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WO2009132772A1 - Procédé de mesure de la teneur en liquide dans la substance cérébrale d'un être vivant par résonance magnétique à imagerie - Google Patents

Procédé de mesure de la teneur en liquide dans la substance cérébrale d'un être vivant par résonance magnétique à imagerie Download PDF

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WO2009132772A1
WO2009132772A1 PCT/EP2009/002779 EP2009002779W WO2009132772A1 WO 2009132772 A1 WO2009132772 A1 WO 2009132772A1 EP 2009002779 W EP2009002779 W EP 2009002779W WO 2009132772 A1 WO2009132772 A1 WO 2009132772A1
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signal
time
pulse
magnetic field
pulses
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English (en)
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Uwe Klose
Benjamin Bender
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Eberhard Karls Universitaet Tuebingen
Universitätsklinikum Tübingen
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Eberhard Karls Universitaet Tuebingen
Universitätsklinikum Tübingen
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/50—NMR imaging systems based on the determination of relaxation times, e.g. T1 measurement by IR sequences; T2 measurement by multiple-echo sequences
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
    • G01N24/08—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects by using nuclear magnetic resonance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
    • G01N24/08—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects by using nuclear magnetic resonance
    • G01N24/082—Measurement of solid, liquid or gas content
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/4806—Functional imaging of brain activation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
    • G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
    • G01R33/5616—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE] using gradient refocusing, e.g. EPI

Definitions

  • the invention relates to a method for measuring the liquor content in the brain substance of a living being, wherein by means of magnetic resonance imaging with the aid of a predetermined sequence of high-frequency field pulses and magnetic field gradient pulses in volume elements of the brain substance defined according to coordinates of a Cartesian coordinate system one for the real Volume fraction of the liquor characteristic signal function measured and from this the volume fraction is determined.
  • a signal model is used to quantitatively evaluate hemodynamic parameters, such as the fraction of oxygen extraction, the blood volume and the concentration of deoxyhemoglobin.
  • the measurement refers to the brain as a whole.
  • a so-called GESSE pulse train with a 90 ° -180 ° excitation is used, as described in the co-author of the article US 6,603,989 Bl. This pulse train is used repeatedly, with a phase-encoded magnetic field gradient being varied. From the received signals, which are each recorded at the same echo time, a slice image can be calculated.
  • the GESSE pulse train offers a high spatial resolution, but only a relatively small one Sensitivity. Further, the sequence of pulse trains necessary for image formation requires a long recording time of 20 seconds or more.
  • the invention is based on the object to provide a method of the type mentioned above, with which it is possible to carry out quantitative measurements of volume fractions of interstitial fluid (ISF interstitial fluid) and cerebrospinal fluid (CSF cerebrospinal fluid) in the entire brain simultaneously. Furthermore, the measuring time should be reduced. The effects of white matter, gray matter (GM Gray Matter) and interstitial fluid / cerebrospinal fluid should be considered.
  • ISF interstitial fluid interstitial fluid
  • CSF cerebrospinal fluid cerebrospinal fluid
  • step b) immediately after step b) switching a second G z magnetic field gradient pulse of the same amplitude, inverse sign and shortened length;
  • step c after a predetermined pause after step c), switching a first G x magnetic field gradient pulse and a predetermined number of second G x magnetic field gradient pulses of mutually equal amplitude and alternating sign; e) recording the excited nuclear magnetic resonance signals at intervals during each of the time periods of the second G x magnetic field gradient pulses;
  • step e) prior to step e) switching a second G y magnetic field gradient pulse whose sign is opposite to that of the first G y magnetic field gradient pulses and whose pulse area is equal to the sum of the pulse areas of the first Gy magnetic field gradient pulses remaining up to Half of the recording intervals according to step e) are switched;
  • each pixel corresponds to a predetermined volume element in the selected slice, and each pixel is assigned a signal value derived from the image in step e);
  • step a) repeating steps a) to h) several times, wherein for each repetition in step a) a different, parallel slice is selected;
  • step d) repeating steps a) to i) several times, wherein for each repetition in step d) the pause varies and the time interval between the time of the maximum of the radio-frequency field pulse and half of the recording intervals according to step e) is determined;
  • step k providing the signal function from the signal values determined in step h) and the time intervals determined in step i).
