Patent Application: US-69643310-A

Abstract:
a system and method for providing a dark - blood technique for contrast - enhanced cardiac magnetic resonance , improving visualization of subendocardial infarcts or perfusion abnormalities that may otherwise be difficult to distinguish from the bright blood pool . in one technique the dark - blood preparation is performed using a driven - equilibrium fourier transform preparation with motion sensitizing gradients which attenuate the signal in the ventricular cavities related to incoherent phase losses resulting from non - steady flow within the heart . this dark - blood preparation preserves the underlying contrast characteristics of the pulse sequence causing a myocardial infarction to be bright while rendering the blood pool dark . when applied to perfusion imaging , this dark - blood preparation will help eliminate artifacts resulting from the juxtaposition of a bright ventricular cavity and relatively dark myocardium .

Description:
an embodiment of the present invention may be implemented on any commercial mri system without necessarily requiring any additional hardware . fig1 illustrates an example such mri system 10 including a data acquisition and display computer 50 coupled to an operator console 0 , a mri real - time control sequencer 52 , and a mri subsystem 54 . the mri subsystem 54 may include xyz magnetic gradient coils and associated amplifiers 68 , a static z - axis magnet 69 , a digital rf transmitter 62 , a digital rf receiver 60 , a transmit / receive switch 64 , and rf coil ( s ) 66 . a dedicated phased - array coil and electrocardiogram ( ecg ) leads l may be used for cardiac applications for synchronization of the control sequencer 52 with the electrical signals of the heart of patient p . the mri subsystem 54 may be controlled in real time by control sequencer 52 to generate magnetic and radio frequency fields that stimulate nuclear magnetic resonance (“ nmr ”) phenomena in a patient p ( e . g ., a human body ) to be imaged . a contrast agent c , such as gd - dtpa for example , is injected intravenously into the patient p . a resulting contrast - enhanced image of the cardiac structures of patient p may be shown on display 58 . display 58 may be implemented through a variety of output interfaces , including a monitor , printer , or data storage . one aspect of an embodiment of the present invention , for attenuating the blood signal in a ventricular cavity to improve contrast between myocardial infarction , scar , or fibrosis , is demonstrated in fig2 ( a ) and fig2 ( b ) . a pulse sequence is played out on the real - time control sequencer 52 with specific timing of magnetic field gradients and rf - pulses to create a post - contrast image of the heart where scar appears bright , and both the blood pool and the normal myocardial signal is depressed . the timing of the inversion - recovery ( ir ) rf - pulse 202 is synchronized to a fixed delay after the ecg trigger 201 , as depicted in fig2 ( a ) . the inversion - recovery rf - pulse 202 imparts t1 contrast weighting by inverting all of the magnetization within the patient p . those skilled in the art will readily understand that other nuclear magnetic resonance preparations and contrast weightings may be used , such as t2 , t2 *, or any other contrast weighting used in mri . once the magnetization from the blood pool has recovered past its null point , the motion - sensitization preparation 203 , depicted in detail in fig2 ( b ) , may be played out by the real - time control sequencer 52 . the motion - sensitization preparation 203 in this aspect may , for example , comprise multiple steps . first , an rf - pulse 211 is played out with the intent of creating transverse magnetization . the total flip angle of this rf - pulse is typically 90 degrees . second , a magnetic field gradient pulse 212 is played out by one or more of the xyz magnetic gradient coils and associated amplifiers 68 . this creates a dispersion of phase angles of spin isochromats which will lead to attenuation in the presence of motion . third , a refocusing rf - pulse 213 is played out to refocus effects of magnetic field inhomogenieties . fourth , another magnetic field gradient pulse 214 is played out . finally , an rf - pulse 215 is played to restore the residual transverse magnetization to longitudinal magnetization . it will be appreciated by those skilled in the art that any of the rf - pulses 211 , 213 , or 215 can be accomplished through a single rf - pulse , a component of a composite rf - pulse , or a series of rf - pulses played in rapid succession . the net effect of motion - sensitizing preparation 203 is to attenuate the signal from the blood pool . motion - sensitizing preparation 203 has very little effect on stationary tissues like the myocardium but a significant effect upon the turbulent blood , suppressing the signal corresponding to the blood pool . with the proper timing , this results in a darker blood pool . following the motion preparation , a suitable readout module 204 consisting of rf - pulses and magnetic field gradients is played out to collect the data . the readout module 204 is played out at a time when the magnetization from the normal myocardium is near or above its null point . any suitable type of magnetic resonance imaging readout module can be used . fig3 ( a ) shows the transverse magnetization during the above - described aspect of the present invention . at time 