United States Patent [191
`Hennig et al.
`
`[11]
`‘[45]
`
`Patent Number:
`Date of Patent:
`
`4,818,940
`Apr. 4, 1989
`
`[75]
`
`[73] Assignee:
`
`[54] METHOD FOR MEASURING NUCLEAR
`MAGNETIC RESONANCE
`Inventors: Jiirgen Hennig, Freiburg; Arno
`Nauerth, Erlenbach, both of Fed.
`Rep. of Germany
`Bruker Medizintechnik GmbH,
`Rheinstetten-Forchheim, Fed. Rep.
`of Germany
`Appl. No.: 98,637
`Filed:
`Sep. 18, 1987
`
`[21]
`[22]
`
`[63]
`
`Related US. Application Data
`Continuation of Ser. No. 774,569, Sep. 10, 1985, aban
`doned.
`Foreign Application Priority Data
`[30]
`Sep. 18, 1984 [DE] Fed. Rep. of Germany ..... .. 3434161
`
`......... .. G01R 33/20
`[51] Int. Cl.4
`[52] US. Cl. ............................ .. 324/309; 324/307
`[53] Field of Search ------------- -- 324/300, 307, 309, 311,
`324/312, 313’ 314
`
`[56]
`
`References Cited
`U‘s' PATENT DOCUMENTS
`4,521,733 6/1985 Bottomley
`4,532,474 7/ 1935 Edelstem --
`I691‘; at
`' ' ' ' '
`' ‘
`4:612:504 9/1986 relcoflilinu'jff ................. .. 324/309
`4,614,195 9/1986 Bottomley et a1’
`324/309 X
`
`324/309
`324/309
`
`FOREIGN PATENT DOCUMENTS
`
`0098426 of 0000 European Pat. Off. .
`
`OTHER PUBLICATIONS
`Journal of Magnetic Resonance, 56, 179-182 (1984).
`Proceedings of the IEEE, vol. 70, No. 10, Oct. 1982. pp.
`1152-1173.
`Electromedia 52 (1984), No. 2, pp. 56-65.
`Primary Examiner—-Michael J. Tokar
`Attorney, Agent, or Firm-Pennie & Edmonds
`[57]
`ABSTRACT
`For recording a nuclear magnetic resonance tomogram
`according to a Fourier-transform method, a Carr-Pur
`cell-Gill-Meiboom pulse sequence is used for the excita
`tion of a body to produce a sequence of spin-echo sig
`nals. A time-limited phase-encoding magnetic gradient
`?eld G); is imposed between each pair of 180° pulses of
`the sequence. The phase-encoding magnetic gradient
`?eld is modi?ed after every 180° pulse so that every
`spin-echo signal corresponds to a different projection of
`the body. The magnetic gradient ?elds used in the re
`corditrkilgtare regullated in irciitensitytand {litigation 1in sutctl;1 a
`pu seo e
`way a aspln-p ase con 11ona eac
`pulse sequence remains effectively constant. Thereby, it
`is possible to construct a complete tomographic record
`ing with a single pulse-sequence excitation, so that the
`time required for such recordings can be reduced to a
`Minion Of the time needed f°r recolding nuclear'mag‘
`netlc-resonance tomograms conventionally.
`
`4,665,365 5/1987 Glover et a1. . . . . .
`. . . . .. 324/309
`4,697,148 9/1987 Strobel et a1. ..................... .. 324/ 309
`
`5 Claims, 4 Drawing Sheets
`
`\ \
`
`\ \ \
`
`13
`
`H
`t I
`“.63
`3
`t'r'
`I l
`1&0"!
`Y |
`
`1
`
`.
`°
`X
`
`T
`
`/
`
`
`*4 73 x s
`‘7. N551.
`'
`‘II
`a
`14;: 141.5
`'
`I
`i
`l ‘L
`ham !
`180°
`Y
`I
`Y
`
`\
`I r‘
`
`IPR2017-00109 - Ex. 2026 - Page 1
`
`

