JPS63220855A - Magnetic resonance diagnostic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic resonance diagnostic apparatus that obtains an MR image of a subject using magnetic resonance phenomena.

(Prior technology) It has been understood that X-ray diagnostic equipment that uses X-rays, which have been the mainstream in the past, will make a great contribution to clinical medicine, but there is a risk that they may be teratogenic or carcinogenic. was there. On the other hand, in recent years, there has been remarkable development of magnetic resonance diagnostic devices that utilize magnetic resonance signals that do not involve the above-mentioned risks.

This magnetic resonance diagnostic device differs from the above-mentioned X-ray diagnostic device in that it places part or all of the subject in a magnetic field and applies predetermined high-frequency pulsed electromagnetic waves (RF waves or R, F pulses) to the subject. The target nuclide inside is excited, and after this excitation, the excited nuclide returns to its original energy state, which is detected by a coil. This detection signal is called an MR multiplied signal and contains various information regarding the target nuclide, which is analyzed and applied to diagnosis. Therefore, there are no problems that occur with conventional X-ray diagnostic equipment. However, since the RF waves use high frequencies, a problem arises in that the subject is heated.

(Problem to be solved by the invention) In other words, the subject (human body) is a conductor, and the irradiated RF waves generate an induced current, and due to the resistance of the human body, the induced current becomes heat, which is absorbed and the result is It is heated as

In particular, the above problem is serious in the multi-slice method in which a plurality of tomographic planes are successively obtained, and it is necessary to limit the number of slices related to the RF wave absorption matrix.

This RF wave membrane absorption amount, RF wave absorption rate (SAR: 5pe
It is determined by the product of the RF wave irradiation amount and the RF wave irradiation amount.

The RF wave absorption rate SAR is proportional to the weight V of the human body, and is determined by the following equation (1).

5AR=Ps-Nτ/TR-1/V-(1) where Ps2 RF wave large input τ to the human body: rectangular RF pulse width, T
R: pulse repetition time, ■=human weight. The number N of multi-slices must satisfy the following condition.

Here, the current standard is SAR<0.
Substitute 4W/N3.

Other parameters other than body weight V in the above equation (2) are determined by the imaging conditions.

In this sense, measuring the weight of the subject is an important element,
Conventionally, the weight of the object to be examined has been determined manually based on the operator's intuition, which has led to problems in that the amount of RF wave membrane absorption is not appropriate and that the work is time-consuming.

An object of the present invention is to provide a magnetic resonance diagnostic apparatus that solves the above-mentioned problems.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a means for automatically measuring the weight of the subject is provided in the bed portion, and the allowable RF is determined based on the measurement result by this means. A calculation means for calculating the wave irradiation amount and the limit number of multi-slices is provided.

(Function) The body weight of the subject can be measured simply by placing it on the bed, and the number of slices can be calculated based on the measurement results, thereby eliminating the inconvenience caused by heating the subject.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention.

In the figure, the apparatus according to the embodiment of the present invention includes a system control section 3 having a control section 1 and a limit number of tomographic plane calculation means 2, a scan controller 4, a bed 5, and a bed 5, which are respectively controlled by the system control section 3. It is configured to include a weight measuring means 6, a gantry device 7 whose scanning is controlled by a scan controller 4, and an input device 8 for inputting photographing conditions and the like.

The gantry device 7 has a uniform static magnetic field generating means and an imaging hole through which the subject can be taken out, and can be placed at any position by transmitting RF pulses to the subject inserted into the imaging hole (not shown). The system is designed to obtain multiple tomographic images.

The bed 5 is, as shown in FIG. 2, an embodiment thereof.
The mount device 7 is placed in a horizontal state while placing the subject Q thereon.
A top plate 5a serving as a subject mounting means that can move in and out of the photographing hole.
The structure includes an upper support part 14 that supports the top plate 5a, and a lower support part 15 that supports the upper support part 14 in the vertical direction via a plurality of spring members 9.

Further, the upper support part 14 and the lower support part 15 have a gap 1 and are supported by the spring member 9.
Changes in this gap H are detected by a gap sensor 10, which is provided toward the right in the figure and constitutes weight measuring means, which will be described later. In other words, this gap H is the top plate 5a.
Since it expands and contracts in proportion to the weight of the subject Q placed thereon, the weight of the subject Q placed thereon can be determined by measuring this expansion/contraction value. In addition, 11 and 12 in the figure are measuring devices for measuring the height of the subject Q placed thereon.
These are attached to a guide member 13 provided along the long axis of the top plate 5a. Further, the lower support portion 15 can be expanded and contracted in the direction of arrow B.

FIG. 3 shows a modified example of the bed. Components that are the same as those shown in FIG. 2 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

The difference between the stand 16 shown in the figure and the bed 5 shown in FIG. 2 is that in the bed 5, the upper support part 14 and the lower support part 15 was detected by the gap sensor 10,
In the illustrated bed 16, the weight of the subject Q is detected by a pressure sensor 17. Pressure fluctuations detected by this pressure sensor 17 are converted into electrical signals.

Details of the measurement device 11 and 12 for measuring the height of the subject Q are given in Section 4.
It is as shown in the figure. This is necessary because the subject Q is placed between the measuring instruments 11 and 12, and the measuring instrument 11 is set so as to come into contact with the head of the subject Q, for example. One end of a rope 12b is attached to a part of this measuring device 11, and the measuring device 12 is attached to the other end. A rotary encoder 12a is attached to this measuring instrument 12, and the other end of the rope 12b is attached to this rotary encoder 12a. From this, when the measuring device 12 is moved in the direction of arrow C using the measuring device 11 as a reference, a pulse is output from the rotary encoder 12a in proportion to the length of the rope. This pulse signal is input to the control section 1. As another embodiment, a plurality of pressure sensors may be arranged at regular intervals in the long axis direction of the top surface of the top plate 5a, and the height may be calculated from this, and a scale may be provided on the side surface of the top plate 5a. It is also possible to measure the height directly and have the operator obtain this value. Alternatively, if such a measuring device is not used, height may be estimated from weight.

