Magnetic resonance imaging apparatus and fluid-enhanced image acquisition method

Patent metadata

Field	Value
Publication number	US-9435871-B2
Application number	US-201213978930-A
Country	US
Kind code	B2
Filing date	Jan 11, 2012
Priority date	Jan 17, 2011
Publication date	Sep 6, 2016
Grant date	Sep 6, 2016

Abstract

In order to acquire an image with enhanced contrast between a fluid portion and a stationary portion without extending the imaging time even when an IR pulse is used as an RF pre-pulse, the RF pre-pulse is applied to a region upstream of an imaging region so as to excite longitudinal magnetization of the fluid portion in a negative direction, an echo signal is measured from the imaging region, and an image with enhanced contrast of the fluid portion with respect to the stationary portion is acquired on the basis of phase information of an image reconstructed by using the echo signal.

First claim

The invention claimed is:

1. A magnetic resonance imaging apparatus comprising:
a measurement control unit configured to control measurement of an echo signal from an imaging region of an object to be examined including a fluid portion, on the basis of a predetermined pulse sequence; and
an arithmetic processing unit configured to obtain an image with enhanced contrast between the fluid portion and a stationary portion using the echo signal, wherein:
the pulse sequence is formed by an RF pre-pulse portion provided with an RF pre-pulse which performs labeling on the fluid portion by exciting the longitudinal magnetization of the fluid portion in a negative direction and a measurement sequence portion configured to measure an echo signal from the imaging region into which the labeled fluid portion is flown; and
the arithmetic processing unit obtains a fluid-enhanced image with enhanced contrast between the fluid portion and the stationary portion based on phase information of the image, and wherein
the measurement control unit performs labeling on the fluid portion by applying the RF pre-pulse to a region upstream from the imaging region, and executes the measurement sequence before the longitudinal magnetization of the labeled fluid portion is recovered to null or above, and wherein:
the RF pre-pulse includes an IR pulse which excites the longitudinal magnetization at α(90<α<270)-degrees; and
the measurement sequence portion includes a transverse magnetization generating RF pulse which generates transverse magnetization by exciting the longitudinal magnetization at β(0<β≦90)-degrees.

2. The magnetic resonance imaging apparatus according to claim 1 , wherein the measurement control unit sets a waiting time (TI) between the IR pulse in the RF pre-pulse portion and the transverse magnetization generating RF pulse in the measurement sequence portion, as the time for maintaining the state that the longitudinal magnetization of the labeled fluid portion by the IR pulse is in a negative direction.

3. The magnetic resonance imaging apparatus according to claim 2 , wherein the measurement control unit controls measurement of the echo signal by differentiating the phase of the transverse magnetization between the labeled fluid portion and the stationary portion by π, right after the application of the transverse magnetization generating RF pulse.

4. A magnetic resonance imaging apparatus comprising:
a measurement control unit configured to control measurement of an echo signal from an imaging region of an object to be examined including a fluid portion, on the basis of a predetermined pulse sequence; and
an arithmetic processing unit configured to obtain an image with enhanced contrast between the fluid portion and a stationary portion using the echo signal, wherein:
the pulse sequence is formed by an RF pre-pulse portion provided with an RF pre-pulse which performs labeling on the fluid portion by exciting the longitudinal magnetization of the fluid portion in a negative direction and a measurement sequence portion configured to measure an echo signal from the imaging region into which the labeled fluid portion is flown; and
the arithmetic processing unit obtains a fluid-enhanced image with enhanced contrast between the fluid portion and the stationary portion based on phase information of the image, and wherein
the arithmetic processing unit, on the basis of the phase image reconstructed using the echo signal measured by the measurement sequence portion, determines the weighting coefficient for each pixel in the image, thereby obtaining the fluid-enhanced image using the weighting coefficient.

5. The magnetic resonance imaging apparatus according to claim 4 , wherein the arithmetic processing unit, on the basis of a phase difference image between the phase image which is reconstructed using the echo signal measured only by the measurement sequence portion and the phase image which is reconstructed using the echo signal measured in the RF pre-pulse portion and the measurement sequence portion, determines the weighting coefficient for each of the pixel, creates a mask image representing the distribution of the weighting coefficient, and multiplies the mask image by the absolute value image of the reconstructed image for each pixel, thereby obtaining the fluid-enhanced image.

6. The magnetic resonance imaging apparatus according to claim 5 , wherein the arithmetic processing unit acquires the weighting coefficient in the phase difference image, by converting the phase of the fluid portion into the value of [0˜1] and converting the phase of the other stationary portion into [1].

7. A magnetic resonance imaging apparatus comprising:
a measurement control unit configured to control measurement of an echo signal from an imaging region of an object to be examined including a fluid portion, on the basis of a predetermined pulse sequence; and
an arithmetic processing unit configured to obtain an image with enhanced contrast between the fluid portion and a stationary portion using the echo signal, wherein:
the pulse sequence is formed by an RF pre-pulse portion provided with an RF pre-pulse which performs labeling on the fluid portion by exciting the longitudinal magnetization of the fluid portion in a negative direction and a measurement sequence portion configured to measure an echo signal from the imaging region into which the labeled fluid portion is flown; and
the arithmetic processing unit obtains a fluid-enhanced image with enhanced contrast between the fluid portion and the stationary portion based on phase information of the image, and wherein
the measurement control unit performs labeling on the fluid portion by applying the RF pre-pulse to a region upstream from the imaging region, and executes the measurement sequence before the longitudinal magnetization of the labeled fluid portion is recovered to null or above, and wherein:
the fluid portion has a first fluid portion and a second fluid portion having different flow directions;
the RF pre-pulse portion includes a first RF pre-pulse and a second RF pre-pulse having different flip angles;
the measurement control unit performs labeling on the first fluid portion by applying the first RF pre-pulse on a first region upstream of the first fluid portion, performs labeling on the second fluid portion by applying the second pre-pulse to a second region upstream of the second fluid portion, and sets the region between the first region and the second region as the imaging region; and
the arithmetic processing unit obtains the fluid-enhanced image by differentiating the contrast between the first fluid portion and the second fluid portion.

8. The magnetic resonance imaging apparatus according to claim 7 , wherein:
the first RF pre-pulse is an IR pulse with flip angle of φ 1 (90<φ 1 <270)-degrees;
the second RF pre-pulse is an IR pulse with flip angle φ 2 (0<φ 2 ≦90)-degrees;
the measurement control unit executes the measurement sequence portion before the longitudinal magnetization of the first fluid portion recovers to null or above; and
the arithmetic processing unit enhances the contrast of the first fluid portion on the basis of the phase information, and enhances the contrast of the second fluid portion on the basis of the signal intensity difference between the fluid portion and the stationary portion.

9. A magnetic resonance imaging apparatus comprising:
a measurement control unit configured to control measurement of an echo signal from an imaging region of an object to be examined including a fluid portion, on the basis of a predetermined pulse sequence; and
an arithmetic processing unit configured to obtain an image with enhanced contrast between the fluid portion and a stati

Assignees

• Hirai Kosuke
• Hitachi Medical Corp

Inventors

• Hirai Kosuke

Classifications

• A61B5/055 Primary

  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging · CPC title

• G01R33/5613

  Generating steady state signals, e.g. low flip angle sequences [FLASH] · CPC title

• G01R33/4836

  using an RF pulse being spatially selective in more than one spatial dimension, e.g. a 2D pencil-beam excitation pulse · CPC title

• G01R33/5602

  by filtering or weighting based on different relaxation times within the sample, e.g. T1 weighting using an inversion pulse · CPC title

• G01R33/4828 Primary

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