JP4162300B2 - Magnetic resonance imaging system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic resonance imaging (hereinafter abbreviated as “MRI”) method for obtaining a tomographic image of a desired portion of a subject using a nuclear magnetic resonance (hereinafter abbreviated as “NMR”) phenomenon, and an image construction signal Prior to the execution of a pulse sequence for obtaining a signal, a method of suppressing a signal in a region that becomes an obstacle to diagnosis by applying a predetermined high-frequency magnetic field pulse (hereinafter referred to as an RF pulse) and a gradient magnetic field pulse (presaturation method) ) And a method suitable for satisfactorily suppressing the signal in the unnecessary area.
[0002]
[Prior art]
As is generally known, MRI is easily affected by movement and flow during measurement, and it is known that false images are generated by being affected by these influences. Since such a false image becomes an obstacle to diagnosis, a method for reducing or suppressing them has been proposed.
[0003]
One method for suppressing such false images is a technique called pre-saturation. In this method, as shown in FIG. 2 (a), when there is a region (unnecessary region) 22 that generates an artifact that becomes a diagnostic obstacle in a part of the human body 21 in the region of interest 20, the signal from that region is suppressed. Therefore, prior to the execution of a pulse sequence (main measurement) for acquiring a signal for image construction, a slice or slab 23 (FIG. 2 (b)) including the region 22 is selected and an RF pulse (presaturation) is selected. RF pulse). After the application of this RF pulse, the spins in the region 23 begin to relax (recover) from the excited state to the initial state. When applying the spin excitation RF pulse in this measurement, the spin excitation angle of the presaturation RF pulse is set so that the longitudinal magnetization component of the spin in the region 23 during recovery is zero. Thereby, in this measurement, the spin in the region 23 does not generate a transverse magnetization component, does not generate a signal, and an image in which the signal in the region 23 is suppressed can be obtained.
[0004]
[Problems to be solved by the invention]
In such a pre-saturation method, a signal from the region 23 should not be generated, but the spin of the region 23 is also applied in the gradient magnetic field application direction (3 by the gradient magnetic field pulse application pattern applied in the pulse sequence of this measurement. A change in phase occurs in the axial direction. Due to this phase change, when the signal is diffused and converged in each of the three axis directions, a signal from the region 23 (hereinafter referred to as a false signal) is mixed during the signal measurement of the main measurement, and a false image is formed on the image obtained by the main measurement. May occur.
[0005]
For example, FIG. 9 shows the phase change in each gradient magnetic field direction of the region 23 when the pulse sequence ((a) to (d)) of presaturation and main measurement is repeated while changing the phase encoding amount. It is shown in g). As can be seen from the figure, in the first iteration, the spin in the region 23 is excited by the presaturation RF pulse 4101 and then applied by the gradient magnetic field pulses 4103 to 4112 in the Gx, Gy, and Gz directions according to the applied amount. Each phase change occurs, and the spin is inverted by the pre-saturation RF pulse 4201 in the next repetition, and further, a phase change corresponding to the applied amount is received by the gradient magnetic field pulses 4203 to 4212 in the Gx, Gy, and Gz directions. As a result, as shown in the figure, when the gradient magnetic field 4211 in the second readout direction is applied, the phase change of the spin in almost three axial directions is 0 or one encode step in the phase encode direction (Gy direction). A signal from the region 23, that is, a false signal is measured together with the measurement signal.
[0006]
Thus, at the time of each signal measurement, the signal excited by the RF pulse for presaturation in the immediately preceding pulse sequence cycle is superimposed, and the superimposed signal has the same phase encoding amount (phase in the Gy direction) for all phase encodings. There is no rotation amount change). As shown in FIG. 2 (b), the image when the false signal generated by such a mechanism is superimposed is a place corresponding to the DC component (or center frequency) in the pre-saturation application area 23 and in the phase encoding direction. A linear false image 24 is superimposed on the.
