Apparatus and method for magnetic resonance angiography utilizing flow pulses and phase-encoding pulses in a same direction

A magnetic resonance imaging apparatus includes an RF coil unit which generates RF pulses toward a subject, and which receives an MR signal from the subject. Gradient magnetic field coils generate a gradient magnetic field for slice selection, a gradient magnetic field for phase encoding and a gradient magnetic field for frequency encoding, respectively. An arithmetic unit generates image data on the basis of the MR signal, and a sequence controller controls phase encoding gradient magnetic field coils in order to generate flow pulses for dephasing or rephasing the MR spin of blood flow within the subject, in the same direction as that of the phase encoding gradient magnetic field.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-295190, filed Oct. 8, 2002, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic resonance imaging apparatus and method which are furnished with MR angiography capable of separating an artery and a vein without using any contrast medium.

2. Description of the Related Art

Magnetic resonance imaging is an imaging method wherein the atomic nucleus spin of a subject located in a static magnetic field is magnetically excited by the radio frequency signal of its Larmor frequency, and wherein an image is reconstructed from a magnetic resonance signal generated with the excitation. One imaging method which has recently come into the limelight in the field of the magnetic resonance imaging, is MR angiography of the type which does not use any contrast medium.

In the MR angiography, flow pulses are used in order to dephase or rephase the magnetization spin of a specified blood flow. Thus, the signal intensity of the specified blood flow is lowered or heightened.

The flow pulses are utilized also for separating and imaging an artery and a vein. By way of example, the artery is assumed an object to-be-handled. Pulse sequences are executed in the diastolic phase and systolic phase of the heart by cardiac synchronization. An image in the diastolic phase and an image in the systolic phase are individually generated, and they are differenced. Thus, the artery is extracted. An extractability here is enhanced by scaling up the intensity difference between an artery signal in the diastolic phase and an artery signal in the systolic phase, and scaling down the intensity difference between a vein signal in the diastolic phase and a vein signal in the systolic phase.

For this purpose, it is important to optimize the time integral value of the intensities of the flow pulses in accordance with blood flow velocities. Since, however, the flow pulses are impressed on the same axis as that of a readout gradient magnetic field for frequency encoding, a temporal space which can be spared for the flow pulses in the pulse sequence is limited. Therefore, the flow pulses cannot be impressed with the optimal time integral value in some cases. Alternatively, an echo time must be sometimes prolonged in order to impress the flow pulses with the optimal time integral value.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to realize MR angiography whose blood flow extractability is high.

A magnetic resonance imaging apparatus comprises an RF coil unit which generates RF pulses toward a subject, and which receives an MR signal from the subject, gradient magnetic field coils which generate a gradient magnetic field for slice selection, a gradient magnetic field for phase encoding and a gradient magnetic field for frequency encoding, respectively, an arithmetic unit which generates image data on the basis of the MR signal, and a sequence controller which controls the phase encoding gradient magnetic field coils in order to generate flow pulses for dephasing or rephasing a spin of a blood flow within the subject, in the same direction as that of the phase encoding gradient magnetic field.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows the schematic construction of a magnetic resonance imaging apparatus according to this embodiment. The magnetic resonance imaging apparatus includes a patient couch section on which a patient P being a subject is laid, a static magnetic field generation section which generates a static magnetic field, a gradient magnetic field generation section which serves to add positional information to the static magnetic field, a transmission/reception section which transmits/receives an RF (radio frequency) signal, a control/calculation section which takes charge of the control of the whole system and image reconstruction, an electrocardiographic measurement section which measures an ECG (electrocardiogram) signal being a signal representative of the cardiac phase of the patient P, and a breathholding command section which commands the patient P to suspend respiration.

The static magnetic field generation section includes a magnet1of, for example, superconducting scheme, and a static magnetic field power source2which feeds current to the magnet1. It generates the static magnetic field H0in the longitudinal direction (the direction of a Z-axis) of a cylindrical opening (diagnostic space) into which the subject P is loosely inserted. Incidentally, a shim coil14is disposed in the magnet section. The shim coil14is fed with current for homogenizing the static magnetic field, from a shim coil power source15under the control of a host computer6to be stated later. The patient couch section can retreatably insert a tabletop bearing the subject P, into the opening of the magnet1.

