JPH0311224B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a method for observing internal tissue using nuclear magnetic resonance. In particular, it relates to correction of image data in nuclear magnetic resonance computer tomography equipment.

[Conventional technology]

Since the data obtained by nuclear magnetic resonance computer tomography equipment contains various noises, it cannot be reconstructed into an image as is. Many of these noises can be corrected by mathematically processing physical characteristics. However, device-specific noise cannot be corrected using general methods. The reference values for correction of such noise are not clear, and therefore the parameters and image levels vary depending on the device. An example is that the DC level of the image data changes from view to view due to variations in the gain of the amplifier or the offset of the analog-to-digital converter.

As a method for correcting changes in the DC level, a method is known in which the average value of received data near the end of each view is used and this is used as the offset for each view. This is because nuclear magnetic resonance diagnostic equipment collects data for a sufficiently longer time than the time it takes to obtain a signal, so the data at the end of each view contains almost no signal components. This method utilizes the fact that the offset value is the direct current component of the view. By averaging this data over a suitable time interval and subtracting it from the data for that view as an offset value, changes in offset that vary from view to view can be corrected.

However, with this method, sufficient correction cannot be made when the offset changes slowly within one view due to fluctuations in high-frequency pulses or gradient magnetic fields, that is, when the offset has a slope. There were flaws.

[Problem that the invention seeks to solve]

The present invention aims to improve the quality of reconstructed diagnostic images by correcting the DC component of observation data obtained by nuclear magnetic resonance.

[Means for solving problems]

The nuclear magnetic resonance data processing method of the present invention applies a static magnetic field, a high-frequency pulse that gives nuclear magnetic resonance, and position information to a signal in a magnet assembly that can be inserted into the inside of the magnet assembly. A method for processing nuclear magnetic resonance data in which a gradient magnetic field is applied to observe a nuclear magnetic resonance signal, and a calculation is performed to construct a nuclear magnetic resonance image from the signal, wherein the observation is specific to the magnet assembly. The above calculation is performed separately under substantially the same conditions for the case where the object is inserted and the case where the subject is inserted, and the above calculation is performed based on the observation data when the specific object is inserted. It is characterized by including an operation for correcting observation data.

Here, as the specific object, a substance whose properties are known, such as air or water, is used.

[Effect]

The method of the present invention is characterized in that at least one of before and after collecting data on the subject, data on air without a subject is collected, and image data is corrected using this data. That is, apart from observing the object, nuclear magnetic resonance signals of a specific object are observed, offset information for the entire receiving system is obtained from the observation data, and actual observation data from the object is corrected using this information. This makes it possible to correct the amount of offset that constantly changes during one view.

〔Example〕

FIG. 1 is a block diagram of a nuclear magnetic resonance computer tomography apparatus according to an embodiment of the present invention.

The magnet assembly 1 includes a static magnetic field coil 2 that applies a constant magnetic field to a subject, an excitation coil 3 that provides a high-frequency pulse to excite the spin of an atomic nucleus, and a magnet assembly that reflects information on the position of the subject in a signal. The present invention includes a gradient coil 4 that applies a gradient magnetic field, and a detection coil 5 that detects nuclear magnetic resonance signals from within the subject. FIG. 1 shows a portion of each of these coils.

The control computer 11 is connected to the sequence storage circuit 12. The sequence storage circuit 12 is connected to a gradient magnetic field drive circuit 13. Gradient magnetic field drive circuit 13
is connected to the gradient coil 4. The static magnetic field power supply 14 is connected to the static magnetic field coil 2 . High frequency oscillator 15
is connected to the gate modulation circuit 16 and the phase detection circuit 19. The gate modulation circuit 16 is connected to a high frequency power amplifier 17 and a phase detection circuit 19. High frequency power amplifier 17 is connected to excitation coil 3 .
The detection coil 5 is connected to a preamplifier 18. Preamplifier 18 is connected to phase detection circuit 19 .
Phase detection circuit 19 is connected to data storage device 20 . Data storage device 20 is connected to interface circuit 21 . The interface circuit 21 is connected to a data processing computer 22. The data processing computer 22 is connected to a display device 23 and a magnetic disk storage device 24 .

The control computer 11 controls the operation of the device of this embodiment. Furthermore, by rewriting the contents of the sequence storage circuit 12, various operation sequences can be realized.

The sequence storage circuit 12 generates a timing signal for collecting observation data of nuclear magnetic resonance signals, and controls the operation of the gradient magnetic field drive circuit 13 and the gate modulation circuit 16. Thereby, the sequence storage circuit 12 controls the generation sequence of gradient magnetic fields and high-frequency pulses.

