JP2007061428A - Nuclear magnetic resonance testing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nuclear magnetic resonance testing apparatus which can express a nuclear magnetic resonance signal intensity in a concerned area of an image of an object to be tested as a ratio to a reference nuclear magnetic resonance signal intensity, that is a relative value, and which can compare the concerned areas of the object to be tested obtained in different series with each other from a view point of the nuclear magnetic resonance signal intensity. <P>SOLUTION: The nuclear magnetic resonance testing apparatus 10 is provided with an image display device 320 which receives an MRI signal released from the object to be tested by a receiver 100, and which displays an image based on the received MRI signal. The nuclear magnetic resonance testing apparatus 10 is also provided with: an input device 330 for designating a reference area of the cross section image of a reference body 200 and the concerned area of the object to be tested in the image; and a CPU 300 for calculating the ratio of the MRI signal intensity of the concerned area to the MRI signal intensity of the reference area. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a nuclear magnetic resonance inspection apparatus.

  MRI (Magnetic Resonance Imaging) used in a nuclear magnetic resonance inspection apparatus utilizes an NMR (nuclear magnetic resonance) phenomenon. The NMR is a technique for examining the properties of a single sample, but the source of the signal is unknown. On the other hand, MRI is a technique for providing position information to NMR and imaging the intensity distribution of nuclear magnetic resonance signals.

Here, the basic principle of NMR will be briefly described.
An atomic nucleus is composed of protons and neutrons, and is regarded as a nuclear spin rotating at an angular momentum I as a whole. Taking hydrogen nuclei as an example, the hydrogen nuclei are composed of one proton and rotate with a spin quantum number of 1/2.

  Since protons have a positive charge, when the nucleus rotates, a magnetic moment μ is generated. Therefore, each atomic nucleus may be considered as a very small magnet. In the case of a ferromagnetic material (for example, iron), the directions of the magnets are aligned, and magnetization occurs as a whole. On the other hand, in a plurality of hydrogen nuclei and the like, each of the hydrogen nuclei itself has a different orientation of the magnet described above, and magnetization does not occur as a whole. However, when the static magnetic field B is applied, the respective hydrogen nuclei are aligned in the direction of the static magnetic field.

  As described above, in the case of a hydrogen nucleus, the spin quantum number is ½, so the energy level is divided into two, −½ and + ½. The difference ΔE between the energy levels can be generally expressed by the following formula (1).

ΔE = γhB / 2π (1)
In the formula (1), γ is a proportional constant (magnetic rotation ratio) inherent to the nucleus, h is a Planck constant, and B is a static magnetic field strength.

By the way, in general, since a force of μ × H is applied to the nucleus by the static magnetic field B, the nucleus precesses around the axis of the static magnetic field at the frequency ω (Larmor frequency) expressed by the following equation (2).
ω = γB (2)
When an electromagnetic wave (radio wave) having a frequency ω is applied to the system in such a state, a nuclear magnetic resonance phenomenon occurs, and in general, the nucleus absorbs energy corresponding to the energy difference ΔE represented by the formula (1), Transition to a higher energy level.

  However, at this time, if there are many various nuclei, not all nuclei cause the nuclear magnetic resonance phenomenon. This is because, since the proportionality constant γ is different for each nucleus, the resonance frequency ω represented by the equation (2) is different for each nucleus, and only a specific nucleus corresponding to the applied frequency resonates.

  Next, the nucleus that has been shifted to a higher level by radio waves returns to the original level after a time determined by a certain time constant (called relaxation time). At this time, a nuclear magnetic resonance signal having an angular frequency ω is emitted from the nucleus that has been shifted to a higher level by radio waves. Here, the relaxation time described above is further divided into a spin-lattice relaxation time (longitudinal relaxation time) T1 and a spin-spin relaxation time (lateral relaxation time) T2.

  In general, when the inspection object is a solid, the spin-spin relaxation time T2 is shortened because the interaction between spins is likely to occur. Further, since the absorbed energy is first transferred to the spin system and then to the lattice system, the spin-lattice relaxation time T1 is much larger than the spin-spin relaxation time T2.

