This is to be 61/314,653 non-provisional application by the provisional application sequence number that V. Deshpande submitted on March 17th, 2010.
The specific embodiment
A kind of system improves the fat suppression in the MR Image Acquisition of using MR pulse train, and this MR pulse train uses one or more RF pulses to form echo and low bandwidth excitation RF pulse.This system advantageously uses different sections to select gradient amplitude to the RF pulse (being also referred to as the low bandwidth excitation) of EPI, selects the gradient counter-rotating together with section, improves the fat suppression in the spin echo EPI Diffusion Imaging.When proton spin turns back to that they are had after initial excitation RF pulse identical start-phase, use the RF burnt pulse of meeting again.Spin-echo sequence uses for example 180 ° of pulses to generate signal echo with the burnt proton spin of meeting again, and gradin-echo uses the burnt gradient of meeting again to maximize remaining cross magnetization.
Fig. 1 illustrates the system 10 that is used to carry out the MR imaging that fat signal suppresses.System 10 is used for signal with spin echo and generates the fat suppression of improving pulse train.In one embodiment, this system uses spin echo disperse EPI sequence.Have the excitation and the burnt pulse of meeting again that gradient is selected in different section by use, for example, improve fat suppression by using the burnt pulse of meeting again of low bandwidth EPI excitation RF pulse and high bandwidth.Alternately, can use the burnt pulse of meeting again of high bandwidth driving pulse and low bandwidth.The section of these two pulses selects gradient amplitude advantageously different.
Basic field magnet 1 generates constant in time high-intensity magnetic field, and with the polarization or the aligning of the nuclear spin of the inspection area that is used for object, the inspection area of described object is such as the part of the human body of for example examine.The high homogeneity of the required main field of magnetic resonance measurement is provided in spherical measurement volumes M, and this sphere measurement volumes M for example is that the part with the human body of examine is incorporated into volume wherein.In order to satisfy homogeneity needs and especially constant influence in order to eliminate, in position locate to install the shimming plate of making by ferromagnetic material.Become influence when eliminating by shim coil 2, this shim coil 2 is controlled by shim current source 15.
In main field 1, use by for example three cylindrical gradient coil system 3 that winding constitutes.Provide electric current by amplifier 14 to each winding, so that on the respective direction of cartesian coordinate system, generate the linear gradient field.First winding of gradient fields system 3 is created on the gradient G on the x direction
x, second winding is created on the gradient G on the y direction
y, and the tertiary winding is created on the gradient G on the z direction
zEach amplifier 14 comprises digital to analog converter, and this digital to analog converter generates gradient pulse by sequence controller 18 controls between in due course.
Location radio frequency (RF) coil 4 in gradient fields system 3, these radio frequencies (RF) coil 4 will be converted to alternating magnetic field by the radio-frequency pulse that radio-frequency power amplifier 16 is launched via multiplexer 6, so that the nuclear spin in the zone of the nuclear in the zone of excitation examine object or examine object and aligning examine object or examine object.In one embodiment, RF coil 4 comprises whole along the subclass of a plurality of RF coils of arranging corresponding to the length segmentation of the volume M of patient's length or a plurality of basically RF coils.In addition, each section RF coil of coil 4 comprises a plurality of RF coils, and described a plurality of RF coils provide by the parallel RF view data that is used to generate single MR image.Use the RF pulse signal to RF coil 4, RF coil 4 produces magnetic field pulse in response, described magnetic field pulse is with spin half-twist or Rotate 180 ° so-called to be used for " spin echo " imaging of the proton in the health of imaging, or rotation is less than or equal to 90 ° angle so-called to be used for " gtadient echo " imaging.In response to applied RF pulse signal, RF coil 4 receives the MR signals, just when the proton of health underexcitation turns back to equilibrium locations by static and gradient magnetic foundation from the signal of the proton of described excitation.To comprise that the nuclear spin echo signal that receives by RF coil 4 is a voltage as the MR conversion of signals of the alternating field that is produced by the precession nuclear spin, this voltage offers the radio frequency receiver processing unit 8 of radio system 22 via amplifier 7 and multiplexer 6.
This radio system 22 is operated under the RF signal transfer mode with the excitation proton, and operates to handle resulting RF echo-signal under receiving mode.Under transmission mode, the RF pulses are transmitted to be enabled in the nuclear magnetic resonance, NMR among the volume M via transmission channel 9 in system 22.Especially, system 22 handles the corresponding RF echo impulse that is associated with pulse train, and this pulse train is used so that the plural Serial No. of numeral to be provided together with sequence controller 18 by component computer 20.This Serial No. is provided as real part and imaginary part via the digital to analog converter in the radio frequency system 22 12, and is provided to transmission channel 9 from this digital to analog converter 12.In transmission channel 9, utilize radio-frequency carrier signal to modulate described pulse train, this radio-frequency carrier signal has the fundamental frequency corresponding to the resonant frequency of the nuclear spin in measurement volumes M.
