Perfusion angiography in conjunction with photoplethysmographic imaging for peripheral vascular disease assessment

Abstract

A perfusion angiography for peripheral vascular disease assessment in combination with photoplethysmographic imaging. An apparatus (13) and method for performing perfusion imaging receives image sequences concurrently acquired by an X-ray imaging device (2) and by a photoplethysmographic imaging device (3). When temporally aligned, the perfusion status of perfused organ tissue is extracted from both image sequences over time and images are generated for display on a display unit (5) that indicate changes in perfusion status at various locations of the perfused organ tissue, thereby capturing both deep and superficial organ tissue perfusion properties. A reduction in image signal intensity in the photoplethysmographic images caused by a bolus of previously administered contrast agent (10) passing through can be used to temporally align the two concurrently acquired image sequences.

Description

Technical Field

[0001] This invention relates to the field of medical imaging devices and methods. More specifically, this invention relates to devices and methods for imaging vascular tissues of peripheral organs using both perfusion angiography and photoplethysmography. Background Technology

[0002] Perfusion angiography represents a widely disseminated and recognized technique for the assessment and management of various diseases in peripheral organs. It relies on the study of the perfusion properties of deep tissues within an organ, successfully imaged by contrast-enhanced X-ray imaging such as two-dimensional fluorescence fluoroscopy. Therefore, perfusion angiography provides valuable insights into the health status of perfused tissues, such as ischemia or vascular reconstruction following angioplasty of obstructed deep vessels.

[0003] European Patent Specification EP-2866643 discloses a patency assessment system in which a photoplethysmography (PPG) interpretation module outputs pixel values ​​in an image representing PPG information collected from blood vessels by a repositionable photosensitive sensor. The PPG image is generated by an image generation module for output to a display. The image generation module is coupled to the PPG interpretation module and thus receives the output pixels. A photosensitive sensor and a light source are mounted on an endoscope such that the photosensitive sensor receives light from the blood vessel in response to light generated by the light source. In one embodiment, the image generation module is configured to overlay the PPG image onto an X-ray image.

[0004] The embodiments described in this disclosure relate to the evaluation of the patency of blood vessels assessed endoscopically, as is typically done during (minimally invasive) invasive surgical interventions involving blood vessels at hand. Therefore, available information regarding the perfusion properties of organ tissues is limited or lacking. Summary of the Invention

[0005] Despite the existence of a quantity of information providing information about the perfusion properties and health status of perfused tissues in deep tissues involving peripheral organs, perfusion angiography delivers only limited information about the total perfusion and more complete three-dimensional perfusion distribution of perfused organ tissues (especially in superficial tissue regions close to the organ's surface). A more complete study of the total perfusion properties of perfused tissues dependent on peripheral organs would allow for more accurate assessment of vascular diseases and a more detailed elucidation of more effective treatment plans and their monitoring.

[0006] Photoplethysmography (PPG) signals collected from single or several vessels by endoscopic devices configured to achieve this purpose are used to assess patency during surgical interventions, but this method is not suitable for studying the perfusion properties of the entire tissue associated with extended peripheral organs such as limbs, e.g., legs or arms.

[0007] The objective of embodiments of the present invention is to provide an imaging method and apparatus that makes information about the overall perfusion properties of perfused peripheral organ tissues available for research and evaluation, wherein the deep perfusion properties of organ tissues, tissue microcirculation, and superficial organ tissue perfusion near the organ surface are revealed.

[0008] The above objectives are achieved by the method and apparatus according to the present invention.

[0009] According to a first aspect of the invention, an apparatus for performing perfusion imaging is provided. The apparatus includes: a first input port configured to receive a first image sequence comprising multiple two-dimensional projection images indicating the perfusion state relative to deep tissue of an organ perfused during imaging; a second input port configured to receive a second image sequence comprising multiple two-dimensional photoplethysmography images indicating the perfusion state relative to surface or near-surface tissue of an organ perfused during imaging, each of the multiple photoplethysmography images comprising multiple image points associated with blood volume values ​​at corresponding multiple different spatial locations on the organ surface; a processing unit configured to extract a first change and a second change of the perfusion state over time from the received first image sequence and the received second image sequence, respectively, and to align the first change and the second change of the perfusion state or amounts derived therefrom in time; and an output port configured to output a perfusion imaging signal for visualizing the aligned first change and second change of the perfusion state or the amounts derived therefrom.

[0010] In a device according to an embodiment of the invention, the processing unit may be configured to align the first and second changes in the perfusion state in time by detecting the passage of a previously delivered contrast agent bolus (e.g., a sudden decrease in the blood volume value at one or more image points in the second image sequence).

[0011] In the device according to an embodiment of the invention, the processing unit may be configured to derive at least one of the group consisting of aligned first and second changes in the perfusion state from a predefined region of interest in the organ tissue: arrival time signal, peak time signal, and time density signal.

[0012] The device according to an embodiment of the present invention may further include: a motion compensation module adapted to counteract motion artifacts in the acquired second image sequence caused by the movement of organ surface tissue or near-surface tissue during imaging.

[0013] The device according to an embodiment of the present invention may further include: a third input port configured to receive a third image sequence including multiple two-dimensional fluorescence images indicating the perfusion state relative to the perfusion state of the organ surface tissue or near-surface tissue perfused during imaging, and the processing unit may further be configured to extract a third change in the perfusion state over time from the acquired third image sequence and to align the first change, the second change, and the third change in the perfusion state over time.

[0014] According to a second aspect of the invention, a perfusion imaging system is described, comprising any of the devices for performing perfusion imaging according to embodiments of the first aspect of the invention. The perfusion imaging system further includes an X-ray imaging device for acquiring a first image sequence and a photoplethysmography (PPG) imaging device for acquiring a second image sequence, the X-ray imaging device being coupled to the first input port and the PPG imaging device being coupled to the second input port. Each of the first and second image sequences comprises multiple two-dimensional images; the two-dimensional images of the first image sequence are projected images indicating the perfusion state relative to deep tissues of an organ being perfused during imaging, and the two-dimensional images of the second image sequence are photoplethysmographic images indicating the perfusion state relative to surface or near-surface tissues of the organ being perfused during imaging. In each of the PPG images, multiple image points are associated with blood volume values ​​at corresponding multiple different spatial locations on the organ surface. The processing unit (also part of the perfusion imaging system, as part of the device for performing perfusion imaging) is configured to initiate simultaneous imaging by the X-ray imaging apparatus and the PPG imaging apparatus, and to extract a first change and a second change in the perfusion state over time from the acquired first image sequence and the acquired second image sequence, respectively. Furthermore, the processing unit is configured to align the first change and the second change in the perfusion state, or the amounts derived therefrom, over time. The aligned first and second changes in the perfusion state, or the amounts derived therefrom, are then visualized in a common image on the display unit of the perfusion imaging system. In an embodiment, the perfusion imaging system may further include a delivery device for delivering a contrast agent to the organ tissue to be perfused during imaging, and the delivery device may be adapted to deliver the contrast agent prior to simultaneous imaging by the X-ray imaging apparatus and the PPG imaging apparatus.

