Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
1999-11-23
2001-11-06
Arana, Louis (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S307000
Reexamination Certificate
active
06313629
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the art of magnetic resonance imaging (MRI). It finds particular application in conjunction with multi-slice acquisitions employing single echo MRI pulse sequences such as field echo (FE) and spin echo (SE) sequences, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications.
Commonly, in MRI, a substantially uniform, temporally constant main magnetic field, B
0
, is set up in an examination region in which a subject being imaged is placed. Via magnetic resonance radio frequency (RF) excitation and manipulations, selected magnetic dipoles in the subject which are otherwise aligned with the main magnetic field are tipped (via RF pulses) into a plane transverse to the main magnetic field such that they precess or resonate. In turn, the resonating dipoles are allowed to decay or realign with the main magnetic field thereby inducing magnetic resonance echoes. The various echoes making up the MRI signal are encoded via magnetic gradients set up in the main magnetic field. The raw data from the MRI apparatus is collected into a matrix commonly known as k-space. Typically, each echo is sampled a plurality of times to generate a data line or row of data points in k-space. The echo or data lines position in k-space is determined by its gradient encoding. Ultimately, employing Inverse Fourier or other known transformations, an image representation of the subject is reconstructed from the k-space data.
At times, due to non-ideal system performance or in the case of some specific data acquisition strategies, MRI signals are distorted or contaminated in either phase or amplitude leading to data inconsistencies in k-space. One potential inconsistency is that from row to row in k-space, each resonance excitation is not precisely the same amplitude or the same phase. Consequently, the result is degraded image quality. Generally, traditional methods of addressing this problem are designed to minimize those known factors affecting image quality, such as gradient non-linearity, etc. One of these methods is, for example, to over sample and use the additionally generated and collected echoes to provide correction factors which are used to adjust the k-space data and compensate for the data inconsistencies. However, while adding proportionally small amounts of time to longer imaging sequences having multi-echo echo-trains, the introduction of these additional echoes, termed navigator echoes, proportionally lengthens imaging sequences by larger amounts for single echo pulse sequences such as SE and/or FE sequences.
Moreover, commonly the navigator echoes are collected at the end of the imaging pulse sequences. Accordingly, data throughput is slowed. That is to say, processing of the k-space image data is delayed until the navigator echoes are collected and processed to generate the correction factors which will operate on the k-space data. As well, the raw MRI data has to be stored until it can be adjusted. Therefore, the efficient throughput achieved by parallel or pipeline data processing is impeded as the correction factors are not readily available upon collection of the relevant k-space data.
The present invention contemplates a new and improved technique for addressing k-space data inconsistencies which overcomes the above-referenced problems and others.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a method of magnetic resonance imaging is provided. The method includes subjecting a number of regions of an object being imaged to a magnetic resonance calibration pulse sequence. Each calibration pulse sequence generates a single calibration echo. Each of the calibration echoes are collected and therefrom correction factors are generated. Thereafter, the method includes subjecting the regions of the object being imaged to a plurality of magnetic resonance imaging pulse sequences. Each of the imaging pulse sequences generates a single imaging echo. Each imaging echo is collected into k-space as a plurality of sampled data points. The plurality of sampled data points are adjusted in accordance with the correction factors as each imaging echo is collected into k-space.
In accordance with another aspect of the present invention, a magnetic resonance imaging apparatus includes a main magnet that generates a temporally constant main magnetic field through an examination region in which an object being imaged is placed. A magnetic gradient generator produces magnetic gradients in the main magnetic field across the examination region. A transmission system includes an RF transmitter that drives an RF coil which is proximate to the examination region. A sequence control manipulates the magnetic gradient generator and the transmission system to produce a plurality of MRI pulse sequences including: (i) a number of calibration sequences which generate calibration echoes, each calibration sequence generating one calibration echo emanating from each of a plurality of slices of the object being imaged; and (ii) a plurality of imaging sequences, each imaging sequence generating one imaging echo such that multiple imaging echoes emanate from each slice. A reception system includes a receiver that receives the calibration echoes and the imaging echoes. A data correction processor determines an image data correction factor from the calibration echoes. The image data correction factor is applied to image data from the imaging echoes prior to the image data filling in k-space. Finally, a reconstruction processor accesses the image data in k-space to reconstruct an image representation of the object, and an output device converts the image representation into a human viewable display.
One advantage of the present invention is short imaging sequences.
Another advantage of the present invention is improved image quality and artifact elimination.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.
REFERENCES:
patent: 5151656 (1992-09-01), Maie et al.
patent: 5621321 (1997-04-01), Liu et al.
patent: 5825185 (1998-10-01), Liu et al.
Bearden Francis H.
Liu Xecheng
Arana Louis
Fay Sharpe Fagan Minnich & McKee LLP
Picker International Inc.
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