[0007]
Accordingly, an object of the present invention is to provide a pre-saturation method that can suppress a false signal generated by the above-described mechanism and satisfactorily reduce a false image on an image.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, by controlling the application phase of the presaturation RF pulse, the signal from the spin excited by the presaturation RF pulse is prevented from being superimposed in the image. That is, in the MRI method of the present invention, in order to suppress a signal from a specific region (unnecessary region) of the subject, a step of applying an RF pulse for presaturation that selects and excites that region, and an image of the subject Applying a high-frequency pulse for selectively exciting nuclear spins in a region to be converted (imaging region), applying a gradient magnetic field for phase encoding the nuclear spins, and nuclear magnetic resonance generated from the nucleus of the subject In the magnetic resonance imaging method of reconstructing the image of the imaging region by repeating the step of measuring a signal while changing the magnitude of the phase encoding gradient magnetic field, the application phase of the RF pulse for presaturation is changed for each application. It is characterized by controlling to.
[0009]
According to the first aspect of the method for controlling the applied phase according to the present invention, of the nuclear magnetic resonance signals measured in the i-th phase encoding and the (i + 1) -th phase encoding, The phase difference between the signals of S1 (i) and S1 (i + 1) is φ1 (i), and the signals from the specific area (false signals) S2 (i) and S2 (i + 1) When the phase difference between signals is φ2 (i), the application phase of the presaturation RF pulse is controlled so as to maintain the relationship of the following equation (1).
[0010]
φ1 (i) −φ2 (i) = φ1 (i + 1) −φ2 (i + 1) + π (1)
Further, according to the second aspect of the application phase control method of the present invention, the inter-signal phase difference φ1 (i) of the main measurement signals S1 (i) and S1 (i + 1) and the false signal S2 (i), The presaturation RF pulse application phase is controlled so that the inter-signal phase difference φ2 (i) of S2 (i + 1) maintains the relationship of the following equation (2).
[0011]
φ1 (i) −φ2 (i) = φrnd (i) (2)
(Where φrnd (i) represents a random value for i and an angle satisfying 0 ≦ φrnd (i) <2π)
Furthermore, according to the third aspect of the method for controlling the applied phase according to the present invention, of the nuclear magnetic resonance signals measured at the k-th and (k + 1) -th repetitions of the above steps, the false signal S2 ( k), when the phase difference between signals of S2 (k + 1) is φ2 (k),
φ2 (k) = φ2 (k-1) + k × Δφ (3)
(Where Δφ represents an arbitrary angle)
Control to keep the relationship.
[0012]
By performing such phase control, even if a signal from a spin existing in an unnecessary region excited by the pre-saturation RF pulse is mixed in the signal of this measurement, it is formed as a high-signal false image in the image. It does not image or appears in a place that does not affect the image even if it forms an image. As a result, it is possible to eliminate a failure in diagnosis due to a false signal.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to embodiments shown in the drawings.
[0014]
FIG. 4 is a diagram showing an outline of an MRI apparatus to which the present invention is applied. This MRI apparatus has a static magnetic field generating magnetic circuit 402 provided with an electromagnet or a permanent magnet that generates a uniform static magnetic field in a space where a subject 401 is placed. A gradient magnetic field generation system 403 that generates a triaxial gradient magnetic field superimposed on the static magnetic field, a transmission system 404 that generates a high-frequency magnetic field that excites the nuclear spins of the nuclei constituting the tissue of the subject, A detection system 405 for detecting a nuclear magnetic resonance signal generated in a subject by application of a high-frequency magnetic field, and a control system (sequencer 407, computer for controlling these gradient magnetic field generation system 403, transmission system 404 and detection system 405 according to a predetermined pulse sequence 408), a computer 408 for performing calculation for image reconstruction based on the signal detected by the detection system 405, and a signal processing system 406, and a display unit (display) for displaying the calculated result image B) and a 428.
[0015]
The gradient magnetic field generation system 403 includes a gradient magnetic field coil 409 and a power supply 410 for generating gradient magnetic fields in three orthogonal directions.
