CN105212958B

CN105212958B - Preparation method, device and the equipment of CT images

Info

Publication number: CN105212958B
Application number: CN201510694658.1A
Authority: CN
Inventors: 楼珊珊; 赵江魏
Original assignee: Neusoft Medical Systems Co Ltd
Current assignee: Neusoft Medical Systems Co Ltd
Priority date: 2015-10-21
Filing date: 2015-10-21
Publication date: 2018-08-21
Anticipated expiration: 2035-10-21
Also published as: CN105212958A

Abstract

This application discloses the preparation method of CT images, device and equipment, this method is applied on Medical Devices, and Medical Devices include at least two bulbs and at least two detectors corresponding at least two bulbs, this method include：Determine the unwrapping wire time interval of the first bulb at least two bulbs；In the unwrapping wire time interval, X-ray can be sent out by controlling first bulb；Other time section except the unwrapping wire time interval, X-ray can not be sent out by controlling first bulb；Corresponding first detector of the first bulb collected data in unwrapping wire time interval are obtained, and collected data obtain CT images in unwrapping wire time interval using the first detector.Technical solution through the invention avoids the scattered rays of a bulb from being irradiated on the corresponding detector of another bulb, and the problems such as avoid the formation of projection error.

Description

CT image obtaining method, device and equipment

Technical Field

The present application relates to the field of medical equipment technologies, and in particular, to a method, an apparatus, and a device for obtaining a CT image.

Background

In medical imaging medical devices, such as CT (Computed Tomography) devices, to increase the scanning speed, a plurality of bulbs, each corresponding to a detector, and a corresponding plurality of detectors may be mounted at different angles of the gantry. During the rotation of the scanning frame, a plurality of ball tubes can simultaneously emit X-rays and be received by the detectors corresponding to the ball tubes. By using the technology, the coverage angle range of the X-ray projection can be multiplied in the same time, so that the data required by the CT image reconstruction can be obtained in a very short time, and the method has great advantages for the imaging of a moving object (such as a heart and the like).

However, in the above-mentioned method, when a plurality of tubes emit X-rays simultaneously, the X-rays emitted from one tube irradiate the surface of the object and are scattered, and the scattered X-rays irradiate the detector corresponding to another tube, so that a projection error is formed on the detector corresponding to another tube, resulting in an artifact or non-uniformity of the CT image. For example, the detector 1 corresponding to the tube 1 receives the X-ray emitted from the tube 1 and also receives the scattered ray generated by the X-ray emitted from other tubes (e.g. the tube 2), thereby forming a projection error.

Disclosure of Invention

The invention provides a method for obtaining CT images of electronic computer tomography, which is applied to medical equipment for obtaining CT images in a scanning mode, wherein the medical equipment comprises at least two bulbs and at least two detectors corresponding to the at least two bulbs, and the method comprises the following steps:

determining a pay-off time interval of a first bulb tube of the at least two bulb tubes;

controlling the first bulb tube to emit X-rays in the paying-off time interval; controlling the first bulb tube not to emit X-rays in other time intervals except the paying-off time interval;

and acquiring data acquired by a first detector corresponding to the first bulb in the pay-off time interval, and acquiring a CT image by using the data acquired by the first detector in the pay-off time interval.

And the pay-off time interval of each first bulb tube and the pay-off time intervals of other bulb tubes do not have a coincidence time interval, or the coincidence time interval between the pay-off time interval of each first bulb tube and the pay-off time intervals of other bulb tubes is smaller than a preset threshold value.

The process of determining the pay-off time interval of the first bulb tube of the at least two bulb tubes specifically includes: determining the pay-off time interval of the first bulb tube as follows: [ (k × N + m) × t, (k × N + m +1) × t);

wherein N is the number of the at least two bulbs; m is the index of the first bulb tube, and the value of m is one numerical value of 0, 1, …, N-2 and N-1; t is the time interval of each paying off; k is the paying-off times of the first bulb tube, and the values of K are 0, 1, … in sequence, and K is the maximum paying-off times of the first bulb tube.

The first bulb tube is controlled to emit X-rays in the paying-off time interval; in other time intervals except the paying-off time interval, controlling the process that the first bulb tube cannot emit X rays, specifically comprising: controlling the output value of the grid voltage corresponding to the first bulb tube to be a first voltage value in the pay-off time interval; controlling the output value of the grid voltage corresponding to the first bulb tube to be a second voltage value in other time intervals except the pay-off time interval; when the output value of the grid voltage is a first voltage value, the first bulb tube can emit X rays; when the output value of the grid voltage is a second voltage value, the first bulb tube cannot emit X rays; the second voltage value is greater than the first voltage value; or,

in the pay-off time interval, controlling the high voltage of the bulb corresponding to the first bulb to output voltage to the first bulb; in other time intervals except the pay-off time interval, controlling the high voltage of the bulb tube corresponding to the first bulb tube not to output voltage to the first bulb tube; when the high voltage of the bulb tube corresponding to the first bulb tube outputs voltage to the first bulb tube, the first bulb tube can emit X rays; when the high voltage of the bulb tube corresponding to the first bulb tube does not output voltage to the first bulb tube, the first bulb tube cannot emit X rays.

The process of controlling the output value of the grid voltage corresponding to the first bulb to be the first voltage value specifically includes: outputting a first signal to a control circuit of grid voltage corresponding to the first bulb, wherein the first signal is used for enabling the control circuit of grid voltage corresponding to the first bulb to output a first voltage value;

the process of controlling the output value of the grid voltage corresponding to the first bulb to be the second voltage value specifically includes: and outputting a second signal to the control circuit of the grid voltage corresponding to the first bulb, wherein the second signal is used for enabling the control circuit of the grid voltage corresponding to the first bulb to output a second voltage value.

The medical equipment only provides one bulb high pressure, and each of the at least two bulbs corresponds to the same bulb high pressure.

The process of obtaining the data collected by the first detector corresponding to the first bulb in the setting-out time interval specifically includes:

acquiring data acquired by the first detector in all paying-off time intervals, and extracting the data acquired by the first detector in the paying-off time intervals from all the acquired data; or,

controlling the first detector to carry out data acquisition in the paying-off time interval; controlling the first detector not to carry out data acquisition in other time intervals except the paying-off time interval; and acquiring all data acquired by the first detector as data acquired in the paying-off time interval.

