Dynamic Apodization Research Articles

Contrast Mechanisms for Tumor Cells by High-frequency Ultrasound

Scanning Acoustic Microscopy (SAM) is a powerful technique for both the non-destructive determination of mechanical and elastic properties of biological specimens and for the ultrasonic imaging at a micrometer resolution. The implication of biomechanical properties during the onset and progression of disease has been established rendering a profound understanding of the relationship between mechanoelastic and biochemical signaling at a molecular level crucial. Computer simulation algorithms were developed for the generation of images and the investigation of contrast mechanisms in high-frequency and ultra-high frequency SAM. Furthermore, we determined the mechanical and elastic properties of HeLa and MCF-7 cells. Algorithms for simulatingV(z)responses were developed based on the ray and wave theory (angular spectrum). Theoretical simulations for high-frequency SAM array designs were performed with the Field II software. In these simulations, we applied phased array beam formation and dynamic apodization and focusing. The purpose of our transducer simulations was to explore volumetric imaging capabilities. The novel transducer arrays designed in this research aim at improving the performance of SAM systems by introducing electronic steering and hence, allowing for the 4D imaging of cells and tissues.

Transducer designs and simulations for high frequency scanning acoustic microscopy for applications in exploring contrast mechanism and the mechanical properties of biological cells

Scanning acoustic microscopy (SAM) has been extensively accepted and utilized for acoustical cellular and tissue imaging including measurements of the mechanical and elastic properties of biological specimen. SAM provides superb advantages: it is a noninvasive method; it can measure mechanical properties of biological cells or tissues; and fixation/chemical staining is not necessary. The first objective of this research is to develop a program for simulating the images and contrast mechanism obtained by high-frequency SAM. Computer simulation algorithms based on Matlab® were built for simulating the images and contrast mechanism. The mechanical properties of HeLa and MCF-7 cells were computed from the V(z) measurement data. Algorithms for simulating V(z) responses involved calculation of the reflectance function and were created based on ray theory and wave theory. The second objective is to design transducer arrays for SAM. Theoretical simulations based on Field II programs of the high frequency ultrasound array designs were performed to enhance image resolution and volumetric imaging capabilities. The new transducer array design will be state-of-the-art in improving the performance of SAM by electronic scanning and potentially providing a four-dimensional image of the specimen. Phased array beam forming and dynamic apodization and focusing were employed in the simulations.

Ultrafast diffraction of tightly focused waves with spatiotemporal stabilization

Experimental studies of ultrafast beam shaping have come about from the need to compensate diffraction-induced dispersive effects in femtosecond laser beams. From a theoretical point of view, chromatic matching of diffracted spherical waves in the vicinity of the geometrical focus is attained by applying conveniently dispersive boundary conditions in the far-field zone, a subject thoroughly analyzed in the paraxial regime. For applications demanding high spatial resolution, however, high-numerical-aperture microscope objectives may be employed instead and would lead to nonparaxiality of the focal wavefields. These circumstances have motivated our investigation. Concretely we report on prerequisites for spectral invariance extended to wide-angle geometries, which provides stabilization of the spatiotemporal response in the Fourier plane. In this context, general boundary conditions are given in the frame of the Debye representation of wavefields. Features of this sort of dynamic apodization (spatial filtering) leading to perfect achromatization are described in detail.

Method and apparatus for receive beamformer system

The present invention includes a fully programmable plurality of multi-channel receivers, each receiver having a digital multi-channel receive processor and a local processor control. Each receive processor includes a first decimator, time delay memory, second decimator, and complex multiplier. The receive beamformer is a computationally efficient system which is programmable to allow processing mode trade-offs among receive frequency, receive spatial range resolution, and number of simultaneous beams received. Each local control receives focusing data from a central control computer and provides final calculation of per-channel dynamic focus delay, phase, apodization, and calibration values for each receiver signal sample. Further, this invention includes a baseband multi-beam processor which has a phase aligner and a baseband filter for making post-beamformation coherent phase adjustments and signal shaping, respectively. The phase aligner maintains scan-line-to-scan-line coherency, such as would be required for coherent image formation. Accordingly, the present system can operate under multiple imaging formats, using a variety of transducers and a variety of modes such as B-mode, M-mode, and color Doppler flow mode.

Two‐dimensional phased array of ultrasonic transducers

A two-dimensional ultrasonic phase array is a rectilinear approximation to a circular aperture and is formed by a plurality of transducers, arranged substantially symmetrical about both a first (X) axis and a second (Y) axis and in a plurality of subarrays, each extended in a first direction (i.e. parallel to the scan axis X) for the length of a plurality of transducers determined for that subarray, but having a width of a single transducer extending in a second, orthogonal (the out-of-scan-plane, or Y) direction to facilitate dynamic focussing and/or dynamic apodization. Each subarray transducer is formed of a plurality of sheets (part of a 2-2 ceramic composite) all electrically connected in parallel by a transducer electrode applied to juxtaposed first ends of all the sheets in each transducer, while a common electrode connects the remaining ends of all sheets in each single X-coordinate line of the array.