Method to measure tissue texture using nmr spectroscopy with VOI length in analysis direction defined by receiver bandwidth

Abstract

To provide a method for selective sampling to assess texture of a specimen by using magnetic resonance (MR).SOLUTION: The method according to the invention excites a specimen and refocuses to provide a sample rod within the specimen. An encoding gradient pulse is applied to induce phase wrap, creating a spatial encode for a specific k-value and orientation. A low non-zero magnitude gradient (140) is then applied and acts as a time dependent phase encode to produce a time varying trajectory through 3D k-space of k-value encodes (146) while simultaneously recording multiple sequential samples (138) of the signal at a sequence of k-values proximate the specific k-value. A receiver bandwidth is set to delineate a length of a VOI within the rod during data sampling. The samples are then post processed at the sequence of k values, and recorded within a time span while the non-zero magnitude gradient is applied, to characterize textural features of tissue in the VOI.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] REFERENCE TO RELATED APPLICATIONS This application is filed on the same assignee as this application, US Pat. TISSUE TEXTURE USING NMR SPECTROSCOPY WI TH VOI LENGTH IN AN ANALYSIS DIRECTION D 2018 1st DEFINED BY RECEIVER BANDWIDTH This application claims priority to U.S. Provisional Patent Application No. 62,769,666, filed January 20, 2011. No. 6,399,433, the disclosure of which is incorporated herein by reference.

[0002] The methods claimed herein are useful in the application of materials in biological systems and in industrial and engineering research. More specifically, the present invention relates to the field of evaluation of microscopic textures in structural assessment. The embodiments disclosed herein include selective excitation of a first slice in a specimen of interest and defining a rod. A second slice-selective refocusing sequence is then performed to obtain the desired analysis method. A gradient is applied along the direction of the beam to define the length of the volume of interest (VOI). A method is provided for sweeping a small range of k values ​​with a given receiver bandwidth. Summary of the Invention [Means for solving the problem]

[0003] The present disclosure provides a selective sampling method for assessing the texture of a specimen using magnetic resonance (MR). A method of selecting a first gradient for a first slice selection in a specimen is provided. A first RF pulse is transmitted at the first slice and a second slice defining a rod in the specimen. Selected for slice-selective refocusing in the region defined by the intersection with the slice. Application of a second gradient selected from the encoding gradients results in the delivery of a second RF pulse. An oblique pulse is applied to induce a phase wrap to obtain the spatial encoding for a particular k value and orientation. Then, a low nonzero magnitude phase-encoder is created, which acts as a time-dependent phase-encoder. A gradient is applied to generate a time-varying trajectory through the 3D k-space of the k-value encoding, while simultaneously over a neighborhood of a particular k value defined by the height of the gradient and the pulse width of the non-zero magnitude By recording multiple consecutive samples of the NMR RF signal at a range of k values, data sampling is performed. First, set the receiver bandwidth narrow enough to define the length of the VOI within the rod. Then , over a series of k values ​​recorded within the time span during which a non-zero magnitude gradient is applied. The samples are post-processed to characterize the texture features of the tissue within the VOI. [Brief description of the drawings]

[0004] [Figure 1] FIG. 2 is an exemplary timing diagram of a pulse sequence for the claimed method showing the timing of a single excitation. [Diagram 2] 1 is a representation of the excited rod or core within the specimen and the VOI finally selected during data sampling. [Diagram 3] 1 is a flow chart illustrating an implementation of a method for texture assessment in a structure of a specimen. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] Referring to the drawings, FIG. 1 shows a schematic diagram of a data acquisition system using the methods claimed herein. 1 shows an example timing diagram of a pulse sequence for performing a 100-MHz RF pulse train. The first RF pulse is employed to excite a selected volume of tissue under investigation. The trace 104 is coincident with a gradient pulse 108 at a first magnetic field gradient represented by trace 106. The first RF pulse 104 excites a single slice or slab of the specimen and The positioning of the slice or slab is determined by the orientation and magnitude of the first gradient and the RF pulse. The negative gradient pulse 110 is a slice or slab pulse. The excitation is rephased within a predetermined thickness of the