The process of controlling the first detector to perform data acquisition specifically includes: outputting a third signal to the first detector, the third signal being used to cause the first detector to perform data acquisition;

the process of controlling the first detector not to perform data acquisition specifically includes: outputting a fourth signal to the first detector, the fourth signal for disabling data acquisition by the first detector.

The invention provides a device for obtaining CT images of electronic Computed Tomography (CT), which is applied to medical equipment for obtaining CT images in a scanning mode, wherein the medical equipment comprises at least two bulbs and at least two detectors corresponding to the at least two bulbs, and the device specifically comprises:

the determining module is used for determining a pay-off time interval of a first bulb tube in the at least two bulb tubes; the control module is used for controlling the first bulb tube to emit X rays in the paying-off time interval; controlling the first bulb tube not to emit X-rays in other time intervals except the paying-off time interval;

and the obtaining module is used for obtaining data collected by the first detector corresponding to the first bulb in the paying-off time interval and obtaining a CT image by utilizing the data collected by the first detector corresponding to the first bulb in the paying-off time interval.

The determining module is specifically configured to determine that the setting-out time interval of the first bulb tube is as follows: [ (k × N + m) × t, (k × N + m +1) × t); wherein N is the number of at least two bulbs; m is an index of the first bulb, and the value of m is one of 0, 1, …, N-2 and N-1; t is the time interval of each paying off; k is the paying-off times of the first bulb tube, and the values of K are 0, 1, …, K in sequence, and K is the maximum paying-off times of the first bulb tube.

The control module is specifically used for controlling the output value of the grid voltage corresponding to the first bulb tube to be a first voltage value in the pay-off time interval; controlling the output value of the grid voltage corresponding to the first bulb tube to be a second voltage value in other time intervals except the pay-off time interval; when the output value of the grid voltage is a first voltage value, the first bulb tube can emit X rays; when the output value of the grid voltage is a second voltage value, the first bulb tube cannot emit X rays; the second voltage value is greater than the first voltage value; or, in the pay-off time interval, controlling the high voltage of the bulb corresponding to the first bulb to output voltage to the first bulb; in other time intervals except the pay-off time interval, controlling the high voltage of the bulb tube corresponding to the first bulb tube not to output voltage to the first bulb tube; when the high voltage of the bulb tube corresponding to the first bulb tube outputs voltage to the first bulb tube, the first bulb tube can emit X rays; when the high voltage of the bulb tube corresponding to the first bulb tube does not output voltage to the first bulb tube, the first bulb tube cannot emit X rays.

The control module is specifically configured to output a first signal to a control circuit of the grid voltage corresponding to the first bulb in a process of controlling an output value of the grid voltage corresponding to the first bulb to be a first voltage value, where the first signal is used to enable the control circuit of the grid voltage corresponding to the first bulb to output the first voltage value; and in the process of controlling the output value of the grid voltage corresponding to the first bulb to be a second voltage value, outputting a second signal to the control circuit of the grid voltage corresponding to the first bulb, wherein the second signal is used for enabling the control circuit of the grid voltage corresponding to the first bulb to output the second voltage value.

The obtaining module is specifically configured to obtain data collected by the first detector in all the pay-off time intervals in the process of obtaining data collected by the first detector corresponding to the first bulb in the pay-off time intervals, and extract data collected by the first detector in the pay-off time intervals from all the data collected in all the pay-off time intervals; or,

The obtaining module is specifically configured to output a third signal to the first detector in a process of controlling the first detector to perform data acquisition, where the third signal is used to enable the first detector to perform data acquisition; and in the process of controlling the first detector not to carry out data acquisition, outputting a fourth signal to the first detector, wherein the fourth signal is used for enabling the first detector not to carry out data acquisition.

The invention provides a medical device for obtaining an electronic Computed Tomography (CT) image in a scanning mode, which specifically comprises: the device comprises a console, a scanning frame, at least two ball tubes and at least two detectors corresponding to the at least two ball tubes; wherein, the control cabinet specifically includes: the processor and the memory are used for storing executable instructions corresponding to the CT image acquisition device; wherein, the processor reads the executable instruction corresponding to the obtaining device of the CT image and is used for executing:

The processor controls the first bulb tube to emit X-rays in the setting-out time interval by reading an executable instruction corresponding to the CT image obtaining device; when the first bulb tube is controlled not to emit X-rays in other time intervals except the paying-off time interval, the method comprises the following steps:

controlling the output value of the grid voltage corresponding to the first bulb tube to be a first voltage value in the pay-off time interval; controlling the output value of the grid voltage corresponding to the first bulb tube to be a second voltage value in other time intervals except the pay-off time interval; when the output value of the grid voltage is a first voltage value, the first bulb tube can emit X rays; when the output value of the grid voltage is a second voltage value, the first bulb tube cannot emit X rays; the second voltage value is greater than the first voltage value; or,

Based on the technical scheme, in the embodiment of the invention, for the first bulb tube of the at least two bulb tubes, the first bulb tube can emit the X-ray only in the pay-off time interval of the first bulb tube, and cannot emit the X-ray in other time intervals, that is, the X-ray is in the off state. Based on the technical scheme, by means of an X-ray turn-off technology, in the process that a plurality of ball tubes rotate along with a scanning frame, the ball tubes are rapidly switched between a turn-off state and a pay-off state in sequence, when one ball tube emits X-rays, other ball tubes cannot emit X-rays and are in the turn-off state, and therefore the scattering influence among different ball tubes can be avoided, scattered rays of one ball tube are prevented from irradiating a detector corresponding to another ball tube, and the problems that projection errors are formed, CT image artifacts are uneven and the like are avoided. Moreover, because the turn-off time of the X-ray of each bulb is short, the emission of the X-ray and the data acquisition of each bulb are approximately continuous in the projection rotating direction when each bulb is seen independently, and the subsequent reconstruction process of the CT image and the resolution and the time resolution of the image are not influenced.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and together with the description, serve to explain the principles of the application.

FIG. 1 is a schematic diagram of one configuration of a medical device of the present application including at least two bulbs;

FIG. 2 is a flow chart of one embodiment of a method for obtaining CT images according to the present disclosure;

FIG. 3 is a schematic structural diagram of a medical apparatus in which a CT image acquisition device of the present application is located;

fig. 4 is a block diagram of an embodiment of a CT image acquisition apparatus according to the present application.

