JPH04138133A - Coil position detecting method and mr device - Google Patents

Abstract

PURPOSE:To accurately detect a coil position in a magnet assembly and arbitrarily change the position by forming a template on the basis of a shading pattern, and undertaking template matching with an MR image obtained with the same surface coil. CONSTITUTION:Before taking a diagnostic image, a template is prepared on the basis of the shading pattern of each of receiving coils 22a to 22d. Thereafter, image data is calculated on the basis of an MR signal obtained from an MR device for reconstructing an MR image for detecting a coil position. In the MR image, there appears a color shade representing a difference in the tissue of a subject, together with shading reflecting the sensitivity distribution of the receiving coils 22a to 22d. Subsequently thereto, template matching is undertaken, using a stored template and the positions of the aforesaid coils 22a to 22d are recognized. Then, the positional coordinate of the aforesaid coils 22a to 22d in a magnet assembly is calculated from a positional coordinate on the MR image for detecting the recognized coil positions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a coil position detection method and an MR device. The present invention relates to a coil position detection method and an MR apparatus for detecting the position.

[Prior Art] Conventionally, when a coil unit (multiphased array coil) in which multiple coils are arranged side by side as a surface coil is used in an MR apparatus, one coil of the same size is used.
Higher S/N is obtained than when using two coils, and one coil of the same size as a small coil placed in parallel.
It is known that a wider sensitivity range can be obtained than when using one coil (see SMRM Society Journal, 7th Ordinary General Meeting, P875, published in 1988).

MR171 equipped with the above coil unit! In F, it is necessary to know the sensitivity distribution of each coil in the magnet assembly, that is, the position of each coil, when combining the MR multiplied signals obtained from each coil so that the S/N is the best.

Conventionally, before feeding the cradle into the magnet assembly, an operator uses a ruler or the like to measure the position of each coil on the coordinate axes set on the cradle. Assuming that the MR device matches the coordinate axes set on the cradle or the coordinate axes set on the magnet assembly,
Each coil is treated as being at the obtained measurement position.

[Problems to be Solved by the Invention] The conventional method described above requires manual measurement each time the coil unit is set on the cradle, which is troublesome and has the problem that errors are likely to occur in the measured values.

Further, there is a problem in that it is difficult to arbitrarily change the position of the coil unit depending on the imaged area to take an image.

Furthermore, if the coil unit is displaced due to the cradle or the coil unit stopping from its predetermined position in the magnet assembly, or coming into contact with the subject, the measurement position may differ from the actual coil position in the magnet assembly. be.

Therefore, an object of this invention is to be able to accurately detect the position of a coil within a magnet assembly with a simple operation, and to
It is an object of the present invention to provide a coil position detection method and an MR apparatus that can perform imaging by arbitrarily changing the position of the coil depending on the imaging area.

[Means for Solving the Problems] The coil position detection method of the present invention includes the steps of creating a template representing shading by a surface coil, and performing template matching using the template on both MR images obtained from a subject. , and a step of recognizing the position of the surface coil on the MR image.

The MR apparatus of the present invention includes a means for creating a template representing shading by a surface coil, and a means for performing template matching using the template for both MR images obtained from a subject, and determining the position of the surface coil on the MR image. Its structural feature is that it is equipped with means for recognizing.

[The MR images obtained using the active co-surface coil reflect the sensitivity distribution of the surface coil in the brightness of each pixel, so the MR images exhibit shading, that is, uneven brightness, which is characteristic of the surface coil.

Therefore, by creating a template from this shading pattern and performing template matching with the above template for both MR images obtained using the same surface coil, it is possible to recognize the position of the surface coil on the MR image. .

If the position on the MR image can be recognized, the position of the surface coil within the magnet assembly can be calculated.

Therefore, after the surface coil and the subject are sent into the magnet assembly, the position of the surface coil can be detected by the MR device.

Note that the template may be generated by calculation from current distribution data of the surface coil.

[Example] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. Note that this invention is not limited to this.

FIG. 2 is a perspective view of a surface coil, and FIG. 3 is a block diagram of an MR apparatus according to an embodiment of the present invention.

In FIG. 2, the coil unit 20 includes four substantially rectangular receiving coils 22 inside a rectangular plate-shaped casing 21.
It is composed of a, 22b, 22c, and 22d arranged in parallel. Each receiving coil 22a, 22b, 2
2c and 22d are lead wires 23a and 23b for separately transmitting the received MR double signal to the preamplifier 9 of the MR device 1.
23c and 23d are connected.