[0015] According to a third aspect of the invention, a method for imaging perfusion properties in relation to a peripheral organ tissue perfusion imaging system is described. Such a method can be performed, for example, when using an apparatus for performing perfusion imaging according to an embodiment of the first aspect of the invention or a perfusion imaging system according to an embodiment of the second aspect of the invention for imaging. The method includes providing a first image sequence acquired and providing a second image sequence acquired simultaneously. The first image sequence includes multiple two-dimensional X-ray projection images indicating the perfusion state relative to deep tissue of an organ to be perfused during imaging, and the second image sequence includes multiple two-dimensional photoplethysmography (PPG) images indicating the perfusion state relative to surface or near-surface tissue of the organ to be perfused during imaging. Each PPG image includes multiple image points associated with blood volume values ​​at corresponding multiple different spatial locations on the organ surface. Next, a first change and a second change in the perfusion state over time are extracted from the acquired first image sequence and the acquired second image sequence, respectively, and the first change and the second change in the perfusion state, or amounts derived therefrom, are aligned temporally. It also generates images for display on a display unit, and the generated images include multiple image signals indicating aligned first and second changes or quantities derived therefrom of the perfusion state at multiple perfused organ tissue locations.

[0016] While conventional X-ray angiography only acquires two-dimensional projection images of the perfusion properties of deep organs and tissues, the combined provision and concurrent use of X-ray imaging and PPG imaging devices during imaging is extending the tissue imaging capabilities of perfusion imaging systems according to embodiments of the invention far beyond those currently available in X-ray perfusion angiography, providing insights into the overall perfusion properties of perfused peripheral organs and tissues. It has been found that meaningful interpretations of both deep and superficial organ perfusion properties based on the temporal changes in the perfusion status of perfused organ tissues extracted from these two image sequences are feasible when these changes are temporally aligned.

[0017] The advantages of embodiments of the present invention are that they obtain the overall perfusion properties of perfused peripheral organs and tissues, combining deep perfusion, microcirculatory redness and superficial perfusion, as well as spatial three-dimensional perfusion distribution information, and making it available for analysis via a single perfusion imaging system during a single perfusion measurement. This allows for more effective management and monitoring of peripheral vascular diseases.

[0018] An advantage of embodiments of the present invention is that existing angiography X-ray imaging devices, protocols, and software can be easily adapted to accommodate the simultaneous acquisition of PPG image sequences.

[0019] Another advantage of embodiments of the present invention is that the two-dimensional X-ray imaging technique used in conventional angiography is extended beyond 2D to provide spatial perfusion distribution in three dimensions.

[0020] In various embodiments of the invention, the attenuation of image signal intensity in PPG images caused by the passage of a clump of previously administered contrast agent delivered by the delivery device of the perfusion imaging system can be used to temporally align two concurrently acquired image sequences. Therefore, an advantage of embodiments of the invention is that image sequences acquired simultaneously by at least two different imaging modalities (X-ray and PPG) can be precisely aligned temporally by detecting a reduction in the amplitude of the image signal in the image sequence acquired by the PPG imaging device, caused by the passage of a previously delivered clump of contrast agent already present in perfusion vascular imaging. No additional equipment or products are required to achieve temporal alignment. This is a surprising and unexpected finding for those skilled in the art who will consider the negative impact or interference of the passage of the clump of contrast material on the PPG imaging process. In summary, the PPG image signal is found in the periodic variations of light absorption or light scattering amplitude in conjunction with changes in pulsatile blood volume at heart rate. Any interference, such as by periodic variations caused by interruptions or replacements in the maintenance of blood flow or any longer-lasting suppression thereof, will provide information conflicting with the type of PPG image signal typically expected for measurements of arterial oxygen saturation or heart rate. However, embodiments of the present invention demonstrate that X-ray perfusion angiography and PPG imaging are two imaging techniques compatible with each other and that interaction mechanisms such as the passage of boluses can benefit from them.

[0021] In embodiments of the method, the term "providing any image" may or may not include receiving such images. Receiving images is intended to include cases where the images were not actually generated using the method. For example, they may have been obtained from elsewhere, by another method, and / or at another time and processed solely by the current method. The method may indeed include both the generation and processing of images.

[0022] The method can be a computer-implemented method, wherein the image is received by a corresponding input unit of an image processing device and / or system.

[0023] In embodiments of the invention, the processing unit is configured to derive quantities from aligned first and second changes in the perfusion state over a predefined region of interest in the organ tissue to be perfused during imaging, wherein the derived quantities are selected from at least one of the group consisting of: arrival time signal, peak time signal, and temporal density signal. The derived quantities, when further studied or visualized on the display unit of the perfusion imaging system, can help medical and healthcare professionals develop a deeper understanding of the overall perfusion properties (especially dynamic perfusion properties) of the perfused organ tissue, for example, with the goal of developing improved treatment plans.

[0024] In various embodiments, the organ to be perfused during imaging is a peripheral organ, such as a limb.

[0025] According to embodiments of the invention, a nonionic iodine contrast agent can be delivered to the peripheral organ tissue by the delivery system of the perfusion imaging system prior to the perfusion imaging method. Such a contrast agent exhibits very few side effects, thereby significantly reducing the health risks to the object being imaged.

[0026] According to an embodiment of the present invention, the perfusion imaging system may include a motion compensation module adapted to counteract motion artifacts in the acquired second image sequence caused by movement of organ surface or near-surface tissue during imaging. Therefore, motion artifacts caused by movement of peripheral organs, their surfaces, or portions thereof (which can potentially affect the accuracy of the perfusion imaging system) can be reduced, minimized, or compensated for.

[0027] Embodiments of the invention can be advantageously combined with fluorescence imaging of perfused organ tissue near the organ surface using a fluorescent agent. This provides additional data on the perfusion properties of peripheral organs for imaging. In such embodiments, the perfusion imaging system may include a camera for acquiring a third image sequence comprising multiple two-dimensional fluorescence images. The fluorescence images indicate the perfusion state relative to the surface or near-surface tissue of the organ to be perfused during imaging. Furthermore, the contrast agent previously delivered by the delivery device may include a fluorescent agent suitable for fluorescence imaging. According to such embodiments, the processing unit may also be configured to simultaneously initiate imaging by the camera with the X-ray imaging apparatus and the PPG imaging apparatus, for extracting a third change in the perfusion state over time from the acquired third image sequence, and for aligning the first, second, and third changes in the perfusion state in time.

[0028] In another aspect, the present invention relates to a computer program product having instructions that, when executed on a data processing device provided with a sequence of acquired images as input, cause the data processing device to perform an imaging method according to a third aspect of the invention. The data processing device may be an image processing device as specified herein, or a system including the data processing device or the image processing device.

[0029] Specific and preferred aspects of the invention are set forth in the appended independent and dependent claims. Where appropriate, features from dependent claims may be combined with features of the independent claim and other dependent claims, not merely as expressly set forth in the claims.

