Patent EP0439119A2 successfully refreshed from Google Patents.
EP0439119A2
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Magnetic resonance imaging system
Assignee: Toshiba Corp
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Filing: 1991-01-22
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Granted: —
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Expires: 2011-01-22
Abstract
Abstract In a magnetic resonance imaging system having an automatic power control function for adjusting the transmission power of an RF pulse so as to set a desired flip angle of a spin, in an automatic power control mode, a plane including only a portion of an object (P) to be examined in an imaging region having a uniform field intensity, e.g., a transaxial plane (39) or a plane (39a, 39b) slightly inclined from the transaxial plane (39), is excited by using a gradient magnetic field Gz in the direction of the body axis of the object (P) as a slice gradient magnetic field regardless of a plane to be imaged. The peak values of MR echo signals are detected while the transmission power of the RF pulse is changed. An RF pulse transmission power at which the maximum peak value appears is detected from these detection values. The transmission power of the RF pulse in imaging, i.e., the output of an RF oscillator (16) having a predetermined frequency, is attenuated on the basis of the relationship between the transmission power and the maximum peak value, thereby adjusting the attenuation (22) amount of an attenuator for supplying a current to an RF coil (34).
Inventors
- 👤 Masatoshi C/O Intellectual Property Div. Hanawa
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 00:44
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/58; G01R33/583
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
323 words
A magnetic resonance imaging system comprising: static magnetic field generating means for generating a static magnetic field in a predetermined imaging region in which an object to be examined is placed; gradient magnetic field applying means for applying a predetermined gradient magnetic field to the imaging region; radio frequency (RF) pulse applying means for applying a uniform RF pulse to the imaging region; sequence control means for controlling said gradient magnetic field applying means and RF pulse applying means in accordance with a predetermined pulse sequence so as to cause said grading magnetic field applying means and said RF pulse applying means to respectively apply the predetermined gradient magnetic field and the RF pulse to the imaging region, thereby causing a magnetic resonance phenomenon in the imaging region; receiving means for receiving a magnetic resonance signal generated by the magnetic resonance phenomenon in the imaging region; and imaging processing means for obtaining a magnetic resonance image by performing predetermined processing including image reconstruction processing for the magnetic resonance signal received by said receiving means, wherein said sequence control means comprises adjusting means for adjusting a power of an RF pulse for imaging prior to imaging processing, characterized in that said adjusting means comprises: first means for exciting magnetic resonance at a slice portion, of the object, crossing the body axis of the object by applying the RF pulse while applying a slice gradient magnetic field in a direction of the body axis; second means for operating said first means with the power of the RF pulse being variously set, and detecting magnetic resonance signals without applying an encode gradient magnetic field, thereby obtaining a relationship between the power of the RF pulse and peak values of the detected magnetic resonance signals; and means for determining the power of the RF pulse for imaging processing on the basis of the relationship obtained by said second means so as to set a desired flip angle.
Claim 2
Dependent Claim
22 words
A system according to claim 1, characterized in that said first means comprises means for exciting magnetic resonance in a transaxial plane.
Claim 3
Dependent Claim
46 words
A system according to claim 1, characterized in that said first means comprises means for exciting magnetic resonance in a plane which crosses the body axis but does not cross two planes at the edges of the imaging region in the direction of the body axis.
Claim 4
Dependent Claim
39 words
A system according to claim 1, characterized in that said first means comprises means for exciting a plane which crosses the body axis but does not include a portion of the object which is located outside the imaging region.
Claim 5
Dependent Claim
54 words
A system according to claim 1, characterized in that said RF pulse applying means comprises an RF oscillator, an attenuator for adjusting the power of the RF pulse by adjusting an amplitude of an output from said oscillator, and an RF coil connected to said attenuator for applying the RF pulse to the object.
Claim 6
Dependent Claim
114 words
A system according to claim 1, characterized in that said adjusting means comprises means for sequentially applying 90° and 180° pulses as RF pulses at predetermined time intervals, means for applying a slice gradient magnetic field when the 90° pulse is applied, means for applying a dephase gradient magnetic field in a read direction perpendicular to the body axis during a time period between application of the 180° pulse and application of the 90° pulse, means for applying a slice gradient magnetic field when the 180° pulse is applied, and means for receiving a magnetic resonance signal while applying a rephase gradient magnetic field in the read direction after application of the 180° pulse.
Claim 7
Dependent Claim
206 words
A magnetic resonance imaging system comprising: imaging means for applying a radio frequency (RF) pulse, a static magnetic field, and a gradient magnetic field to an object to be examined so as to excite magnetic resonance at a specific slice portion of the object, and detecting a magnetic resonance signal generated by the magnetic resonance excitation, thereby obtaining image data of the specific slice portion; and power setting means for setting a power of the RF pulse to be applied to the object by said imaging means, characterized in that said power setting means comprising: means for exciting a slice portion, which includes a portion of the object in an imaging region having a uniform field intensity but does not include a portion, of the object, outside the imaging region, prior to imaging, means for detecting a magnetic resonance signal and detecting a peak value thereof, means for detecting peak values of magnetic resonance signals obtained when the slice portion is excited with a transmission power of an excitation pulse being set to be various values, thereby detecting a maximum peak value, and means for determining a transmission power for imaging on the basis of a transmission power at which the maximum peak value is obtained.
Claim 8
Dependent Claim
20 words
A system according to claim 7, characterized in that said power setting means comprises means for exciting a transaxial plane.
Claim 9
Dependent Claim
50 words
A system according to claim 7, characterized in that said power setting means comprises means for exciting magnetic resonance in a plane which crosses a body axis of the object but does not cross two planes at the edges of the imaging regions in a direction of the body axis.
Claim 10
Dependent Claim
52 words
A system according to claim 7, characterized in that said power setting means comprises means for determining a transmission power for imaging, on the basis of the transmission power at which the maximum peak value is obtained, so as to set a flip angle of a spin to be 90° or 180°.
Claim 11
Independent Claim
146 words
A method of adjusting a transmission power of an excitation radio frequency (RF) pulse in a magnetic resonance imaging system, characterized by comprising: a first step of exciting a slice portion which includes a portion of an object to be examined in an imaging region but does not include a portion, of the object, located outside the imaging region, regardless of a slice portion to be imaged, prior to imaging, receiving a magnetic resonance signal, and detecting a peak value of the received signal; a second step of repeating the first step while variously changing an excitation power; a third step of detecting an excitation power at which a maximum peak value of a magnetic resonance signal is obtained; and a fourth step of determining a transmission power of an RF pulse for imaging on the basis of the excitation power detected in the third step.
Claim 12
Dependent Claim
20 words
A method according to claim 11, characterized in that the first step includes the step of exciting a transaxial plane.
Claim 13
Dependent Claim
47 words
A method according to claim 11, characterized in that the first step includes the step of exciting a plane which crosses a body axis of the object but does not cross two planes at the edges of the imaging region in a direction of the body axis.
Claim 14
Dependent Claim
54 words
A method according to claim 11, characterized in that the fourth step includes the step of determining a transmission power for imaging, on the basis of the excitation power at which the maximum peak value of the magnetic resonance signal is obtained, so as to set a flit angle to be 90° or 180°.
References Cited (Backward Citations)
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