Detailed Description

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein is meant to encompass any and all possible combinations of one or more of the associated listed items.

It is to be understood that although the terms first, second, third, etc. may be used herein to describe various information, such information should not be limited to these terms. These terms are only used to distinguish one type of information from another. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information, without departing from the scope of the present application. Depending on the context, moreover, the word "if" as used may be interpreted as "at … …" or "when … …" or "in response to a determination".

The embodiment of the method for obtaining a CT image provided by the present application can be applied to various medical devices for obtaining a CT image by a scanning manner, and the medical devices may include, but are not limited to, a CT device, and the like. Taking a CT apparatus as an example, the CT apparatus scans a slice with a certain thickness of a scanned object, for example, a part (such as a heart) of a human body, by using X-rays to obtain a CT image.

CT apparatus generally comprises a gantry, a bulb (also called X-ray source), a detector, and a scanning bed, wherein the bulb and the detector are fixed on the gantry, and an object to be scanned is placed on the scanning bed between the bulb and the detector. During scanning, the bulb and detector rotate with the gantry about a center of rotation, and the relative positions of the bulb and detector remain unchanged. During the scanning process, the bulb tube emits X-rays, the X-rays pass through an object to be scanned on the scanning bed and are received by the detector and converted into digital signals (namely data), and the digital signals can be converted into CT images which can be observed by human eyes after being processed.

In order to improve the time resolution of a moving object (such as the heart), the coverage angle range of X-ray projection is improved in multiples within the same time, and the data required for CT image reconstruction is obtained within a very short time, at least two ball tubes and at least two detectors corresponding to the at least two ball tubes can be fixed on a scanning frame, wherein each ball tube corresponds to one detector. During the rotation of the scanning frame, a plurality of ball tubes can simultaneously emit X-rays and be received by the detectors corresponding to the ball tubes. As shown in fig. 1, a bulb 1 and a detector 1 corresponding to the bulb 1, a bulb 2 and a detector 2 corresponding to the bulb 2, and a bulb 3 and a detector 3 corresponding to the bulb 3 are fixed to the gantry. The X-rays emitted from the bulb 1 are received by the detector 1, the X-rays emitted from the bulb 2 are received by the detector 2, and the X-rays emitted from the bulb 3 are received by the detector 3.

In fig. 1, the number of the bulbs installed on the gantry is 3, and 3 detectors corresponding to the 3 bulbs are installed, and 3 bulbs are only an example, and may be 2 or more than 4 in practical application.

In the multi-bulb scanning technology, in the rotation process of a scanning frame, a bulb 1, a bulb 2, a bulb 3, a detector 1, a detector 2 and a detector 3 all rotate along with the scanning frame, the bulb 1, the bulb 2 and the bulb 3 simultaneously emit X rays, and the detector 1, the detector 2 and the detector 3 simultaneously acquire three groups of data, so that each detector can acquire 1/3 circles of projection data every time the scanning frame rotates 1/3 circles, and 3 detectors can acquire a complete circle of projection data, thereby improving the time resolution of scanning of a moving object.

However, in the above manner, the X-ray emitted from the bulb 1 is not only received by the detector 1, but scattered when the X-ray irradiates the surface or the inside of the scanned object, and the scattered X-ray is received by the detectors 2 and 3, so that a projection error is formed between the detectors 2 and 3, resulting in an artifact or unevenness of the CT image. Similarly, the X-ray emitted from the tube 2 is received by the detector 2, and the X-ray is scattered when it irradiates the surface or the inside of the scanned object, and the scattered X-ray is received by the detector 1 and the detector 3, so that a projection error is formed between the detector 1 and the detector 3, which causes an artifact or non-uniformity of the CT image. The X-ray emitted from the tube 3 is received by the detector 3, and the X-ray is scattered when it irradiates the surface or the inside of the scanned object, and the scattered X-ray is received by the detector 1 and the detector 2, so that a projection error is formed between the detector 1 and the detector 2, and an artifact or unevenness of the CT image is caused.

In view of the above findings, an embodiment of the present invention provides a method for obtaining a CT image, which is applied to a medical apparatus for obtaining a CT image by a scanning manner, the medical apparatus including at least two bulbs and at least two detectors corresponding to the at least two bulbs, and referring to fig. 2, the method may include the following steps:

step 201, determining a pay-off time interval of a first bulb tube of at least two bulb tubes.

In the embodiment of the invention, a coincidence time interval does not exist between the pay-off time interval of each first bulb tube and the pay-off time intervals of other bulb tubes, or the coincidence time interval between the pay-off time interval of each first bulb tube and the pay-off time intervals of other bulb tubes is smaller than a preset threshold value. In addition, all the time intervals are occupied by the pay-off time intervals of all the bulbs, and unoccupied time intervals do not exist.

The preset threshold may be set arbitrarily according to practical experience, for example, the preset threshold is set through experience or experimental data, for example, the preset threshold is set to 0.0001 second, or set to one ten thousandth of the pay-off time interval, and the like. For the setting of the preset threshold, as long as it is ensured that the coincidence time interval between the pay-off time interval of the first bulb and the pay-off time intervals of the other bulbs is less than the preset threshold, the actual result is not affected basically.

In the embodiment of the present invention, the process of determining the line release time interval of the first bulb of the at least two bulbs may specifically include, but is not limited to, the following manners: determining the pay-off time interval of the first bulb tube as follows: [ (k × N + m) × t, (k × N + m +1) × t). Wherein N is the number of at least two bulbs; m is an index of the first bulb, and the value of m is one of 0, 1, …, N-2 and N-1; t is the time interval of each paying off; k is the paying-off times of the first bulb tube, and the values of K are 0, 1, … in sequence, and K is the maximum paying-off times of the first bulb tube. [) indicates that the payoff time interval contains (k × N + m) × t, but not (k × N + m +1) × t.

Of course, in practical applications, the method for determining the pay-off time interval of the first bulb is not limited to the above-mentioned method, and it is only required to ensure that there is no overlapping time interval between the pay-off time interval of each first bulb in the at least two bulbs and the pay-off time intervals of other bulbs, and other determining methods are not described in detail in this embodiment.

As shown in fig. 1, at least two bulbs may include a bulb 1, a bulb 2, and a bulb 3, and the number N of the at least two bulbs is 3, and the index of the bulb 1 is 0, the index of the bulb 2 is 1, and the index of the bulb 3 is 2. Based on this, the pay-off time interval of the bulb 1 can be: [ (k × 3+0) × t, (k × 3+0+1) × t). When the value of K is 0, 1, …, and K, the setting-out time interval of the bulb tube 1 is: [0, t), [3 × t, 4 × t), [6 × t, 7 × t) …, [ (3K) × t, (3K +1) × t). The pay-off time interval of the bulb 2 may be: [ (k × 3+1) × t, (k × 3+1) × t). When the value of K is 0, 1, …, and K, the setting-out time interval of the bulb tube 2 is: [ t, 2 × t), [4 × t, 5 × t), [7 × t, 8 × t) …, [ (3K +1) × t, (3K +2) × t). The pay-off time interval of the bulb 3 may be: [ (k × 3+2) × t, (k × 3+2+1) × t). When the value of K is 0, 1, …, and K, the setting-out time interval of the bulb tube 3 is: [2 × t, 3 × t), [5 × t, 6 × t), [8 × t, 9 × t) …, [ (3K +2) × t, (3K +3) × t).

Obviously, the setting-out time interval of the bulb 1 is different from the setting-out time interval of the bulb 2, the setting-out time interval of the bulb 1 is different from the setting-out time interval of the bulb 3, and the setting-out time interval of the bulb 2 is different from the setting-out time interval of the bulb 3. Furthermore, the pay-off time interval of the bulb 1, the bulb 2 and the bulb 3 is just divided into (3K +3) × t time intervals on average. Further, assuming that t is 1 ms and K is 2, the bulb 1 obtains the pay-off time interval [0, 1 ms ], the bulb 2 obtains the pay-off time interval [1 ms, 2 ms ], and the bulb 3 obtains the pay-off time interval [2 ms, 3 ms). Then, the bulb 1 gets the pay-off time interval [3 ms, 4 ms ], the bulb 2 gets the pay-off time interval [4 ms, 5 ms), and the bulb 3 gets the pay-off time interval [5 ms, 6 ms). Then, the bulb 1 gets the pay-off time interval [6 ms, 7 ms ], the bulb 2 gets the pay-off time interval [7 ms, 8 ms ], and the bulb 3 gets the pay-off time interval [8 ms, 9 ms ].

Step 202, controlling the first bulb tube to emit X rays in a pay-off time interval of the first bulb tube; and controlling the first bulb tube not to emit X-rays in other time intervals except the paying-off time interval of the first bulb tube. Based on this, it is possible to have only one and only one bulb emitting X-rays in each time interval.

In the embodiment of the invention, in the pay-off time interval of the first bulb tube, the first bulb tube is controlled to emit X rays; controlling the process that the first bulb cannot emit the X-ray in other time intervals than the paying-off time interval of the first bulb specifically may include but is not limited to the following modes:

in a first mode, in a pay-off time interval of a first bulb tube, controlling an output value of grid voltage corresponding to the first bulb tube to be a first voltage value; and controlling the output value of the grid voltage corresponding to the first bulb tube to be a second voltage value in other time intervals except the pay-off time interval of the first bulb tube. When the output value of the grid voltage is a first voltage value, the first bulb tube can emit X rays; when the output value of the grid voltage is a second voltage value, the first bulb tube cannot emit X rays; the second voltage value is greater than the first voltage value.

In the embodiment of the present invention, the process of controlling the output value of the grid voltage corresponding to the first bulb to be the first voltage value may specifically include, but is not limited to, the following manners: and outputting a first signal to a control circuit of the grid voltage corresponding to the first bulb, wherein the first signal is used for enabling the control circuit of the grid voltage corresponding to the first bulb to output a first voltage value. The process of controlling the grid voltage output value corresponding to the first bulb to be the second voltage value may specifically include, but is not limited to, the following manners: and outputting a second signal to the control circuit of the grid voltage corresponding to the first bulb, wherein the second signal is used for enabling the control circuit of the grid voltage corresponding to the first bulb to output a second voltage value.

The first signal may be a high level signal, and the second signal may be a low level signal. Alternatively, the first signal may be a low level signal and the second signal may be a high level signal.

Each bulb can be independently controlled by using a grid voltage, namely each bulb corresponds to a unique control circuit of the grid voltage, and the control circuit is used for providing the grid voltage for the bulb.

The principle of emitting X-rays by the bulb tube can be as follows: an electron beam is generated at the bulb cathode and impinges on the bulb anode to generate X-rays, thereby emitting X-rays, and the location on the anode where the X-rays are generated (spot) is called the focal point. In practice, in order to obtain different sizes of the focal spots or to locate the focal spots at the same position of the anode, a voltage, called grid voltage, may be applied in a direction perpendicular to the cathode electron beam. When the output value of the grid voltage is large, the electron beam that can reach the anode is very weak or even disappears, and thus the generated X-rays are weak or even not generated. When the output value of the grid voltage is small, the electron beam reaching the anode is strong, and the generated X-ray is strong. Therefore, by constantly changing the output value of the grid voltage, the intensity of the electron beam can be changed, and then the X-ray can be rapidly changed between the presence and absence.

Based on the above principle, in the embodiment of the present invention, during the pay-off time interval of the first bulb, it is necessary to ensure that the first bulb can emit X-rays, so that the output value of the grid voltage corresponding to the first bulb is controlled to be a normal voltage value (first voltage value), at this time, the electron beam generated by the cathode of the bulb can strike the anode of the bulb to generate X-rays, and at this time, the X-rays are in an on state. In other time intervals except the pay-off time interval of the first bulb tube, it is necessary to ensure that the first bulb tube cannot emit X-rays, so that the output value of the grid voltage corresponding to the first bulb tube is controlled to be a sufficiently large voltage value (second voltage value), at this time, the electron beam generated by the bulb tube cathode cannot impact the bulb tube anode, and cannot generate X-rays, and at this time, the X-rays are in an off state.

Wherein the first voltage value can be any voltage value between 400V-500V, when the first voltage value is changed between 400V-500V, the moving speed of the electron beam can be changed, and then the X-ray is changed rapidly. The second voltage value may be a voltage value greater than a specific voltage value (e.g., 800V), and when the second voltage value is greater than the specific voltage value, the electron beam generated by the tube cathode may not strike the bulb anode.

As shown in fig. 1, in the time interval [0, t), the output value of the grid voltage corresponding to the bulb 1 is controlled to be the first voltage value, the output values of the grid voltages corresponding to the bulb 2 and the bulb 3 are controlled to be the second voltage value, the bulb 1 can emit X-rays, and the bulb 2 and the bulb 3 cannot emit X-rays. In the time interval [ t, 2 × t ], the output value of the grid voltage corresponding to the bulb 2 is controlled to be a first voltage value, the output values of the grid voltages corresponding to the bulb 1 and the bulb 3 are controlled to be a second voltage value, the bulb 2 can emit X-rays, and the bulb 1 and the bulb 3 cannot emit the X-rays. In the time interval [2 × t, 3 × t), the output value of the grid voltage corresponding to the bulb 3 is controlled to be a first voltage value, the output values of the grid voltages corresponding to the bulb 1 and the bulb 2 are controlled to be a second voltage value, the bulb 3 can emit X-rays, and the bulb 1 and the bulb 2 cannot emit X-rays. In the time interval [3 × t, 4 × t), the output value of the grid voltage corresponding to the bulb 1 is controlled to be a first voltage value, the output values of the grid voltages corresponding to the bulb 2 and the bulb 3 are controlled to be a second voltage value, the bulb 1 can emit X-rays, and the bulb 2 and the bulb 3 cannot emit X-rays. By analogy, in a time interval [ (3K +2) × t, (3K +3) × t), the output value of the grid voltage corresponding to the control bulb 3 is a first voltage value, the output values of the grid voltages corresponding to the control bulb 1 and the control bulb 2 are second voltage values, the control bulb 3 emits X-rays, and the control bulb 1 and the control bulb 2 cannot emit X-rays.

Based on this, when the bulb 1 emits X-rays, the bulbs 2 and 3 cannot emit X-rays. When the bulb 2 emits X-rays, the bulbs 1 and 3 cannot emit X-rays. When the bulb 3 emits X-rays, the bulbs 1 and 2 cannot emit X-rays. Therefore, when any one bulb tube emits X-rays, all other bulbs are in the off state, and the scattering influence among different bulbs is avoided.

In the second mode, in the pay-off time interval of the first bulb, the high voltage of the bulb corresponding to the first bulb is controlled to output voltage to the first bulb; controlling the high voltage of the bulb tube corresponding to the first bulb tube not to output voltage to the first bulb tube in other time intervals except the pay-off time interval of the first bulb tube; when the high voltage of the bulb corresponding to the first bulb outputs voltage to the first bulb, the first bulb can emit X rays; when the high voltage of the bulb tube corresponding to the first bulb tube does not output voltage to the first bulb tube, the first bulb tube cannot emit X rays.

Wherein, the medical equipment can only provide one bulb high pressure, and every bulb in at least two bulbs all corresponds this same bulb high pressure. Under the condition, in the pay-off time interval of the first bulb tube, the high voltage of the bulb tubes corresponding to at least two bulb tubes is controlled to be switched to the first bulb tube, so that the high voltage of the bulb tubes outputs voltage to the first bulb tube; and in other time intervals except the pay-off time interval of the first bulb tube, controlling the high voltage of the bulb tube to be switched to other bulb tubes, so that the high voltage of the bulb tube does not output voltage to the first bulb tube and outputs voltage to other bulb tubes. Of course, the medical device may also provide a bulb high voltage for each bulb, and the bulb high voltage corresponding to each bulb outputs a voltage or does not output a voltage to the bulb, which is not described in this embodiment of the present invention.

In the embodiment of the invention, when at least two bulbs exist, one bulb high pressure is not required to be configured for each bulb, but one bulb high pressure is configured for all the bulbs, so that the number of the bulb high pressures is reduced. Based on the bulb high voltage configured for all bulbs, the bulb high voltage can output voltage to each bulb, but at the same time, the bulb high voltage can only output voltage to one bulb, namely, the bulb high voltage is controlled to output voltage to the first bulb in the pay-off time interval of the first bulb, and at the moment, the bulb high voltage does not output voltage to other bulbs.

In the above process, the principle of X-ray emission from the bulb has been described, and the first process is that the cathode of the bulb generates an electron beam, and one premise of the cathode of the bulb generating the electron beam is that the high voltage of the bulb is applied to the cathode of the bulb to output a voltage. When the bulb cathode is output with voltage, the bulb cathode can generate electron beams; when the bulb cathode is not output with a voltage, the bulb cathode is not able to generate an electron beam. Based on this, when the bulb high voltage outputs voltage to the bulb, the cathode of the bulb can generate electron beams, the bulb can emit X-rays, and the cathodes of the other bulbs cannot generate electron beams and can not emit X-rays because the other bulbs are not output voltage.

As shown in fig. 1, in the time interval [0, t), the tube high voltage is controlled to output a voltage to the tube 1, and at this time, the tube 2 and the tube 3 are not output a voltage, the tube 1 can emit X-rays, and the tube 2 and the tube 3 cannot emit X-rays. And in a time interval [ t, 2 × t ], controlling the bulb tube high voltage to output voltage to the bulb tube 2, wherein the bulb tube 1 and the bulb tube 3 are not output voltage, the bulb tube 2 can emit X rays, and the bulb tube 1 and the bulb tube 3 cannot emit the X rays. And in a time interval [2 × t, 3 × t), controlling the bulb tube high voltage to output voltage to the bulb tube 3, wherein the bulb tube 1 and the bulb tube 2 are not output voltage at the time, the bulb tube 3 can emit X rays, and the bulb tube 1 and the bulb tube 2 cannot emit the X rays. And in a time interval [3 × t, 4 × t), the high voltage of the bulb tube is controlled to output voltage to the bulb tube 1, the bulb tube 2 and the bulb tube 3 are not output voltage at the moment, the bulb tube 1 can emit X rays, and the bulb tube 2 and the bulb tube 3 cannot emit the X rays. By analogy, in a time interval [ (3K +2) × t, (3K +3) × t), the high voltage of the bulb tube is controlled to output voltage to the bulb tube 3, at the moment, the bulb tube 1 and the bulb tube 2 are not output voltage, the bulb tube 3 can emit X rays, and the bulb tube 1 and the bulb tube 2 cannot emit the X rays. When the bulb 1 emits X-rays, the bulbs 2 and 3 cannot emit X-rays. When the bulb 2 emits X-rays, the bulbs 1 and 3 cannot emit X-rays. When the bulb 3 emits X-rays, the bulbs 1 and 2 cannot emit X-rays. Therefore, when any one bulb tube emits X-rays, all other bulbs are in the off state, and scattering influence among different bulbs is avoided.