In FIG. 3, in the MR apparatus 1, a computer 2 controls the overall operation based on instructions from a console 13.

Based on the stored sequence, the sequence controller 3 operates the magnetic field drive circuit 4 to generate a static magnetic field and a gradient magnetic field with the static magnetic field coil and gradient magnetic field coil of the magnet assembly 5. Also controls the gate modulation circuit 7,
The RF signal generated by the RF transmitting circuit 6 is modulated and applied to the transmitting coil in the magnet assembly S from the RF power amplifier 8.

Receiving coil 22a22b in magnet assembly S
, 22c, MR multiplied signal obtained at 22d,
The signal is input to the computer 2 via a preamplifier 9, a phase detector 10, and an A/D converter 11 provided separately for each receiving coil 22a, 22b, 22c, and 22d.

The computer 2 calculates image data by combining the MR multiplied signals obtained from each A/D converter 11, and displays the image on the display device 12.

Next, a procedure for implementing the coil position detection method of the present invention using the MR apparatus 1 will be described with reference to FIGS. 1 and 4.

Before capturing a diagnostic image, the MR apparatus 1 uses the coil unit 20 to obtain both MR images from the subject. Then, each of the receiving coils 22a, 22 in which both the MR images are displayed is
A template is created based on the shading patterns b, 22c, and 22d (step R1).

At this time, the subject has the receiving coil 22a,
It is preferable that the shading of 22b, 22c, and 22d appears clearly.

The MR device 1 stores the created template.

Next, as shown in FIG. 4(a), the coil unit 20 and the subject M are set on the cradle 32 movably provided on the table 31 (step R2).

Subsequently, the cradle 32 is moved to the position shown in FIG. 4(b).
As shown in FIG. 2, the coil unit 20 and the subject M are positioned within the cylindrical cavity 5a of the magnet assembly 5 (step R3).

Therefore, the MR apparatus 1 measures the MR multiplied signal for coil position detection via each receiving coil 22a, 22b, 22c, and 22d of the coil unit 20 (step Sl). Preferably, this step is performed with a fast scan.

Next, the MR apparatus 1 calculates image data based on the obtained MR multiplied signal and reconstructs an MR image for coil position detection (step S2). At that time, the image data is smoothed by applying an appropriate low-pass filter. This step is performed in a normal image reconstruction routine.

The above MR image for coil position detection includes the receiving coil 22
In addition to shading reflecting the sensitivity distribution of a, 22 b, 22 c, and 22 d, shading representing differences in the tissues of the subject also appears.

The reason why smoothing is performed during image reconstruction is to prevent errors from occurring due to shading representing differences in the tissues of the subject when the MR device 1 recognizes the shading pattern and creates a template. .

Subsequently, the MR apparatus 1 performs template matching on the MR image for coil position detection using the stored template (step S3). By template matching, the MR device 1 can detect the MR position of the coil.
Receiving coils 22a, 22b, 22c, 22d on the image
Recognize the location of.

Therefore, the MR device 1 uses the recognized coil position detection MR
The position coordinates within the magnet assembly 5 are calculated from the position coordinates on the image. In this way, each receiving coil 22a on the coordinate axis set in the magnet assembly 5
, 22b, 22c.

The position of 22d can be detected (step 84).
.

As described above, each receiving coil 22a, 22b, 22
Once the positions of 22c and 22d are known, the MR system [1 performs a scan to form a diagnostic image, and proceeds to the step of obtaining both diagnostic MR images.

In the above description, one template is used, but each receiving coil 22a, 22b, 22c.

If you create several templates by changing the inclination of the receiving coils 22d with respect to the You can also know its direction.

FIG. 6 is a conceptual diagram of template matching.

In Figure 6, t (x, y) is the template T
The weighting factor at the point (x, y) of f (x, y)
represents the brightness of a pixel at the point (x, y) of the MR image Im for coil position detection.

In template matching, as shown in FIG.
The template T is superimposed on the R image Tm so as to be at the point P(i, j), and the degree of similarity between the template T and the overlapping partial pattern of the MR image 1m for coil position detection is measured, and the value is calculated as the point P(i).

j) is a method of determining the probability that a detection target exists.

If the above operation is performed over the entire MR image Im for coil position detection, the position where the degree of similarity is maximum will be detected, so the MR apparatus 1 detects the detection target, that is, the receiving coils 22a, 22b, 22c, and 22d at that position. recognize that it is located.

