CN107280698B - Prospective electrocardio-gating-based mouse heart imaging system and method - Google Patents
Prospective electrocardio-gating-based mouse heart imaging system and method Download PDFInfo
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Abstract
The invention belongs to the technical field of image processing, and discloses a prospective type electrocardio-gating based mouse heart imaging system and method, which comprises the following steps: the electrocardiosignal acquisition front end is used for acquiring real-time heartbeat information of the mouse during CT image acquisition; the control board card is used for generating a trigger level by acquiring the electrocardio information of the mouse and triggering the X-ray detector to finish the acquisition of a mouse projection image; and the Micro-CT acquisition system is used for reconstructing 360 projection data. According to the method, the moving phase of the heart of the mouse is judged by capturing the electrocardio information of the living mouse and extracting the R wave crest of the electrocardio signal of the mouse, and the R wave crest triggers an X-ray detector to acquire the projection data sequence of the heart part of the mouse by utilizing the Micro-CT imaging technology, so that a plurality of phase images of the heart of the mouse in the whole heart moving period under each angle are obtained, and the reconstructed images of a plurality of phases of the heart of the mouse in a complete heart beating period are recovered.
Description
Technical Field
The invention belongs to the technical field of image processing, and particularly relates to a prospective type electrocardio-gating mouse heart imaging system and method.
Background
Micro-CT is used as a medical imaging system aiming at small animals, and compared with the traditional medical CT, the Micro-CT has the characteristic of high imaging resolution, the spatial resolution can reach the micron level, and meanwhile, the reconstruction precision is higher than that of the traditional medical CT. Micro-CT imaging is of great importance for cardiac imaging, whereas conventional Micro-CT imaging has some problems: because the gating technology is used for time-sharing phase extraction of projection data, the traditional dynamic Micro-CT system has the problem that only one image can be acquired by triggering a light source each time, so that the acquisition speed is too low, the exposure of X-rays is greatly increased, and the efficiency is reduced; the shortening of the acquisition time means that the exposure time is reduced, so that the contrast of the image is lower, and the signal-to-noise ratio of the reconstruction result is reduced.
In summary, the problems of the prior art are as follows: the traditional Micro-CT imaging has the defects that the acquisition speed is too low, the exposure of X rays is greatly increased, and the efficiency is reduced; the contrast of the image is low, and the signal-to-noise ratio of the reconstruction result is reduced.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a prospective electrocardio-gated mouse heart imaging system and method.
The invention is realized in this way, a mouse heart imaging system based on prospective cardiac gating comprises:
the front-end electrocardiosignal acquisition module is used for acquiring real-time heartbeat information of the mouse during CT image acquisition;
the DSP signal processing board card is used for generating a trigger level by acquiring the electrocardio information of the mouse and triggering the X-ray detector to finish the acquisition of a mouse projection image;
the Micro-CT medical image acquisition system is connected with the DSP signal processing board card through RS232 and used for scanning a plurality of cross sections of an object to be scanned according to 360 degrees and reconstructing 360 projection data.
The invention also aims to provide a prospective cardiac gating-based mouse cardiac imaging method of the prospective cardiac gating-based mouse cardiac imaging system, which comprises the following steps: the method comprises the following steps:
firstly, a mouse is placed on an objective table and positioned between an X-ray source and an X-ray detector, a required imaging area is placed in an effective field of view of the detector, the front end of a bipolar lead is inserted into muscle tissues of a left forelimb and a right hind limb of the mouse, and the tail end of a silver needle is connected with a button type electrocardiogram lead connector;
secondly, the double-electrode lead is connected into an electrocardio acquisition module, the electrocardio acquisition module is fixed on the rear side of a mouse and is positioned outside an effective visual field of an X-ray detector, and the analog output end of the electrocardio module is connected into an AD conversion input interface of a DSP signal processing board card;
thirdly, an AD conversion module of the DSP signal processing board card receives the input of the analog electrocardiosignal, records the maximum potential value of the analog input quantity of the electrocardiosignal of the mouse, takes the time when the numerical value is generated as the diastolic time of the heart beat of the mouse, and generates a TTL level change from 0 to 1 at the time when the maximum value is detected to be close to, wherein the high level lasts for more than 2ms, and the shortest maintenance time required for triggering the X-ray detector is reached;
step four, the DSP signal processing board judges the time between two wave crests of the mouse electrocardiosignal through the AD conversion module, and judges the number of motion phases to be acquired in a complete period of the heart beat of the mouse according to the integral time required by the detector;
determining the configuration parameters of the PC to the X-ray detector according to the number of the single-period phases obtained in the step four, and configuring the single-frame exposure time, the total frame number of the image sequence, the Binning parameters, the detector trigger mode and the detector scanning mode of the detector;
starting a turntable of the Micro-CT system to enable, starting to capture a heartbeat signal of the mouse, sending a trigger signal to the X-ray detector by the DSP signal processing board card at the R peak of the electrocardiogram of the mouse, and finishing the acquisition of projection data under a single angle;
and step seven, after the acquisition of each angle is finished, the computer controls the large disc to rotate by an angle, and then the operation in the step six is repeated until the acquisition of the projection data of 360 angles is finished.