[0006] The second RF pulse 112 is followed by a gradient pulse 11 with a second gradient represented by trace 114. 6 is transmitted simultaneously to excite slice-selective refocusing of spins, and this second tissue slice The slice intersects with the first slice or slab mentioned above (this second RF pulse 112 tilts the net magnetic vector antiparallel to B0, causing a spin reversal and subsequent This results in refocusing and therefore between the 90° and 180° RF pulses. (This results in a signal echo at a time point after the 180° RF pulse, which corresponds to the time With respect to the first higher value gradient pulse 118, the sample body is Crusher or "spoiler" gradients designed to induce large phase wraps over the product. A similar tilt pulse 122 at the end of pulse 116 is a 180 degree RF inversion pulse. Since the 180 pulse arrives 112 seconds later, this phase wrap is removed. Excitations that do not exist before the 180° RF pulse, such as excitations from defects in the , and therefore is not refocused by the second crusher, and therefore the signal Crushers 118 and 122 are shown on only one axis in FIG. Note, however, that the crushers can be on any combination of shafts.

[0007] The second RF pulse combines with the applied second gradient to produce a second gradient. 2, thereby allowing the lateral movement of the rod or core 206 through the specimen. A lateral dimension is defined by the intersection of the first slice 202 and the second slice 204. It provides slice-selective refocusing of the signal in the region being focused. There are many ways to create an internally excited rod using oblique pulses and RF excitation. The parameter selection for the various methods is done with SNR optimization in mind. As described herein, slice-selective excitation and mutually orthogonal slices can be used. The rod or core 206 produced by the laser-selective refocusing pulse is shown in FIG. It is being done.

[0008] The encoding gradient pulse 126 on the trace 114 is In general, we set the initial phase wrap and therefore the k-value encoding according to the vector of the machine gradient. The Tor connection allows the k-value encoding to be oriented in any direction, but makes it easy to visualize. The negative encoding gradient pulse 126 is represented as being on the second gradient to The phase is wound so that echo signal acquisition begins at the selected k value in the signal. Then, the k value can be incremented or changed in direction. The encoding gradient pulse 126 is shown separated from the second gradient pulse 116. However, it can also be combined with pulse 122.

[0009] A low non-zero magnitude phase encoding gradient that acts as a time-dependent phase encode. 0 is applied, and data sample 142 is compared to the time-varying k value seen in trace segment 146. The initial k value 144 is obtained from the equation for the initial k value and the subsequent time-varying k value 146. The encoder 140 does not have to be aligned with the axis of the excited rod. The encoding gradients are aligned with the defined direction of the VOI and are described below. Thus, by definition it is aligned with the analysis direction.

[0010] The receive gate 133 is opened to receive an RF signal, which is then fed to a signal tracer 136. 1 as pulse 134 at trace 136. The RF signal at trace 136 is It is a representation of only the signal present in the receive gate window, and does not show the actual details of the RF signal outside the window. Sampling is done as represented by trace 138, trace 1 We start with an initial k value of 144, as seen in Figure 24. At the scale of the drawing, the sampling rate is not large enough. The individual triggers of the analog-to-digital converter (A / D) are marked on trace 138. Note that the receiver bandwidth is scaled during data sampling (as shown in Figure 2). 206) is configured to define a length 208 of a VOI 210 within a rod or core 206. The initial phase wrap is designed to provide an initial k value with a magnitude that corresponds to the low SNR region. The encoding gradient 126 can be employed to select the The gradient pulses with non-zero magnitude can be wound up to the lowest or highest k value. , imposed in the direction necessary to reach the other limit in k-space to define the texture. (Increasing or decreasing k). In an exemplary implementation, the wavelength range of 0.050 to 0.100 mm; Bzero=1T, 50 ms read time for H1 nucleus (4.258MHz / T) (i.e. A gradient of 23.5 mT / m and a bandwidth of approximately 500 Hz are used. OI analysis length of 5 mm can be obtained. In practice, the data is stored in a later data The first step is to analyze the data and post-select multiple subsets of VOIs of bandwidth within the data. The first VOI is acquired, which has a relatively wide bandwidth.

[0011] The echoes are refocused during the same excitation and are phase-encoded with a gradient of the same magnitude as the phase-encoding gradient 140. However, it can be read out again with the opposite phase encoding gradient and swept over the same k range. This allows for the implementation of phase cycling, resulting in a higher SNR.

[0012] An additional benefit of using the bandwidth to select the sample length is that within the first bandwidth The bandpass can be offset in either direction to allow excitation along the same rod as was originally excited. This allows access to samples in slightly different regions of a given specimen. , the location of the width dimension 208 may also be set by the center frequency of the selected bandwidth. In this manner, the rod 2 defined by the first and second slices 202, 204 06. Multiple VOIs along the received broadband This can be done by post-processing the dataset.

