Towards a Digital Twin of Coronary Stenting: A Suitable and Validated Image-Based Approach for Mimicking Patient-Specific Coronary Arteries

Considering the field of application involving stent deployment simulations, the exploitation of a digital twin of coronary stenting that can reliably mimic the patient-specific clinical reality could lead to improvements in individual treatments. A starting step to pursue this goal is the development of simple, but at the same time, robust and effective computational methods to obtain a good compromise between the accuracy of the description of physical phenomena and computational costs. Specifically, this work proposes an approach for the development of a patient-specific artery model to be used in stenting simulations. The finite element model was generated through a 3D reconstruction based on the clinical imaging (coronary Optical Coherence Tomography (OCT) and angiography) acquired on the pre-treatment patient. From a mechanical point of view, the coronary wall was described with a suitable phenomenological model, which is consistent with more complex constitutive approaches and accounts for the in vivo pressurization and axial pre-stretch. The effectiveness of this artery modeling method was tested by reproducing in silico the stenting procedures of two clinical cases and comparing the computational results with the in vivo lumen area of the stented vessel

Modeling of an implantable device for remote arterial pressure measurement

Cardiovascular diseases are the leading causes of illness and death in Europe, having a major impact on healthcare costs. An intelligent stent (e-stent), capable of obtaining and transmitting measurements of physiological parameters, can be a useful tool for real-time monitorization of arterial blockage without patient hospitalization. In this paper, a behavioral model of a pressure sensing-based e-stent is proposed and simulated under several restenosis conditions. Special attention has been given to the need of an accurate fault model, obtained from realistic finite-element simulations, to ensure long-term reliability; particularly for those faults whose behavior cannot be described by usual analytical models

Implantable Sensor System for Remote Detection of a Restenosis Condition

Part 7: Perceptional SystemsInternational audienceThe increase of life expectancy in the European Union, and the high risk of cardiovascular diseases associated with age, are some of the main factors to contribute to the rise of healthcare costs. An intelligent stent (e-stent), capable of obtaining and transmitting real-time measurements of physiological parameters for its clinical consultation, can be a useful tool for long-term monitoring, diagnostic, and early warning system for arterial blockage without patient hospitalization. In this paper, a behavioural model of capacitive Micro-Electro-Mechanical (MEMS) pressure sensor is proposed and simulated under several restenosis conditions. Special attention has been given to the need of an accurate fault model, obtained from realistic finite-element simulations,to ensure long-term reliability; particularly for those faults whose behavior cannot be easily described by an analytical model

On the Material Constitutive Behavior of the Aortic Root in Patients with Transcatheter Aortic Valve Implantation

Background: Transcatheter aortic valve implantation (TAVI) is a minimally invasive procedure used to treat patients with severe aortic valve stenosis. However, there is limited knowledge on the material properties of the aortic root in TAVI patients, and this can impact the credibility of computer simulations. This study aimed to develop a non-invasive inverse approach for estimating reliable material constituents for the aortic root and calcified valve leaflets in patients undergoing TAVI. Methods: The identification of material parameters is based on the simultaneous minimization of two cost functions, which define the difference between model predictions and cardiac-gated CT measurements of the aortic wall and valve orifice area. Validation of the inverse analysis output was performed comparing the numerical predictions with actual CT shapes and post-TAVI measures of implanted device diameter. Results: A good agreement of the peak systolic shape of the aortic wall was found between simulations and imaging, with similarity index in the range in the range of 83.7% to 91.5% for n.20 patients. Not any statistical difference was observed between predictions and CT measures of orifice area for the stenotic aortic valve. After TAVI simulations, the measurements of SAPIEN 3 Ultra (S3) device diameter were in agreement with those from post-TAVI angio-CT imaging. A sensitivity analysis demonstrated a modest impact on the S3 diameters when altering the elastic material property of the aortic wall in the range of inverse analysis solution. Conclusions: Overall, this study demonstrates the feasibility and potential benefits of using non-invasive imaging techniques and computational modeling to estimate material properties in patients undergoing TAVI

Scattering of X-rays in diagnostic radiology:computed radiography, digital radiography, mobile digital radiography and mobile C-arm fluoroscopy

Abstract. The medical use of X-ray-based imaging modalities has increased in the last decade. During imaging scattered radiation is generated, and the staff can be exposed to it in various situations, including when holding the patient or conducting an interventional operation. To be able to minimize the exposure it is essential to have knowledge of the distribution of the scattered radiation. In this study scattered radiation maps where implemented based on direct measurements with dosimeters in various distances, angles and heights using an anthropomorphic phantom as a scattering object. Measurements were done using multiple imaging modalities and parameters. Maps were intended for educational purposes to be used in the radiation protection training of the staff. Thorax PA and LAT measurements in a standing position demonstrated that the scattered radiation is directed strongly back from the phantom towards the X-ray tube. Scatter intensity being stronger in the LAT imaging. On the other hand, pelvis AP measurements in a supine position demonstrated that the radiation is directed relatively equally to all directions when the horizontal plane perpendicular to the primary beam central axis is considered. The use of the pelvic shield in Thorax measurements and the radiation protection blanket in Pelvis measurements did not affect scattering with the applied measurement method. Also using 50kg weighing child’s imaging parameters did not have effect on the scattering as the same phantom was used. Measurements done using fluoroscopy with urological experiment parameters demonstrated that the scattered radiation is directed relatively equally to all directions when the horizontal plane perpendicular to the primary beam central axis is considered. However, there is an emphasis on the scatter at the end of the patient table where the operating physician would be positioned, and accordingly a decrease on the scatter at the opposite end. The use of the lamella radiation protection curtain on the physician’s end of the operation table decreased the measured dose rates of the dosimeter, that was placed lower than patient table surface level and therefore was shielded by the curtain. Bedside Thorax measurements with a mobile imaging system demonstrated that the scattered radiation is directed relatively equally to all direction when the horizontal plane perpendicular to the primary beam central axis is considered. Also, when these measurements are compared to the previous stationary Thorax measurements, it is evident that scattered radiation dose rates with the mobile system are lower. As the used dosimeter system measures personal dose equivalent Hp(10) rate, the cumulative dose values calculated based on the exposure time can be used as an estimate of the overall effective dose. Dose received by the healthcare professionals is small in Thorax and Pelvis imaging in a possible holding situation when compared to the annual dose limit of radiation workers. On the other hand, the estimated dose of the physician is clearly higher in a fluoroscopy-guided urological operation. Yet the magnitude of the physician’s dose is on the level that it is unlikely to exceed the annual dose limit. Lowest estimated effective doses were gotten in the bedside Thorax examination, where the dose received by the personnel correspond to 12 and 8 seconds of background radiation on 0.7- and 1-meter distances to the scatter radiation origin, respectively.

In-vitro and in-vivo imaging of coronary artery stents with Heartbeat OCT

To quantify the impact of cardiac motion on stent length measurements with Optical Coherence Tomography (OCT) and to demonstrate in vivo OCT imaging of implanted stents, without motion artefacts. The study consists of: clinical data evaluation, simulations and in vivo tests. A comparison between OCT-measured and nominal stent lengths in 101 clinically acquired pullbacks was carried out, followed by a simulation of the effect of cardiac motion on stent length measurements, experimentally and computationally. Both a commercial system and a custom OCT, capable of completing a pullback between two consecutive ventricular contractions, were employed. A 13 mm long stent was implanted in the left anterior descending branch of two atherosclerotic swine and imaged with both OCT systems. The analysis of the clinical OCT images yielded an average difference of 1.1 ± 1.6 mm, with a maximum difference of 7.8 mm and the simulations replicated the statistics observed in clinical data. Imaging with the custom OCT, yielded an RMS error of 0.14 mm at 60 BPM with the start of the acquisition synchronized to the cardiac cycle. In vivo imaging with conventional OCT yielded a deviation of 1.2 mm, relative to the length measured on ex-vivo micro-CT, while the length measured in the pullback acquired by the custom OCT differed by 0.20 mm. We demonstrated motion artefact-free OCT-imaging of implanted stents, using ECG triggering and a rapid pullback

Population-specific material properties of the implantation site for transcatheter aortic valve replacement finite element simulations

Patient-specific computational models are an established tool to support device development and test under clinically relevant boundary conditions. Potentially, such models could be used to aid the clinical decision-making process for percutaneous valve selection; however, their adoption in clinical practice is still limited to individual cases. To be fully informative, they should include patient-specific data on both anatomy and mechanics of the implantation site. In this work, fourteen patient-specific computational models for transcatheter aortic valve replacement (TAVR) with balloon-expandable Sapien XT devices were retrospectively developed to tune the material parameters of the implantation site mechanical model for the average TAVR population. Pre-procedural computed tomography (CT) images were post-processed to create the 3D patient-specific anatomy of the implantation site. Balloon valvuloplasty and device deployment were simulated with finite element (FE) analysis. Valve leaflets and aortic root were modelled as linear elastic materials, while calcification as elastoplastic. Material properties were initially selected from literature; then, a statistical analysis was designed to investigate the effect of each implantation site material parameter on the implanted stent diameter and thus identify the combination of material parameters for TAVR patients. These numerical models were validated against clinical data. The comparison between stent diameters measured from post-procedural fluoroscopy images and final computational results showed a mean difference of 2.5 ± 3.9%. Moreover, the numerical model detected the presence of paravalvular leakage (PVL) in 79% of cases, as assessed by post-TAVR echocardiographic examination. The final aim was to increase accuracy and reliability of such computational tools for prospective clinical applications