  • an echo planar imaging (EPI) pulse train is employed which, by receiving multiple signals after only one RF excitation, enables the image data necessary for image calculation to be acquired within 50 ms with minimal echo time.
  • EPI pulse train has a somewhat worse spatial resolution than the GESSE pulse train used in the prior art.
  • the spatial resolution is sufficient for voxels of 2 * 2 * 2 mm 3 , which are sufficient for the measurements of interest here.
  • the EPI pulse train has the already mentioned advantage of a considerably shorter measurement time, so that only the recording of a high number of data records with different echo times can be realized in a measurement time that is tolerable for patients.
  • this measurement of a volume data set is repeated several times, wherein a different echo time TE is used for each repetition measurement.
  • a signal function representing the dependence of the nuclear magnetic resonance signal S in that volume element on the echo time TE.
  • the signals in each pixel are analyzed as a function of the echo time, preferably after a correction of possible head movements during the recording of the sequences of volume measurements.
  • the method according to the invention makes it possible to quantify the pathophysiological features of hydrocephalus in a non-invasive manner. Furthermore, early manifestations of normal-pressure hydrocephalus (NPH Normal Pressure Hydrocephalus), in which no specific occurrence of cerebrospinal fluid is yet to be recorded.
  • NPH Normal Pressure Hydrocephalus normal-pressure hydrocephalus
  • steps i) and j) are interchanged, and in step j) steps a) to h) and in step i) steps a) to i) are repeated.
  • This measure has the advantage that, depending on the individual case, the measurements parameterized according to TE can be carried out immediately after measurement of a layer for this layer or only after measurement of the total volume for this volume.
  • the amplitude of the high-frequency field pulse is set such that the nuclear resonance excitation angle in the selected slice is between 10 ° and 90 °.
  • the G x magnetic field gradient pulses have a substantially trapezoidal profile with a plateau and if, in step e), the nuclear magnetic resonance signals were recorded during the time span of the plateau or additionally during the duration of the rise and fall times of the trapezoidal profile become.
  • the latter measure has the advantage that the data acquisition time is shortened.
  • first of all the temporal course of the signal S (TE) is determined according to the relationship:
  • TE echo time from the middle of the high-frequency field pulse (Bi (t))
  • ⁇ f frequency shift or chemical shift of the NMR cerebrospinal fluid signal relative to the NMR tissue signal
  • ⁇ phase shift of the NMR cerebrospinal fluid signal relative to the NMR tissue signal.
  • ⁇ o (n. m. .lambda..sub.c) / (n c. c m) (1-.lambda..sub.c) + n. m,. .lambda..sub.c)
  • n c relative spin density of CSF (ISF / CSF)
  • rric relative magnetization of cerebrospinal fluid (ISF / CSF) at the time of excitation.
  • This measure has the advantage that the desired volume fraction of the liquor can be determined with relatively simple means and high reliability.
  • starting values for the best adaptation are obtained by approximating a logarithmic representation of the signal profile with at least one first-order polynomial.
  • This measure has the advantage that the accuracy of determining the volume fraction is further increased.
  • the sequence of EPI sequences is changed in a conventional manner such that after each measurement with an echo time, which is required for the evaluation according to equation (1), a measurement of the entire volume with a small, always constant echo time is performed (control measurement).
  • the data obtained from these measurements can be used to determine a rotation matrix for each of these control measurements using a conventional method for determining head movements, the application of which compensates for head movement on the measurement data obtained.
  • the rotation matrix of the previous control measurement is used to compensate for possible head movement.