Further, the specific relationship in the fourth step is as follows:
the single period phase number is equal to the heart cycle/single projection integration time.
Further, controlling an X-ray detector to acquire images by adopting a hardware external trigger working mode, generating a short-time high level by a DSP signal processing board card, and inputting the high level into a Sync In interface of the X-ray detector; after receiving a trigger request from the DSP signal processing board card, the X-ray detector starts to acquire images after a non-fixed time period and puts an acquisition result into a cache; after the projection image sequence of the whole heart motion cycle is acquired at one angle, the computer takes out the data in the cache, decodes and stores the data, numbers the data according to the scanning angle and the motion state, and stores the data in the computer.
Furthermore, after data acquisition is finished, the data acquired at each angle are split according to the stored definition of the SMV files, and are grouped according to phases, that is, projection data with the same phase in 360 SMV files are extracted and grouped, and single-phase data reconstruction is performed.
Further, the signal processing method of the DSP signal processing board card includes:
firstly, carrying out initialization configuration on a DSP signal processing board card;
step two, initializing the analog-digital converter and setting a relevant working mode; setting the working frequency of the analog-to-digital converter to be 25MHz of the standard working frequency, and then enabling the clock of the analog-to-digital converter;
step three, completing the configuration work of a system Timer 0; the working frequency of the Timer0 is selected to be 150MHz, the minimum time precision of the Timer0 Timer is 1 microsecond, the Timer interrupt time interval is set to be 1 millisecond, and an interrupt counter of a system Timer can store counting information with the length of 32 bits;
step four, CPU interrupt enabling is carried out, the CPU receives an interrupt request from a system timer, the DSP signal processing board card uninterruptedly reads a serial port receiving area, and whether a gate control request signal from the DSP signal processing board card exists or not is judged; when the DSP signal processing board card sends a gating request to the DSP signal processing board card, the card end of the DSP signal processing board card responds to the request signal and starts global interruption;
step five, the DSP signal processing board continuously and repeatedly reads the serial port receiving area, and whether a servo motor enabling switch operation signal sent by the DSP signal processing board exists or not is judged;
step six, when waiting for the DSP signal processing board card to send the servo enabling operation signal through the serial port, the DSP signal processing board card is in an open state in a global interruption mode; when the DSP signal processing board card program runs to an interrupt function, reading the value of the GPIO pin, jumping out of the interrupt function when the servo motor is not in a closed state, and re-receiving the request of the DSP signal processing board card; when the servo motor is in a closed state, the DSP signal processing board card starts AD conversion, and meanwhile, the Timer0 interrupts the self-increment of the counter;
step seven, after the DSP signal processing board card system is reset, the digital quantity of the wave peak of the mouse electrocardio R wave is judged in the first 3 seconds, and the DSP signal processing board card continuously carries out AD conversion;
step eight, after the interrupt function is entered again, when the DSP signal processing board card judges that the AD sampling value is an R wave crest, the pin of the GPIO01 is pulled up immediately for 3 milliseconds, and the X-ray detector is triggered to collect the projection data.
