US 6,700,374 B1 · EPI calibration method to minimize ghosting in reconstructed images

Abstract

A method of magnetic resonance imaging is provided. It includes supporting a subject in an examination region of an MRI scanner (A), and applying an EPI pulse sequence with the MRI scanner (A) to induce a detectable magnetic resonance signal from a selected region of the subject. The magnetic resonance signal are received and demodulated to generate raw data. Applied to the raw data are a pair of ghost reducing correction factors (θ,Δ). The pair of corrections factors (θ,Δ) included a phase correction (θ) and a read delay (Δ). The phase correction (θ) compensates for phase errors in the raw data, and the read delay (Δ) effectively shifts a data acquisition window (120) under which the raw data was collected to thereby align the raw data in k-space. The correction factors affect how data is loaded into k-space to generate k-space data, and the k-space data is subjected to a reconstruction algorithm to generate image data. Thereafter, values for the pair of correction factors (θ,Δ) are derived from the image data.

Claims24

Dependent claims

A method of magnetic resonance imaging comprising:

(a) applying an EPI pulse sequence with an MRI scanner to induce a detectable magnetic resonance signal from a selected region of a subject positioned in the MRI scanner;
(b) receiving and demodulating the magnetic resonance signal to generate raw data;
(c) applying a pair of ghost reducing correction factors to the raw data, said pair of corrections factors including a phase correction factor and a data alignment correction factor, wherein the phase correction factor compensates for phase errors in the raw data and the data alignment correction factor effectively shifts a data acquisition window under which the raw data was collected to thereby align the raw data with respect to itself in k-space;
(d) loading the correction factor affected data into k-space to generate a k-space data matrix;
(e) subjecting the k-space data matrix to an algorithm to reconstruct actual image data therefrom;
and,
(f) calculating values for the pair of correction factors using the reconstructed actual image data from step (e).

4 more elements

A method of magnetic resonance imaging comprising:

(a) supporting a subject in an examination region of an MRI scanner;
(b) conducting an iterative calibration procedure, said iterative calibration procedure comprising:
(i) applying a calibration EPI pulse sequence with the MRI scanner to induce a detectable magnetic resonance signal from a selected region of the subject, said calibration EPI pulse sequence having phase encoding gradient pulses of a first amplitude;
(ii) receiving and demodulating the magnetic resonance signal to generate raw data;
(iii) applying a pair of ghost reducing correction factors to the raw data, said pair of corrections factors including a phase correction and an alignment correction, wherein the phase correction compensates for phase errors in the raw data and the alignment correction effectively shifts a data acquisition window under which the raw data was collected to thereby align the raw data with respect to itself in k-space;
(iv) loading the correction factor affected data into k-space to generate a k-space data matrix;
(v) subjecting the k-space data matrix to a reconstruction algorithm to generate actual image data;
and,
(vi) calculating values for the pair of correction factors from the actual image data such that with each ensuing repetition of the calibration procedure the calculated values are used for the pair of correction factors applied in the step (iii) that follows;
and,
(c) upon completion of the iterative calibration procedure, designating the last calculated values for use as the correction factors in a subsequent imaging experiment directed to the selected region of the subject.

8 more elements

A method of magnetic resonance imaging comprising:

(a) supporting a subject in an examination region of an MRI scanner;
(b) conducting an iterative calibration procedure, said iterative calibration procedure comprising:
(i) applying a calibration EPI pulse sequence with the MRI scanner to induce a detectable magnetic resonance signal from a selected region of the subject, said calibration EPI pulse sequence having phase encoding gradient pulses of a first amplitude;
(ii) receiving and demodulating the magnetic resonance signal to generate raw data;
(iii) applying a pair of ghost reducing correction factors to the raw data, said pair of corrections factors including a phase correction factor and a data alignment correction factor, wherein the phase correction factor compensates for phase errors in the raw data and the data alignment correction factor effectively shifts a data acquisition window under which the raw data was collected to thereby align the raw data with respect to itself in k-space;
(iv) loading the correction factor affected data into k-space to generate a k-space data matrix;
(v) subjecting the k-space data matrix to a reconstruction algorithm to generate actual image data;
and,
(vi) calculating values for the pair of correction factors from the actual image data such that with each ensuing repetition of the calibration procedure the calculated values are used for the pair of correction factors applied in the step (iii) that follows;
(c) upon completion of the iterative calibration procedure, designating the last calculated values for use as the correction factors in a subsequent imaging experiment directed to the selected region of the subject;
and,
(d) conducting the calibration procedure a series of times such that designated values for pairs of correction factors are experimentally obtained for a number of corresponding selected regions of the subject, said number of corresponding selected regions of the subject being taken from a series of selected regions, wherein the number of corresponding selected regions of the subject includes less than all the selected regions in the series thereof.

9 more elements

An MRI scanner comprising:

a main magnet that generates a substantially uniform temporally constant main magnetic field through an examination region wherein an object being imaged is positioned;
a magnetic gradient generator that produces magnetic gradients in the main magnetic field across the examination region;
a transmission system which includes an RF transmitter that drives an RF coil which is proximate to the examination region;
a sequence control which manipulates the magnetic gradient generator and the transmission system to produce an EPI pulse sequence, said EPI pulse sequence inducing a detectable magnetic resonance signal from the object;
a reception system which includes a receiver that receives and demodulates the magnetic resonance signal to obtain raw data;
a k-space storage device into which the raw data is loaded as a k-space data matrix;
a reconstruction processor that subjects the k-space data matrix to a reconstruction algorithm to generate image data which is loaded into an image data storage device;
an output device that produces human-viewable image representations of the object from the image data;
and,
an automatic ghost reducing means which automatically generates from the image data correction factors that are applied to the raw data for reducing ghosting in the image representations, wherein the correction factors include a phase correction factor and a data alignment correction factor, said phase correction factor compensating for phase errors in the raw data and said data alignment correction factor effectively shifting a data acquisition window under which the raw data is collected to thereby adjust an alignment of the raw data.

7 more elements

Dependencies are inferred from the claim text.

EPI calibration method to minimize ghosting in reconstructed images

Life of this patent

EPI calibration method to minimize ghosting in reconstructed images

Life of this patent

Abstract

Claims24