Shreyas S Vasanawala

US Patent:

6452387, Sep 17, 2002

Filed:

Mar 7, 2001

Appl. No.:

09/801424

Inventors:

Brain A. Hargreaves - Stanford CA
Shreyas Vasanawala - Stanford CA
John M. Pauly - Redwood City CA
Dwight G. Nishimura - Palo Alto CA

Assignee:

Board of Trustees of the Leland Stanford Junior University - Palo Alto CA

International Classification:

G01V 300

US Classification:

324300, 324307

Abstract:

A steady-state condition for tipped nuclear spins is accelerated or catalyzed by first determining magnetization magnitude of the steady state and the scaling magnetization along one axis (Mz) to at least approximate the determined magnetization magnitude. Then the scaled magnetization is rotated to coincide with a real-valued eigenvector extension of the tipped steady-state magnetization. Any error vector will then decay to the steady-state condition without oscillation. In one embodiment, the magnetic resonance imaging utilizes steady-state free precession (SSFP). The scaling and rotating steps are followed by the steps of applying read-out magnetic gradients and detecting magnetic resonance signals from the tipped nuclear spins. The magnetization magnitude is determined by eigenvector analysis, and the eigenvector extension is a real-valued eigenvector determined in the analysis.

US Patent:

6922054, Jul 26, 2005

Filed:

Aug 18, 2003

Appl. No.:

10/643286

Inventors:

Brian A. Hargreaves - Menlo Park CA, US
Shreyas Vasanawala - Stanford CA, US

Assignee:

The Board of Trustees of The Leland Stanford Junior University - Palo Alto CA

International Classification:

G01V003/00

US Classification:

324307

Abstract:

Magnetic resonance imaging of a body uses steady state free precession with material separation for the selective imaging of two species, such as blood or fat. The refocusing property of SSFP is used with signal phase detection to suppress either water or lipid. Phase and/or frequency of the RF excitation pulse and repetition time are selected so that resonant frequencies of water, fw, and lipid, fl, are on opposite sides of the signal null frequency.

US Patent:

8538115, Sep 17, 2013

Filed:

Aug 17, 2011

Appl. No.:

13/211905

Inventors:

Tao Zhang - Stanford CA, US
Michael Lustig - Berkeley CA, US
Shreyas S. Vasanawala - Stanford CA, US
John M. Pauly - Stanford CA, US

Assignee:

The Board of Trustees of the Leland Stanford Junior University - Palo Alto CA
The Regents of the University of California - Oakland CA

International Classification:

G06K 9/00
G06K 9/32

US Classification:

382131, 382294

Abstract:

A three dimensional image, in a phased array magnetic resonance imaging (MRI) system is provided. Three dimensional k-space data within an auto calibration signal (ACS) region and outside the ACS region are acquired. The k-space data within the ACS region are converted into hybrid space ACS data. Compression matrices and alignment matrices of the compression matrices for the hybrid space ACS data are found along a readout direction. Alignment matrices are multiplied to the compression matrices to achieve the properly-aligned compression matrices along the readout direction. All k-space data are converted into hybrid space. The properly-aligned compression matrices are applied to the hybrid space data to provide compressed data with fewer channels. The compressed data are used to form a three dimensional image.

US Patent:

8638096, Jan 28, 2014

Filed:

Oct 19, 2010

Appl. No.:

12/907764

Inventors:

Tao Zhang - Stanford CA, US
Michael Lustig - Berkeley CA, US
John M. Pauly - Stanford CA, US
Shreyas S. Vasanawala - Stanford CA, US

Assignee:

The Board of Trustees of the Leland Stanford Junior University - Palo Alto CA

International Classification:

G01R 33/56

US Classification:

324309, 324307, 324312, 324322, 382131, 600410

Abstract:

A computer implemented method for magnetic resonance imaging is provided. A 3D Fourier Transform acquisition is performed with two phase encode directions, wherein phase code locations are chosen so that a total number of phase encodes is less than a Nyquist rate, and closest distances between phase encode locations takes on a multiplicity of values. Readout signals are received through a multi-channel array of a plurality of receivers. An autocalibrating parallel imaging interpolation is performed and a noise correlation is generated. The noise correlation is used to weight a data consistency term of a compressed sensing iterative reconstruction. An image is created from the autocalibration parallel imaging using the weighted data consistency term. The image is displayed.

US Patent:

20110248712, Oct 13, 2011

Filed:

Apr 9, 2010

Appl. No.:

12/757782

Inventors:

Thomas Grafendorfer - Meno Park CA, US
Paul David Calderon - Castro Valley CA, US
Fraser Robb - Aurora OH, US
James S. Tropp - Berkeley CA, US
Greig Cameron Scott - Palo Alto CA, US
Shreyas Vasanawala - Stanford CA, US

International Classification:

G01R 33/44

US Classification:

324307

Abstract:

A system and method for generating preamplifier feedback in magnetic resonance imaging (MRI) systems are provided. A preamplifier arrangement for the MRI system includes a plurality of preamplifiers with each of the preamplifiers connected to a different channel of a multi-channel coil array of the MRI system. The preamplifier arrangement further includes a feedback network connected to each of the plurality of preamplifiers with each of the feedback networks configured to generate negative feedback at one or more oscillation frequencies.

US Patent:

63073684, Oct 23, 2001

Filed:

May 14, 1999

Appl. No.:

9/312025

Inventors:

Shreyas S. Vasanawala - Mountain View CA
John M. Pauly - Redwood City CA
Dwight G. Nishimura - Palo Alto CA

Assignee:

Board of Trustees of the Leland Stanford Junior University - Palo Alto CA

International Classification:

G01V 300

US Classification:

324309

Abstract:

A fast, spectrally-selective steady-state free precession (SSFP) imaging method is presented. Combining k-space data from SSFP sequences with certain phase schedules of radiofrequency excitation pulses permits manipulation of the spectral selectivity of the image. For example, lipid and water can be rapidly resolved. The contrast of each image depends on both T. sub. 1 and T. sub. 2, and the relative contribution of the two relaxation mechanisms to image contrast can be controlled by adjusting the flip angle. Several applications of the technique are presented, including fast musculoskeletal imaging, brain imaging, and angiography. The technique is referred to herein as linear combination steady-state free precession (LCSSFP) and fluctuating equilibrium magnetic resonance (FEMR).

US Patent:

20220375141, Nov 24, 2022

Filed:

May 13, 2021

Appl. No.:

17/319316

Inventors:

- Stanford CA, US
Shreyas S. Vasanawala - Stanford CA, US
Frank Ong - Palo Alto CA, US

International Classification:

G06T 11/00
G06T 7/11
A61B 5/055
A61B 5/00

Abstract:

A method for MR imaging includes acquiring with an MR imaging apparatus undersampled k-space imaging data having one or more temporal dimensions and two or more spatial dimensions; transforming the undersampled k-space imaging data to image space data using zero-filled or sliding window reconstruction and sensitivity maps; decomposing the image space data into a compressed representation comprising a product of spatial and temporal parts, where the spatial part comprises spatial basis functions and the temporal part comprises temporal basis functions; processing the spatial basis functions and temporal basis functions to produce reconstructed spatial basis functions and reconstructed temporal basis functions, wherein the processing iteratively applies conjugate gradient and convolutional neural network updates using 2D or 3D spatial and 1D temporal networks; and decompressing the reconstructed spatial basis functions and reconstructed temporal basis functions to produce a reconstructed MRI image having one or more temporal dimensions and two or more spatial dimensions.

US Patent:

20220260660, Aug 18, 2022

Filed:

Feb 16, 2022

Appl. No.:

17/673003

Inventors:

- Stanford CA, US
- Washington DC, US
Julio A. Oscanoa Aida - Stanford CA, US
Shreyas S. Vasanawala - Stanford CA, US

International Classification:

G01R 33/563
G01R 33/56
A61B 5/026
A61B 5/00
G06N 3/04

Abstract:

A method for phase-contrast magnetic resonance imaging (PC-MRI) acquires undersampled PC-MRI data using a magnetic resonance imaging scanner and reconstructs MRI images from the undersampled PC-MRI data by reconstructing a first flow-encoded image using a first convolutional neural network, reconstructing a complex difference image using a second convolutional neural network, combining the complex difference image and the first flow-encoded image to obtain a second flow-encoded image, and generating a velocity encoded image from the first flow-encoded image and second flow-encoded image using phase difference processing.