US5565776A
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Magnetic resonance imaging apparatus
Assignee: Toshiba Corp
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Filing: 1995-08-23
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Granted: 1996-10-15
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Expires: 2015-08-23
Abstract
Abstract An excitation pulse, a first refocusing pulse, and a second refocusing pulse are sequentially applied, a flow encode pulse for producing a phase shift in accordance with the velocity of a fluid is applied before the second refocusing pulse, an echo signal is observed after the application of the second refocusing pulse, and a velocity image is reconstructed on the basis of the echo signal. The application phases of the excitation pulse, the first refocusing pulse, and the second refocusing pulse, and the flip angles of the first and second refocusing pulses, are so adjusted that the intensity of the echo signal from the fluid changes in accordance with the velocity. In a stationary part, the absolute value of a spin echo component and the absolute value of a stimulated echo component are equal, and the phase difference between them is 180°. That is, the signal in the stationary part is essentially 0. In a fluid, the absolute values of the spin echo component and the stimulated echo component are equal, and the phase difference between them approaches 0° with increasing velocity. That is, the signal intensity in the fluid increases as the velocity increases. Accordingly, only an echo signal from the fluid can be observed. The intensity of this echo signal increases with velocity. On the basis of the echo signal, the fluid, rather than the stationary part, is imaged, and a velocity image whose luminance changes in accordance with the velocity is reconstructed.
Inventors
- 👤 Hitoshi Kanazawa
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 00:50
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/54; G01R33/56; G01R33/563; G01R33/56308; G01R33/56316
Claims Analysis
Total Claims: 36
Claim 1
Independent Claim
200 words
A magnetic resonance imaging apparatus for imaging a fluid having a velocity, comprising: magnetic gradient coil means for applying a magnetic gradient field to said fluid; radio-frequency transceiver means for applying an RF signal to said fluid, and for receiving echo signals therefrom; sequencer means for sequentially causing an excitation pulse, a first refocusing pulse, having a first flip angle, and a second refocusing pulse, having a second flip angle, to be applied by said radio-frequency transceiver means and for causing said radio-frequency transceiver means to receive said echo signals from said fluid after said second refocusing pulse; said sequencer means for further causing a magnetic flow encode pulse to be applied by said magnetic gradient coil means after said excitation pulse but prior to said second refocusing pulse; means for adjusting the application phases of said excitation pulse, said first refocusing pulse, and said second refocusing pulse, and for adjusting the angle of said first flip angle, and said second flip angle whereby the intensity of said echo signals received by said radio-frequency transceiver means varies in accordance with said velocity of said fluid; and means for reconstruction an image of said fluid based upon said echo signals received.
Claim 2
Dependent Claim
200 words
A magnetic resonance imaging apparatus for imaging a fluid having a velocity, comprising: magnetic gradient coil means for applying a magnetic gradient field to said fluid; radio-frequency transceiver means for applying an RF signal to said fluid, and for receiving echo signals therefrom; sequencer means for sequentially causing an excitation pulse, a first refocusing pulse, having a first flip angle, and a second refocusing pulse, having a second flip angle, to be applied by said radio-frequency transceiver means and for causing said radio-frequency transceiver means to receive said echo signals from said fluid after said second refocusing pulse; said sequencer means for further causing a magnetic flow encode pulse to be applied by said magnetic gradient coil means after said excitation pulse but prior to said second refocusing pulse; means for adjusting the application phases of said excitation pulse, said first refocusing pulse, and said second refocusing pulse, and for adjusting the angle of said first flip angle, and said second flip angle whereby the intensity of said echo signals received by said radio-frequency transceiver means varies in accordance with said velocity of said fluid; and means for reconstruction an image of said fluid based upon said echo signals received.
Claim 3
Dependent Claim
80 words
An apparatus according to claim 1, wherein said adjusting means adjusts said first flip angle of the first refocusing pulse such that a magnetization spin caused to flip by the first refocusing pulse has a transverse magnetization component and a longitudinal magnetization component, the transverse magnetization component has a spin echo component, and the longitudinal magnetization component has a stimulated echo component, and each echo signal is a composite signal of the spin echo component and the stimulated echo component.
Claim 4
Dependent Claim
52 words
An apparatus according to claim 2, wherein the adjusting means adjusts the first flip angle of the first refocusing pulse and the second flip angle of the second refocusing pulse such that an absolute value of the spin echo component and an absolute value of the stimulated echo component are substantially equal.
Claim 5
Dependent Claim
44 words
An apparatus according to claim 3, wherein the first flip angle α 1 ° of the first refocusing pulse and the second flip angle α 2 ° of the second refocusing pulse are adjusted to satisfy the following equation: sin(α.sub.1 /2)·sin(α.sub.2 /2)=2·cos(α.sub.1 /2)·cos(α.sub.2 /2).