`

`US. Patent Apr. 4, 1989
`US. Patent
`Apr. 4, 1989
`
`Sheet 1 of 4
`Sheet 1 of 4
`
`4,818,940
`4,818,940
`
`h-T—d
`
`
`
`|PR2017-OO‘|09 - EX. 2026 - Page 2
`
`IPR2017-00109 - Ex. 2026 - Page 2
`
`

`

`US. Patent Apr. 4, 1989
`
`Sheet 2 01'4
`
`4,818,940
`
`WWW
`WM Fig.3
`
`IPR2017-00109 - Ex. 2026 - Page 3
`
`

`

`US. Patent Apr. 4, 1989
`
`Sheet 3 of 4
`
`4,818,940
`
`11 I
`E11
`
`12 I
`E21
`
`I
`E12
`
`I
`E22
`
`I
`E13
`
`|
`E11.
`
`I
`E15 I
`
`l
`E16
`
`I
`E23
`
`I
`E21.
`
`I
`E25
`
`l
`E26
`
`L
`E17
`
`|
`E27
`
`In I
`
`I
`
`I
`
`I
`
`I
`
`|
`
`I
`
`III I IQEIIILJII I;
`
`E11.
`
`E15
`Fig. l»
`
`E12
`
`E13
`
`IPR2017-00109 - Ex. 2026 - Page 4
`
`

`

`US. Patent Apr. 4, 1989
`
`' Sheet 4 of4
`
`4,818,940
`
`180°
`Y
`
`Fig. 5
`
`IPR2017-00109 - Ex. 2026 - Page 5
`
`

