Multi-source Static CT System for Heart Scanning and Its Imaging Method

Abstract

The present invention discloses a multi-source static CT system for cardiac scanning, comprising an X-ray source ring, a detector ring, a Z-directional shielding collimator, an X-Y directional shielding collimator and a control unit. Among them, the Z-directional shielding collimator is used to limit the ray width in the Z direction; the X-Y directional shielding collimator is arranged below the Z-directional shielding collimator and is used to limit the ray width in the X-Y direction; the control unit is used to realize the switching between the general scanning mode and the cardiac scanning mode; in the cardiac scanning mode, the control unit controls the X-Y directional shielding collimator to reduce the ray width of the ray beam in the X-Y direction, so that the width of a single ray beam only covers the cardiac region. The multi-source static CT system and its imaging method provided by the present invention can adopt a multi-source parallel exposure mode to further improve the time resolution of the multi-source static CT system to meet the clinical requirements of cardiac dynamic scanning.

Description

Technical Field

[0001] The present invention relates to a multi-source static CT system, and also relates to a corresponding imaging method and an electrocardiogram gating circuit. Background Art

[0002] Cardiac CT is a non-invasive examination that can be completed within a few minutes by intravenous injection of a contrast agent, and the degree of anastomosis with coronary angiography can reach up to 90%. At present, cardiac CT enhanced examination has been widely used in clinical practice due to its advantages of non-invasiveness, safety, relatively less X-ray radiation, and being easily accepted by patients. When performing a cardiac scan on a CT scan object, it is necessary to determine the phase (such as the diastolic phase and the systolic phase) for CT scanning. Generally, the relative phase of about 75% of the diastolic phase and about 30% of the systolic phase are used for CT scanning. And dual-source CT devices are usually used in cases where it is desired to achieve as high a temporal resolution as possible during CT scanning, for example, to generate tomographic images of a beating heart.

[0003] In the PCT international application with the international publication number WO2018 / 153382, a static real-time CT imaging system adapted to the requirements of a large field of view and its imaging method are disclosed. The static real-time CT imaging system includes a multi-focus annular X-ray source and an annular photon detector; wherein, the multi-focus annular X-ray source is composed of a plurality of scanning X-ray sources arranged in a ring, and the annular photon counting detector is composed of a plurality of photon counting detector modules arranged in a ring; each scanning X-ray source alternately emits a wide beam of X-rays, and after passing through the object to be measured, it is projected onto the corresponding photon counting detector module, and a non-inverse geometric imaging method is adopted between the scanning X-ray source and the corresponding photon counting detector module; each photon counting detector module operates in an overlapping manner, and sends the corresponding exposure information to the data acquisition and processing unit, and real-time reconstruction and visualization reproduction of the image are completed in the data acquisition and processing unit. However, this static real-time CT imaging system is not specifically developed for cardiac scan requirements, and still needs further improvement in meeting medical clinical needs. Summary of the Invention

[0004] The primary technical problem to be solved by the present invention is to provide a multi-source static CT system for cardiac scan.

[0005] Another technical problem to be solved by the present invention is to provide an imaging method for cardiac scan.

[0006] Still another technical problem to be solved by the present invention is to provide an electrocardiogram gating circuit for cardiac scan.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] According to the first aspect of the embodiments of the present invention, a multi-source static CT system for cardiac scanning is provided, including an X-ray source ring, a detector ring, a Z-directional shielding collimator, an X-Y directional shielding collimator, and a control unit. Among them,

[0009] the Z-directional shielding collimator is used to limit the ray width in the Z direction;

[0010] the X-Y directional shielding collimator is arranged below the Z-directional shielding collimator, and the X-Y directional shielding collimator is used to limit the ray width in the X-Y direction;

[0011] the control unit is used to realize the switching between the general scanning mode and the cardiac scanning mode;

[0012] In the cardiac scanning mode, the control unit controls the X-Y directional shielding collimator to reduce the ray width of the ray beam in the X-Y direction, so that the width of a single ray beam only covers the cardiac region.

