JP4371510B2 - Magnetic resonance imaging system - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a magnetic resonance imaging (hereinafter referred to as MRI) apparatus, and more particularly, to an MRI apparatus suitable for interventional processing in which processing is performed while monitoring the body temperature.
[0002]
[Prior art]
In recent years, attention has been focused on a treatment method that achieves the same effect with minimal invasiveness, rather than a surgical treatment in which a scalpel is inserted into a patient. For example, it is a treatment method in which a needle is inserted percutaneously under X-ray fluoroscopy and the affected part of the herniated disc is evaporated by laser irradiation. Similarly, there is a cryosurgery treatment method in which a cryogen is poured under X-ray fluoroscopy and the affected part is frozen and excised. These minimally invasive therapeutic methods under X-ray fluoroscopy are called interventional treatments and are beginning to become popular because they can satisfy the therapeutic effects.
[0003]
Alternatively, hyperthermia treatment methods that selectively irradiate tumor cells, which are considered to be heat-sensitive, by raising the temperature of a part of the body tissue by irradiating the affected area with electromagnetic waves or infrared rays have attracted attention.
[0004]
[Problems to be solved by the invention]
Since the above-mentioned interventional treatment is performed under X-ray fluoroscopy, there is a problem of X-ray exposure for the operator and the patient. In addition, there are problems that the degree of transpiration and resection of the affected area cannot be evaluated during the operation, and the temperature change of the normal tissue around the affected area cannot be grasped.
[0005]
In addition, hyperthermia therapy requires extremely accurate control of the boundary temperature between the death of normal cells and tumor cells. However, there was no means for accurately measuring the temperature and temperature distribution in the body non-invasively during treatment.
[0006]
On the other hand, several methods have been developed to know the temperature in the body from the nuclear magnetic resonance (hereinafter referred to as NMR) signal of the body tissue by MRI. The main methods are as follows: 1) Grasping that the relaxation time of the NMR signal changes with temperature, and calculate the temperature from the amount of change. 2) The change in the resonance frequency of the NMR signal is measured along with the temperature change, and the temperature is calculated from the change frequency and the phase change amount. 3) There is a method of measuring the diffusion constant depending on the temperature of the NMR signal to obtain the temperature (Japanese Patent Publication No. 6-14911).
[0007]
However, in the above-described interventional treatment, the measurement of the temperature change at the treatment site must be performed together with the monitoring of the form. However, the above-described temperature measurement cannot depict the form with high spatial resolution, so these temperature measurements are performed. Is not applied to monitor the progress of treatment such as therapy. As an image display means, there is no MRI apparatus capable of displaying a combination of an MRI image showing the form and function and a temperature distribution diagram or a temperature display of an examination site.
[0008]
The present invention has been made in view of the above problems, and an object thereof is to provide an MRI apparatus suitable for performing interventional while monitoring the temperature of a treatment site under MRI imaging. Another object of the present invention is to provide an MRI apparatus capable of substantially displaying a tomographic image and temperature information for determining the progress of a therapeutic treatment. Furthermore, an object of the present invention is to provide an MRI apparatus that can provide information indicating the temperature of a treatment site in a form that is easy for a person performing the treatment to use.
[0009]
[Means for Solving the Problems]
The MRI apparatus of the present invention that achieves the above object comprises a static magnetic field generating means for generating a constant magnetic field strength, a gradient magnetic field generating means for generating a magnetic field strength gradient, a means for generating a high-frequency magnetic field, Means for detecting NMR signals, calculation / display means for reconstructing a tomographic image of the subject using the NMR signals and displaying the results, and control means for controlling these means, the calculation / display means Comprises means for calculating a numerical value indicating a temperature change of the examination region of the subject and an image indicating a temperature distribution, and means for alternately or simultaneously displaying the calculated temperature information and the tomographic image.
[0010]
In the present invention, the temperature information means all information related to temperature such as a numerical value indicating a temperature change, a temperature distribution image, a graph in which the numerical value indicating the temperature change is processed, and an isotherm.
[0011]
In a preferred embodiment of the present invention, the control means performs control to measure the NMR signal for temperature measurement while measuring the NMR signal for the tomographic image of the subject, and reconstructs the NMR signal for the tomographic image. A tomographic image and temperature information obtained by calculating an NMR signal for temperature measurement are displayed simultaneously or alternately.