Step 203, obtaining data collected by the first detector corresponding to the first bulb in the pay-off time interval, and obtaining a CT image by using the data collected by the first detector in the pay-off time interval.

In the embodiment of the present invention, the process of obtaining data collected by the first detector corresponding to the first bulb in the pay-off time interval may specifically include, but is not limited to, the following manners: and acquiring data acquired by the first detector in all paying-off time intervals, and extracting the data acquired by the first detector in the paying-off time intervals from all the acquired data. Or, in the paying-off time interval, controlling the first detector to acquire data; controlling the first detector not to carry out data acquisition in other time intervals outside the paying-off time interval; all the data acquired by the first detector are acquired in the paying-off time interval.

The process of controlling the first detector to perform data acquisition may specifically include, but is not limited to, the following ways: a third signal is output to the first detector, the third signal being used to cause data acquisition by the first detector. The process of controlling the first detector not to perform data acquisition may specifically include, but is not limited to, the following ways: a fourth signal is output to the first detector, the fourth signal being used to disable data acquisition by the first detector.

The third signal may be a high level signal, and the fourth signal may be a low level signal. Alternatively, the third signal may be a low level signal and the fourth signal may be a high level signal.

As shown in fig. 1, the data acquired by the detector 1 corresponding to the bulb 1 in all the pay-off time intervals [0, 9 msec) can be obtained, and the data acquired in the pay-off time intervals [0, 1 msec ], [3 msec, 4 msec ], and [6 msec, 7 msec ] can be extracted from all the acquired data. The data collected by the detector 2 corresponding to the bulb 2 in all pay-off time intervals [0, 9 milliseconds) can be obtained, and the data collected in the pay-off time intervals [1, 2 milliseconds ], [4 milliseconds, 5 milliseconds ], [7 milliseconds, 8 milliseconds) can be extracted from all the collected data. The data collected by the detector 3 corresponding to the bulb 3 in all pay-off time intervals [0, 9 milliseconds) can be obtained, and the data collected in the pay-off time intervals [2, 3 milliseconds ], [5 milliseconds, 6 milliseconds ], [8 milliseconds, 9 milliseconds) can be extracted from all the collected data.

Assuming that 100 data are collected by the detector every millisecond, 900 data are collected by the detector 1 in total, the 1 st to 100 th data are data collected by the detector 1 in the paying-off time interval [0, 1 millisecond), the 301 st and 400 th data are data collected by the detector 1 in the paying-off time interval [3 millisecond, 4 millisecond), the 601 st and 700 th data are data collected by the detector 1 in the paying-off time interval [6 millisecond, 7 millisecond), therefore, the detector 1 discards the data of the 101 st, 401 st, 600 th and 701 st. The detector 2 acquires 900 data in total, the 101 st-200 th data is the data acquired by the detector 2 in the paying-off time interval [1, 2 ms), the 401 st-500 th data is the data acquired by the detector 2 in the paying-off time interval [4 ms, 5 ms), and the 701 th-800 th data is the data acquired by the detector 2 in the paying-off time interval [7 ms, 8 ms), so that the detector 2 discards the data of the 1 st-100 th, 201 st-400 th, 501 st-700 th and 801 st-900 th. The detector 3 acquires 900 data in total, the 300 th data in 201-.

For another example, as shown in fig. 1, the detector 1 corresponding to the control bulb 1 acquires the 1 st to 100 th data in the paying-off time interval [0, 1 msec "), the detector 2 corresponding to the control bulb 2 acquires the 101 st and 200 th data in the paying-off time interval [1, 2 msec), and the detector 3 corresponding to the control bulb 3 acquires the 201 st and 300 th data in the paying-off time interval [2, 3 msec). In addition, the control detector 1 acquires 400 th data in the paying-off time interval [3, 4 milliseconds), the control detector 2 acquires 500 th data in the paying-off time interval [4, 5 milliseconds), and the control detector 3 acquires 600 th data in the paying-off time interval [5, 6 milliseconds). The control detector 1 acquires 700 th data in the paying-off time interval [6, 7 milliseconds), the control detector 2 acquires 800 th data in the paying-off time interval [7, 8 milliseconds), and the control detector 3 acquires 900 th data in the paying-off time interval [8, 9 milliseconds).

Based on the above two ways, the CT image can be obtained by using the data of 1-100, 301-400, and 601-700 collected by the detector 1, the data of 101-200, 401-500, and 701-800 collected by the detector 2, and the data of 201-300, 501-600, and 801-900 collected by the detector 3, which are collected by the detector 1, and the process of obtaining the CT image is not repeated.

Corresponding to the embodiment of the method for acquiring the CT image, the application also provides an embodiment of a device for acquiring the CT image and medical equipment.

Fig. 3 is a schematic diagram of a hardware structure of a medical device according to the present application, which is exemplified by a CT device. The medical equipment obtains CT images in a scanning mode, and the medical equipment specifically comprises: a console 310, a gantry 320, at least two bulbs 330, and at least two detectors 340 corresponding to the at least two bulbs 330. The console 310 specifically includes: a processor 311 and a memory 312 for storing executable instructions corresponding to the CT image obtaining device 300. The CT image obtaining apparatus 300 in the storage 312 is a logical apparatus, and when a CT image needs to be obtained, the processor 311 may read the computer program instructions corresponding to the CT image obtaining apparatus 300 from the storage 312 into the memory for operation. In one example, the processor 311 reads the executable instructions corresponding to the CT image obtaining apparatus 300 and is configured to:

In another example, when determining the pay-off time interval of the first bulb of the at least two bulbs by reading the executable instructions corresponding to the CT image obtaining device 300 in the memory 312, the processor 311 does not have a coincidence time interval between the pay-off time interval of each first bulb and the pay-off time intervals of the other bulbs, or the coincidence time interval between the pay-off time interval of each first bulb and the pay-off time intervals of the other bulbs is smaller than a preset threshold.