[0013] As shown in FIG. 3, a further aspect of the disclosed method is to provide a method for detecting a plurality of Iterate over an array of VOIs for measured or derived values, and analyze each VOI in the array. Plot measurements as intensity or color on a 2D or 3D grid that matches the structure of the sample being measured. The present invention relates to a method for generating an image that displays the distribution of a specified texture. is particularly well suited for efficiently collecting a large number of VOI measurements. For each VOI, a VOI was selected to cover the portion of the specimen intended for analysis for the first VOI. After setting the center frequency and a sufficiently large bandwidth, the difference between the subsets of VOIs is calculated. Iteratively select a center frequency and bandwidth that are such that the center frequency and bandwidth are post-processed along the axis of the gradient (rod 206). (filtering) to produce a 1D image of the measured (or derived) values ​​at each iteration. In the time domain, the excitation, signal acquisition and recovery times for one rod are further By interleaving with further excitation, signal acquisition and recovery for the non-inserted rods, This allows efficient acquisition of 1D images of multiple rods.

[0014] This further aspect is achieved when the rod 206 crosses a boundary between different texture types within the specimen. provides a sensitive method for locating boundaries of structures within the specimen being analyzed. Setting the bandwidth within multiple narrow ranges within the first bandwidth during post-processing can be done by determining the location of the boundaries. This has the effect of increasing the resolution for identifying the

[0015] As described with respect to FIG. 1, excitation pulses and gradients are incorporated to generate a first slide through the specimen. A first RF pulse is transmitted with a first gradient selected for phase selection (step 301 ) defined by the intersection of the first slice and the second slice that defines the rod in the specimen. By applying a second gradient selected for slice-selective refocusing in the region to be Then, a second RF pulse is transmitted (step 302). applied to induce phase wrapping to create a spatial encoding for a particular k value and orientation. (Step 303). A low non-zero magnitude eigenvalue is generated that acts as a time-dependent phase encoding. Applying the gradient generates a time-varying trajectory through the 3D k-space that encodes the k values. (Step 304). During data sampling, define the length of a first VOI within the rod. A first receiver bandwidth is set (step 305) to receive multiple consecutive NMR RF signals. The subsequent samples are taken at a particular k value defined by the height of the non-zero magnitude gradient and the pulse width. Then, the non-zero k values ​​are recorded simultaneously over a range of k values ​​over a neighborhood of The samples at a series of k values ​​recorded within the time span during which the magnitude gradient was applied are The receiver band is processed for one or more further bandwidths within the first receiver bandwidth. Resetting the width provides one or more subsets of the VOI (step 30 6) Alternatively or in combination, one or more alternative centers within the first receiver bandwidth. Frequencies are selected to provide one or more subsets of the VOI (step 307). In the time domain, the excitation, signal acquisition and recovery times for the rod are calculated without further crossing. By interleaving with further excitation, signal acquisition and recovery for the smaller rods, A 1D image of a number of non-intersecting rods is created (step 308). A selected set of VOIs in a first bandwidth is calculated to provide an array of VOIs for the derived values. By iterating the passband, each VOI in the array is filtered to a 2D or 3D image that matches the structure of the specimen. The distribution of measured textures can be plotted as intensity or color on a 3D grid. This enables the generation of an image representing the fabric (step 309). To identify the boundaries of the first bandwidth, a plurality of bands are detected within the range having a bandwidth smaller than the first bandwidth. Setting the bandwidth increases the resolution for locating the boundaries (step 310). .

[0016] Although various embodiments of the present invention have been described in detail in accordance with the requirements of the patent statutes, those skilled in the art will appreciate that the present invention is Modifications and substitutions to the specific embodiments disclosed herein will be apparent. Such modifications are within the scope and spirit of the present invention as defined in the following claims. .

