

Richard R. Rzedzian - Lexington MA

Assignee:

Advanced NMR Systems, Inc. - Woburn MA

International Classification:

G01R 3320

US Classification:

324312

Abstract:

A method of high-speed imaging is employed in which less than 100% of the spatial frequency domain (k-space) is sampled. In one embodiment, the trajectory extends over the k-space origin, and the information acquired from the extension is used to compensate for any phase errors. If the same number of points are collected as in a full k-space acquisition, signal bandwidth is maintained, and spatial frequency response is increased. In a second embodiment, two or more partial k-space acquisitions are performed and then pieced together in a "mosaic" prior to Fourier transformation. In a further embodiment, partial k-space acquisitions in the direction of the readout gradient are combined with interleaved acquisitions in the direction of the phase-encoding gradient to avoid discontinuities.

US Patent:

47407484, Apr 26, 1988

Filed:

Dec 3, 1986

Appl. No.:

6/937529

Inventors:

Richard R. Rzedzian - Lexington MA

Assignee:

Advanced NMR Systems, Inc.

International Classification:

G01R 3320

US Classification:

324309

Abstract:

A method of high-speed magnetic resonance imaging in which the object to be imaged is placed in a high static magnetic field. Nuclear spins are excited in an image area in a selected plane of the object by superimposing a slice-selection gradient along an axis and applying a pulse of radio frequency magnetic field. Following an encoding pulse sequence and rephasing of the nuclear spins by the application of a 180. degree. radio frequency pulse, mutually orthogonal phase-encoding and readout gradients are alternately applied in the image plane to effect a traversal through spatial frequency domain (k-space). If phase errors vary slowly in time, only a partial k-space trajectory is required. Chemical shift is eliminated either by the application of a suppression pulse of RF field or by tailoring the frequency spectrum of the rephasing pulse so as to preclude rephasing of one or other of the chemical moieties.