Non-invasive functional assessment of coronary artery stenosis including simulation of hyperemia by changing resting microvascular resistance

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:
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• where μ is blood viscosity, Ls is a length of the at least one stenosis region, q is a flow rate, As is a cross-sectional area of the at least one stenosis region, A0 is a cross-sectional area of a non-stenosis region in the at least one coronary artery, ρ is a blood density, r0 is a radius of the non-stenosis region in the at least one coronary artery, and Kv, Kt and Ku 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.

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
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• ,
• where μ is blood viscosity, Ls is a length of the at least one stenosis region, q is a flow rate, As is a cross-sectional area of the at least one stenosis region, A0 is a cross-sectional area of a non-stenosis region in the at least one coronary artery, ρ is a blood density, r0 is a radius of the non-stenosis region in the at least one coronary artery, and Kv, Kt and Ku 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.