Claim 6
Dependent Claim
41 words
An apparatus according to claim 4, wherein the first flip angle α 1 ° of the first refocusing pulse and the second flip angle α 2 ° of the second refocusing pulse are set such that α 1 °=α 2 °=109.5°.
Claim 7
Dependent Claim
82 words
An apparatus according to claim 2, wherein the adjusting means adjusts the application phases of the excitation pulse, the first refocusing pulse, and the second refocusing pulse such that in a stationary part the phase of the spin echo component and the phase of the stimulated echo component has a phase difference of 180°, and in the fluid the phase difference between the phase of the spin echo component and the phase of the stimulated echo component approaches 0° with increasing velocity.
Claim 8
Dependent Claim
53 words
An apparatus according to claim 6, wherein the adjusting means adjusts the application phase φ 0 of the excitation pulse, the application phase φ 1 , of the first refocusing pulse, and the application phase φ 2 of the second refocusing pulse to satisfy 2·φ.sub.0 -3·φ.sub.1 +φ.sub.2 =2·n·π where n is an integer.
Claim 9
Dependent Claim
50 words
An apparatus according to claim 7, wherein the adjusting means adjusts the application phase φ 0 of the excitation pulse, the application phase φ 1 of the first refocusing pulse, and the application phase φ 2 of the second refocusing pulse such that φ 0 =φ 1 =φ 2 =0°.
Claim 10
Dependent Claim
29 words
An apparatus according to claim 8, wherein all of the excitation pulse, the first refocusing pulse, and the second refocusing pulse are applied with respect to the X axis.
Claim 11
Dependent Claim
47 words
An apparatus according to claim 6, wherein the adjusting means sets the first flip angle of the first refocusing pulse and the second flip angle of the second refocusing pulse such that absolute values of the spin echo component and the stimulated echo component are substantially equal.
Claim 12
Dependent Claim
47 words
An apparatus according to claim 10, wherein the adjusting means sets the first flip angle α 1 ° of the first refocusing pulse and the second flip angle α 2 ° of the second refocusing pulse are to satisfy the following equation: sin(α.sub.1 /2)·sin(α.sub.2 /2)=2·cos(α.sub.1 /2)·cos(α.sub.2 /2).
Claim 13
Dependent Claim
43 words
An apparatus according to claim 11, wherein the adjusting means sets the first flip angle α 1 ° of the first refocusing pulse and the second flip angle α 2 ° of the second refocusing pulse such that α 1 °=α 2 °=109.5°.
Claim 14
Dependent Claim
31 words
An apparatus according to claim 1, wherein the echo signals are phase and frequency encoded, and the velocity image is reconstructed by performing a two-dimensional Fourier transformation of the echo signals.
Claim 15
Dependent Claim
25 words
An apparatus according to claim 1, wherein the echo signals are repetitively acquired after the second refocusing pulse while a gradient magnetic field is reversed.
Claim 16
Dependent Claim
28 words
An apparatus according to claim 1, wherein the echo signals are repetitively acquired after the second refocusing pulse while the first and second refocusing pulses are repetitively applied.
Claim 17
Dependent Claim
75 words
An apparatus according to claim 1, wherein said sequences means further causes a prescan to be performed such that the echo signals are repetitively acquired while the flip angle of one of the first and second refocusing pulses is fixed and the flip angle of the other is changed, and the flip angle of the other is adjusted such that the intensity of the echo signal in a stationary part is at or near 0.
Claim 18
Independent Claim
119 words
A method of imaging a moving fluid having a velocity in a magnetic resonance imaging apparatus having a magnetic gradient coil means, a radio-frequency transceiver means, and image reconstruction means, said method comprising: sequentially applying by said radio frequency transceiver means; an RF excitation pulse; a first refocusing RF pulse having a first angle; a second refocusing RF pulse having a second angle; applying a flow encoded magnetic gradient pulse by said magnetic gradient coil means after said RF excitation pulse and prior to said second refocusing RF pulse; receiving RF echo signals from said moving fluid by said radio-frequency transceiver means; reconstructing an image of said fluid based upon said echo signals received by said image reconstruction means.
Claim 19
Independent Claim
119 words
A method of imaging a moving fluid having a velocity in a magnetic resonance imaging apparatus having a magnetic gradient coil means, a radio-frequency transceiver means, and image reconstruction means, said method comprising: sequentially applying by said radio frequency transceiver means; an RF excitation pulse; a first refocusing RF pulse having a first angle; a second refocusing RF pulse having a second angle; applying a flow encoded magnetic gradient pulse by said magnetic gradient coil means after said RF excitation pulse and prior to said second refocusing RF pulse; receiving RF echo signals from said moving fluid by said radio-frequency transceiver means; reconstructing an image of said fluid based upon said echo signals received by said image reconstruction means.