Further, the method for decoding and storing the projection data acquired by the detector of the DSP signal processing board includes:
firstly, searching a bus of a computer;
secondly, after the X-ray detector is searched, the configuration of the X-ray detector is realized through a Dexela1512 type detector;
thirdly, configuring a servo motor, calling a dynamic link library function of the fixed-height control board card to open the motion controller, setting a card number of the current motion controller and reading a system clock of the motion controller; judging the current state of the motor;
step four, serial port configuration, namely, the computer configures the X-ray source through the RS232 serial port and configures the current and the voltage of the X-ray source;
fifthly, connecting the computer with the DSP signal processing board card control board through a serial port; when the dynamic imitator starts to move, the computer enters a waiting state, a serial port buffer area is continuously checked, and whether signals from the DSP signal processing board card exist or not is judged; when the DSP signal processing board card end finishes capturing the motion period of the dynamic imitation body, writing the period value into the serial port and reading the period value by the serial port of the computer;
sixthly, configuring parameters of the X-ray detector by the computer, wherein the parameters comprise the number of projection sequence frames, the exposure time of single projection, the trigger mode of the detector and the selection of a high-sensitivity/high-dynamic working mode;
seventhly, configuring the number of frames of projection data in one triggering period of the X-ray detector by using a mouse electrocardiosignal period parameter fed back by the DSP signal processing board card gating unit; after acquiring a mouse electrocardio period value, dividing the motion phase of the dynamic dummy according to the exposure time of single projection data of a detector, wherein the sequence number of a projection image is obtained by dividing the mechanical motion period of the heart of the mouse by the exposure time of single projection data of an X-ray detector, and is the number of the divided motion phases in a complete motion period of the heart beat of the mouse;
eighthly, selecting a trigger mode of the X-ray detector, setting the detector into an external hardware trigger mode, controlling the detector to enter a trigger waiting state by a computer, and then finishing the trigger work of the detector by a DSP signal processing board card gate control unit;
ninth, the detector enters a waiting state of a trigger signal, and the computer software displays the number of frames of the image captured by the current X-ray detector and quickly refreshes the parameters; when the detector receives an external trigger signal from the DSP signal processing board card, the detector starts to acquire images according to configured parameters, and acquired projection data are written into a computer cache through a Camera Link high-speed transmission line;
step ten, after the detector is triggered and finishes the acquisition work each time, checking whether 360-degree data acquisition of the heart of the mouse is finished, if the acquisition work of all angles is not finished, controlling a GTS400 motion control card by computer software, and realizing the rotation of the Micro-CT large disc through a servo motor driver, wherein the rotation angle is 1 degree; when the 360-degree image data are acquired, the program is ended.
The invention also aims to provide a Micro-CT system provided with the mouse heart imaging system based on the prospective electrocardio-gating.
The invention has the advantages and positive effects that: the method comprises the steps of capturing live mouse electrocardio information, extracting an R wave crest of mouse electrocardiosignals, judging mechanical motion phases of a mouse heart, and collecting projection data sequences of the mouse heart by utilizing a Micro-CT imaging technology under the phases, so that a plurality of phase images of the mouse in the whole heart mechanical motion period under each angle are obtained, the Micro-CT adopts a 'rotation-stop' scanning mode to work, and after 360-degree projection images are collected, image reconstruction is carried out by utilizing multi-phase image sequences under all angles, so that reconstructed images of a plurality of phases of the mouse heart in a whole heart beat period are recovered. The method has the advantages that the projection image sequence acquisition technology of the X-ray detector is utilized, so that the projection images of all the mouse motion phases in a heart beat period can be acquired at one time in one motion period (namely one heart beat period) of the mouse heart, the method replaces the method that the conventional Micro-CT dynamic imaging technology can only acquire one projection image in one heart beat period, and the working efficiency of the system is improved.
Drawings
FIG. 1 is a schematic structural diagram of a mouse heart imaging system based on prospective cardiac gating according to an embodiment of the present invention;
in the figure: 1. a front end electrocardiosignal acquisition module; 2. a DSP signal processing board card; 3. Micro-CT medical image acquisition system.
Fig. 2 is a flowchart of lower computer programming according to an embodiment of the present invention.
Fig. 3 is a design flowchart of corresponding upper computer acquisition software provided in the embodiment of the present invention.
FIG. 4 is a schematic timing diagram of an acquisition operation mode of a Micro-CT cardiac gating detector according to an embodiment of the present invention.
Fig. 5 is a flowchart of a mouse heart imaging method based on prospective cardiac gating according to an embodiment of the present invention.
Fig. 6 is a schematic diagram of a reconstruction result performed by using data acquired by a gating technique according to an embodiment of the present invention.
Fig. 7 is a schematic diagram of a reconstruction result acquired without using a gating technique according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The following detailed description of the principles of the invention is provided in connection with the accompanying drawings.
As shown in fig. 1, the mouse heart imaging system based on prospective cardiac gating according to the embodiment of the present invention includes:
the front end electrocardiosignal acquisition module 1 is used for acquiring real-time heartbeat information of a mouse during CT image acquisition;
the DSP signal processing board card 2 generates a trigger level by acquiring the electrocardio information of the mouse and triggers the X-ray detector to finish the acquisition of a mouse projection image;
Micro-CT medical image collection system 3 is connected with DSP signal processing integrated circuit board 2 through RS232, mainly comprises carousel, X ray detector and X light source, and whole Micro-CT will adopt the rotary drum formula structure, and it is similar to the CT that uses clinically, and detector and X ray source are then fixed in on a rotatable barrel frame this moment, and the one week of rotation around the measured object during scanning realizes the image acquisition of multi-angle, and the sample is put and is kept the position unchangeable on the objective table at barrel frame center. And a translation stage is arranged below each X-ray source and can be used for adjusting the relative positions of the X-ray source and the X-ray detector. The small animals are placed on an object stage at the center of the turntable, the large disc rotates at a constant speed when images are collected, multi-angle scanning is achieved, and the small animals are placed in the center and are fixed.
