Low-pass filtered non-respiratory breath hold saline contrast combined with cardiac mirror backfilling electrical impedance lung perfusion imaging method
By employing low-pass filtering technology and cardiac mirror backfilling, we can achieve breath-hold saline angiography without breathing, which solves the interference problem caused by prolonged breathing in existing technologies, and improves the accuracy of lung perfusion imaging and the ease of clinical application.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- PEKING UNION MEDICAL COLLEGE HOSPITAL
- Filing Date
- 2025-12-03
- Publication Date
- 2026-06-26
Smart Images
Figure CN122271990A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of medical imaging technology, specifically to a method for electrical impedance tomography of lung perfusion imaging using low-pass filtered non-breathing-screen saline angiography combined with cardiac image complementation. Background Technology
[0002] EIT (Extracorporeal Intervention) is a non-invasive, continuous, real-time, and radiation-free bedside imaging technique primarily used for monitoring lung ventilation and perfusion (blood flow). EIT lung perfusion imaging typically employs hypertonic saline contrast imaging, where a high-conductivity contrast agent (10 ml, 10% saline) is injected via a bolus injection through a central vein. Changes in pleural electrical resistance are then collected, and a local resistance-time curve based on saline contrast is established to reflect regional lung perfusion. To minimize interference from respiration on electrical resistance, the procedure is required during apnea (breath-holding), when the total pleural resistance remains relatively constant, thus better reflecting the effect of saline contrast imaging.
[0003] Chinese Patent Publication No. CN111449657A discloses a bedside lung ventilation-perfusion electrical impedance tomography method based on saline contrast imaging, establishing an image monitoring device, an image monitoring system, and a pulmonary embolism diagnostic system, thus improving the quality of blood perfusion imaging. Chinese Patent Publication No. CN114723844A discloses a method, system, and device for reconstructing pulsation perfusion images corrected by saline contrast imaging, combining pulmonary vascular pulsation and hypertonic saline contrast imaging, and using pulsation maps and generated correction factors to achieve... Real-time, precise lung perfusion imaging has been disclosed in Chinese patent publications CN115035208A and CN114723844A. A method, system, device, and computer-readable storage medium for non-invasive lung perfusion and regional V / Q imaging are also disclosed. These methods involve introducing blood flow impedance data from saline angiography into a pulsatogram using a correction factor, generating a saline-corrected pulsatogram-perfusion image. A lung ventilation / perfusion map is then constructed by combining the patient's lung ventilation map with the saline-corrected pulsatogram-perfusion image.
[0004] The aforementioned patents all require breath-holding of at least 8 seconds during saline-contrast EIT lung perfusion imaging to reduce respiratory impedance interference. This 8-second breath-hold significantly interferes with clinical applications, as it is equivalent to no ventilation, often necessitating additional sedation or muscle relaxant treatment. Furthermore, 8-second breath-holding can negatively impact oxygenation and circulation. For critically ill patients with spontaneous breathing, breath-holding exceeding 8 seconds is often difficult to perform, resulting in low saline-contrast imaging success rates. Therefore, this approach does not meet current needs. To address this, we propose a low-pass filtered, non-breath-hold saline-contrast imaging method combined with cardiac image-based contrast enhancement for electrical impedance lung perfusion imaging. Summary of the Invention
[0005] The purpose of this invention is to provide a low-pass filtered non-breath-hold saline angiography combined with cardiac image contrast for lung perfusion imaging. This method separates the thoracic impedance caused by tidal breathing from the thoracic impedance caused by saline angiography, determines the time interval of saline flow through the lung region, and generates lung perfusion impedance tomography by fitting the maximum slope of the impedance curve. This reduces the influence of lung perfusion images in the cardiac region, further improves the accuracy of lung perfusion imaging, effectively solves the technical bottleneck of breath-holding saline angiography, and performs saline injection angiography without breath-holding, greatly reducing the interference of breath-holding on respiratory and circulatory functions. This improves the ease of clinical application and expands the clinical application scenarios, thus solving the problems mentioned in the background art.
[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for electrical impedance tomography (EIT) of the lungs using low-pass filtered non-breathing breath-hold saline angiography combined with cardiac image contrast, comprising the following steps:
[0007] S1: Connect the subject to a lung electrical impedance monitoring instrument to continuously collect chest electrical impedance signals and determine whether the subject's respiratory tidal impedance variation meets the imaging criteria. When the global tidal impedance variation is less than 20% per minute, it is considered that the saline contrast-enhanced lung perfusion examination without breath-holding can be performed.
[0008] S2: After confirming that the respiratory tidal resistance variation meets the imaging criteria, the subject is injected with contrast agent to perform imaging.
[0009] S3: During the contrast-enhanced imaging process, continuously acquire electrical impedance signals until the contrast agent is completely cleared, and analyze the acquired electrical impedance signal data to obtain the impedance drop signal;
[0010] S4: Perform feature analysis on the lung impedance decrease signal, and combine the cardiac image with the lung perfusion image based on the feature analysis results.
[0011] Preferably, the step of connecting the subject to a pulmonary electrical impedance monitoring instrument to continuously collect chest electrical impedance signals and determine whether the subject's respiratory tidal impedance variability meets the imaging criteria specifically includes:
[0012] The instrument is activated to continuously collect the subject's chest impedance signal, obtaining a continuous signal curve that includes the complete changes in the inspiratory and expiratory phases;
[0013] Automatically identify the inspiratory peaks and expiratory valleys in the continuous signal curve, divide the continuous signal period based on the identified inspiratory peaks and expiratory valleys, and mark the start and end time points of each period.
[0014] The maximum and minimum impedance values within each segmented respiratory cycle were extracted, and the relative coefficient of variation was used as a quantitative indicator to calculate the tidal impedance variation of the subjects.
[0015] Determine whether the respiratory tidal impedance variation meets the imaging criteria based on the calculation results of the respiratory tidal impedance variation value;
[0016] When the tidal resistance variation per minute is less than 20%, it is determined that angiographic EIT lung perfusion examination without breath-holding can be performed.
[0017] Preferably, after confirming that the respiratory tidal resistance variation meets the imaging criteria, the subject is injected with saline to perform imaging, specifically including:
[0018] Prepare 10 ml of saline contrast agent, which is 10% NaCl. Before the contrast agent is performed, confirm that the subject has a central venous catheter.
[0019] Pulmonary perfusion angiography is performed by rapidly injecting saline contrast agent directly into the subject through a central venous catheter.
[0020] During the contrast imaging process involving the injection of saline contrast agent, the subject does not need to hold their breath; they can simply maintain their original breathing state.
[0021] Preferably, the step of continuously acquiring impedance signals during the contrast-enhancing process until the contrast agent is completely cleared, and analyzing the acquired impedance signal data, specifically includes:
[0022] Signal acquisition begins when the saline contrast agent is injected and continues until the contrast agent is completely cleared. Key time points are marked simultaneously during the acquisition process: injection start time, injection end time, impedance signal begins to decrease, impedance drops to the lowest value, and signal recovers to 90% of baseline.
[0023] The acquired analog resistance signal is converted into a digital signal by an ADC chip, and the resistance value in the digital signal is converted into an impedance value.
[0024] The converted impedance data are sorted by time series to generate the original angiography impedance curve, and the angiography impedance curve data is then subjected to low-pass filtering.
[0025] Based on the filtered impedance curve, a threshold for identifying impedance drop signals is set:
[0026] Monitoring begins at the start of injection. When the impedance value drops by more than 10% from the baseline and lasts for ≥0.5 seconds, it is considered an effective drop signal, and the start of the injection end time is taken as the beginning of the injection end time.
[0027] When the impedance value drops to its lowest point and begins to rise again, it is determined to be the endpoint of the decline. The time when the impedance signal begins to decline is the impedance decline signal generated after the saline contrast agent enters the lung area.
[0028] Preferably, the low-pass filtering of the contrast impedance curve data specifically includes:
[0029] Select angiographic impedance curve data that is lower than the patient's respiratory rate, and further optimize the low-pass filter frequency;
[0030] The angiography impedance curve data were filtered using an optimized low-pass filter frequency, and the lung perfusion analysis time window of the angiography impedance curve data was determined.
[0031] After low-pass filtering of the contrast impedance curve data, the shape of the contrast impedance curve data changes. The initial time T0 when the saline contrast agent first enters the lung area is determined based on the change in the shape of the contrast impedance curve data.
[0032] The lung perfusion analysis impedance range and lung perfusion impedance signal are determined based on the initial time T0 when the saline contrast agent first enters the lung region;
[0033] Lung perfusion images were constructed using lung perfusion analysis impedance intervals and lung perfusion impedance signals.
[0034] Preferably, determining the initial time T0 of the first entry of saline contrast agent into the lung region based on the morphological changes of the contrast impedance curve data specifically includes:
[0035] To determine the lung region pixels in the right dorsal quadrant of the ventilatory impedance curve, select the pixel with the highest tidal impedance as the representative lung pixel.
[0036] If there are no suitable pixels in the right dorsal quadrant, then consider the areas far from the heart in the left dorsal or right ventral quadrants in turn.
[0037] After determining the initial time of saline contrast agent entering the lung region and representative lung region pixels, the impedance-time curves of the pixels are analyzed to obtain the initial time T0 of saline contrast agent reaching the lung region after passing through the right heart.
[0038] Preferably, after determining the initial time of the saline contrast agent entering the lung region and representative lung region pixels, the impedance-time curve of the pixels is analyzed to obtain the initial time of the saline contrast agent reaching the lung region after passing through the right heart. Specifically, this includes drawing a parallel line from the lowest point of the baseline expiratory impedance and intersecting it with the initial point where the contrast impedance of the saline contrast agent begins to decrease after injection. This intersection point is taken as the initial time T0 of the saline contrast agent entering the lung region, i.e., the initial time of the saline contrast agent reaching the lung region after passing through the right heart.
[0039] Preferably, the construction of lung perfusion images using lung perfusion analysis impedance intervals and lung perfusion impedance signals specifically includes:
[0040] Determine the time interval of the lung perfusion analysis curve, and take the time of the lowest point of the overall resistance during the contrast process as the endpoint T1 of the saline contrast agent passing through the lung area;
[0041] The impedance curves selected during the T0-T1 time period reflect the process of saline contrast agent initially entering the lung area for perfusion until it begins to leave the lung area. T1 is the point of lowest global impedance, indicating that the saline contrast agent begins to leave the lung area.
[0042] Lung perfusion images were constructed using the resistance versus time curves of various lung regions during the T0-T1 time period.
[0043] Preferably, the step of performing feature analysis on the lung impedance decrease signal and combining the feature analysis results with the cardiac image to backfill lung perfusion images specifically includes:
[0044] Feature analysis was performed on the lung impedance decrease signal to extract the rising edge slope, peak time, falling edge duration, and waveform amplitude characteristic parameters.
[0045] Based on the real-time acquired lung impedance decrease signal, the impedance signal waveform that the saline contrast agent should produce in the outflow tract region when leaving the heart is predicted, and key time nodes such as the start time and peak time of the predicted signal are recorded.
[0046] Using the time axis as a reference, the predicted cardiac outflow tract impedance signal is waveform-aligned with the actual acquired signal;
[0047] Calculate the time difference between the corresponding feature points of the two sets of signals respectively, and take the average of the differences of multiple feature points as the final time difference parameter;
[0048] The lung perfusion images were supplemented by combining the final temporal difference parameters with cardiac imagery.
[0049] Preferably, the step of combining the final temporal difference parameters with the cardiac image to retrograde lung perfusion image specifically includes:
[0050] The lung and cardiac pixels were determined based on the angiography impedance curve data obtained from low-pass filtering.
[0051] Extract the core features of the impedance curve for each pixel, including the basic impedance value, the magnitude of impedance change, and the trend of change;
[0052] The interval T1-T2 is divided into the interval T1 to 2T1-T0 and the interval 2T1-T0 to T2.
[0053] Based on the time difference parameter, a three-dimensional data matrix is constructed with time as the horizontal axis, pixel position as the vertical axis, and the impedance value after inversion as the gray value.
[0054] By mapping grayscale values, a three-dimensional matrix is converted into a two-dimensional temporal image sequence. Frame fusion processing is then performed on the image sequence to enhance image clarity, ultimately yielding cardiac lung perfusion images that can intuitively reflect the flow of saline contrast agent within the heart and the lung perfusion process.
[0055] Compared with the prior art, the beneficial effects of the present invention are:
[0056] This invention performs angiography by directly injecting saline solution without breath-holding, and uses pulmonary electrical impedance monitoring technology to acquire thoracic impedance signal data during the angiography process. Then, through low-pass filtering, an optimized filtering frequency is determined to separate the thoracic impedance caused by tidal breathing from that caused by saline injection angiography. Further analysis of the thoracic impedance change curve caused by saline injection angiography after low-pass filtering determines the time interval of saline flow through the lung region. By fitting the maximum slope of the impedance curve, a pulmonary perfusion electrical impedance tomography image is generated. Finally, by combining cardiac mirror images for backfilling, the influence of pulmonary perfusion images in the cardiac region is reduced, further improving the accuracy of pulmonary perfusion imaging. This effectively solves the technical bottleneck of breath-holding saline angiography during breath-holding, greatly reducing the interference of breath-holding on respiratory and circulatory processes, improving the simplicity of clinical application and expanding the clinical application scenarios. Attached Figure Description
[0057] Figure 1 This is a schematic diagram of the electrical impedance lung perfusion imaging method of the present invention, which combines low-pass filtered non-breathing breath-hold saline angiography with cardiac mirror-reinforcement.
[0058] Figure 2 This is an image of the tidal ventilation system of the present invention;
[0059] Figure 3 This is a diagram showing the initial moment when the saline contrast agent enters the lung region, as determined by the present invention.
[0060] Figure 4 This is a schematic diagram illustrating the determination of the analysis interval T0-T1 according to the present invention;
[0061] Figure 5 This is a schematic diagram illustrating the use of mirror images to perform inverse complementation on lung perfusion images according to the present invention;
[0062] Figure 6 This is a comparison diagram of the effects of the present invention and traditional methods;
[0063] Figure 7 A non-mirror-image fitted lung perfusion map including the cardiac region time segment;
[0064] Figure 8 Non-mirror fitting of lung perfusion maps excluding the cardiac region time period;
[0065] Figure 9 This is a mirror-fitted lung perfusion map of the present invention. Detailed Implementation
[0066] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0067] To address the issue that current techniques, in order to reduce interference from respiratory impedance, require breath-holding of at least 8 seconds, which can significantly interfere with clinical applications and necessitates additional treatment with sedation or muscle relaxants, and can also adversely affect oxygenation and circulation, especially for critically ill patients with spontaneous breathing, breath-holding exceeding 8 seconds is often difficult to perform, resulting in low success rates for saline angiography. Please refer to [link to relevant documentation]. Figures 1-9 This embodiment provides the following technical solution:
[0068] A low-pass filtered non-breathing-hold saline angiography combined with cardiac refraction complementation for electrical impedance to lung perfusion imaging includes the following steps:
[0069] S1: Connect the subject to a lung electrical impedance monitoring instrument to continuously collect chest electrical impedance signals and determine whether the subject's respiratory tidal impedance variation meets the imaging criteria. When the global tidal impedance variation is less than 20% per minute, it is considered that the saline contrast-enhanced lung perfusion examination without breath-holding can be performed.
[0070] S2: After confirming that the respiratory tidal resistance variation meets the imaging criteria, the subject is injected with contrast agent to perform imaging.
[0071] S3: During the contrast-enhanced imaging process, continuously acquire electrical impedance signals until the contrast agent is completely cleared, and analyze the acquired electrical impedance signal data to obtain the impedance drop signal;
[0072] S4: Perform feature analysis on the lung impedance decrease signal, and combine the cardiac image with the lung perfusion image based on the feature analysis results.
[0073] The subject is connected to a pulmonary electrical impedance monitoring device to continuously collect chest impedance signals and determine whether the subject's respiratory tidal impedance variability meets the imaging criteria, specifically including:
[0074] The instrument is activated to continuously collect the subject's chest impedance signal for at least 3 minutes, ensuring coverage of at least 15 complete respiratory cycles (the respiratory rate for normal adults is calculated as 12-20 breaths / minute), and to obtain a continuous signal curve containing the complete changes in the inspiratory and expiratory phases.
[0075] Automatically identify the inspiratory peaks and expiratory valleys in the continuous signal curve, divide the continuous signal period based on the identified inspiratory peaks and expiratory valleys, and mark the start and end time points of each period.
[0076] The maximum and minimum impedance values within each segmented respiratory cycle were extracted, and the relative coefficient of variation was used as a quantitative indicator to calculate the tidal impedance variation of the subjects. At the same time, the duration of each cycle was recorded, the average respiratory rate was calculated, and the deviation of variation assessment caused by abnormal respiratory rate (<10 breaths / minute or >25 breaths / minute) was excluded.
[0077] Determine whether the respiratory tidal impedance variation meets the imaging criteria based on the calculation results of the respiratory tidal impedance variation value;
[0078] When the tidal resistance variation per minute is less than 20%, it is determined that angiographic EIT lung perfusion examination without breath-holding can be performed.
[0079] After confirming that the respiratory tidal resistance variation meets the imaging criteria, the subject is injected with saline to perform imaging, which specifically includes:
[0080] Prepare 10 ml of saline contrast agent, which is 10% NaCl. Before the contrast agent is performed, confirm that the subject has a central venous catheter.
[0081] Pulmonary perfusion angiography is performed by rapidly injecting saline contrast agent directly into the subject through a central venous catheter.
[0082] During the contrast imaging process involving the injection of saline contrast agent, the subject does not need to hold their breath; they can simply maintain their original breathing state.
[0083] During the contrast-enhanced imaging process, electrical impedance signals are continuously acquired until the contrast agent is completely cleared, and the acquired impedance signal data is analyzed, specifically including:
[0084] Signal acquisition begins when the saline contrast agent is injected and continues until the contrast agent is completely cleared. Key time points are marked simultaneously during the acquisition process: injection start time, injection end time, impedance signal begins to decrease, impedance drops to the lowest value, and signal recovers to 90% of baseline.
[0085] The acquired analog resistance signal is converted into a digital signal by an ADC chip, and the resistance value in the digital signal is converted into an impedance value.
[0086] The converted impedance data are sorted by time series to generate the original angiography impedance curve, and the angiography impedance curve data is then subjected to low-pass filtering.
[0087] Based on the filtered impedance curve, a threshold for identifying impedance drop signals is set:
[0088] Monitoring begins at the start of injection. When the impedance value drops by more than 10% from the baseline and lasts for ≥0.5 seconds, it is considered an effective drop signal, and the start of the injection end time is taken as the beginning of the injection end time.
[0089] When the impedance value drops to its lowest point and begins to rise again, it is determined to be the endpoint of the decline. The time when the impedance signal begins to decline is the impedance decline signal generated after the saline contrast agent enters the lung area.
[0090] Low-pass filtering is performed on the contrast impedance curve data, specifically including:
[0091] Select contrast impedance curve data below the patient's respiratory rate and further optimize the low-pass filter frequency; separate the saline contrast agent injection impedance signal through low-pass filtering, import the data into the filter software, and select an appropriate low-pass filter frequency. To reduce the interference of the respiratory impedance signal on the saline contrast agent signal and achieve separation of the respiratory impedance signal and the saline contrast agent contrast impedance signal, a low-pass filter of 0.17Hz is optimal.
[0092] The angiography impedance curve data were filtered using an optimized low-pass filter frequency, and the lung perfusion analysis time window of the angiography impedance curve data was determined.
[0093] After low-pass filtering of the contrast impedance curve data, the shape of the contrast impedance curve data changes. The initial time T0 when the saline contrast agent first enters the lung area is determined based on the change in the shape of the contrast impedance curve data.
[0094] The lung perfusion analysis impedance range and lung perfusion impedance signal are determined based on the initial time T0 when the saline contrast agent first enters the lung region;
[0095] Lung perfusion images were constructed using lung perfusion analysis impedance intervals and lung perfusion impedance signals.
[0096] The initial time T0 of the first entry of saline contrast agent into the lung region is determined based on the changes in the morphology of the contrast impedance curve data, specifically including:
[0097] To determine the lung region pixels in the right dorsal quadrant of the ventilatory impedance curve, select the pixel with the highest tidal impedance as the representative lung pixel.
[0098] If there are no suitable pixels in the right dorsal quadrant, then consider the areas far from the heart in the left dorsal or right ventral quadrants in turn.
[0099] After determining the initial time of saline contrast agent entering the lung region and representative lung region pixels, the impedance-time curves of the pixels are analyzed to obtain the initial time T0 of saline contrast agent reaching the lung region after passing through the right heart.
[0100] After determining the initial time of saline contrast agent entering the lung region and representative lung region pixels, the impedance-time curves of the pixels are analyzed to obtain the initial time when the saline contrast agent initially reaches the lung region after passing through the right heart. Specifically, this includes drawing a line parallel to the lowest point of baseline expiratory impedance and intersecting it with the initial point where the contrast impedance of the saline contrast agent begins to decrease after injection. This intersection point is taken as the initial time T0 when the saline contrast agent enters the lung region, i.e., the initial time when the saline contrast agent initially reaches the lung region after passing through the right heart.
[0101] Lung perfusion imaging is constructed using lung perfusion analysis impedance intervals and lung perfusion impedance signals, specifically including:
[0102] Determine the time interval of the lung perfusion analysis curve, and take the time of the lowest point of the overall resistance during the contrast process as the endpoint T1 of the saline contrast agent passing through the lung area;
[0103] The impedance curves selected during the T0-T1 time period reflect the process of saline contrast agent initially entering the lung area for perfusion until it begins to leave the lung area. T1 is the point of lowest global impedance, indicating that the saline contrast agent begins to leave the lung area.
[0104] Lung perfusion images were constructed using the resistance-time variation curves (slope fitting) of various lung regions during the T0-T1 time period.
[0105] Feature analysis was performed on the lung impedance decrease signal, and the lung perfusion images were supplemented based on the feature analysis results using cardiac image refraction, specifically including:
[0106] Feature analysis was performed on the lung impedance decrease signal to extract key feature parameters such as the rise slope, peak time, fall duration, and waveform amplitude.
[0107] Based on the real-time acquired lung impedance decrease signal, the impedance signal waveform that the saline contrast agent should produce in the outflow tract region when leaving the heart is predicted, and key time nodes such as the start time and peak time of the predicted signal are recorded.
[0108] Using the time axis as a reference, the predicted cardiac outflow tract impedance signal is aligned with the actual acquired signal waveform. Precise matching is performed on characteristic points such as the start point of the rising edge, the peak point, and the end point of the falling edge of the two sets of signals to ensure the relevance and accuracy of the comparison.
[0109] Calculate the time difference between the corresponding feature points of the two sets of signals, focusing on the difference between the predicted start time and the actual start time, and the difference between the predicted peak time and the actual peak time. Take the average of the differences of multiple feature points as the final time difference parameter. If the time difference parameter is positive, it indicates that the contrast agent actually leaves the heart later than the predicted time; if it is negative, it indicates that the actual time is earlier than the predicted time.
[0110] The lung perfusion images were supplemented by combining the final temporal difference parameters with cardiac imagery.
[0111] Based on the final temporal difference parameters combined with cardiac image-based lung perfusion images, specifically including:
[0112] The lung and cardiac pixels were determined based on the angiography impedance curve data obtained from low-pass filtering.
[0113] Extract the core features of the impedance curve for each pixel, including the basic impedance value, the magnitude of impedance change, and the trend of change;
[0114] The T1-T2 interval is divided into the T1 to 2T1-T0 interval (equal in duration to the baseline T0-T1 interval) and the 2T1-T0 to T2 interval. For the former, the mirrored predicted impedance value generated in step three is directly used for filling; for the latter, based on the impedance decreasing trend in the T1 to 2T1-T0 interval, an exponential decay model is used for fitting and extrapolation to ensure the continuity and physiological rationality of the impedance signal change. During the extrapolation process, a lower impedance limit (not lower than 80% of the baseline impedance value) needs to be set to avoid abnormal values that do not conform to physiological reality.
[0115] Based on the time difference parameter, a three-dimensional data matrix is constructed with time as the horizontal axis, pixel position as the vertical axis, and the impedance value after inversion as the gray value.
[0116] By mapping grayscale values, the impedance range is linearly converted to a grayscale range of 0-255, with lower impedance corresponding to higher grayscale values. This transforms the three-dimensional matrix into a two-dimensional temporal image sequence. Frame fusion processing is then performed on the image sequence to enhance image clarity, ultimately yielding cardiac lung perfusion images that visually reflect the flow of saline contrast agent within the heart and the lung perfusion process.
[0117] Twenty subjects were selected. Ten subjects underwent contrast imaging using the conventional saline contrast method with breath-holding, while the other ten subjects underwent contrast imaging using the low-pass filtered non-breath-hold saline contrast method combined with cardiac refraction and electrical impedance tomography (EIP) of this application. The contrast results are as follows: Figure 6As shown, the final lung perfusion images of the two methods are highly correlated, with a correlation coefficient of 0.98, indicating that the image quality of this application is consistent with the traditional breath-holding method. However, there are significant differences in acquisition conditions and signal curve characteristics. The curve of the traditional saline contrast breathing breath-holding method exhibits regular high-frequency fluctuations (corresponding to high-frequency characteristics of respiration or sampling), with a significant signal drop segment (pink area) in the approximately 500-1000 range. The overall curve fluctuates at a high frequency and has strong rhythmicity. The low-pass filtered non-breathing breath-holding saline contrast combined with cardiac image contrast-assisted lung perfusion imaging significantly reduces the curve fluctuation frequency, presenting a gentle wave-like shape. The morphology of the signal drop segment (pink area) is also different from that of the breath-holding group, and the overall curve is smoother with high-frequency components filtered out.
[0118] Lung perfusion mapping was performed on 3 subjects, with non-mirror image fitting used for 2 subjects. The fitting results are as follows: Figure 7 and Figure 8 As shown, another subject used mirror-image fitting of lung perfusion, and the results were as follows. Figure 9 As shown:
[0119] Figure 7 A non-mirror-fitted lung perfusion map, including the cardiac region time period, shows that cardiac signals have a significant impact, and pulmonary perfusion blood flow is concentrated in the cardiac region. Figure 8 The non-mirror-fitted lung perfusion map excludes the cardiac region time period. It can be seen that, excluding the time period when saline reaches the heart, cardiac perfusion is missing. Figure 9 By fitting a mirror image of the lung perfusion map, including the cardiac region time period, it can be seen that the perfusion of the lung regions overlapping with the cardiac region can also be observed.
[0120] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "include," "contain," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.
[0121] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.
Claims
1. A method for electrical impedance tomography (EIP) of the lungs using low-pass filtered non-breathing-hold saline angiography combined with cardiac image contrast, characterized in that: Includes the following steps: S1: Connect the subject to a lung electrical impedance monitoring instrument to continuously collect chest electrical impedance signals and determine whether the subject's respiratory tidal impedance variation meets the imaging criteria. When the global tidal impedance variation is less than 20% per minute, it is considered that the saline contrast-enhanced lung perfusion examination without breath-holding can be performed. S2: After confirming that the respiratory tidal resistance variation meets the imaging criteria, the subject is injected with contrast agent to perform imaging. S3: During the contrast-enhanced imaging process, continuously acquire electrical impedance signals until the contrast agent is completely cleared, and analyze the acquired electrical impedance signal data to obtain the impedance drop signal; S4: Perform feature analysis on the lung impedance decrease signal, and combine the cardiac image with the lung perfusion image based on the feature analysis results.
2. The method for low-pass filtered non-breathing-hold saline angiography combined with cardiac image contrast-enhanced lung perfusion imaging according to claim 1, characterized in that, The process of connecting the subject to a pulmonary electrical impedance monitoring device to continuously collect chest electrical impedance signals and determine whether the subject's respiratory tidal impedance variability meets the imaging criteria specifically includes: The instrument is activated to continuously collect the subject's chest impedance signal, obtaining a continuous signal curve that includes the complete changes in the inspiratory and expiratory phases; Automatically identify the inspiratory peaks and expiratory valleys in the continuous signal curve, divide the continuous signal period based on the identified inspiratory peaks and expiratory valleys, and mark the start and end time points of each period. The maximum and minimum impedance values within each segmented respiratory cycle were extracted, and the relative coefficient of variation was used as a quantitative indicator to calculate the tidal impedance variation of the subjects. Determine whether the respiratory tidal impedance variation meets the imaging criteria based on the calculation results of the respiratory tidal impedance variation value; When the tidal resistance variation per minute is less than 20%, it is determined that angiographic EIT lung perfusion examination without breath-holding can be performed.
3. The method for low-pass filtered non-breathing-hold saline angiography combined with cardiac image contrast-enhanced lung perfusion imaging according to claim 1, characterized in that, After confirming that the respiratory tidal impedance variation meets the imaging criteria, the subject is injected with saline to perform imaging, which specifically includes: Prepare 10 ml of saline contrast agent, which is 10% NaCl. Before the contrast agent is performed, confirm that the subject has a central venous catheter. Pulmonary perfusion angiography was performed by directly and rapidly injecting saline contrast agent into the subject's body through a central venous catheter. During the contrast imaging process involving the injection of saline contrast agent, the subject does not need to hold their breath; they can simply maintain their original breathing state.
4. The method for low-pass filtered non-breathing-hold saline angiography combined with cardiac image contrast-enhanced lung perfusion imaging according to claim 1, characterized in that, The process of continuously acquiring electrical impedance signals during contrast administration until the contrast agent is completely cleared, and analyzing the acquired electrical impedance signal data, specifically includes: Signal acquisition begins when the saline contrast agent is injected and continues until the contrast agent is completely cleared. Key time points are marked simultaneously during the acquisition process: injection start time, injection end time, impedance signal begins to decrease, impedance drops to the lowest value, and signal recovers to 90% of baseline. The acquired analog resistance signal is converted into a digital signal by an ADC chip, and the resistance value in the digital signal is converted into an impedance value. The converted impedance data are sorted by time series to generate the original angiography impedance curve, and the angiography impedance curve data is then subjected to low-pass filtering. Based on the filtered impedance curve, a threshold for identifying impedance drop signals is set: Monitoring begins at the start of injection. When the impedance value drops by more than 10% from the baseline and lasts for ≥0.5 seconds, the start of the effective drop signal is determined as the end of injection. When the impedance value drops to its lowest point and begins to rise again, it is determined to be the endpoint of the decline. The time when the impedance signal begins to decline is the impedance decline signal generated after the saline contrast agent enters the lung area.
5. The method for low-pass filtered non-breathing-hold saline angiography combined with cardiac image contrast enhancement according to claim 4, characterized in that, The low-pass filtering of the angiography impedance curve data specifically includes: Select angiographic impedance curve data that is lower than the patient's respiratory rate, and further optimize the low-pass filter frequency; The angiography impedance curve data were filtered using an optimized low-pass filter frequency, and the lung perfusion analysis time window of the angiography impedance curve data was determined. After low-pass filtering of the contrast impedance curve data, the shape of the contrast impedance curve data changes. The initial time T0 when the saline contrast agent first enters the lung area is determined based on the change in the shape of the contrast impedance curve data. The lung perfusion analysis impedance range and lung perfusion impedance signal are determined based on the initial time T0 when the saline contrast agent first enters the lung region; Lung perfusion images were constructed using lung perfusion analysis impedance intervals and lung perfusion impedance signals.
6. The method for low-pass filtered non-breathing-hold saline angiography combined with cardiac image contrast-enhanced lung perfusion imaging according to claim 5, characterized in that, The determination of the initial time T0 of the first entry of saline contrast agent into the lung region based on the morphological changes of the contrast impedance curve data specifically includes: To determine the lung region pixels in the right dorsal quadrant of the ventilatory impedance curve, select the pixel with the highest tidal impedance as the representative lung pixel. If there are no suitable pixels in the right dorsal quadrant, then consider the areas far from the heart in the left dorsal or right ventral quadrants in turn. After determining the initial time of saline contrast agent entering the lung region and representative lung region pixels, the impedance-time curves of the pixels are analyzed to obtain the initial time T0 of saline contrast agent reaching the lung region after passing through the right heart.
7. The method for low-pass filtered non-breathing-hold saline angiography combined with cardiac image contrast enhancement according to claim 6, characterized in that, After determining the initial time of the saline contrast agent entering the lung region and representative lung region pixels, the impedance-time curve of the pixels is analyzed to obtain the initial time when the saline contrast agent initially reaches the lung region after passing through the right heart. Specifically, this includes drawing a parallel line from the lowest point of baseline expiratory impedance and intersecting it with the initial point when the contrast impedance of the saline contrast agent begins to decrease after injection. This intersection point is taken as the initial time T0 when the saline contrast agent enters the lung region, i.e., the initial time when the saline contrast agent initially reaches the lung region after passing through the right heart.
8. The method for low-pass filtered non-breathing-hold saline contrast agent contrast imaging combined with cardiac image-reverse complementation for lung perfusion imaging according to claim 5, characterized in that, The construction of lung perfusion images using lung perfusion analysis impedance intervals and lung perfusion impedance signals specifically includes: Determine the time interval of the lung perfusion analysis curve, and take the time of the lowest point of the overall resistance during the contrast process as the endpoint T1 of the saline contrast agent passing through the lung area; The impedance curves selected during the T0-T1 time period reflect the process of saline contrast agent initially entering the lung area for perfusion until it begins to leave the lung area. T1 is the point of lowest global impedance, indicating that the saline contrast agent begins to leave the lung area. Lung perfusion images were constructed using the resistance versus time curves of various lung regions during the T0-T1 time period.
9. The method for low-pass filtered non-breathing-hold saline angiography combined with cardiac image contrast-enhanced lung perfusion imaging according to claim 1, characterized in that, The process of performing feature analysis on the lung impedance decrease signal and combining the feature analysis results with cardiac image-based lung perfusion images specifically includes: Feature analysis was performed on the lung impedance decrease signal to extract the rising edge slope, peak time, falling edge duration, and waveform amplitude characteristic parameters. Based on the real-time acquired lung impedance decrease signal, the impedance signal waveform that the saline contrast agent should produce in the outflow tract region when leaving the heart is predicted, and key time nodes such as the start time and peak time of the predicted signal are recorded. Using the time axis as a reference, the predicted cardiac outflow tract impedance signal is waveform-aligned with the actual acquired signal; Calculate the time difference between the corresponding feature points of the two sets of signals respectively, and take the average of the differences of multiple feature points as the final time difference parameter; The lung perfusion images were supplemented by combining the final temporal difference parameters with cardiac imagery.
10. The method for low-pass filtered non-breathing-hold saline angiography combined with cardiac image contrast-enhanced lung perfusion imaging according to claim 9, characterized in that, The step of combining the final temporal difference parameters with the cardiac image to retrograde lung perfusion images specifically includes: The lung and cardiac pixels were determined based on the angiography impedance curve data obtained from low-pass filtering. Extract the core features of the impedance curve for each pixel, including the basic impedance value, the magnitude of impedance change, and the trend of change; The interval T1-T2 is divided into the interval T1 to 2T1-T0 and the interval 2T1-T0 to T2. Based on the time difference parameter, a three-dimensional data matrix is constructed with time as the horizontal axis, pixel position as the vertical axis, and the impedance value after inversion as the gray value. By mapping grayscale values, a three-dimensional matrix is converted into a two-dimensional temporal image sequence. Frame fusion processing is then performed on the image sequence to enhance image clarity, ultimately yielding cardiac lung perfusion images that can intuitively reflect the flow of saline contrast agent within the heart and the lung perfusion process.