[0016]
The transmission system 404 includes a synthesizer (high frequency generation circuit) 411 that generates a constant high frequency signal, a modulator 412, a preamplifier 413, and an irradiation coil 414a. The high frequency signal generated from the synthesizer 411 is controlled by the control system. The signal is modulated by the modulator 412 at the timing of and is sent to the irradiation coil 414a via the preamplifier 413. Thereby, a high frequency magnetic field (RF) pulse having a predetermined envelope is applied to the subject from the irradiation coil.
[0017]
Here, the synthesizer 411 includes an oscillator and a delay circuit that transmits a high frequency generated by the oscillator at a predetermined timing, and the delay amount of the delay circuit is controlled by a control system. Thereby, the phase of the high frequency signal generated from the synthesizer 411 can be controlled, and as a result, an RF pulse having an arbitrary phase can be generated from the irradiation coil.
[0018]
The detection system 405 includes a reception coil 414b, an amplifier 415, a quadrature phase detector 416, and an A / D converter 417, and a nuclear magnetic resonance signal (high frequency magnetic field) from the subject detected by the reception coil 414b is Two-phase signals are detected by the quadrature detector 416 through the amplifier 415, converted into digital signals by the A / D converter 417, and sent to the computer 408.
[0019]
The computer 408 performs an operation such as Fourier transform on the two series of signals to reconstruct an image of the subject and display it on the display 428. Data and calculation results during the calculation are stored in the storage devices 424 to 427 of the signal processing system 406.
[0020]
The computer 408 also functions as a control system for controlling the gradient magnetic field generation system 403, the transmission system 404, and the detection system 405, sends commands to the sequencer 407, and sets the drive timings of the gradient magnetic field generation system, transmission system, and detection system to predetermined values. In accordance with the pulse sequence, the image is taken by a desired photographing method. In the present invention, imaging using a pre-saturation method is performed, and at this time, the phase of the RF pulse is controlled to suppress false images.
[0021]
Hereinafter, a photographing method according to the present invention will be described with reference to FIGS.
[0022]
The pulse sequence of the pre-saturation method employed in the imaging method of the present invention is the same as the pulse sequence of the conventional pre-saturation method. For example, as shown in FIG. In order to suppress, the RF pulse 31 and the gradient magnetic fields 35 and 32 are applied. Here, the gradient magnetic field 35 is a gradient magnetic field for selecting an unnecessary region 22 shown in FIG. 2A. By applying a gradient magnetic field in the Gy and Gz directions as shown in the figure, the gradient magnetic field 35 is perpendicular to the paper surface including the region 22. Directional slabs (regions) 23 (FIG. 2 (b)) can be selectively excited. The gradient magnetic field 32 applied after the irradiation with the RF pulse 31 is a spoil gradient magnetic field that diffuses the phase of the excited spin and further suppresses the signal from the spin.
[0023]
The sequence of this measurement 33 is not particularly limited, but here, a gradient echo (GrE) system sequence is illustrated. First, an RF pulse 34 is applied together with a gradient magnetic field Gx36 that selects a cross section to be imaged, and then a phase. After applying the gradient magnetic field Gy37 for encoding and the gradient magnetic field Gz38 in the readout direction, the echo signal is measured while applying the gradient magnetic field Gz39 in the readout direction for signal measurement. The gradient magnetic field Gz38 in the readout direction is a preliminary pulse for adjusting the peak position of the echo signal.
[0024]
Using the pulse sequence as shown in FIG. 3 as a unit, the number of echo signals necessary for reconstructing one image is repeatedly measured while changing the intensity of the gradient magnetic field Gy37 in the phase encoding direction.
[0025]
In the imaging method according to the present invention, when performing imaging according to such a pulse sequence, the RF pulse 31, the RF pulse 34, and the phase of the echo signal to be measured are controlled every repetition, and excited by this measurement. Control is performed so that the phase of the signal (false signal) from the unnecessary region has a specific relationship with the phase of the signal from the region (hereinafter, simply referred to as the main measurement signal).