`

`1
`
`METHOD FOR MEASURING NUCLEAR
`MAGNETIC RESONANCE
`
`5
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`This is a continuation of US. application Ser. No.
`774,569, ?led Sept. 10, 1985, and now abandoned.
`The invention concerns a method for measuring nu
`clear magnetic resonance in selected regions of a body
`for the purpose of producing body cross sections (NMR
`tomography). In this process, the body is subjected to a
`selection gradient outside a homogeneous magnetic
`?eld and excited with a 90° pulse. Afterwards, the selec
`tion gradient is replaced by temporally de?ned phase
`encoding gradients and recording gradients. Finally,
`the specimen is exposed to a sequence of 180° pulses,
`which together with the 90° pulse form a Carr-Purcell
`Gill-Meiboom pulse sequence (CPGM sequence). The
`duration of radiofrequency application and the intensity
`of the gradient ?elds are determined by the appearance
`of the pulse sequence in such a way that the rephasing
`conditions are satis?ed for all gradient ?elds. In so do
`ing, with every excitation, several nuclear induction
`signals are produced in the form of so-called spin echos.
`With regard to modi?cations of the phase-encoding
`gradients according to the 2D-FT image construction
`process, the signals are the mathematically converted
`into image signals.
`This type of method is described in German patent
`application No. P 34 14 634.2 concerning the state of
`technology. In this patent application, various possibili
`ties are treated for satisfying rephasing conditions
`through application of a CPGM sequence. Satisfying
`the rephasing conditions is a prerequisite for being able
`to apply this type of CPGM sequence for NMR tomog
`raphy and especially for the production of images ac
`cording tothe ZD-FT method. Violation of the rephas
`ing conditions results in image-errors. The image-errors
`precluded the use of such CPGM sequence for NMR
`40
`tomography extensively until that time. As with con
`ventional NMR spectrography, it is also the case with
`the method under discussion that the use of CPGM
`sequences has the goal of obtaining a multitude of simi
`lar images, which either' can be added up for improving
`the signal-noise ratio or else produce data on the tem
`poral development of the spin-echos, especially con
`cerning the spin-spin relaxation time T2.
`However, the present invention does not deal with
`either the problem of the signal-noise ratio or an exact
`T2 determination. The practical application of NMR
`tomography has suffered until now under the necessity
`of taking a multitude of single measurements in order to
`obtain the requisite measured values for image recon
`struction. Another difficulty has been the fact that the
`time required for a single measurement is relatively
`long, because it includes the relaxation time that must be
`waited for before every new excitation. In this respect,
`there appear to be physically determined limits to re
`ducing the measurement.
`Nevertheless, it is the underlying task of this inven
`tion to achieve a signi?cant reduction of measurement
`time for NMR tomography.
`According to the invention, this problem is solved by
`changing the intensity and/or duration of the phase~
`encoding gradient after every 180° pulse.
`Using the invention’s method, the application of
`CPGM sequence for the ZD-FT method is not applied
`
`4,818,940
`2
`to improving the signal-noise ratio by manipulating the
`multitude of spin-echos by means of an excitation. The
`application of CPGM sequence for the ZD-Ff method
`is also not applied to making an exact T2 determination.
`Rather, by means of altering the phase-encoding gradi
`ent after every 180° pulse, a multitude of different echo
`signals are obtained, which are responsible for the
`image content in a dependency on the phase-encoding
`gradient in various manners. In this way, it is possible to
`obtain the echo-signals which are necessary for image
`reconstruction as a reaction to only a few excitations
`and in the limiting case, to only one excitation. The
`invention’s method accordingly results in a reduction of
`the test times for a fraction of what was necessary up
`until now. This is extraordinarily important especially
`for the use of NMR tomography in human medicine.
`The 2D-FT image reconstruction method proceeds
`on the assumption that the signals obtained for each of
`the single measurements that are to be analyzed have
`the same amplitude for a prescribed intensity level. This
`condition is not satis?ed in the application of the inven
`tion’s method, because the signal amplitude decreases
`with increasing time interval from the excitation owing
`to the relaxation processes. The result is a certain reduc
`tion in the image quality, which is expressed in a back
`ground lightening. But especially in the ?eld of medi
`cine, this can easily be tolerated because in that case
`what matters more is the contrast between tissues with
`different T; values. The T2 contrast can, however, be
`varied by the invention’s method by changing the as
`signment of the different phase-encoding gradients to
`the successive 180° pulses. In particular, if the echo
`signals of several excitations are used for reconstruction
`of the image, then an interlocked assignment of the
`different values of the phase-encoding gradient can
`occur for the echo signals assigned to the single excita
`tions, whereby a lightening of the image background is
`avoided for the most part. Indeed, with the use of the
`same CPGM sequence, a sort of step-up distance differ
`ence occurs relative to the amplitudes of the single echo
`signals, which gives rise to interfering side-bands. Nev
`ertheless, there is a simple possibility for eliminating
`gradations and thereby this type of interfering side
`bands. This possibility lies in the variation of the time
`interval between the 90° pulse and the ?rst 180° pulse
`with every excitation with a fraction of the interval
`between the 180° pulses inversely proportional to the
`number of repetitions. In this way, the echo signals
`caused by the various excitations can be shifted against
`each other in relation to the excitation time in such a
`manner that the echo signals are separated proportion
`ately according to the measurement interval de?ned by
`an excitation. By doing this, they represent a continuous
`decrease of the signal amplitude and not the gradation
`resulting in side-bands.
`The invention not only offers the possibility of pro
`ducing a strengthening of the T2 contrast by means of
`the ingenious assignment of the different values of the
`phase-encoding gradients to the temporally successive
`echo signals, but the invention also allows for the con
`trol and particularly the increase of the T1 contrast.
`This is done by having each new excitation occur with
`each repeated excitation of the specimen before a com
`plete relaxation has occurred for the spin-moments ex
`cited by the preceding CPGM sequence. As a result of
`this procedure, the spin-moments, which have not yet
`relaxed owing to the large T1, are not registered by the
`
`45
`
`65
`
`IPR2017-00109 - Ex. 2026 - Page 6
`
`