  • FIG. 1 a shows an example of an EPI pulse train as used according to the invention in the context of the present method
  • FIG. 1 b shows the pulse sequence of FIG. 1, but with a second, larger echo time
  • FIG. 1c shows the pulse sequence of FIG. 1, but with a third, even greater echo time
  • FIG. 2 shows an extremely schematic sequence of EPI pulse sequences according to FIGS. 1a to 1c with pulse sequences connected therebetween for a movement correction;
  • FIG. 3 is a nuclear spin tomographic image of a human brain in a transverse plane for the identification of six volume elements on which the inventive method is carried out in an embodiment of the invention
  • FIG. 4 a shows measurement signals, determined by means of nuclear magnetic resonance, on three of the volume elements of white matter of the brain mass designated in FIG. 3, in a linear ordinate scale;
  • FIG. 4b shows measurement signals, determined by means of nuclear magnetic resonance, on three further of the volume elements of gray matter of the brain mass designated in FIG. 3, in a linear ordinate scale;
  • FIG. 4c shows the measurement signals of FIG. 4a in a logarithmic ordinate scale
  • FIG. 4d shows the measurement signals of FIG. 4b in a logarithmic ordinate scale
  • FIGS. 5 a-c are nuclear spin tomographic images of the brain of FIG. 3, showing the standard deviation SD of the residual sum (residuals) in basal and frontal regions;
  • Figures 5d-f are photographs similar to Figures 5a-c, but showing the volume fraction of the liquor
  • FIG. 6 shows a table representing different measured values of test parameters for two test persons as well as the mean value from the measured values of the two test persons;
  • FIGS. 7a-d histograms of different measured values of test parameters.
  • FIGS. 8 a - d are nuclear spin tomographic images of the brain of FIG. 2a; representing various measured values of test parameters.
  • MR Magnetic Resonance
  • stimulation of the imaging signals is accomplished using different sequences of RF field pulses and magnetic field gradient pulses, collectively referred to as "bursts" or “sequences".
  • bursts or “sequences”.
  • special impulse sequences are used which are referred to in the art as EPI (Echo-Planar Imaging) and GRE-EPI (Gradient-Echo Planar Imaging). Details can be found in the article by Mansfield, P., "Real-Time Echo-Planar Imaging by NMR” in British Medical Bulletin, 40, pp. 187-190 (1984).
  • FIG. 1 a shows an example of a pulse sequence, which is denoted overall by 10 and serves to measure the liquor content in brain substance.
  • a layer in the brain of a subject is examined.
  • the layer is perpendicular to an axis z of a Cartesian coordinate system x, y, z, wherein the axis z corresponds to the longitudinal axis of the body of the subject.
  • the position of the layer along the z-axis can be defined.
  • the entire volume of the brain can thus be detected.
  • magnetic field gradient pulses Gx, Gy, and Gz are used in a manner known per se, which briefly superimpose field field gradients in the x, y, or z direction on the homogeneous basic field of the EPI measurement and simplify them below
  • the gradients Gx, Gy and Gz, as shown in Figure Ia, in practice have a trapezoidal shape, because the magnetic field at start-up builds up approximately linearly to a final value of a desired plateau level or at power off linearly decreases from the final value to zero.
  • a high-frequency field pulse rf is used, ie a short-time sampled high-frequency signal of the nuclear magnetic resonance Excitation frequency.
  • the timing of the high frequency field pulse rf has a predetermined envelope which is adjustable to select a slice. Details are known to the person skilled in the art.
  • a first G z gradient 12 is switched, ie irradiated onto the examined brain, and at the same time a high-frequency field pulse 14 whose envelope is selected such that nuclear resonance is excited in a rectangular-cross-section layer.
  • the amplitude of the high-frequency field pulse 14 is adjusted so that within the thus selected layer, the excitation angle of the nuclear magnetic resonance is between 10 ° and 90 °.
  • the time of the maximum amplitude of the high-frequency field pulse 14 is designated in FIG. 1a with to.
  • a second G z gradient 16 is switched, which has the same amplitude as the first G z gradient 12, a contrast opposite sign and a shortened length. More precisely, the amplitude below the second G z - Gradienren 16 the Integra! the amplitude of the first G z -gradient 12 from the time to be to the end.
  • the second G z gradient 16 causes refocusing of the transverse magnetization dephased by the excitation.
  • a first G x gradient 18 is then switched, followed by a sequence of a predetermined number of identical second G ⁇ gradients 20 a, 20 b, 20 c. etc., each with alternating sign.
  • the first G ⁇ gradient 18 is shortened compared to the following second G x gradients 20a, 20b, 20c, etc., and serves for the pre-dephasing of the transverse magnetization.
  • the number of these second G x gradients 20a, 20b, 20c, etc. determines the resolution of the image to be picked up by the selected layer.
  • 128 second Gx gradients 20i are also required unless additional methods of measuring time reduction (eg, parallel imaging or partial Fourier imaging) are used.