Claim 20
Dependent Claim
18 words
The method of claim 17 wherein said flow encoded pulse is a bipolar pulse having a polarity reversal.
Claim 21
Dependent Claim
28 words
The method of claim 18 wherein said bipolar pulse is applied such that the magnetic intensity change is along the direction of the flow of the moving fluid.
Claim 22
Dependent Claim
74 words
The method of claim 17 further comprising: adjusting said first angle such that a magnetization spin caused by said first RF refocusing pulse has a transverse magnetization component and a longitudinal magnetization component; and wherein said transverse magnetization component has a spin echo component and wherein said longitudinal component has a stimulated echo component; and wherein each of said echo signals is a composite signal of the spin component and the stimulated echo component.
Claim 23
Dependent Claim
35 words
The method of claim 20 further comprising: adjusting said first and second angles such that an absolute value of the spin echo component and an absolute value of the stimulated echo component are substantially equal.
Claim 24
Dependent Claim
27 words
The method of claim 21 wherein a said first and second angles (α 1 and α 2 respectively) are adjusted such that sin(α.sub.1 /2)·sin(α.sub.2 /2)=2·cos(α.sub.1 /2)·cos(α.sub.2 /2).
Claim 25
Dependent Claim
19 words
The method of claim 22 wherein said first and second angles are adjusted such that α.sub.1 =α.sub.2 =109.5°. 24.
Claim 26
Dependent Claim
78 words
The method of claim 20 further comprising: adjusting the application phase of said RF excitation pulse, the first refocusing RF pulse, and the second refocusing RF pulse such that in a stationary part the phase of the spin echo component and the phase of the stimulated echo component has a phase difference of 180°, and in the fluid the phase of the spin echo component and the phase of the stimulated echo component approaches 0° with increasing velocity.
Claim 27
Dependent Claim
55 words
The method of claim 24 wherein said adjusting step adjusts the application phase φ 0 of said RF excitation pulse, the application phase φ 1 of said first refocusing RF pulse, and the application phase φ 2 of said second refocusing RF pulse in accordance with 2·φ.sub.0 -3·φ.sub.1 +φ.sub.2 =2·n·π where R is an integer.
Claim 28
Dependent Claim
28 words
The method of claim 25 wherein said adjusting step adjusts the application phase φ 0 , φ 1 , and φ 2 such that φ.sub.0 =φ.sub.1 =φ.sub.2 =0°.
Claim 29
Dependent Claim
27 words
The method of claim 26 wherein said RF excitation pulse, said first refocusing RF pulse and said second refocusing RF pulse are applied in the X axis.
Claim 30
Dependent Claim
35 words
The method of claim 24 wherein said adjusting step adjusts the first angle and the second angle such that the absolute values of the spin echo component and the stimulated echo component are substantially equal.
Claim 31
Dependent Claim
32 words
The method of claim 28 wherein said adjusting step adjusts the first angle (α 1 ) and the second angle (α 2 ) satisfy the following equation: sin(α.sub.1 /2)·sin(α.sub.2 /2)=2·cos(α.sub.1 /2)·cos(α.sub.2 /2).
Claim 32
Dependent Claim
25 words
The method of claim 29 wherein said first angle (α 1 ) and the second angle (α 2 2) are such that α.sub.1 =α.sub.2 =109.5°.
Claim 33
Dependent Claim
20 words
The method of claim 17 wherein said reconstructing step further comprises: performing a two-dimensional Fourier transformation of the echo signals.
Claim 34
Dependent Claim
29 words
The method of claim 17 further comprising: repetitively receiving RF echo signals from said moving fluid after the second RF refocusing pulse while a gradient magnetic field is reversed.
Claim 35
Dependent Claim
33 words
The method of claim 17 further comprising: repetitively receiving RF echo signals from said moving fluid after the second RF refocusing pulse while the first and second RF refocusing pulses are repetitively applied.
Claim 36
Dependent Claim
64 words
The method of claim 17 wherein said RF echo signals are repetitively received while the flip angle of one of the first and second RF refocusing pulse is fixed and the flip angle of the other is changed, and the flip angle of the other is adjusted such that the intensity of the echo signal in the stationary part is at or near zero.
References Cited (Backward Citations)
US5225779A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1999-10-15 | 2000-04-15 | 2000-10-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2003-10-15 | 2004-04-15 | 2004-10-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2007-10-15 | 2008-04-15 | 2008-10-15 | $7700.00 | Window Closed / Lapsed |