[0013] Preferably, in the cardiac scanning mode, sequential exposure with multiple ray sources exposed simultaneously at the same moment is adopted.

[0014] Preferably, in the general scanning mode, two adjacent exposures are performed by two ray sources corresponding to two non-overlapping detectors of the projections.

[0015] According to the second aspect of the embodiments of the present invention, a static CT imaging method for cardiac scanning is provided. Among them, scanning is performed in a multi-source parallel manner; and the width of the X-ray in the X-Y direction is limited by the X-Y directional shielding collimator, so that the detectors of multiple ray sources do not overlap with each other.

[0016] Preferably, Idle_A = It, Idle_B = 2×Rt + 3×It

[0017] Among them, the exposure time is Rt, the idle time between two exposures is It, the time from the end of the exposure of the first ray source to the start of the exposure of the second ray source is Idle_A, and the afterglow time is Idle_B.

[0018] According to the third aspect of the embodiments of the present invention, a cardiac gating circuit is provided, including: an acquisition workstation responsible for parsing the restoration of the electrocardiogram (ECG) signal; an nvSync node which is an electrical node for receiving the exposure timing; the signal output of the electrocardiograph outputs the ECG signal to the ifBox circuit board; the ifBox circuit board is responsible for processing the ECG signal to implement the timing logic relationship in the above timing diagram; on this circuit board, the ECG signal is processed analogously and output to the ADC inside the FPGA, and the MCU inside the FPGA realizes ADC sampling and encapsulates the ADC sampling data into an Ethernet protocol and transmits it to the acquisition workstation through the MAC and PHY; the detection processing processes the ECG signal to identify the R wave and synchronously outputs a phase discrimination pulse, and the FPGA internally generates a corresponding gating timing waveform according to the phase discrimination pulse.

[0019] Preferably, the pre-exposure shoulder region and the post-exposure shoulder region are set to zero, so that the C signal is always the exposure region. At this time, D allows the Spot signal pulse to be output throughout the time of C, realizing retrospective ECG image acquisition.

[0020] Preferably, the pre-exposure shoulder region and the post-exposure shoulder region are set with corresponding parameters according to requirements. Then the exposure region of the C signal shows that there is a time when exposure is allowed in one heartbeat cycle. At this time, D allows the Spot signal pulse to be output only in the exposure region, realizing prospective ECG image acquisition.

[0021] Preferably, the method for the above cardiac gating circuit to implement the phase discrimination pulse includes: the circuit board does not set a dedicated detection processing circuit, but uses the sampling signal of the ADC, and compares the data of the ADC with the set data threshold value to identify the R wave and generate the phase discrimination pulse.

[0022] The multi-source static CT system for cardiac scanning and its imaging method provided by the present invention adopt a multi-source parallel exposure mode, further improving the time resolution of the static CT system to cope with cardiac dynamic scanning. At the same time, the present invention also designs the exposure timing. Under this timing, the requirement for the afterglow performance of the scintillator material of the entire ring detector is reduced, thereby reducing the cost of the detector. Description of the Drawings

[0023] Figure 1A It is a schematic diagram of the FOV projection in the general scanning mode;

[0024] Figure 1B It is a schematic diagram of the FOV projection in the cardiac scanning mode;

[0025] Figure 2 It is a schematic diagram of the six-source parallel exposure timing;

[0026] Figure 3 It is the effect diagram of the Z-directional occlusion collimator, the X-Y directional occlusion collimator and the comprehensive occlusion;

[0027] Figure 4 It is the functional structure of the collimator control board;

[0028] Figure 5 It is the electrocardiogram gating circuit timing;

[0029] Figure 6 It is the electrocardiogram gating circuit;

[0030] Figure 7 It is the exposure timing schematic. Specific embodiments

[0031] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0032] Based on the existing static real-time CT imaging system, the present invention designs a collimator structure with variable field of view. This structure provides two kinds of ray constraints. One constraint has a large X-ray collimation range, and the other constraint has a small X-ray beam range. In these two cases, the normal FOV and the FOV of the heart are satisfied respectively.

[0033] In Figure 1A and Figure 1B , taking an X-ray projection as an example respectively, the schematic diagrams of a standard FOV projection and a heart FOV projection are given. Among them, the heart FOV projection is smaller than the standard FOV projection. It can be seen that the number of detectors used for the X-ray projection under the X-ray beam constraint of the heart FOV is relatively reduced.

[0034] In view of this feature, a working mode of parallel exposure of multiple ray sources is designed. In an embodiment of the present invention, 6 ray sources are simultaneously exposed at the same moment. It should be noted that 6 ray sources are only for illustrative purposes. In other embodiments, the number of ray sources can be 3, 4, 8, 12, etc., and there is no specific limitation on this.

[0035] As Figure 2 shown, in an embodiment of the present invention, the ray sources are divided into 6 groups, and each group has N ray sources. At a certain moment, the first-numbered ray sources of the 6 groups are simultaneously exposed. After the exposure is completed, the second-numbered ray sources of the 6 groups are simultaneously exposed, and so on in turn until the Nth-numbered ray sources of each group are exposed. This is one cycle. According to the need of the system scanning length, the number of such cycles is controlled to achieve the scanning of the patient.

[0036] II. Collimator structure and control description:

[0037] The present invention also provides a collimator structure for realizing the above-mentioned change in X-ray width. As Figure 3As shown in the figure, the collimator is divided into upper and lower layers. The first layer is the Z-direction shielding collimator, which is a fixed structure and determines the size of the ray passing through the window according to the geometric relationship of the system. The second layer is the X-Y direction shielding collimator, which consists of two shielding tungsten sheets and a transmission structure. Through the transmission structure, the physical positions of the two tungsten sheets can be adjusted, so that the ray passing through the window changes, and thus different sizes of X-ray passing through the window can be obtained. After assembling the two collimators together, a comprehensive X-ray collimation effect is obtained, in which the ray passing through window 2 adapts to the standard FOV, and the ray passing through window 1 adapts to the cardiac FOV.

[0038] Correspondingly, the collimator device is equipped with a control board, such as Figure 4 shows the functional structure of the control board. The control board consists of a controller, a communication interface, a drive circuit and a feedback circuit. The communication interface communicates with the central controller in the existing multi-source static CT system to obtain the instruction for collimator field of view switching. The controller generates a mechanical communication protocol, and thus generates a control signal to drive the transmission mechanism of the collimator through the drive circuit, so that the position of the X-Y direction collimator changes to implement the instruction for collimator field of view switching. At the same time, the feedback circuit feeds back the state of the transmission structure to the controller, and the controller obtains the state of the transmission mechanism to determine whether the field of view switching instruction is completed.

[0039] III. Electrocardiogram synchronization

[0040] In order to further improve the time resolution and better acquire the images of the dynamic heart, an electrocardiogram gating circuit timing is designed to fuse the real-time electrocardiogram analog signal and the image exposure information, which is suitable for both retrospective electrocardiogram image acquisition and prospective electrocardiogram image acquisition.

[0041] Such as Figure 5 shown. In Figure 5 , A represents a normal electrocardiogram signal, B represents the phase discrimination signal of the electrocardiogram signal, which detects the position of the R-wave upstroke of the electrocardiogram signal and generates a square wave signal at this position. Heartbeat cycle and other data can be obtained according to this square wave signal. Then, a heartbeat cycle is divided into an exposure area, a pre-exposure shoulder area and a post-exposure shoulder area, as shown by C in the figure. Only in the exposure area is the exposure action triggered to generate a Spot signal, as shown by D in the figure.

[0042] Therefore, under this model, by setting the lengths of the exposure area, pre-exposure shoulder area, and post-exposure shoulder area of C, the electrocardiogram gating signal, i.e., the waveform of D, can be achieved. If the pre-exposure shoulder area and the post-exposure shoulder area are set to zero, the C signal is always in the exposure area. At this time, D allows the Spot signal pulse to output throughout the time of C. This situation corresponds to retrospective electrocardiogram image acquisition. If the pre-exposure shoulder area and the post-exposure shoulder area are set with corresponding parameters according to requirements, the exposure area of the C signal shows that there is a time when exposure is allowed in one cardiac cycle. At this time, D allows the Spot signal pulse to output only in the exposure area. This situation corresponds to prospective electrocardiogram image acquisition.

[0043] According to this idea, a special electrocardiogram gating circuit is designed in the present invention, and its circuit principle is as Figure 6 shown. In Figure 6 , the acquisition workstation is responsible for parsing the restoration of the electrocardiogram signal. The nvSync node is an electrical node that receives the exposure timing. The signal output of the electrocardiogram monitor outputs the electrocardiogram signal to the ifBox circuit board. The ifBox circuit board is responsible for processing the electrocardiogram signal to achieve the timing logic relationship in the above timing diagram. In this circuit board, the electrocardiogram signal is processed analogously and output to the ADC inside the FPGA. The MCU inside the FPGA realizes ADC sampling and encapsulates the ADC sampling data into a network protocol and transmits it to the acquisition workstation through the MAC and PHY. The detection processing processes the electrocardiogram signal to identify the R wave and synchronously outputs a phase discrimination pulse. The corresponding gating timing waveform is generated inside the FPGA according to the phase discrimination pulse.

[0044] Another way to implement the phase discrimination pulse is that in this way, the circuit board does not set a dedicated detection processing circuit, but uses the sampling signal of the ADC to identify the R wave and generate a phase discrimination pulse by comparing the ADC data with the set data threshold.

[0045] IV. Timing for Reducing the Requirements for Detector Afterglow

[0046] In the existing static CT exposure timing, the ray sources take turns to perform the exposure action. Taking Figure 7 as an example, according to the markings in the figure, the conventional static CT exposure sequence is: ray source #1-1 → ray source #1-2 → …… → ray source #1-N → ray source #2-1 → …… ray source #2-N → ray source #3-1 → …… ray source #3-N → ray source #1-1 → ……, exposing all the ray sources in sequence. In this mode, since the adjacent two ray sources are exposed in sequence, and there is an overlapping part of the detectors corresponding to the projections of the two ray sources, therefore, the time period from the end of the exposure of the first ray source to the start of the exposure of the second ray source (defined as Idle_A) determines the afterglow parameter of the detector scintillator material.

[0047] In the present invention, a new exposure timing sequence is defined, which requires that two adjacent exposures are not completed by two adjacent radiation sources, but by two radiation sources corresponding to two non-overlapping detectors in the projections. As Figure 7 shown, the optimal exposure sequence is: radiation source #1-1 → radiation source #2-1 → radiation source #3-1 → radiation source #1-2 → …… radiation source #1-N → radiation source #2-N → radiation source #3-N → radiation source #1-1 → ……, completing the rotation exposure of all radiation sources. Correspondingly, the afterglow time of the detector scintillator material is determined to be from the end of the first projection exposure to the start of the fourth projection exposure (defined as Idle_B).

[0048] If the exposure time is defined as Rt and the idle time between two exposures is It, then, Idle_A = It, Idle_B = 2×Rt + 3×It, thereby effectively reducing the requirement for the afterglow time of the detector. For example: Rt = It = 1ms, then Idle_A = 1ms, Idle_B = 5ms, and the afterglow requirement of the detector is extended from 1ms to 5ms, thus reducing the performance requirements for the detector scintillator material and contributing to the reduction of the detector cost.

[0049] In summary, the key point of the present invention is to design a working mode of simultaneous exposure of multiple radiation sources, thereby improving the time resolution of static CT scans.

[0050] In coordination with this, a collimator with an adjustable field of view in the XY direction is designed. In the working mode of simultaneous exposure of multiple sources, by adjusting and reducing the size of the collimator field of view, it is ensured that there is no overlap in the FOV projections under the condition of simultaneous exposure of multiple sources.

[0051] In coordination with this, in the mode of simultaneous exposure of multiple sources, for cardiac scans, a method for implementing electrocardiogram gating is designed to synchronously fuse real-time analog electrocardiogram signals and exposure information, and at the same time, the functions of prospective and retrospective electrocardiogram gating can be realized.

[0052] At the same time, an alternating rotation exposure timing sequence is applied, which prolongs the time interval during which the same detector segment is irradiated, reduces the requirements for the afterglow performance of the detector, and thus reduces the cost space of the detector.

[0053] The above has described in detail the multi-source static CT system and its imaging method for cardiac scans provided by the present invention. For those of ordinary skill in the art, any obvious changes made to it without departing from the essence of the present invention will constitute an infringement of the patent right of the present invention and will bear corresponding legal responsibilities.

Claims

1. A multi-source static CT system for cardiac scanning, characterized in that It includes an X-ray source ring, a detector ring, a Z-direction shielding collimator, an X-Y direction shielding collimator and a control unit. Among them, the Z-direction shielding collimator is used to limit the ray width in the Z direction; The X-Y direction shielding collimator is arranged below the Z-direction shielding collimator, and the X-Y direction shielding collimator is used to limit the ray width in the X-Y direction; The control unit is used to realize the switching between the general scanning mode and the cardiac scanning mode. Among them, in the cardiac scanning mode, sequential exposure with multiple ray sources exposing simultaneously at the same moment is adopted; in the general scanning mode, two adjacent exposures are carried out by two ray sources corresponding to two non-overlapping detectors of two projections; In the cardiac scanning mode, the control unit controls the X-Y direction shielding collimator to reduce the ray width of the ray beam in the X-Y direction, so that the width of a single ray beam only covers the cardiac region.

2. A multi-source static CT imaging method for cardiac scanning, implemented based on the multi-source static CT system described in claim 1, characterized in that It includes the following steps: Two adjacent exposures are not completed by two adjacent ray sources, but by two ray sources corresponding to two non-overlapping detectors of two projections.

3. The multi-source static CT imaging method according to claim 2, characterized in that: Scanning is carried out in a multi-source parallel manner; and the X-Y direction shielding collimator is used to limit the width of the X-ray in the X-Y direction, so that the detectors of multiple ray sources do not overlap with each other.

4. The multi-source static CT imaging method according to claim 2, characterized in that: Idle_A = It, Idle_B = 2×Rt + 3×It Among them, the exposure time is Rt, the idle time between two exposures is It, the time from the end of the exposure of the first ray source to the start of the exposure of the second ray source is Idle_A, and the afterglow time is Idle_B.

5. An electrocardiogram gating circuit is used in the multi-source static CT system according to claim 1, and is characterized in that It includes: The acquisition workstation is responsible for parsing and restoring the electrocardiogram signal; The nvSync node is an electrical node that receives the exposure timing. The signal output of the electrocardiograph outputs the electrocardiogram signal to the ifBox circuit board; the ifBox circuit board is responsible for processing the electrocardiogram signal to realize the timing logic relationship in the timing diagram. Among them, on the ifBox circuit board, the electrocardiogram signal is processed analogously and output to the ADC inside the FPGA. The MCU inside the FPGA realizes ADC sampling and encapsulates the ADC sampling data into an Ethernet protocol and transmits it to the acquisition workstation through the MAC and PHY; the detection processing circuit processes the electrocardiogram signal to identify the R wave and synchronously outputs a phase discrimination pulse, and the FPGA internally generates a corresponding gating timing waveform according to the phase discrimination pulse.

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