The mouse heart imaging system based on prospective electrocardio-gating provided by the embodiment of the invention is realized by an upper computer and a lower computer:
a flow chart of a program design part of the lower computer (the DSP signal processing board card) is shown in fig. 2, and the specific method is as follows:
1. firstly, the program will perform initialization configuration on the DSP signal processing board card, wherein the complete movement of the program from the ROM to the RAM and the configuration work of the GPIO pin will be completed in the part.
2. After the basic initialization of the DSP signal processing board card is completed, the initialization work of the ADC and the setting of the relevant working mode are carried out. Firstly, the setting of the working clock of the ADC module needs to set the working frequency of the ADC to the standard working frequency of 25MHz, and then the clock of the ADC is enabled. The working mode of the ADC is set as sequential sampling, frequency division processing is not carried out under 25MHz, continuous sampling is set, coverage sequencing is started, and an A0 sampling channel is selected.
3. The configuration work of the system Timer0 is completed. The operating frequency of the Timer0 is selected to be 150MHz, the minimum time precision of the Timer0 Timer is 1 microsecond, and the interrupt time interval of the Timer is set to be 1 millisecond, so that the interrupt counter of the system Timer can store counting information with the length of 32 bits.
4. After the configuration work of the ADC and the setting of the system timer are finished, CPU interrupt enabling is carried out, and at the moment, the CPU receives an interrupt request from the system timer. And then, the DSP signal processing board card continuously reads the serial port receiving area and judges whether a gating request signal from the upper computer exists or not. When the upper computer sends a gating request to the DSP signal processing board card, the DSP signal processing board card end responds to the request signal and starts global interruption.
And 5, continuously and repeatedly reading the serial port receiving area by the DSP signal processing board card, and judging whether a servo motor enabling switch operation signal sent by the upper computer exists or not. If the DSP signal processing board card verifies that a private server motor enabling starting signal sent by the upper computer is received, the electromagnetic relay is conducted and controlled through controlling a pin of the GPIO02, the electromagnetic relay can be regarded as a switch, when the GPIO02 pin of the DSP signal processing board card outputs a high level, the electromagnetic relay is in a conducting state, a driver of the servo motor is enabled at the moment, and the computer can conduct motion control on the Micro-CT turntable through the control card. When the computer controls the large disc to rotate for an angle, the computer sends a servo enabling closing signal to the DSP signal processing board card, and the DSP signal processing board card pulls down the GPIO02 pin after receiving the signal, so that the servo enabling closing operation is realized.
6. When waiting for the host computer to send the servo enabling operation signal through the serial port, the DSP signal processing board card is in an open state in a global interrupt mode, and at the moment, the DSP signal processing board card can be normally interrupted through the Timer0 to enter an interrupt function. When the DSP signal processing board card program runs to an interrupt function, the value of the GPIO pin is read firstly, the servo motor is ensured to be in a closed state at the moment, if the servo motor is not in the closed state, the interrupt function is jumped out, and the request of the upper computer is accepted again. When the servo motor is in a closed state, the DSP signal processing board card starts to perform AD conversion, and meanwhile, the Timer0 interrupts the self-increment of the counter.
7. After the DSP signal processing board card system is reset, the first 3 seconds are utilized to judge the digital quantity of the wave peak of the mouse electrocardio R wave, at the moment, the DSP signal processing board card continuously carries out AD conversion, when a larger value of the AD conversion appears, the smaller value appearing before is covered, and the largest digital quantity is stored and recorded as Max. Then, using an array A5 with storage space 5 to circularly store the successively collected electrocardiosignal data, only when the array elements are all greater than 0.95Max, and it is satisfied that the third element A2 of the array is at the maximum value of the array elements, A0, A1 are progressively increased, A3, A4 are progressively decreased, said moment is approximately regarded as the diastolic moment of mechanical movement of mouse heart. According to the judgment of the R wave peak, the mouse heartbeat period can be obtained according to the interrupt count value of the Timer0 between adjacent wave peaks, and the unit is millisecond. After the DSP signal processing board card calculates the heartbeat period of the mouse, the information is fed back to the computer through the RS232 serial port.
8. After the interruption function is entered again, once the DSP signal processing board card judges that the AD sampling value is the R wave crest, the GPIO01 pin is pulled up immediately and lasts for 3 milliseconds, so that the X-ray detector is triggered to acquire projection data. After the X-ray detector is successfully triggered, the DSP signal processing board card can not wait for the detector to finish acquisition and immediately enters the next system interrupt stage, and the acquisition and storage operations of the acquired data of the X-ray detector are finished by the computer.
