A segmented calculation system and method for coronary blood flow reserve

Abstract

A technical solution disclosed in the present invention provides a segmented calculation system for coronary blood flow reserve, and another technical solution of the present invention provides a segmented calculation method for coronary blood flow reserve. The segmented calculation system and method for coronary blood flow reserve provided by the present invention only require the import of coronary angiography images at rest and maximum hyperemia, and can measure the coronary blood flow reserve CFR without the use of a guidewire and a temperature sensor, so there is no need to inject room temperature saline into the patient's coronary artery multiple times. On the one hand, the present invention reduces the trauma suffered by the patient, reduces the difficulty of surgical operation, greatly shortens the operation time, and saves surgical costs. On the other hand, the present invention can not only output the average blood flow reserve value of the coronary artery, but also output the local blood flow reserve values ​​corresponding to the proximal, middle and distal segments of the coronary artery. The measurement results are more comprehensive, reducing the influence of each branch on the average blood flow reserve value.

Description

Technical Field

[0001] The present invention relates to a segmented calculation system and a segmented calculation method of coronary blood flow reserve. Background Art

[0002] The heart is one of the most important organs in the human body and the driving force behind human blood circulation. Its proper functioning is determined by the blood supply of the coronary artery system, thus assessing its blood supply capacity is of great clinical significance. Three functional indices are currently commonly used in the clinical diagnosis of coronary circulation: fractional flow reserve (FFR), index of microvascular resistance (IMR), and coronary flow reserve (CFR). The fractional flow reserve is primarily used for functional assessment of coronary artery stenosis, while the microvascular resistance index is primarily used to assess coronary microcirculation. Coronary flow reserve, defined as the ratio of maximum coronary artery blood flow to baseline blood flow, reflects the ability of the coronary arteries to respond to increased oxygen demand. It comprehensively considers the combined blood supply capacity of the epicardial large vessels and microcirculation and can effectively assess myocardial ischemia.

[0003] In current clinical practice, the most widely used method for measuring coronary blood flow reserve is the "thermodilution method." First, this method requires measuring blood flow transit time at rest and in the state of maximum hyperemia, making it an invasive examination technique. Second, the measurement process requires the use of additional temperature sensors and multiple injections of normal saline, which increases the difficulty of operation and prolongs the examination time. Therefore, this method poses a great challenge to both patients and surgeons. On the other hand, this method simulates the changes in blood flow in the original definition through changes in blood flow transit time. The final measured CFR value is the average value of the entire blood vessel, which is not sensitive enough to blood supply abnormalities and cannot accurately locate abnormalities. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the "thermodilution method" not only requires the use of a guide wire to deliver the temperature sensor to the distal end of the blood vessel, but also requires multiple injections of normal saline into the patient's coronary artery, which has problems such as high operational difficulty, high cost and high trauma.

[0005] In order to solve the above technical problems, a technical solution of the present invention is to provide a segmented calculation system for coronary blood flow reserve, which is characterized by comprising:

[0006] A length-frame number curve generation module is used to obtain a resting state blood vessel length-frame number curve and a maximum hyperemia state blood vessel length-frame number curve based on a resting state image sequence and a maximum hyperemia state image sequence, respectively;

[0007] a blood vessel segmentation module, configured to process the angiography image at rest and the angiography image at maximum hyperemia, respectively, to obtain blood vessel segmentation information of a target vessel proximal segment, a target vessel mid-segment, and a target vessel distal segment of the target vessel at rest, and blood vessel segmentation information of a target vessel proximal segment, a target vessel mid-segment, and a target vessel distal segment of the target vessel at maximum hyperemia;

[0008] The frame number calculation module is used to calculate the frame number differences N1, N2, and N3 corresponding to the proximal, middle, and distal segments of the target vessel in the resting state, as well as the frame number differences n1, n2, and n3 corresponding to the proximal, middle, and distal segments of the target vessel in the maximum hyperemia state, as follows:

[0009] N1 or n1 = frame1 - frame0

[0010] N2 or n2 = frame2 - frame1

[0011] N3 or n3 = frame3 - frame2

[0012] Wherein, frame0 is the abscissa of the first non-zero point in the vessel length-frame number curve, indicating that the contrast agent has just flowed into the coronary artery ostium; frame1 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the length of the proximal segment of the target vessel, indicating that the contrast agent has just flowed through the proximal segment of the target vessel; frame2 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the total length of the proximal segment and the middle segment of the target vessel, indicating that the contrast agent has just flowed through the middle segment of the target vessel; frame3 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the total length of the proximal segment, the middle segment, and the distal segment of the target vessel, indicating that the contrast agent has just flowed through the distal segment of the target vessel.