  • additional methods of measuring time reduction eg, parallel imaging or partial Fourier imaging
  • data 22 a, 22 b, 22 c, etc. are recorded, which by means of an analog-to-digital converter (ADC) in in a known manner were obtained from nuclear magnetic resonance signals of the investigated layer.
  • ADC analog-to-digital converter
  • the number of data 22a, 22b, 22c, etc. is equal to the number of G x gradients 20i.
  • the data can also be recorded during the rise and fall times of the gradient.
  • G y gradients so-called blip gradients 24 a, 24 b, 24 c, etc., of the same sign, which are required for the phase coding of the measured signal, are respectively switched for a short time.
  • a further, individual G y gradient 26 is switched whose sign is opposite to the sign of the blip gradient 24 a, 24 b, 24 c, etc.
  • the amplitude of the further G y gradient 26 is chosen so that at a time t, after about half of the data recording intervals, the integral over the time course of all previously connected Blip gradient 24 a, 24 b, 24 c, etc., ie their summed pulse area, equal to the negative integral over the time course of the further G y gradient 26, ie the pulse area.
  • the time interval between the time to of the maximum of the high-frequency field pulse 14 and the time ti is referred to as echo time TE.
  • the echo time TEi of the EPI pulse train 10 in the example shown in FIG. 1a is 60 ms.
  • the acquisition of all data 22a, 22b, 22c, etc. of the EPI pulse train 10 enables the calculation of a complete image of the excited layer.
  • the image can, as mentioned, for example, consist of 128 x 128 pixels, each of which a signal or measured value S is assigned.
  • the measurement is now repeated with the high frequency field pulse 14 being modulated to excite another parallel layer. That way you can For example, 30 adjacent layers are measured, so that a total of a volume data set of 128 x 128 x 30 measurements for a particular area of the examined brain or the whole brain is formed.
  • FIG. 1 b shows an EPI pulse train 10 ', which is identical to the EPI pulse train 10 from FIG. 1 a, except that the echo time TE 2 is 100 ms.
  • FIG. 1c also shows a corresponding EPI pulse train 10 ", in which the echo time TE3 is set at 140 ms.
  • These different echo times TEi, TE2 and TE3 are set by dimensioning the pause ⁇ it, ⁇ 2 t and ⁇ 3t accordingly.
  • FIG. 2 shows for this purpose a series of EPI pulse trains 10 according to Figure Ia to Ic, in which the aforementioned, stepwise displacement by TE n , TE n + I, TE n + 2, Te n + 3 ••• is indicated. Between these EPI pulse trains 10, a short pulse train 30 is connected in each case.
  • pulse sequences result in an image representation of the respective measured slice, which serves to correct movements of the subject.
  • the images produced by the successive pulse sequences 30 are compared with each other, and a sequence of rotation matrices of the eventual movement is calculated, which the subject has executed between two EPI pulse trains 10, 10 ', 10 ", etc., by, for example, for each Echo time TE a 3x3 matrix is calculated.
  • This vector can be used to correct the image representations generated by the EPI pulse trains 10, 10 ', 10 ", etc., and thus to align them anatomically correctly
  • FIG. 3 shows a nuclear spin tomographic image representation of a section through a brain in a transverse plane.
  • voxels volume elements of interest
  • the location of voxels 1 to 6 within one and the same plane is merely a simplified representation.
  • the voxels can, of course, also be present in lesser and greater numbers and distributed over several levels in three-dimensional space.
  • the method according to the invention generally makes it possible to map the liquor content to any desired specifications within the measuring volume.
  • the voxels 1 to 3 are in white matter, hereinafter WM, and the voxels 4 to 6 in gray matter, hereafter GM.
  • FIGS. 4a and 4c show signals for the voxels 1 to 3 and in FIGS 4b and 4d signals for the voxels 4 to 6, which were generated with the EPI pulse trains 10, 10 ', 10 "according to FIGS Point in the illustrated curves corresponds the measured value S determined with an EPI pulse sequence 10 according to FIGS. 1a to 1c at the location of the relevant voxel at the echo time TE plotted in the abscissa.
  • the signals S are plotted in the ordinate direction in arbitrary units, once linear (FIGS. 4a and 4b) and once logarithmically (FIGS. 4c and 4d).
  • the time axis is parameterized in the abscissa direction in all representations of FIGS. 4a to 4d for the echo time TE in ms.
  • the zero point of the coordinate systems is the time t 0 in FIG. 1a.
