# US 11,896,416 B2 · Method for calculating coronary artery fractional flow reserve on basis of myocardial blood flow and CT images

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- Number: US 11,896,416 B2
- Document ID: US11896416B2
- Status: Granted
- Kind: B2
- Application number: 17/328,550
- Filed: 2021-05-24
- Published: 2021-09-09
- Granted: 2024-02-13
- Earliest claimed: 2018-11-28
- Assignees: Suzhou Rainmed Medical Technology Co., Ltd.
- Applicants: Suzhou Rainmed Medical Technology Co., Ltd.
- Inventors: Yunfei Huo; Guangzhi Liu; Xingyun Wu; Zhiyuan Wang
- Web page: https://patentgrep.com/patent/US11896416B2

## CPC

- A61B 6/507: {for determination of haemodynamic parameters, e.g. perfusion CT}
- G06T 7/0012: {Biomedical image inspection}
- A61B 5/026: Measuring blood flow {(A61B3/1233, A61B3/1241 take precedence)}
- A61B 6/032: {Transmission computed tomography [CT]}
- A61B 6/503: {for diagnosis of the heart}
- A61B 6/504: {for diagnosis of blood vessels, e.g. by angiography}
- A61B 6/5217: {extracting a diagnostic or physiological parameter from medical diagnostic data}
- A61B 6/5235: {combining images from the same or different ionising radiation imaging techniques, e.g. PET and CT}
- A61B 6/5247: {combining images from an ionising-radiation diagnostic technique and a non-ionising radiation diagnostic technique, e.g. X-ray and ultrasound}
- G06T 7/11: Region-based segmentation
- G06T 7/155: involving morphological operators
- G06T 7/187: involving region growing; involving region merging; involving connected component labelling
- G06T 12/30: Image post-processing, e.g. metal artefact correction
- G16H 30/40: for processing medical images, e.g. editing
- G16H 50/30: for calculating health indices; for individual health risk assessment
- G16H 50/50: for simulation or modelling of medical disorders
- G06T 2207/10081: Computed x-ray tomography [CT]
- G06T 2207/20156: Automatic seed setting
- G06T 2207/30048: Heart; Cardiac
- G06T 2207/30104: Vascular flow; Blood flow; Perfusion
- G06T 2211/404: Angiography
- G06T 2211/412: Dynamic
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G16H: HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA

## Abstract

A method for calculating coronary artery fractional flow reserve includes determining myocardial volume by extracting myocardial images; locating a coronary artery inlet and accurately segmenting coronary arteries; generating a grid model required for calculation by edge detection of coronary artery volume data; determining myocardial blood flow in a rest state and CFR by non-invasive measurement; calculating the total flow at the coronary artery inlet in a maximum hyperemia state; determining the flow in different blood vessels in the coronary artery tree in the maximum hyperemia state and then determining flow velocity V1 in the maximum hyperemia state; using V1 as the flow velocity at the coronary artery inlet and calculating a pressure drop ΔP from the coronary artery inlet to a distal end of a coronary stenosis, and a mean intracoronary pressure Pd at the distal end of the stenosis Pd=Pa−ΔP, and calculating fractional flow reserve.

## Claims

### Claim 1

A method for calculating coronary artery fractional flow reserve based on myocardial blood flow and CT image, comprising the following steps:
S01: segmenting the CT image of heart, obtaining an image of heart via a morphological operation, subjecting the image of heart to a histogram analysis to obtain an image contains ventricular and atrial, obtaining a myocardial image by making a difference between the image of heart and the image contains ventricular and atrial, determining a myocardial volume by the myocardial image;
S02: obtaining a full aortic complementary image by processing an aortic image, obtaining the aortic image containing a coronary artery inlet through regional growth of the full aortic complementary image, and obtaining an image containing the coronary artery inlet according to the aortic image containing the coronary artery inlet and the full aortic complementary image to determine the coronary artery inlet by the image containing the coronary artery inlet;
S03: extracting a coronary artery through regional growth by taking the coronary artery inlet as a seed point on the myocardial image, calculating an average gray and average variance of the coronary artery, and along a direction of the coronary artery, extracting a coronary artery tree according to a gray distribution of the coronary artery;
S04: binarizing the coronary artery image, drawing an isosurface image to obtain a three-dimensional grid image of the coronary artery;
S05: calculating a total flow at the coronary artery inlet in a maximum hyperemia state, Qtotal=myocardial volume×myocardial blood flow×CFR, and CFR being the coronary flow reserve;
S06: calculating a blood flow velocity V1 in a hyperemia state;
S07: calculating a pressure drop ΔP from the coronary artery inlet to a distal end of a coronary artery stenosis using V1 as an inlet flow velocity of coronary artery stenosis blood vessel, using Pd=Pa−ΔP calculating a mean intracoronary pressure Pd at the distal end of the coronary artery stenosis, wherein Pa is a mean aortic pressure, and obtaining the fractional flow reserve using FFR=Pd/Pa.

### Claim 2 (depends on 1)

The method for calculating coronary artery fractional flow reserve based on myocardial blood flow and CT image according to claim 1, wherein after obtaining the image containing the coronary artery inlet in step S02, the image containing the coronary artery inlet is subjected to a connected domain analysis, and each connected domain is identified by different gray labels to determine the coronary artery inlet.

### Claim 3 (depends on 1)

The method for calculating coronary artery fractional flow reserve based on myocardial blood flow and CT image according to claim 1, wherein in step S02, based on a feature that an aortic cross-section is circular, an ascending aortic and a center line are extracted from the image of heart to obtain the aortic image.

### Claim 4 (depends on 1)

The method for calculating coronary artery fractional flow reserve based on myocardial blood flow and CT image according to claim 1, wherein binarizing the coronary artery image in step S04 comprises: going through voxels in the coronary artery image, remaining a pixel value unchanged if a voxel pixel is equal to 0; and setting the pixel value to 1 to obtain new data if the voxel pixel is not equal to 0.

### Claim 5 (depends on 1)

The method for calculating coronary artery fractional flow reserve based on myocardial blood flow and CT image according to claim 1, wherein in step S05, myocardial blood flow in a rest state and coronary flow reserve (CFR) are determined by cardiac ultrasound (MCE) or single photon emission computed tomography (SPECT) or positron emission tomography (PET) or cardiac nuclear magnetic (MRI) or CT perfusion.

### Claim 6 (depends on 1)

The method for calculating coronary artery fractional flow reserve based on myocardial blood flow and CT image according to claim 1, wherein step S06 comprises:
S61: determining a blood flow in any one of blood vessels in the tree using Q=Qtotal×(V/Vtotal)3/4 based on a flow volume scale and a cardiac surface coronary artery tree obtained using a three-dimensional reconstruction of a cardiac CT, wherein Vtotal is a sum volume of blood in all cardiac surface coronary artery obtained using the three-dimensional reconstruction of the cardiac CT, V is a sum volume of blood in any one of blood vessels and its downstream blood vessel in the cardiac surface coronary artery tree;
S62: determining the blood flow velocity in any one of blood vessel in the tree using V1=Q/D based on the flow volume scale and the cardiac surface coronary artery tree obtained using the three-dimensional reconstruction of the cardiac CT, wherein D is an average diameter of the blood vessel.

### Claim 7 (depends on 1)

The method for calculating coronary artery fractional flow reserve based on myocardial blood flow and CT image according to claim 1, wherein step S07 specifically comprises:
solving three-dimensional grids of blood vessels, and solving a continuity and Navier-Stokes equations using numerical methods:
∇·{right arrow over (V)}=0 [A1]
ρ
⁢
∂
V
→
∂
t
+
ρ
⁢
V
→
·
∇
V
→
=
-
∇
P
+
V
·
μ
⁡
(
∇
V
→
+
(
∇
V
→
)
T
)
[
A2
]
wherein, {right arrow over (V)}, P, ρ, μ are flow velocity, pressure, blood flow density, blood flow viscosity, respectively;
an inlet boundary condition being: the inlet flow velocity V1 of the coronary stenosis vessel in the maximum hyperemia state;
calculating a pressure drop of each coronary artery stenosis through three-dimensional computational fluid dynamics to obtain ΔP1, ΔP2, ΔP3 . . . , calculating the pressure drop from the coronary artery inlet to the distal end of the coronary artery stenosis using ΔP=ΣΔPi (i=1, 2, 3 . . . ), and obtaining the mean intracoronary pressure Pd at the distal end of the stenosis using Pd=Pa−ΔP, wherein Pa is the mean aortic pressure.

### Claim 8 (depends on 1)

The method for calculating coronary artery fractional flow reserve based on myocardial blood flow and CT image according to claim 1, wherein step S07 comprises:
based on the geometric structure reconstructed by CT, straightening blood vessel with stenosis, constructing a two-dimensional axisymmetric model, dividing two-dimensional grids, and solving a continuity and Navier-Stokes equation by numerical methods:
1
r
⁢
∂
∂
r
(
ru
r
)
+
∂
u
z
∂
z
=
0
[
A3
]
ρ
⁡
(
∂
u
r
∂
t
+
u
r
⁢
∂
u
r
∂
r
+
u
z
⁢
∂
u
r
∂
z
)
=
-
∂
p
∂
r
+
μ
[
1
r
⁢
∂
∂
r
(
r
⁢
∂
u
r
∂
r
)
+
∂
2
u
r
∂
z
2
-
u
r
r
2
]
[
A4
]
ρ
⁡
(
∂
u
z
∂
t
+
u
r
⁢
∂
u
z
∂
r
+
u
z
⁢
∂
u
z
∂
z
)
=
-
∂
p
∂
z
+
μ
[
1
r
⁢
∂
∂
r
(
r
⁢
∂
u
z
∂
r
)
+
∂
2
u
z
∂
z
2
]
[
A5
]
wherein, ρ represents the density of blood, uz and ur represent the flow velocity in the z direction and r direction, respectively, μ represents the dynamic viscosity of the blood, and p represents the pressure of the blood;
an inlet boundary condition being: the inlet flow velocity V1 of the coronary stenosis vessel in the maximum hyperemia state;
calculating a pressure drop of each coronary artery stenosis through two-dimensional computational fluid dynamics to obtain ΔP1, ΔP2, ΔP3 . . . , calculating the pressure drop from the coronary artery inlet to the distal end of the coronary stenosis using ΔP=ΣΔPi (i=1, 2, 3 . . . ), and obtaining the mean intracoronary pressure Pd at the distal end of the stenosis using Pd=Pa−ΔP, wherein Pa is the mean aortic pressure.

### Claim 9 (depends on 8)

The method for calculating coronary artery fractional flow reserve based on myocardial blood flow and CT image according to claim 8, wherein the step S07 further comprises: for different types of bends of the blood vessels, calculating a pressure difference from the inlet to an outlet using a three-dimensional model; in comparison with a calculation of two-dimensional axisymmetric model, establishing a correction coefficient database, which is used to store coefficients for correcting the two-dimensional axisymmetric results through various types of bending;
after obtaining the pressure, obtaining a corrected pressure difference from the inlet to the outlet with reference to the correction coefficients in the database, and then calculating FFR by the corrected pressure difference.