The upper computer software (computer acquisition software) of the mouse heart imaging system based on the prospective cardiac gating provided by the embodiment of the invention is matched with the DSP signal processing board card to configure relevant exposure parameters of the X-ray detector and set a trigger mode of the detector, and completes the decoding and storage work of the projection data acquired by the detector, and the specific software design flow is shown in FIG. 3, and the method comprises the following steps:
1. when the program is started, the system searches the bus of the computer to ensure that the X-ray detector is positioned on the bus, if the detector device is not found on the bus of the computer, a prompt box for the device which is not found is popped up, and the program is terminated.
2. After the X-ray detector is successfully searched, the system hangs the device on the bus, at this time, the configuration of the X-ray detector can be realized through a function provided by a software development kit of the Dexela1512 type detector, at this time, the detector parameters required to be configured are incomplete, and the detector is temporarily hung on the bus to enter a state to be configured.
3. The program will then proceed with the configuration of the servo motors. Before a program runs, a Kerr Morgan servo motor driver needs to be ensured to be in a power-on state, a motor enabling switch needs to be ensured to be turned on, and the driver is connected with a computer through a fixed height GTS400 motion control board card. On the basis of ensuring that the hardware setting and connection are correct, initializing the servo motor, calling a dynamic link library function of the fixed-height control board card to open the motion controller, then setting the card number of the current motion controller and reading the system clock of the motion controller. The initialization process also needs to judge the current state of the motor, and if the motor is in a motion state under the current condition, the motor stops moving. After the initialization operation is completed, the program will return a boolean value, which when returned to TRUE indicates that the initialization was successful.
4. And then the software realizes the configuration of a serial port, and the PC communicates with the X-ray source and the DSP signal processing board card through the serial port. The computer configures the X-ray source through the RS232 serial port, needs to configure the current and the voltage of the X-ray source, and generally sets the tube voltage to be 50kV, the tube current to be 300uA, and the focal spot size to be a middle focal spot. Meanwhile, the X-ray source information monitoring module feeds the current real-time voltage and current parameters of the X-rays back to the computer, so that a user can observe the X-rays conveniently.
5. Meanwhile, the computer is connected with the DSP signal processing board card control board through a serial port. The baud rate of serial communication will be set to 9600, with 8-bit data bits, 1-bit stop bit, no parity. It should be noted that when the servo motor is powered on to move, strong magnetic field interference can be generated, and a common 3-wire RS232 serial port line can be influenced by the magnetic field, so that normal serial port communication between a computer and a DSP signal processing board card is influenced. Therefore, the RS232 interface is converted into the RS422 interface, and the driving capability and the anti-interference capability of the serial port transmission line are improved in a mode of externally connecting a 5V stabilized voltage power supply. Because the interface conversion of the RS232 and the RS422 is completely finished by hardware, the corresponding computer software and DSP signal processing board card programs do not need to be changed. When the dynamic imitator starts to move, the computer enters a waiting state, and the serial port buffer area is continuously checked to see whether signals from the DSP signal processing board card exist or not. When the DSP signal processing board card end finishes capturing the motion period of the dynamic imitator, the period value is written into the serial port and is read by the serial port of the computer.
6. And then, a computer is required to carry out parameter configuration on the X-ray detector, wherein the parameters comprise the number of projection sequence frames, the exposure time of a single projection, the triggering mode of the detector and the selection of a high-sensitivity/high-dynamic working mode.
7. The configuration of the number of projection data frames in one triggering period of the X-ray detector needs to use the mouse electrocardiosignal period parameters fed back by the DSP signal processing board card gating unit. After the program obtains the mouse electrocardio period value, the program divides the motion phase of the dynamic dummy according to the exposure time of single projection data of the detector, the sequence number of the projection image is obtained by dividing the mechanical motion period of the mouse heart by the exposure time of single projection data of the X-ray detector, and the sequence number of the projection image is the number of the divided motion phases in a complete motion period of the mouse heart beat.
8. The trigger mode of the X-ray detector needs to be selected, the detector is set to be in an external hardware trigger mode, the computer controls the detector to enter a trigger waiting state, and then the DSP signal processing board card gate control unit finishes the trigger work of the detector.
9. When the detector configuration is completed, the detector enters a waiting state of a trigger signal, and the computer software displays the number of frames of the image captured by the X-ray detector at present and quickly refreshes the parameters. When the detector receives an external trigger signal from the DSP signal processing board card, the detector starts to acquire images according to configured parameters, and acquired projection data are written into a computer cache through a Camera Link high-speed transmission line. After all image binary data in a trigger period are acquired and written into the computer cache, the software completes the decoding operation of the original data in the cache area, and stores the decoded raw data to the appointed position of the computer according to the parameters set by the detector.