  • Optimally adapted mathematical functions are then determined for these pointwise measured signal profiles S (TE) with the aid of a compensation calculation, which results in the characteristic values of interest, in particular the real volume fraction ⁇ o of the liquor consisting of interstitial fluid ISF and cerebrospinal fluid CSF. Since the contributions of ISF and CSF are not separable, the term "ISF / CSF" is used below for the CSF.
  • volumetric fraction ⁇ o of the liquor is determined according to the invention from the measured signal curves or the mathematical models generated therefor.
  • T 2 is the transverse relaxation time
  • R 2 ' is the additional transverse relaxation rate that results from local inhomogeneities of the magnetic field.
  • a model is inadequate because the brain substance consists of several components with different transverse relaxation times.
  • a small first component of water protons trapped between the myelin bilayers has a T 2 of about 15 ms.
  • the essential component consisting of intracellular tissue water has a T 2 of about 70 to 86 ms.
  • a third, small component associated with the interstitial fluid and the cerebrospinal fluid has a T 2 of more than 150 ms.
  • the ISF / CSF signal has a frequency shift ⁇ f, also referred to as chemical shift, and a phase shift ⁇ relative to the protons of the brain tissue.
  • the extracellular signal can therefore be given as follows:
  • the complete model of the nuclear magnetic resonance signal of the brain according to the present invention is thus:
  • ⁇ c is the proportion of the ISF / CSF signal in the total signal.
  • the real volume fraction ⁇ o of the ISF / CSF depends on the signal component ⁇ c, the parameters of the EPI pulse sequence 10 and properties of the tissue components. ⁇ o can be obtained from the following equation, taking into account the parameters of the above-mentioned GRE-EPI pulse train and magnetic properties of the brain tissue:
  • n, and n c the relative spin densities of the brain tissue or the liquor ISF / CSF denote.
  • n, 0.66, which represents an average value for mixed brain tissue.
  • the quantities m and m c as already mentioned, give the component-specific duration amplitude of the magnetization of brain tissue or ISF / CSF, which can be calculated for the EPI pulse sequence 10 with a flip angle of 90 ° by the following relationship:
  • Tic the longitudinal relaxation time for CSF CSF and CSF and T R is the repetition time of the EPI pulse train.
  • the method according to the invention was carried out on two subjects (22 or 20 years old). For measurement, a whole-body tomograph with a field strength of 3 T was used (Trio, Siemens Er Weg). It was worked with a GRE-EPI pulse train. For each image, fifteen 3mm thick disks with a distance factor of 33% were interleaved. The remaining parameters of the GRE-EPI pulse train were: field of view (FoV Field of View) 192 x 192 mm, sampling matrix 64 x 64, echo spacing 0.47 ms, bandwidth 2,520 Hz per pixel for subject 1 and 2,298 Hz for subject 2. Zur To reduce the noise level, four averages were made, with the total recording time of one measurement being 25 seconds.
  • the remaining image parameters corresponded to the previously described EPI pulse train.
  • the recorded images were first converted into the ANALYZE-7 format using the SPM2 software (http://www.fil.ion.ucl.ac.uk/spm). Then the data was shifted by means of SPM2 for the motion correction already mentioned above in connection with FIG.
  • a first-order polynomial designated 55 in FIG. 4c ie a straight line
  • a TE 71 ms in all voxels
  • So_ari y a value of an interpolated initial signal interpolated from the early echo times.
  • the initial volume fraction ⁇ c of the liquor was assumed to be Soiate / Soeariy, or to 1 if Soiate> Soeariy.
  • ⁇ c was assumed to be 5%.
  • T 2 * the T 2 * of the internal signal (brain tissue) was assumed to be 49 ms, which roughly corresponds to values from the literature.
  • ⁇ f an initial estimate of 5 kHz was used, which also corresponds to information from the literature, for example the essay by He et al.
  • the adaptation of the proposed signal model for all voxels in the examined brain was performed voxel-by-voxel with a nonlinear least-square algorithm from the Matlab Optimization Toolbox (The MathWorks, Inc.).
  • the adaptation of the examined values was to fixed value ranges:
  • T 2 * c is the T 2 * of the external signal (liquor).
  • the quality of fit was quantified by determining the standard deviation (SD Standard Deviation) of the error sum (residual) for each voxel.
