Determination of a trigger signal for imaging

Abstract

A system 100 and method for determining a trigger signal for imaging using an imaging system 40 are provided. The method includes a step S10 of measuring patient-specific characteristics of a patient 30, where the patient-specific characteristics are measured when the patient 30 is located at a first position 51 with respect to the imaging system 40; a step S20 of generating a patient-specific model based on the patient-specific characteristics; a step S30 of measuring a trigger waveform of the patient 30, where the trigger waveform is measured when the patient 30 is located at a second position 52 with respect to the imaging system 40, and the second position 52 is different from the first position 51; and a step S40 of determining a trigger signal based on the patient-specific model and the trigger waveform, where the trigger signal is configured to trigger the imaging system 40 to acquire an image of the patient 30 in a time-resolved manner.

Description

Technical Field

[0001] The present invention relates to a system and method for determining a trigger signal for imaging using an imaging system.

Background Art

[0002] For example, contact photoplethysmography (PPG) and electrocardiogram (ECG) measured by a finger oximeter are used for cardiac triggering or gating of scans in standard magnetic resonance imaging (MRI) and computed tomography (CT) systems.

[0003] MRI typically uses a trigger based on ECG measurement for scans that require synchronization with the heartbeat and / or cardiac phase. The ECG measurement holds the so-called R peak, signaling the electrical activity that initiates myocardial contraction, i.e., the start of systole. Based on the R peak, an MRI trigger sequence consisting of a preparation pulse (prepulse) and a plurality of acquisition windows is initiated. Such ECG-based triggers can suffer from drawbacks such as complex electrode placement, multiple wires that can limit patient comfort, and interference with imaging quality due to magnetic field interference.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, the feasibility of cardiac-triggered MRI using camera-based PPG of the human face has been shown. A fully or semi-automated non-contact camera PPG solution can significantly simplify the clinical MRI workflow and eliminate magnetic field interference with the signal since no contact sensors are required.

[0005] However, compared to ECG-based triggers, a possible limitation of camera PPG-based triggers is that there is a patient-specific delay between the R peak commonly used for cardiac triggers and the trigger derived from the PPG signal. This delay is caused by the pulse transit time from the heart to the peripheral skin site and can result in inaccurate triggers unless compensated for.

[0006] U.S. Patent Application Publication No. 2017 / 055934A1 discloses a method and system for determining a trigger signal. The method for determining a trigger signal for an imaging device is based on receiving a film of the surface of a first body part of a patient. In one embodiment, the image values within a region in the image of the film are averaged. The noise of the image values within the region is reduced by the averaging process. The film is converted into a series of time signals based on the averaging process. The conversion is performed such that the series of time signals is a measure of the timing pattern of blood circulation in the region.

[0007] Camera-based PPG requires a certain amount of processing to achieve robust trigger detection. This can result in a costly delay in the workflow before the actual triggered scan begins.

[0008] Therefore, it is necessary to improve the speed and accuracy of triggered imaging.

Means for Solving the Problem

[0009] The present invention provides an apparatus for improving the speed and accuracy of triggered imaging.

[0010] The present invention is defined by the independent claims. Advantageous embodiments are defined in the dependent claims.

[0011] According to a first aspect of the present invention, there is provided a method for determining a trigger signal for imaging using an imaging system. The method includes a step of measuring a patient-specific characteristic of a patient, the patient-specific characteristic being measured when the patient is located at a first position relative to the imaging system, a step of generating a patient-specific model based on the patient-specific characteristic, a step of measuring a trigger waveform of the patient, the trigger waveform being measured when the patient is located at a second position relative to the imaging system, the second position being different from the first position, and a step of determining a trigger signal based on the patient-specific model and the trigger waveform, the trigger signal being configured to trigger the imaging system to acquire an image of the patient in a time-resolved manner.

[0012] Patient-specific characteristics are measured characteristics related to the physiology or physical characteristics of the patient, such as, but not limited to, heart rate, respiration, oxygenation, blood pressure, cardiac cycle, temperature, weight, height, body mass index, etc. Patient-specific characteristics can be certain, one or several measurement points, amplitudes, frequencies, phases, shapes, signal-to-noise levels, etc. of physiological measurements. This characteristic or combination of characteristics can be used to model patient-specific parameters in a patient-specific model. Similarly, the trigger waveform is a time-resolved measurement of the patient's physiological parameters, such as, but not limited to, heart rate, respiration, oxygenation, cardiac cycle, temperature, etc. The trigger signal directly or indirectly triggers the acquisition of an image of the patient using the imaging system at a certain point in time.