[0026]
That is, as shown in the flowchart of FIG. 1, first, the application phase of the pre-saturation RF pulse 31 is set to a specific phase Ph1 (11) and applied (12). Next, the application phase of the RF pulse 34 of the main measurement 33 is set to a specific phase Ph2 (13) and applied (14). The setting of the phase of these RF pulses can be controlled by controlling the generation timing of the high frequency in the synthesizer as already described. The signal measurement phase is set to Ph3 (15), and the signal is measured (16). The phase of the signal measurement can be set by controlling the phase of the reference signal for detection in the quadrature detector. Such phase control steps 11 to 16 are repeated until the necessary addition in the same phase encoding is completed (17), and then the phase encoding amount is changed, and steps 11 to 17 are repeated until the measurement of all phase encodings is completed. Repeat (18) to finish shooting.
[0027]
In this case, the phases Ph1, Ph2, and Ph3 are set so that even if a false signal is mixed when measuring the signal of this measurement, the false signal is not imaged or even if it is imaged, the image is not affected. Be controlled.
[0028]
Hereinafter, a specific embodiment of the presaturation RF pulse application phase control method will be described.
[0029]
FIG. 5 and FIG. 6 are diagrams showing a presaturation RF pulse application phase control method in the first embodiment of the present invention. FIG. 5 and FIG. 6 are phase control flows in the measurement of adjacent phase encodes, respectively. Is shown.
[0030]
First, as shown in FIG. 5, the application phase of the pre-saturation RF pulse 31 is set to Φ1 (601). This phase Φ1 can be an arbitrary value. An RF pulse is applied at the set phase (602). Next, the application phase Φ of the main measurement RF pulse 34 is set to 0 (603), and the main measurement RF pulse is applied (604). The signal measurement phase Φ is set to 0 (605), and the signal is measured (606). The processes from 601 to 606 are repeated until the signal addition necessary for the same phase encoding is completed (607). After the signal addition is completed, the signal measurement corresponding to all the phase encodings necessary for the image configuration is completed. If so, the process ends (608). If signal measurement has not been completed for all phase encodings, the next phase encoding amount (i + 1) is set (609), and the process proceeds to processing 611 in FIG.
[0031]
In the measurement by the next phase encoding, the application phase of the presaturation RF pulse 31 is set to (Φ1 + π) (611), and the RF pulse is applied at the set phase (612). In subsequent steps 613 to 617, setting the application phase Φ of the RF pulse for measurement to 0 and applying it, and setting the phase Φ of signal measurement to 0 and measuring are the same as the previous measurement (FIG. 5). It is the same. Also in this measurement, steps 611 to 616 are repeated until the necessary addition is completed, and after the addition is completed, when signal measurement in all phase encodings is not completed (618), the next phase encoding amount is set (619) ), The process proceeds to process 601 in FIG. The application phase Φ1 of the presaturation RF pulse set in the process 601 in the next cycle is assumed to be the same as the initially set value.
[0032]
In this way, both the application phase of the main measurement RF pulse and the signal measurement phase are always set to 0, and the application phase of the presaturation RF pulse is changed by π between adjacent phase encodings, thereby The signal has a constant phase for all phase encodings, but the phase of the false signal excited by the presaturation RF pulse is inverted by 180 ° for each adjacent phase encoding.
[0033]
That is, the signal phase difference between two adjacent image forming signals measured in the i-th phase encoding and (i + 1) -th phase encoding is φ1 (i), and the signal level between two adjacent false signals When the phase difference is φ2 (i), the following formula (1)
φ1 (i) -φ2 (i) = φ1 (i + 1) -φ2 (i + 1) + π (1)
Will be maintained.
[0034]
As a result, the false signal is located at the highest frequency, that is, at the image end on the reconstructed image. As described above, since the false signal always receives the same amount of phase rotation for all the phase encoding amounts, the false image due to the false signal appears linearly at the extreme end position of the image by image reconstruction. . Therefore, the false image due to the false signal is not superimposed on the inside of the image and does not become an obstacle to diagnosis.
[0035]
In the above embodiment, the case where both the application phase Ph2 of the measurement RF pulse and the signal measurement phase Ph3 are set to 0 has been described. However, in MRI, the RF pulse application phase Ph2 and the signal measurement phase Ph3 are set. For example, various combinations are possible such that one is set to 0 and the other is set to π, and this embodiment can be implemented with any combination thereof. That is, in this embodiment, it is only necessary that the change in the phase of the main measurement RF pulse and the change in the phase of the presaturation RF pulse in the measurement of two adjacent phase encodings satisfy the relationship of Expression (1). Therefore, by setting the application phase Ph1 of the RF pulse for presaturation so as to satisfy the relationship of the expression (1) with respect to the application phase Ph2 of the RF pulse, the same effect as in the present embodiment can be obtained.
[0036]
In the flowcharts of FIGS. 5 and 6, the case where the application phase of the presaturation RF pulse is constant (Φ1 or Φ1 + π) in the same phase encoding has been described. However, in the repetition of the pulse sequence by addition, Control of the presaturation RF pulse application phase that cancels out the false signals to be measured may be added. That is, for example, when measurement is performed by adding twice, the application phase of the RF pulse for presaturation can be controlled so that the phase of the false signal in the first measurement and the phase of the false signal in the next measurement are inverted. Also in this case, the relationship between the phase difference of the main measurement signal and the phase difference of the false signal in the measurement of the adjacent phase encoding is maintained as in the equation (1). Thereby, in addition to the effect of causing the false image to appear at the edge of the image, the effect of reducing the false image itself can be obtained.
[0037]
Next, a second embodiment of the present invention will be described. In this embodiment, the application phase of the pre-saturation RF pulse is controlled so as not to form an image due to a false signal in the main measurement image. FIG. 7 is a diagram showing a method of controlling the presaturation RF pulse application phase in the second embodiment.
[0038]
After the measurement is started, first, the application phase of the presaturation pulse RF pulse is set to a random value Φrnd (71). An RF pulse is applied with this set phase (72). In the following steps 73 to 77, the application phase Φ of the measurement RF pulse is set to 0 and applied, and the signal measurement phase Φ is set to 0 and the signal is measured as in the embodiment shown in FIG. It is the same. The steps from applying the pre-saturation RF pulse (72) to signal measurement (76) are repeated until the necessary signal addition is completed. After completing the signal addition, set the next phase encoding (79), newly set the presaturation RF pulse application phase to a random value Φrnd (71), and step 72- until the necessary signal addition is completed Repeat 77. The above measurement is repeated until all the phase encoding necessary for the image configuration is completed (78).
[0039]
By measuring the signal by performing such phase control, the signals of this measurement all have a constant phase for each phase encoding, but the phase of the false signal excited by the pre-saturation RF pulse is for each phase encoding. It becomes a random value. That is, the phase difference φ2 (i) between the false signal in the i-th phase encoding measurement and the false signal in the (i + 1) -th phase encoding measurement is equal to the corresponding phase difference φ1 (i) of the main measurement signal. Control is performed so as to satisfy the relationship of Expression (2).
[0040]
φ1 (i) −φ2 (i) = φrnd (i) (2)
(Where φrnd (i) is a random value for i and satisfies 0 ≦ φrnd (i) <2π)
As a result, the false signal is randomly distributed in the phase encoding direction on the reconstructed image. Therefore, the false signal is not superimposed as a high-signal false image gathered inside the image, and does not hinder diagnosis.
[0041]
Also in this embodiment, the case where both the signal application phase and the signal measurement phase of this measurement are set to 0 has been described, but these can be any combination that can be taken in MRI as in the previous embodiment. There are similar effects.