[0030] For the purpose of summarizing the invention and the advantages achieved compared to the prior art, certain objectives and advantages of the invention have been described above. It should be understood, of course, that not all such objectives or advantages can be achieved according to any particular embodiment of the invention. Therefore, for example, those skilled in the art will recognize that the invention can be implemented or practiced in a way that achieves or optimizes one or a set of advantages as taught herein without necessarily achieving other objectives or advantages as may be taught or implied herein.

[0031] The above and other aspects of the invention will become apparent from the embodiments described below, and will be illustrated with reference to the embodiments described below. Attached Figure Description

[0032] The invention will now be further described by way of example with reference to the accompanying drawings, in which:

[0033] Figure 1 A perfusion imaging system according to an embodiment of the present invention is shown.

[0034] Figure 2 This is a flowchart explaining the steps of an imaging method for assessing the perfusion properties of tissues in a peripheral organ to be perfused, according to an embodiment of the present invention.

[0035] The accompanying drawings are merely illustrative and not restrictive. In the drawings, for illustrative purposes, the size of some elements may be exaggerated and they are not drawn to scale. Dimensions and relative dimensions do not necessarily correspond to actual reductions for the practice of the invention.

[0036] Any reference numerals in the claims should not be construed as limiting the scope. Detailed Implementation

[0037] This invention will be described with reference to specific embodiments and certain accompanying drawings, but is not limited thereto but only by the claims. The terms first, second, etc., used in this specification and claims are used to distinguish between similar elements and are not necessarily used to describe order, whether temporally, spatially, in rank, or in any other way. It should be understood that the terms thus used are interchangeable where appropriate, and the embodiments of the invention described herein can operate in orders other than those described or illustrated herein.

[0038] It should be noted that the term "comprising" as used in the claims should not be construed as limited to the modules listed below; it does not exclude other elements or steps. Therefore, it should be interpreted as specifying the presence of the stated features, integers, steps, or components as mentioned, but not excluding the presence or addition of one or more other features, integers, steps, or components, or groups thereof. Thus, the scope of the expression "device comprising modules A and B" should not be limited to a device that only includes components A and B. It means that, with respect to the invention, the only relevant components of the device are A and B.

[0039] Throughout this specification, the reference to "an embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. Therefore, the phrase "in one embodiment" or "in an embodiment" appearing in various places throughout this specification does not necessarily refer to all of the same embodiment, but may refer to all of the same embodiment. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, as will be apparent to those skilled in the art from this disclosure.

[0040] Similarly, it should be recognized that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, drawing, or description thereof for the purpose of streamlining the disclosure and aiding in understanding one or more of the various inventive aspects. However, this approach of the disclosure should not be construed as reflecting an intention to claim more features than expressly recited in each claim. Rather, as reflected in the appended claims, inventive aspects lie in fewer than all the features of a single foregoingly disclosed embodiment. Therefore, the claims that follow the detailed description are hereby expressly incorporated into this detailed description, wherein each claim stands alone as a separate embodiment of the invention.

[0041] Furthermore, although some embodiments described herein include some features included in other embodiments without other features, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments, as will be understood by those skilled in the art.

[0042] Numerous specific details are set forth in the specification provided herein. However, it should be understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0043] definition

[0044] In the context of this invention, perfusion involves the passage of bodily fluids such as blood and lymph through the vascular system and through organs and tissues to maintain their proper function. More specifically, perfusion is often characterized in terms of the volume of fluids such as blood delivered to an organ or tissue. The state of perfusion thus involves the amount of blood (or other bodily fluids under study) delivered to an organ or tissue over time and can be expressed, among other things, as a flow rate, i.e., the amount or volume of fluid delivered per unit time, or as the combined amount or volume of fluid delivered over a predetermined time span.

[0045] Perfusion organs generally refer to peripheral organs, such as the limbs, but can also refer to internal organs, such as the heart, brain, intestines, or kidneys, if exposed during the intervention. Therefore, organ surfaces generally refer to the skin and the proximal surfaces extending to the dermis and subcutaneous tissue. However, for internal organs, the organ surfaces exposed during the intervention can also involve surrounding tissue structures such as muscle, fat, or membranes.

[0046] For perfusion imaging purposes, macrocirculation refers to the arteries of the macrovascular system, while microcirculation refers to arterioles, capillary beds, and lymphatic capillaries.

[0047] Figure 1An example of a perfusion imaging system 1 according to an embodiment of the present invention is shown. The heart of the perfusion imaging system 1 is a device 13 for performing perfusion imaging, also referred to as a workstation. The perfusion imaging system 1 includes an X-ray imaging device 2 and a PPG imaging device 3. During imaging, an organ 6 to be perfused (e.g., a peripheral organ, such as a limb, such as an arm, leg, hand, or foot) is positioned relative to the X-ray imaging device 2 and the PPG imaging device 3 in such a way that at least a predefined region of interest of the organ 6 can be imaged simultaneously by both imaging devices 2 and 3. For example, a leg or arm can be positioned on an object support during perfusion imaging and can also be stabilized by appropriate fixation modules (such as supports, wedges, sponges, contouring pads, straps, etc.). The workstation 13 or console of the perfusion imaging system 1 is connected to the X-ray imaging device 2 and the PPG imaging device 3 at a first input port 20 and a second input port 21 (e.g., directly or via a network). Therefore, in this embodiment, device 13 is a device for processing perfusion imaging data. This data is generated by both imaging devices 2 and 3. The first and second input ports can be separate device features, or they can be integrated into a single device feature. In the illustrated embodiment, workstation 13 includes a processing unit 4, an image merging module 7, and a motion compensation module 8. Simultaneous acquisition by the two imaging devices 2 and 3 can be triggered by an acquisition command issued through the processing unit. The X-ray imaging device 2 and the PPG imaging device 3 then each acquire multiple two-dimensional images, such as tens to hundreds of images, in parallel and at a predetermined frame rate, such as 3 frames per second or more, which can be the same or different for the two imaging devices 2 and 3. The processing unit 4 is not limited to a single processor or controller, but more generally describes multiple processors, multiple shared processors, digital signal processors, distributed processing elements, or other suitable data processing modules. The processing unit 4 may include dedicated hardware for performing functions related to the motion compensation module 8 and the merging module 7, or may be equipped with hardware for running computer software with segments performing the defined functions. Furthermore, the processing unit 4 may be provided with its own memory, into which computer software segments (e.g., software modules such as the motion compensation module 8 and the merging module 7) can be loaded and stored. As described in further detail below, the function of motion compensation module 8 is to detect and compensate for motion artifacts in the image sequence acquired by at least the PPG imaging device 3, such as uncontrolled motion of the perfused organ or organ surface relative to the PPG imaging device 3. As described in further detail below, the function of merging module 7 is to merge 2D and 3D views of the same perfused organ.