The gradient magnetic field generation section includes a gradient magnetic field coil unit3which is built in the magnet1. The gradient magnetic field coil unit3includes three sets (sorts) of x-, y- and z-coils3x-3zwhich serve to generate gradient magnetic fields in the directions of an X-axis, a Y-axis and the Z-axis orthogonal to one another. The gradient magnetic field section further includes a gradient magnetic field power source4which feeds currents to the x-, y- and z-coils3x-3z. More specifically, the gradient magnetic field power source4feeds the pulse currents for causing the x-, y- and z-coils3x-3zto generate the gradient magnetic fields, under the control of a sequencer5to be stated later.

When the pulse currents which are fed from the gradient magnetic field power source4to the x-, y- and z-coils3x-3zare controlled, the directions of a gradient magnetic field Gs in a slice direction, a gradient magnetic field Gpe in a phase encoding direction and a gradient magnetic field Gro in a frequency encoding direction (readout direction) can be set and altered at will by combining the gradient magnetic fields in the directions of the three axes X, Y and Z. The gradient magnetic fields in the slice direction, phase encoding direction and readout direction are superposed on the static magnetic field H0.

The transmission/reception section includes an RF (radio frequency) coil7which is disposed near the patient P in a radiographic space inside the magnet1, and a transmitter8T and a receiver8R which are connected to the RF coil7. Under the control of the sequencer5to be stated later, the transmitter8T feeds the RF coil7with the RF current pulses of the Larmor frequency for exciting nuclear magnetic resonance (NMR), while the receiver8R receives an MR signal (radio frequency signal) received by the RF coil7. The received signal is subjected to various items of signal processing, so as to form corresponding digital data.

Further, the control/calculation section includes the sequencer (also called “sequence controller”)5, the host computer6, an arithmetic unit10, a storage unit11, a display unit12and an input unit13. Among them, the host computer6functions to give the sequencer5pulse sequence information in accordance with a stored software procedure, and to generalize the operations of the whole apparatus including the sequencer5.

The sequencer5includes a CPU and a memory, and it stores the pulse sequence information sent from the host computer6, so as to control the series of operations of the gradient magnetic field power source4, transmitter8T and receiver8R in accordance with the information. Here, the “pulse sequence information” signifies all information items which are required for operating the gradient magnetic field power source4, transmitter8T and receiver8R in accordance with a series of pulse sequences, and it contains, for example, information items on the intensities, impression time periods and impression timings of the pulse currents which are impressed on the x-, y- and z-coils3x-3z. Besides, the sequencer5receives the digital data (MR signal) outputted by the receiver8R and transfers the data to the arithmetic unit10.

The pulse sequences may well be of two-dimensional (2D) scan or three-dimensional (3D) scan if the Fourier transform method is applicable. Besides, regarding the forms of pulse trains, it is possible to apply the SE (spin echo) method, the FE (field gradient echo) method, the FSE (fast SE) method, the EPI (echo planar imaging) method, the fast asymmetric SE method (FASE: technique in which the FSE method is combined with the half-Fourier method), etc.

Besides, the arithmetic unit10receives the digital data of the MR signal sent through the sequencer5from the receiver8R, so as to execute the arrangement of original data (also called “raw data”) into a Fourier space (also called “k-space” or “frequency space”) and two-dimensional or three-dimensional Fourier transform processing for reconstructing the original data into an actual space image, and to execute the synthesis processing of image data. Incidentally, the Fourier transform processing may well be allotted to the host computer6.

The storage unit11can save, not only the original data and reconstruction image data, but also image data subjected to various items of processing. The display unit12displays an image. Besides, information items containing the sorts of parameters, a scan condition, the sorts and parameters of pulse sequences, and an image processing method as desired by an operator, can he inputted to the host computer6through the input unit13.

Besides, a speech generator19is included as a breathholding command unit. The speech generator19can vocally emit the messages, for example, of the start and end of breathholding when commanded by the host computer6.

Further, the electrocardiographic measurement section includes an ECG sensor17which is stuck on the surface of the body of the patient P and which detects an ECG signal as an electric signal, and an ECG unit18which subjects the sensor signal to various items of processing including digitization processing and which outputs the processed signal to the host computer6and the sequencer5. The measurement signal produced by the electrocardiographic measurement section is used by the host computer6and the sequencer5when prep scan and imaging scan are executed by the cardiac synchronization method.