[0013] The proposed method can measure one or more patient-specific characteristics, and the generation of a patient-specific model from such characteristics can be initiated already before the patient arrives at the second location where the trigger waveform is measured, which can be advantageous for the speed and accuracy of the imaging trigger workflow. The second location can further be the position of the patient when the imaging system is triggered to acquire an image of the patient. In this way, the combination of patient-specific information and the measured trigger waveform can form the basis for an accurate imaging trigger without causing unnecessary delays in the workflow.

[0014] In one embodiment of the present invention, at the first location, the anatomical structure of the patient of interest is located substantially outside the bore of the imaging system, and at the second location, the anatomical structure of the patient of interest is located substantially inside the bore of the imaging system.

[0015] The anatomical structure of the patient of interest is the part of the patient where the trigger is determined and / or the body part imaged by the imaging system. When the anatomical structure of the patient of interest is outside the bore of the imaging system, for example, during the patient preparation phase, the patient time inside the bore can be reduced by measuring patient-specific characteristics. In this way, the total workflow time can be reduced and the patient comfort can be enhanced. The bore of the imaging system can be, for example, the bore of a computed tomography (CT) system, a magnetic resonance imaging (MRI) system, or a molecular imaging system such as positron emission tomography (PET) or single photon emission computed tomography (SPECT), or any combination of such systems.

[0016] In one embodiment of the present invention, the trigger waveform has a waveform derived from photoplethysmography (PPG), and the step of measuring the trigger waveform includes measurement by a sensor, preferably a camera.

[0017] Instead of a plurality of electrocardiogram (ECG) sensors arranged in contact with a patient, measuring a trigger waveform using, for example, camera-based PPG can have multiple advantages such as automating or simplifying the workflow and avoiding magnetic field interference of the ECG signal.

[0018] The sensor is preferably a 2D or 3D camera sensor or the like configured to non-contact measure PPG parameters from visible light, infrared light, or light of other wavelengths. However, other sensor technologies such as transmissive or reflective PPG sensors in proximity to or in contact with the patient, non-contact measurements by radar or LIDAR, etc. can also be considered for measuring the waveform derived from PPG.

[0019] In one embodiment of the present invention, the patient-specific characteristic has a characteristic derived from PPG, and the step of measuring the patient-specific characteristic includes measurement by a sensor, preferably a camera.

[0020] Similar to the trigger waveform, measuring patient-specific parameters using, for example, camera-based PPG can speed up and simplify the imaging and / or patient preparation workflow, either alone or in combination with other measurements.

[0021] The sensor used to measure the patient-specific characteristic including the characteristic derived from PPG may be the same sensor as the sensor used to measure the trigger waveform. The sensor may also be a separate sensor of the same, similar, or different type or function as the sensor used to measure the trigger waveform. By way of example, both sensors can be sensors configured to measure a camera-based PPG signal, for example.

[0022] In one embodiment of the present invention, the patient-specific model includes a patient-specific PPG waveform profile.

[0023] Modeling a patient-specific model that includes a PPG waveform profile, such as a template morphology and / or the amplitude of the waveform, is advantageous for rapid and accurate imaging triggering. This can be particularly important when the trigger waveform has a waveform derived from the PPG. In one embodiment of the present invention, the patient-specific model includes a patient-specific pulse transit time. Similar to the patient-specific waveform profile, information regarding the patient-specific pulse transit time can be advantageous for rapid and accurate imaging triggering. In one embodiment of the present invention, the patient-specific model includes a patient-specific reliability factor for camera-based PPG parameters. The patient-specific reliability factor can provide an indication of the reliability, quality, and / or robustness of camera-based PPG for a particular patient and / or situation. For example, if the reliability is low, additional or alternative measurements for camera-based PPG may be required to accurately trigger based on the trigger waveform. Having such information at an early stage can save bore time and / or avoid the need for repeated sets of image acquisition. In one embodiment of the present invention, the step of determining the trigger signal includes calculating a plurality of PPG markers, the PPG markers being derived from the trigger waveform and / or the patient-specific PPG waveform profile, and the PPG markers being configured to predict the R peak. The PPG markers are specific PPG features of the PPG waveform, such as the inter-beat interval, waveform features, phase, etc. Calculating a plurality of PPG markers can be advantageous as it can improve the accuracy and / or robustness when the PPG markers predict the R peak from, for example, camera-based PPG.

[0024] In one embodiment of the present invention, the above-described PPG markers include a diastolic PPG marker and a flash PPG marker.

[0025] In one embodiment of the present invention, the method includes the steps of deriving timing parameters from the trigger waveform and / or the patient-specific model, and scanning a patient triggered by the trigger signal, the scan being configured to generate imaging scan data.

[0026] In one embodiment of the present invention, the method further includes an image forming step, and the image forming step forms an image of a patient based on the processing of imaging scan data and timing parameters.

[0027] This can be advantageous because using the trigger waveform and / or timing parameters from a patient-specific model can help improve the quality and / or speed of image formation.

[0028] According to another aspect of the present invention, there is provided a computer program configured to cause a processing unit to execute any computer-executable method steps according to any of the above methods when executed by at least one processing unit.

[0029] According to another aspect of the present invention, there is provided a computer-readable medium storing the above computer program.

[0030] According to a second aspect of the present invention, there is provided a system for determining a trigger signal for imaging a patient using an imaging system, the system including a patient-specific characteristic sensor configured to measure patient-specific characteristics of the patient when the patient is located at a first position relative to the imaging system, a trigger waveform sensor configured to measure a trigger waveform of the patient when the patient is located at a second position relative to the imaging system, and a processing unit configured to receive the patient-specific characteristics, generate a patient-specific model based on the patient-specific characteristics, receive the trigger waveform, and determine an imaging trigger signal based on the patient-specific model and the trigger waveform.

[0031] In one embodiment of the present invention, at least one of the patient-specific characteristic sensor and / or the trigger waveform sensor is a sensor, preferably a camera, and such a sensor is configured to measure a sensor-based PPG signal.

[0032] According to another aspect of the present invention, there is provided an imaging system having a system for determining a trigger signal, which is preferably a computed tomography system or a magnetic resonance imaging system.

[0033] These and other aspects of the present invention will become apparent from the embodiments described below and will be described with reference thereto.

Brief Description of the Drawings

[0034]

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Modes for Carrying Out the Invention

[0035] A schematic diagram of a system 100 for determining a trigger signal according to an embodiment of the present invention is shown in FIG. 1. Patient 30 is placed on the table of imaging system 40. In this example, it is proposed to use the external bore camera sensor 10 to measure patient-specific characteristics that can be used to model the patient's physiology during the preparation phase before sending the patient into the bore for a trigger scan using the in-bore camera sensor 20.

[0036] Many imaging system environments already provide ceiling-mounted cameras that enable monitoring of patients during a preparation phase before moving the table into the bore. Thus, such camera sensors can be further used, for example, for remote PPG analysis. The patient-specific characteristic sensor 10 and the trigger waveform sensor 20 are connected to a processing unit (not shown) via a wired or wireless connection.

[0037] In the example shown in FIG. 1, the two sensors are separate camera sensors at different positions. However, it is also possible that the patient-specific characteristic sensor 10 and the trigger waveform sensor 20 are the same sensor and / or are arranged at the same position. For example, a camera-based sensor having a field of view both inside and outside the bore of the imaging system 40.

[0038] In FIG. 1a, the patient 30 is in a first position 51 during the preparation phase. At the first position 51, the anatomical structure of the patient of interest, such as the chest or head or another body part, is substantially outside the bore of the imaging system 40. It should be noted that FIG. 1a shows the patient on the table associated with the imaging system, but it is also conceivable that the first position 51 is further away from the imaging system, such as in another room used for preparation.

[0039] During the preparation phase shown in FIG. 1a, when the patient is in the first position 51, patient-specific characteristics are measured by the camera sensor 10. The measured values can be combined with measured values from additional sensors that are remote or in contact with the patient. Examples of such measured characteristics include, but are not limited to, characteristics derived from PPG such as pulse wave waveform, heart rate, respiratory rate, blood pressure, the relationship between pulsatile characteristics and the R peak of the ECG, PPG peak detection rate, etc. Based on one or more patient-specific characteristics, a patient-specific model can be generated in the processing unit. Non-limiting examples of such patient-specific models that can be generated from patient-specific characteristics measured by the camera sensor 10 include a patient-specific PPG waveform profile, a patient-specific pulse transit time, or a patient-specific reliability coefficient of camera-based PPG parameters.