`

`4,818,940
`3
`next excitation and therefore do not produce any sig
`nals. The contrast to the regions with short T1 is intensi
`?ed in which a completed relaxation of the spin
`moments has occurred, which at this stage yield a full
`signal.
`The very short measuring time, which is required for
`the determination of the requisite measurement values
`for the 2D-FT image-reconstruction method, also offers
`the possibility of applying the invention with a 3D-FT
`image-reconstruction method. The special advantage of
`the image-reconstruction method with ZD-Fourier
`transformation is that it also produces very good images
`when the homogeneity of the magnetic ?eld is not very
`great. This advantage would still be increased signi?
`cantly with its extension to the three-dimensional vol
`ume. The signi?cant reduction of the test time made
`possible by the invention now permits the extension to
`three-dimensional space. Accordingly, the invention
`also is concerned- with a method by which another‘
`phase-encoding gradient is used as the selection gradi
`ent and the image-reconstruction occurs according to
`the 3D-FT method.
`The invention is described in more detail and clari?ed
`in the following sections in light of the examples shown
`in the diagram. The characteristics to be learned from
`the description and the diagram can ?nd application by
`other realizations of the invention singly on their own
`or severally in any combination. Shown are:
`FIG. 1 The Time Diagram of a CPGM-Pulse Se
`quence and of the Gradient Fields, As They Find Use in
`an Embodiment of the Invention’s Method;
`FIGS. 2 and 3 Diagrams Which Show the In?uence
`on the Image Contrast of the Assignment of the Differ
`ent Phase Gradients to the Various Echo Signals;
`35
`FIG. 4 A'Diagram to Elucidate the Interlocking of
`Recording Sequences in Relation to the Phase Gradi
`ent; and
`FIG. 5 A Diagram Which Illustrates a Modi?ed
`CPGM-Sequence for the Avoidance of Image Errors.
`The invention’s method can be performed on every
`NMR tomograph whose oscillator is con?gured to
`generate I-IF-pulse sequences and whose magnet ar
`rangement permits the generation of switchable gradi
`ent ?elds, one of which coincides with the direction of
`the homogeneous magnetic ?eld necessary for the pro
`duction of NMR spectra. A suitable tomograph, for
`example, is the applicant’s BMT 1100 type whole-body
`tomograph.
`With the invention’s method, according to its es
`sence, one is dealing with a 2D-FT method, whereby
`the body, which is preferably excited selectively in the
`area of a cross section, is exposed to a time-limited
`phase-encoding gradient before the switching-on of the
`recording gradient. The spin-echoes obtained on the
`basis of the excitation and phase-encoding are subjected
`to a two-dimensional Fourier transformation, which
`yields signals'assigned to single image points, and the
`amplitude of the signals is proportional to the intensity
`of the image points. For every element-of-volume to be
`analyzed, that is, for every image point, a projection
`(that is, the generation of a spin-echo) is required after
`plotting another phase-encoding gradient. Since until
`now a separate excitation of the specimen was required
`for the generation of a spin-echo under a particular,
`assigned phase gradient, a substantial expenditure of
`time was devoted to the generation of an image accord
`ing to the 2D-FT process.
`
`4
`Instead of this, with the invention’s method, a spin
`echo pulse-sequence is used and a modi?ed phase
`encoding gradient is established before the generation