Next, the operation of this embodiment will be described. In this embodiment, as shown inFIG. 2, the prep scan (preparatory scan) is performed before the imaging scan. The purpose of the prep scan is to investigate the optimal scan condition of the imaging scan. The imaging scan will be first explained, followed by the prep scan.

As shown inFIGS. 3 and 4, the imaging scan is performed twice in a systolic phase and a diastolic phase by utilizing cardiac synchronization. Besides, as shown inFIG. 5, an image Isys generated from a magnetic resonance signal acquired in the systolic phase, and an image Idia generated from a magnetic resonance signal acquired in the diastolic phase are differenced by the arithmetic unit10. Owing to the differencing, an artery, for example, is extracted for a target blood flow, and a stationary part and a vein can be reduced. A condition suitable for the extraction of the target blood flow is determined by the prep scan.

Here, when the artery is exemplified for the target blood flow, the “optimal condition” is a condition under which the difference of artery signals becomes large between in the systolic phase and the diastolic phase, whereas the difference of vein signals becomes small between in the systolic phase and the diastolic phase. Flow pulses include the “rephase type” which heightens signal intensities, and the “dephase type” which lowers the signal intensities. Any of three choices; to adopt the rephase type, to adopt the dephase type, and to use no flow pulses, is selected. Further, when the flow pulses of the rephase type or the dephase type are adopted, the time integral value of the intensities of the flow pulses is determined.

FIGS. 6 and 7show two typical sorts of pulse sequences of the imaging scan which applies the FASE method. In the pulse sequences shown inFIG. 6, flow-compensation (flow-comp.) pulses indicated by hatching are adopted as the flow pulses of the rephase type. In the pulse sequences shown inFIG. 7, flow-spoiled (flow-spoil) pulses indicated by hatching are adopted as the flow pulses of the dephase type.

As is well known, the FASE method applies half-Fourier reconstruction to the fast SE method wherein a plurality of echoes are acquired by one time of excitation. Echo signals are arranged from near the center (zero encoding) of the k-space toward the outer edge thereof in succession. Radio-frequency magnetic field pulses (excitation pulses) whose flip angle is 90° are impressed together with slice-selecting gradient magnetic field pulses Gs. Thereafter, while radio-frequency magnetic field pulses (phase-inverted pulses) whose flip angle is 180° are being repeatedly impressed, the echo signals are repeatedly acquired in the existence of frequency-encoding (readout) gradient magnetic field pulses Gro. Since three-dimensional imaging is adopted here, the echo signals are endowed with phase encoding by gradient magnetic field pulses Gpe, and with slice encoding by the gradient magnetic field pulses Gs.

Here, as shown inFIG. 8, a phase encoding direction PE is set to be substantially parallel to the direction of the target blood flow (here, artery AR). Thus, the running direction of the artery AR can be imaged without being omitted, more clearly than in a case where the phase encoding direction PE is set at a direction orthogonal to the blood flow direction. It has been generally known that the blood flow represented by a pulmonary blood vessel or the hepatic portal vein is somewhat short in the transverse relaxation time (T2). It has been revealed that the blood flow of shorter T2widens in the half-value width of a signal as compared with the CSF (cerebrospinal fluid) or articular fluid of long T2. It can be said that, as compared with the CSF or articular fluid of long T2, the blood of short T2(artery) is apparently and equivalently stretched in its width in the phase encoding direction per pixel. It is accordingly indicated that the whole image of the blood (artery) becomes less sharp in the phase encoding direction than that of the CSF or articular fluid.

Therefore, when the phase encoding direction PE is brought into substantial agreement with the blood flow direction, it can be positively utilized that the degree of spread (unsharpness) on the pixel, of the signal value of the blood of short T2in the phase encoding direction PE is higher than in the case of long T2, and the blood flow is emphasized. Accordingly, when the optimal MRA image (that is, the optimal delay time) for the cardiac synchronization is to be selected as stated above, the selection is more facilitated.

Besides, the flow pulses, the flow-comp. pulses inFIG. 6or the flow-spoil pulses inFIG. 7need to be set in the direction of the target blood flow. They can be formed by the phase encoding gradient magnetic field Gpe for the reason that the phase encoding direction PE is brought into agreement with the blood flow direction.