In another example, the processor 311, when determining the time interval of the line laying of the first bulb of the at least two bulbs by the executable instructions corresponding to the obtaining apparatus 300 reading the CT image in the memory 312, may include: determining the pay-off time interval of the first bulb tube as follows: [ (k × N + m) × t, (k × N + m +1) × t); wherein N is the number of at least two bulbs; m is an index of the first bulb, and the value of m is one of 0, 1, …, N-2 and N-1; t is the time interval of each paying off; k is the paying-off times of the first bulb tube, and the values of K are 0, 1, … in sequence, and K is the maximum paying-off times of the first bulb tube.

In another example, the processor 311 controls the first bulb to emit X-rays during the line-releasing time interval according to the corresponding executable instruction of the obtaining apparatus 300 that reads the CT image in the memory 312; when the first bulb is controlled not to emit the X-ray in other time intervals than the paying-off time interval, the method may include: controlling the output value of the grid voltage corresponding to the first bulb tube to be a first voltage value in the pay-off time interval; controlling the output value of the grid voltage corresponding to the first bulb tube to be a second voltage value in other time intervals except the pay-off time interval; when the output value of the grid voltage is a first voltage value, the first bulb tube can emit X rays; when the output value of the grid voltage is a second voltage value, the first bulb tube cannot emit X rays; the second voltage value is greater than the first voltage value; or, in the pay-off time interval, controlling the high voltage of the bulb corresponding to the first bulb to output voltage to the first bulb; in other time intervals except the pay-off time interval, controlling the high voltage of the bulb tube corresponding to the first bulb tube not to output voltage to the first bulb tube; when the high voltage of the bulb tube corresponding to the first bulb tube outputs voltage to the first bulb tube, the first bulb tube can emit X rays; when the high voltage of the bulb tube corresponding to the first bulb tube does not output voltage to the first bulb tube, the first bulb tube cannot emit X rays.

In another example, when the processor 311 controls the output value of the grid voltage corresponding to the first bulb to be the first voltage value by the executable instruction corresponding to the obtaining apparatus 300 reading the CT image in the memory 312, the method may include: outputting a first signal to a control circuit of grid voltage corresponding to the first bulb, wherein the first signal is used for enabling the control circuit of grid voltage corresponding to the first bulb to output a first voltage value; when the output value of the grid voltage corresponding to the first bulb is controlled to be the second voltage value, the method may include: and outputting a second signal to the control circuit of the grid voltage corresponding to the first bulb, wherein the second signal is used for enabling the control circuit of the grid voltage corresponding to the first bulb to output a second voltage value.

In another example, when the processor 311 obtains the data acquired by the first detector corresponding to the first bulb in the pay-off time interval through the executable instructions corresponding to the obtaining device 300 reading the CT image in the memory 312, the processor may include: acquiring data acquired by the first detector in all paying-off time intervals, and extracting the data acquired by the first detector in the paying-off time intervals from all the acquired data; or, in the paying-off time interval, controlling the first detector to acquire data; controlling the first detector not to carry out data acquisition in other time intervals except the paying-off time interval; and acquiring all data acquired by the first detector as data acquired in the paying-off time interval. Further, when controlling the first detector to perform data acquisition, the method includes: outputting a third signal to the first detector, the third signal being used to cause the first detector to perform data acquisition; when the first detector is controlled not to carry out data acquisition, the method comprises the following steps: outputting a fourth signal to the first detector, the fourth signal for disabling data acquisition by the first detector.

Referring to fig. 4, which is a block diagram of an embodiment of an apparatus for obtaining CT images according to the present application: the device is applied to medical equipment for obtaining CT images in a scanning mode, the medical equipment comprises at least two bulbs and at least two detectors corresponding to the at least two bulbs, and the device specifically comprises:

the determining module 11 is configured to determine a pay-off time interval of a first bulb tube of the at least two bulb tubes;

the control module 12 is used for controlling the first bulb tube to emit X-rays in the paying-off time interval; controlling the first bulb tube not to emit X-rays in other time intervals except the paying-off time interval;

the obtaining module 13 is configured to obtain data acquired by the first detector corresponding to the first bulb in the pay-off time interval, and obtain a CT image by using the data acquired by the first detector corresponding to the first bulb in the pay-off time interval.

In the embodiment of the invention, a coincidence time interval does not exist between the pay-off time interval of each first bulb tube and the pay-off time intervals of other bulb tubes, or the coincidence time interval between the pay-off time interval of each first bulb tube and the pay-off time intervals of other bulb tubes is smaller than a preset threshold value.

The determining module 11 is specifically configured to determine that the setting-out time interval of the first bulb tube is as follows: [ (k × N + m) × t, (k × N + m +1) × t); wherein N is the number of at least two bulbs; m is an index of the first bulb, and the value of m is one of 0, 1, …, N-2 and N-1; t is the time interval of each paying off; k is the paying-off times of the first bulb tube, and the values of K are 0, 1, … in sequence, and K is the maximum paying-off times of the first bulb tube.

The control module 12 is specifically configured to control an output value of the grid voltage corresponding to the first bulb to be a first voltage value in the pay-off time interval; controlling the output value of the grid voltage corresponding to the first bulb tube to be a second voltage value in other time intervals except the pay-off time interval; when the output value of the grid voltage is a first voltage value, the first bulb tube can emit X rays; when the output value of the grid voltage is a second voltage value, the first bulb tube cannot emit X rays; the second voltage value is greater than the first voltage value; or, in the pay-off time interval, controlling the high voltage of the bulb corresponding to the first bulb to output voltage to the first bulb; in other time intervals except the pay-off time interval, controlling the high voltage of the bulb tube corresponding to the first bulb tube not to output voltage to the first bulb tube; when the high voltage of the bulb tube corresponding to the first bulb tube outputs voltage to the first bulb tube, the first bulb tube can emit X rays; when the high voltage of the bulb tube corresponding to the first bulb tube does not output voltage to the first bulb tube, the first bulb tube cannot emit X rays.