`of each new echo signal, so that every single spin-echo
`for an echo sequence, which has been generated by one
`single excitation, is characteristic for a different projec
`tion. Of course, there is the prerequisite that in the
`course of the pulse sequence and of the repeatedly es
`tablished phase-encoding gradients and recording gra
`dients, no changes occur in the excitation condition of
`the spin moments, which result in an image adultera
`tion. Therefore, care must be taken that the rephasing
`requirements are satisfied for the recording gradients
`and also for the phase-encoding gradients, that is, that
`the Gill-Meiboom requirement is met for the Carr-Pur
`cell-Gill-Meiboom pulse sequence used.
`An example of a pulse- and gradient-?eld sequence,
`by which the Gill-Meiboom requirement is satis?ed, is
`shown in FIG. 1. This sequence includes a common
`CPGM sequence of HF-pulses with an initial 90° pulse
`1, by means of which the specimens are excited by the
`application of a selection gradient G2 selectively in the
`area of a cross section de?ned by the selection gradient.
`In the normal way, the 90° selection pulse 1 is then
`followed by 180° pulses 3, 4, 5, and 6, which cause a
`rephasing of the spin moments that were induced by
`selection pulse 1 and were dephased after the excitation,
`so that in a known way spin-echos 13, 14, 15 are formed,
`which appear in the same time interval 1' from the pre
`ceding 180° pulse as this 180° pulse has from selection
`pulse 1, that is, the preceding spin-echo. In the embodi
`ment example presented, all these intervals are the same.
`The phase-encoding required for the 2D-FT method
`is brought about by establishing a phase-encoding gradi
`ent Gx. And it is true that from time to time, this gradi
`ent is switched on in connection to an 180° pulse and
`ended again before the appearance of the spin-echo. In
`FIG. 1, the switching-on of the phase-encoding gradi
`ent by means of the pulse-like sequence of curves is
`illustrated. The different height of these curve-paths
`demonstrates that the phase-encoding gradient has an
`other intensity each time, so that it results in a different
`phase-encoding. The phase-encodings caused by the
`different phase-encoding gradients must nevertheless
`constantly start from the same initial state, if they are
`supposed to produce results that can be evaluated.
`Therefore, it is necessary to cancel the effect of every
`phase-encoding, before a new phase-encoding occurs.
`With the embodiment example of the invention’s
`method presented, this occurs through constructing the
`phase-encoding gradient with the same intensity and
`duration, however, with reverse positive direction,
`symmetrical to the appearance of the echo-signal, as
`curves 33, 34, and 35 show. The effect of the reversal of
`negative phase-encoding gradient 33 on the dephasing
`spin-moments is exactly as great as the effect of the
`preceding phase-encoding gradient 23 on the rephasing
`spin-moments, so that at the time of the 180° pulse 4,
`exactly the same phase condition prevails as at the time
`of the preceding 180° pulse 3. correspondingly, this is
`valid for the phase-encoding gradients 24, 34, or 25, 36,
`etc.
`correspondingly, care must also be taken for an ar
`rangement of the recording gradient, 43, 44, 45 symmet
`rical to the echo-signal, that its in?uence on the rephas
`ing and the dephasing spin-system is completely the
`same, so that the in?uence of the recording gradient is
`also negated.
`
`55
`
`65
`
`IPR2017-00109 - Ex. 2026 - Page 7
`
`