[0013] CFR calculation module, used to calculate:

[0014] The average blood flow reserve (CFR) of the target vessel is CFR = (N1 + N2 + N3) / (n1 + n2 + n3);

[0015] Blood flow reserve CFR1 of the proximal segment of the target vessel, CFR1 = N1 / n1;

[0016] Blood flow reserve CFR2 in the middle segment of the target vessel, CFR2 = N2 / n2;

[0017] The blood flow reserve of the distal segment of the target blood vessel is CFR3, CFR3 = N3 / n3.

[0018] Preferably, the length-frame number curve generation module obtains the resting state blood vessel length-frame number curve and the maximum hyperemia state blood vessel length-frame number curve using the same processing method, including the following steps:

[0019] Step 101: Segment the image sequence frame by frame using a first AI model to obtain multiple segmented images;

[0020] Step 102: Process each segmented image frame, extract the blood vessel centerline and calculate the blood vessel length. Combined with the frame number information of each segmented image frame in the image sequence, an initial blood vessel length-frame number curve can be generated.

[0021] Preferably, after step 102, the method further includes the following steps:

[0022] Step 103: Smoothing and interpolation processing are performed on the initial blood vessel length-frame number curve to obtain a final blood vessel length-frame number curve.

[0023] Preferably, the vessel segmentation module obtains the vessel lengths of the proximal main branch, the middle main branch, and the distal main branch of the target vessel in the resting state and the vessel lengths of the proximal main branch, the middle main branch, and the distal main branch of the target vessel in the maximum hyperemia state using the same processing method, including the following steps:

[0024] Step 201: using a second AI model to identify a bifurcation point on a target blood vessel, and dividing the target blood vessel into a proximal main branch segment, a middle main branch segment, and a distal main branch segment based on the identified bifurcation point;

[0025] Step 202: Based on the centerline information obtained by segmentation using the first AI model, the lengths of the blood vessels corresponding to the proximal, middle, and distal segments are calculated and recorded as L1, L2, and L3, respectively.

[0026] Preferably, in step 201, the second AI model is used to identify the bifurcation points on the target blood vessel to obtain the first bifurcation point, the second bifurcation point and the third bifurcation point, with the coronary artery ostium of the target blood vessel as the starting identification point, the third bifurcation point as the ending identification point, the blood vessel segment between the starting identification point and the first bifurcation point as the proximal segment of the target blood vessel, the blood vessel segment between the first bifurcation point and the second bifurcation point as the middle segment of the target blood vessel, and the blood vessel segment between the second bifurcation point and the third bifurcation point as the distal segment of the target blood vessel.

[0027] Another technical solution of the present invention is a segmented calculation method for coronary blood flow reserve, characterized by comprising the following steps:

[0028] Step 1: segmenting the resting-state angiography image sequence and the maximum hyperemia-state angiography image sequence of the target blood vessel, thereby obtaining a resting-state blood vessel length-frame number curve and a maximum hyperemia-state blood vessel length-frame number curve;

[0029] Step 2: performing bifurcation point identification on the resting-state angiography image and the maximum hyperemia-state angiography image, respectively, to obtain vascular segmentation information of the target vessel proximal segment, target vessel mid-segment, and target vessel distal segment of the target vessel in the resting-state, and vascular segmentation information of the target vessel proximal segment, target vessel mid-segment, and target vessel distal segment of the target vessel in the maximum hyperemia-state;

[0030] Step 3: Calculate the frame number differences N1, N2, and N3 corresponding to the proximal, middle, and distal segments of the target vessel in the resting state, and the frame number differences n1, n2, and n3 corresponding to the proximal, middle, and distal segments of the target vessel in the maximum hyperemia state, and we have:

[0031] N1 or n1 = frame1 - frame0

[0032] N2 or n2 = frame2 - frame1

[0033] N3 or n3 = frame3 - frame2

[0034] Wherein, frame0 is the abscissa of the first non-zero point in the vessel length-frame number curve, indicating that the contrast agent has just flowed into the coronary artery ostium; frame1 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the length of the proximal segment of the target vessel, indicating that the contrast agent has just flowed through the proximal segment of the target vessel; frame2 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the total length of the proximal segment and the middle segment of the target vessel, indicating that the contrast agent has just flowed through the middle segment of the target vessel; frame3 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the total length of the proximal segment, the middle segment, and the distal segment of the target vessel, indicating that the contrast agent has just flowed through the distal segment of the target vessel.

[0035] Step 4: Calculate the average blood flow reserve (CFR) of the target vessel, CFR = (N1 + N2 + N3) / (n1 + n2 + n3);

[0036] Calculate the blood flow reserve CFR1 of the proximal segment of the target vessel, CFR1 = N1 / n1;

[0037] Calculate the blood flow reserve (CFR2) in the middle segment of the target vessel, CFR2 = N2 / n2;

[0038] Calculate the blood flow reserve CFR3 of the distal segment of the target vessel, CFR3 = N3 / n3.

[0039] As can be seen from the above technical content, the segmented coronary blood flow reserve calculation system and method provided by the present invention only requires the import of resting and maximally hyperemic coronary angiography images, and can measure the coronary blood flow reserve (CFR) without the use of a guidewire or temperature sensor. Therefore, there is no need to repeatedly inject room temperature saline into the patient's coronary arteries. Compared with the traditional "thermodilution method," the present invention reduces patient trauma, lowers surgical difficulty, significantly shortens operative time, and saves surgical costs. Furthermore, the present invention can output not only the average blood flow reserve value of the coronary artery, but also the local blood flow reserve values ​​corresponding to the proximal, middle, and distal segments of the coronary artery. This provides more comprehensive measurement results and reduces the impact of each branch on the average blood flow reserve value. The present invention is more sensitive to blood flow reserve abnormalities and is more conducive to locating the vascular branch where the abnormality occurs, thus having considerable clinical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the segmentation results of the first AI model;

[0041] Figure 2 It is a schematic diagram of the length-frame number curve;

[0042] Figure 3 Schematic diagram of blood vessel segmentation;

[0043] Figure 4 Schematic diagram of frame number calculation. DETAILED DESCRIPTION

[0044] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0045] This embodiment discloses a segmented calculation scheme for coronary blood flow reserve, whose processing flow is mainly divided into four functional modules, namely a length-frame number curve generation module, a blood vessel segmentation module, a frame number calculation module, and a CFR calculation module.

[0046] Length-frame number curve generation module:

[0047] In coronary angiography, a specific image sequence consists of multiple frames of images, and the time interval between each frame remains constant. Therefore, the image sequence can temporally display the entire filling process of the coronary arteries with contrast agents, which can fully simulate the flow state of blood in the blood vessels.

[0048] In the length-frame number curve generation module, the first AI model is first used to segment the image sequence frame by frame to obtain a multi-frame segmentation binary image. Figure 1 The figure shows the segmentation results of a certain embodiment. Next, each frame of the segmented binary image is processed, such as with a thinning algorithm, to extract the vessel centerline and calculate the vessel length. This initial vessel length-frame number curve is generated by combining the frame number information of each frame of the segmented binary image in the image sequence. This vessel length-frame number curve is then smoothed and interpolated to obtain the final vessel length-frame number curve.

[0049] By performing the above processing on the input image sequence of resting state and the image sequence of maximum hyperemia state, two corresponding blood vessel length-frame number curves can be obtained. Figure 2 Schematic diagram of a blood vessel length-frame number curve in a certain embodiment.