0 an inversion recovery rf - pulse 202 is applied which inverts the magnetization . the magnetization of the blood , myocardium , and infarct recover with their respective t1 relaxation times . as the blood and infarct have short t1 relaxation times they recover rapidly . when the blood signal has recovered past the zero point , the motion - sensitization preparation 203 is played out . this primarily attenuates the signal from the blood pool , but also slightly attenuates signal from the myocardium and the infarct . at a suitable time when the myocardial signal has recovered past its null point the readout module 204 can be played out . the timing from the inversion recovery rf - pulse 202 to the readout pulse sequence module 204 is chosen so that the signal from the normal myocardium will be near but above the null point . this time is referred to as ti . fig3 ( b ) demonstrates the difference in signal intensity ( contrast ) between both the infarct and normal myocardium ( shown as “ contrast infarct - normal ”) and the infarct and blood ( shown as “ contrast infarct - blood ”). note that these contrast curves are fairly flat for a range of ti times . the figure also shows ( shown as “ signal infarct ”) that the signal from infarcted myocardium or scar continues to increase as ti is increased , which leads to a higher signal - to - noise ( snr ) ratio for the infarct as ti is increased . fig4 demonstrates an example of images obtained with fig4 ( a ) as the conventional bright - blood ir - flash delayed enhancement imaging pulse sequence and fig4 ( b ) as the motion - sensitized dark - blood delayed enhancement pulse sequence , as depicted in fig2 ( a ) and fig2 ( b ) , respectively . these example images were obtained on a commercial 1 . 5 t magnetic resonance scanner in a canine subject with chronic myocardial infarction . imaging was performed about 5 - 10 minutes after injection of 0 . 15 mg / kg of gd - dtpa ( magnevist ). sequence parameters included : field of view — 300 mm ; matrix — 192 × 114 ; te — 2 . 7 ms ; spatial resolution — 1 . 6 × 2 . 3 × 10 mm ; lines per segment — 12 ; bandwidth — 400 hz / pixel ; acquisition duration — 16 heartbeats . the motion - sensitization preparation 203 in this example ( image of fig4 ( b ) ) is composed of a bir - 4 composite rf - pulse consisting of 3 components : a 90 degree pulse , a 180 degree pulse , and a negative 90 degree pulse . unipolar magnetic field gradients are applied in the thru - plane direction with amplitude of 20 mt / m and a duration of 1 ms each on either side of the 180 degree pulse ( see fig3 ). the effective b - value ( diffusion attenuation coefficient ) was 0 . 25 s / mm ^ 2 . in the image as shown in fig4 ( a ) , the image obtained with the conventional pulse sequence ( no dark - blood preparation ), the infarct in the inferior wall is not easily distinguished from the blood pool . in the image as shown in fig4 ( b ) , the dark - blood pulse sequence image , the infarct - blood pool border is clearly visible . the b - value used for imaging the myocardial cavity is generally smaller than that for vessel wall imaging . furthermore , the quicker recovery times when contrast is given , and inherent strain ( contraction ) of the heart require shortening the timing of the preparation . an aspect of an embodiment of the present invention for attenuating the blood signal in a ventricular cavity to improve contrast and eliminate dark - rim artifacts for first - pass contrast - enhanced imaging of the heart is demonstrated in fig5 . a pulse sequence is played out on the real - time control sequencer 52 with specific timing of magnetic field gradients and rf - pulses to create an image where the signal from the blood pool is attenuated during first - pass perfusion . the timing of the pulse sequence for the first slice position is typically timed to the ecg 501 . the same perfusion pulse sequence 500 is played out a number of times within each r - r interval of the ecg each at a different slice position to evaluate perfusion at multiple locations within the target ventricle . the perfusion pulse sequence 500 begins with a saturation recovery preparation module consisting of an rf - pulse , or combination of rf - pulses used to impart t1 weighting to the magnetization of the myocardium and blood pools . this is customarily , but not limited to a 90 degree pulse . a series of gradient pulses , sr rf - pulse 502 , are applied to spoil the residual transverse magnetization following this preparation . at a suitable time prior to the beginning of a readout module 504 , a motion - sensitization preparation 503 such as , but not limited to the one described in fig2 ( b ) is played out . this motion - sensitization preparation 503 attenuates the signal from the blood pool in proportion to its incoherent motion . following motion - sensitization preparation 503 , a suitable readout module 504 consisting of multiple rf - pulses and magnetic field gradients is performed . the magnetization preparation is compatible with any readout scheme . for perfusion imaging typically single - shot rapid imaging modules are utilized . the same pulse sequence 500 is applied to all of the slices each r - r interval during first pass of the contrast agent c . given the rapid t1 relaxation time of blood during first - pass of a gadolinium contrast agent at peak concentration the blood pool signal is decreased but not completely suppressed . this however , should be adequate for suppression of certain dark - rim artifacts . it should be apparent to one skilled in the art that many types of nuclear magnetic resonance preparations may be used and that the sr rf - pulse 502 may be accomplished through a single rf - pulse , a component of a composite rf - pulse , or a series of rf - pulses played in rapid succession . furthermore it should be apparent that the motion sensitized preparation is compatible with other contrast preparations schemes aimed at imparting t1 , t2 , t2 *, or any other contrast weighting used in mri . fig6 demonstrates magnetization relaxation curves for the above exemplary implementation of our method . the magnetization curves are representative of the relaxation times during first - pass perfusion imaging with a typical concentration of a gadolinium contrast agent . the application of sr pulse 502 , a combination of rf - pulses totaling 90 degrees with gradient spoiling destroys the longitudinal and transverse magnetization of all species . as the blood pool has the shortest t1 relaxation time it recovers the fastest . normal myocardium has an intermediate t1 and recovers slower , and hypoperfused myocardium has the longest t1 and recovers the slowest . prior to the application of a readout module 504 , the motion - sensitization preparation 503 is played out to attenuate the signal from the blood pool . during the readout the magnetization continues to recover , so the blood pool signal will have either a very low amplitude or amplitude intermediate to that of the normal and hypoperfused myocardium . fig7 demonstrates example images obtained from the pulse sequence described herein during first - pass of a gadolinium - based contrast agents demonstrating attenuation of the blood pool signal . these example images were obtained on a commercial 1 . 5 t magnetic resonance scanner in a canine . imaging was gated to the ecg and was performed continuously during injection of 0 . 075 mg / kg of gd - dtpa ( magnevist ). images were obtained for 40 heartbeats during the first pass of the contrast agent . sequence parameters included : flash gradient echo readout module ; field of view — 360 × 162 mm ; matrix — 160 × 54 ; te 1 . 1 ms ; spatial resolution — 2 . 3 × 3 × 8 mm ; bandwidth — 650 hz / pixel ; acquisition duration per image — 250 ms ; saturation time — 120 ms . the blood pool is completely suppressed within the ventricular cavity except for the time during peak blood - pool gadolinium concentration . the signal is completely suppressed by the preparation , but recovery of magnetization during the readout module results in a bright signal . improved suppression of the blood pool signal will be achievable with more rapid readout modules . fig8 illustrates integrating motion sensitization into a readout module , according to one aspect of an embodiment of the present invention . an inversion or saturation pulse is applied to create desired t 1 weighting . following the contrast preparation , a excitation pulse is applied ( for example a 90 degree pulse ), followed by a train of rf pulses ( for example a 180 degree pulse ) with a motion - sensitizing magnetic field gradient between each set of refocusing pulses . this is repeated m times , where m can be varied to achieve a desired amount of motion sensitization . within the same train of refocusing modules following the motion sensitizing module , individual readouts are acquired within the same set of refocusing gradients which can be repeated n times . thus , the motion sensitization and readout is performed in m + n intervals within a train of refocusing pulses after a single excitation pulse . the degree of t2 weighting can be determined by the location of the center of k - space acquisition during the readout train . fig9 illustrates a nuclear magnetic resonance preparation for imparting contrast weighting and concurrently attenuating a blood signal by dephasing the blood magnetization with motion - sensitization , to render the blood dark without requiring exchange of blood from the slice of interest or specific timing related to the relaxation parameters of the blood , according to one aspect of an embodiment of the present invention . in an embodiment for performing contrast - enhanced late gadolinium enhancement with dark - blood signal , as shown , a t1 - weighting 180 degree rf pulse ( 901 ) is applied ( this could be replaced with a partial inversion , or a saturation or partial saturation pulse without loss of generality ). this inversion pulse inverts the sign of the magnetization in the heart muscle and cavity ( 902 ). after allowing a time for the magnetization to recover via longitudinal ( t1 relaxation ), the motion sensitizing preparation is applied ( 904 ). the motion sensitizing preparation converts the longitudinal magnetization into transverse magnetization , and preferentially dephases the transverse magnetization of the blood due to its inherent incoherent motion . as this preparation is not spatially selective , it will attenuate the signal from blood irrespective of the location of the blood relative to the imaging slice of interest without requiring exchange of blood out of the slice of interest . the final rf - pulse of the motion sensitizing preparation converts the transverse magnetization to longitudinal magnetization , which will then evolve based on the t1 - properties of the blood , infarct , and normal myocardium , respectively , during the readout module ( 905 ). the total time for t1 - preparation ( 906 ) is the time between the t1 - weighting inversion pulse and the center of k - space for the readout module . as the motion sensitizing preparation is kept short in duration , it minimally affects the t1 - recovery curve of normal myocardium and infarct . it should be appreciated that as discussed herein , a subject may be a human or any animal . it should be appreciated that an animal may be a variety of any applicable type , including , but not limited thereto , mammal , veterinarian animal , livestock animal or pet type animal , etc . as an example , the animal may be a laboratory animal specifically selected to have certain characteristics similar to human ( e . g . rat , dog , pig , monkey ), etc . it should be appreciated that the subject may be any applicable human patient , for example . the following patents , applications and publications as listed below and throughout this document are hereby incorporated by reference in their entirety herein . the devices , systems , compositions , computer program products , and methods of various embodiments of the invention disclosed herein may utilize aspects disclosed in the following references , applications , publications and patents and which are hereby incorporated by reference herein in their entirety : 1 . kim r j , wu e , rafael a , chen e l , parker m a , simonetti o et al ., “ the use of contrast - 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slice acquisition with black blood contrast ”, dec . 24 , 2002 . 26 . u . s . pat . no . 6 , 526 , 307 b2 , foo , “ method and apparatus to improve myocardial infarction detection with blood pool signal suppression ”, feb . 27 , 2003 . 26 . u . s . pat . no . 6 , 662 , 037 b2 , foo , “ method and apparatus to improve myocardial infarction detection with blood pool signal suppression ”, dec . 9 , 2003 . 27 . u . s . pat . no . 7 , 369 , 887 b2 , fayad , et al ., “ rapid multislice black blood double - inversion recovery technique for blood vessel imaging , may 6 , 2008 . 28 . u . s . patent application publication no . us 2009 / 0005673 a1 , rehwald , et al ., “ dark blood delayed enhancement magnetic resonance viability imaging techniques for assessing subendocardial infarcts ”, jan . 1 , 2009 . in summary , while the present invention has been described with respect to specific embodiments , many modifications , variations , alterations , substitutions , and equivalents will be apparent to those skilled in the art . the present invention is not to be limited in scope by the specific embodiment described herein . indeed , various modifications of the present invention , in addition to those described herein , will be apparent to those of skill in the art from the foregoing description and accompanying drawings . accordingly , the invention is to be considered as limited only by the spirit and scope of the following claims , including all modifications and equivalents . still other embodiments will become readily apparent to those skilled in this art from reading the above - recited detailed description and drawings of certain exemplary embodiments . it should be understood that numerous variations , modifications , and additional embodiments are possible , and accordingly , all such variations , modifications , and embodiments are to be regarded as being within the spirit and scope of this application . for example , regardless of the content of any portion ( e . g ., title , field , background , summary , abstract , drawing figure , etc .) of this application , unless clearly specified to the contrary , there is no requirement for the inclusion in any claim herein or of any application claiming priority hereto of any particular described or illustrated activity or element , any particular sequence of such activities , or any particular interrelationship of such elements . moreover , any activity can be repeated , any activity can be performed by multiple entities , and / or any element can be duplicated . further , any activity or element can be excluded , the sequence of activities can vary , and / or the interrelationship of elements can vary . unless clearly specified to the contrary , there is no requirement for any particular described or illustrated activity or element , any particular sequence or such activities , any particular size , speed , material , dimension or frequency , or any particularly interrelationship of such elements . accordingly , the descriptions and drawings are to be regarded as illustrative in nature , and not as restrictive . moreover , when any number or range is described herein , unless clearly stated otherwise , that number or range is approximate . when any range is described herein , unless clearly stated otherwise , that range includes all values therein and all sub ranges therein . any information in any material ( e . g ., a united states / foreign patent , united states / foreign patent application , book , article , etc .) that has been incorporated by reference herein , is only incorporated by reference to the extent that no conflict exists between such information and the other statements and drawings set forth herein . in the event of such conflict , including a conflict that would render invalid any claim herein or seeking priority hereto , then any such conflicting information in such incorporated by reference material is specifically not incorporated by reference herein .