`

`4,818,940
`5
`The application of selection gradient Gz during the .
`180° pulses, as it occurs with the method presented, is -
`not necessary if it is a matter of broad-band pulses for
`the 180° pulses. The invention’s method, however,
`makes possible the establishment of the selection gradi
`ent during the 180° pulses, so that frequency-selective
`pulses can be used here, whereby it can be a matter of
`pulses of relatively longer duration and lower energy in
`contrast to broad-band pulses. Also here, by means of a
`symmetrical arrangement of the selection gradient to
`the 180° pulses, care is taken that the phase relationship
`of the spin system is not disturbed.
`It is to be understood that the pulse and gradient ?eld
`system presented is not the only possible one to satisfy
`the rephasing requirements or the Gill-Meiboom re
`quirement. In U.S. Pat. No. 4,697,148 (“the ‘148 pa
`tent”). The invention’s method is not dependent on a
`certain pulse and gradient ?eld sequence, in as much as
`care is only taken that the Gill-Meiboom requirement is
`‘satis?ed. The use of the conventional CPGM sequence
`and the gradient ?elds of equal intensity that are ar
`ranged symmetrically to it has the advantage that such
`pulse and ?eld sequences can be generated with espe
`cially low effort.
`Despite maintaining the rephasing or CPGM require
`ment, it cannot be avoided that as a consequence of the
`relaxation processes, the amplitude of spin-echos 13, 14,
`and 15 decreases corresponding to relaxation curve 7, as
`shown in FIG. 1. As a result of this, the single points of
`the image obtained are weighted with the different
`relaxation functions coordinated with these image
`points. If the image plotting occurs with M echos per
`excitation and if ~ P projections or echo signals with
`different phase-encoding gradient are needed for the
`generation of an image, in order to reconstruct an image
`matrix of the size B><B=P, then every echo signal
`representing a projection Em’P can be understood as the
`sum of the image elements of the signals originating
`from the single image elements Sm:
`Em'p='uSxy,
`where:
`
`20
`
`30
`
`6
`selected, whereby it is possible to vary the image con
`trast determined by the weighting for different applica
`tions.
`Next let us consider the case in which the number M
`of echos per excitation and the number P of projections
`with different phase-encoding gradient are the same, so
`that the total image can thus be recorded with a single
`excitation. Thereby the modi?cation of the phase
`encoding gradient can occur in such a way that with the
`?rst echo, the dephasing ¢,,,,-,, is present and with the
`last echo, the dephasing ~4>max iS present. Thereby, the
`null point of the phase displacement can be placed at
`any random point of the echo sequence. FIGS. 2 and 3
`present the influence of displacing the phase null point
`to different locations for structures with different T2
`times.
`In FIG. 2, bars 51, 52, and 53 represent the signal
`intensity which results from the spin density of three
`different regions with different relaxation times T2 di
`rectly after the excitation, thus still unin?uenced by
`relaxation. Region 51 has a long T2; region 52, a me
`dium; and region 53, a short T2.
`Fields B to F of FIG. 2 reproduce the intensities of
`the same regions 51 to 53, as they are shown in ?eld A
`of FIG. 2, as they arise with application of the inven
`tion’s method and with displacement of the null points
`of the phase gradient to the excited echo signals. One
`obtains the intensities of ?eld B, when the null point of
`the phase gradient is present at echo No. 32 with a
`recording of 256 echo signals. correspondingly, the
`null point of the phase gradient for the signals of ?eld C
`lie at echo 64; for the signals of ?eld D, at echo 96; for
`the signals of ?eld E, at echo 128; and for the signals of
`?eld F, at echo 1. It is evident that the absolute height
`of the signals is changed as well as the relationship of
`the signals, which are correlated with regions with
`different T2. A maximal signal is produced in ?eld C
`with very good contrast. Note the increased signal
`height at the edges of the regions, which can be traced
`back to the decrease of amplitude of the echo signals as
`a result of relaxation. Analogous to FIG. 2, FIG. 3
`represents signal intensities which, however, do not
`relate to regions but rather to single image points.
`If the image recording occurs with more than one
`excitation, then the phase gradient can be distributed
`among the echo-signals of the various excitations in
`such a manner, that with the ?rst activation, from clam-n
`to (1)1, with the next activation from qbl to (in, and with
`the last activation, from a value cbn to ¢max there is an
`increase. However, an interlocking can also be pre
`sumed, as is shown in FIG. 4 for the echos brought
`about by excitations I1 to In. This interlocking, as it is
`shown in the last line of FIG. 4, is to be understood in
`relation to a uniformly increasing phase gradient from
`<i>min to chm“, so that respectively the ?rst echo signals
`E11 to E,“ of the various excitations I1 to In are assigned
`to the ?rst consecutive values of the phase gradient,
`whereupon the second echo signals E12 to E"; of the
`various excitations then follow, etc. Thereby, of course,
`an amplitude gradation results, which can severely im
`pair the image quality. This gradation can be eliminated,
`nevertheless, by modi?cation of the excitation process
`for reciprocal displacement of the echo signals caused
`by the various excitations in such a way that they all
`have the same time interval from each other and conse
`quently also have an amplitude following the relaxation
`curve and constantly decreasing. For this purpose, it
`
`W'Uz
`
`(1)
`
`45
`
`‘Because the amplitude of the signals Sm originating
`from the single image elements decreases with the relax
`ation function Rx,y(t) of the pixel, then it is valid that:
`
`Sx,y=Ax,y~Rx,y (m-21)
`
`(2)
`
`50
`
`where:
`Axyy is the initial value of the signal amplitude, and 1'
`is the time interval between the 180° pulses of the
`CPGM sequence
`Corresponding to this, Equation (1) becomes:
`
`55
`
`The single echo signals, thus, are weighted with the
`relaxation-function of the single image points. Corre
`spondingly, the signals which reproduced the intensity
`of the single image points and which were obtained by
`the Fourier transformation, are also weighted with the
`relaxation-function of the pixel. This weighting is de
`pendent on the coordination of the P phase-encoding
`gradients to the M’s of the echo-signals obtained with
`every excitation. This coordination can be arbitrarily
`
`60
`
`65
`
`IPR2017-00109 - Ex. 2026 - Page 8
`
`

