MR imaging scan using ECG-prep scan

Abstract

An ECU-prep scan is used to set an optimum time phase in both systole and diastole of the heart. At each of the different time phases, an imaging scan is started to acquire a plurality of sets of echo data. An artery/vein visually separated blood flow image is produced from the echo data. The imaging scan uses a half-Fourier technique, for example. This provides high-quality blood flow images with shorter scan time, without injecting a contrast medium. Additionally, with a readout gradient pulse applied substantially parallel with a direction of slowly flowing blood, a scan is performed in synchronism with an optimally determined cardiac time phase. The readout gradient pulse has a dephasing pulse for enhancing differences in a flow void effect depending on blood flow velocities. This enables slow-speed flows, such as blood flows in the inferior limb, to be depicted without fail.

What is claimed is: 
     
       1. An MRI system for obtaining an image relating to fluid within a region to be imaged of an object, comprising:
 a time phase setting unit configured to set two different cardiac time phases falling into a systole and a diastole of a cardiac cycle of the object;   a scanning unit configured to perform, toward the region to be imaged of the object, an MR imaging scan starting in turn at each of the two cardiac time pahses set by the time phase setting unit to acquire two sets of echo data, the MR imaging scan comprising a first scan starting at one of the two cardiac time phases falling in the systole and a second scan starting at the other of the two cardiac time phases falling in the diastole, both the first scan and the second scan being based on a half-Fourier technique; and   an image producing unit configured to produce, from the two sets of echo data acquired by the scanning unit, the image relating to the fluid.   
     
     
       2. The MRI system of  claim 1 , wherein the scanning unit is configured to perform both the first and second scans, respectively, on either the same slice of the region or a volume of the region specified by each slice encodes. 
     
     
       3. The MRI system of  claim 1 , wherein the first scan is is carried out using a pulse sequence generating an echo signal to map echo data in a central region of a first k-space for producing the image, the central region corresponding to a lower-frequency region in a phase-encode direction of the first k-space, and
 the second scan is carried out using a pulse sequence generating an echo signal to map echo data in both a central region and one of both end regions other than the central region of a second k-space for producing the image, the central region corresponding to a lower-frequency region in a phase-encode direction of the second k-space and both of the end regions corresponding to a higher-frequency region in the phase-encode direction of the second k-space.   
     
     
       4. The MRI system of  claim 3 , wherein the image producing unit includes duplicating means for duplicating echo data existing in one end region of the second k-space to one of both end regions of the first k-space, the one end region of the first k-space being yet to be mapped with echo data, and calculating means for calculating, with regard to each of the first and second k-spaces, additional echo data based on the half-Fourier technique so that the calculated additional echo data is mapped into the remaining end region being yet to be mapped. 
     
     
       5. The MRI system of  claim 4 , wherein the image producing means includes arterial phase image producing means for obtaining one of echo data and image data representing an arterial phase image through a predetermined type of calculation executed between one of echo data of the first k-space and image data thereof and one of echo data of the second k-space and image data thereof. 
     
     
       6. The MRI system of  claim 5 , wherein the predetermined type of calculation executed by the arterial phase image producing means is one of subtraction, weighted difference calculation, and addition. 
     
     
       7. The MRI system of  claim 5 , wherein the image producing unit includes venous phase image producing means for obtaining one of echo data and image data thereof representing a venous phase image by executing subtraction between one of echo data of image data representing the arterial phase image obtained by the arterial phase image producing means and one of echo data of the second k-space and image data thereof. 
     
     
       8. The MRI system of  claim 1 , wherein each of the first and second scans is either one of a two-dimensional scan and a three-dimensional scan. 
     
     
       9. The MRI system of  claim 1 , wherein the unit is configured to execute the MR imaging scan with a pulse sequence based on one of an EPI (Echo Planar Imaging) technique and an FSE (Fast Spin Echo) technique. 
     
     
       10. The MRI system of  claim 1 , wherein the time phase setting unit has detecting means for detecting a signal indicative of the cardiac time phases of the object, preparing means for obtaining a plurality of MR images by executing a preparing MR sequence a plurality of times toward the region to be imaged of the object at different timings from a heartbeat reference wave appearing cyclically in the signal detected by the detecting means, and means for determining the two cardiac time phases from the plurality of MR images obtained by the preparing means. 
     
     
       11. The MRI system of  claim 10 , wherein the signal indicative of the cardiac time phases is an ECG signal of the object and the heartbeat reference wave is an R-wave of the ECG signal. 
     
     
       12. The MM system of  claim 1 , wherein the scanning unit is configured to execute a pulse sequence including readout gradient pulse of which applied direction is substantially in accordance with a moving direction of the fluid. 
     
     
       13. The MM system of  claim 12 , wherein the readout gradient pulse has a main pulse for reading out the echo signal and a control pulse for controlling behaviors of magnetic spins of the fluid concerning a phase of the magnetic spins, the control pulse being added to the main pulse on a time axis thereof. 
     
     
       14. The MM system of  claim 13 , wherein the control pulse is a pulse responsible for at least one of dephasing and rephasing of the magnetic spins. 
     
     
       15. The MRI system of  claim 13 , further comprising a unit configured to control an intensity of the control pulse in accord with a flow velocity of the fluid. 
     
     
       16. An MR imaging method of obtaining an image relating to fluid within a region to be imaged of an object, comprising:
 setting two different cardiac time phases falling into a systole and a diastole of a cardiac cycle of the object;   performing toward the region to be imaged of the object, an MR imaging scan starting in turn at each of the two cardiac time phases to acquire two sets of echo data, the MR imaging scan comprising a first scan starting at one of the two cardiac time phases falling in the systole and a second scan starting at the other of the two cardiac time phases falling in the diastole, both of the first scan and the second scan being based on a half-Fourier technique; and   producing, from the two sets of acquired echo data, the image relating to the fluid.   
     
     
       17. An MRI system for obtaining an image relating to fluid within an object, in which the object placed in a static magnetic field is subjected to a scan based on a pulse sequence including a readout gradient pulse, comprising:
 a time phase setting unit configured to set a cardiac time phase of the object;   a scanning unit configured to perform the scan at the cardiac time phase to acquire an echo signal from the object under a condition that an applied direction of the readout gradient pulse is substantially in accordance with a moving direction of the fluid in motion within the object; and   an image producing unit configured to produce, from the echo signal, the image relating to the fluid,   wherein the readout gradient pulse has a main pulse for reading out the echo signal and a control pulse for controlling behaviors of magnetic spins of the fluid concerning a phase of the magnetic spins, the control pulse being added to the main pulse along a time axis of the main pulse.   
     
     
       18. The MRI system of  claim 17 , wherein the control pulse is a pulse responsible for at least one of dephasing and rephasing of the magnetic spins. 
     
     
       19. The MRI system of  claim 18 , wherein the readout gradient pulse has a main pulse for reading out the echo signal and a control pulse for controlling behaviors of magnetic spins of the fluid concerning a phase of the magnetic spins, the control pulse being added to the main pulse along a time axis of the main pulse. 
     
     
       20. The MRI system of  claim 19 , wherein the control pulse is a pulse responsible for at least one of dephasing and rephasing of the magnetic spins. 
     
     
       21. The MRI system of  claim 20 , wherein the control pulse belonging to the readout gradient pulse in the pulse sequence used for each of the first and second scans is formed as a pulse responsible for at least one of the dephasing and rephasing. 
     
     
       22. The MRI system of  claim 20 , wherein the control pulse belonging to the readout gradient pulse in the pulse sequence used for the first scan executed at one of the two cardiac time phases is formed as a pulse responsible for the dephasing and the control pulse belonging to the readout gradient pulse in the pulse sequence used for the second scan executed at the other cardiac time phase is formed as a pulse responsible for the rephasing. 
     
     
       23. The MRI system of  claim 22 , wherein the time phase setting is configured to set the one cardiac time phase falling into a diastole of the object and set the other cardiac time phase falling into a systole of the object. 
     
     
       24. The MRI system of  claim 19 , wherein the control pulse is changeable in a wave area thereof. 
     
     
       25. The MRI system of  claim 17 , comprising a unit for controlling an intensity of the control pulse in accord with a flow velocity of the fluid. 
     
     
       26. An MRI system for obtaining an image relating to fluid within an object, in which the object placed in a static magnetic field is subjected to a scan based on a pulse sequence including a readout gradient pulse, comprising:
 a time phase setting unit configured to set a cardiac time phase of the object;   a scanning unit configured to perform the scan at the cardiac time phase to acquire an echo signal from the object under a condition that an applied direction of the readout gradient pulse is substantially in accordance with a moving direction of the fluid in motion within the object; and   an image producing unit configured to produce, from the echo signal, the image relating to the fluid,   wherein the time phase setting unit is configured to set two cardiac time phases of the object,   the scanning unit is configured to acquire data comprising two sets of echo signals by applying first and second scans to the object at the two cardiac time phases, respectively; and   the image producing unit is configured to produce an image of the fluid from the data.   
     
     
       27. The MRI system of  claim 26 , wherein the scanning unit is configured to sequentially perform the first and second scans on either the same slice of the region or volume of the region specified by each slice encode during one time of imaging for the object. 
     
     
       28. The MRI system of  claim 26 , wherein the fluid is a blood flow within the object. 
     
     
       29. The MRI system of  claim 28 , wherein the blood flow consists of an artery and a vein slowly flowing in an inferior limb of the object, and
 the image producing unit has artery/vein image producing means that produces images in which the artery and vein are visually separated from each other.   
     
     
       30. The MRI system of  claim 26 , wherein each of the first and second scans is formed based on a half-Fourier technique. 
     
     
       31. The MRI system of  claim 30 , wherein the first scan carried out using a pulse sequence generating an echo signal to map echo data in a central region of a first k-space for producing the image, the central region corresponding to a lower-frequency region in a phase-encode direction of the first k-space, and
 the second scan is carried out using a pulse sequence generating an echo signal to map echo data in both of a central region and one of both end regions other than the central region of a second k-space for producing the image, the central region corresponding to a lower-frequency region in a phase-encode direction of the second k-space and both of the end regions corresponding to a higher-frequency region in the phase-encode direction of the second k-space.   
     
     
       32. The MRI system of  claim 31 , wherein the image producing unit has duplicating means for duplicating echo data existing in the one end region of the second k-space to on of both end regions of the first k-space, the one end region of the first k-space being yet to be mapped with echo data, and calculating means for calculating, in each of the first and second k-spaces, additional echo data based on the half-Fourier technique so that the calculated additional echo data is mapped into the remaining end region being yet to be mapped. 
     
     
       33. The MRI system of  claim 32 , wherein the image producing unit includes arterial phase image producing means for obtaining one of echo data and image data representing an arterial phase image through a predetermined type of calculation executed between one of echo data of the first k-space and image data thereof and one of echo data of the second k-space and image data thereof. 
     
     
       34. The MRI system of  claim 33 , wherein the predetermined type of calculation executed by the arterial phase image producing means is one of subtraction, weighted difference calculation, and addition. 
     
     
       35. The MRI system of  claim 33 , wherein the image producing unit includes venous phase image producing means for obtaining one of echo data and image data thereof representing a venous phase image by executing subtraction between one of echo data of image data representing the arterial phase image obtained by the arterial phase image producing means and one of echo data of the second k-space and image data thereof. 
     
     
       36. The MR 1  system of  claim 30 , wherein each of the first and second scans is either one of a two-dimensional scan and a three-dimensional scan. 
     
     
       37. The MRI system of  claim 30 , wherein the time phase setting unit has detecting means for detecting a signal indicative of the cardiac time phases of the object, preparing means for obtaining a plurality of MR images by executing a preparing MR sequence a plurality of times toward the region to be imaged of the object at different timings from a heartbeat reference wave appearing cyclically in the signal detected by the detecting means, and means for determining the two cardiac time phases from the plurality of MR images obtained by the preparing means. 
     
     
       38. The MRI system of  claim 37 , wherein the signal indicative of the cardiac time phases is either an EGG signal or a PPG signal of the object and the heartbeat reference wave is an R-wave of either of the ECG signal or the PPG signal. 
     
     
       39. The MRI system of  claim 26 , wherein the pulse sequence used by each of the first and second scans is composed of a train of pulses based on one of a FASE (Fast Asymmetric SE) technique, EPI (Echo Planar Imaging) technique, FSE (Fast Spin Echo) technique, and SE (Spin Echo) technique. 
     
     
       40. An MR imaging method of obtaining an image relating to fluid within a region to be imaged of an object, comprising:
 setting a cardiac time phase of an object;   performing, toward the region to be imaged of the object, a scan at the cardiac time phase with use of a pulse sequence including a readout gradient pulse of which applied direction is substantially in accordance with a moving direction of fluid in motion within the object, so that an echo signal is acquired; and   producing, from the echo signal, the image relating to the fluid,   wherein the readout gradient pulse has a main pulse to read out the echo signal and at least one of a dephase pulse and a rephase pulse responsible for dephasing and rephasing phases of magnetic spins of the fluid, respectively, the at least one pulse being added to the main pulse along a time axis of the main pulse.   
     
     
       41. An MRI system for obtaining an image relating to fluid within a region to be imaged of an object, comprising:
 a magnet for generating a static magnetic field in which an object is placed;   an RF coil device through which an RF magnetic field is transmitted to the object and an echo signal emanated from the object is received;   a transmitter for transmitting the RF magnetic field to the object through the RF coil device, the RF magnetic field being based on a pulse sequence;   a gradient power supply for applying a gradient based on the pulse sequence to the object through a gradient coil;   a receiver for receiving the echo signal through the RF coil device, the echo signal being generated in response to performance of the pulse sequence;   a calculating unit for producing the echo signal received by the receiver into the image; and   a controller for controlling operations of the transmitter, receiver and gradient power supply in conformity with the pulse sequence,   wherein the controller controls the operations of transmitter, receiver and gradient power supply so that two different cardiac time phases falling into a systole and a diastole of a cardiac cycle of the object are set, and, as the pulse sequence, an imaging scan is executed in synchronism with each of the two different cardiac time phases in turn to acquire two sets of the echo signal, the imaging scan comprising a first scan starting at one of the two cardiac time phases falling in the systole and a second scan starting at the other of the two cardiac time phases falling in the diastole, both of the first scan and the second scan being based on a half-Fourier technique, and   the calculating unit produces the image relating to the fluid within the region to be imaged of the object from the two sets of the echo signal acquired correspondingly to each of the two different cardiac time phases.   
     
     
       42. An MRI system for obtaining an image relating to fluid within a region to be imaged of an object, comprising:
 a magnet for generating a static magnetic field in which an object is placed;   an RF coil device through which an RF magnetic field is transmitted to the object and an echo signal emanated from the object is received;   a transmitter for transmitting the RF magnetic field to the object through the RF coil device, the RF magnetic field being based on a pulse sequence;   a gradient power supply for applying a gradient based on the pulse sequence to the object through a gradient coil;   a receiver for receiving the echo signal through the RF coil device, the echo signal being generated in response to performance of the pulse sequence;   a calculating unit for producing the echo signal received by the receiver into the image; and   a controller for controlling operations of the transmitter, receiver and gradient power supply in conformity with the pulse sequence,   wherein the controller controls the operations of transmitter, receiver and gradient power supply so that a cardiac time phase of the object is set and, as the pulse sequence, a pulse sequence for an imaging scan is executed in synchronism with the cardiac time phase, the imaging-scan pulse sequence including a readout gradient pulse of which applied direction being substantially in accordance with a moving direction of fluid in motion within the object,   the calculating unit produces the image relating to the fluid within the object from the echo signal acquired through the receiver correspondingly to performance of the imaging-scan pulse sequence, and   wherein the readout gradient pulse has a main pulse to read out the echo signal and a control pulse to control behaviors of magnetic spins of the fluid concerning a phase of the magnetic spins, the control pulse being added to the main pulse along a time axis of the main pulse.   
     
     
       43. The MRI system of  claim 42 , wherein the control pulse is formed into a pulse responsible fore at least one of dephasing and rephasing the magnetic spins. 
     
     
       44. The MRI system of  claim 43 , wherein the cardiac time phase comprises two cardiac time phases falling into a systole and a diastole of the object, respectively, and
 the imaging scan consists of a first scan and a second scan made to start at the two cardiac time phases, respectively.   
     
     
       45. An MRI system for obtaining an image relating to fluid within a region to be imaged of an object, comprising:
 time phase setting means for setting two different cardiac time phases falling into a systole and a diastole of a cardiac cycle of the object;   scanning means for performing, toward the region to be imaged of the object, an MR imaging scan starting in turn at each of the two cardiac time phases set by the time phase setting means to acquire two sets of echo data, the MR imaging scan comprising a first scan starting at one of the two cardiac time phases falling in the systole and a second scan starting at the other of the two cardiac time phases falling in the diastole, both the first scan and the second scan being based on a half-Fourier technique; and   image producing means for producing, from the two sets of echo data acquired by the scanning means, the image relating to the fluid.   
     
     
       46. An MRI system comprising:
 a host computer configured to perform, toward fluid in a region to be imaged of an object placed in a static magnetic field, a 3D scan after a predetermined delay time from a trigger signal generated from a biosignal of the object, the 3D scan being performed so as to acquire a predetermined number of slice-encoded echo data sets, being repeated every two or more heartbeats, and being performed by using a pulse sequence including a flow control gradient pulse; and   to generate a 3D fluid image of the region of the object based on the predetermined number of slice-encoded echo data sets,   wherein an intensity of the flow control gradient pulse is controlled in accordance with flow speeds of the fluid by the host computer.   
     
     
       47. The MRI system of claim 46, wherein the intensity of the flow control gradient pulse is controlled in accordance with the flow speeds of blood by the host computer. 
     
     
       48. The MRI system of claim 46, wherein:
 the flow control gradient pulse is added to a gradient pulse body; and   the intensity of the flow control gradient pulse is controlled separately from the gradient pulse body by the host computer.   
     
     
       49. The MRI system of claim 46, wherein the flow control gradient pulse is a dephasing pulse, and the intensity of the dephasing pulse is controlled by the host computer. 
     
     
       50. The MRI system of claim 49, wherein the intensity of the dephasing pulse is reduced as a speed of the fluid becomes higher, and the intensity of the dephasing pulse is controlled by the host computer. 
     
     
       51. The MRI system of claim 46, wherein the flow control gradient pulse is a rephasing pulse, and the intensity of the rephasing pulse is controlled by the host computer. 
     
     
       52. The MRI system of claim 46, wherein:
 the biosignal is an ECG (electrocardiogram) signal or a PPG (peripheral gating) signal; and   the 3D scan is performed in each of a systole and a diastole by the host computer.   
     
     
       53. The MRI system of claim 52, wherein the flow control gradient pulse for the 3D scan in systole is a dephasing pulse, while the flow control gradient pulse for the 3D scan in diastole is a rephasing pulse, and each of the intensity of the dephasing pulse and the intensity of the rephasing pulse is controlled by the host computer. 
     
     
       54. The MRI system of claim 53, wherein the intensity of the dephasing pulse is reduced as a speed of the fluid becomes higher, and the intensity of the dephasing pulse is controlled by the host computer. 
     
     
       55. The MRI system of claim 52, wherein the 3D scan in systole and the 3D scan in diastole are performed sequentially by the host computer. 
     
     
       56. The MRI system of claim 52, wherein after the predetermined number of slice-encoded echo data sets for generating the 3D fluid image in systole are acquired, the predetermined number of slice-encoded echo data sets for generating the 3D fluid image in diastole are acquired in the 3D scan performed by the host computer. 
     
     
       57. The MRI system of claim 52, wherein the 3D scan in systole and the 3D scan in diastole are performed alternately in each slice encoding by the host computer. 
     
     
       58. The MRI system of claim 57,
 wherein the host computer is further configured to perform weighted subtraction between the 3D fluid image obtained by the 3D scan in systole and the 3D fluid image obtained by the 3D scan in diastole.   
     
     
       59. The MRI system of claim 46, wherein the region to be imaged of the object is an inferior limb, and the 3D fluid image of the inferior limb is generated by the host computer. 
     
     
       60. The MRI system of claim 46, further comprising:
 an input device configured to input, through an operation of a user, information for specifying the region to be imaged of the object and the intensity of the flow control gradient pulse, wherein the 3D scan using the pulse sequence including the flow control gradient pulse is performed by the host computer in accordance with the input intensity of the flow control gradient pulse, and wherein the input device is connected to the host computer.   
     
     
       61. The MRI system of claim 46, wherein the flow control gradient pulse is applied along an applied direction of a read out gradient pulse in the 3D scan performed by the host computer. 
     
     
       62. An MRI system comprising:
 a host computer configured to perform, toward an inferior limb of an object placed in a static magnetic field, a 3D scan after a predetermined delay time from a trigger signal generated from a PPG (peripheral gating) signal of the object, the 3D scan being performed so as to acquire a predetermined number of slice-encoded echo data sets, being repeated every two or more heartbeats, and being performed using a pulse sequence including a flow control gradient pulse; and   to generate a 3D blood image of the inferior limb of an object based on the predetermined number of slice-encoded echo data sets,   wherein an intensity of the flow control gradient pulse is controlled in accordance with flow speeds of a fluid in a region to be imaged by the host computer.