[0040] In FIG. 1b, the patient 30 is in the second position 52 during the scan phase. At the second position 52, the anatomical structure of the patient of interest is substantially inside the bore of the imaging system 40. At the second position 52, a trigger waveform is measured by the camera sensor 20, in this example an in-bore camera. The trigger waveform can be derived from camera-based PPG measurements using the camera sensor 20. The processing unit receives the trigger waveform and determines an imaging trigger signal. The trigger signal is configured to trigger the imaging system 40 to acquire an image of the patient 30 in a time-resolved manner.

[0041] Several potential advantages can be contemplated from a system as shown in FIG. 1, and patient-specific characteristics can be measured already during the patient preparation phase and / or at least before the patient 30 further moves into the bore of the imaging system 40. Examples include the following;

[0042] Knowledge of patient-specific PPG models such as PPG waveform morphology, PPG amplitude, pulse propagation time delay, etc. simplifies accurate and fast timing of camera-based acquisitions such as MRI and CT acquisition windows.

[0043] Images of MRI cardiac cine movies are generally annotated using time stamps relative to the R-peak defined as time zero. This is possible using prior knowledge of the delay.

[0044] MRI cardiac cine movies are typically presented for diagnosis and comparison starting from the time of the R-peak. This is possible using prior knowledge of the delay.

[0045] Functional evaluation of cardiac images regarding ejection fraction and wall motion is simplified and / or made more accurate using knowledge of the timing relative to the R-peak.

[0046] Triggering with little delay between the R-peak and the trigger requires a patient-specific PPG template and an initial calibration time to initialize this model. If such calibration can be performed beforehand by the processing unit without relying on in-bore measurements, expensive in-bore time can be saved.

[0047] If the camera-based PPG signal quality can be pre-evaluated to calculate a patient-specific reliability factor for camera-based PPG parameters, this can have a significant positive effect on the workflow time. For example, in the case of triggered MRI, if the patient is already inside the bore and the in-bore camera 20 detects insufficient patient-specific PPG signal quality, the workflow becomes dramatically longer. In that case, the patient 30 has to be removed again, the MR coil has to be removed, the ECG electrodes have to be applied, the MR coil has to be applied again, and then the patient 30 has to be repositioned inside the bore.

[0048] In the example shown in FIG. 1, the out-of-bore camera 10 is placed above (or at the side) of the patient 30 lying on the table and measures physiological signals from the patient's skin (e.g., chest or face area). The physiological signal may be a PPG signal, but may also include other physiological signals. In some cases, an ECG sensor is also used. The ECG signal measured by the ECG sensor may be measured, for example, in synchronization with the camera PPG signal.

[0049] Today's ECG detection for MRI triggering is typically based on at least four electrodes on the bare chest. Here, since the ECG signal can be corrupted by interference with the MR field, at least four electrodes are typically required for robust R-peak detection within the bore. For the purpose of initializing to measure patient-specific characteristics and calculate a patient-specific model, it is possible to apply only two ECG electrodes for synchronous measurement of PPG and ECG outside the bore. The electrodes can be applied, for example, to the wrists or hands of patient 30. Such an ECG set can greatly simplify the workflow. Furthermore, if the electrodes are removed before the patient enters the bore, the in-bore trigger waveform is measured, for example, with a camera PPG, so the ECG electrodes, leads, and detection circuits do not need to be MR-compatible. In some cases, it can be contemplated that the ECG electrodes can be simple handles or conductive fields on both sides of the patient support that can be held by the patient for a few seconds as long as data is required to calibrate the model.

[0050] Figure 2 shows an example of the relationship between patient-specific characteristics measured when patient 30 is in the first position 51, a patient-specific model, and a trigger signal measured when patient 30 is in the second position 52.

[0051] Figure 2a schematically shows the measured patient-specific characteristics when patient 30 is in the first position 51. In this example, the signal derived from the PPG is measured by a patient-specific characteristic sensor 10 such as a camera PPG sensor. In addition, the ECG signal is measured using an ECG sensor. As shown in Figures 2b and 2c, a patient-specific model can be calculated using the synchronized camera PPG-derived signal and ECG signal.

[0052] Figure 2b shows the generated PPG waveform profile that can be used as a patient-specific PPG template to enable rapid triggering. The PPG waveform profile is a robust PPG cardiac cycle averaged from multiple PPG cycles, such as measured by the face or chest camera PPG of Figure 2a. Since this model is based on patient-specific characteristics measured when the patient is in the first position 51, the model can be initialized before the patient moves further into the bore of the imaging system 40.

[0053] Similarly, Figure 2c shows the generated R-peak regression model that models the relationship between the camera PPG features and the measured R-peaks of the ECG. The input to the model is derived from patient-specific characteristics measured at the first position 51. The model can associate certain PPG features (e.g., inter-beat interval, waveform features, phase), so-called PPG markers, with the pulse transit time between the R-peak and the systolic valley of the camera PPG signal. Thus, such a regression model can be used to predict / regress the R-peak position from the camera-based PPG waveform.

[0054] Figure 2d shows the trigger waveform measured when the patient 30 moves further into the bore of the imaging system 40. In this example, the trigger waveform is derived only from the camera-based PPG measurements when the patient is in the second position 52. Thus, no ECG is required inside the imaging system to measure the trigger waveform.

[0055] As shown in Figure 2e, the previously generated PPG waveform profile (Figure 2b) can be used to quickly identify the PPG cycles within the trigger waveform, which can be used for trigger detection. Since the construction of the model has already been initialized in the workflow, high-speed triggering is made possible.

[0056] Similarly, as shown in Figure 2f, the pre-constructed R-peak regression model (Figure 2c) can be used to enable accurate triggering by predicting the R-peaks of the ECG from the camera-based trigger waveform.

[0057] The trigger signal is generated based on the identified cardiac cycle and R peak, and as a result, the imaging system is triggered to acquire an image of the patient.

[0058] In the example shown in FIG. 2, patient-specific characteristics used to model the patient-specific pulse transit time are measured during the patient preparation phase by a combination of camera-based PPG and ECG. Alternatively, the pulse transit time and related parameters can also be modeled from PPG measurements such as multi-site PPG imaging without the need for an ECG.

[0059] FIG. 3 shows multi-site PPG imaging. In this example, the PPG signal is acquired simultaneously from the patient's face and palm using a ceiling camera that can be a patient-specific characteristic sensor 10. Information regarding the simultaneous signals between the face and palm can be used to estimate a surrogate transit time. Such a surrogate transit time can be used to improve the accuracy of R peak regression from the PPG signal.

[0060] Additional parameters such as the patient's height, age, body mass index, etc. can further be used to further improve the model.

[0061] To improve the robustness of PPG marker detection from the trigger waveform, multiple PPG markers can be generated in combination with the patient-specific PPG waveform profile. In this way, one marker can predict the next, thereby improving the robustness of the model.

[0062] Instead of generating a single patient-specific PPG waveform profile, it is also possible to generate a number of profiles related to a specific cardiac cycle duration or a range of cardiac cycle durations. Generating different profiles for each range of cycle duration can be motivated by the fact that arterial blood flow velocity and the time curves of heart beats and related physiological quantities as PPG signals do not simply scale linearly when the heart rate changes. Instead, some parts of the cardiac cycle are extended in time (typically, the diastolic pause), while other parts remain more or less unchanged (such as systole).

[0063] In each waveform profile, one or more PPG markers can be defined. Of particular relevance are the zero crossings in this signal. Negative zero crossings are related to the maximum blood volume change at the observation point, e.g., on the forehead with camera PPG, in response to heart contraction. Positive zero crossings are associated with diastole and typically precede the R peak of the ECG. By generating multiple markers from a single waveform profile, it becomes possible to track the current phase of the PPG signal in the cardiac cycle.

[0064] Detection of the PPG marker can be performed, for example, as follows. The waveform profile can be shifted so that it starts and stops at zero crossings. In this way, two waveform profiles are generated, each having a complete heart waveform, one waveform profile starting and ending at the positive-going zero crossing, and the second waveform profile starting and ending at the negative-going zero crossing.

[0065] Both waveforms are shown in Figure 4a, and the PPG waveform profile is stretched or time-distorted to cover 33 samples. This concept is to check whether the latest received PPG waveform sample corresponds to the last sample of these prototypes. If so, the corresponding marker is generated.

[0066] A patient-specific PPG signal can be decomposed using a patient-specific model. The model describes the waveform as consisting of three parts: a PPG waveform profile, a low-frequency (LF) signal component, and a noise component. The LF signal component can be modeled as a low-order polynomial. More formally, given a discrete-time PPG signal segment s(n), n = [1,...,N], a prototype p(n), and an LF signal component b(n), the signal is described as follows. s = αp + b + e In the above equation, e(n) represents an error signal that accounts for noise (such as measurement noise) and disturbances, and α is a scale factor. The signal component b captures PPG variations related to signal drift and respiration within the PPG (and thus at frequencies lower than the heart rate). Various methods for arriving at such a decomposition are known. For example, a least-squares fitting procedure can be used to achieve the decomposition, in which case windowing can be used to emphasize the importance of specific portions of the segment in the fitting.

[0067] The decomposed signal can be analyzed in terms of its strength, for example, with respect to energy. A good fit is obtained if the energy associated with the PPG component p is significantly larger than the energy associated with e. Further evidence to support the generation of a marker would be that the coefficient α is positive. Further evidence is that considering the next segment consisting of a single simple shifted input signal, the coefficient α becomes lower or the balance between the energies of (αp) and e becomes less favorable. In these or other ways, a determination can be made that a marker has occurred.

[0068] Since the current cardiac cycle length is empirically unknown, the system operates at various lengths. Thus, the detection has an additional dimension, namely an additional dimension along the scale (cardiac cycle length). Further, various cues for the presence of markers must be examined over this additional dimension. A hard decision may be implemented based on thresholding, a more statistically similar approach may be used, or a neural network can be trained to generate the final decision mechanism.

[0069] Examples of multiple generated PPG markers for improving R-peak prediction are shown in FIG. 4b. More specifically, for example, by observing the blood volume change induced by the induced cardiac contraction, at least one marker that precedes but is close to the R-peak and at least a second marker indicating that the R-peak has occurred are selected, and the prediction can be improved. The PPG markers are generated in this case during diastole and at the moment of the maximum blood volume change, the flash phase, or in the vicinity thereof. The diastolic PPG marker (asterisk in FIG. 4b) usually occurs immediately before the R-peak, and the flash-phase PPG marker (circle in FIG. 4b) usually occurs immediately after the R-peak. Thus, the two combinations improve the timely prediction of the R-peak.

[0070] In the above description, some embodiments of the present invention have been described in detail. One aspect of the present invention is also shown in FIG. 5, which shows a flowchart representing a method for determining a trigger signal. This method has the following steps: - Step (S10) of measuring the patient-specific characteristics of the patient. The patient-specific characteristics are measured when the patient is located at a first position with respect to the imaging system; - Step (S20) of generating a patient-specific model based on the patient-specific characteristics; - Step (S30) of measuring the trigger waveform of the patient. The trigger waveform is measured when the patient is located at a second position with respect to the imaging system. The second position is different from the first position; - Step (S40) of determining a trigger signal based on a patient-specific model and a trigger waveform. The trigger signal is configured to trigger an imaging system to acquire an image of the patient in a time-resolved manner.

[0071] Similarly, FIG. 6 shows a flowchart representing a method for determining a trigger signal for starting a scan according to an embodiment of the present invention. In this case, in addition to what is shown in FIG. 5, the method further includes a step (S35) of deriving timing parameters from a trigger waveform and / or a patient-specific model, and a step (S50) of scanning a patient triggered by the trigger signal, and the step of scanning (S50) is configured to generate imaging scan data.

[0072] In addition to realizing a more robust trigger from the measured trigger waveform, a patient-specific model, for example including a PPG marker, can include timing parameters that can be further utilized during the image workflow. An image formation process (S60) that combines scan data to generate an image or video sequence can use such timing parameters as additional information for controlling the image formation process. For example, such timing parameters can also be used, by weighting or as a correction factor for data acquired in different data acquisition windows.

[0073] For example, in MRI, knowledge of timing parameters such as the distance between prepulse generation and data acquisition timing can be used to improve image formation. Alternatively, the trigger mechanism can be configured to maintain more stringent requirements regarding the distance from a certain prepulse to the acquisition window. In this case, information regarding the occurrence of each MR sequence event, such as the motion state of the myocardium, can be used during the image formation process.

[0074] FIG. 7 shows an embodiment of the present invention, and the method shown in FIG. 6 further includes an image forming step (S60), and the image forming step (S60) forms a patient's image based on the processing of imaging scan data and timing parameters.

[0075] It should be noted that the above-described embodiments illustrate rather than limit the present invention, and those skilled in the art can design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The term "comprising" does not exclude the presence of other elements or steps than those listed in the claim. The words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. The present invention can be implemented by means of hardware having several distinct elements and / or by means of a processor suitably programmed. In device claims listing several means, several of these means may be embodied by one and the same item of hardware. Advantageously, the means recited in mutually different dependent claims can be used in combination.

Description of Reference Signs

[0076] 100 System for determining a trigger signal 10 Patient-specific characteristic sensor 20 Trigger waveform sensor 30 Patient 40 Imaging system 51 First position 52 Second position S10 Measure patient-specific characteristics S20 Generate a patient-specific model S30 Measure the trigger waveform S35 Derive timing parameters S40 Determine the trigger signal S50 Scan the patient S60 Image forming process

Claims

1. A method for determining a trigger signal for imaging using an imaging system, A step of measuring a patient's unique characteristics, wherein the patient's unique characteristics are measured when the patient is positioned at a first position relative to the imaging system. The steps include generating a patient-specific model based on the patient-specific characteristics, A step of measuring the trigger waveform of the patient, wherein the trigger waveform is measured when the patient is positioned at a second position relative to the imaging system, and the second position is different from the first position. A step of determining a trigger signal based on the patient-specific model and the trigger waveform, wherein the trigger signal triggers the imaging system to acquire images of the patient in a time-resolved manner. A method of having.

2. The method according to claim 1, wherein, at the first position, the anatomical structure of the patient of interest is located substantially outside the bore of the imaging system, and at the second position, the anatomical structure of the patient of interest is located substantially inside the bore of the imaging system.

3. The method according to claim 1 or 2, wherein the trigger waveform has a waveform derived from photoplethysmography (PPG), and the step of measuring the trigger waveform includes measurement by a sensor or camera.

4. The method according to claim 1 or 2, wherein the patient-specific characteristics have characteristics derived from photoplethysmography (PPG), and the step of measuring the patient-specific characteristics includes measurement using a sensor or camera.

5. The method according to claim 1 or 2, wherein the patient-specific model has a patient-specific photoplethysmography (PPG) waveform profile.

6. The method according to claim 1 or 2, wherein the patient-specific model has a patient-specific pulse transit time.

7. The method according to claim 1 or 2, wherein the patient-specific model has patient-specific reliability coefficients for camera-based photoplethysmography (PPG) parameters.

8. The method according to claim 5, wherein the step of determining the trigger signal comprises calculating a plurality of photoplethysmography (PPG) markers, the PPG markers being derived from the trigger waveform and / or the patient-specific PPG waveform profile, and the PPG markers being configured to predict the R peak.

9. The method according to claim 8, wherein the PPG marker comprises an expanded phase PPG marker and a flash phase PPG marker.

10. A step of deriving timing parameters from the trigger waveform and / or the patient-specific model, The steps include scanning a patient triggered by the trigger signal, and the scan being configured to generate imaging scan data. A step of forming an image, wherein the image of the patient is formed based on the processing of the imaging scan data and the timing parameters, The method according to claim 1 or 2, further comprising:

11. A computer program, when executed by at least one processing unit, is configured to cause the processing unit to perform the steps of the method according to claim 1 or 2.

12. A computer-readable medium storing the computer program described in claim 11.

13. A system for determining a trigger signal for imaging a patient using an imaging system, When the patient is positioned at a first position relative to the imaging system, a patient-specific characteristic sensor measures the patient's unique characteristics, When the patient is positioned in a second position relative to the imaging system, a trigger waveform sensor measures the trigger waveform of the patient, A processing unit that receives the patient-specific characteristics, generates a patient-specific model based on the patient-specific characteristics, receives a trigger waveform, and determines a trigger signal based on the patient-specific model and the trigger waveform, A system that has

14. An imaging system having the system described in claim 13, wherein the imaging system is a computed tomography system or a magnetic resonance imaging system.

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