`

`4,818,940
`7
`8
`suffices to vary with each excitation the time interval
`image by means of a variation of the repetition rate
`between the 90° pulse and the ?rst l80° pulse by a frac
`between the single excitations. If the excitation interval
`tion of the interval between the 180° pulses inversely
`is selected so short that spins with large T1 have not yet
`proportional to the number of repetitions.
`relaxed, then these spins are not registered with the next
`FIG. 5 again shows the beginning of a CPGM se
`excitation and therefore also cannot produce a signal.
`quence with the echo signals obtained from it. The 90'‘
`From this, a signi?cant intensity difference is created
`selection pulse 1 causes an initial induction signal 61,
`between regions with large and small T1.
`which normally is not evaluated. The dephasing of the
`We claim:
`signal is then cancelled after a time T by the 180° pulse
`1. A nuclear-magnetic-resonance Fourier-transform
`3, so that it again results in rephasing after a time 1' and
`tomographic method for imaging cross sections of a
`therewith the creation of echo signal 13. Additional
`body, the method comprising exposing the body to a
`180° pulses 4, 5, etc., then follow after this, in relation to
`homogeneous magnetic ?eld, superimposing upon the
`the ?rst 180° pulse, in each case in the interval 21', which
`body a time-limited selection magnetic gradient ?eld,
`produce the corresponding echo signals, of which echo
`during the selection magnetic gradient ?eld irradiating
`' signal 14 is still shown in FIG. 5. The amplitude of the
`the body with an essentially 90° pulse, subsequently
`echo signals decreases corresponding to relaxation
`irradiating the body with a timed sequence of essentially
`curve 7. To this extent, FIG. 5 agrees with FIG. 1.
`180° pulses to produce a sequence of spin-echo nuclear
`In order to obtain a relative chronological displace
`induction signals, the relative phases and spacing of the
`ment of the echo signals with several excitations, the
`90° pulse and the 180° pulses being selected to de?ne a
`interval of the 180“ pulse from the 90° pulse is length
`20
`Carr-Purcell-Gill-Meiboom pulse sequence so that a
`ened by 'r/ n with the next excitation, if n is the number
`spin-echo nuclear induction signal occurs in an interval
`of planned excitations. Consequently, echo signal 73,
`between each pair of adjacent essentially 180° pulses in
`which is produced by the time-delayed 180° pulse 63,
`the pulse sequence, during the sequence of essentially
`also appears in the interval 7+7‘ from 180° pulse 73 so
`180° pulses superimposing upon the body a sequence of
`that in contrast to the ?rst echo signal 13 of the ?rst
`time-limited phase-encoding magnetic gradient ?elds
`excitation, it is displaced by the time ZT/n. The next
`and time-limited recording magnetic gradient ?elds,
`180° pulse 64 is then produced again in the interval 1'
`each phase-encoding magnetic gradient ?eld being im
`from echo signal 73 so that from now on the pulse and
`posed during a time interval between a pair of adjacent
`signal interval uses 21' and the previously accomplished
`essentially 180° pulses of the Carr-Purcell-Gill-Mei
`displacement of the echo signals remains held over the
`boom pulse sequence, a portion of the phase-encoding
`entire sequence. FIG. 5 shows the case for n=3. With
`magnetic gradient ?eld being imposed between the ?rst
`the next excitation, an additional displacement to T/n
`essentially 180° pulse of the pair of pulses and a mid
`takes place again so that uniform, chronological inter
`point of the spin-echo nuclear induction signal occur
`locking is achieved for all echo signals.
`ring between the pair of pulses, each recording mag
`In relation to the ?rst echo signal 73, the process
`netic gradient ?eld being imposed during the time inter
`elucidated with FIG. 5 can be considered as an ad
`val between a pair of adjacent essentially 180° pulses of
`vancement of the excitation time at Z'r/n instead of the
`the Carr-Purcell-Gill-Meiboom pulse sequence coinci