[0050] Vessel segmentation module:

[0051] In the vessel segmentation module, the second AI model is first used to identify the bifurcation points on the target vessel. Figure 3 is a schematic diagram of blood vessel segmentation. Figure 3 As shown, the thick solid line is the main branch blood vessel segmented by the first AI model, and the first bifurcation point, the second bifurcation point, and the third bifurcation point are the blood vessel bifurcation points identified by the second AI model, corresponding to branch 1, branch 2, and branch 3, respectively.

[0052] Using the coronary artery ostium as the starting point and the third bifurcation as the ending point, the first and second bifurcation points can be used to divide the main branch into three segments: the proximal segment, the middle segment, and the distal segment. Based on the centerline information obtained by the first AI model, the corresponding vessel lengths of the proximal, middle, and distal segments can be calculated, denoted as L1, L2, and L3, respectively.

[0053] By processing the angiography images in the resting state and the angiography images in the maximum hyperemia state respectively, the corresponding vascular segmentation information in the two states can be obtained.

[0054] Frame calculation module:

[0055] The vascular length-frame number curve corresponding to the image sequence has been calculated in the length-frame number curve generation module, and this curve is denoted as L = f(frame). The vascular lengths L1, L2, and L3 corresponding to the proximal, middle, and distal segments of the main branch vessels have been calculated in the vascular segmentation module. Therefore, the total lengths of the main branch vessels at the first, second, and third bifurcation points are L1, L1+L2, and L1+L2+L3, respectively.

[0056] Figure 4Schematic diagram of frame number calculation. The starting point of the vessel length-frame number curve corresponds to the coronary artery ostium, and the horizontal coordinate is marked as frame0, indicating that the contrast agent has just flowed into the coronary artery ostium; the intersection of the curve L=f(frame) and the straight line L=L1 corresponds to the first bifurcation point, and the horizontal coordinate is marked as frame1, indicating that the contrast agent has just flowed to the first bifurcation point; the intersection of the curve L=f(frame) and the straight line L=L1+L2 corresponds to the second bifurcation point, and the horizontal coordinate is marked as frame2, indicating that the contrast agent has just flowed to the second bifurcation point; the intersection of the curve L=f(frame) and the straight line L=L1+L2+L3 corresponds to the third bifurcation point, and the horizontal coordinate is marked as frame3, indicating that the contrast agent has just flowed to the third bifurcation point.

[0057] The frame number differences corresponding to the proximal, middle, and distal segments of the main branch vessels in the resting state are N1, N2, and N3, respectively. The calculation formula is as follows:

[0058] N1=frame1-frame0

[0059] N2=frame2-frame1

[0060] N3=frame3-frame2

[0061] Similarly, the frame number differences corresponding to the proximal, middle, and distal segments of the main branch vessels under the maximum congestion state can be calculated respectively, and are recorded as n1, n2, and n3.

[0062] CFR calculation module:

[0063] The average blood flow reserve of the main branch vessel is recorded as CFR, and the blood flow reserves of the proximal, middle, and distal segments are CFR1, CFR2, and CFR3 respectively. In the frame calculation module, the frame difference corresponding to each segment of the main branch vessel at rest and maximum hyperemia has been calculated. The calculation formula for each blood flow reserve value of the main branch vessel is as follows:

[0064] CFR=(N1+N2+N3) / (n1+n2+n3)

[0065] CFR1=N1 / n1

[0066] CFR2=N2 / n2

[0067] CFR3=N3 / n3

[0068] Example 1

[0069] This example calculates the coronary flow reserve of the left anterior descending coronary artery. In this example, branches 1 and 2 described in the present invention correspond to the first diagonal branch and the second diagonal branch, respectively. The calculation results show:

[0070] CFR=2.17CFR1=2.63CFR2=1.63CFR3=1.25

[0071] The calculation results show that a CFR3 value less than 2 indicates ischemic symptoms in the distal anterior descending artery. Although CFR2 is also less than 2, since CFR2 is jointly influenced by the anterior descending artery and the second diagonal branch and is significantly higher than CFR3, it can be concluded that there is no obvious evidence of ischemia in the second diagonal branch. Similarly, there is no obvious evidence of ischemia in the first diagonal branch. In this example, if CFR>2 is used solely based on the mean blood flow reserve value, it indicates that there is no ischemic risk in the anterior descending artery. In other words, the blood supply abnormality in the distal anterior descending artery is masked by the good blood flow reserve capacity of the first and second diagonal branches.

[0072] Example 2

[0073] This example is a calculation of the coronary blood flow reserve of the circumflex branch. In this example, the branches 1 and 2 described in the present invention correspond to the first obtuse marginal branch and the second obtuse marginal branch, respectively. The calculation results show:

[0074] CFR=2.08CFR1=1.83CFR2=2.45CFR3=2.5

[0075] From the calculation results, it can be seen that CFR3>2, which means that there is no obvious evidence of ischemia in the distal circumflex branch, and CFR1<2, which indicates that there must be abnormal blood flow reserves in the first and second obtuse marginal branches. Then, the numerical differences between CFR1, CFR2, and CFR3 were compared respectively, and it was found that there was an obvious difference between CFR1 and CFR2, but the difference between CFR2 and CFR3 was very small. This phenomenon shows that the blood flow reserve capacity of the second obtuse marginal branch is slightly lower than that of the distal circumflex branch, but there is no obvious evidence of ischemia as a whole, but there is a greater risk of ischemia in the first obtuse marginal branch. In this embodiment, CFR>2, if only the average blood flow reserve value is used as the basis for judgment, it indicates that the circumflex branch has no ischemic risk, that is, the blood supply abnormality of the first obtuse marginal branch is masked by the acceptable blood flow reserve capacity of the second obtuse marginal branch and the distal circumflex branch.

Claims

1. A segmented calculation system for coronary blood flow reserve, characterized in that: include: A length-frame number curve generation module is used to obtain a resting state blood vessel length-frame number curve and a maximum hyperemia state blood vessel length-frame number curve based on a resting state image sequence and a maximum hyperemia state image sequence, respectively; a blood vessel segmentation module, configured to process the angiography image at rest and the angiography image at maximum hyperemia, respectively, to obtain blood vessel segmentation information of a target vessel proximal segment, a target vessel mid-segment, and a target vessel distal segment of the target vessel at rest, and blood vessel segmentation information of a target vessel proximal segment, a target vessel mid-segment, and a target vessel distal segment of the target vessel at maximum hyperemia; The frame number calculation module is used to calculate the frame number differences N1, N2, and N3 corresponding to the proximal, middle, and distal segments of the target vessel in the resting state, as well as the frame number differences n1, n2, and n3 corresponding to the proximal, middle, and distal segments of the target vessel in the maximum hyperemia state, as follows: N1 or n1 = frame1 - frame0 N2 or n2 = frame2 - frame1 N3 or n3 = frame3 - frame2 Wherein, frame0 is the abscissa of the first non-zero point in the vessel length-frame number curve, indicating that the contrast agent has just flowed into the coronary artery ostium; frame1 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the length of the proximal segment of the target vessel, indicating that the contrast agent has just flowed through the proximal segment of the target vessel; frame2 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the total length of the proximal segment and the middle segment of the target vessel, indicating that the contrast agent has just flowed through the middle segment of the target vessel; frame3 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the total length of the proximal segment, the middle segment, and the distal segment of the target vessel, indicating that the contrast agent has just flowed through the distal segment of the target vessel. CFR calculation module, used to calculate: The average blood flow reserve (CFR) of the target vessel is CFR = (N1 + N2 + N3) / (n1 + n2 + n3); Blood flow reserve CFR1 of the proximal segment of the target vessel, CFR1 = N1 / n1; Blood flow reserve CFR2 in the middle segment of the target vessel, CFR2 = N2 / n2; The blood flow reserve of the distal segment of the target blood vessel is CFR3, CFR3 = N3 / n3.

2. The segmented calculation system for coronary blood flow reserve according to claim 1, characterized in that: The length-frame number curve generation module obtains the resting state blood vessel length-frame number curve and the maximum hyperemia state blood vessel length-frame number curve using the same processing method, including the following steps: Step 101: Segment the image sequence frame by frame using a first AI model to obtain multiple segmented images; Step 102: Process each segmented image frame, extract the blood vessel centerline and calculate the blood vessel length. Combined with the frame number information of each segmented image frame in the image sequence, an initial blood vessel length-frame number curve can be generated.