The weight measuring means 6 receives an electric signal from the gap sensor 10 or the pressure sensor 17 and calculates the weight of the subject Q placed on the top plate 5a.

First, when obtaining a tomographic image of the entire subject Q, it is sufficient to convert the weight to weight based on the output signal from the sensor, but when obtaining a tomographic image of a part of the body, the following procedure is required. Bye.

Assuming a standard subject model shown as R in Fig. 5, vote W(t
) in advance. The height (horizontal axis) of this standard subject model R is set to 1, and the weight is set to 1.

Note that the vertical axis is the weight at the position of the tomographic plane. Normally, the weight distribution of the specimen is almost constant regardless of individual differences, so
This is expressed as W(t). Then, the weight of that part is Vl
Then, Vl = T: W(t)dt (3). In addition, K is the measured total weight of the subject Q, a is h/L shown in FIG. 6, L is the value determined by the measuring device 11.12, and h is the distance h from the top of the head. By the way, it shows that it has been disconnected. To be more specific, when a standard-sized subject is divided into tomographic planes of thickness Δh perpendicular to the body axis, it is determined from the cross-sectional weight q (h) at a distance i1h from the subject's head using the following equation.

Shi=h/Lo...
(4) Here, Lo is the height of the standard subject model, T.

indicates the weight of the standard specimen model. And actually,
The weight ■ at the point (ba>) shown in Figure 6 is calculated by the following formula (6
) is determined by

V=T l//: w(od t - (6) Furthermore,
If the coil surrounds almost the entire subject, it may be simply determined from heavy IT as V=k. In this case, the coefficient is a constant close to 1.

The limit number of tomographic planes calculation means 2 is provided with a plurality of tables as shown in FIG. 7 for each pupil shadow condition.

This table represents the weight V (Kg) of the subject on the horizontal axis and the number N of tomographic planes on the vertical axis based on the formulas (11 and (2)), and the RF pulse repetition time R is 200, 300.
.

500, 1000 in sec).

Therefore, from the input device 8, the nine shadow conditions (RF wave input Ps to the human body, rectangular RF pulse width τ, pulse repetition time TR)
When the output V from the weight measurement means 6 of the subject is input, the number N of tomographic planes corresponding to the intersection with the straight line on the extension of the weight v is selected and output to the control unit 1. It is supposed to be done. In the control unit 1, the selected number N
Based on this, the scan controller 4 is controlled to perform scanning.

The operating procedure of the magnetic resonance diagnostic apparatus configured as described above,
Explain the effects.

The operator places the subject Q on the top plate 5a of the bed 5. The weight of the placed subject Q is detected by the gap sensor 10 or the pressure sensor 17, and based on this detection, the weight measuring means 6 automatically calculates the weight. In this way, the present invention eliminates the error caused by estimating weight or estimating height based on the operator's intuition, and
Accurate test weight can be determined.

The operator inputs photographing conditions and the like using the input means 8.

Then, an @shadow start button (not shown) is pressed.

At this time, the limit number of tomographic planes calculation means 2 calculates the limit number of tomographic planes N@ by the above-described operation, and in response to this, the control unit 1 gives an instruction to the jump scan controller 4 to start imaging. In this way, since the operator does not have to judge the number of tomographic planes before photographing the tomographic planes, the work can be performed accurately, safely, and quickly.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the invention.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to provide a magnetic resonance diagnostic apparatus that can prevent the adverse effects of a temperature rise caused by RF pulse irradiation on a subject.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the device of the present invention, Fig. 2 is a side view of an embodiment of a bed, Fig. 3 is a side view of a modified version of the bed, and Fig. 4 is a height measuring device. A perspective view of the external appearance of the embodiment, FIG. 5 is an explanatory diagram of the standard subject model that is the basis for calculating the subject weight, FIG. 6 is an explanatory diagram of the subject weight calculation, and FIG. 7 is the calculation within the tomographic plane number calculation means. It is an explanatory diagram showing an example of a table. DESCRIPTION OF SYMBOLS 1... Control part, 2... Critical fault plane number calculation means, 3.
...System control unit, 4.Scan controller, 5.Bed, 5a.
...Top plate, 6. Weight measurement means, 7. Frame device,
8... Input device, 9... Spring member, 10... Gap sensor. Agent Patent Attorney Nori Chika Ken Can Zhou Dai Hu Qu Hu Fig. 5 Fig. 6

Claims (2)

[Claims] (1) It has a pedestal device equipped with a uniform static magnetic field generating means and a bed equipped with a pedestal mounting means on which a subject is placed and which can at least move in and out of the pedestal, and In a magnetic resonance diagnostic apparatus that obtains magnetic resonance signals of a plurality of tomographic planes of a subject by irradiation, a measuring means for measuring the weight of a subject placed on the subject mounting means, and a measurement from the weight measuring means. A magnetic resonance diagnostic apparatus comprising: a calculation means for calculating the critical number of tomographic planes based on the relationship between the result and the allowable RF wave absorption amount of the subject. (2) The magnetic resonance diagnostic apparatus according to claim 1, wherein the weight measuring means has a function of measuring a portion of the weight in relation to the height of the subject.