John Pitre

Computational Fluid Dynamics Modeling of the Burr Orbital Motion in Rotational Atherectomy with Particle Image Velocimetry Validation

Rotational atherectomy (RA) uses a high-speed rotating burr introduced via a catheter through the artery to remove hardened atherosclerotic plaque. Current clinical RA technique lacks consensus on burr size and rotational speed. The rotating burr orbits inside the artery due to the fluid force of the blood. Different from a common RA technique of upsizing burrs for larger luminal gain, a small burr can orbit to treat a large lumen. A 3D computational fluid dynamics (CFD) model was developed to simulate the burr motion and study the fluid flow and force in RA. A particle image velocimetry experiment was conducted to measure and validate the flow field including the radial and axial velocities and a pair of counter-rotating vortices near the burr equator in CFD. The hydraulic force on the burr and the contact force between the burr and the arterial wall were estimated by CFD. The contact force can be reduced by using smaller burr and lower rotational speed. Utilizing the small burr orbital motion has the potential to be an improved RA technique.

Design and Testing of a Single-Element Ultrasound Viscoelastography System for Point-of-Care Edema Quantification

Management of fluid overload in patients with end-stage renal disease represents a unique challenge to clinical practice because of the lack of accurate and objective measurement methods. Currently, peripheral edema is subjectively assessed by palpation of the patients extremities, ostensibly a qualitative indication of tissue viscoelastic properties. New robust quantitative estimates of tissue fluid content would allow clinicians to better guide treatment, minimizing reactive treatment decision making. Ultrasound viscoelastography (UVE) can be used to estimate strain in viscoelastic tissue, deriving material properties that can help guide treatment. We are developing and testing a simple, low-cost UVE system using a single-element imaging transducer that is simpler and less computationally demanding than array-based systems. This benchtop validation study tested the feasibility of using the UVE system by measuring the mechanical properties of a tissue-mimicking material under large strains. We generated depth-dependent creep curves and viscoelastic parameter maps of time constants and elastic moduli for the Kelvin model of viscoelasticity. During testing, the UVE system performed well, with mean UVE-measured strain matching standard mechanical testing with maximum absolute errors ≤4%. Motion tracking revealed high correlation and signal-to-noise ratios, indicating that the system is reliable.

The feasibility of using compression bioimpedance measurements to quantify peripheral edema

Abstract The accurate assessment of body fluid volume is important in many clinical situations, especially in the determination of “dry weight” in a dialysis setting. Currently, no clinically applicable diagnostic system exists to determine the mechanical properties that accurately characterize peripheral edema in an objective and quantitative manner. We have developed a method for quantifying the impact of compression on the electrical properties of tissue by measuring stress-induced changes in bioimpedance (BIS). Using this method, we simultaneously measured the impedance and mechanical response of a tissue mimicking material (tofu) under both quasi-static and dynamic loading conditions. Our results demonstrate a temporal quantification of viscoelastic properties using a viscoelastic phantom tissue model.

Evaluation of a model-based poroelastography algorithm for edema quantification

A critical component of end stage renal disease treatment is optimal fluid management. Patients with reduced kidney function risk developing fluid overload, and many dialysis patients exceed recommended levels of fluid retention, leading to frequent clinical intervention and higher mortality. Despite this, current clinical standards of care rely on reactive semi-quantitative tests to grade fluid overload and peripheral edema. Poroelastography has been proposed as a quantitative means of estimating fluid overload in peripheral edema, but clinical studies have met limited success, in part because of measurement noise. We developed a new poroelastography method based on an inverse problem formulation to address the shortcomings of current methods. Our technique iteratively minimizes the error between ultrasound displacement measurements and the solution of a Biot poroelastic model. This formulation does not depend on noise-amplifying derivatives and ratios. We tested our algorithm in a simulation study using...

Magnetic linear actuator for vascular access surveillance

Vascular access (VA) surveillance to guide care is essential for dialysis patients. Non-linear, patient specific formation of stenoses reduce VA efficiency. Various methods are used to monitor blood flow or pressure. However, these are surrogates for stenosis rather than direct measurements. There is also no reimbursement for VA surveillance and measurements consume clinician time, making more frequent measurements difficult. Hemodynamic variability increases the chance of infrequent observations missing stenosis formation. This paper presents a specialized ultrasound system intended to slide between the dialysis needles and provide operator independent VA geometry and volume flow during treatment. Specific attention is paid toward the magnetic design of the Lorentz force linear actuator. Experimental results indicate that the system can successfully collect Doppler flow information across a tissue-mimicking flow phantom vessel.

Optimization of a magnetic linear transducer actuator using computational fluid dynamics

Ultrasound transducer arrays represent the current standard for medical ultrasound imaging applications. Despite this, the development of low-cost imaging systems is typically limited to single element wobbler transducers. We have developed a novel single element transducer system that is able to replicate the function of expensive linear arrays. This system uses a Lorentz force linear motor to mechanically sweep a single element transducer along a linear path. In order to optimize our systems operating characteristics for high speed imaging applications, we have performed a fluid dynamics analysis of the drag generated as a result of the transducer motion. Analytical and finite element models are derived for the motion of a rectangular cylinder through a confined channel. Our analysis reveals that small changes to the actuator housing geometry can drastically reduce drag, allowing us to achieve higher imaging frame rates. In addition, we predict the formation of an alternating vortex street that may introduce an additional source of vibration.