Method and apparatus for determining a system frequency in magnetic resonance imaging

Patent metadata

Field	Value
Publication number	US-2016274156-A1
Application number	US-201615074212-A
Country	US
Kind code	A1
Filing date	Mar 18, 2016
Priority date	Mar 20, 2015
Publication date	Sep 22, 2016
Grant date	—

Abstract

In a method, device and magnetic resonance (MR) system for determining a system frequency in MR imaging, a frequency spectrum of a region under examination is acquired. A cost function (FOM) is determined that encompasses the difference between a parameterized model function having assigned parameters that is to be optimized, and the acquired frequency spectrum. The cost function is subsequently minimized. Furthermore, the parameters of the optimized parameterized model function assigned to the determined minimum are determined and the system frequency is calculated on the basis of the determined parameters.

First claim

I claim as my invention:

1 . A method for determining a system frequency for magnetic resonance (MR) imaging, comprising:
operating an MR data acquisition unit to acquire a frequency spectrum of an examination region in the MR scanner; providing said frequency spectrum to a computer and, in said computer, automatically determining a cost function that represents a difference between a predetermined model function having assigned parameters, which is to be optimized, and the acquired frequency spectrum; in said computer, executing a minimization algorithm that minimizes said cost function; in said computer, executing an optimization algorithm that optimizes said model function, to obtain an optimized parameterized model function, and determining parameters of said optimized parameterized model function corresponding to the minimized cost function; and in said computer, using the determined parameters to determine said system frequency and emitting an electronic signal from said computer representing said system frequency.

2 . A method as claimed in claim 1 comprising employing, as said parameterized model function, a parameterized model function having a center frequency of a maximum of a frequency spectrum modeled by said parameterized model function, and comprising, as parameters, a width and an amplitude.

3 . A method as claimed in claim 1 comprising determining said cost function as a sum of squares of the difference between the parameterized model function and the acquired frequency spectrum.

4 . A method as claimed in claim 1 wherein said parameterized model function comprises, as parameters, a width and an amplitude, and wherein said cost function comprises weighting parameters that restrict differences of the respective widths and heights of multiple maxima of said parameterized model function.

5 . A method as claimed in claim 1 comprising optimizing said cost function in an iterative optimization algorithm using a plurality of sets of alternative start values that are respectively determined for respective center frequencies of different substances, with each set of alternative start values being respectively for one of said different substances, and minimizing said cost function for each of said sets of alternative start values.

6 . A method as claimed in claim 5 wherein said different substances are water, fat and silicone.

7 . A method as claimed in claim 5 comprising, in said computer, evaluating a quality of the optimization of the cost function dependent on whether function values of the minimized cost function undershoot a threshold value.

8 . A method as claimed in claim 7 comprising using, as the minimized cost function, the minimized cost function, respectively obtained from said different sets of start values that has the lowest minimized function value.

9 . A method as claimed in claim 8 comprising evaluating said minimization of said cost function by determining whether a frequency function of the determined parameters of the optimized parameterized model function has a single maximum.

10 . A method as claimed in claim 9 comprising, when said frequency spectrum of said optimized parameterized model function has said single maximum, determining, in said computer, an additional maximum of said frequency spectrum of the optimized parameterized model function by reducing said threshold, and determining a substance assigned to said single maximum dependent on a position of said additional maximum in said frequency spectrum of the optimized parameterized model function.

11 . A method as claimed in claim 10 comprising calculating said system frequency as a weighted mean value calculation depending on the frequency value of a primary maximum and a frequency value of at least one secondary maximum of the optimized modeled frequency spectrum, each weighting in said weighted mean comprising a determined amplitude of respective maxima of the optimized parameterized model function.

12 . A method as claimed in claim 11 wherein said different substances are water, fat and silicone, and comprising weighting the maximum for water with a value 1 when calculating said system frequency.

13 . A system frequency determination device for determining a system frequency in magnetic resonance (MR) imaging, comprising:
a computer having an input interface that receives a frequency spectrum of an examination region in the MR scanner; said computer being configured to automatically determine a cost function that represents a difference between a predetermined model function having assigned parameters, which is to be optimized, and the acquired frequency spectrum; said computer being configured to execute a minimization algorithm that minimizes said cost function; said computer being configured to execute an optimization algorithm that optimizes said model function, to obtain an optimized parameterized model function, and determining parameters of said optimized parameterized model function corresponding to the minimized cost function; and said computer being configured to use the determined parameters to determine said system frequency and to emit an electronic signal from said computer representing said system frequency.

14 . A magnetic resonance (MR) imaging apparatus comprising:
an MR data acquisition scanner; a control computer configured to operate the MR data acquisition unit to acquire a frequency spectrum of an examination region in the MR scanner; said control computer being configured to automatically determine a cost function that represents a difference between a predetermined model function having assigned parameters, which is to be optimized, and the acquired frequency spectrum; said control computer being configured to execute a minimization algorithm that minimizes said cost function; said control computer being configured to execute an optimization algorithm that optimizes said model function, to obtain an optimized parameterized model function, and determining parameters of said, optimized parameterized model function corresponding to the minimized cost function; and said control computer being configured to use the determined parameters to determine said system frequency and to emit an electronic signal from said computer representing said system frequency.

15 . A non-transitory, computer-readable data storage medium encoded with programming instructions, said storage medium being loaded into a control computer of a magnetic resonance (MR) apparatus, which comprises an MR data acquisition scanner, said programming instructions causing said control computer to:
operate an MR data acquisition unit to acquire a frequency spectrum of an examination region in the MR scanner; automatically determine a cost function that represents a difference between a predetermined model function having assigned parameters, which is to be optimized, and the acquired frequency spectrum; execute a minimization algorithm that minimizes said cost function; execute an optimization algorithm that optimizes said model function, to obtain an optimized parameterized model function, and determining parameters of said optimized parameterized model function corresponding to the minimized cost function; and use the determined parameters to determine said system frequency and emit an electronic signal from said computer representing said system frequency.

Assignees

• Siemens Ag

Inventors

• Niederloehner Daniel

Classifications

• G01R33/5607

  by reducing the NMR signal of a particular spin species, e.g. of a chemical species for fat suppression, or of a moving spin species for black-blood imaging · CPC title

• G01R23/16 Primary

  Spectrum analysis; Fourier analysis · CPC title

• G01R33/4828 Primary

  Resolving the MR signals of different chemical species, e.g. water-fat imaging · CPC title

• G01R33/64

  using cyclotron resonance (G01R33/24 takes precedence) · CPC title

• G01R33/583

  Calibration of signal excitation or detection systems, e.g. for optimal RF excitation power or frequency (G01R33/246 takes precedence) · CPC title