`lengthening of times described between the 90° pulse
`dent with the occurrence of the spin-echo nuclear in
`and the ?rst 180° pulse with the corresponding length
`duction signal between the pair of pulses, the phase—
`ening of the time between the ?rst 180° pulse and the
`encoding magnetic gradient ?elds being changed after
`?rst echo, respectively, at r/n. The 90° pulse could also
`each essentially 180° pulse in accordance with a Fouri
`be followed already after the time 'r/n by a 180° pulse,
`er-transform tomographic imaging method, the form
`which results in the generation of an echo signal after an
`and timing of each time-limited magnetic gradient ?eld
`additional time r/n. Therewith, a rephasing condition is
`relative to the substantially 180° pulses and the spin
`achieved shifted by 2'r/n opposite the 90° pulse. Further
`echo nuclear induction signals being selected so that
`180° pulses can then be related to the rephasing condi
`spin dephasing which arises during the magnetic gradi
`tion, so that the next 180° pulse is then displaced by
`ent ?eld is substantially cancelled at the end of the time
`2r/n opposite to the 180° pulses of the ?rst sequence.
`limited gradient ?eld so that a spin phase condition at
`The same result could also be achieved by obtaining the
`the time of each essentially 180° pulse subsequent to the
`excitation produced by the 90° pulse by means of a
`?rst such pulse is substantially the same as a spin phase
`spin-locking pulse of duration Z'r/n. The use of the
`condition at the time of the preceding essentially 180°
`described methods leads again to an echo multiplied by
`pulse, sampling and digitizing the spin-echo nuclear
`the relaxation function, as it was explained above. Of
`induction signals to form digitized nuclear signal data,
`course, the dwell-time for the ZD-Fourier transforma
`and combining such digitized nuclear signal data in
`tion appears shortened by the factor l/n, which results
`accordance with the Fourier-transform tomographic
`in a decrease of the T2 contrast of the image, because
`pixels are now also still presented with short T2 times.
`method to form a tomographic image of the cross sec
`tion of the body.
`The invention is not limited to the described realiza
`2. Method according to claim 1, characterized by the
`tion of the invention’s method. On the one hand, the
`high recording speed makes it possible to extend the
`body being excited repeatedly in succession with Carr
`Purcell-Gill-Meiboom sequences and being subject to
`method also to a 3D-FT method, by which a selection
`gradient is used in the form of another phase-encoding
`different phase-encoding magnetic gradient ?elds with
`gradient, for which the same criteria are valid for the
`the successive excitations.
`phase-encoding gradient Gx discussed above. In apply
`3. Method according to claim 2, characterized by the
`ing the phase-encoding gradient Gx, care must be taken
`time interval between the 90° pulse and the ?rst 180°
`that the rephasing requirements are met, that is, thus,
`pulse as well as between the ?rst two 180° pulses being
`the Gill-Meiboom requirement. In addition, the possi
`increased with every excitation by a fraction of the
`bility exists of producing yet another T1v contrast in the
`constant interval between the remaining 180° pulses
`
`45
`
`25
`
`35
`
`55
`
`65
`
`IPR2017-00109 - Ex. 2026 - Page 9
`
`

`

`4,818,940
`10
`9
`inversely proportionate to the planned number of repe
`another phase-encoding magnetic gradient field being
`used as a selection magnetic gradient field and the
`titions.
`-
`4. Method according to claim 2, characterized by
`image reconstruction occurring according to a three-di
`each repeated excitation occurring before a complete
`mensional nuclear-magnetic-resonance Fourier-trans
`relaxation of the spin-moments excited by the preceding
`form tomographic method.
`Carr-Purcell-Gill-Meiboom sequence has taken place.
`5. Method according to claim 1 characterized by
`*
`1‘
`*
`
`#
`
`1i
`
`5
`
`1O
`
`15
`
`20
`
`25
`
`35
`
`45
`
`50
`
`55
`
`65
`
`IPR2017-00109 - Ex. 2026 - Page 10
`
`