[0042]
Further, in the flowchart shown in FIG. 7, the case where the application phase of the pre-saturation RF pulse is constant is shown in the same phase encoding measurement (in the addition loop), but the signal addition (77) feedback loop is set before the step 71. In other words, the application phase of the presaturation RF pulse may be controlled to be a random value Φrnd for each excitation. Even when the applied phase is controlled in this way, the same effect as in the embodiment shown in FIG. 7 can be obtained.
[0043]
Alternatively, in this embodiment, the application phase of the pre-saturation RF pulse may be controlled so as to cancel the false signals measured continuously in the repetition of the pulse sequence by addition. For example, when measurement is performed by adding twice, the application phase of the RF pulse for presaturation is controlled so that the phase of the false signal in the first measurement and the phase of the false signal in the next measurement are inverted. In this case, such an application phase control step is added immediately before the presaturation RF pulse application step (72), and the feedback loop of the addition (77) is returned to before the added step. . Thereby, in addition to the false image dispersion effect by the relationship of Formula (2), the effect of reducing the false signal can be obtained.
[0044]
FIG. 8 is a diagram showing a presaturation RF pulse application phase control method according to the third embodiment. In this embodiment, a signal from a region excited by the presaturation RF pulse is gradually increased for each excitation. The application phase of the RF pulse for presaturation is controlled so as to change (gradual increase or decrease), thereby preventing the false signal from being superimposed as a high-signal false image gathered in the main measurement image.
[0045]
That is, after the measurement is started, first, in step 801, the number of excitations k is initialized to 0, and at the same time, the application phase Φ2 of the presaturation RF pulse is set to the initial value Φ1. This Φ1 may be arbitrary. Next, the application phase Φ2 of the RF pulse for presaturation pulse is set according to the following equation (3 ′) (802).
[0046]
Φ2 = Φ 1 + k × φ (3 ')
(In the formula, φ represents an arbitrary angle)
After applying the RF pulse at the set phase (803), the number of excitations k is set to (k + 1) (804). In subsequent steps 805 to 808, the application phase Φ of the main measurement RF pulse is set to 0 and applied, and the measurement is performed with the signal measurement phase set to 0 as in the first and second embodiments. It is the same.
[0047]
Also in this case, steps 802 to 808 are repeated until the signal addition is completed (809), but in this embodiment, the application phase Φ2 of the RF pulse for presaturation pulse changes every excitation, and the number of excitations k increases. Each time it increases by φ.
[0048]
If signal measurement has not been completed for all phase encodings after the necessary signal addition is completed (810), the next phase encoding amount is set (811), and steps 802 to 809 are repeated. If the signal measurement corresponding to all the phase encoding necessary for the image configuration has been completed, the process is terminated.
[0049]
By controlling the phase in this way, the phase of the signal of this measurement is constant, whereas for the false signal, the measurement after the k-th excitation and the (k + 1) -th as shown in the following equation (3) The phase difference φ2 (k) between the two adjacent false signals obtained by the measurement after excitation is always changed by k × Δφ,
φ2 (k) = φ2 (k-1) + k × Δφ (3)
(Where Δφ represents an arbitrary angle)
The false signal whose phase is controlled in this way does not form a false image on the reconstructed image. Therefore, there is no obstacle to diagnosis.
[0050]
Also in this embodiment, the application phase of the signal of the main measurement and the phase of the signal measurement can be any combination that can be taken in the MRI, and the same effect can be obtained.
[0051]
In the three embodiments described above, the case where the phase encoding is changed by one encoding step every time the pulse sequence is repeated has been described. However, the present invention is not limited to this. In addition, the pulse sequence of this measurement can be implemented in the same manner with a pulse sequence other than the gradient echo method shown by 33 in FIG. 3, and the same effect can be obtained.
