Non-invasive functional assessment of coronary artery stenosis including simulation of hyperemia by changing resting microvascular resistance
A method and system for non-invasive assessment of coronary artery stenosis is disclosed. Patient-specific anatomical measurements of the coronary arteries are extracted from medical image data of a patient acquired during rest state. Patient-specific rest state boundary conditions of a model of coronary circulation representing the coronary arteries are calculated based on the patient-specific anatomical measurements and non-invasive clinical measurements of the patient at rest. Patient-specific rest state boundary conditions of the model of coronary circulation representing the coronary arteries are calculated based on the patient-specific anatomical measurements and non-invasive clinical measurements of the patient at rest. Hyperemic blood flow and pressure across at least one stenosis region of the coronary arteries are simulated using the model of coronary circulation and the patient-specific hyperemic boundary conditions. Fractional flow reserve (FFR) is calculated for the at least one stenosis region based on the simulated hyperemic blood flow and pressure.
1. A method for non-invasive assessment of coronary artery stenosis, comprising:
extracting patient-specific anatomical measurements of the coronary arteries from medical image data of a patient acquired during a rest state;
automatically detecting at least one stenosis region in at least one coronary artery from the medical image data;
calculating by a processor patient-specific rest state boundary conditions of a model of coronary circulation representing the coronary arteries using the patient-specific anatomical measurements and non-invasive clinical measurements of the patient at rest, wherein calculating the patient-specific rest state boundary conditions comprises calculating a resting microvascular resistance at a termination of each of a plurality of branches of the coronary arteries using the patient-specific anatomical measurements and the non-invasive clinical measurements of the patient at rest;
calculating by a processor patient-specific hyperemic boundary conditions of the model of coronary circulation using the rest boundary conditions and a model for simulated hyperemia, wherein the model for simulated hyperemia simulates hyperemia in the patient by changing only the resting microvascular resistance at a termination of each of a plurality of branches of the coronary arteries to a hyperemic microvascular resistance calculated as a function of the resting microvascular resistance at the termination of each of the plurality of branches without changing blood pressure or heart rate boundary conditions, and wherein calculating the patient-specific hyperemic boundary conditions comprises calculating the hyperemic microvascular resistance at the termination of each of the plurality of branches using the calculated resting microvascular resistance by:
calculating a resting average peak velocity as a function of a measured heart rate and a measured systolic blood pressure of the patient,
calculating a coronary flow velocity reserve (CFVR) value for each branch of the coronary arteries as a function of the resting average peak velocity and an age of the patient,
calculating a patient-specific total coronary resistance index (TCRI) as a function of the CFVR value and an estimated resting mean arterial pressure (MAP), and
calculating the hyperemic microvascular resistance at the termination of each of the plurality of branches as a function of the calculated resting microvascular resistance and the patient-specific TCRI;
simulating by a processor hyperemic blood flow and pressure across the at least one automatically detected stenosis region of the at least one coronary artery using the model of coronary circulation and the patient-specific hyperemic boundary conditions, wherein the model of coronary circulation comprises a reduced order stenosis pressure drop model representing the at least one stenosis region and the reduced order stenosis pressure drop model calculates a pressure drop across the at least one stenosis region as a sum of a viscous term, a turbulent term, and an inertance term:
Δ
P
s
=
μ
K
v
2
π
r
0
3
q
+
ρ
K
t
2
A
0
2
(
A
0
A
s
-
1
)
2
q
q
+
ρ
K
u
L
s
A
0
∂
q
∂
t
,
where μ is blood viscosity, L s is a length of the at least one stenosis region, q is a flow rate, A s is a cross-sectional area of the at least one stenosis region, A 0 is a cross-sectional area of a non-stenosis region in the at least one coronary artery, ρ is a blood density, r 0 is a radius of the non-stenosis region in the at least one coronary artery, and K v , K t and K u are viscous, turbulent, and inertance coefficients, respectively; and
calculating by a processor fractional flow reserve (FFR) of the at least one stenosis region using the simulated hyperemic blood flow and pressure.
2. The method of claim 1 , wherein the coronary circulation model comprises one-dimensional computational models representing the coronary arteries and aorta of the patient.
3. The method of claim 2 , wherein the reduced order stenosis pressure drop model representing the at least one stenosis region is coupled to the one-dimensional computational model representing the at least one coronary artery.
4. The method of claim 3 , wherein the reduced order stenosis pressure drop model representing the at least one stenosis region is coupled to the one-dimensional computational model representing the at least one coronary artery using a momentum equation that includes a pressure drop determined by the turbulent term as a loss term.
5. The method of claim 1 , wherein calculating the resting microvascular resistance at the termination of each of the plurality of branches using the patient-specific anatomical measurements and the non-invasive clinical measurements of the patient at rest comprises:
calculating the mean arterial pressure (MAP) as a function of the measured heart rate, the measured systolic blood pressure, and a measured diastolic blood pressure of the patient;
calculating a total resting coronary flow as a function of a product of an estimated stress value, a mass of a left ventricle of the patient, and the measured heart rate; and
calculating the resting microvascular resistance at the termination of each of the plurality of branches as a function of the MAP and the total resting coronary flow.
6. The method of claim 5 , wherein calculating a total resting coronary flow as a function of a product of an estimated stress value, a mass of a left ventricle of the patient, and the measured heart rate comprises:
calculating the estimated stress value as a function of the measured systolic blood pressure, a diameter of the left ventricle of the patient at end-diastole, and a posterior wall thickness of the left ventricle.
7. The method of claim 5 , wherein calculating a total resting coronary flow as a function of a product of an estimated stress value, a mass of a left ventricle of the patient, and the measured heart rate comprises:
calculating the estimated stress value as
Stress
=
0.334
·
SBP
·
LVDd
LVPWT
·
(
1
+
LVPWT
LVDd
)
,
where SBP is the measured systolic blood pressure, LVDd is a diameter of the left ventricle of the patient at end-diastole, and LVPWT is a posterior wall thickness of the left ventricle of the patient; and
calculating the total resting coronary flow as
Q rest =0.0218·Stress· M LV ·HR·10 −3 +120.11,
where M LV is the mass of the left ventricle of the patient and HR is the measured heart rate.
8. The method of claim 1 , wherein calculating a resting average peak velocity as a function of a measured heart rate and a measured systolic blood pressure of the patient comprises:
calculating the resting average peak velocity as rAPV=0.0009·SBP·HR+5.925 where SBP is the measure systolic blood pressure and HR is the measure heart rate.
9. The method of claim 1 , wherein calculating a patient-specific total coronary resistance index (TCRI) as a function of the CFVR value and an estimated resting mean arterial pressure (MAP) comprises:
calculating the patient-specific
TCRI
as
1
TCRI
=
MAP
rest
MAP
rest
-
Δ
MAP
.
CFVR, wherein MAP rest is the estimated resting mean MAP and ΔMAP is a predetermined constant value.
10. The method of claim 1 , wherein calculating the hyperemic microvascular resistance at the termination of each of the plurality of branches as a function of the calculated resting microvascular resistance and the patient-specific TCRI comprises:
calculating the hyperemic microvascular resistance at the termination of each of the plurality of branches as a product of the calculated resting microvascular resistance and the patient-specific TCRI.
11. The method of claim 2 , wherein the coronary circulation model further comprises lumped models representing coronary microvascular beds, each coupled to a termination of a one-dimensional computational model representing a coronary artery branch.
12. The method of claim 1 , wherein calculating the resting microvascular resistance at the termination of each of the plurality of branches using the patient-specific anatomical measurements and the non-invasive clinical measurements of the patient at rest comprises:
calculating the mean arterial pressure (MAP) as a function of the measured heart rate, the measured systolic blood pressure, and a measured diastolic blood pressure of the patient;
calculating a resting myocardial perfusion as a function of a rate-pressure product that is a product of the measured heart rate and the measured systolic blood pressure of the patient;
calculating a total resting coronary flow as a function of the calculated resting myocardial perfusion and a mass of a left ventricle of the patient; and
calculating the resting microvascular resistance at the termination of each of the plurality of branches as a function of the MAP and the total resting coronary flow.
13. The method of claim 12 , wherein the mass of the left ventricle is estimated from the medical image data of the patient.
14. The method of claim 1 , wherein calculating fractional flow reserve (FFR) of the at least one stenosis region using the simulated hyperemic blood flow and pressure comprises:
calculating the FFR of the at least one stenosis region as a ratio of a mean simulated hyperemic pressure distal to the at least one stenosis and a mean simulated hyperemic aortic pressure over a cardiac cycle.
15. An apparatus for non-invasive assessment of coronary artery stenosis, comprising:
a processor; and
a memory storing computer program instructions, which when executed by the processor cause the processor to perform operations comprising:
extracting patient-specific anatomical measurements of the coronary arteries from medical image data of a patient acquired during a rest state;
automatically detecting at least one stenosis region in at least one coronary artery from the medical image data;
calculating patient-specific rest state boundary conditions of a model of coronary circulation representing the coronary arteries using the patient-specific anatomical measurements and non-invasive clinical measurements of the patient at rest, wherein calculating the patient-specific rest state boundary conditions comprises calculating a resting microvascular resistance at a termination of each of a plurality of branches of the coronary arteries using the patient-specific anatomical measurements and the non-invasive clinical measurements of the patient at rest;
calculating patient-specific hyperemic boundary conditions of the model of coronary circulation using the rest boundary conditions and a model for simulated hyperemia, wherein the model for simulated hyperemia simulates hyperemia in the patient by changing only the resting microvascular resistance at a termination of each of a plurality of branches of the coronary arteries to a hyperemic microvascular resistance calculated as a function of the resting microvascular resistance at the termination of each of the plurality of branches without changing blood pressure or heart rate boundary conditions, and wherein calculating the patient-specific hyperemic boundary conditions comprises calculating the hyperemic microvascular resistance at the termination of each of the plurality of branches using the calculated resting microvascular resistance by:
calculating a resting average peak velocity as a function of a measured heart rate and a measured systolic blood pressure of the patient,
calculating a coronary flow velocity reserve (CFVR) value for each branch of the coronary arteries as a function of the resting average peak velocity and an age of the patient,
calculating a patient-specific total coronary resistance index (TCRI) as a function of the CFVR value and an estimated resting mean arterial pressure (MAP), and
calculating the hyperemic microvascular resistance at the termination of each of the plurality of branches as a function of the calculated resting microvascular resistance and the patient-specific TCRI;
simulating hyperemic blood flow and pressure across the at least one automatically detected stenosis region of the at least one coronary artery using the model of coronary circulation and the patient-specific hyperemic boundary conditions, wherein the model of coronary circulation comprises a reduced order stenosis pressure drop model representing the at least one stenosis region and the reduced order stenosis pressure drop model calculates a pressure drop across the at least one stenosis region as a sum of a viscous term, a turbulent term, and an inertance term:
Δ
P
s
=
μ
K
v
2
π
r
0
3
q
+
ρ
K
t
2
A
0
2
(
A
0
A
s
-
1
)
2
q
q
+
ρ
K
u
L
s
A
0
∂
q
∂
t
,
where μ is blood viscosity, L s is a length of the at least one stenosis region, q is a flow rate, A s is a cross-sectional area of the at least one stenosis region, A 0 is a cross-sectional area of a non-stenosis region in the at least one coronary artery, ρ is a blood density, r 0 is a radius of the non-stenosis region in the at least one coronary artery, and K v , K t and K u are viscous, turbulent, and inertance coefficients, respectively; and
calculating fractional flow reserve (FFR) of the at least one stenosis region using the simulated hyperemic blood flow and pressure.
16. The apparatus of claim 15 , wherein the coronary circulation model comprises one-dimensional computational models representing the coronary arteries and aorta of the patient.
17. The apparatus of claim 15 , wherein calculating the resting microvascular resistance at the termination of each of the plurality of branches using the patient-specific anatomical measurements and the non-invasive clinical measurements of the patient at rest comprises:
calculating the mean arterial pressure (MAP) as a function of the measured heart rate, the measured systolic blood pressure, and a measured diastolic blood pressure of the patient;
calculating a resting myocardial perfusion as a function of a rate-pressure product that is a product of the measured heart rate and the measured systolic blood pressure of the patient;
calculating a total resting coronary flow as a function of the calculated resting myocardial perfusion and a mass of a left ventricle of the patient; and
calculating the resting microvascular resistance at the termination of each of the plurality of branches as a function of the MAP and the total resting coronary flow.
18. A non-transitory computer readable medium storing computer program instructions for non-invasive assessment of coronary artery stenosis, the computer program instructions when executed by a processor cause the processor to perform operations comprising:
extracting patient-specific anatomical measurements of the coronary arteries from medical image data of a patient acquired during a rest state;
automatically detecting at least one stenosis region in at least one coronary artery from the medical image data;
calculating patient-specific rest state boundary conditions of a model of coronary circulation representing the coronary arteries using the patient-specific anatomical measurements and non-invasive clinical measurements of the patient at rest, wherein calculating the patient-specific rest state boundary conditions comprises calculating a resting microvascular resistance at a termination of each of a plurality of branches of the coronary arteries using the patient-specific anatomical measurements and the non-invasive clinical measurements of the patient at rest;
calculating patient-specific hyperemic boundary conditions of the model of coronary circulation using the rest boundary conditions and a model for simulated hyperemia, wherein the model for simulated hyperemia simulates hyperemia in the patient by changing only the resting microvascular resistance at a termination of each of a plurality of branches of the coronary arteries to a hyperemic microvascular resistance calculated as a function of the resting microvascular resistance at the termination of each of the plurality of branches without changing blood pressure or heart rate boundary conditions, and wherein calculating the patient-specific hyperemic boundary conditions comprises calculating the hyperemic microvascular resistance at the termination of each of the plurality of branches using the calculated resting microvascular resistance by:
calculating a resting average peak velocity as a function of a measured heart rate and a measured systolic blood pressure of the patient,
calculating a coronary flow velocity reserve (CFVR) value for each branch of the coronary arteries as a function of the resting average peak velocity and an age of the patient,
calculating a patient-specific total coronary resistance index (TCRI) as a function of the CFVR value and an estimated resting mean arterial pressure (MAP), and
calculating the hyperemic microvascular resistance at the termination of each of the plurality of branches as a function of the calculated resting microvascular resistance and the patient-specific TCRI;
simulating hyperemic blood flow and pressure across the at least one automatically detected stenosis region of the at least one coronary artery using the model of coronary circulation and the patient-specific hyperemic boundary conditions, wherein the model of coronary circulation comprises a reduced order stenosis pressure drop model representing the at least one stenosis region and the reduced order stenosis pressure drop model calculates a pressure drop across the at least one stenosis region as a sum of a viscous term, a turbulent term, and an inertance term:
Δ
P
s
=
μ
K
v
2
π
r
0
3
q
+
ρ
K
t
2
A
0
2
(
A
0
A
s
-
1
)
2
q
q
+
ρ
K
u
L
s
A
0
∂
q
∂
t
,
where μ is blood viscosity, L s is a length of the at least one stenosis region, q is a flow rate, A s is a cross-sectional area of the at least one stenosis region, A 0 is a cross-sectional area of a non-stenosis region in the at least one coronary artery, ρ is a blood density, r 0 is a radius of the non-stenosis region in the at least one coronary artery, and K v , K t and K u are viscous, turbulent, and inertance coefficients, respectively; and
calculating fractional flow reserve (FFR) of the at least one stenosis region using the simulated hyperemic blood flow and pressure.
19. The non-transitory computer readable medium of claim 18 , wherein the coronary circulation model comprises one-dimensional computational models representing the coronary arteries and aorta of the patient.
20. The non-transitory computer readable medium of claim 18 , wherein calculating the resting microvascular resistance at the termination of each of the plurality of branches based on the patient-specific anatomical measurements and the non-invasive clinical measurements of the patient at rest comprises:
calculating the mean arterial pressure (MAP) as a function of the measured heart rate, the measured systolic blood pressure, and a measured diastolic blood pressure of the patient;
calculating a resting myocardial perfusion as a function of a rate-pressure product that is a product of the measured heart rate and the measured systolic blood pressure of the patient;
calculating a total resting coronary flow as a function of the calculated resting myocardial perfusion and a mass of a left ventricle of the patient; and
calculating the resting microvascular resistance at the termination of each of the plurality of branches as a function of the MAP and the total resting coronary flow.
21. The non-transitory computer readable medium of claim 18 , wherein calculating fractional flow reserve (FFR) of the at least one stenosis region using the simulated hyperemic blood flow and pressure comprises:
calculating the FFR of the at least one stenosis region as a ratio of a mean simulated hyperemic pressure distal to the at least one stenosis and a mean simulated hyperemic aortic pressure over a cardiac cycle.