JP3343391B2 - MRI equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MRI apparatus capable of warning a rise in the temperature of a gradient coil before executing a scan sequence in the MRI apparatus.

[0002]

2. Description of the Related Art MRI apparatus (magnetic resonance imaging apparatus)
Is an apparatus for observing a nuclear magnetic resonance (NMR) phenomenon and capturing a tomographic image of a subject. In this MRI, an object is observed by detecting a radio frequency (RF) signal generated by an NMR phenomenon in the object.

Further, a minute gradient magnetic field for adding spatial information to an NMR signal is used to select a direction, a plane, and a line in a projection restoration method or a selective irradiation method. In order to generate the gradient magnetic field, a current is supplied from a gradient magnetic field power supply circuit to a three-axis gradient magnetic field coil of x, y, and z.

[0004]

In this type of gradient magnetic field coil, heat generation is a serious problem due to its properties. In recent years, heat generation has been increasing with the speeding up of scanning. Therefore, it is expected that the temperature of the gradient magnetic field coil gradually increases during the execution of the scan sequence, making it difficult to execute the scan.

[0005] In order to cope with such a situation, a device has been proposed in which a temperature sensor is attached to the gradient magnetic field coil to measure the temperature, and when the temperature rises to a predetermined temperature, the scan sequence is stopped.

This type is disclosed in Japanese Patent Application Laid-Open No. 3-261455.
JP-A No. 2-61950 and JP-A-4-176.
No. 440 (Japanese Patent Application No. 2-303879). However, if the scanning is stopped in the middle of the scanning sequence as described above, there is a problem that data and measurement time obtained by the previous scanning are wasted.

The present invention has been made in view of the above points, and an object of the present invention is to provide an MRI apparatus capable of estimating a gradient magnetic field coil temperature during a scan before starting a scan and outputting an alarm. That is.

[0008]

SUMMARY OF THE INVENTION The above object is achieved by applying a high frequency rotating magnetic field to an R atom emitted from an excited nucleus.
In an MRI apparatus that detects F energy, a temperature detecting unit that detects a temperature of a gradient magnetic field coil, a scan parameter setting unit that sets a scan parameter for MRI scan, a scan parameter set by the scan parameter setting unit, Temperature estimating means for estimating the temperature of the gradient magnetic field coil during scanning or at the end of scanning with reference to the temperature of the gradient magnetic field coil detected by the temperature detecting means, and at the time of performing or ending the scanning estimated by the temperature estimating means And an alarm output means for outputting an alarm about the execution of the scan according to the temperature of the MRI.

[0009]

According to the set parameters, the temperature rise of the gradient magnetic field coil is predicted, and the temperature of the gradient magnetic field coil during the scan starts scanning according to the measured temperature before the scan of the gradient magnetic field coil is started and the predicted temperature rise. As expected before. An alarm is output based on the predicted temperature before the start of scanning.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing a schematic configuration of a main part of an MRI apparatus according to an embodiment of the present invention. In FIG. 1, a scan parameter setting means 11 is for setting various parameters at the time of scanning.
Expect a temperature rise of 0. The alarm output means 13 outputs an alarm based on the result of the prediction of the temperature of the gradient magnetic field coil 40 by the prediction means 12. The temperature detecting means 41 is for measuring the temperature of the gradient magnetic field coil 40.

FIG. 2 is a configuration diagram showing a schematic configuration of the entire MRI apparatus of the present embodiment. The operator console 10 includes a display device and an input device. The operator console 10 includes a scan parameter setting unit 11, a prediction unit 12, and an alarm output unit 13. The scan controller 20 generates a gradient magnetic field coil drive current signal based on the scan parameters input on the operator console 10 and transmits the signal to the gradient magnetic field power supply 30. The gradient magnetic field power supply 30 generates a gradient magnetic field drive current according to a predetermined scan parameter. The gradient magnetic field drive current is supplied to the gradient magnetic field coil 40.

The operation of the apparatus according to this embodiment will be described with reference to the flowchart of FIG. At the start of scanning, scan parameters are input via scan parameter setting means 11 installed on the operator console 10 (step 1 in FIG. 3). The scan parameters include the type of pulse sequence,
There are various setting values. For example, data (numerical values) such as a repetition period, an echo time, an echo number, a matrix number, an imaging range, and a slice thickness.

