Correcting for main magnetic field inhomogeneity in MRI scanners
First Claim
1. A method of correcting for main magnetic field (B0) inhomogeneity in a Magnetic Resonance Imaging (MRI) scanner during a scanning sequence which includes the acquisition of successive volumes by means of Magnetic Resonance (MR) pulse sequences, comprising:
- after an acquisition of a volume in the scanning sequence;
applying, by the MRI scanner, a first three-dimensional volumetric navigator and obtaining a first navigator image,applying, by the MRI scanner, a second three-dimensional volumetric navigator after the first navigator and obtaining a second navigator image, wherein the first and second navigators have different echo times;
after the first and second navigator images have been obtained and before the acquisition of the next volume in the scanning sequence;
determining a magnetic field map by complex division of the first and second navigator images;
using the magnetic field map to determine parameters required to adjust the homogeneity of the main magnetic field (B0), the determined parameters including a zero order shim which is estimated from the magnetic field map based on a least-squares fit; and
adjusting the MRI scanner based on the determined parameters by adjusting a system central frequency of the MRI scanner, the system central frequency being adjusted by adjusting a phase and frequency for a Numerically Controlled Oscillator (NCO) of the MRI scanner for all radiofrequency (RF) excitation pulses of the MRI scanner and for Analog to Digital Converter (ADC) pulses of the MRI scanner for both the scanning sequence and for the first and second navigators.
2 Assignments
0 Petitions
Accused Products
Abstract
A method for correcting for main magnetic field (B0) inhomogeneity in a Magnetic Resonance Imaging (MRI) scanner is disclosed. The method includes applying a first and a second three-dimensional volumetric navigator after an acquisition of a volume in a scanning sequence and before the next volume is acquired. From a resultant pair of navigator images, a magnetic field map is obtained by complex division of the pair of navigator images, and the field map is used to determine parameters to adjust the MRI scanner to compensate for B0 inhomogeneity. The navigators may excite only a portion of an entire object to be imaged, so that adjustment of the MR scanner can be done slice-by-slice or slab-by-slab. Motion correction can also be implemented by comparing the first navigator to a stored reference image and updating for motion before acquisition of the next volume in the scanning sequence.
8 Citations
18 Claims
-
1. A method of correcting for main magnetic field (B0) inhomogeneity in a Magnetic Resonance Imaging (MRI) scanner during a scanning sequence which includes the acquisition of successive volumes by means of Magnetic Resonance (MR) pulse sequences, comprising:
-
after an acquisition of a volume in the scanning sequence; applying, by the MRI scanner, a first three-dimensional volumetric navigator and obtaining a first navigator image, applying, by the MRI scanner, a second three-dimensional volumetric navigator after the first navigator and obtaining a second navigator image, wherein the first and second navigators have different echo times; after the first and second navigator images have been obtained and before the acquisition of the next volume in the scanning sequence; determining a magnetic field map by complex division of the first and second navigator images; using the magnetic field map to determine parameters required to adjust the homogeneity of the main magnetic field (B0), the determined parameters including a zero order shim which is estimated from the magnetic field map based on a least-squares fit; and adjusting the MRI scanner based on the determined parameters by adjusting a system central frequency of the MRI scanner, the system central frequency being adjusted by adjusting a phase and frequency for a Numerically Controlled Oscillator (NCO) of the MRI scanner for all radiofrequency (RF) excitation pulses of the MRI scanner and for Analog to Digital Converter (ADC) pulses of the MRI scanner for both the scanning sequence and for the first and second navigators. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
-
Specification