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, 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 three-dimensional first vascular model that represents the cardiac vasculature recorded in the medical images by
determining image centerlines and homologous branches among the image centerlines for the first and second medical images through branches of the cardiac vasculature,
determining vascular dimensions of locations along the determined image centerlines among the identified homologous branches using the first and second medical images, the vascular dimensions including at least one of vascular diameters, vascular cross-sectional areas, or vascular radii of the branches of the cardiac vasculature at the locations along the determined image centerlines, and
for each of the locations along the determined image centerlines, combining the vascular dimensions to determine dimensions for the three-dimensional first vascular model of the cardiac vasculature;
determining, by the image processing circuitry, first values for a characteristic of flow along the determined image centerlines using the determined dimensions in the first vascular model, the first values for the characteristic of flow including first resistances;
generating, by the image processing circuitry, a second vascular model from the first vascular model through normalization by making at least one modification to at least one of a vascular diameter, a vascular radius, or a vascular cross-sectional area to create normalized determined dimensions;
determining at least one of a blood volume of the cardiac vasculature or a normal blood flow through the cardiac vasculature represented by the normalized determined dimensions;
determining, by the image processing circuitry, second values for the characteristic of flow along the image centerlines of the second vascular model using the normalized determined dimensions and at least one of the normal blood flow or the blood volume, the second values for the characteristic of flow including second resistances;
calculating, by the image processing circuitry, a flow index quantifying the vascular function for each of the locations along the cardiac vasculature based on a ratio of the first resistance to the second resistance; and
causing the flow index to be displayed.
2. The method of claim 1 , wherein a one-dimensional resistance model is created for the determined first resistances.
3. The method of claim 2 , wherein the second vascular model includes a second one-dimensional resistance model that is created for the determined second resistances.
4. The method of claim 1 , wherein, for each of the locations along the cardiac vasculature of the three-dimensional first vascular model, the ratio includes a summation of the first and second resistances that is divided by the second resistance.
5. The method of claim 1 , wherein the first resistances correspond to resistances contributed by at least one of a stenosis, a lesion, natural vessel narrowing, a bifurcation, or a trifurcation of the cardiac vasculature and the second resistances correspond to myocardial resistances.
6. The method of claim 1 , wherein each of the locations along the cardiac vasculature is part of a blood vessel segment.
7. The method of claim 1 , wherein the first resistance (R) for each of the locations along the cardiac vasculature is determined based on equation (1),
R
=
128
μ
π
∫
dl
d
4
(
equation
1
)
where μ is blood viscosity, d is the dimension of the cardiac vasculature at the respective location of the three-dimensional first vascular model, and l is a length of the respective location of the cardiac vasculature represented by the three-dimensional first vascular model.
8. The method of claim 1 , wherein the locations along the cardiac vasculature of the three-dimensional first vascular model are spaced apart by a distance that is between 0.1 millimeters (“mm”) and 5 mm.
9. The method of claim 1 , wherein the first medical image and the second medical image include 2-D angiographic images.
10. The method of claim 1 , further comprising:
for each of the locations along the cardiac vasculature of the three-dimensional first vascular model, compare the ratio to a predetermined value; and
display an indication for stent placement or treatment based on the comparison being below the predetermined value,
wherein the predetermined value is between 0.75 and 0.8.
11. The method of claim 1 , wherein for each of the locations along the cardiac vasculature of the three-dimensional first vascular model, the ratio includes a Fractional Flow Ratio (“FFR”) value.