Finish via multiplexer 6 from being transferred to the conversion that receives operation.The 4 transmitting RF pulses of RF coil are activated at nuclear proton spin among the measurement volumes M and the RF echo-signal that acquires.Correspondingly the magnetic resonance signal of Huo Deing is carrying out demodulation in the receptor processing unit 8 in RF system 22 under the phase sensitive mode, and converts the real part and the imaginary part of measuring-signal to via corresponding analog-digital converter 11, and handles by tomography computer 17.Tomography computer 17 comes reconstructed image according to the treated RF echo impulse data of obtaining.Under the control of component computer 20, carry out the processing of RF data, view data and control sequence.In response to predetermined pulse train control sequence, the generation and the spatial respective scanned of k-of sequence controller 18 control expectation pulse trains.The reception of the magnetic resonance signal of especially, the switching of sequence controller 18 control magnetic gradients between in due course, the transmission of RF pulse and RF echo data form with definite phase place and amplitude.Synthesizer 19 is determined the sequential of the operation of RF system 22 and sequence controller 18.Carry out the selection of the suitable control sequence that is used to generate the MR image via terminal (control station) 21 and the demonstration of the nuclear spin image that generated by the user, this terminal (control station) 21 comprises keyboard and one or more screen.System 10 uses magnetic field gradient and radio-frequency (RF) excited to create image.Component computer 20 is transformed into the k-spatial data that obtains on the cartesian grid, and three dimensional fourier transform (3DFT) method is used to deal with data to form final image.
Component computer 20 when obtaining the image of fat signal with inhibition automatically (perhaps in response to user command) via terminal 21 input adopt and the MR imaging device of guidance system 10.The 22(RF of RF system signal generator) generates the RF pulse of spin echo signal version, comprise RF driving pulse and the RF after this RF driving pulse burnt pulse of meeting again.Comprise that magnetic field section selects the magnetic gradient field system 3 of gradient generator to generate the first and second different sections and select magnetic field gradients, to use with RF driving pulse and the RF burnt pulse of meeting again accordingly respectively.This first and second different section selects magnetic field gradient advantageously to have different substantially amplitudes.The guiding of the MR imaging control unit of component computer 20 uses the RF pulse that generated and different sections to select magnetic field gradient to suppress the obtaining of MR imaging data of fat signal substantially.
Have the section selection magnetic field gradient that gradient intensity is selected in different sections if use, then chemical shift causes the different space displacement of fat signal and water signal in response to excitation with meeting again burnt pulse, thereby prevents reunion Jiao of fat signal.If gradient enough low (corresponding to the pulse long enough) is selected in the section of one of pulse, then there is advantageously improved (and may be basic perfect) fat suppression.Required, as the bandwidth of the function of the burnt pulse bandwidth of meeting again be:
System 10 advantageously adopts the gradient inverting method to select gradient amplitude together with the difference section of the excitation RF pulse that is used for EPI (being called the low bandwidth excitation), to reduce the required prolongation of RF pulse.This be since Spatial Mismatch be in now rightabout (as discuss after a while as shown in Fig. 3) obtain.Select in section under the situation of gradient counter-rotating,
(for
,
Have nothing to do), equation 4
Spend the bandwidth of pulses greater than 90 of equation 1.Therefore, advantageously reduced the required RF pulse duration with gradient counter-rotating.The section profile of more than analyzing each pulse of hypothesis is ideal substantially.In fact, because defective section profile, space displacement needs higher.Before the EPI excitation, except the excitation and the burnt pulse of meeting again, also use the fat suppression pulse, with the section profile defective of the explanation excitation and the burnt pulse of meeting again.
Fig. 2 illustrates indication mechanism 10(Fig. 1) how to use different sections to select gradient that the diagram of fat signal inhibition is provided for the excitation and the burnt pulse of meeting again.Fig. 2 illustrates the locus that the contrast time draws, this locus indication in response to the RF pulse of the MR imaging anatomical slice 225 that is used for comprising fat and water at the space displacement of fatty and hydromagneticization.System 10 uses low bandwidth (gradient intensity is selected in low section) the 90 degree RF driving pulses 210 that generated by RF system 22, these low bandwidth 90 degree RF driving pulses 210 make from the fat 220 of water 223 different spatial owing to chemical shift is energized.Similarly, by RF system 22 generate and have different sections select gradient intensity (the RF bandwidth different) with driving pulse 210 and section select the RF of the gradient counter-rotating burnt pulse 212 of meeting again, act on fat 230 from another different spatial.Especially, act on fat 230 RF pulse 212 have high section select gradient intensity (than the high RF bandwidth of driving pulse 210) and section select the gradient counter-rotating, described fatty 230 have aspect magnetization than by driving pulse 210 previous magnetized fatty 220 space displacements that lack.In addition, the 2nd RF that generates by RF system 22 meet again that burnt pulse 214 has that gradient intensity (than the high RF bandwidth of driving pulse 210) is selected in high section and section select the gradient counter-rotating, and only act on water, so fat be can't see the burnt pulse 214 of reunion and therefore the fat magnetization is damaged, and this has advantageously suppressed the MR fat signal.
Fig. 3 illustrates indication and how to use different sections to select gradient to obtain the diagram that fat signal suppresses to the excitation and the burnt pulse of meeting again, and the section of the burnt pulse of wherein meeting again selects gradient to be inverted.System 10 uses low bandwidth (gradient intensity is selected in low section) the 90 degree RF driving pulses 310 that generated by RF system 22, these low bandwidth 90 degree RF driving pulses 310 make in the section 325 from the fat 320 of water 323 different spatial owing to chemical shift is energized.Similarly, generate and have different sections by RF system 22 and select gradient intensity (the RF bandwidth different) and section to select the RF of the gradient counter-rotating burnt pulse 312 of meeting again, act on fat 330 from another different spatial with driving pulse 310.Especially, act on fat 330 RF pulse 312 and have high section and select gradient intensity (than the high RF bandwidth of driving pulse 310) and section to select the gradient counter-rotating, this fat 330 has aspect magnetization than by driving pulse 310 magnetized fatty 320 space displacements that lack.The fatty displacement because counter-rotating section selection gradient has been reversed, so the requirement to fatty displacement during encouraging reduces, therefore this cause higher admissible section to select gradient intensity, just higher RF bandwidth, and this higher RF bandwidth is corresponding to shorter RF pulse.In addition, the 2nd RF that generates by RF system 22 meet again that burnt pulse 314 has that gradient intensity (than the high RF bandwidth of driving pulse 310) is selected in high section and section select the gradient counter-rotating, and only act on water, so fat be can't see the burnt pulse 314 of reunion and therefore the fat magnetization is damaged, and this advantageously suppresses the MR fat signal.
Fig. 4 illustrates 10(Fig. 1 by system) the spin echo EPI pulse train that provides improved fat suppression to adopt is provided, this spin echo EPI pulse train comprises that RF pulse 403, magnetic section select gradient pulse 405, magnetic gradient pulses phase place 407 and magnetic gradient read pulse 409.Before EPI excitation RF pulse 423, use spectral selectivity fat suppression (FS) RF pulse 420.Pulse 423 is the sine pulses with the bandwidth that can be selected by the user.System 10 uses the burnt pulse 426 of meeting again of 180 degree, and the burnt pulse 426 of meeting again of this 180 degree comprises that having the polar section opposite with driving pulse 423 selects the burnt pulse of meeting again of the high bandwidth of gradient.System 10 uses burnt pulse 429, the 2 180 degree burnt pulse 429 of meeting again of meeting again of the 2 180 degree and comprises as select having with driving pulse 423 essentially identical polar sections as shown in the gradient pulse 405 to select the burnt pulse of meeting again of the high bandwidth of gradients in section.System 10 obtains the MR data with the echo time (TE) 430 in single-shot EPI reads.
Fig. 5 illustrates three MRI images that utilize following three kinds of fat suppression schemes to obtain from two patients: (a) standard fat suppression scheme; (b) fat suppression of the gradient counter-rotating of gradient is selected in the section of the burnt pulse of utilization reunion; And (c) fat suppression that the section of burnt pulse selects the gradient counter-rotating of gradient and use low bandwidth driving pulse (driving pulse of gradient is selected in just low section) of meeting again.These images are had a mind to amplify to emphasize fatty element.Especially, image 505 is to use the known fat suppression method of a fat suppression pulse of application before driving pulse to obtain, and the residual fat signal that causes image artifacts 520 is shown.Image 510 utilization has the section of the burnt pulse of meeting again and selects the fat suppression pulse train of the gradient counter-rotating of gradient to obtain, and so that the fat suppression better than image 505 to be provided, but this image 510 still presents the pseudo-shadow 525 of not repressed fat signal.The section that image 515 utilization has a burnt pulse of meeting again select gradient the gradient counter-rotating fat suppression pulse train and use low bandwidth driving pulse (driving pulse of gradient is selected in just low section) to obtain, to suppress the fat signal effect substantially fully.