[0048] Although workstation 13 is shown in proximity to imaging devices 2 and 3, embodiments of the invention are not limited to this specific arrangement. For example, according to other embodiments, workstation 13 may be mounted at a remote location and accessed via a network connection. Preferably, workstation 13 also includes a memory for storing image sequences acquired by X-ray imaging device 2 and PPG imaging device 3 during perfusion imaging of organ 6, previously acquired images, or image information about the organ (e.g., previously acquired X-ray scans, magnetic resonance imaging scans, ultrasound scans), if available. Alternatively or additionally, an external storage device may be accessed, for example via a network interface, to retrieve or transmit image sequences acquired by X-ray imaging device 2 and PPG imaging device 3 during perfusion imaging of organ 6, or previously acquired images, or image information about the organ, for storage.

[0049] The display unit 5 of the perfusion imaging system 1 can be coupled to the output port 23 of the workstation 13 in any suitable manner (e.g., wired or wireless). The display unit 5 can be part of the workstation 13 or can be provided separately. In an exemplary embodiment of the invention, the display unit 5 can be provided as a display panel, a monitor, an interactive touchscreen, etc. Combined perfusion maps of the perfusion properties of deep and superficial tissues of an organ are displayed in a single image by the display unit 5.

[0050] A delivery device 9 for delivering contrast agent to sites of perfusion of deep and superficial tissues of an organ can be removably connected to a container filled with contrast agent 10. By way of example, the delivery device 9 is provided as a catheter and adapted to be exposed to a blood vessel at one of its distal portions, which supplies blood to the perfused organ, to receive fluid at its other distal portion not exposed to a blood vessel, and, upon receipt, to deliver the fluid to the exposed distal portion and into the blood vessel. The contrast agent 10 for X-ray perfusion angiography can be provided in a syringe or perfusion pump connected to the fluid receiving distal portion of the catheter.

[0051] A typical PPG imaging device 3 includes a light source 3a (e.g., a light-emitting diode) for emitting light in the visible and / or infrared spectrum and a camera 3b for detecting light emitted by the light source 3a and reflected from the surface of the organ 6 or the proximal surface of the organ during imaging. In sufficiently bright environments, such as bright ambient light strong enough to detect reflected signals above the background noise using the camera 3b, the light source 3a can be replaced by a light source that generates bright ambient light. The PPG imaging device 3 enables non-invasive and non-contact imaging of blood volume changes on or immediately below the surface of the perfused organ. In this example, the PPG imaging device 3 is configured to operate in reflective mode, and the camera 3b collects light reflected from the organ surface (e.g., skin) or proximal surface (e.g., dermis or subcutaneous tissue) as multiple raw PPG signals. For thick peripheral organs such as the leg or arm, a reflective configuration of the PPG imaging device 3 is preferred because any transmitted light signal will be strongly attenuated. This does not limit embodiments of the invention to a reflective-only configuration of the PPG imaging device 3. Technicians will understand that the PPG imaging device 3 can be configured to operate in transmission mode when the organ 6 to be perfused and imaged is very thin (e.g., a finger or part thereof), thereby allowing for the detection of observable amounts of transmitted light.

[0052] A fluorescence imaging camera 11 is also used to detect fluorescence emitted when a fluorescent dye, comprised of contrast agent 10, approaches the perfused surface tissue of organ 6. Figure 1 The diagram shows a portion of the perfusion imaging system 1. The fluorescent dye can be excited by a dedicated light source or by ambient light, which can be the same light source as light source 3a of the PPG imaging device 3. In addition to and concurrently with the image sequences acquired by the X-ray imaging device 2 and the PPG imaging device 3, the fluorescence imaging camera 11 can advantageously acquire a third image sequence from which further perfusion properties of superficial tissues of the organ can be inferred. In some embodiments of the invention, the fluorescence imaging camera 11 can be the camera 3a of the PPG imaging device 3 amplified with a switchable color filter. In other embodiments of the invention, the fluorescence imaging camera 11 can be positioned at a different angle than the camera 3a of the PPG imaging device 3, for example, it can be positioned facing and imaging an organ surface opposite to the organ surface imaged by the camera 3a. The fluorescence imaging camera 11 can be coupled to a third input port 22 of the workstation 13 for delivering its captured image sequences to the processing unit 4 for further processing. Furthermore, the perfusion imaging system 1 may include a blood holding and releasing module 12, such as an inflatable cuff. In use, this provides a structure that allows for changes in the amplitude of the PPG image signal in the image acquired by the PPG imaging device 3.

[0053] In the preceding examples, the two imaging devices 2 and 3 can be combined into a single device or provided as separate devices. The latter option is particularly suitable for upgrading existing X-ray imaging devices 2 (which often have significant installation costs) by supplementing them with PPG imaging device 3 (which can be installed more easily and at a reduced cost). If provided as separate devices, X-ray imaging device 2 and / or PPG imaging device 3 may still include additional structural elements, and / or the perfusion imaging system 1 may provide additional components that facilitate the relative positioning, orientation, alignment, and stability of X-ray imaging device 2 and PPG imaging device 3 during imaging. For example, additional structural elements or additional components may include supports for the light source 3a and camera 3b, coupled to one end of one or more flexible arms fastened to a wall or ceiling of the X-ray imaging device 2 or a room (e.g., an operating room). Furthermore, embodiments of the invention are not limited to... Figure 1 The robotic C-arm X-ray device 2 is shown in the diagram. Various other X-ray imaging devices 2 can be conceived and can be provided alternatively, including robotic or non-robotic devices, computed tomography (CT) X-ray imaging systems, two-dimensional fluorescence fluoroscopy X-ray imaging devices, and others. In embodiments of the invention, the processing unit 4 can be configured to control the positioning and orientation of components of the X-ray imaging device 2 and / or components of the PPG imaging device 3, for example, relative to the perfused organ 6. Furthermore, the processing unit 4 can be configured to control the movement of the robotic delivery device 9 and the injection rate of the contrast agent 10.

[0054] Now refer to Figure 2 A method for imaging the perfusion properties of peripheral organ tissues used for perfusion (e.g., perfusion organ tissues of the limbs such as the leg or arm) is described. The steps of this method can often be performed within the context of a more detailed and complex medical procedure, such as as part of a preoperative / postoperative management assessment or diagnosis, where it helps assist healthcare professionals in making their decisions or revealing diagnostically relevant factors. Some steps of a more detailed medical procedure in a broader context can be surgical in nature and immediately precede or follow the method for imaging the perfusion properties of peripheral organ tissues used for perfusion according to embodiments of the invention. In such cases, it should be understood that steps typically performed before or after the method for imaging the perfusion properties of peripheral organ tissues used for perfusion, or independently of said method, are not the subject matter of the invention as defined by the claims. (See reference...) Figure 2 The described method for imaging the perfusion properties of peripheral organ tissues related to perfusion can be adapted from the previously described method. Figure 1The perfusion imaging system is executed by elements within it. Therefore, the following description links the steps of the method to individual elements of the perfusion imaging system to provide a comprehensive example of performing the method. References to elements of the perfusion imaging system are illustrative only and do not limit the scope of the associated imaging methods. In a broader context, a medical imaging workflow using embodiments of a method for imaging the perfusion properties of peripheral organ tissues for perfusion can be initiated manually, such as by a healthcare worker interacting with a workstation or console to issue a start command, or can be initiated automatically, such as when alignment is achieved. This corresponds to Figure 2The flowchart begins with a "Start" box. Then, several steps of the medical imaging process typically follow prior to the steps of an embodiment of the method for imaging the perfusion properties of peripheral organ tissues related to perfusion: a control signal is issued and sent to a delivery device to trigger the injection of a predetermined amount of contrast agent-containing fluid (designated "CA delivery"), and another control signal is issued and sent to the X-ray imaging unit and the PPG imaging unit shortly after triggering the concurrent acquisition of a first and a second image sequence, respectively designated by two time-related boxes, "X-ray" and "PPG". The issuance and timing of the control signals are typically handled by the processing unit of the workstation that generates them. The concurrent image acquisition by the X-ray imaging unit and the PPG imaging unit, and optionally also by a fluorescence imaging camera, typically begins with a delay relative to the delivery of the contrast agent by the delivery device to account for the proximity of the contrast agent bolus to the region of interest being imaged. Such a delay is known or can be estimated from existing X-ray angiography imaging protocols. The acquired first image sequence, second image sequence, and optionally third fluorescence image sequence are stored on a workstation's memory device or a memory device connectable to the workstation for access to the image sequences, for example, via a network connection. At the start of a more general medical imaging procedure, the catheter of the exemplary delivery device has already been installed with due care. The administration of the contrast agent is supervised by a healthcare professional and occurs prior to the steps of an embodiment of the method for imaging the perfusion properties of peripheral organ tissues to be perfused. Even when administered intravenously at a peripheral location (e.g., the popliteal artery), the delivery of contrast agents is considered a safe routine clinical procedure involving only limited and rare health risks and associated side effects. Specifically, allergies based on the pharmaceutical substance itself can be ruled out through a preliminary assessment of the patient's individual health status and the appropriate selection of the substance; for example, non-ionic iodinated contrast materials are widely accepted due to the presence of few or no allergic side effects. It should be noted that the introduction of the catheter as part of the delivery device and the injection of the contrast agent, for example, when performed on a training model of the organ to be perfused or in a virtual training reality environment, are not associated with any health risks to the subject. Additionally, the blood supply to the perfused organ can be temporarily, locally, or globally blocked and subsequently restored by blood retention and release modules, such as pressure cuffs or compression strips with pressure elements. The associated dynamic changes in blood volume supplied to the organ tissue to be perfused during imaging can be observed in the resulting sequence of acquired images.

[0055] Next, steps of an embodiment of a method for imaging the perfusion properties of peripheral organ tissues used for perfusion are described. Two boxes, “Seq 1” and “Seq 2”, correspond to the steps of providing the acquired first image sequence and second image sequence, respectively. Here, the acquired first image sequence refers to an image sequence comprising multiple two-dimensional X-ray projection images indicating the perfusion state relative to the deep tissues of the organ that have been perfused during imaging, and the acquired second image sequence refers to an image sequence comprising multiple two-dimensional PPG images indicating the perfusion state relative to the surface or near-surface tissues of the same organ that have been perfused during imaging. Each PPG image includes multiple image points, such as individual pixels, pixel clusters, or segmented image regions, associated with blood volume values ​​at corresponding multiple different spatial locations on the organ surface (e.g., different locations on the skin of the limbs, different locations along the legs, ankles, and feet, and others). The first and second image sequences are further characterized by the fact that they are acquired simultaneously. The simultaneity of acquisition can be determined, for example, by overlapping imaging intervals defined by the start and end times in the data recording structure included in or associated with the two image sequences, or by comparing the timestamps of each image in a plurality of images labeled in the first and second image sequences. If a third image sequence or even additional image sequences exist, for example, obtained by a fluorescence imaging camera, then such a third image sequence or additional image sequence can also be provided and its acquisition simultaneity can be verified. Providing image sequences includes directly receiving the acquired images, for example, as a video stream. For example, a perfusion imaging system workstation is directly connected to an X-ray imaging apparatus and / or a PPG imaging apparatus to receive the acquired images directly from the apparatus as a data stream, such as a video stream. Providing image sequences also includes providing access to a data storage device on which one or more image sequences are stored. For example, the workstation's memory can be accessed, and the first imaging sequence or the second imaging sequence, or both, have been sent thereto for storage during the acquisition step. The first and second imaging sequences can also be accessed from a memory device remotely connected to a workstation (e.g., a remote server or distributed storage system), or can be provided as data stored on a computer-readable media (e.g., CD, DVD, USB device, optical storage medium, flash memory device, SD card, magnetic storage medium, etc.).

[0056] The following steps can be performed by a processing unit of a workstation, for example, when following instructions from a computer program. This processing unit is not limited to a single processor or controller, but more generally describes multiple processors, multiple shared processors, digital signal processors, distributed processing elements, or other suitable data processing modules. The processing unit may include dedicated hardware for performing the functions involved in the following steps or hardware for running computer software having segments that perform the defined functions. Furthermore, the processing unit may be provided with its own memory in which computer software segments (e.g., software modules) can be loaded and stored. Preferably, a second image sequence of PPG images and a third image sequence of fluorescence images (if provided) are applied to and processed by a motion compensation module (e.g., a software module of computer software loaded into the workstation's memory, whose instructions are executed by the processing unit). Motion artifacts are often caused by unwanted or uncontrolled movement of the perfused organ or at least a portion thereof during imaging. In response to increased blood pressure, small muscle contractions or arterial deformation, and vibrations of the perfusion imaging device reaching the perfused organ via organ support structures or fixation modules, can cause relative movement of the perfused and imaged organ or its surface relative to the PPG imaging device (e.g., relative to a light detection camera, for which a predetermined region of interest has been defined for each image in the second image sequence). If the relative movement becomes significant, then the correspondence between multiple image points in each PPG image (e.g., individual pixels, pixel clusters, or segmented image regions in each PPG image associated with blood volume values) and multiple different spatial locations on the organ surface, as determined, for example, in a reference PPG image (e.g., the first PPG image in the second image sequence), is lost. This potential loss of correspondence, either partially or entirely, in the second image sequence can be remedied by a motion compensation module. For this purpose, the motion compensation module can be adapted to detect organ or organ surface motion in PPG images exceeding a predetermined threshold, determine a motion vector for each detected motion with respect to a PPG reference image or a previous PPG image, and compensate for each detected motion by remapping multiple image points in each PPG image to multiple different spatial locations on the organ surface based on the determined motion vectors, thereby restoring the correspondence. Motion estimation algorithms known in the art can be used to implement the corresponding steps of the motion compensation module, such as motion estimation based on optical flow, block matching, or image registration techniques (e.g., including feature selection and tracking). If, in addition to a second image sequence provided by a camera of the PPG imaging device, a third image sequence is provided by a fluorescence imaging camera, then the two cameras can form a stereo camera pair. For this stereo camera pair, the corresponding image points (if identified in the acquired third and second image sequences, respectively) can be used to estimate the fundamental matrix, which also allows for the motion detection and determination of motion vectors.If motion of an organ or part thereof is detected in the second image sequence, then the motion is compensated for (“compensated”) by the motion compensation module, resulting in the creation of a stabilized second image sequence designated as “Seq 2 stable”. If no motion is detected, then the original second image sequence is also used as the stabilized second image sequence without modification. The same applies to optional third image sequences or additional image sequences (if provided). Embodiments of the invention do not preclude the possibility that the first image sequence can also be compensated for motion artifacts (if necessary), for example, to improve perfusion properties for more accurate measurements.

[0057] In another step, a first change and a second change in perfusion state over time are extracted from the acquired first image sequence, the acquired second image sequence, and each additional acquired image sequence for resolving the perfusion state of organ tissue over time. If organ motion has been detected, the acquired and stabilized image sequences are used to extract the corresponding changes in perfusion state over time. The first change in perfusion state over time may involve (e.g., during a first pass) an increase or decrease in the density of the delivered contrast agent diffused into and extracted from the deep tissue of the organ. Selecting an X-ray projection image of the first image sequence as an X-ray reference image, the first change in perfusion state can be extracted as a measurable, quantized change in each of a plurality of image signals in each X-ray projection image of the first image sequence relative to a corresponding plurality of image signals in the X-ray reference image. The image signals among the plurality of thus extracted image signals may correspond to individual pixel values ​​or groups of pixel values, such as integrated pixel values ​​on segmented regions or regions of interest in the X-ray projection images of the first image sequence. Therefore, for each extracted X-ray image signal defined with respect to a reference X-ray image of the first image sequence, a first time-sequential sequence or time curve can be generated, wherein the amount of change in the image signal at a given image number or a given image acquisition time, i.e., the extracted first change in perfusion state over time, is assigned to that given image number or that given image acquisition time. The image acquisition time can be retrieved from an annotated timestamp or can be calculated based on the acquisition start time and acquisition frame rate of the image sequence, and can be stored in an image sequence data record or in the workstation's memory device. The second change in perfusion state over time can involve the increase or decrease in the volume of blood replaced or diluted when the delivered contrast agent (e.g., during the first pass) reaches, diffuses into, and is extracted from the organ surface tissue or organ proximal tissue. If a PPG reference signal has been selected, then the replacement or dilution of the blood volume by the contrast agent can be observed as a spatially resolved change in each of the multiple image signals for each PPG image of the second image sequence. Similar to the change in perfusion state over time for a first extraction of a first image sequence, the image signals among multiple extracted image signals for each PPG image can correspond to individual pixel values ​​or groups of pixel values, such as integrated pixel values ​​on segmented regions or regions of interest in the PPG images of a second image sequence. Therefore, a second time-ordered sequence or time curve can be generated for each extracted PPG image signal defined with respect to a reference PPG image of the second image sequence. It is often useful to extract the envelope signal for each PPG image signal, since various PPG image signals are typically characterized by the amplitude of oscillations resulting from blood pressure oscillations at the frequency of a heartbeat.Next, the "detection drop" step detects a decrease in the amplitude of the X-ray image signal and the PPG signal or the extracted PPG envelope signal. For example, this decrease in amplitude can be detected as a decrease below a predetermined threshold, a decrease equal to or greater than a predetermined signal amplitude ratio, or a decrease equal to or greater than a predetermined slope of the time curve. At its first passage through the perfused organ tissue, the contrast agent acts as a concentrated bolus, rapidly replacing the circulating blood in the macrovascular and microvascular systems of the perfused organ, where a sudden drop in blood volume detectable by the PPG imaging device and an amount of X-ray reaching the X-ray detector of the X-ray imaging device are not absorbed. Since the signal amplitudes of both the X-ray signal and the PPG signal are reduced, this sudden decrease can advantageously be used as an alignment marker to temporally align the first and second changes in the perfusion state over time, for example, temporally aligning the X-ray signal and the PPG (envelope) signal. The alignment step of the extracted first and second changes, "alignment," may include comparing the time value in the portion of the organ's deep tissue where a decrease / decrease is first detected with the time value in the corresponding adjacent portion of the organ's surface or near-surface tissue where a decrease / decrease is first detected. For example, visually or algorithmically identified adjacent portions of the deep and superficial tissues of a perfused organ (e.g., through image registration on a contoured image) can be analyzed for the first occurrence of a sudden decrease in the magnitude of the extracted first and second changes, respectively. If the detected time values ​​for the first and second acquired image sequences do not match, either the first or second image sequence may be shifted forward or backward in time to uniformly decrease or increase the time value of each image in the shifted image sequence until a match is found and the two image sequences are aligned in time. The alignment step may include interpolation between two or more acquired images of the first and / or second image sequences to obtain a more accurate temporal alignment, for example, if the two frame rates used for acquisition are different or if the diffusion time constant between deep and superficial tissues is taken into account.

[0058] Contrast agents containing fluorescent compounds will cause a sudden increase in the amount of fluorescence captured by the fluorescence imaging camera acquiring the third image sequence. Therefore, if the third image sequence is provided, the fluorescence image signal in the third image sequence is preferably aligned with the X-ray signal and PPG image signal by detecting bursts or spikes rather than drops.

[0059] In the “Signal Derivation” step, various quantities related to the perfusion properties of organ tissue can be derived from aligned X-ray and PPG time curves. For example, the time curves can be averaged or integrated within a predetermined region of interest, or the arrival or peak times of the amplitude of the time curves can be determined. Embodiments of the invention are not limited to the specific quantities listed as examples, and other quantities for assessing changes in perfusion status may prove useful. For instance, perfusion propagation velocity can be estimated based on the discrete derivatives of the extracted and aligned X-ray and PPG time curves and multiple thresholds applied to distinguish between high propagation velocities, normal propagation velocities, and slow propagation velocities.

[0060] During the “merging” step, a previously acquired 3D view (if available) of the organ perfused during perfusion imaging is merged with a 2D view of the perfusion nature (i.e., extracted two-dimensional image signals or any derived quantities thereof from the temporally aligned first and (stabilized) second image sequences). The 3D view of the organ can be obtained (the “3D view” step) as a 3D reconstruction of a previously acquired dataset of three-dimensional images, such as CT projection data from a preoperative CT scan of the same organ. The 3D view of the organ can be stored as 3D object data on a workstation’s memory device or a workstation-accessible memory device. The merging of the 2D view with the previously acquired 3D view generates a correspondence between data points (e.g., voxels in 3D space or pixels in 2D projection space) in the 3D object data used for the 3D view and data points associated with the 2D view (e.g., pixel elements or contours of segmented regions in various temporally aligned X-ray projection images of the first image sequence and PPG images of the second image sequence). Known 2D / 3D image registration algorithms (rigid or non-rigid or affine transformations, point set matching, feature-based meshes, etc.) can be provided for this purpose, and the 2D images of the first or second image sequence can be resampled at a higher resolution if required. As a result of the merging step, the PPG image signal associated with points on or immediately below the organ surface (e.g., skin, which is a two-dimensional surface in 3D space) can be linked with data points (e.g., voxels) in a 3D view of the organ, which also represents the outer surface of the organ, thereby obtaining the missing depth component.

[0061] In the "Generate / Send to Display" step, an image for viewing on a monitor is generated and sent to a display unit, such as a monitor on a workstation. A processing unit (which may include a dedicated graphics processor) is generating the image based on the combined perfusion map, for example, generating a color-coded heatmap to align the magnitudes of the first and second changes over time at individual pixel elements of the image to be displayed, representing the perfusion status of deep and superficial tissues of the organ at a common scale. Preferably, if the generated image is the result of a combination of 2D and 3D views of the perfused organ, the image for display is generated by determining the color value at each pixel element of the image using a 2D / 3D fusion algorithm such as alpha fusion. For example, the processing unit can determine the saturation value or alpha channel value of each pixel based on scene lighting, viewing angle, and overlapping image objects (e.g., overlapping polygons of mesh objects). This allows the generation of an image for display where the color-coded combined perfusion map is illustrated as a superimposed image of the 3D reconstructed image of the organ, using an established correspondence between the 3D and 2D views of the organ, as provided by the merging module. Presenting the combined perfusion maps as an overlay of a 3D reconstruction of the organ facilitates orientation and improves the visual examination experienced by the person viewing the image. This image can also be generated interactively to provide regular image updates to the viewer in response to changing viewing conditions, such as when interactively rotating the 3D reconstructed image with the combined perfusion map overlay according to different viewing angles, when interactively selecting perfused organ tissue portions (e.g., skin or deep tissue) to be enabled or disabled in the displayed image, or when interactively switching between different derived quantities (e.g., time to peak, time to arrival, area under the curve, etc.) reflecting changes in the perfusion state over time in aligned first and second changes.

[0062] Embodiments of the present invention can be successfully applied to the medical screening, diagnosis, and treatment process for peripheral artery disease, particularly for severe limb ischemia (CLI), for which the proposed perfusion imaging system and method can actively assist in making critical decisions, such as deciding to perform amputation or vascular reconstruction intervention. Routine risk assessment factors for CLI, such as blood pressure measurements and related ankle pressure or ankle-brachial index, can provide data on the health status of the macroscopic vascular system, but may only inaccurately or insufficiently account for arterial calcification. Moreover, the health status of the microcirculation remains undetected, although it is important for good tissue perfusion. In the context of CLI, the organ to be perfused can be the leg, and the predetermined region of interest can correspond to the area defined around the ankle and foot. Then, an X-ray imaging device and a PPG imaging device simultaneously acquire a first image sequence of X-ray angiographic projection images and a second image of PPG images, thereby capturing the passage, diffusion, and extraction of the delivered contrast agent over time in the deep and superficial tissues of the organ within the region of interest. The changes in the perfusion status of deep and superficial tissues of an organ over time are represented by time-varying image signals in the X-ray projection images of the first image sequence and the PPG images of the second image sequence, respectively. Therefore, extracting the time-varying image signals from the X-ray projection images of the first image sequence and the PPG images of the second image sequence allows for a successful mapping of organ tissue perfusion under the skin and skin perfusion over time. To combine and correlate the two perfusion measurements (one concerning deep tissue perfusion and the other concerning superficial skin perfusion), various extracted time-varying image signals from the X-ray projection images of the first image sequence and the PPG images of the second image sequence are aligned temporally. This can be achieved, for example, by detecting the moment when a sudden decrease in the amplitude of the time-varying image signal in the X-ray projection image integrated over the region of interest occurs and comparing it with a similarly detected moment when a sudden decrease in the amplitude of the time-varying image signal in the PPG image integrated over the region of interest occurs. If the comparison indicates that the two moments are different from each other, then either the first image sequence or the second image sequence is shifted temporally to make the two moments equal to each other. For example, the timestamps of the labeled images in the first or second image sequence are incremented or decremented together until the two times match. Various quantities can be derived from the aligned time-varying image signals in the X-ray projection image and the PPG image. For instance, a time-density curve for the region of interest can adequately express the changes in perfusion status beneath and within the skin. This time-density curve is obtained by integrating the image signals from the X-ray projection image and the PPG image over the region of interest. These two time-density curves can be combined into a single graph and presented to the physician.It is also possible to integrate the area under the time density curve obtained for each pixel in the region of interest (e.g., each image signal from the X-ray projection image and each relevant image signal from the PPG image within the region of interest). Another quantity of interest that can be derived to quantify the perfusion status of deep and superficial tissues of an organ is the peak time density. An image can then be generated and displayed to the physician showing the derived quantity of interest as a composite perfusion map, for example, represented as a color-coded perfusion map (thermograph) of the foot and ankle. In a preferred embodiment, a previously obtained 3D X-ray image of the organ is superimposed with the composite perfusion map, which facilitates spatial orientation and visual examination of the results shown in the displayed perfusion map. The displayed map illustrates, for example, whether the circulatory flow is within the normal velocity range (peak time) or whether there is a pathological decrease in velocity from the ankle to the toes, or some evidence of redness. In addition, the diagrams shown can also resolve the 3D distribution of macro- and micro-circulatory flows, for example, they can clearly show whether a foot wound (e.g., an ulcer that requires increased blood supply to heal) may be located there or whether the skin surface in which the wound may be at risk of developing has been perfused.

[0063] In embodiments of the invention, the contrast agent delivered by the delivery device may include a nonionic iodine contrast material (e.g., iodixanol 320 mg iodine / ml), which has the advantage of significantly diffusing into the pore space of the perfused organ during the first round, thereby allowing for improved detection of the perfusion properties of the microcirculation. Preferably, the nonionic iodine contrast material is combined with a fluorescent dye such as indocyanine green (ICG). This allows for the simultaneous acquisition of PPG and fluorescence images by a fluorescence imaging camera (i.e., a camera that detects fluorescence emitted by the dye) to further monitor the perfusion properties of superficial tissues of the organ, such as skin perfusion. The elution of dye molecules into and out of the superficial tissues of the organ is detected in this manner.

[0064] In embodiments of the invention, the PPG imaging apparatus can be used in the absence of an X-ray imaging apparatus for additional image sequences to acquire PPG images, for example, in combination with temporary obstruction of blood flowing into the perfused organ by a pressure cuff, followed by restored blood flow to the perfused organ after the cuff is released. The restricted blood flow caused by the pressure cuff induces a decrease in the PPG image signal amplitude that is similar to, but not exactly the same as, the signal amplitude of the contrast agent bolus passage. For example, well-controlled pressurization (e.g., inflation) and depressurization (e.g., deflation) rates of the pressure cuff can be used advantageously to create blood flow patterns obtained from the passage of an unusable bolus in many different ways. A non-limiting example of a flow pattern created in that manner is the slow release of cuff pressure in contrast to a rapid decrease in cuff pressure, which provides additional insights into the perfusion properties of the organ evolving on different timescales. In addition, one advantage is that the cuff can be repeatedly and with controlled pauses in pressurization and depressurization, and the possibility of multiple passes of the contrast agent material bolus is limited on the one hand by the dispersion and decrease of the concentration of multiple passes of the same bolus, and on the other hand by the burden on the subject (especially the subject's kidneys) of multiple bolus applications.

[0065] Furthermore, embodiments of the present invention can acquire X-ray projection images of a first image sequence as subtraction images with enhanced angiography. For example, the X-ray imaging device of the perfusion imaging system is configured to operate in digital subtraction angiography (DSA) mode.

[0066] Although the invention has been described and illustrated in detail in the accompanying drawings and the foregoing description, such description and illustration should be considered illustrative or exemplary rather than restrictive. By studying the drawings, specification, and appended claims, those skilled in the art will be able to understand and implement other variations of the disclosed embodiments in practicing the claimed invention. Although specific measures are recited in mutually different dependent claims, this does not indicate that combinations of these measures cannot be advantageously used. Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. An apparatus (13) for processing perfusion images, comprising: A first input port (20) is configured to receive a first image sequence comprising multiple X-ray perfusion angiography images indicating the perfusion status relative to deep tissues of the organ (6). A second input port (21) is configured to receive a second image sequence comprising multiple two-dimensional photoplethysmography images indicating the perfusion state relative to the surface or near-surface tissue of the organ (6), each of the multiple photoplethysmography images comprising multiple image points associated with blood volume values ​​at corresponding multiple different spatial locations on the surface of the organ. Processing unit (4) is configured to extract a first change and a second change in the perfusion state over time from a received first image sequence and a received second image sequence, respectively; align the first change in the perfusion state over time with the second change or a quantity derived therefrom; and detect the passage of a previously delivered contrast agent bolus by detecting a decrease in the amplitude of the image signal in the second image sequence. The output port (23) is configured to output a perfusion imaging signal for visualizing the aligned first and second changes of the perfusion state or the quantities derived therefrom.

2. The device according to claim 1, wherein, The processing unit (4) is configured to derive at least one of the following from a predefined region of interest in the organ based on the aligned first and second changes in the perfusion state: arrival time signal, peak time signal, and time density signal.

3. The device according to claim 1 further includes a motion compensation module (8), the motion compensation module being configured to counteract motion artifacts in the acquired second image sequence caused by organ surface tissue motion or near-surface tissue motion during imaging.

4. The device according to claim 1, further comprising a third input port configured to receive a third image sequence, the third image sequence comprising multiple two-dimensional fluorescence images indicating the perfusion status relative to the surface or near-surface tissue of the organ (6), wherein, The processing unit (4) is further configured to extract a third change in the perfusion state over time from the acquired third image sequence and align the first change, the second change and the third change in the perfusion state over time.

5. A perfusion imaging system (1), comprising: The apparatus for processing perfusion images according to any one of claims 1 to 4, An X-ray imaging device (2) is used to acquire the first image sequence, and the X-ray imaging device (2) is connected to or can be connected to the first input port (20). A photoplethysmography imaging device (3) for acquiring the second image sequence, the photoplethysmography imaging device (3) being connected to or capable of being connected to the second input port (21), and The processing unit (4) is configured to initiate simultaneous imaging by the X-ray imaging device and the photoplethysmography imaging device.

6. The perfusion imaging system according to claim 5, further comprising: Display unit (5), which is used to visualize the aligned first and second changes of the perfusion state or the quantities derived therefrom in a public image, the display unit being connected to or being able to be connected to the output port (23).

7. The perfusion imaging system of claim 6, further comprising an image merging module (7), the image merging module being configured to map the aligned first and second changes of the perfusion state or the quantities derived therefrom to a three-dimensional reconstructed image of the organ, wherein, The display unit (5) is configured to display aligned first and second variations or quantities derived therefrom of the mapped perfusion state as an overlay image of the three-dimensional reconstructed image of the organ.

8. The perfusion imaging system according to claim 5, wherein, The photoplethysmography imaging device (3) includes a light source (3a) for emitting light in the visible spectrum and / or the infrared spectrum and a camera (3b) for detecting light emitted by the light source and reflected from the surface or near the surface of the organ (6) during imaging.

9. The perfusion imaging system according to any one of claims 5 to 8, which is dependent on claim 4, further comprising a camera (11) for acquiring a third image sequence comprising multiple two-dimensional fluorescence images indicating the perfusion status relative to the surface or near-surface tissue of the organ (6), the camera being connected to or being connectable to the third input port (22).

10. The perfusion imaging system according to any one of claims 5 to 8, further comprising a blood retention and release module (12) to cause a significant reduction in the blood volume value at one or more image points in the second image sequence during imaging.

11. The perfusion imaging system according to claim 10, wherein, The blood retention and release module (12) is an inflatable cuff.

12. A method for imaging perfusion properties related to peripheral organ tissues, the method comprising: A first image sequence is provided, comprising multiple X-ray perfusion angiography images indicating the perfusion status relative to the deep tissues of the perfused organ during imaging. A second image sequence acquired simultaneously is provided, comprising multiple two-dimensional photoplethysmography images indicating the perfusion state relative to the perfusion state of the organ surface or near-surface tissue perfused during imaging. Each of the multiple photoplethysmography images includes multiple image points associated with blood volume values ​​at corresponding multiple different spatial locations on the organ surface. The first and second changes in the perfusion state over time are extracted from the acquired first image sequence and the acquired second image sequence, respectively. Aligning the first change in the perfusion state with the second change or the amount derived therefrom in time, and detecting the passage of the previously delivered contrast agent bolus by detecting a decrease in the amplitude of the image signal in the second image sequence, and An image is generated for display on a display unit, the image comprising multiple image signals indicating aligned first and second changes or quantities derived therefrom of the perfusion state at multiple perfused organ tissue locations.

13. The method of claim 12, further comprising: A third image sequence is provided, acquired simultaneously with the first and second image sequences, the third image sequence including multiple two-dimensional fluorescence images indicating the perfusion state relative to the perfusion state of the organ surface or near-surface tissue perfused during imaging; a third change in the perfusion state over time is extracted from the third image sequence; and the first, second, and third changes in the perfusion state are aligned temporally.

14. The method of claim 12 or 13, further comprising applying motion compensation to at least the plurality of photoplethysmographic images of the acquired second image sequence to counteract motion artifacts caused by movement of tissue on or near the surface of the organ during imaging.

15. A computer program product comprising instructions that, when executed on a data processing device provided with a sequence of acquired images as input, cause the data processing device to perform the method according to any one of claims 12 to 14.

Images