10. When the detector is triggered and the acquisition work is completed each time, the program checks whether the 360-degree data acquisition of the heart of the mouse is completed or not, if the acquisition work of all angles is not completed, the GTS400 motion control card is controlled by computer software, the rotation of the Micro-CT large disc is realized through a servo motor driver, and the rotation angle is 1 degree. When the 360-degree image data are acquired, the program is ended.
The invention applies a hardware type external triggering working mode of the X-ray detector, namely, a PC is responsible for parameter configuration of the X-ray detector, but a triggering signal for commanding the detector to carry out actual exposure operation is sent to a third party device to complete, and a control board card based on a DSP signal processing board card chip is used for completing the generation of the external triggering signal.
As shown in fig. 5, the mouse heart imaging method based on prospective cardiac gating according to the embodiment of the present invention includes the following steps:
firstly, a mouse is placed on an objective table and positioned between an X-ray source and an X-ray detector, a required imaging area is placed in an effective field of view of the detector, the front end (silver needle) of a bipolar lead is inserted into muscle tissues of the left forelimb and the right hind limb of the mouse, the tail end of the silver needle is connected with a button type electrocardiogram lead connector, and the contact area is increased by conductive adhesive;
secondly, the double-electrode lead is connected into an electrocardio acquisition module, the electrocardio acquisition module is fixed on the rear side of a mouse and is positioned outside an effective visual field of an X-ray detector, and the analog output end of the electrocardio module is connected into an AD conversion input interface of a DSP signal processing board card;
thirdly, an AD conversion module of the DSP signal processing board card receives the input of the analog electrocardiosignal, records the maximum potential value of the analog input quantity of the mouse electrocardiosignal, takes the time when the value is generated as the diastolic time of the heart beat of the mouse, and generates a TTL level change from 0 to 1 at the time when the value is measured to be close to the maximum value, wherein the high level lasts for more than 2ms so as to reach the shortest maintenance time required for triggering the X-ray detector;
step four, the DSP signal processing board judges the time between two wave crests of the mouse electrocardiosignal through the AD conversion module, and judges the number of motion phases to be acquired in a complete period of the heart beat of the mouse according to the integration time required by the detector, and the specific relation is as follows:
the single-period phase number is equal to the heartbeat period/single projection integral time;
determining the configuration parameters of the PC to the X-ray detector according to the number of the single-period phases obtained in the step four, and configuring the single-frame exposure time, the total frame number of the image sequence, the Binning parameters, the detector trigger mode and the detector scanning mode of the detector;
starting a turntable of the Micro-CT system to enable, starting to capture a heartbeat signal of the mouse, sending a trigger signal to the X-ray detector by the DSP signal processing board card at the R peak of the electrocardiogram of the mouse, and finishing the acquisition of projection data under a single angle;
and step seven, after the acquisition of each angle is finished, the computer controls the large disc to rotate by an angle, and then the operation in the step six is repeated until the acquisition of the projection data of 360 angles is finished.
In the fifth step, considering that the beating frequency of the heart of the mouse is relatively fast, in order to accurately distinguish the heart of the mouse from obvious differences under different heartbeat phase states, the exposure time of the detector is not too long, the shortest exposure time under the current Binning parameters is recommended to be selected for projection data scanning, and the Binning parameters are set to be the shortest exposure time of the detector;
the total frame number of the sequence of the detector is consistent with the number of the single-period phases obtained in the fourth step, but the obvious difference between different motion phases is considered during reconstruction, the time required by reconstruction is shortened as much as possible, all motion phases can not be completely reconstructed, reconstruction is carried out at intervals of a fixed value, and the number of the motion states obtained by final reconstruction is reduced;
for an X-ray detector, a software trigger mode different from a general Micro-CT system is adopted, a hardware external trigger working mode is adopted to control the X-ray detector to carry out image acquisition, a DSP signal processing board card generates a short-time high level, and the short-time high level is input into a Sync In interface of the X-ray detector; after receiving a trigger request from the DSP signal processing board card, the X-ray detector starts to acquire images after a non-fixed time period (the time period is determined by the remaining scanning time of the X-ray detector, which is not acquired in the last frame), and the acquisition result is put in a cache; after the projection image sequence of the whole heart motion cycle is acquired at one angle, the computer takes out the data in the cache, decodes and stores the data, numbers the data according to the scanning angle and the motion state, and stores the data in the computer.
After data acquisition is finished, the data acquired at each angle are split according to the stored definition of the SMV files, and are grouped according to phases, namely projection data with the same phase in 360 SMV files are extracted and grouped, and then single-phase data reconstruction is carried out.
