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Treeby B.E.,University College London | Jaros J.,Brno University of Technology | Rohrbach D.,Lizzi Center for Biomedical Engineering | Cox B.T.,University College London
IEEE International Ultrasonics Symposium, IUS | Year: 2014

A new model for simulating elastic wave propagation using the open-source k-Wave MATLAB Toolbox is described. The model is based on two coupled first-order equations describing the stress and particle velocity within an isotropic medium. For absorbing media, the Kelvin-Voigt model of viscoelasticity is used. The equations are discretised in 2D and 3D using an efficient time-stepping pseudospectral scheme. This uses the Fourier collocation spectral method to compute spatial derivatives and a leapfrog finite-difference scheme to integrate forwards in time. A multi-axial perfectly matched layer (M-PML) is implemented to allow free-field simulations using a finite-sized computational grid. Acceleration using a graphics processing unit (GPU) is supported via the MATLAB Parallel Computing Toolbox. An overview of the simulation functions and their theoretical and numerical foundations is described. © 2014 IEEE. Source

Filoux E.,Lizzi Center for Biomedical Engineering | Filoux E.,Vermon SA | Sampathkumar A.,Lizzi Center for Biomedical Engineering | Chitnis P.V.,Lizzi Center for Biomedical Engineering | And 3 more authors.
Review of Scientific Instruments | Year: 2013

This paper presents a combined ultrasound and photoacoustic (PA) imaging (PAI) system used to obtain high-quality, co-registered images of mouse-embryo anatomy and vasculature. High-frequency ultrasound (HFU, >20 MHz) is utilized to obtain high-resolution anatomical images of small animals while PAI provides high-contrast images of the vascular network. The imaging system is based on a 40 MHz, 5-element, 6 mm aperture annular-array transducer with a 800 μm diameter hole through its central element. The transducer was integrated in a cage-plate assembly allowing for a collimated laser beam to pass through the hole so that the optical and acoustic beams were collinear. The assembly was mounted on a two-axis, motorized stage to enable the simultaneous acquisition of co-registered HFU and PA volumetric data. Data were collected from all five elements in receive and a synthetic-focusing algorithm was applied in post-processing to beamform the data and increase the spatial resolution and depth-of-field (DOF) of the HFU and PA images. Phantom measurements showed that the system could achieve high-resolution images (down to 90 μm for HFU and 150 μm for PAI) and a large DOF of >8 mm. Volume renderings of a mouse embryo showed that the scanner allowed for visualizing morphologically precise anatomy of the entire embryo along with corresponding co-registered vasculature. Major head vessels, such as the superior sagittal sinus or rostral vein, were clearly identified as well as limb bud vasculature. © 2013 AIP Publishing LLC. Source

Jafari S.,University Pierre and Marie Curie | Diou O.,University Paris - Sud | Mamou J.,Lizzi Center for Biomedical Engineering | Renault G.,French Institute of Health and Medical Research | And 3 more authors.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2014

Liquid-core nanoparticles are promising candidates for targeted ultrasound-controlled therapy, but their acoustic detection remains challenging. High-frequency (20 to 40 MHz) tone burst sequences were implemented with a programmable ultrasound biomicroscope to characterize acoustic response from perfluorooctyl bromide-core nanoparticles with thick poly(lactide-coglycolide) (PLGA) shells. Radio-frequency signals were acquired from flowing solutions of nanoparticles with two different shell-thickness-to-particle-radius ratios, solid PLGA nanoparticles, and latex nanobeads (linear controls). Normalized fundamental (20 MHz) and second-harmonic power spectral density (PSD) increased with particle concentration and was highest for the thinnest shelled particles. The second-harmonic PSD was detectable from the nanoparticles for peak rarefactional pressures (PRP) from 0.97 to 2.01 MPa at 23 cycles and for tone bursts from 11 to 23 cycles at 2.01 MPa. Their second-harmonic-to-fundamental ratio increased as a function of PRP and number of cycles. Within the same PRP and cycle ranges, the second-harmonic-to-fundamental ratios from matched concentration solutions of latex nanobeads and solid PLGA nanoparticles was more weakly detectable but also increased with PRP and number of cycles. Nanoparticles were detectable under flow conditions in vitro using the contrast agent mode of a high-frequency commercial scanner. These results characterize linear acoustic response from the nanoparticles (20 to 40 MHz) and demonstrate potential for their highfrequency detection. © 1986-2012 IEEE. Source

Sparks R.,Rutgers University | Sparks R.,Case Western Reserve University | Bloch B.N.,Boston University | Feleppa E.,Lizzi Center for Biomedical Engineering | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

In this work, we present a novel, automated, registration method to fuse magnetic resonance imaging (MRI) and transrectal ultrasound (TRUS) images of the prostate. Our methodology consists of: (1) delineating the prostate on MRI, (2) building a probabilistic model of prostate location on TRUS, and (3) aligning the MRI prostate segmentation to the TRUS probabilistic model. TRUS-guided needle biopsy is the current gold standard for prostate cancer (CaP) diagnosis. Up to 40% of CaP lesions appear isoechoic on TRUS, hence TRUS-guided biopsy cannot reliably target CaP lesions and is associated with a high false negative rate. MRI is better able to distinguish CaP from benign prostatic tissue, but requires special equipment and training. MRI-TRUS fusion, whereby MRI is acquired pre-operatively and aligned to TRUS during the biopsy procedure, allows for information from both modalities to be used to help guide the biopsy. The use of MRI and TRUS in combination to guide biopsy at least doubles the yield of positive biopsies. Previous work on MRI-TRUS fusion has involved aligning manually determined fiducials or prostate surfaces to achieve image registration. The accuracy of these methods is dependent on the reader's ability to determine fiducials or prostate surfaces with minimal error, which is a difficult and time-consuming task. Our novel, fully automated MRI-TRUS fusion method represents a significant advance over the current state-of-the-art because it does not require manual intervention after TRUS acquisition. All necessary preprocessing steps (i.e. delineation of the prostate on MRI) can be performed offline prior to the biopsy procedure. We evaluated our method on seven patient studies, with B-mode TRUS and a 1.5 T surface coil MRI. Our method has a root mean square error (RMSE) for expertly selected fiducials (consisting of the urethra, calcifications, and the centroids of CaP nodules) of 3 .39 ± 0.85 mm. © 2013 SPIE. Source

Ketterling J.,Lizzi Center for Biomedical Engineering
Proceedings of Meetings on Acoustics | Year: 2013

A high-frequency (HF) imaging system based on a custom 5-element, 40-MHz annular array was used to study cardiovascular development of mouse embryos. High-frame-rate imaging of the heart dynamics was achieved using a retrospective reconstruction method based on electrocardiogram (ECG) waveforms and respiratory gating. The ECG signals were obtained by measuring blood-flow velocities in major arteries of in-vivo mouse embryos using a custom, HF Doppler apparatus made from two, 20-MHz, single-element, PZT transducers. Co-registered M-mode data were acquired from the annular array excited with a 5-channel pulser/receiver. A synthetic-focusing algorithm was used to improve spatial resolution (< 100 μm), depth-of-field (> 10 mm) and signal-to-noise ratio (> 45 dB). This technique was used on embryos aged from 11.5 to 14.5 days and provided high-resolution, morphologically correct B-mode cine-loops of the heart chamber dynamics at frame rates of 1 kHz. The ultra-fine temporal resolution (1 ms) permitted precise quantification of the mean cardiac cycle length and detailed visualization of fast events such as opening and closing of the mitral valve. The speckle characteristics of the high-resolution images could be used to assess blood flow and to quantify myocardial strain at each developmental stage of the embryonic heart. © 2013 Acoustical Society of America. Source

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