Claims

1. Selective Sampling Method for Assessing Tissue Texture Using Magnetic Resonance (MR) It is a law, Transmitting a first RF pulse with a first gradient selected for a first slice selection in the specimen. and The intersection of the first slice and the second slice defines a rod within the specimen. of a second gradient selected for slice-selective refocusing within the defined region; transmitting a second RF pulse according to the application; An encoding gradient pulse is applied to induce phase wrapping to a particular k value and orientation. creating a spatial encoding for A low non-zero magnitude signal having a first magnitude that acts as a time-dependent phase encode. applying gradients to generate a time-varying trajectory through the 3D k-space of the k-value encoding; A plurality of consecutive samples of the NMR RF signal are sampled based on the height and pulse width of the non-zero magnitude gradient. In a single excitation, the excitation is performed over a range of k values ​​over a neighborhood of the particular k value defined by the and simultaneously recording the During the data sampling, a first receiving step is performed to define a length of a VOI within the rod. setting a machine bandwidth; the series of data recorded during the time span during which the non-zero magnitude gradient is applied; 3. Post-processing the samples at k values ​​of characterizing the The method includes:

2. A refocusing step, Apply a low non-zero magnitude gradient that has a magnitude equal to the first magnitude but in the opposite direction a step of: Simultaneously recording a plurality of successive samples of the NMR RF signal at the inversion of the series of k values. , sweeping back through the same k value range, allowing for the implementation of phase cycling. P The method of claim 1 further comprising:

3. The central circumference of the first receiver bandwidth for positioning the VOI along the rod. The method of claim 1 further comprising the step of selecting a wave number.

4. The post-processing step may further include: resetting the receiver bandpass for providing one or more subsets of the VOI; The method of claim 3 , comprising:

5. The post-processing step may include selecting one or more alternative center frequencies within the first receiver bandwidth. and providing one or more subsets of the VOIs. Method of posting.

6. In the time domain, the excitation, signal acquisition and recovery times for the rod are further crossed Multiple rods can be interleaved with further excitation, signal acquisition and recovery for rods that do not have The method of claim 3 further comprising the step of creating a 1D image of the head.

7. A magnetic resonance (MR) microscope is used to generate an image showing the distribution of the measured texture in the specimen. ) comprising the steps of: Transmitting a first RF pulse with a first gradient selected for a first slice selection in the specimen. and The intersection of the first slice and the second slice defines a rod within the specimen. of a second gradient selected for slice-selective refocusing within the defined region; transmitting a second RF pulse according to the application; An encoding gradient pulse is applied to induce phase wrapping to a particular k value and orientation. creating a spatial encoding for Applying a low non-zero magnitude gradient that acts as a time-dependent phase encoding, k-value generating a time-varying trajectory through the 3D k-space of the encoding; During data sampling, a first receiving element is used to define a length of a first VOI within the rod. setting a transmission bandwidth; A plurality of consecutive samples of the NMR RF signal are sampled based on the height and pulse width of the non-zero magnitude gradient. A scan line is formed by simultaneously recording at a range of k values ​​over a neighborhood of the particular k value defined by a scan width. Tep and the series of gradients recorded within a time span during which the non-zero magnitude gradient was applied; post-processing the samples at k values ​​of 100 k, repeating passbands within the first bandwidth, and taking multiple measurements providing an array of VOIs for a given or derived value; Each VOI in the array is intensity-mapped onto a 2D or 3D grid that matches the structure of the specimen. or plotting it as color to generate an image showing the distribution of the measured textures. Steps and The method includes:

8. A method for using magnetic resonance (MR) to identify boundaries of measured textures in a specimen. It is a law, Transmitting a first RF pulse with a first gradient selected for a first slice selection in the specimen. and The intersection of the first slice and the second slice defines a rod within the specimen. of a second gradient selected for slice-selective refocusing within the defined region; transmitting a second RF pulse according to the application; An encoding gradient pulse is applied to induce phase wrapping to a particular k value and orientation. creating a spatial encoding for Applying a low non-zero magnitude gradient that acts as a time-dependent phase encoding, k-value generating a time-varying trajectory through the 3D k-space of the encoding; During data sampling, to define a length of a first VOI within said rod, including a boundary. setting a first receiver bandwidth to A plurality of consecutive samples of the NMR RF signal are sampled based on the height and pulse width of the non-zero magnitude gradient. A scan line is formed by simultaneously recording at a range of k values ​​over a neighborhood of the particular k value defined by a scan width. Tep and The series of k recorded in the time span during which the non-zero magnitude gradient was applied. post-processing the samples at a value to generate a plurality of ranges having a bandwidth smaller than the first bandwidth; setting the bandwidth within a certain range, thereby increasing the resolution for locating the boundary Steps and The method includes:

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