Since the flow pulses are formed by the phase encoding gradient magnetic field Gpe, a temporal margin is afforded more than in case of forming the flow pulses by the frequency encoding gradient magnetic field Gro as in the prior art, and echo intervals can be shortened. Moreover, the flow pulses can be impressed with intensities which are necessary and sufficient for the separation between the artery and the vein.

Incidentally, although in the above, the flow pulses have been impressed in the phase encoding direction so as to image the blood flow in this direction, it is also possible that, as shown in each ofFIGS. 9-12, flow pulses are impressed, not only in the phase encoding direction Gpe, but also the frequency encoding direction Gro, thereby to image also a blood flow in this direction.

FIG. 9shows an example in which flow pulses of the same type as that in the phase encoding direction Gpe, here, flow pulses (flow-comp.) of the rephase type are impressed in the frequency encoding direction Gro.FIG. 10shows an example in which flow pulses of the same type as that in the phase encoding direction Gpe, here, flow pulses (flow-spoiled) of the dephase type are impressed in the frequency encoding direction Gro.FIG. 11shows an example in which flow pulses of the type different from that in the phase encoding direction Gpe are impressed in the frequency encoding direction Gro. More specifically, the flow pulses (flow-comp.) of the rephase type are impressed in the phase encoding direction Gpe, whereas the flow pulses (flow-spoiled) of the dephase type are impressed in the frequency encoding direction Gro. Alternatively, the flow pulses (flow-spoiled) of the dephase type are impressed in the phase encoding direction Gpe, whereas the flow pulses (flow-comp.) of the rephase type are impressed in the frequency encoding direction Gro. In some cases, as shown inFIG. 12, the blood flow is emphasized when the flow pulses are not impressed. Which of the patterns inFIGS. 9-12the flow pulses are impressed in, is selected depending upon, for example, the part of the body. By way of example, the pattern inFIG. 10is suitable for the periphery, the pattern inFIG. 11for the renal vein, and the pattern inFIG. 12for the chest.

The systolic phase image Isys and the diastolic phase image Idia are acquired by the imaging scan as stated above, and they are differenced simply or in weighted fashion, whereby the artery, for example, is extracted for the target blood flow, and an image in which the stationary part and the vein are reduced is obtained. The condition suitable for the extraction of the target blood flow is determined by the prep scan. As stated before, the “optimal condition” is defined as the condition under which the difference of the signals from the target blood flow becomes as large as possible between in the systolic phase and the diastolic phase, whereas the difference of the signals from the nontarget blood flow becomes as small as possible between them.

FIG. 13shows the general tendencies of the respective signal intensities of the artery and the vein in the systolic phase and the diastolic phase, as to the case where the flow pulses are impressed in the rephase type (flow-compensation), the case where the flow pulses are impressed in the dephase type (flow-spoiled), and the case (original) where the flow pulses are not impressed. As stated before, the “optimal condition” for the separation between the artery and the vein is the condition under which the difference of the signals from the target blood flow becomes as large as possible between in the systolic phase and the diastolic phase, whereas the difference of the signals from the nontarget blood flow becomes as small as possible. They are determined depending upon whether the target blood is the artery or the vein, and also upon the blood flow velocities thereof.

In this embodiment, as shown inFIG. 14, the prep scan is actually executed under various conditions before the imaging scan, and the differenced image between the systolic phase image and the diastolic phase image is generated for each set of the conditions. Further, an operator (inspector) visually checks such differenced images, and he/she selects an image of the highest separability between the target blood flow and the nontarget blood flow from among the differenced images. Thereafter, the imaging scan is executed under the same flow pulse conditions as those of the pulse sequences with which the original signals of the selected image are acquired, that is, the conditions that the flow pulses of the rephase type or the dephase type are impressed or that the flow pulses are not used, and that the same intensities as those of the gradient magnetic field pulses as the flow pulses are set.

FIGS. 15 and 16show a simple prep scan, whileFIGS. 17 and 18show an example of a prep scan for setting detailed conditions. The simple prep scan is done for the purpose of selecting any of the application of the rephase type flow pulses (flow-comp.), the application of the dephase type flow pulses (flow-spoiled), and the non-application (original) of the flow pulses. The detailed prep scan is done for the purpose of selecting intensities suitable for the flow pulses, in addition to the selection of any of the application of the rephase type flow pulses (flow-comp.), the application of the dephase type flow pulses (flow-spoiled), and the non-application (original) of the flow pulses. The prep scan of either of the types is selected by the operator beforehand.

With either of the types, the prep scan is executed by the same method as that of the imaging scan (here, by the FASE method), but in conformity with two-dimensional imaging. More specifically, radio-frequency magnetic field pulses (excitation pulses) whose flip angle is 90° are impressed together with slice-selecting gradient magnetic field pulses Gs. Thereafter, while radio-frequency magnetic field pulses (phase-inverted pulses) whose flip angle is 180° are being repeatedly impressed, echo signals are repeatedly acquired in the existence of frequency-encoding (readout) gradient magnetic field pulses Gro. Unlike the imaging scan, however, the prep scan adopts the two-dimensional imaging in order to shorten a prep scan time. Accordingly, the echo signals are endowed with phase encoding by the gradient magnetic field pulses Gpe, but they are not subjected to slice encoding. Besides, in the prep scan, the phase encoding direction PE is set to be substantially parallel to the direction of the target blood flow (the artery AR inFIG. 8) as in the imaging scan.

With the simple type, as shown inFIG. 15or16, a two-dimensional FASE-method pulse sequence which applies rephase type flow pulses (flow-comp.), a two-dimensional FASE-method pulse sequence which applies dephase type flow pulses (flow-spoiled), and a two-dimensional FASE-method pulse sequence (original) which does not apply flow pulses are executed in the systolic phase or the diastolic phase by utilizing cardiac synchronization.

An image which is reconstructed on the basis of echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence applying the rephase type flow pulses (flow-comp.), and an image which is reconstructed on the basis of echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence applying the rephase type flow pulses (flow-comp.) are differenced simply or in weighted fashion, and the differenced image is displayed.

Likewise, an image which is reconstructed on the basis of echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence applying the dephase type flow pulses (flow-spoiled), and an image which is reconstructed on the basis of echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence applying the dephase type flow pulses (flow-spoiled) are differenced simply or in weighted fashion, and the differenced image is displayed.

Besides, likewise, an image which is reconstructed on the basis of echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence not applying the flow pulses, and an image which is reconstructed on the basis of echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence not applying the flow pulses are differenced simply or in weighted fashion, and the differenced image is displayed.

The operator visually checks the three sorts of images, and he/she selects the image in which the target blood flow, for example, the artery is extracted most clearly.

The imaging scan condition is set at the same flow condition as that of the selected image by the host computer6and the sequencer5. More specifically, in case of selecting the differenced image between the image which is reconstructed on the basis of the echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence applying the rephase type flow pulses (flow-comp.), and the image which is reconstructed on the basis of the echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence applying the rephase type flow pulses (flow-comp.), the imaging scan condition is set at a three-dimensional FASE-method pulse sequence which applies the rephase type flow pulses (flow-comp.).

Besides, in case of selecting the differenced image between the image which is reconstructed on the basis of the echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence applying the dephase type flow pulses (flow-spoiled), and the image which is reconstructed on the basis of the echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence applying the dephase type flow pulses (flow-spoiled), the imaging scan condition is set at a three-dimensional FASE-method pulse sequence which applies the dephase type flow pulses (flow-spoiled).

Further, likewise, in case of selecting the differenced image between the image which is reconstructed on the basis of the echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence not applying the flow pulses, and the image which is reconstructed on the basis of the echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence not applying the flow pulses, the imaging scan condition is set at a three-dimensional FASE-method pulse sequence which does not apply the flow pulses.

On the other hand, when the prep scan of the detailed setting type has been selected, it proceeds as shown inFIGS. 17 and 18. An image which is reconstructed on the basis of echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence applying the rephase type flow pulses (flow-comp.) whose flow compensation effect is +3, namely, whose gradient magnetic field intensity is triple a reference intensity, and an image which is reconstructed on the basis of echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence applying the rephase type flow pulses (flow-comp.) whose flow compensation effect is +3, namely, whose gradient magnetic field intensity is triple the reference intensity are differenced simply or in weighted fashion, and the differenced image is displayed.

An image which is reconstructed on the basis of echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence applying the rephase type flow pulses (flow-comp.) whose flow compensation effect is +2, namely, whose gradient magnetic field intensity is double the reference intensity, and an image which is reconstructed on the basis of echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence applying the rephase type flow pulses (flow-comp.) whose flow compensation effect is +2, namely, whose gradient magnetic field intensity is double the reference intensity are differenced simply or in weighted fashion, and the differenced image is displayed.

An image which is reconstructed on the basis of echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence applying the rephase type flow pulses (flow-comp.) whose flow compensation effect is +1, namely, whose gradient magnetic field intensity is the reference intensity, and an image which is reconstructed on the basis of echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence applying the rephase type flow pulses (flow-comp.) whose flow compensation effect is +1, namely, whose gradient magnetic field intensity is the reference intensity are differenced simply or in weighted fashion, and the differenced image is displayed.

Besides, an image which is reconstructed on the basis of echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence not applying the flow pulses, and an image which is reconstructed on the basis of echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence not applying the flow pulses are differenced simply or in weighted fashion, and the differenced image is displayed.

An image which is reconstructed on the basis of echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence applying the dephase type flow pulses (flow-spoiled) whose flow compensation effect is −1 (flow suppression effect is +1), namely, whose gradient magnetic field intensity is the reference intensity, and an image which is reconstructed on the basis of echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence applying the dephase type flow pulses (flow−spoiled) whose flow compensation effect is −1 (flow suppression effect is +1), namely, whose gradient magnetic field intensity is the reference intensity are differenced simply or in weighted fashion, and the differenced image is displayed.

An image which is reconstructed on the basis of echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence applying the dephase type flow pulses (flow-spoiled) whose flow compensation effect is −2 (flow suppression effect is +2), namely, whose gradient magnetic field intensity is double the reference intensity, and an image which is reconstructed on the basis of echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence applying the dephase type flow pulses (flow−spoiled) whose flow compensation effect is −2 (flow suppression effect is +2), namely, whose gradient magnetic field intensity is double the reference intensity are differenced simply or in weighted fashion, and the differenced image is displayed.

An image which is reconstructed on the basis of echoes acquired in the systolic phase by the two-dimensional FASE-method pulse sequence applying the dephase type flow pulses (flow-spoiled) whose flow compensation effect is −3 (flow suppression effect is +3), namely, whose gradient magnetic field intensity is triple the reference intensity, and an image which is reconstructed on the basis of echoes acquired in the diastolic phase by the two-dimensional FASE-method pulse sequence applying the dephase type flow pulses (flow-spoiled) whose flow compensation effect is −3 (flow suppression effect is +3), namely, whose gradient magnetic field intensity is triple the reference intensity are differenced simply or in weighted fashion, and the differenced image is displayed.

The operator visually checks the seven sorts of images, and he/she selects the image in which the target blood flow, for example, the artery is extracted most clearly.

The imaging scan condition is set at the same flow condition as that of the selected image by the host computer6and the sequencer5. More specifically, in case of selecting the differenced image which corresponds to the two-dimensional FASE-method pulse sequence that applies the rephase type flow pulses (flow-comp.) having any of the flow compensation effects, the imaging scan condition is set at a three-dimensional FASE-method pulse sequence which applies the rephase type flow pulses (flow-comp.) having the same flow compensation effect, namely, the same gradient magnetic field intensity.

Besides, in case of selecting the differenced image which corresponds to the two-dimensional FASE-method pulse sequence that does not apply the flow pulses, the imaging scan condition is set at a three-dimensional FASE-method pulse sequence which does not apply the flow pulses.

Further, in case of selecting the differenced image which corresponds to the two-dimensional FASE-method pulse sequence that applies the dephase type flow pulses (flow-spoiled) having any of the flow suppression effects, the imaging scan condition is set at a three-dimensional FASE-method pulse sequence which applies the dephase type flow pulses (flow-spoiled) having the same flow suppression effect, namely, the same gradient magnetic field intensity.

Incidentally the numbers of stages of the flow compensation effect and the flow suppression effect which are attained in the prep scan of the detailed type can be set at will by the operator.

As thus far described, according to this embodiment, in an imaging scan, phase encoding pulses Gpe are impressed substantially in agreement with the direction of a target blood flow, and flow pulses are impressed in a phase encoding direction, whereby the effect of emphasizing the blood flow can be realized. Moreover, a temporal margin can be afforded to the flow pulse impression so as to shorten echo intervals and to impress the flow pulses at intensities necessary and sufficient for separating an artery and a vein.