Plane wave ultrasound imaging using a single short, broadband planar source pulse generated by photoacoustic excitation, was demonstrated.

We demonstrate the feasibility of intravascular ultrasound (IVUS) chirp imaging as well as chirp reversal ultrasound contrast imaging at intravascular ultrasound frequency. Chirp excitations were emitted with a 34 MHz single crystal intravascular transducer and compared to conventional Gaussian-shaped pulses of equal acoustic pressure. The signal to noise ratio of the chirp images was increased by up to 9 dB relative to the conventional images. Imaging of contrast microbubbles was implemented by chirp reversal, achieving a contrast to tissue ratio of 12 dB. The method shows potential for intravascular imaging of structures in and beyond coronary atherosclerotic plaques including vasa vasorum.

Photoacoustic signals originating from weak sources can be hard to discriminate from higher intensity signals resulting from the photoacoustic background. In order to reveal these weaker signals we propose a method where the expected background signal is subtracted from the actual signals. In this method an ultrasound image provides the geometry for the pressure distribution used in a photoacoustic wave field simulation. The simulated photoacoustic signals are subtracted from the actual recordings and the residual is used for image reconstruction. This method was successfully validated experimentally with a vessel phantom containing three optical absorption irregularities within the vessel wall.

The carotid artery (CA) is one of the main arteries of interest to cardiovascular research, because of the clinical relevance of CA plaques as culprits of stroke and the accessibility of the CA for cardiovascular health screening. Viscoelastic properties of the arterial wall and of possible lesions within are key components for clinical evaluation of the CA. These viscoelastic properties can be assessed by monitoring the interaction of the wall with a passing arterial pulse wave using ultrasound (US) imaging. The local wall motion (position, velocity, and acceleration) may contain high frequency components and hence a full understanding of tissue mechanics in the CA requires very high frame rate imaging. In this paper we present a high density motion analysis of the CA based on an arterial pulse wave imaged with 2.5 up to 35 kHz frame rate US imaging.

Biomedical tissues usually show inhomogeneity in their acoustic mediumparameters. These inhomogeneities cause refraction and scattering of diagnosticand therapeutic ultrasound waves. A method that is able to model the effects ofinhomogeneity in the attenuation and in the nonlinearity is essential for thedesign of transducers for new ultrasound modalities and the development of novelultrasound applications. The Iterative Nonlinear Contrast Source (INCS) methodhas originally been designed for the accurate modeling of nonlinear acousticwave fields in homogeneous media. It considers the nonlinear term from theWestervelt equation as a distributed contrast source, and the correspondingintegral equation is solved using an iterative Neumann scheme. This paperpresents an extension of the INCS method that can handle inhomogeneity in theattenuation and in the coefficient of nonlinearity. Results are presented forthe one-dimensional case. These show that in this case the presented methodcorrectly predicts the effects related to nonlinear propagation and scatteringby inhomogeneities in the attenuation and the coefficient of non-linearity.

Research on nonlinear medical ultrasound has been increased over the lastdecade and has resulted in a wide range of numerical methods for the modeling ofthe nonlinear distortion of a propagating pressure wave. However, when appliedto realistic configurations, the majority of these methods are eithercomputationally expensive or limited by the applied approximations. TheIterative Nonlinear Contrast Source (INCS) method is able to accurately computethe pulsed nonlinear pressure wave field that is generated in a largethree-dimensional domain by an arbitrary transducer transmitting under a largesteering angle. The method is based on the Neumann iterative solution of anonlinear integral equation that is equivalent to the Westervelt equation. Toimprove the performance of the method, it would be beneficial to employiterative schemes (e.g. Conjugate Gradient based schemes) that are efficient forsolving linear integral equations. This motivates the development of alinearized version of the INCS method, as presented in this paper. To test thepresented approach, a Bi-CGSTAB scheme is used to solve the linearizedWestervelt equation. For the one-dimensional case, results are obtained andcompared with the solution obtained with the original INCS method, and theFubini solution. All the results have been obtained up to the third harmoniccomponent and are in agreement with each other.