A gradient magnetic field drive circuit 13 is connected to each of the x-axis, y-axis, and z-axis gradient coils 4 and applies a gradient magnetic field within the magnet assembly.

The high frequency oscillator 15, the gate modulation circuit 16, and the high frequency power amplifier 17 are connected to the magnet assembly 1.
A high-frequency pulse is applied to the air or the subject to excite the atoms that make up the air or the subject. High frequency oscillator 15 generates a high frequency signal. The gate modulation circuit 16 operates the high frequency oscillator 1 according to the timing signal from the sequence storage circuit 12.
The high frequency signal outputted by 5 is modulated to generate a high frequency pulse. The high frequency power amplifier 17 amplifies the power of the high frequency pulse output from the gate modulation circuit 16 and supplies it to the exciting coil 3.

Preamplifier 18 and phase detection circuit 19 collect nuclear magnetic resonance signals. The preamplifier 18 amplifies the nuclear magnetic resonance signal detected by the detection coil 5. The phase detection circuit 19 refers to the output signal of the high frequency oscillation circuit 15 and performs phase detection on the output of the preamplifier 18 . The observation data obtained by this is
The data is stored in the data storage device 20 and sent to the data processing computer 22 through the interface circuit 21.

The feature of the present invention lies in the control sequence of this device. That is, the data processing computer 22 stores observation data of the air and the object in the magnetic disk storage device 24, further corrects the observation data of the object using the air observation data as correction data, and uses this observation data. It is reconstructed into an image and displayed on the display device 23.

FIG. 2 is a flowchart showing the collection of correction data by the apparatus of this embodiment.

The correction data is based on the same conditions as the actual data collection for the air inside the magnet assembly 1.
Collected using the same parameters. The required number of views of air observation data are collected and averaged, and the resulting data is stored in the magnetic disk storage device 2.
Record in the correction file No. 4. The correction data recorded in the correction file represents changes within one view of the offset of the amplifier and analog-to-digital converter provided in this device.

FIG. 3 is a flowchart showing correction of observation data of a subject by the apparatus of this embodiment.

Correction data is subtracted for each view from the observation data of all views, further image processing calculations are performed, and this data is stored in the magnetic disk storage device 24 again as image data. Thereby, images can be displayed on the display device 23 as needed.

In this example, the air observation data of the magnet assembly 1 was used as the correction data.
The present invention can also be practiced using water and other specific substances.

As an application of the present invention, there is a method in which data is collected by applying a gradient magnetic field without applying a high-frequency pulse while the subject is inserted into the magnet assembly 1, and this data is used as offset data on the receiving side. The present invention can also be carried out by

In addition to subtraction, calculations for correction include
There are many correction methods, such as dividing to normalize, multiplying or adding the reciprocal, or calculating after taking the logarithm, and the present invention can be implemented using these as well. Can be done.

〔Effect of the invention〕

As explained above, the data processing method using nuclear magnetic resonance according to the present invention makes it possible to easily correct the amount of offset that constantly changes during one view. As a result, clear diagnostic images can be obtained, which is highly effective in medical diagnosis.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a nuclear magnetic resonance computer tomography apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart showing the collection of correction data. FIG. 3 is a flowchart showing correction of observation data of a subject. 1... Magnet assembly, 2... Static magnetic field coil, 3... Excitation coil, 4... Gradient coil, 5
...Detection coil, 11...Control computer, 12...
Sequence storage circuit, 13... Gradient magnetic field drive circuit, 14... Static magnetic field power supply, 15... High frequency oscillator, 16... Gate modulation circuit, 17... High frequency power amplifier, 18... Preamplifier, 19... Phase Detection circuit, 20...Data storage device, 21...Interface circuit, 22...Data processing computer, 2
3...Display device, 24...Magnetic disk storage device.

Claims (1)

[Claims] 1. A static magnetic field, a high-frequency pulse that causes nuclear magnetic resonance, and a gradient magnetic field that reflects position information in a signal are applied to a magnet assembly that has a shape that allows the subject to be inserted into the magnet assembly. In the nuclear magnetic resonance data processing method, the above observation is performed by inserting a specific object into the magnet assembly. The above calculation is performed separately under substantially the same conditions for the case where the object is inserted and the case where the object is inserted, and the above calculation corrects the observed data when the object is inserted by the observation data when the specific object is inserted. A method for processing nuclear magnetic resonance data, characterized by including calculation. 2 Claim 1 in which the specific object is air
The method for processing nuclear magnetic resonance data described in Section 1. 3. The method for processing nuclear magnetic resonance data according to claim 1, wherein the specific object is water.