The effect of the present invention will be described in detail with reference to comparative experiments.
In the process of testing the system performance, a moving dummy rotating at a high speed is used for carrying out Micro-CT dynamic acquisition, the moving speed of the dummy is close to that of a mouse heart, and the movement is 500 complete cycles per minute. Fig. 6 shows the reconstruction of data acquired using the gating technique of this patent, and fig. 7 shows the reconstruction acquired without the gating technique. It can be seen that the high-speed moving phantom can be captured by using the gating technology and the phantom image at a certain moment in the reconstruction can be successfully reconstructed, and the reconstruction result without using the gating technology is disordered. Because the heart motion amplitude of the mouse is much smaller than that of a phantom, the prospective gating technology can well adapt to the heart beat frequency and amplitude of the mouse, and an ideal acquisition result is obtained.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (6)
1. A mouse heart imaging system based on prospective cardiac gating is characterized by comprising:
the front-end electrocardiosignal acquisition module is used for acquiring real-time heartbeat information of the mouse during CT image acquisition;
the DSP signal processing board card is used for generating a trigger level by acquiring the electrocardio information of the mouse and triggering the X-ray detector to finish the acquisition of a mouse projection image;
the Micro-CT medical image acquisition system is connected with the DSP signal processing board card through RS232, is used for scanning projection data of an object to be scanned according to 360 degrees, and is used for reconstructing the projection data of 360 degrees;
the mouse heart imaging method based on the prospective electrocardio-gating of the mouse heart imaging system based on the prospective electrocardio-gating comprises the following steps: the method comprises the following steps:
firstly, a mouse is placed on an objective table and positioned between an X-ray source and an X-ray detector, a required imaging area is placed in an effective field of view of the X-ray detector, the front end of a bipolar lead is inserted into muscle tissues of a left forelimb and a right hind limb of the mouse, and the tail end of a silver needle is connected with a button type electrocardiogram lead connector;
secondly, the double-electrode lead is connected into an electrocardio acquisition module, the electrocardio acquisition module is fixed on the rear side of a mouse and is positioned outside an effective visual field of an X-ray detector, and the analog output end of the electrocardio module is connected into an AD conversion input interface of a DSP signal processing board card;
thirdly, an AD conversion module of the DSP signal processing board card receives the input of the analog electrocardiosignal, records the mouse electrocardio R peak of the analog input quantity of the mouse electrocardiosignal, takes the moment of the numerical value as the diastolic moment of the heart beat of the mouse, and generates a TTL level change from 0 to 1 at the moment of measuring the maximum value, and the high level is continuously more than 2ms to reach the shortest maintenance time required to trigger the X-ray detector;
step four, the DSP signal processing board judges the time between two wave crests of the mouse electrocardiosignal through the AD conversion module, and judges the number of motion phases to be acquired in a complete period of the heart beat of the mouse according to the integration time required by the X-ray detector;
determining the configuration parameters of the PC to the X-ray detector according to the number of the single-period phases obtained in the step four, and configuring the single-frame exposure time, the total frame number of the image sequence, the Binning parameters, the detector trigger mode and the detector scanning mode of the detector;
starting a rotary table of the X-ray source and the Micro-CT system to enable, starting to capture a mouse heartbeat signal, sending a trigger signal to the X-ray detector by the DSP signal processing board card at the R peak of the mouse electrocardio, and collecting a projection image sequence of the whole heart motion period;
and step seven, after the acquisition of each angle is finished, the computer controls the large disc to rotate by an angle, and then the operation in the step six is repeated until the acquisition of the projection data of 360 degrees is finished.
2. The prospective cardiac gating system for mice according to claim 1, wherein the specific relationship among the four steps is as follows:
the single period phase number is equal to the heart cycle/single projection integration time.
3. The prospective cardiac gating system for mice according to claim 1, wherein a hardware external trigger working mode is adopted to control an X-ray detector to acquire images, a DSP signal processing board card generates a short-time high level, and the short-time high level is input into a Sync In interface of the X-ray detector; after receiving a trigger request from the DSP signal processing board card, the X-ray detector starts to acquire images after a non-fixed time period and puts an acquisition result into a cache; after the projection image sequence of the whole heart motion cycle is acquired at one angle, the computer takes out the data in the cache, decodes and stores the data, numbers the data according to the scanning angle and the motion state, and stores the data in the computer.
4. The prospective cardiac gating system for mice as claimed in claim 1, wherein after the data acquisition is completed, the image sequence acquired at each angle is split and grouped by phase, that is, the projection images with the same phase in the 360-degree projection data are combined to participate in the reconstruction.