The control module 12 is specifically configured to output a first signal to a control circuit of the grid voltage corresponding to the first bulb in a process of controlling an output value of the grid voltage corresponding to the first bulb to be a first voltage value, where the first signal is used to enable the control circuit of the grid voltage corresponding to the first bulb to output the first voltage value; and in the process of controlling the output value of the grid voltage corresponding to the first bulb to be a second voltage value, outputting a second signal to the control circuit of the grid voltage corresponding to the first bulb, wherein the second signal is used for enabling the control circuit of the grid voltage corresponding to the first bulb to output the second voltage value.

In the embodiment of the invention, the medical equipment only provides one bulb high pressure, and each of the at least two bulbs corresponds to the same bulb high pressure.

The obtaining module 13 is specifically configured to, in the process of obtaining data collected by a first detector corresponding to the first bulb in the setting-out time interval, obtain data collected by the first detector in all setting-out time intervals, and extract data collected by the first detector in the setting-out time interval from all data collected in all setting-out time intervals; or,

The obtaining module 13 is specifically configured to output a third signal to the first detector in a process of controlling the first detector to perform data acquisition, where the third signal is used to enable the first detector to perform data acquisition; and in the process of controlling the first detector not to carry out data acquisition, outputting a fourth signal to the first detector, wherein the fourth signal is used for enabling the first detector not to carry out data acquisition.

The implementation process of the functions and actions of each module in the above device is specifically described in the implementation process of the corresponding step in the above method, and is not described herein again. For the device embodiments, since they substantially correspond to the method embodiments, reference may be made to the partial description of the method embodiments for relevant points. The above-described embodiments of the apparatus are merely illustrative, wherein the modules described as separate parts may or may not be physically separate, and the parts displayed as modules may or may not be physical modules, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of the application. One of ordinary skill in the art can understand and implement it without inventive effort.

Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.

It will be understood that the present application is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the application is limited only by the appended claims.

Claims

1. A method for obtaining CT images in electronic computed tomography, the method being applied to a medical apparatus for obtaining CT images by scanning, the medical apparatus including at least two bulbs and at least two detectors corresponding to the at least two bulbs, the method comprising the steps of:

determining a pay-off time interval of a first bulb tube of the at least two bulb tubes; the process of determining the pay-off time interval of the first bulb tube of the at least two bulb tubes specifically includes: determining the pay-off time interval of the first bulb tube as follows: [ (k × N + m) × t, (k × N + m +1) × t); wherein N is the number of the at least two bulbs; m is the index of the first bulb tube, and the value of m is one numerical value of 0, 1, …, N-2 and N-1; t is the time interval of each paying off; k is the paying-off times of the first bulb tube, and the values of K are 0, 1, … in sequence, and K is the maximum paying-off times of the first bulb tube;

2. The method of claim 1, wherein the pay-off time interval of each first bulb is not coincident with the pay-off time intervals of the other bulbs, or the coincidence time interval between the pay-off time interval of each first bulb and the pay-off time intervals of the other bulbs is less than a preset threshold.

3. The method of claim 1, wherein during the payoff time interval, controlling the first bulb to emit X-rays; in other time intervals except the paying-off time interval, controlling the process that the first bulb tube cannot emit X rays, specifically comprising:

4. The method of claim 3,

5. The method of claim 3, wherein the medical device provides only one bulb high pressure and each of the at least two bulbs corresponds to the same bulb high pressure.

6. The method according to claim 1, wherein the process of obtaining the data collected by the first detector corresponding to the first bulb in the pay-off time interval specifically comprises:

7. The method of claim 6,

8. An apparatus for obtaining CT images of electronic Computed Tomography (CT), wherein the apparatus is applied to a medical device for obtaining CT images in a scanning manner, the medical device includes at least two bulbs and at least two detectors corresponding to the at least two bulbs, and the apparatus specifically includes:

the determining module is used for determining a pay-off time interval of a first bulb tube in the at least two bulb tubes; the determining module is specifically configured to determine that the setting-out time interval of the first bulb tube is as follows: [ (k × N + m) × t, (k × N + m +1) × t); wherein N is the number of at least two bulbs; m is an index of the first bulb, and the value of m is one of 0, 1, …, N-2 and N-1; t is the time interval of each paying off; k is the paying-off times of the first bulb tube, and the values of K are 0, 1, … in sequence, and K is the maximum paying-off times of the first bulb tube;

the control module is used for controlling the first bulb tube to emit X rays in the paying-off time interval; controlling the first bulb tube not to emit X-rays in other time intervals except the paying-off time interval;

9. The apparatus of claim 8, wherein the pay-off time interval of each first bulb is not overlapped with the pay-off time intervals of the other bulbs, or the overlapped time interval between the pay-off time interval of each first bulb and the pay-off time intervals of the other bulbs is less than a preset threshold.

10. The apparatus of claim 8,

the control module is specifically used for controlling the output value of the grid voltage corresponding to the first bulb tube to be a first voltage value in the pay-off time interval; controlling the output value of the grid voltage corresponding to the first bulb tube to be a second voltage value in other time intervals except the pay-off time interval; when the output value of the grid voltage is a first voltage value, the first bulb tube can emit X rays; when the output value of the grid voltage is a second voltage value, the first bulb tube cannot emit X rays; the second voltage value is greater than the first voltage value; or,

11. The apparatus of claim 10,

12. The apparatus of claim 10, wherein the medical device provides only one bulb high pressure, and each of the at least two bulbs corresponds to the same bulb high pressure.

13. The apparatus of claim 8,

14. The apparatus of claim 13,

15. A medical device for obtaining CT images of electronic Computed Tomography (CT) by scanning is characterized by specifically comprising: the device comprises a console, a scanning frame, at least two ball tubes and at least two detectors corresponding to the at least two ball tubes; wherein, the control cabinet specifically includes: the processor and the memory are used for storing executable instructions corresponding to the CT image acquisition device; wherein, the processor reads the executable instruction corresponding to the obtaining device of the CT image and is used for executing:

16. The apparatus according to claim 15, wherein the processor controls the first bulb to emit X-rays during the setting-out time interval by reading executable instructions corresponding to the CT image obtaining device; when the first bulb tube is controlled not to emit X-rays in other time intervals except the paying-off time interval, the method comprises the following steps: