Methodology for implementing patient-specific spatial boundary condition during a cardiac cycle from phase-contrast MRI for hemodynamic assessment.

Pulmonary insufficiency (PI) can render the right ventricle dysfunctional due to volume overloading and hypertrophy. The treatment requires a pulmonary valve replacement surgery. However, determining the right time for the valve replacement surgery has been difficult with currently employed clinical techniques such as, echocardiography and cardiac MRI. Therefore, there is a clinical need to improve the diagnosis of PI by using patient-specific (PS) hemodynamic endpoints. While there are many reported studies on the use of PS geometry with time varying boundary conditions (BC) for hemodynamic computation, few use spatially varying PS velocity measurement at each time point of the cardiac cycle. In other words, the gap is that, there are limited number of studies which implement both spatially- and time-varying physiologic BC directly with patient specific geometry. The uniqueness of this research is in the incorporation of spatially varying PS velocity data obtained from phase-contrast MRI (PC-MRI) at each time point of the cardiac cycle with PS geometry obtained from angiographic MRI. This methodology was applied to model the complex developing flow in human pulmonary artery (PA) distal to pulmonary valve, in a normal and a subject with PI. To validate the methodology, the flow rates from the proposed method were compared with those obtained using QFlow software, which is a standard of care clinical technique. For the normal subject, the computed time average flow rates from this study differed from those obtained using the standard of care technique (QFlow) by 0.8 ml/s (0.9%) at the main PA, by 2 ml/s (3.4%) at the left PA and by 1.4 ml/s (3.8%) at the right PA. For the subject with PI, the difference was 7 ml/s (12.4%) at the main PA, 5.5 ml/s (22.6%) at the left PA and 4.9 ml/s (18.0%) at the right PA. The higher percentage differences for the subject with PI, was the result of overall lower values of the forward mean flow rate caused by excessive flow regurgitation. This methodology is expected to provide improved computational results when PS geometry from angiographic MRI is used in conjunction with PS PC-MRI data for solving the flow field.

Magnetic resonance derived myocardial strain assessment using feature tracking.

PURPOSE: An accurate and practical method to measure parameters like strain in myocardial tissue is of great clinical value, since it has been shown, that strain is a more sensitive and earlier marker for contractile dysfunction than the frequently used parameter EF. Current technologies for CMR are time consuming and difficult to implement in clinical practice. Feature tracking is a technology that can lead to more automatization and robustness of quantitative analysis of medical images with less time consumption than comparable methods. METHODS: An automatic or manual input in a single phase serves as an initialization from which the system starts to track the displacement of individual patterns representing anatomical structures over time. The specialty of this method is that the images do not need to be manipulated in any way beforehand like e.g. tagging of CMR images. RESULTS: The method is very well suited for tracking muscular tissue and with this allowing quantitative elaboration of myocardium and also blood flow. CONCLUSIONS: This new method offers a robust and time saving procedure to quantify myocardial tissue and blood with displacement, velocity and deformation parameters on regular sequences of CMR imaging. It therefore can be implemented in clinical practice.

Concurrent assessment of epicardial coronary artery stenosis and microvascular dysfunction using diagnostic endpoints derived from fundamental fluid dynamics principles.

BACKGROUND: Simultaneously measured pressure and flow distal to coronary stenoses can be combined, in conjunction with anatomical measurements, to assess the status of both the epicardial and microvascular circulations. METHODS AND RESULTS: Assessments of coronary hemodynamics were performed using fundamental fluid dynamics principles. We hypothesized that the pressure-drop coefficient (CDPe; trans-stenotic pressure drop divided by the dynamic pressure in the distal vessel) correlates linearly with epicardial and microcirculatory resistances concurrently. In 14 pigs, simultaneous measurements of distal coronary arterial pressure and flow were performed using a dual sensor-tipped guidewire in the setting of both normal and disrupted microcirculation, with the presence of epicardial coronary lesions of lt; 50% area stenosis (AS) and > 50% AS. The CDPe progressively increased from lesions of < 50% AS to > 50% AS and had a higher resolving power (45 +/- 22 to 193 +/- 140 in normal microcirculation; 248 +/- 137 to 351 +/- 140 in disrupted microcirculation) as compared to fractional flow reserve (FFR) and coronary flow reserve (CFR). Strong multiple linear correlation was observed for CDPe with combined FFR and CFR (r = 0.72; p < 0.0001). Further, the ratio of maximum pressure drop coefficient evaluated at the site of stenosis and its theoretical limiting value of minimum cross-sectional area was also able to distinguish different combinations of coronary artery diseases. CONCLUSIONS: The CDPe can be readily obtained during routine pressure and flow measurements during cardiac catheterization. It is a promising clinical diagnostic parameter that can independently assess the severity of epicardial stenosis and microvascular impairment.