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Much of the current knowledge of human cardiovascular pathologies and treatment strategies has been gained from understanding the cardiac physioiogies and functions in small animal models, such as mice, rats, and zebrafish. In this paper, we present the development of a high-frame-rate duplex ultrasound biomicroscopy (UBM) capable of B-mode imaging and pulsed-wave (PW) Doppler measurement for in vivo cardiovascular investigation in small animals. A frame rate of 200 frames per second (fps) was accomplished at a view of 5 mm x 8 mm, using a novel high-speed sector probe and specially designed lightweight transducers. In a reduced lateral view of 1.2 mm, a frame rate of 400 fps was achieved to examine more detailed cardiac motion. The UBM utilized transducers with different center frequencies (40-75 MHz) and geometries, which made it useful for various applications in small animal cardiac imaging. The highest spatial resolution the UBM achieved was 25 [micro]m x 56 [micro]m. In addition, the image-guided PW Doppler implemented in the UBM demonstrated the detection of the velocity of a moving wire as low as 0.1 mm/s, and flow in a polyimide tube as small as 200 [micro]m in diameter. Furthermore, the UBM achieved a 15-[micro]V minimal detectable signal and a 60-dB dynamic range using a low-cost PCB-based design. Finally, sample in vivo cardiac images of mouse and zebrafish hearts were given. These results showed that the UBM integrated with B-mode and PW Doppler is useful to investigate the pathophysiological mechanism in the cardiovascular studies.

A percutaneous ventricular assist device (pVAD) is an extracorporeal cardiac assist system that supports the failing ventricle in advanced stage heart failure by bypassing blood from the venous to the arterial circulation through a blood pump. The system can be implanted in a Cath lab using standard interventional techniques, and typically consists of a venous or atrial drainage cannula, the VAD (or blood pump), and an arterial perfusion cannula. Because the device allows clinicians the freedom of choosing the configuration and size of the cannulae based on the patient's body size and the size of the artery, it is extremely difficult but important to be able to predict the amount of blood flow that the device can provide before it is implanted to support the patient. In this paper, we develop a novel method that can be used to accurately predict the mean flow rate that the device can provide to the patient based on the size and configuration of the arterial cannula, the pump speed, and the patient's left atrial and mean arterial pressures. To do this, we first develop a nonlinear electric circuit model for the pVAD. This model includes a speed dependent voltage source and flow dependent resistors to simulate the pressure-flow relationship in the various cannulae in the device. We show that the flow rate through the device can be determined by solving a quadratic equation whose coefficients are scaled depending on the size and configuration of the arterial cannula. The model and prediction method were tested experimentally on a test loop supported by the TandemHeart pVAD (Cardiacassist, Inc., Pittsburgh, PA). A comparison of the predicted flow rates obtained from our method with experimental data shows that our method can predict the flow rates accurately with error indices less than 6 % for all test conditions over the entire range of intended use of the device. Computer simulations of the pVAD model coupled to a cardiovascular model showed that the accuracy of the method in estimating the mean flow rate is consistent over the normal range of operation of the device regardless of the pulsatility introduced by the cardiovascular system. This method can be used as an additional too to assist cardiologists in choosing a proper arterial cannulae configurations and sizes for pVAD patients. It can also be used as a tool to train clinical personnel to operate the device under different physiological conditions. Index Terms--Blood pump modeling, cardiovascular system, nonlinear circuit analysis, performance prediction, ventricular assist device (VAD).

A four-dimensional mapping (three spatial dimensions + time) of myocardial strain-rate would help to describe the mechanical properties of the myocardium, which affect important physiological factors such as the pumping performance of the ventricles. Strain-rate represents the local instantaneous deformation of the myocardium and can be calculated from the spatial gradients of the velocity field. Strain-rate has previously been calculated using one-dimensional (ultrasound) or two-dimensional (2-D) magnetic resonance imaging) techniques. However, this assumes that myocardial motion only occurs in one direction or in one plane, respectively. This paper presents a method for calculation of the time-resolved three-dimensional (3-D) strain-rate tensor using velocity vector information in a 3-D spatial grid during the whole cardiac cycle. The strain-rate tensor provides full information of both magnitude and direction of the instantaneous deformation of the myocardium. A method for visualization of the full 3-D tensor is also suggested. The tensors are visualized using ellipsoids, which display the principal directions of strain-rate and the ratio between strain-rate magnitude in each direction. The presented method reveals the principal strain-rate directions without a priori knowledge of myocardial motion directions. Index Terms--Cardiovascular system, kinematics, magnetic resonance imaging.