When the scan parameters are thus input (time t1 in FIG. 5), the prediction means 12 in the operator console 10 before the start of the scan (time t2 in FIG. 5).
The alarm output means 13 performs the following operation.

When the scan parameters are input, the operator console 10 calculates a current pattern to be supplied to the gradient coil 40 with reference to the scan parameters. Then, referring to the current pattern supplied to the gradient coil 40, the heat estimating means 12a in the estimating means 12 is referred to.
Finds the effective current Irms, and the time estimating means 12b finds the energizing time t of the gradient coil 40. The effective current Irms in this case is obtained by integrating from the time 0 to the time TR by the following equation (1).

[0015]

(Equation 1)

FIG. 4 is a waveform diagram showing an example of a current pattern supplied to the coil when the spin echo method is used.
Here, (1) indicates an RF pulse, and (2),
(3) and (4) show the current waveform supplied to the gradient coil 40.

Since Q = RI ² and R depends on the temperature, these effective current Irms, the temperature To of the gradient magnetic field coil 40 measured by the temperature detecting means 41 and the energizing time t
The calorific value estimating means 12c obtains the calorific value Q and the temperature rise ΔT due to the calorific value Q (step 4 in FIG. 3).

Further, referring to the current temperature To of the gradient magnetic field coil 40 measured by the temperature detecting means 41 (at the time of inputting the parameter) and the above-mentioned temperature rise ΔT due to the calorific value Q, the temperature of the gradient magnetic field coil 40 during scanning is determined. Predict Te (FIG. 3, step 5). The prediction of the temperature may be a continuous prediction of the temperature during the scan including the end of the scan, or may be a prediction of the temperature only at the end of the scan. The temperature detection of the gradient magnetic field coil 40 by the temperature detecting means 41 may be performed by a temperature sensor or by indirect temperature measurement by passing a predetermined current as described later.

Here, two types of temperatures Ts1 and Ts2 are predetermined as the temperature of the gradient magnetic field coil 40. The temperature Ts2 is an allowable temperature, and if the temperature exceeds Ts2, it is necessary to stop scanning. On the other hand, the temperature Ts1 is a warning temperature close to the allowable temperature (for example, Ts2−20 = Ts1).
This is a temperature region where it is not necessary to stop the scan until Ts2 is exceeded beyond Ts1, but care must be taken.

Therefore, the alarm output means 13 outputs a necessary message according to the expected temperature Te of the gradient magnetic field coil 40 during scanning. This message is displayed on the display of the operator console 10.

The expected temperature Te is determined, and Ts1 <Te <
If it is Ts2 (step 6 in FIG. 3), the gradient coil 40
Is output (step 7 in FIG. 3).

On the other hand, if Te ≧ Ts2 (step 8 in FIG. 3), the gradient coil 40
Means that the temperature exceeds the predetermined warning temperature,
A scan disapproval message is output (step 9 in FIG. 3). In this case, a message indicating that scanning is not permitted is output to the operator console 10.

Therefore, unless the result of the temperature estimation of the gradient magnetic field coil 40 indicates that the scanning is not permitted, the scanning is performed according to the instruction of the operator console 10.
The operator console receiving the warning message from the alarm output means 13 starts scanning at a predetermined time t2. On the other hand, when a message indicating that scanning is not permitted is output, the operator console 10 does not start scanning.

With the above-described configuration, there is no occurrence of a situation in which scanning is stopped due to a temperature rise of the gradient magnetic field coil 40 during scanning and data is wasted as in the conventional case.

FIG. 6 is an explanatory diagram for explaining the operation of the temperature measuring means 41. The gradient coil 40 has an L component and an R component.
Since it has components, it can be represented by the circuit of FIG. Here, when a current i flows through the gradient magnetic field coil 40, a voltage v generated at both ends thereof is v = Ri + L · d
i / dt (2)

Therefore, by observing the behavior of the current i (t) when a certain voltage V0 is applied, the differential equation of the equation (2) can be solved. When a constant steady DC current is passed, the inductance can be neglected, and the equation (2) becomes V = Ri. From this, the resistance R can be known.

In general, the resistance value R in a conductor is substantially a linear function of temperature. If the resistance value at 0 ° C. is R0, the temperature is τ, and the temperature coefficient of the resistance is ρ, R = R0 + ρτ. Can be approximated. Thus, the temperature of the gradient magnetic field coil 40 can be measured by knowing the resistance of the gradient magnetic field coil 40.

