Gonzalo Maso Talou

Improving Cardiac Phase Extraction in IVUS Studies by Integration of Gating Methods

Goal: Coronary intravascular ultrasound (IVUS) is a fundamental imaging technique for atherosclerotic plaque assessment. However, volume-based data retrieved from IVUS studies can be misleading due to the artifacts generated by the cardiac motion, hindering diagnostic, and visualization of the vessel condition. Then, we propose an image-based gating method that improves the performance of the preexisting methods, delivering a gating in an appropriate time for clinical practice. Methods: We propose a fully automatic method to synergically integrate motion signals from different gating methods to improve the cardiac phase estimation. Additionally, we present a local extrema identification method that provides a more accurate extraction of a cardiac phase and, also, a scheme for multiple phase extraction mandatory for elastography-type studies. Results: A comparison with three state-of-the-art methods is performed over 61 in-vivo IVUS studies including a wide range of physiological situations. The results show that the proposed strategy offers: 1) a more accurate cardiac phase extraction; 2) a lower frame oversampling and/or omission in the extracted phase data (error of 1.492 ± 0.977 heartbeats per study, mean ± SD); 3) a more accurate and robust heartbeat period detection with a Bland-Altman coefficient of reproducibility (RPC) of 0.23 s, while the second closest method presents an RPC of 0.36 s. Significance: The integration of motion signals performed by our method shown an improvement of the gating accuracy and reliability.

Mechanical Characterization of the Vessel Wall by Data Assimilation of Intravascular Ultrasound Studies

Atherosclerotic plaque rupture and erosion are the most important mechanisms underlying the sudden plaque growth, responsible for acute coronary syndromes and even fatal cardiac events. Advances in the understanding of the culprit plaque structure and composition are already reported in the literature, however, there is still much work to be done toward in-vivo plaque visualization and mechanical characterization to assess plaque stability, patient risk, diagnosis and treatment prognosis. In this work, a methodology for the mechanical characterization of the vessel wall plaque and tissues is proposed based on the combination of intravascular ultrasound (IVUS) imaging processing, data assimilation and continuum mechanics models within a high performance computing (HPC) environment. Initially, the IVUS study is gated to obtain volumes of image sequences corresponding to the vessel of interest at different cardiac phases. These sequences are registered against the sequence of the end-diastolic phase to remove transversal and longitudinal rigid motions prescribed by the moving environment due to the heartbeat. Then, optical flow between the image sequences is computed to obtain the displacement fields of the vessel (each associated to a certain pressure level). The obtained displacement fields are regarded as observations within a data assimilation paradigm, which aims to estimate the material parameters of the tissues within the vessel wall. Specifically, a reduced order unscented Kalman filter is employed, endowed with a forward operator which amounts to address the solution of a hyperelastic solid mechanics model in the finite strain regime taking into account the axially stretched state of the vessel, as well as the effect of internal and external forces acting on the arterial wall. Due to the computational burden, a HPC approach is mandatory. Hence, the data assimilation and computational solid mechanics computations are parallelized at three levels: (i) a Kalman filter level; (ii) a cardiac phase level; and (iii) a mesh partitioning level. To illustrate the capabilities of this novel methodology toward the in-vivo analysis of patient-specific vessel constituents, mechanical material parameters are estimated using in-silico and in-vivo data retrieved from IVUS studies. Limitations and potentials of this approach are exposed and discussed.

TCT-573 Head-to-head comparison between coronary computed tomography angiography (CCTA) and intravascular ultrasound (IVUS) tridimensional models: a geometric point of view

Tridimensional reconstruction of the coronary arteries have played a major role in the understanding of the onset and progression of atherosclerotic plaque, plaque rupture and its hemodynamics repercussion. Our aim is to validate an automated algorithm that allows obtaining tridimensional model from

TCT-535 Coronary computed tomography angiography (CCTA) blood flow model, how we can improve it? Insights based on comparison with intravascular ultrasound (IVUS) tridimensional model.

RESULTS For deferred lesions, the risk of MACE had significant inverse relationship with FFR (adjusted hazard ratio [aHR], 1.06; 95% confidence interval [CI], 1.05 1.08; P<0.001). However, this relationship was not observed in revascularized lesions (aHR, 1.00; 95% CI, 0.99 1.02; P1⁄40.69). For lesions with FFR of 0.76, the risk of MACE was not significantly different between deferred and revascularized lesions. Conversely, in lesions with FFR of 0.75, the risk of MACE was significantly lower in revascularized lesions than in the deferred lesions (for FFR 0.71 0.75, aHR, 0.47; 95% CI, 0.24 0.89; P1⁄40.021, and for FFR 0.70, aHR 0.47; 95% CI, 0.26 0.84; P1⁄40.012).