  • the MPRAGE (Magnetization-Prepared Rapid Acquisition Gradient Echo) dataset was subdivided into GM, WM and CSF using SPM2 software.
  • the obtained probability that a measured voxel belongs to WM, GM or CSF was used as a partial volume fraction.
  • Summing over all 1 mm 3 voxels within the larger voxels of the GRE-EPI pulse sequences using Matlab software yielded the individual volume fractions that were later used to distinguish between WM and GM.
  • FIGS. 4a to 4d show representative representations of the free induction decay FID in the six voxels 1 to 3 of WM and 4 to 6 of GM.
  • the signals were generated with thirty-seven GRE-EPI bursts and Figures 4a-4d show the signal drop over a wide range of TE (0 to 300 ms), which is possible due to the high sensitivity of the EPI pulse train 10 shown in Figure Ia , This range is significantly wider than in the prior art.
  • the GESSE pulse sequence described in the aforementioned article by He et al. For example, because of its lower sensitivity, it allows only measurements up to about TE 120 ms.
  • FIGS. 4a and 4b show the original measurements as solid, dotted and dash-dotted lines with linear ordinate dimension Ldb.
  • FIGS. 4c and 4d show the original measurements in the logarithmic ordinate scale as measuring points +, * and x and the mathematically adapted models as solid lines.
  • TE> 100 ms there is a range of lower decay (voxels 1 to 3 for WM) or even a signal increase (voxels 4 to 6 for GM). This range can not be measured with the known methods, as already mentioned.
  • the SD in the voxels with high ⁇ o that is to say with a high volume fraction of the liquor ISF / CSF, proves to be higher in the brain tissue and in the basal and frontal brain regions.
  • the voxels in the range of GM generally have a higher SD than the voxels in the range of WM.
  • the table in Figure 6 summarizes the results for the voxels with a partial volume fraction of at least 70% for WM and GM respectively in both subjects.
  • the chemical shift ( Figure 8b) shows no Gaussian distribution and therefore the mean and SD can not fully describe the data.
  • a better estimate of the average data in this case is the median value.
  • the median value for the WM voxels was 3.8 and 3.7 Hz for subject 1 and subject 2 and 3.9 Hz for the GM We-Le of both subjects.
  • FIGS. 7a to 7d summarize the results for some adaptation parameters of one of the subjects.
  • Figure 8a shows a typical section through a brain from the T 2 -weighted anatomical data set with a voxel size of lxlxl mm 3 .
  • the remaining figures of FIGS. 8b to 8d show the volume fraction ⁇ o of the liquor ISF / CSF, the chemical shift ⁇ f of the liquor and the phase shift ⁇ of the liquor.
  • the voxel size here is 3x3x4 mm 3 .
  • the scale in Figures 8b and 6d is limited to 15 Hz and 60%, respectively, for better contrast in areas consisting mainly of WM and GM.
  • the chemical shift ⁇ f images show below-average levels around the ventricles and higher levels of GM and voxels near the surface of the brain.
  • ISF interstitial fluid interstitial fluid
  • MRS magnetic resonance spectroscopy n relative spin density of brain tissue n c relative spin density of cerebrospinal fluid (ISF / CSF)
  • NPH Normal Pressure Hydrocephalus m, relative magnetization of brain tissue at the time of stimulation ra c relative magnetization of cerebrospinal fluid (ISF / CSF) at the time of excitation rf radiofrequency field pulse
  • R2 transversal relaxation rate R2 1 / T2

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Abstract

L'invention concerne un procédé écho-planaire en tranches multiples, en mode rafale, de mesure de la teneur en liquide dans la substance cérébrale d'un être vivant, procédé selon lequel la variation de signal est évaluée par approximation, en fonction du temps d'écho pour chaque élément de volume, par une variation bi-exponentielle, dont on déduit la fraction volumique de liquide.
PCT/EP2009/002779 2008-04-30 2009-04-16 Procédé de mesure de la teneur en liquide dans la substance cérébrale d'un être vivant par résonance magnétique à imagerie Ceased WO2009132772A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102008022325.5 2008-04-30
DE200810022325 DE102008022325A1 (de) 2008-04-30 2008-04-30 Verfahren zum Messen des Liquorgehalts in der Hirnstubstanz eines Lebewesens

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