[0052]
【The invention's effect】
According to the magnetic resonance imaging method of the present invention, by controlling the phase of the pre-saturation RF pulse, a spurious signal emitted from an unnecessary region spin excited by the pre-saturation RF pulse can be imaged even if it is imaged. Since it is positioned at the edge or not formed as a high-signal false image on the image, it is possible to perform an efficient and accurate diagnosis without causing any obstacle to diagnosis.
[Brief description of the drawings]
FIG. 1 is a diagram showing a phase control procedure of a presaturation RF pulse according to the present invention. FIG. 2A is a diagram showing an image of a subject and an unnecessary portion existing therein, and FIG. FIG. 3 is a diagram showing an example of a pulse sequence including pre-saturation. FIG. 4 is a diagram showing an overall configuration of an MRI apparatus to which the present invention is applied. FIG. FIG. 6 is a flowchart showing a part of the procedure according to the first embodiment of the method. FIG. 6 is a flowchart showing another portion of the procedure according to the first embodiment of the MRI method of the present invention. FIG. 8 is a flowchart illustrating the procedure according to the third embodiment of the MRI method of the present invention. FIG. 9 is a diagram illustrating generation of a false image in the presaturation method. ]
23 ... Signal suppression area by pre-saturation
24 ... Fake statue
31… RF pulse for pre-saturation
34… RF pulse for this measurement

Claims (2)

A transmission system that applies a high-frequency pulse that excites a nuclear spin constituting the subject, a gradient magnetic field generation system that applies a gradient magnetic field that phase encodes the nuclear spin, and a signal from a specific region of the subject are detected. A presaturation radio frequency comprising a detection system and a control system for controlling the transmission system, the gradient magnetic field generation system, and the detection system, and selecting and exciting the region to suppress a signal from a specific region of the subject Applying a pulse; applying a radio frequency pulse that selectively excites nuclear spins in a region of the subject to be imaged; applying a gradient magnetic field that phase encodes the nuclear spins; Repeating the step of measuring the nuclear magnetic resonance signal generated from the nucleus while changing the magnitude of the phase encoding gradient magnetic field. The magnetic resonance imaging apparatus that reconstructs an image of the region to be imaged,
The control system controls the application phase of the pre-saturation high-frequency pulse so as to maintain the relationship of the following formula (2).
Of the nuclear magnetic resonance signals measured in the i-th phase encoding and (i + 1) -th phase encoding, the signal phase difference between the signals S1 (i) and S1 (i + 1) from the region to be imaged is φ1 (i), when the signal phase difference between the signals S2 (i) and S2 (i + 1) from the specific region is φ2 (i),
φ1 (i) −φ2 (i) = φrnd (i) (2)
(Where φrnd (i) represents a random value for i and an angle satisfying 0 ≦ φrnd (i) <2π) A transmission system that applies a high-frequency pulse that excites a nuclear spin constituting the subject, a gradient magnetic field generation system that applies a gradient magnetic field that phase encodes the nuclear spin, and a signal from a specific region of the subject are detected. A presaturation radio frequency comprising a detection system and a control system for controlling the transmission system, the gradient magnetic field generation system, and the detection system, and selecting and exciting the region to suppress a signal from a specific region of the subject Applying a pulse; applying a radio frequency pulse that selectively excites nuclear spins in a region of the subject to be imaged; applying a gradient magnetic field that phase encodes the nuclear spins; Repeating the step of measuring the nuclear magnetic resonance signal generated from the nucleus while changing the magnitude of the phase encoding gradient magnetic field. The magnetic resonance imaging apparatus that reconstructs an image of the region to be imaged,
The magnetic resonance imaging apparatus characterized in that the control system controls the application phase of the pre-saturation high-frequency pulse so as to maintain the relationship of the following equation (3).
Among the nuclear magnetic resonance signals measured in the k-th and (k + 1) -th iterations of each step, the signal level of the signals S2 (k) and S2 (k + 1) from the specific region When the phase difference is φ2 (k),
φ2 (k) = φ2 (k-1) + k × Δφ (3)
(Where Δφ represents an arbitrary angle)

Images