Calculating a fractional flow reserve
A method for vascular assessment is disclosed. The method, in some embodiments, comprises receiving a plurality of 2-D angiographic images of a portion of a vasculature of a subject, and processing the images to produce a stenotic model over the vasculature, the stenotic model having measurements of the vasculature at one or more locations along vessels of the vasculature. The method, in some embodiments, further comprises obtaining a flow characteristic of the stenotic model, and calculating an index indicative of vascular function, based, at least in part, on the flow characteristic in the stenotic model.
1. A computer-implemented method for assessing a vascular function of a cardiac vasculature having a stenotic segment, the method comprising:
receiving, from a medical imaging device, in image processing circuitry a first medical image of the cardiac vasculature recorded at a first projection angle and a second medical image of the cardiac vasculature recorded at a second projection angle;
determining, by the image processing circuitry, a first vascular model modeling the cardiac vasculature recorded in the medical images by
determining image centerlines for the first and second medical images through branches of the cardiac vasculature,
identifying homologous branches among the image centerlines for the first and second medical images by orientating the image centerlines of the first and second images with respect to each other based on a difference between the first and second projection angles,
identifying connected branches using route tracing beginning at ends of the image centerlines for the first and second medical images for each of the identified branches that are homologous among the first and second medical images, and
creating the first vascular model using the determined image centerlines, the identified homologous branches, and the identified connected branches of the cardiac vasculature;
determining, by the image processing circuitry, a first value for a characteristic of flow through the stenotic segment in the first vascular model;
generating, by the image processing circuitry, a second vascular model from the first vascular model by making at least one modification to at least one of a vascular diameter, a vascular radius, or a vascular cross-sectional area of at least a portion of the stenotic segment in the first vascular model, which produces a difference in the characteristic of flow for the second vascular model;
determining, by the image processing circuitry, a second value for the characteristic of flow through the stenotic segment for the second vascular model; and
calculating, by the image processing circuitry, a flow index quantifying the vascular function of the cardiac vasculature modeled by the first vascular model,
wherein the calculating is based on comparing first and second values for the characteristic of flow in said first and said second vascular models.
2. The method of claim 1 , wherein the first medical image and the second medical image include 2-D angiographic images.
3. The method of claim 2 , wherein the 2-D angiographic images are of sufficient resolution to allow determination of vascular width within 10%, for a vessel segment following an at least third branch point from a main human coronary artery.
4. The method of claim 1 , wherein said flow index is calculated based on a ratio of corresponding flow characteristics of said first and second vascular models.
5. The method of claim 1 , wherein said at least one characteristic of flow comprises a flow rate.
6. The method of claim 5 , wherein said flow index comprises an index representing a Fractional Flow Reserve index comprising a ratio of a first maximal flow through the stenotic segment, to a second maximal flow through the stenotic segment with the stenosis removed.
7. The method of claim 5 , further comprising determining a recommendation for revascularization based on the flow index.
8. The method of claim 1 , wherein said first and said second vascular models comprise connected branches of vascular segment data, each said branch being associated with a corresponding vascular resistance to flow.
9. The method of claim 8 , wherein said first vascular model includes a radially 3-D description of a vascular wall of the cardiac vasculature.
10. The method of claim 1 , wherein said second vascular model comprises an estimated re-vascularized vessel that has a diameter larger than the stenotic segment in said first vascular model.
11. The method of claim 1 , wherein said second vascular model comprises a normalized vessel obtained by normalizing the stenotic segment based on properties of a neighboring astenotic segment.
12. The method of claim 1 , wherein the first and second values of the characteristic of flow are calculated based on properties of a plurality of vascular segments in flowing connection with the stenotic segment.
13. The method of claim 1 , further comprising:
identifying in said first vascular model the stenotic segment and a crown of vascular branches downstream of the stenotic segment;
calculating a resistance to fluid flow in said crown; and
calculating a second flow index based on a volume of said crown, and on a contribution of the stenotic segment to said resistance to fluid flow.
14. The method of claim 1 , wherein each vascular model corresponds to a portion of the vasculature which extends at least three bifurcations of the vasculature distally beyond the stenotic segment.
15. The method of claim 2 , wherein the first vascular model comprises paths along vascular segments of the cardiac vasculature, each of said paths being mapped along its extent to positions in 2-D angiographic images.
16. The method of claim 1 , wherein each vascular model corresponds to a portion of the cardiac vasculature which extends distally as far as resolution of said images allows determination of vascular width within 10% to a vessel segment following an at least third branch point from a main human coronary artery.
17. A non-transitory computer software product, comprising a computer-readable medium in which program instructions are stored, which instructions, when read by a computer, cause the computer to execute the method according to claim 1 .
18. A system for assessing a vascular function of a cardiac vasculature having a stenotic segment, the system comprising a computer configured to:
receive, from a medical imaging device, a first medical image of the cardiac vasculature recorded at a first projection angle and a second medical image of the cardiac vasculature recorded at a second projection angle;
determine a first vascular model modeling the cardiac vasculature recorded in the medical image by
determining image centerlines for the first and second medical images through branches of the cardiac vasculature,
identifying homologous branches among the image centerlines for the first and second medical images by orientating the image centerlines of the first and second images with respect to each other based on a difference between the first and second projection angles,
identifying connected branches using route tracing beginning at ends of the image centerlines for the first and second medical images for each of the identified branches that are homologous among the first and second medical images, and
creating the first vascular model using the determined image centerlines, the identified homologous branches, and the identified connected branches of the cardiac vasculature;
determine a first value for a characteristic of flow in the first vascular model through the stenotic segment;
generate a second vascular model from the first vascular model which produces at least one modification to at least one of a vascular diameter, a vascular radius, or a vascular cross-sectional area of at least a portion of the stenotic segment, which alters said at least one characteristic of flow;
further determine a second value for the characteristic of flow through the stenotic segment for the second vascular model; and
calculate a flow index quantifying the vascular function of the cardiac vasculature modeled by the first vascular model,
wherein the computer calculates the flow index by comparing first and second values for the characteristic of flow in said first and said second model.
19. The system of claim 18 , wherein said computer is configured to calculate said flow index within 5 minutes of the acquisition of said medical images.
20. The method of claim 1 , wherein the modification of the second vascular model from the first vascular model comprises neglecting the limitation of flow by the stenotic segment.