3. The segmented calculation system for coronary blood flow reserve according to claim 2, characterized in that: After step 102, the method further includes the following steps: Step 103: Smoothing and interpolation processing are performed on the initial blood vessel length-frame number curve to obtain a final blood vessel length-frame number curve.

4. The segmented calculation system for coronary blood flow reserve according to claim 2, characterized in that: The vessel segmentation module uses the same processing method to obtain the vessel lengths of the proximal main branch, the middle main branch, and the distal main branch of the target vessel in the resting state and the vessel lengths of the proximal main branch, the middle main branch, and the distal main branch of the target vessel in the maximum hyperemia state, including the following steps: Step 201: using a second AI model to identify a bifurcation point on a target blood vessel, and dividing the target blood vessel into a proximal main branch segment, a middle main branch segment, and a distal main branch segment based on the identified bifurcation point; Step 202: Based on the centerline information obtained by segmentation using the first AI model, the lengths of the blood vessels corresponding to the proximal, middle, and distal segments are calculated and recorded as L1, L2, and L3, respectively.

5. The segmented calculation system for coronary blood flow reserve according to claim 4, characterized in that: In step 201, the second AI model is used to identify the bifurcation points on the target blood vessel to obtain the first bifurcation point, the second bifurcation point, and the third bifurcation point. The coronary artery ostium of the target blood vessel is used as the starting identification point, the third bifurcation point is used as the ending identification point, the blood vessel segment between the starting identification point and the first bifurcation point is the proximal segment of the target blood vessel, the blood vessel segment between the first bifurcation point and the second bifurcation point is the middle segment of the target blood vessel, and the blood vessel segment between the second bifurcation point and the third bifurcation point is the distal segment of the target blood vessel.

6. A segmented calculation method for coronary blood flow reserve, characterized in that: The following steps are involved: Step 1: segmenting the resting-state angiography image sequence and the maximum hyperemia-state angiography image sequence of the target blood vessel, thereby obtaining a resting-state blood vessel length-frame number curve and a maximum hyperemia-state blood vessel length-frame number curve; Step 2: performing bifurcation point identification on the resting-state angiography image and the maximum hyperemia-state angiography image, respectively, to obtain vascular segmentation information of the target vessel proximal segment, target vessel mid-segment, and target vessel distal segment of the target vessel in the resting-state, and vascular segmentation information of the target vessel proximal segment, target vessel mid-segment, and target vessel distal segment of the target vessel in the maximum hyperemia-state; Step 3: Calculate the frame number differences N1, N2, and N3 corresponding to the proximal, middle, and distal segments of the target vessel in the resting state, and the frame number differences n1, n2, and n3 corresponding to the proximal, middle, and distal segments of the target vessel in the maximum hyperemia state, and we have: N1 or n1 = frame1 - frame0 N2 or n2 = frame2 - frame1 N3 or n3 = frame3 - frame2 Wherein, frame0 is the abscissa of the first non-zero point in the vessel length-frame number curve, indicating that the contrast agent has just flowed into the coronary artery ostium; frame1 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the length of the proximal segment of the target vessel, indicating that the contrast agent has just flowed through the proximal segment of the target vessel; frame2 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the total length of the proximal segment and the middle segment of the target vessel, indicating that the contrast agent has just flowed through the middle segment of the target vessel; frame3 is the abscissa corresponding to the first point in the vessel length-frame number curve that reaches the total length of the proximal segment, the middle segment, and the distal segment of the target vessel, indicating that the contrast agent has just flowed through the distal segment of the target vessel. Step 4: Calculate the average blood flow reserve (CFR) of the target vessel, CFR = (N1 + N2 + N3) / (n1 + n2 + n3); Calculate the blood flow reserve CFR1 of the proximal segment of the target vessel, CFR1 = N1 / n1; Calculate the blood flow reserve (CFR2) in the middle segment of the target vessel, CFR2 = N2 / n2; Calculate the blood flow reserve CFR3 of the distal segment of the target vessel, CFR3 = N3 / n3.

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