On the other hand, when the object to be examined is a liquid, the molecules move freely, so that the energy exchange between the spin-spin and the spin-lattice is easy to occur.
In MRI, a gradient magnetic field is applied to give position information when measuring a nuclear magnetic resonance signal generated from a nuclear spin constituting a subject tissue by the above-described NMR phenomenon. As this gradient magnetic field, gradient magnetic fields in three axial directions, ie, a slice encode direction, a phase encode direction, and a frequency encode direction, which are orthogonal to each other, are used. Then, a signal encoded by the gradient magnetic field can be reconstructed as a two-dimensional or three-dimensional image by performing Fourier transform.

  By the way, in a nuclear magnetic resonance examination apparatus, when imaging is performed based on a nuclear magnetic resonance signal emitted from an examination object, a window level, a TR (repetition time), a TE (echo time), and the like are adjusted. Thus, the image is adjusted to the most visible black and white contrast.

  However, there is no unit in the nuclear magnetic resonance signal intensity, and white and black contrasts are set according to the model of the nuclear magnetic resonance inspection apparatus. Conventionally, nuclear magnetic resonance signal intensities are used to form white and black contrast images in one MRI imaging (one series), and images obtained in this one series are used. Is used for diagnosis. However, it is difficult to compare with the intensity of the nuclear magnetic resonance signal obtained in the series (between other groups) imaged at other occasions because there is no unit in the nuclear magnetic resonance signal.

  The object of the present invention is to express the nuclear magnetic resonance signal intensity in the region of interest of the image to be inspected as a ratio with the reference nuclear magnetic resonance signal intensity, that is, a relative value, and to obtain examinations obtained in different series. An object of the present invention is to provide a nuclear magnetic resonance inspection apparatus capable of comparing target regions of interest from the viewpoint of nuclear magnetic resonance signal intensity.

  In order to achieve the above object, according to the first aspect of the present invention, a nuclear magnetic resonance signal is received by a receiving means, and an image based on the received nuclear magnetic resonance signal is displayed on a display means. In the resonance examination apparatus, a designation unit that designates the region of interest to be examined in the image, and a calculation unit that calculates a ratio of the nuclear magnetic resonance signal intensity of the region of interest to a reference nuclear magnetic resonance signal intensity The gist of the present invention is a nuclear magnetic resonance inspection apparatus.

  The invention of claim 2 is a nuclear magnetic resonance inspection apparatus for receiving a nuclear magnetic resonance signal emitted from a test object and a reference body by a receiving means and displaying an image based on the received nuclear magnetic resonance signal on a display means. In the image, designation means for designating a reference region of the reference body and a region of interest to be inspected, and a ratio of the nuclear magnetic resonance signal intensity of the region of interest to the nuclear magnetic resonance signal intensity of the reference region The gist of the present invention is a nuclear magnetic resonance inspection apparatus comprising a calculation means for calculating.

According to a third aspect of the present invention, in the first or second aspect of the present invention, there is provided storage means for storing the calculated ratio.
The invention of claim 4 is characterized in that in claim 1 or claim 2, an output means for outputting the calculated ratio is provided.

  According to the first and second aspects of the invention, the intensity of the nuclear magnetic resonance signal in the region of interest of the image to be examined can be expressed as a ratio to the reference nuclear magnetic resonance signal intensity, that is, as a relative value. Comparison of regions of interest to be examined obtained in different series can be made in terms of nuclear magnetic resonance signal intensity.

  According to the invention of claim 3, for example, when the ratio (that is, the relative value) calculated in another series is stored in the storage means, the ratio and the region of interest of the inspection object obtained in the current series are obtained. Comparison with the ratio of the nuclear magnetic resonance signal intensity at.

  According to the invention of claim 4, since the calculated ratio can be output by the output means, the output ratio (relative value) can be used at the output destination.

A nuclear magnetic resonance apparatus embodying the present invention will be described below with reference to FIGS.
The nuclear magnetic resonance inspection apparatus 10 includes a magnet 20 that generates a static magnetic field and a gradient magnetic field generating coil 30 that generates a gradient magnetic field. The inspection object K is disposed in the magnet 20 and the gradient magnetic field generating coil 30. The gradient magnetic field generating coil 30 is composed of three-axis gradient magnetic field coils orthogonal to each other, and can form an X-direction gradient magnetic field, a Y-direction gradient magnetic field, and a Z-direction gradient magnetic field, respectively. The directions of the three axes are the X-axis direction, the Y-axis direction, and the Z-axis direction shown in FIG. In addition, the nuclear magnetic resonance inspection apparatus 10 includes a sequencer 40.

  The sequencer 40 outputs a command (control signal) to the gradient magnetic field power source 50 and the high frequency transmitter 60, applies a gradient magnetic field and a radio frequency pulse (RF signal) that is a radio wave to the inspection target K, and controls the pulse sequence. Have been to do. The high frequency pulse is applied to the inspection object K by the high frequency transmitter 90 via the high frequency modulator 70 and the high frequency amplifier 80.

  An MRI signal as a nuclear magnetic resonance signal generated from the inspection object K is received by a receiver 100 as a receiving means. The MRI signal is sent to the CPU 300 via the amplifier 110, the phase detector 120, and the AD converter 130, and the CPU 300 performs signal processing. Further, the CPU 300 can store an image based on signals, measurement conditions, or MRI signals in a storage device 310 as storage means. Further, the CPU 300 displays the result of the image processing on a display unit and an image display device 320 as an output unit. The CPU 300 is connected to an input device 330 as a designation unit. The input device 330 includes a keyboard and a pointing device such as a mouse. When an operator gives an input instruction from the input device 330, the CPU 300 can control each of the units connected to the CPU 300 in accordance with the input instruction. The CPU 300 corresponds to a calculation unit.

  The sequencer 40 controls each unit so that each unit constituting the nuclear magnetic resonance examination apparatus 10 operates at a programmed timing and intensity. Of these programs, a program that describes the application timing of the high frequency pulse, the application of the gradient magnetic field, the reception of the MRI signal, and the strength of the high frequency pulse and the gradient magnetic field is called an imaging sequence.

Now, the operation of the nuclear magnetic resonance inspection apparatus 10 configured as described above will be described.
First, when the nuclear magnetic resonance inspection apparatus 10 is used, the reference body 200 is attached near the inspection target portion of the patient, which is the inspection target K (in this embodiment, on the skin of the lumbar portion). The outer shape of the reference body 200 is not particularly limited, but may be a shape that can be arranged near the examination target site of the patient. An appropriate shape such as a sheet shape, a flat plate shape thicker than the sheet, or a cubic shape may be used.

  In this embodiment, the reference body 200 is made of a polymer gel. A polymer gel is a swollen body in which a polymer forms a three-dimensional network structure by chemical bonds or by interactions between molecular chains such as crystallization and molecular entanglement, and holds solvent molecules in the voids. . In particular, the polymer preferably has a hydrocarbon in the main chain. Examples of the polymer having a hydrocarbon in the main chain include polyolefin, polystyrene, polyvinyl, and polyacryl. Further, since the polymer gel is in a gel form, the whole can maintain mechanical strength and can fix the liquid component. The reference body 200 is not limited to the polymer gel, and may be any material that is uniformly composed of a compound containing hydrogen atoms.

In this embodiment, Kitecko (Ultrasound Standoff Pads No. 3520k manufacturer: 3M Pharmaceutical Co., Ltd.) was used as the polymer gel. Kitecko is classified into many types based on the chemical structure of the structural unit (CU) of the polymer, but hydrogen atoms are incorporated into the structure with aliphatic hydrocarbons as the main chain (example: structural unit). (CU) chemical formula _{C 16 H 8 C l2 F 4} O 3). Kitecko contains no magnetic material. Since Kitecko is very flexible, it is linked to the movement of the location to be imaged at the site of the patient to be examined. Moreover, it is preferable to arrange the reference body 200 in the vicinity of the inspection target part.

  The MRI image is acquired by a known method. Since image acquisition is not an essential part of the invention, detailed description is omitted. For example, a known imaging sequence using a spin echo method, a gradient echo method, an EPI (Echo Plana Imaging) method, or the like is used as a sequencer 40. To run.

  Then, the CPU 300 acquires the MRI signal in the sliced portion via the receiver 100 or the like according to the imaging sequence executed by the sequencer 40. Then, the CPU 300 performs image processing such as Fourier transform based on the acquired MRI signal, and displays a two-dimensional image on the image display device 320. When performing this image display, the CPU 300 displays each pixel constituting the image with a luminance proportional to the intensity of the MRI signal. That is, the luminance depends on the distribution density of hydrogen nuclei.

  For example, FIG. 3 shows an imaging sequence by the gradient echo method, where the horizontal axis represents time and the vertical axis represents the intensity of a high-frequency pulse, a gradient magnetic field, or the like. In the figure, a high-frequency pulse 502 is applied simultaneously with a gradient magnetic field 501 in the Z direction (slice encoding direction) to excite hydrogen nuclei inside a desired slice. Then, when the polarity of the gradient magnetic field in the X direction (frequency encoding direction) is reversed from negative (−) to positive (+), an echo (nuclear magnetic resonance signal), that is, an MRI signal 504 is generated. Reference numeral 505 denotes application of a gradient magnetic field in the Y direction (phase encoding direction). In FIG. 3, TR is a repetition time, and TE is an echo time.

FIG. 2 is a flowchart for calculating the intensity ratio of the MRI signal executed by the CPU 300 by an input operation performed by the operator using the input device 330.
In step 10 (hereinafter, step is referred to as S), the CPU 300 determines whether or not the input mode of the reference area has been set by input from the input device 330, for example, a keyboard. If there is an input mode setting for the reference area, in S20, the CPU 300 determines whether a pixel in the reference area is designated by the input device 330, for example, a pointing device.

  A specific example will be described with reference to FIG. FIG. 4 shows a state in which a tomographic image (MRI image) of the examination target region of the patient is displayed on the display screen 320a of the image display device 320. In FIG. 4, 200 G represents a cross-sectional image region of the reference body 200. Reference numeral 500 denotes a cross-sectional image of the examination target region of the patient.

  As shown in the figure, in S20, when a pixel of a specific area (for example, an area indicated by 200B) as a reference area is designated by the pointing device in the cross-sectional image area 200G of the reference body 200, the CPU 300 " “Yes”. In S30, the CPU 300 calculates the intensity of the MRI signal of the pixel in the specified specific area 200B.

  Next, in S <b> 40, the CPU 300 determines whether or not the input mode of the region of interest has been set by input from the input device 330, for example, a keyboard. If there is a region-of-interest input mode setting, in S50, the CPU 300 determines whether a pixel of the region of interest has been designated by the input device 330, for example, a pointing device.

  A specific example will be described with reference to FIG. In FIG. 4, reference numeral 500 </ b> A indicates the region of interest of the operator in the cross-sectional image 500 of the examination target region of the patient. When specifying the specific area 200B, an area close to the area of interest 500A is specified. In general, in the MRI gantry 10a of the nuclear magnetic resonance inspection apparatus 10, the signal intensity between the central portion and the periphery thereof differs due to the difference in magnetic force. For example, in general, in the same image, the intensity of the MRI signal is different between the central muscle and the peripheral muscle. For this reason, when the specific region 200B and the region of interest 500A are close to each other, the same level of magnetic force is applied, which is advantageous in selecting the reference region. In FIG. 4, when 500C is set as the region of interest, the region 200D adjacent to the region of interest 500C in FIG. 4 is preferably used as the reference region.

  If the pixel of the region of interest is designated by the pointing device in S50, the CPU 300 determines “YES”. In S60, the CPU 300 calculates the intensity of the MRI signal of the pixel designated in the region of interest.

  In subsequent S70, the CPU 300 calculates the ratio of the MRI signal intensity of the designated pixel of the reference area and the region of interest (MRI signal intensity of the pixel of interest area / MRI signal intensity of the pixel of the reference area), and the calculation result Are stored in the storage device 310 and displayed on the display screen 320a.

Now, the characteristics of the nuclear magnetic resonance inspection apparatus 10 configured as described above will be described below.
(1) The nuclear magnetic resonance inspection apparatus 10 of the present embodiment receives an MRI signal (nuclear magnetic resonance signal) emitted from an inspection object by a receiver 100 (receiving means) and displays an image based on the received MRI signal. An image display device 320 (display means) is provided. The nuclear magnetic resonance inspection apparatus 10 includes, in the image, an input device 330 (designating means) for designating a reference region of a cross-sectional image of the reference body 200, the region of interest 500A to be examined, and the like. A CPU 300 (calculation means) that calculates the ratio of the MRI signal intensity of the region of interest 500A or the like to the MRI signal intensity is provided.

  As a result, in the present embodiment, the CPU 300 calculates the ratio of the MRI signal intensity of the region of interest 500A to be inspected with respect to the MRI signal intensity of the reference region, whereby each region of the image to be inspected is set as a relative value. Can be represented. As a result, when images are obtained with respect to a common inspection target in different series, each region of the inspection target image obtained in any series is reliable as long as the reference region is common. It can also be expressed as a relative value. That is, it is possible to give a unit of MRI signal intensity.

  (2) In the present embodiment, the storage device 310 that stores the calculated ratio is provided. As a result, for example, the ratio (that is, the relative value) calculated in the other series can be stored in the storage device 310. Therefore, the ratio and the ratio of the MRI signal intensity in the region of interest of the examination target obtained this time are obtained. Can be compared.

  (3) In this embodiment, the image display device 320 (output unit) that outputs the calculated ratio is provided. As a result, since the calculated ratio can be displayed (output) by the image display device 320, the displayed ratio (relative value) can be used for diagnosis of the inspection target.

  (4) In measuring the MRI signal intensity, the MRI can obtain an arbitrary cross section, and has excellent contrast resolution. Therefore, when the reference body 200 is pasted in the vicinity of the inspection target K and the MRI signal intensity in the reference body 200 is calculated (measured) together with the inspection target portion, for example, the MRI signal intensity in the reference body 200 is converted to 100, If the MRI signal intensity in the region to be inspected is converted based on this, it can be expressed as a value (unit).

In addition, this invention is not limited to the said embodiment, You may change as follows.
In the above embodiment, a reference region pixel that is a cross-sectional image of the reference body 200 is specified and the MRI signal intensity of the pixel is calculated. It is not limited to that. For example, in the cross-sectional image 500, when an object corresponding to the reference body 200 is prepared in advance, an area corresponding to the reference body 200 in the cross-sectional image 500 may be set as the reference area. That is, the reference MRI signal may be an MRI signal in an area in the inspection target.

In the above-described embodiment, the nuclear magnetic resonance examination apparatus capable of displaying a two-dimensional image is embodied. However, the nuclear magnetic resonance examination apparatus capable of displaying a three-dimensional image may be embodied.
In the above embodiment, the ratio of the MRI signal intensity between the region of interest 500A of the cross-sectional image 500 and the reference region of the reference body 200 in FIG. 4 is calculated, but the calculation method is not limited to this. For example, if the method of applying a magnetic force, that is, the level of the applied magnetic force is the same in the entire cross-sectional image region 200G of the reference body 200 and the region of interest 500C of the cross-sectional image 500, the region of interest 500A and the reference The ratio of the MRI signal intensity of the pixels in the region 200D may be calculated.

1 is an explanatory diagram of a schematic configuration of a nuclear magnetic resonance inspection apparatus 10. FIG. The flowchart which CPU300 performs. Shooting sequence by gradient echo method. Explanatory drawing which shows the display state of the MRI image of the display screen 320a.

Explanation of symbols

100: Receiver (receiving means)
310 ... Storage device (storage means)
320 ... Image display device (display means and output means)
330 ... Input device (specifying means)

Claims (4)

In a nuclear magnetic resonance inspection apparatus that receives a nuclear magnetic resonance signal emitted from an inspection object by a receiving unit and displays an image based on the received nuclear magnetic resonance signal on a display unit.
A designation means for designating a region of interest to be examined in the image;
A nuclear magnetic resonance inspection apparatus, comprising: a calculation means for calculating a ratio of a nuclear magnetic resonance signal intensity of the region of interest to a reference nuclear magnetic resonance signal intensity. In a nuclear magnetic resonance inspection apparatus for receiving a nuclear magnetic resonance signal emitted from an inspection object and a reference body by a receiving means and displaying an image based on the received nuclear magnetic resonance signal on a display means,
A designation means for designating a reference region of the reference body and a region of interest to be examined in the image;
A nuclear magnetic resonance inspection apparatus, comprising: a calculation means for calculating a ratio of a nuclear magnetic resonance signal intensity of the region of interest to a nuclear magnetic resonance signal intensity of the reference area.   The nuclear magnetic resonance examination apparatus according to claim 1, further comprising a storage unit that stores the calculated ratio.   The nuclear magnetic resonance inspection apparatus according to claim 1, further comprising an output unit that outputs the calculated ratio.

Images