That is, the resistance R is obtained by flowing a constant steady DC current through the gradient magnetic field coil 40.
The temperature of the gradient coil 40 can be determined from the resistance R. Therefore, the temperature of the gradient magnetic field coil 40 can be measured by the control from the operator console 10. This eliminates the risk of disturbing the gradient magnetic field due to the provision of the temperature sensor. Also, the gradient magnetic field coil 4
The temperature sensor attached to 0 is not exposed to high power high frequency. Further, there is an advantage that the existing power supply and the detection circuit can be used as they are, and the number of components is not unnecessarily increased. Note that a temperature sensor can be used if necessary.

FIG. 7 is an explanatory diagram for explaining the operation of another embodiment of the present invention. Here, the temperature of the gradient magnetic field coil 40 when a plurality of scans are performed as a series of operations is shown. Here, the scan parameter setting means 11 can set a plurality of scans as a series of operations, and the estimating means 12 estimates the temperature at each point in the series of operations.

When a plurality of scans are instructed as a series of operations by setting the scan parameters, the estimating means 12 estimates the temperature rise of the gradient coil 40 at each point in the series of scans. Actually, the temperature of the gradient magnetic field coil 40 decreases in accordance with the scan pause time. Therefore, the temperature Te is estimated in consideration of this.

In this case as well, the alarm output means 13 outputs a time point before the start of the scan expected to satisfy Te> Ts1 or Te ≧ Ts2 depending on the expected temperature Te of the gradient magnetic field coil 40. To output the required message. For example, if a continuous scan is instructed and it is expected that a warning temperature or a scan disallowed temperature will be reached when some scans are performed,
Display the message when the expected result is obtained.

It should be noted that, even if a scan is already started by setting a certain parameter and another parameter is input, and subsequent scans are continuously performed, the scan that has already started is performed. By controlling so that the operation is stopped at the end of the scan, the subsequent scan is not wasted.

[0033]

As described above in detail, according to the present invention, the scan parameter and the temperature of the gradient coil are referred to to estimate the temperature of the gradient coil during the scan, so that the scan can be performed before the start of the scan. It is possible to realize an MRI apparatus capable of predicting the gradient coil temperature during execution and outputting an alarm.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a main part of an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an overall configuration of an apparatus according to an embodiment of the present invention.

FIG. 3 is a flowchart showing the operation of one embodiment of the present invention.

FIG. 4 is a time chart showing the operation of one embodiment of the present invention.

FIG. 5 is a characteristic diagram showing the operation of one embodiment of the present invention.

FIG. 6 is a circuit diagram for explaining the operation of the device according to one embodiment of the present invention.

FIG. 7 is a characteristic diagram showing the operation of one embodiment of the present invention.

[Explanation of symbols]

 11 Scan parameter setting means 12 Prediction means 13 Alarm output means 41 Temperature detection means

Claims (3)

(57) [Claims] An MRI for detecting RF energy emitted from an excited nucleus given a high-frequency rotating magnetic field
In the apparatus, temperature detecting means (41) for detecting the temperature of the gradient magnetic field coil
Scan parameter setting means (11) for setting scan parameters for MRI scanning; scan parameters set by the scan parameter setting means (11) and gradient magnetic field coils detected by the temperature detection means (41). Temperature estimating means (12) for estimating the temperature of the gradient magnetic field coil at the time of scan execution or at the end of scanning by referring to the temperature; An MRI apparatus comprising: an alarm output unit (13) for outputting an alarm regarding (1). 2. A temperature estimating means (12) for estimating the amount of heat generated in the gradient magnetic field coil by referring to the set parameters; and a scan sequence by referring to the set parameters. Execution time estimating means (12b) for estimating the execution time of the gradient magnetic field coil; the temperature of the gradient magnetic field coil; 2. An MRI apparatus according to claim 1, further comprising: an arrival temperature estimating means for estimating the temperature. 3. The temperature estimating means (12) estimates the temperature of the gradient magnetic field coil in consideration of the amount of heat accumulated in each scan sequence when a plurality of scan sequences are continuously executed. The MR according to claim 1, wherein (13) outputs an alarm at a point in time before the start of a scan in which the temperature is expected to exceed a predetermined value.
I device.