Fig. 6 be shown in carry out in the MR imaging that fat signal suppresses and by the 10(Fig. 1 of system) flow chart of the process carried out.Step 612 after the beginning of step 611, RF signal generator 22 generates the RF pulse of spin echo signal versions, comprises RF driving pulse and the RF after this RF driving pulse burnt pulse of meeting again.In step 617, comprise that magnetic field section selects the magnetic gradient field system 3 of gradient generator, generate first section of together using and select magnetic field gradient with the RF driving pulse, and generation and the RF second section selection magnetic field gradient that burnt pulse together uses of meeting again.This first and second different section selects magnetic field gradient to have different substantially amplitudes.In one embodiment, magnetic field section selection gradient generator generates the first and second different sections with opposite polarity and selects magnetic field gradient.First section selects magnetic field gradient to have following amplitude: the Spatial Mismatch that this amplitude is selected as feasible fat is slice thickness and because the summation of the Spatial Mismatch that the second section selection gradient causes at least.Second section selects magnetic field gradient to have following amplitude: the Spatial Mismatch that this amplitude is selected as feasible fat is slice thickness and because the summation of the Spatial Mismatch that the first section selection gradient causes at least.
In one embodiment, RF signal generator 22 generates the burnt pulse of a succession of reunion in step 619, and the magnetic field section selects gradient generator to generate the section selection gradient amplitude different to the burnt pulse of alternative reunion.In step 623, component computer 20(MR imaging control unit) obtaining of MR imaging data that the RF pulse that generated and different section selection magnetic field gradients suppressed fat signal substantially used in guiding (control).In addition, RF signal generator 22 is ignored use spectral selectivity fat suppression RF pulse before the RF driving pulse, and still, in another embodiment, generator 22 is created on the spectral selectivity fat suppression RF pulse of using before the RF driving pulse.The process of Fig. 6 stops in step 631.
The processor of Shi Yonging is to be used to carry out the device that is stored in the machine readable instructions that is used to execute the task on the computer-readable medium herein, and can comprise any or combination in hardware and the firmware.Processor can also comprise the memorizer of the executable machine instructions that storage is used to execute the task.Processor acts on information as follows: by manipulation, analysis, modification, conversion or transmission information to use by executable program or massaging device; And/or by routing information to output device.Processor can use or comprise the performance of controller for example or microprocessor, and uses executable instruction to be adjusted the special function that can not be carried out by general purpose computer to carry out.Processor can with any other processor coupling (but electrically and/or for example comprising execution unit) to realize mutual between them and/or to communicate by letter.User interface processor or generator are the well known elements that is used to generate display image or its part that comprises electronic circuit or software or both combinations.User interface comprises makes the user to install mutual one or more display images with processor or other.
Comprise as executable application programs used herein being used to adjust processor implementing the code or the machine readable instructions of predetermined function that described predetermined function such as operating system, context data obtain system or for example in response to those functions of other information processing systems of user command or input.Executable program is code segment or the executable application programs part that one or more particular procedures are carried out in one section code or machine readable instructions, subroutine or other different being used to.These processes can comprise: receive input data and/or parameter, carry out function to the input data executable operations that received and/or in response to the input parameter that is received, and dateout and/or the parameter that obtains is provided.Comprise one or more display images as the user interface of using (UI) herein, these one or more display images are generated by user interface processor and make the user to carry out data mutual and that make it possible to be associated with processor or other devices and obtain and processing capacity.
UI also comprises executable program or executable application programs.This executable program or executable application programs are adjusted user interface processor to generate the signal of expression UI display image.These signals are provided for display device, and this display device display image is watched for the user.Executable program or executable application programs are also from the user input apparatus received signal, and described user input apparatus such as keyboard, mouse, light pen, touch screen or any other permission user provide the device of data to processor.This processor is handled the UI display image in response to the signal that receives from input equipment under the control of executable program or executable application programs.By this way, the user uses input equipment and display image mutual, makes that the user can be mutual with processor or other devices.Function herein and treatment step can automatically be carried out or completely or partially carry out in response to user command.The behavior that automatically performs (comprising step) is in response to executable instruction or device operation and carries out, and need not the user and directly starts the behavior.
The system of Fig. 1-6 and process are not exclusiveness.Can draw other system according to principle of the present invention and reach identical purpose with process.Though invention has been described with reference to specific embodiment, be appreciated that here shown in and described embodiment and variant only be for illustration purpose.Those skilled in the art can implement the modification to current design, and do not depart from scope of the present invention.System uses different sections to select gradient to the excitation in the spin echo signal EPI sequence with the burnt pulse of meeting again, for example to obtain fat suppression.In addition, in alternative embodiment, these processes and application program can be positioned on one or more (for example distributed) blood processor on the unitary network of connection layout 1.The function that provides among Fig. 1-6, image control and any of step can completely or partially be realized with hardware, software or both combinations.