The similarity S(i, j) at the point P(i, j) is expressed, for example, by the following equation.

Here, f (i, j) is the brightness of the pixel of the MR image Im for coil position detection at the point P (i, j), and t
(i, j) is the weighting coefficient of the template T at the point P(i, j), and a and b are the lengths of the template T in the X-axis direction and the y-axis direction, respectively.

In template matching, the above equation (1) may be calculated directly, but in order to speed up the calculation, it is preferable to use a method using Fourier transform.

The above-mentioned receiving coils 22 a, 22 b, 22
c.

In addition to the template that reflects the sensitivity distribution of 22d, a template that binarizes this sensitivity distribution may be used. This allows calculations to be performed faster.

FIG. 5 is a flowchart showing another embodiment of the coil position detection method of the present invention.

In the embodiment described above, smoothing is performed during image reconstruction in order to reduce the influence of shading representing differences in tissue of the subject appearing in the MR image for coil position detection. However, in an MR image for coil position detection obtained from a human body, it may be difficult to recognize a shading pattern even after smoothing.

The embodiment shown in FIG. 5 is designed to eliminate the influence of the tissue of the subject.

In FIG. 5, steps R1 to R3 are the same as in the embodiment of FIG.

In steps S1 and S2, an MR signal for coil position detection is measured in the same manner as in the embodiment shown in FIG. 1, and a first MR image for coil position detection is reconstructed from this MR multiplied signal.

Let Mn (x, y) be the brightness of the pixel at both the obtained MR image points (x, y).

Here, n is each receiving coil 22a, 22b, 22c, 2
With the coil number indicating 2d, n=1. It is 2°3.4.

In step S3, instead of the coil unit 20, a body coil with uniform sensitivity distribution is used to measure the MR signal for coil position detection.

In step S4, a second MR image for coil position detection is reconstructed from the obtained MR multiplied signal.

Let B (x, y) be the brightness of the pixel at the point (x, y) of the second MR image obtained in this way.

In step S5, the ratio Mn (x, y) /B (x, y) of the brightness Mn (x, y) in the first MR image for coil position detection to the brightness B (x, y) in the second MR image is taken,
The brightness Mn (x, y) in the first MR image is corrected. This correction can eliminate the influence of the tissue of the subject.

If the value of B (x, y) is smaller than a predetermined threshold, it is calculated as Mn (X, Y)/B (x, y)=0.

In step S6, the first M for corrected coil position detection is
Regarding the R image, template matching is performed in the same manner as in the above embodiment, and in step S7 each receiving coil 22a,
The positions of 22b, 22c, and 22d are detected.

In the above explanation, a scan is performed to obtain an MR signal for coil position detection before obtaining a diagnostic MR multiplied signal, but only a scan is performed to obtain both diagnostic MR images, and both MR images obtained by Then, template matching may be performed.

This eliminates the need for scanning to obtain the MR signal for coil position detection.

Further, the template may be generated by calculation from current distribution data of the surface coil.

Further, the coil unit 20 may be a transmitting/receiving coil.

[Effects of the Invention] The coil position detection method and MR device of the present invention can accurately detect the position of the coil in the magnet assembly with a simple operation, and can arbitrarily change the position of the coil depending on the imaging area. can be imaged.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the procedure of an embodiment of the coil position detection method of the present invention, FIG. 2 is a perspective view of an embodiment of a coil unit used in the coil position detection method of the present invention, and FIG. An overall block diagram of an embodiment of the MR device of the invention, FIG. 4 is an explanatory diagram of the magnet assembly, and FIG.
The figure is a flowchart showing the procedure of another embodiment of the coil position detection method of the present invention, and FIG. 6 is a conceptual diagram of template matching. (Explanation of symbols) 1...MR device 5...Magnet assembly 20...Coil unit 21...Casing 22a, 22b, 22c, 22d-=Receiving coil T...
-Template Im...MR image for coil position detection 31...Table 32...Cradle M...Subject

Claims (1)

[Claims] 1. Creating a template representing shading by the surface coil, and MR obtained from the subject.
A coil position detection method comprising the steps of performing template matching on an image using the template and recognizing the position of a surface coil on the MR image. 2. Means for creating a template representing shading by the surface coil; and means for performing template matching using the template on an MR image obtained from a subject and recognizing the position of the surface coil on the MR image. An MR device characterized by: