A cardiac CT scanning detection method and exposure control method

Abstract

The present invention discloses a cardiac CT scanning detection method and exposure control method. The method collects, collects statistics, and calculates and analyzes the heartbeat status of each different test person. Based on the heartbeat characteristics of different patients, the heartbeat cycle during scanning is predicted, and the exposure control scheme is automatically selected and adjusted. The method classifies the time fluctuation of the R-R part of the heartbeat cycle and predicts the current cycle time. This method improves the accuracy of the exposure starting point, reduces the exposure time, reduces the radiation dose to the person during the scanning process, and improves the scanning success rate.

Description

Technical Field

[0001] The present invention relates to the technical field of CT cardiac scanning, and in particular to a cardiac CT scanning detection method and an exposure control method. Background Art

[0002] As one of the primary areas for CT scanning, the heart and its coronary arteries have long been a key and challenging area for CT applications. Because the heart is constantly beating, the scan captures images from different beat intervals, resulting in blurring and artifacts when the computer reconstructs the three-dimensional image. Since X-rays are harmful to the human body, minimizing the radiation dose received by patients during CT scans is a key technological advancement.

[0003] Currently, during cardiac scanning, some synchronization technology is required for the heart, also known as ECG synchronization technology. This technology uses ECG and other ECG gating devices to assist in completing cardiac scanning. There are currently two gating technologies: prospective gating and retrospective gating. ECG devices (such as electrocardiogram monitors) are used to detect heart movement and detect ECG changes during the cardiac cycle as a reference for heart movement.

[0004] Prospective gating involves the system first detecting changes in cardiac motion during the cardiac cycle. When data acquisition requirements are met, sequential scanning is initiated, emitting X-ray acquisition signals. This pre-set acquisition window, followed by triggering the scan when the system detects that this condition has been met, is called prospective gating. Retrospective gating differs significantly from prospective gating in that it continuously initiates scanning and collects data throughout the cardiac cycle. The inclusion of an ECG gating device allows for monitoring cardiac phases throughout the cardiac cycle. Scanning continues throughout the cardiac cycle, combining images from different scan phases. After the scan is complete, images of approximately the same phase are reconstructed and combined. Images acquired at different cardiac phases are used to reconstruct images of different cardiac phases, resulting in images of the heart that resemble those at different times during a continuous cardiac cycle.

[0005] Prospective ECG gating is suitable for patients with stable heart rate. The scan is prone to failure, but the patient's radiation dose is small. Retrospective ECG gating is suitable for patients with irregular heart rate, premature beats, and faster heart rate. The success rate is high, but the patient's radiation dose is large.

[0006] Each cardiac cycle in a patient's electrocardiogram (ECG) consists of a series of regular waveforms: the P wave, the QRS complex, and the T wave. During a cardiac scan, parameters must be set on the host computer to control the scan during a period of relatively stable heartbeats. The QRS peak represents the maximum heartbeat and is easiest to detect. Therefore, during a scan, the ECG monitor emits a pulse signal upon detecting the QRS peak. The control system uses this pulse signal as a reference for scanning control. This pulse signal is called the ECG_TRIGGER signal. When using prospective gating, the CT system sets a trigger point based on the ECG_TRIGGER signal. This trigger point is delayed by a time, called T_delay, from the rising edge of the ECG_TRIGGER signal. The CT scan begins after the trigger time T_delay is reached. When the heart rate is stable, the T_delay time is also relatively stable, making the scan more likely to succeed. However, when the patient's heart rate is irregular, using the same T_delay time for scanning can easily lead to scan failure. Summary of the Invention

[0007] Technical purpose: To overcome the shortcomings of the existing technology, the present invention proposes a cardiac CT scanning detection method and exposure control method that can sample the heartbeat status of each patient and perform statistics and data calculation and analysis. According to the heartbeat characteristics of different patients, the heartbeat cycle during scanning is predicted, and the exposure control scheme is automatically selected and adjusted. The exposure start time and exposure duration are accurately adjusted, which can reduce the radiation dose and greatly increase the scanning success rate. It is suitable for patients with irregular heartbeats.

[0008] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution:

[0009] A cardiac CT scanning and detection method is provided. An electrocardiogram (ECG) monitor is connected to detect ECG signals. When the output of the ECG monitor is higher than a set threshold level, the CT system detects the ECG signal, first detecting the peak of the QRS wave, and then sequentially inferring the T wave and P wave based on the R wave peak of the QRS wave. The process of detecting the peak of the QRS wave includes: first statistically detecting the maximum value and the maximum rising slope of the ECG signal obtained by AD sampling within a period of time T, and using these to establish a detection threshold. In the subsequent detection process, when the AD sampling value reaches a threshold established based on the maximum value and the maximum slope and begins to decrease in value, it is considered that the peak of the QRS wave has arrived. After the peak of the R wave, the peak of the second wave is the T wave, and the peak of the third wave is the P wave. After the scan is completed, the established detection threshold is reset to zero. After a new patient's ECG signal is connected, a new detection threshold is re-established based on the ECG signal.

[0010] A cardiac CT scan exposure control method uses the above-mentioned cardiac CT scan detection method for detection, detects the fluctuation of several cardiac cycles through an electrocardiogram monitor, and detects the electrocardiogram signals detected by the electrocardiogram monitor to obtain P waves, T waves, and QRS waves. RR time fluctuation classification intervals are set, and the time value of the RR portion within the cardiac cycle is counted. The duration of the current cardiac cycle is predicted based on the time fluctuation of the RR portion in the detected cardiac cycle, and the exposure start time and exposure duration are set to obtain a cardiac exposure image.

[0011] Preferably, the process of predicting the duration of the current heartbeat cycle based on the time fluctuation of the RR part in the detected heartbeat cycle includes: setting the RR part time fluctuation grading interval, the first-level interval is 0-5ms, the second-level interval is 5-10ms, the third-level interval is 10-20ms, and the fourth-level interval is above 20ms; in the first-level interval, the RR part duration LAST_TIME_RR of the previous heartbeat cycle is used as the RR part duration CURRENT_TIME_RR of the current heartbeat cycle; in the second-level interval, the average duration AVERAGE_TIME_RR of the RR part in the detected heartbeat cycle is used as the RR part duration CURRENT_TIME_RR of the current heartbeat cycle, and in the third-level interval, LAST_TIME_RR and AVERAGE_TIME_RR are assigned different weight ratios η, CURRENT_TIME_RR=(LAST_TIME_RR×η+AVERAGE_TIME_RR×(1-η), where η=(MAX_TIME_RR-MIN_TIME_RR) / AVERAGE_TIME_RR and MAX_TIME_RR indicate the maximum value of the RR portion of the detected heart cycle, and MIN_TIME_RR indicates the minimum value of the RR portion of the detected heart cycle. Within the four-level interval, there is no need to predict the duration, and the entire exposure is within the T wave to P wave interval.

[0012] Preferably, within the three-level interval, the present invention assigns a correction coefficient α to the calculation of CURRENT_TIME_RR based on the fluctuation pattern of the duration of the RR portion of the cardiac cycle; that is, CURRENT_TIME_RR = (LAST_TIME_RR × η + AVERAGE_TIME_RR × (1-η)) × α. The process of obtaining the correction coefficient α includes: statistically calculating the durations of the RR portion, PR portion, and RT portion of the cardiac cycle, denoted as TIME_RR, TIME_PR, and TIME_RT, respectively; and fitting the fluctuation curves of TIME_RR, TIME_PR, and TIME_RT in the coordinate system.

[0013] When TIME_RR and TIME_PR have no fluctuation relationship: if TIME_RR and TIME_RT fluctuate in the same direction, α=CURRENT_TIME_RT / LAST_TIME_RT, where LAST_TIME_RT represents the duration of the RT portion of the previous cycle and CURRENT_TIME_RT represents the duration of the RT portion of the current cycle; if TIME_RR and TIME_RT fluctuate in different directions, α= LAST_TIME_RT / CURRENT_TIME_RT;

[0014] When TIME_RR and TIME_RT have no fluctuation relationship: if TIME_RR and TIME_PR fluctuate in the same direction, α = AVERAGE_TIME_PR / LAST_TIME_PR, where LAST_TIME_PR represents the duration of the PR portion of the previous cycle and AVERAGE_TIME_PR represents the duration of the PR portion of the average cycle; if TIME_RR and TIME_PR fluctuate in different directions, α = LAST_TIME_PR / AVERAGE_TIME_PR;

[0015] When TIME_RR has a fluctuating relationship with TIME_PR and TIME_RT, α is calculated by weighted average based on the impact of TIME_PR and TIME_RT on TIME_RR;

[0016] When TIME_RR has no fluctuation relationship with TIME_PR and TIME_RT, α takes the value of 1.

[0017] Preferably, in the present invention, when there is a fluctuation relationship between TIME_RR, TIME_PR, and TIME_RT, the process of performing weighted averaging includes:

[0018] In one cycle, the RR segment duration predicted based on TIME_PR alone and the RR segment duration predicted based on TIME_RT alone are compared with the actual detected RR segment duration to confirm the influence factors of TIME_RT and TIME_PR on TIME_RR. and :

[0019] ; ; Where A represents the difference between the actual TIME_RR and the duration predicted based on TIME_RT, and B represents the difference between the actual TIME_RR and the duration predicted based on TIME_PR;

[0020] ; Indicates the correction factor calculated based on TIME_RT alone, Indicates that only TIME_ Calculated correction factor.

[0021] Preferably, within the three-level interval, before the formal scanning cycle, a verification cycle is set, and the correction coefficient is verified according to the difference between the CURRENT_TIME_RR calculated by the correction coefficient and the actual RR end cycle. When the difference is less than the preset difference, the exposure start time and exposure duration are set according to the CURRENT_TIME_RR calculated by the correction coefficient. When the difference is greater than the preset difference, the correction coefficient is corrected twice or full exposure of the TP segment is adopted.

[0022] Preferably, the process of setting the exposure start time and exposure duration of the present invention includes: setting the exposure delay time T_delay starting from the R wave peak according to the predicted duration of the current cardiac cycle RR portion CURRENT_TIME_RR within the range of the first to third intervals:

[0023] When the RR fluctuation range is within the first and second level intervals:

[0024] T_delay = CURRENT_TIME_RR × center_phase - exposure_time / 2, where center_phase is the preset cycle phase and exposure_time is the preset exposure time.

[0025] When the RR fluctuation range is within the third level range:

[0026] T_delay = CURRENT_TIME_RR × center_phase - (exposure_time + T_add) / 2, where T_add represents the maximum value of the time fluctuation between two adjacent ECG cycles;

[0027] When the RR part fluctuation amplitude is within the fourth level range: T_delay = TIME_RT, the exposure time is TIME_TP.

[0028] Preferably, the preset cycle phase of the present invention is 50%-90%.

[0029] Beneficial effects: The cardiac CT scanning detection method and exposure control method provided by the present invention have the following beneficial effects:

[0030] 1. The present invention collects, collects statistics and performs data calculation and analysis on the heartbeat status of each different tester. According to the heartbeat characteristics of different patients, the heartbeat cycle during scanning is predicted, and the exposure control scheme is automatically selected and adjusted.

[0031] 2. The present invention classifies the fluctuations of the RR part of the cardiac cycle and predicts the current cycle time, thereby improving the accuracy of the exposure starting point, reducing the exposure time, and reducing the radiation dose borne by personnel during the scanning process.

[0032] 3. For people whose heart beat cycle fluctuates greatly, the present invention adopts the TP full-segment exposure method. The combined detection method can accurately control the exposure process according to the detection situation within one beat cycle. Although a single scan prolongs the time, it can improve the success rate of the scan and avoid the damage to the human body caused by repeated exposure scans.

[0033] 4. The present invention performs statistics and fitting on the durations of the RR part, PR part, and RT part respectively, and can seek the correlation between the durations. Therefore, within the same cycle, the duration of the RR part can be corrected according to the durations of the PR part and the RT part, which is more accurate. In addition, during the exposure scan cycle, since the durations of the PR part and the RT part are obtained first, the current duration of the RR part can be inferred more accurately based on this, so as to perform accurate exposure scanning.

[0034] 5. In the third-level interval, the present invention takes the maximum fluctuation in the ECG cycle into account when calculating the exposure delay time, which can avoid the problem of insufficient exposure scanning time caused by a late exposure starting point and the need for repeated scanning.

[0035] 6. After predicting the duration of the RR portion of the current cycle through the correction coefficient, the present invention sets a verification period before formally performing the exposure scan. This can be used to perform secondary adjustment and correction of the correction coefficient to further improve the accuracy of the prediction. At the same time, when accurate prediction is impossible or the number of corrections is too many, the TP segment exposure method can be directly used to improve the scanning efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0037] Figure 1 Schematic diagram of the cardiac cycle exposure scanning principle of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be described more clearly and completely below by way of a preferred embodiment in conjunction with the accompanying drawings, but the present invention is not limited to the scope of the embodiment.

[0039] like Figure 1As shown, a complete heart cycle consists of RR parts, namely P wave, QRS complex wave and T wave. When scanning the heart, it is necessary to set parameters according to the host computer to control the scanning to occur within a relatively stable period of time. The QRS peak represents the maximum heartbeat and is the easiest to detect. Therefore, during a scan, the ECG monitor emits a pulse signal after detecting the QRS peak. The control system uses this pulse signal as a reference for scanning control. This pulse signal is called the ECG_TRIGGER signal. When using prospective gating, the CT system sets a trigger point based on the ECG_TRIGGER signal. This trigger point is delayed by a time, called T_delay, from the rising edge of the ECG_TRIGGER signal. The TP segment corresponds to the heart's diastole, while the remaining segments (RT and PR) correspond to the heart's systole. During the cardiac cycle, motion is relatively slow at the end of diastole, known as the TP segment. This segment can be roughly considered a brief period of stillness. If CT exposure occurs within this segment, the reconstructed image from the acquired data will produce a relatively stable three-dimensional perspective view of the heart scan. Therefore, it is crucial to accurately predict the heart cycle at the time of scanning, accurately calculate T_delay, and select the appropriate exposure duration to maximize scan success rates.

[0040] The present invention provides a cardiac CT scanning detection method, which uses an electrocardiogram (ECG) monitor for connection detection and transmits an ECG signal to a control system of a CT scanning device. When the output of the ECG monitor is higher than a set threshold level, it indicates that the connection has been completed. The CT system detects the ECG signal, first detecting the peak of the QRS wave, and then sequentially inferring the T wave and the P wave based on the R wave peak of the QRS wave. The process of detecting the peak of the QRS wave includes: first statistically detecting the maximum value and the maximum rising slope of the ECG signal obtained by AD sampling within a period of time T, and setting a detection threshold based on the above. In a subsequent detection process, when the AD sampling value reaches a threshold set based on the maximum value and the maximum slope and begins to decrease in value, it is considered that the peak of the QRS wave has arrived. After the peak of the R wave, the peak of the second wave is the T wave, and the peak of the third wave is the P wave. After the scan is completed, because the maximum value and the maximum slope corresponding to the R wave may vary from person to person, the detection threshold needs to be reset. After a new patient's ECG signal is connected, a new detection threshold is set based on the ECG signal.

[0041] After the three peaks are successfully detected, the real-time statistics of the RR part of the heart cycle are recorded as TIME_RR, the RT part as TIME_RT, and the PR part as TIME_PR. The three average times AVERAGE_TIME_RR, AVERAGE_TIME_RT, and AVERAGE_TIME_PR are calculated in real time based on the number of complete ECG cycles received. In addition, the fluctuation between two adjacent TIME_RR times needs to be calculated to control the exposure of the heart scan.

[0042] The process of predicting the duration of the current heartbeat cycle based on the time fluctuation of the RR part in the detected heartbeat cycle includes: setting the RR part time fluctuation grading interval, the first-level interval is 0-5ms, the second-level interval is 5-10ms, the third-level interval is 10-20ms, and the fourth-level interval is above 20ms; in the first-level interval, the RR part duration LAST_TIME_RR of the previous heartbeat cycle is used as the RR part duration CURRENT_TIME_RR of the current heartbeat cycle; in the second-level interval, the average duration AVERAGE_TIME_RR of the RR part in the detected heartbeat cycle is used as the RR part duration CURRENT_TIME_RR of the current heartbeat cycle; in the third-level interval, LAST_TIME_RR and AVERAGE_TIME_RR are assigned different weight ratios η, CURRENT_TIME_RR=(LAST_TIME_RR×η+AVERAGE_TIME_RR×(1-η), where η=(MAX_TIME_RR-MIN_TIME_RR) / AVERAGE_TIME_RR and MAX_TIME_RR indicate the maximum value of the RR portion of the detected heart cycle, and MIN_TIME_RR indicates the minimum value of the RR portion of the detected heart cycle. Within the four-level interval, there is no need to predict the duration, and the entire exposure is within the T wave to P wave interval.

[0043] Since the duration of the heart beat cycle fluctuates greatly within the third-level interval, there will still be deviations if only the average duration and the duration of the previous cycle are used. The present invention introduces a correction coefficient α for correction, that is, CURRENT_TIME_RR=(LAST_TIME_RR×η+AVERAGE_TIME_RR×(1-η))×α. At the same time, a certain exposure time is added to ensure the integrity of the scan data. The maximum value of the time fluctuation between two adjacent ECG cycles in the previous statistical data is taken, and this fluctuation time is recorded as T_add. The process of obtaining the correction coefficient α includes: counting the duration of the RR, PR, and RT parts within the heartbeat cycle, recorded as TIME_RR, TIME_PR, and TIME_RT respectively; fitting the fluctuation curves of TIME_RR, TIME_PR, and TIME_RT in the coordinate system, and observing the correlation between the fluctuation trends of the three; when TIME_RR and TIME_PR have no fluctuation relationship: if TIME_RR and TIME_RT fluctuate in the same direction, α=CURRENT_TIME_RT / LAST_TIME_RT, where LAST_TIME_RT represents the duration of the RT part of the previous cycle and CURRENT_TIME_RT represents the duration of the RT part of the current cycle; if TIME_RR and TIME_RT fluctuate in different directions, α=LAST_TIME_RT / CURRENT_TIME_RT;

[0044] When TIME_RR and TIME_RT have no fluctuation relationship: if TIME_RR and TIME_PR fluctuate in the same direction, α = AVERAGE_TIME_PR / LAST_TIME_PR, where LAST_TIME_PR represents the duration of the PR portion of the previous cycle and AVERAGE_TIME_PR represents the duration of the PR portion of the average cycle; if TIME_RR and TIME_PR fluctuate in different directions, α = LAST_TIME_PR / AVERAGE_TIME_PR;

[0045] When TIME_RR fluctuates with TIME_PR and TIME_RT, α is calculated by weighted average based on the impact of TIME_PR and TIME_RT on TIME_RR. The weighted average process includes:

[0046] In one cycle, the RR segment duration predicted based on TIME_PR alone and the RR segment duration predicted based on TIME_RT alone are compared with the actual detected RR segment duration to confirm the influence factors of TIME_RT and TIME_PR on TIME_RR. and :

[0047] ; ; Where A represents the difference between the actual TIME_RR and the duration predicted based on TIME_RT, and B represents the difference between the actual TIME_RR and the duration predicted based on TIME_PR;

[0048] ; Indicates the correction factor calculated based on TIME_RT alone, Indicates that only TIME_ Calculated correction factor

[0049] When TIME_RR has no fluctuation relationship with TIME_PR and TIME_RT, α takes the value of 1.

[0050] After predicting the RR segment duration of the current cycle through the correction coefficient α, the present invention also verifies the predicted result before formally performing the scan. When the difference between the predicted period and the actual measured period is within the set range, which is generally set to 10ms, it means that the predicted value is available, and the exposure start time and exposure duration can be set according to the predicted period duration. When the difference is greater than 10ms, the deviation between the predicted value and the actual value is too large, and the correction coefficient α can be corrected. The correction coefficient can be increased or decreased according to the size of the deviation to make the predicted value closer to the actual value and maintain the deviation within 10ms. After the second correction, it is verified again. If it meets the requirements, exposure can be performed normally. If the deviation still exceeds the setting, it means that the patient's heart rate cycle fluctuation range is large. In order to improve the scanning success rate, the TP segment exposure method can be directly selected.

[0051] For situations where the fluctuation range is in the first and second intervals, scanning can be performed according to the conventional exposure method and exposure time: T_delay = CURRENT_TIME_RR × center_phase - exposure_time / 2, where center_phase is the preset cycle phase, which is 50%-90%, generally 75%, and exposure_time is the preset exposure time.

[0052] When the RR fluctuation range is within the third level range:

[0053] T_delay = CURRENT_TIME_RR × center_phase - (exposure_time + T_add) / 2. The exposure time is appropriately extended to fully acquire the image in one scan process and avoid the need for repeated exposure scans.

[0054] When the RR fluctuation amplitude is within the fourth level range: Since the fluctuation is irregular and the variation is large, T_delay = TIME_RT and the exposure time is TIME_TP. By coordinating with the detection method, according to the signal emitted by the detection, the exposure is synchronized to complete the scan. Combined with the post-ECG editing strategy, the data interval is selected for scanning and image reconstruction.

[0055] When the solution of the present invention is actually applied, the control system sends two control parameters: center phase center_phase and exposure duration exposure_time. Among them, center_phase is used to control the position of exposure in the ECG cycle, and exposure_time is used to control the time of X-ray exposure. When the ECG signal of the person to be tested is connected to the ECG acquisition module, the collected ECG signal is detected to detect the QRS wave, T wave and P wave, and then the time and fluctuation of each stage in a complete heartbeat cycle are counted, and it is determined whether it is within the set classification range, and then different exposure strategies are selected for scanning exposure.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A cardiac CT scan exposure control method, characterized in that: The electrocardiogram (ECG) monitor is used to detect the fluctuations of several heartbeat cycles, and the ECG signals detected by the ECG monitor are demodulated to obtain P waves, T waves, and QRS waves. The RR time fluctuation classification interval is set, and the time value of the RR part in the heartbeat cycle is counted. The duration of the current heartbeat cycle is predicted based on the time fluctuations of the RR part in the detected heartbeat cycle, and the exposure start time and exposure duration are set to obtain a heart exposure image. The process of detecting the ECG signal detected by the ECG monitor includes: connecting the ECG monitor to detect the ECG signal; when the output of the ECG monitor is higher than the set threshold level, the CT system detects the ECG signal, first detecting the peak of the QRS wave, and then inferring the T wave and P wave in sequence based on the R wave peak of the QRS wave; the process of detecting the peak of the QRS wave includes: first statistically detecting the maximum value and the maximum rising slope of the ECG signal obtained by AD sampling within a period of time T, and formulating a detection threshold based on this; in the subsequent detection process, when the AD sampling value reaches the threshold formulated according to the maximum value and the maximum slope and begins to decrease in value, it is considered that the peak of the QRS wave has arrived, and the peak of the second wave after the R wave peak is the T wave, and the peak of the third wave is the P wave; after completing the scan, the formulated detection threshold is cleared, and after a new patient's ECG signal is connected, a new detection threshold is re-set based on the ECG signal; The process of predicting the duration of the current heartbeat cycle based on the time fluctuation of the RR part in the detected heartbeat cycle includes: setting the RR part time fluctuation grading interval, the first-level interval is 0-5ms, the second-level interval is 5-10ms, the third-level interval is 10-20ms, and the fourth-level interval is above 20ms; in the first-level interval, the RR part duration LAST_TIME_RR of the previous heartbeat cycle is used as the RR part duration CURRENT_TIME_RR of the current heartbeat cycle; in the second-level interval, the average duration AVERAGE_TIME_RR of the RR part in the detected heartbeat cycle is used as the RR part duration CURRENT_TIME_RR of the current heartbeat cycle; in the third-level interval, LAST_TIME_RR and AVERAGE_TIME_RR are assigned different weight ratios η, CURRENT_TIME_RR=(LAST_TIME_RR×η+AVERAGE_TIME_RR×(1-η), where η=(MAX_TIME_RR-MIN_TIME_RR) / AVERAGE_TIME_RR and MAX_TIME_RR indicate the maximum value of the RR portion of the detected heart cycle, and MIN_TIME_RR indicates the minimum value of the RR portion of the detected heart cycle. Within the four-level interval, there is no need to predict the duration, and the entire exposure is within the T wave to P wave interval.

2. The cardiac CT scan exposure control method according to claim 1, characterized in that: Within the three-level interval, a correction coefficient α is applied to the calculation of CURRENT_TIME_RR based on the fluctuation pattern of the RR portion of the cardiac cycle. That is, CURRENT_TIME_RR = (LAST_TIME_RR × η + AVERAGE_TIME_RR × (1-η)) × α. The correction coefficient α is obtained by calculating the duration of the RR, PR, and RT portions of the cardiac cycle, denoted as TIME_RR, TIME_PR, and TIME_RT, respectively; and fitting the fluctuation curves of TIME_RR, TIME_PR, and TIME_RT in the coordinate system. When TIME_RR and TIME_PR have no fluctuation relationship: if TIME_RR and TIME_RT fluctuate in the same direction, α=CURRENT_TIME_RT / LAST_TIME_RT, where LAST_TIME_RT represents the duration of the RT portion of the previous cycle and CURRENT_TIME_RT represents the duration of the RT portion of the current cycle; if TIME_RR and TIME_RT fluctuate in different directions, α= LAST_TIME_RT / CURRENT_TIME_RT; When TIME_RR and TIME_RT have no fluctuation relationship: If TIME_RR and TIME_PR fluctuate in the same direction, and the fluctuation of TIME_PR is small in the middle of each heartbeat, α = AVERAGE_TIME_PR / LAST_TIME_PR, where LAST_TIME_PR represents the duration of the PR portion of the previous cycle, and AVERAGE_TIME_PR represents the average duration of the PR portion. If TIME_RR and TIME_PR fluctuate in different directions, α = LAST_TIME_PR / AVERAGE_TIME_PR. When TIME_RR has a fluctuating relationship with TIME_PR and TIME_RT, α is calculated by weighted average based on the impact of TIME_PR and TIME_RT on TIME_RR; When TIME_RR has no fluctuation relationship with TIME_PR and TIME_RT, α takes the value of 1.

3. The cardiac CT scan exposure control method according to claim 2, characterized in that: When TIME_RR, TIME_PR, and TIME_RT all have a fluctuating relationship, the weighted averaging process includes: In one cycle, the RR segment duration predicted based on TIME_PR alone and the RR segment duration predicted based on TIME_RT alone are compared with the actual detected RR segment duration to confirm the influence factors of TIME_RT and TIME_PR on TIME_RR. and : ; ; Where A represents the difference between the actual TIME_RR and the duration predicted based on TIME_RT, and B represents the difference between the actual TIME_RR and the duration predicted based on TIME_PR; ; Indicates the correction factor calculated based on TIME_RT alone, Indicates the correction factor calculated based on TIME_PR alone.

4. A cardiac CT scan exposure control method according to claim 2 or 3, characterized in that: In the third-level interval, before the formal scanning cycle, a verification cycle is set. The correction coefficient is verified based on the difference between the CURRENT_TIME_RR calculated with the correction coefficient and the actual RR end cycle. When the difference is less than the preset difference, the exposure start time and exposure duration are set according to the CURRENT_TIME_RR calculated with the correction coefficient. When the difference is greater than the preset difference, the correction coefficient is corrected twice or full exposure of the TP segment is adopted.

5. The cardiac CT scan exposure control method according to claim 2, characterized in that: The process of setting the exposure start time and exposure duration includes: setting the exposure delay time T_delay from the R wave peak as the starting point based on the predicted duration of the RR portion of the current heart beat cycle CURRENT_TIME_RR within the range of level 1 to level 3: When the RR fluctuation range is within the first and second level intervals: T_delay = CURRENT_TIME_RR × center_phase - exposure_time / 2, where center_phase is the preset cycle phase and exposure_time is the preset exposure time. When the RR fluctuation range is within the third level range: T_delay = CURRENT_TIME_RR × center_phase - (exposure_time + T_add) / 2, where T_add represents the maximum value of the time fluctuation between two adjacent ECG cycles; When the RR part fluctuation amplitude is within the fourth level range: T_delay = TIME_RT, the exposure time is TIME_TP.

6. The cardiac CT scan exposure control method according to claim 5, characterized in that: The preset cycle phase is 50%-90%.

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