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;
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 by:
calculating a resting mean arterial pressure (MAP) as a function of a measured heart rate, a 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 a measured heart rate, and
calculating the resting microvascular resistance at the termination of each of the plurality of branches as a function of the resting MAP and the total resting coronary flow;
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 by calculating a hyperemic microvascular resistance at the termination of each of the plurality of branches using the calculated resting microvascular resistance, wherein calculating a hyperemic microvascular resistance at the termination of each of the plurality of branches using the calculated resting microvascular resistance comprises:
determining a patient-specific total coronary resistance index (TCRI) using the measured heart rate of the patient; 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,
wherein the model for simulated hyperemia simulates hyperemia in the patient by changing only the resting microvascular resistance to the hyperemic microvascular resistance calculated as a function of the calculated resting microvascular resistance and the patient-specific TCRI at the termination of each of the plurality of branches without adjusting blood pressure or heart rate boundary conditions;
simulating by a processor hyperemic blood flow and pressure across at least one manually or automatically defined stenosis region of 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; 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 using a momentum equation that includes a pressure drop determined by the turbulent term as a loss term.
4. 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.
5. The method of claim 1 , wherein the mass of the left ventricle is estimated from the medical image data of the patient.
6. The method of claim 1 , wherein determining a patient-specific total coronary resistance index (TCRI) using the measured heart rate of the patient comprises:
calculating a resting average peak velocity as a function of the measured heart rate and the 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; and
calculating the patient-specific TCRI for each branch as a function of the CFVR value and the calculated resting MAP.
7. The method of claim 6 , 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.
8. The method of claim 6 , wherein calculating a patient-specific total coronary resistance index (TCRI) for each branch as a function of the CFVR value and an estimated resting mean arterial pressure (MAP) comprises:
calculating the patient specific TCRI for each branch 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.
9. The method of claim 6 , 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 for each branch.
10. The method of claim 1 , wherein determining a patient-specific total coronary resistance index (TCRI) using the measured heart rate of the patient comprises:
calculating the patient-specific TCRI as a function of the measured heart rate of the patient.
11. 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.
12. The method of claim 1 , wherein the reduced order stenosis pressure drop model calculates the pressure drop across the at least one stenosis region as:
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.
13. The method of claim 1 , wherein calculating a total resting coronary flow as a function of a product of an estimated stress value, a mass of the 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.
14. The method of claim 1 , wherein calculating a total resting coronary flow as a function of a product of an estimated stress value, a mass of the 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.
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;
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 by:
calculating a resting mean arterial pressure (MAP) as a function of a measured heart rate, a 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 a measured heart rate, and
calculating the resting microvascular resistance at the termination of each of the plurality of branches as a function of the resting MAP and the total resting coronary flow;
calculating patient-specific hyperemic boundary conditions of the model of coronary circulation using the rest boundary conditions and a model for simulated hyperemia by calculating a hyperemic microvascular resistance at the termination of each of the plurality of branches using the calculated resting microvascular resistance, wherein calculating a hyperemic microvascular resistance at the termination of each of the plurality of branches using the calculated resting microvascular resistance comprises:
determining a patient-specific total coronary resistance index (TCRI) using the measured heart rate of the patient; 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,
wherein the model for simulated hyperemia simulates hyperemia in the patient by changing only the resting microvascular resistance to the hyperemic microvascular resistance calculated as a function of the calculated resting microvascular resistance and the patient-specific TCRI at the termination of each of the plurality of branches without adjusting blood pressure or heart rate boundary conditions;
simulating hyperemic blood flow and pressure across at least one manually or automatically defined stenosis region of 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; 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. 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;
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 by:
calculating a resting mean arterial pressure (MAP) as a function of a measured heart rate, a 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 a measured heart rate, and
calculating the resting microvascular resistance at the termination of each of the plurality of branches as a function of the resting MAP and the total resting coronary flow;
calculating patient-specific hyperemic boundary conditions of the model of coronary circulation using the rest boundary conditions and a model for simulated hyperemia by calculating a hyperemic microvascular resistance at the termination of each of the plurality of branches using the calculated resting microvascular resistance, wherein calculating a hyperemic microvascular resistance at the termination of each of the plurality of branches using the calculated resting microvascular resistance comprises:
determining a patient-specific total coronary resistance index (TCRI) using the measured heart rate of the patient; 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,
wherein the model for simulated hyperemia simulates hyperemia in the patient by changing only the resting microvascular resistance to the hyperemic microvascular resistance calculated as a function of the calculated resting microvascular resistance and the patient-specific TCRI at the termination of each of the plurality of branches without adjusting blood pressure or heart rate boundary conditions;
simulating hyperemic blood flow and pressure across at least one manually or automatically defined stenosis region of 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; and
calculating fractional flow reserve (FFR) of the at least one stenosis region using the simulated hyperemic blood flow and pressure.
18. The non-transitory computer readable medium of claim 17 , wherein the coronary circulation model comprises one-dimensional computational models representing the coronary arteries and aorta of the patient.
19. The non-transitory computer readable medium of claim 17 , wherein determining a patient-specific total coronary resistance index (TCRI) using the measured heart rate of the patient comprises:
calculating a resting average peak velocity as a function of the measured heart rate and the 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; and
calculating the patient-specific TCRI for each branch as a function of the CFVR value and the calculated resting MAP.
20. The non-transitory computer readable medium of claim 17 , wherein determining a patient-specific total coronary resistance index (TCRI) using the measured heart rate of the patient comprises:
calculating the patient-specific TCRI as a function of the measured heart rate of the patient.
21. The non-transitory computer readable medium of claim 17 , 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.