5. The prospective cardiac gating mouse imaging system according to claim 1, wherein the signal processing method of the DSP signal processing board comprises:
firstly, carrying out initialization configuration on a DSP signal processing board card;
step two, initializing work of the ADC and setting related working modes; setting the working frequency of the ADC to be 25MHz of the standard working frequency, and then enabling the ADC clock;
step three, completing the configuration work of a system Timer 0; the working frequency of the Timer0 is selected to be 150MHz, the minimum time precision of the Timer0 Timer is 1 microsecond, the Timer interrupt time interval is set to be 1 millisecond, and an interrupt counter of a system Timer can store counting information with the length of 32 bits;
step four, CPU interrupt enabling is carried out, the CPU receives an interrupt request from a system timer, the DSP signal processing board card uninterruptedly reads a serial port receiving area, and whether a gate control request signal from the DSP signal processing board card exists or not is judged; when the DSP signal processing board card sends a gating request to the DSP signal processing board card, the card end of the DSP signal processing board card responds to the request signal and starts global interruption;
step five, the DSP signal processing board continuously and repeatedly reads the serial port receiving area, and whether a servo motor enabling switch operation signal sent by the DSP signal processing board exists or not is judged;
step six, when waiting for the DSP signal processing board card to send the servo enabling operation signal through the serial port, the DSP signal processing board card is in an open state in a global interruption mode; when the DSP signal processing board card program runs to an interrupt function, reading the value of the GPIO pin, jumping out of the interrupt function when the servo motor is not in a closed state, and re-receiving the request of the DSP signal processing board card; when the servo motor is in a closed state, the DSP signal processing board card starts AD conversion, and meanwhile, the Timer0 interrupts the self-increment of the counter;
step seven, after the DSP signal processing board card system is reset, the digital quantity of the wave peak of the mouse electrocardio R wave is judged in the first 3 seconds, and the DSP signal processing board card continuously carries out AD conversion;
step eight, after the interrupt function is entered again, when the DSP signal processing board card judges that the AD sampling value is an R wave crest, the pin of the GPIO01 is pulled up immediately for 3 milliseconds, and the X-ray detector is triggered to collect the projection data.
6. The prospective cardiac gating system for mice according to claim 1, wherein the method for decoding and storing the projection data acquired by the detector of the DSP signal processing board comprises:
firstly, searching a bus of a computer;
secondly, after the X-ray detector is searched, parameter configuration is carried out on the X-ray detector;
thirdly, configuring a servo motor, opening the motion controller, setting the card number of the current motion controller and reading the system clock of the motion controller; judging the current state of the servo motor;
fourthly, configuring an X-ray source, wherein the computer configures the X-ray source through an RS232 serial port, and configures the current and the voltage of the X-ray source;
fifthly, connecting the computer with the DSP signal processing board card control board through a serial port; when the computer enters a waiting state, the serial port buffer area is continuously checked whether signals from the DSP signal processing board card exist or not; when the DSP signal processing board card end finishes capturing the mouse electrocardio-motion period, writing the period value into the serial port, and reading the period value by the serial port of the computer;
sixthly, configuring parameters of the X-ray detector by the computer, wherein the parameters comprise the number of projection sequence frames, the exposure time of single projection, the trigger mode of the detector and the selection of a high-sensitivity/high-dynamic working mode;
seventhly, configuring the number of frames of projection data in one triggering period of the X-ray detector by using a mouse electrocardiosignal period parameter fed back by the DSP signal processing board card gating unit; after acquiring a mouse electrocardio period value, dividing the motion phase of the heart of the mouse according to the exposure time of single projection data of a detector, wherein the sequence number of projection images is obtained by dividing the motion period of the heart of the mouse by the exposure time of single projection data of an X-ray detector, and the sequence number of the projection images is the number of the divided motion phases in a complete motion period of the heart beat of the mouse;
eighthly, selecting a trigger mode of the X-ray detector, setting the detector into an external hardware trigger mode, controlling the detector to enter a trigger waiting state by a computer, and then finishing the trigger work of the detector by a DSP signal processing board card gate control unit;
ninth, the detector enters a waiting state of a trigger signal, and the computer software displays the number of frames of the image captured by the current X-ray detector and quickly refreshes the parameters; when the detector receives an external trigger signal from the DSP signal processing board card, the detector starts to acquire images according to configured parameters, and acquired projection data are written into a computer cache through a Camera Link high-speed transmission line;
step ten, after the detector is triggered and finishes the acquisition work each time, checking whether 360-degree data acquisition of the heart of the mouse is finished, if the acquisition work of all angles is not finished, controlling a servo motor by computer software to realize the rotation of the Micro-CT large disk, wherein the rotation angle is 1 degree; when the 360-degree image data are acquired, the program is ended.
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