[0012]
In another preferred aspect of the present invention, the control means creates signal intensity data for tomographic images and phase data for temperature information calculation using the NMR signal obtained from the subject, and regenerates the signal intensity data. The configured tomographic image and the temperature information calculated from the phase data are displayed simultaneously or alternately.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described below with reference to the drawings.
[0014]
FIG. 1 shows an overall configuration diagram of an MRI apparatus to which the present invention is applied. The MRI apparatus shown in FIG. 1 includes a static magnetic field generation magnet 2, a gradient magnetic field generation system composed of a gradient magnetic field coil 3 and a gradient magnetic field power supply 4, and a high frequency magnetic field generation system composed of a high frequency coil 5 and a high frequency power amplifier 6. A detection coil 7 for detecting NMR signals, a receiver 8 (signal processing system), a sequencer 9 (control system) for controlling the gradient magnetic field generation system and the high-frequency magnetic field generation system according to a predetermined imaging sequence, and a computer 10 and an arithmetic processing system composed of a storage device 11, an operation system composed of a first display 12, a second display 13, and an operator console 14, and a table 15 for carrying the subject 1.
[0015]
Some units are installed in the electromagnetic shield chamber 16 so that external electromagnetic noise is not mixed into the detection coil 7. For this reason, the unit in the shield room and the external unit are connected via the filter circuit 17.
[0016]
The static magnetic field generating magnet 2 generates a uniform and stable magnetic field strength in a space including the examination site of the subject 1. As a means for generating a magnetic field, there is a permanent magnet, a normal conducting coil, or a superconducting coil system. In the apparatus shown in FIG. 1, a pair of opposing superconducting coils 18 and an iron yoke that constitutes a magnetic circuit so as to surround the superconducting coil 18 are used. Assembled in 19. With such a configuration, the entrance of the subject 1 of the static magnetic field generating magnet 2 can secure a wide space, and the operator can directly perform treatment or the like on the subject 1 arranged in the magnet 2. Treatment can be given. Further, the spherical space including the examination site of the subject 1 is adjusted to a uniformity of 3 ppm or less, for example. The performance of this magnet enables MR fluoroscopy and echo planar imaging (EPI) imaging functions that take MRI images in real time.
[0017]
The static magnetic field generating magnet 2 may be an open type having a structure in which a pair of permanent magnets are arranged one above the other. In this case, since the periphery of the subject is open, treatment such as treatment can be performed more easily.
[0018]
The gradient magnetic field generation system includes a gradient magnetic field coil 3 (x, y, and z are integrally shown in the figure) wound so as to change the magnetic flux density in three axial directions of x, y, and z orthogonal to each other. It is composed of a gradient magnetic field power source 4 for driving each of the gradient magnetic field coils 3 of x, y and z. The gradient magnetic field pulses Gx, Gy, Gz consisting of three axes are changed by driving the gradient magnetic field power source 4 in accordance with a control signal from the sequencer 9 to be described later to change the current value flowing through the gradient coil 3. To be applied. This gradient magnetic field is used to grasp the spatial distribution of NMR signals obtained from the examination site described later.
[0019]
The high-frequency magnetic field system includes a high-frequency coil 5 that generates a high-frequency magnetic field for resonantly exciting the nucleus of the examination site of the subject 1 and a high-frequency power amplifier 6 that causes a high-frequency current to flow through the high-frequency coil 5. The high frequency power amplifier 6 is also controlled by the control signal of the sequencer 9. The operating frequency of the high-frequency power amplifier 6 is matched with the resonance frequency of the inspection target nucleus determined by the magnetic field strength of the apparatus. The target nucleus is usually hydrogen.
[0020]
The detection coil 7 has a function of detecting an NMR signal, which is a high-frequency magnetic field of excited hydrogen nuclei at the examination site of the subject 1, as an electrical signal. This detection coil 7 is provided with a gap so that therapeutic treatment can be performed simultaneously during the MRI examination. The receiver 8 has an analog / digital conversion function of amplifying and detecting a weak NMR signal detected by the detection coil 7 and converting it to a digital signal that can be processed by the computer 10 thereafter. The operation timing of the receiver 8 is also controlled by the sequencer 9, and the NMR signal converted into digital data is connected to the computer 10.
[0021]
The arithmetic processing system includes a computer 10, a storage device 11 for storing images and the like, a first display 12 for displaying processed data, a second display 13, and a console 14 for operating the MRI apparatus. Here, the second display is arranged in the vicinity of the magnet 2 so that the operator (not shown in the figure) can confirm the display contents during treatment such as treatment. The computer 10 processes the NMR signal of the examination site of the subject 1 and determines the temperature of the examination site based on not only the anatomical tomographic image of the examination site but also the frequency, phase displacement, and relaxation time of the NMR signal. Is calculated and displayed on the first display 12 and the second display 13.
[0022]
The computer 10 is connected to a sequencer 9 that controls the operation of each unit described above, and sends commands necessary for control to the sequencer 9.
[0023]
In the MRI apparatus of the present invention, the control system composed of the computer 10 and the sequencer 9 performs the following control.
1) Measurement and display of continuous morphological or functional images, while measuring temperature at desired intervals, and displaying morphological or functional images and temperature information (numerical values, phase images, etc.) simultaneously. Alternatively, continuous temperature measurement and monitoring are performed, and during that time, shape measurement is performed at a desired interval, and temperature information and a shape image are displayed simultaneously.
2) Using the NMR signal obtained by continuous measurement, temperature information and a morphological or functional image are created and displayed in parallel.
[0024]
These functions are incorporated in the computer 10 as a program, and the computer 10 performs calculations such as image reconstruction and temperature calculation using the obtained NMR signals according to this program. Selection of functions, setting of a sequencer executed in each function, shooting conditions, display conditions, and the like can be performed via the console 14.
[0025]
FIG. 2 shows the configuration of the image display portion of the computer 10 that enables simultaneous display of temperature information and morphological images. The image memory 202 and the graphic memory 203 are memories for storing image data and character / numerical data processed in the arithmetic unit. Data is sent to and written into these memories sent via the data bus 201. Image data is data of tomographic images and phase images created by Fourier transforming NMR signals, and character / numerical data are temperature numerical values, temperature distribution contour lines, temperature change graphs, and the like.
[0026]
Data in the image memory 202 is input to the look-up table memory 205 for each image. Data in the graphic memory 203 is input to the table memory 206 for each display unit.
[0027]
The control circuit 204 sends control signals 209 and 210 relating to the display of these data to the look-up table memory 205 and the table memory 206, respectively. That is, when the density or gradation of the displayed image is set by the operator's operation, a signal 209 for these processes is input from the control circuit 204 to the lookup table memory 205, where the density and gradation are input. Processing related to is performed. Further, display / non-display of temperature information is selected by a signal 210 from the control circuit 204.
[0028]
The signals of the look-up table memory 205 and the table memory 206 are added by the synthesis circuit 207, converted into a video signal by the D / A circuit 208, and input to the first display 12 and the second display 13.
[0029]
Next, the operation of the MRI apparatus having such a configuration will be described.
[0030]
FIG. 3 is a flowchart showing an example of a process of performing an interventional treatment for treating an affected area while monitoring the temperature of the examination site with the MRI apparatus shown in FIG. FIG. 4 shows images displayed on the first display and the second display.
[0031]
First, a high-frequency coil 7 for detecting an NMR signal is attached to an examination site of the subject 1, for example, a trunk, and is arranged at the center of the magnet 2 (step 301).
[0032]
Next, a tomographic image is taken along the body axis of the trunk, which is the examination site (step 302). This is a preliminary measurement for determining a cross section including a needle route and a treatment site, for example, and is imaged by a known sequence such as a spin echo method. The captured image 401 is displayed on the first display 12 and the second display 13 as shown in FIG.
[0033]
The surgeon specifies a new tomographic plane B including the treatment site based on the displayed image 401 (step 303), and takes an image of the new tomographic plane by high-speed imaging (step 304). This operation is continuously repeated. For example, MR fluoroscopy described later is selected as the high-speed imaging method.
[0034]
Images obtained by this continuous shooting are displayed on the first display 12 and the second display 13. Thus, the surgeon can perform the operation of the biopsy (percutaneous stylus) with the image 402 substantially in real time.
[0035]
When it is confirmed from the image 402 that the needle has reached the treatment site, transpiration treatment of the affected area by laser irradiation is performed (step 305). This treatment process is confirmed by continuously taking morphological images and displaying them on the first display 12 and the second display 13 (step 306). In this case, if necessary, a functional image may be taken and displayed. Alternatively, imaging may be performed by changing imaging conditions such as changing the field of view of the image in order to image the treatment site with high resolution. In this manner, the imaging and display are continuously and repeatedly executed, thereby providing a real-time image to the operator.
[0036]
In the process of such continuous imaging, the temperature of the examination site is monitored at regular intervals. The time interval of the temperature monitor is set by the operator inputting a value of a time interval suitable for monitoring the temperature to the computer 10 according to the treatment. The value of this time interval can be changed according to the course of treatment. That is, the monitoring interval can be changed by an input from the computer 10 even during the treatment.
[0037]
In the temperature monitor, it is first determined whether or not a certain time has elapsed since the start of the transpiration treatment (step 307). When a certain time has elapsed, the computer 10 instructs the sequencer to execute a temperature measurement sequence. The temperature measurement sequence may be the same as or different from the high-speed imaging method executed in steps 304 and 306.
[0038]
By executing this temperature measurement sequence, the NMR signal of the surrounding tissue including the treatment site is measured (step 308). The NMR signal measured here is a signal including a temperature change as a phase change, and the temperature can be calculated by processing this with the computer 10, and a temperature distribution diagram can be constructed. The calculation of the temperature change will be described later. The temperature information thus obtained (temperature change or temperature distribution diagram as numerical values) is displayed on the first display 12 and the second display 13.
[0039]
The temperature information is displayed alternately with the tomographic image 403 as necessary, or repeatedly with a constant period. For example, as shown in FIG. 4, a temperature or temperature distribution display 405 is displayed as a part of the tomographic image 404. indicate.
[0040]
Such temperature measurement is performed at every time interval set in the course of treatment, and the temperature information is updated and displayed on the first display 12 and the second display 13 each time (steps 306 to 308).
[0041]
After confirming the progress of treatment on the tomogram, the examination and treatment are finished, and the subject is taken out of the magnet 2 and finished (steps 309 and 310).
[0042]
By configuring as described above, the surgeon can always observe the progress of the treatment with MRI images during treatment, and can monitor the temperature change related to the treatment action at regular time intervals.
[0043]
Next, the photographing sequence in steps 304 (306) and step 308 will be described.
[0044]
As described above, in step 304, continuous high-speed imaging such as MR fluoroscopy is performed. FIG. 5 is a diagram showing a sequence by gradient echo as an example of the high-speed imaging method, and FIG. 6 is a diagram for explaining MR fluoroscopy.
[0045]
Gradient echo sequence is a well-known sequence applied to MR fluoroscopy, but in brief, it is a slice to selectively excite nuclear spins on the tomographic plane perpendicular to the body axis. In a state where a selective gradient magnetic field pulse (here, a y-axis gradient magnetic field pulse) 501 is applied, the current of the high-frequency pulse 502 is passed through the high-frequency coil 5. Next, the phase encoding gradient magnetic field pulse (Z-axis gradient magnetic field pulse here) 503 is applied, and the phase of the precession of the excited nuclear spin is encoded along the z-axis. Further, in the state in which the readout gradient magnetic field pulse (x-axis gradient magnetic field pulse) 504 is applied, the precession of the nuclear spin is detected by the receiving detection coil 7 as an NMR signal. The received NMR signal is converted into, for example, 256 digital signals by the receiver 8 and recorded in the memory of the computer 10.
[0046]
Such detection of the NMR signal is repeated while changing the intensity of the z-axis gradient magnetic field pulse 503. The intensity of the z-axis gradient magnetic field pulse 503 is repeated, for example, from the first value to the 128th value, thereby collecting data necessary for reconstruction of one tomographic image.
[0047]
In the figure, a gradient magnetic field pulse 506 on the y axis and a gradient magnetic field pulse 507 on the x axis are used to forcibly relieve the residual component of the precession of the nuclear spin in the immediately preceding measurement in the repeated measurement. Also, the y-axis gradient magnetic field pulse 508 and the x-axis gradient magnetic field pulse 509 cancel the phase shift between the above-described nuclear spin precession in the y-axis direction and the x-axis direction, and can be detected as an NMR signal with the maximum amplitude. It is used to
[0048]
FIG. 6 is a diagram for explaining the sequential creation of successive images 601, 602, 603,... From repetition of such NMR signal measurement, in which the y-axis gradient magnetic field and the x-axis gradient magnetic field are omitted. From the application of the high frequency pulse to the measurement of the NMR signal is the same as the sequence shown in FIG. 5, and the first view of the measurement of the NMR signal at the first value of the phase encoding gradient magnetic field (z-axis gradient magnetic field) pulse 503 is performed. The measurement of the NMR signal at the second value is referred to as the second view. The same applies to the third value and below.
[0049]
As described above, the NMR signal of each view is recorded as a digital signal in the memory of the computer 10. For example, when the measurement of the NMR signal up to the 128th view is completed, the NMR signal of a 128 × 256 matrix is stored in the memory of the computer 10. It will be recorded. The computer 10 two-dimensionally Fourier transforms the NMR signal of this matrix to obtain a tomographic image on the xz plane. This tomographic map 601 is displayed on the first display 12 and the second display 13.
[0050]
In continuous shooting, when the NMR signal is measured up to the 128th view, the z-axis gradient magnetic field pulse 503 is set to the first value again, and the NMR signal from the first view to the 128th view in the next cycle is sequentially measured. The
[0051]
The computer performs a two-dimensional Fourier transform of the new 128 × 256 matrix data obtained by adding the NMR signal of the first view of the next cycle to the NMR signal of the first cycle from the second view to the 128th view, and generates a tomogram 602. Constitute.
[0052]
Sequentially, a tomogram 603 is constructed from 128 × 256 matrix data obtained by adding the NMR signals from the third view to the 128th view and the next first view and second view NMR signals. By performing the image construction process in this way, new tomographic maps are displayed on the first display 12 and the second display 13 at each time interval for measuring the NMR signal of a single view. Assuming that the measurement time of the first view is about 50 milliseconds in the sequence of FIG. 5, 20 images are updated per second, so that the operator observes changes on the images in real time. can do.
[0053]
FIG. 7 is a diagram showing a measurement sequence for obtaining the temperature distribution performed in step 308. This sequence is also the same gradient echo sequence as the sequence shown in FIG. 5, and is set under the same conditions. That is, the same cross section as that measured in step 304 is excited, the NMR signal 705 is measured as, for example, 128 points of discrete data, the intensity of the phase encoding gradient magnetic field (z axis) 703 is changed, and the NMR signal is repeatedly generated. measure. The matrix data (for example, 128 × 128) obtained by this is recorded in the memory of the computer 10.
[0054]
The computer 10 performs a two-dimensional Fourier transform on this matrix data to obtain a phase diagram S (t) of the signal of each pixel. In this case, the NMR signal of the nuclear spin at the time of starting laser treatment (time 0) (equal to 36 degrees of body temperature) is measured in advance, and the phase of the signal of each pixel in the phase diagram S (0) at this time The echo time TE (time from excitation with the high-frequency pulse 701 until detection of the peak of the NMR signal 705) is adjusted so that becomes zero. By doing so, the phase of the phase diagram S (t) can be measured as a phase change of the resonance frequency of the NMR signal caused by a temperature change during the time t.
[0055]
Here, when the phases of S (0) and S (t) are compared for each pixel, a phase displacement amount ΔS (t) accompanying a temperature change corresponding to the position is obtained by calculation. Generally, the relationship between the phase shift amount ΔS (t) and the temperature change ΔT (t) is expressed by the following equation.
ΔT = ΔS / (TE × f × 0.01 × 10−6 × 360)
(Where f is the resonance frequency and TE is the echo time) From this equation, the temperature change during the treatment process, that is, the change from 36 degrees can be obtained.
[0056]
As described above, in step 308 of the temperature monitor, while the laser irradiation treatment is continued, the above temperature measurement is repeated at a constant time interval Δt. In this case, the temperature of the body tissue may be obtained from the change between the phase obtained in each temperature measurement and the reference phase diagram S (0), but the phase change is sequentially obtained based on the phase obtained in the immediately preceding measurement. Thus, it is possible to obtain a change with time in the temperature of the body tissue that minimizes the error.
[0057]
An example of such temperature measurement is shown in FIG. Here, the phase diagram S (t) obtained by the temperature measurement sequence (FIG. 7) at the time t is used as a reference (801). From this measurement time, at the time (t + Δt) after Δt set in step 307, the temperature measurement sequence is executed again to measure the 128 × 128 matrix NMR signal, and the phase diagram S (t + Δt) is calculated. Then, the phase change φ for each pixel in the phase diagram S (t + Δt) and the reference phase diagram S (t) is obtained (803). A temperature change between Δt is obtained from this phase change (804). Next, when a further Δt has elapsed from the time (t + Δt), the phase diagram S (t + 2Δt) is obtained again, and this time, S (t + Δt) and S (t Find the phase change of + 2Δt). In this way, by using the latest phase diagram for comparison calculation, if Δt is short, errors such as movement of the subject can be eliminated, and an accurate temperature change amount of the position information can be obtained.
[0058]
As a method of calculating the temperature change, in addition to the method of calculating from the above-described phase difference, for example, a diffusion constant depending on the temperature of the NMR signal described in Japanese Patent Publication No. 6-14911 is measured to determine the temperature change. A known method such as a method for obtaining the value can be employed.
[0059]
Next, the display method of the image obtained in step 304 (306) and the temperature information obtained in step 308 will be described.
[0060]
9A to 9C are diagrams showing examples of temperature display by the first display 12 and the second display 13, respectively. In (a), the temperature distribution calculated from the NMR signal measured in step 308 is displayed on the right half of the display 901 (the morphological image or functional image, hereinafter simply referred to as the morphological image) 901 for observing the therapeutic effect taken in step 306. Is displayed on the left half. In this case, the temperature distribution may be subjected to predetermined color coding so that the temperature can be recognized at a glance. For example, the hue can be changed sequentially from blue to yellow to red from 30 degrees to 50 degrees in steps of 5 degrees. With this display, the surgeon can proceed with the treatment while grasping the progress of treatment and the temperature around the treatment site.
[0061]
In (b), the morphological image is displayed on the entire surface of the display, and the temperature distribution diagram 903 is reduced and displayed so as to be movable to an arbitrary position on the display. According to this display method, a morphological image can be displayed in a large size, and a temperature distribution window screen 903 can be displayed on a part distant from the region of interest.
[0062]
In (c), the morphological image is displayed on the entire surface of the display, and the temperature calculated from the NMR signal is displayed by superimposing the contour line 904 and the numerical value 905 on the corresponding part of the morphological image. By selecting such a display method, it is possible to observe the treatment process and monitor the temperature with one image.
[0063]
FIGS. 10 (a) and 10 (b) show another example of the temperature display method. In FIG. 10 (a), the examination site is designated with a pointer (cursor) 1002 on the morphological image 1001, and the designated position is displayed. The temperature is numerically displayed at a desired position (a position that does not interfere with the morphological image) 1003 on the screen. This display method makes it possible to accurately grasp the temperature of the target site.
[0064]
FIG. 10 (b) shows a method of displaying the temperature change of the target part on the time axis. As described above, since the temperature measurement measures the change every moment, it is plotted with respect to the time axis to draw a graph. By adopting such a display method, it is possible to predict the time for the target portion to reach the target temperature from the temperature change curve. Such a temperature change curve can be displayed by providing a window at a position that does not interfere with the observation of the region of interest on the screen.
[0065]
As described above, the first embodiment of the present invention has been described. In this embodiment, in the process of continuously capturing images for observing the therapeutic effect, NMR signals are measured for temperature measurement at arbitrary time intervals. Temperature information such as temperature distribution charts, temperature values, graphs, etc. created using this function is displayed at the same time as an image for observing the treatment effect, thereby intervening with temperature changes such as cryosurgery and hyperthermia. Can effectively perform national treatment.
[0066]
In the above embodiment, the high-speed imaging sequence performed in step 304 (306) and the temperature measurement sequence performed in step 308 are exemplified by the gradient echo sequence (FIGS. 5 and 7). The present invention is not limited to this, and various modifications are possible. For example, a spin echo method sequence shown in FIG. 11 may be employed.
[0067]
The sequence by the spin echo method applies a 180 ° high frequency pulse at a predetermined time TE / 2 after excitation by a 90 ° high frequency pulse, inverts the phase of the nuclear spin, and measures an NMR signal as a spin echo. Since the phase of the nuclear spin diffused by the magnetic field distortion other than the gradient magnetic field can be matched, an image without the influence of the magnetic field distortion can be obtained. Therefore, it is suitable when priority is given to the drawing of the form.
[0068]
Even in this sequence by the spin echo method, if the echo time TE is set so that the phase error of the NMR signal is canceled at room temperature (for example, 36 ° C.), the diffusion constant and chemical shift value of the nuclear spin in thermal treatment Changes the phase of the NMR signal in TE slightly. Therefore, the temperature change can be calculated by obtaining the phase shift amount of the measured NMR signal.
[0069]
Next, a second embodiment of the present invention will be described with reference to the flowchart of FIG. In FIG. 12, the same steps as those in the flowchart of FIG. 3 are indicated by the same numbers. Also in this embodiment, after the subject is arranged at the center of the magnet, a tomographic image along the body axis is acquired, and a cross section including the treatment site is set based on the acquired tomographic image. The steps (301 to 304) until the start of the treatment are performed in the same manner as in the first embodiment shown in FIG.
[0070]
That is, the images 402 are displayed on the first display 12 and the second display 13 by continuous imaging (for example, MR fluoroscopy). In the next step 305, transpiration treatment of the affected area by laser irradiation is performed.
[0071]
Simultaneously with the start of the transpiration treatment, the NMR signal of the cross section including the treatment site is measured (311). The computer 10 calculates the NMR signal and obtains a distribution diagram of NMR signal intensity and a phase diagram of the NMR signal. As is well known, since an NMR signal has intensity information and phase information, an intensity distribution diagram, that is, a morphological image and a phase diagram can be obtained from the same signal. Also in step 311, a gradient echo method sequence may be employed when priority is given to high-speed imaging as an imaging sequence, and a spin echo method sequence may be employed when priority is given to morphological images.
[0072]
The morphological image is displayed on the first display 12 and the second display 13. At this time, similarly to the processing shown in FIG. 6, by displaying the absolute value while sequentially exchanging the NMR signals of one view, the image is updated every measurement time of one view, and the operator can observe the image in real time. It becomes possible.
[0073]
On the other hand, for the phase information, the first phase diagram S (t1) is obtained when 128 × 128 matrix data is obtained, and then the next phase diagram S (t2) is obtained when all 128 view signals are replaced. Ask. Next, the temperature change is obtained by calculation from the phase change of each pixel in these phase diagrams. The temperature calculation is the same as in the embodiment of FIG. In this way, each time the 128 view signals are sequentially switched, a phase diagram is obtained, and by calculating the temperature change sequentially from the phase difference from the previous phase diagram, as in the measurement shown in FIG. An accurate temperature change amount of the position information can be obtained by eliminating the error.
[0074]
The temperature information thus obtained is displayed on the first display 12 and the second display 13 simultaneously or alternately with the NMR signal intensity distribution map. As the display method of the temperature information, any display method such as a temperature distribution diagram, a numerical display, and a graph can be selected as in the first embodiment.
[0075]
In the example described above, the morphological image (absolute value diagram) is updated every 1 view measurement (about 50 milliseconds), and the temperature information is updated every 128 view measurements (about 6.4 seconds). After confirming the progress of the treatment on the tomogram, the operator finishes the examination and treatment, and removes the subject 1 from the magnet 2 and finishes (steps 309 and 310). When the treatment is continued, the process returns to step 305 and step 311 and the tomographic image capturing, display / temperature measurement, and display are repeated.
[0076]
According to the second embodiment of the present invention, a morphological and functional image (absolute value diagram of NMR signals) of a tomographic plane for observing the progress of treatment and a temperature distribution diagram (NMR) showing temperature changes associated with treatment. (Calculated from the phase diagram of the signal) can be obtained with the same measurement sequence, and the system configuration can be simplified.
[0077]
In the above embodiments, the case where temperature monitoring is performed in the process of continuously capturing morphological images has been described. However, the present invention is not limited to these embodiments, and morphological image capturing and temperature measurement are performed in any combination. It is also included in the scope of the present invention.
[0078]
【The invention's effect】
According to the present invention, as a function of the control means of the MRI apparatus, a function of arbitrarily combining temperature measurement in one imaging process is provided, and a form image and temperature information are combined and displayed as a function of the display means. By providing the function, it is possible to surely proceed the treatment while grasping the temperature of the treatment site, particularly in the interventional treatment accompanied by the heat treatment. Further, by providing not only a temperature distribution diagram but also a numerical function and a graph function as a temperature display function, temperature information that can be easily used by an operator can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of an MRI apparatus to which the present invention is applied.
FIG. 2 is a diagram showing a configuration of a display unit of the MRI apparatus.
FIG. 3 is a flowchart showing an embodiment of an inspection by the MRI apparatus of the present invention.
4 is a diagram showing a display example of a display in the inspection flow of FIG. 3;
FIG. 5 is a diagram showing an example of a high-speed imaging sequence employed in the MRI apparatus of the present invention.
FIG. 6 is a view for explaining continuous imaging and image processing employed in the MRI apparatus of the present invention.
FIG. 7 is a diagram showing an example of a temperature measurement sequence employed in the MRI apparatus of the present invention.
FIG. 8 is a flowchart showing an embodiment of temperature measurement according to the present invention.
FIG. 9 is a view showing a display example of a display by the MRI apparatus of the present invention.
FIG. 10 is a diagram showing another display example of the display by the MRI apparatus of the present invention.
FIG. 11 is a diagram showing another example of an imaging sequence employed in the MRI apparatus of the present invention.
FIG. 12 is a flowchart showing another embodiment of the inspection by the MRI apparatus of the present invention.
[Explanation of symbols]
1 …… Subject
2 …… Magnet
3 …… Gradient field coil
4 …… Gradient magnetic field power supply
5 …… High frequency coil
6 …… High frequency power amplifier
7 …… Detection coil
8 …… Receiver
9 …… Sequencer
10 …… Calculator
11 …… Storage device
12 …… First display
13 …… Second display
14 …… Console
15 …… Table

Claims (8)

A static magnetic field generating means for generating a constant magnetic field intensity, a gradient magnetic field generating means for generating a magnetic field strength gradient, a means for generating a high-frequency magnetic field, a means for detecting a nuclear magnetic resonance signal from the subject, and the nucleus A calculation / display means for reconstructing a morphological image or functional image of a subject using a magnetic resonance signal and displaying the result, and a control means for controlling each of these means,
The calculation / display unit includes a calculation unit that calculates a temperature change of the examination site of the subject, and a unit that displays the calculated temperature change as a contour line on the reconstructed image,
In the nuclear magnetic resonance signal measurement for temperature measurement controlled by the control means, an echo time (TE) is set at a time when the phase error of the nuclear magnetic resonance signal becomes zero at the same temperature as the body temperature of the subject. Magnetic resonance imaging apparatus.   The control means performs control for measuring a nuclear magnetic resonance signal for temperature measurement while measuring a nuclear magnetic resonance signal for a tomographic image of the subject, and reconstructs the nuclear magnetic resonance signal for a tomographic image 2. The magnetic resonance imaging apparatus according to claim 1, wherein temperature information obtained by calculating a nuclear magnetic resonance signal for temperature measurement is superimposed on the image as a contour line and displayed on the calculation / display means.   The control means creates signal intensity data for tomographic images and phase data for temperature information calculation using a nuclear magnetic resonance signal obtained from the subject, and reconstructs the signal intensity data. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the temperature information calculated from the phase data is displayed as a contour line on the calculation / display unit. The calculation and display means, said display a reconstructed image on the entire surface of said means for displaying, according to claim 2 wherein the temperature information the reconstructed image and displaying the window screen to the screen displayed, or 3. The magnetic resonance imaging apparatus according to 3. 4. The magnetic resonance imaging apparatus according to claim 2, wherein the calculation / display unit displays the temperature information so as to overlap with a corresponding position of the reconstructed image displayed on the display unit. 5. The calculation / display unit receives designation of a position on the reconstructed image via the display unit, and displays the temperature information corresponding to the designated position on the screen on which the reconstructed image is displayed. The magnetic resonance imaging apparatus according to claim 2 , wherein the magnetic resonance imaging apparatus is a magnetic resonance imaging apparatus.   The magnetic resonance imaging apparatus according to claim 1, wherein the calculation / display unit plots the calculated temperature change with respect to a time axis and displays the plot on the display unit. A static magnetic field generating means for generating a constant magnetic field intensity, a gradient magnetic field generating means for generating a magnetic field strength gradient, a means for generating a high-frequency magnetic field, a means for detecting a nuclear magnetic resonance signal from the subject, and the nucleus A calculation / display means for reconstructing a morphological image or functional image of a subject using a magnetic resonance signal and displaying the result, and a control means for controlling each of these means,
The calculation / display unit includes a calculation unit that calculates a temperature change of the examination region of the subject, and a unit that displays the calculated temperature change as a color-coded display in which the hue is changed for each temperature.
In the nuclear magnetic resonance signal measurement for temperature measurement controlled by the control means, an echo time (TE) is set at a time when the phase error of the nuclear magnetic resonance signal becomes zero at the same temperature as the body temperature of the subject. Magnetic resonance imaging apparatus.

Images