This paper describes the method of using the finite-element analysis software, PZFlex, to direct the
design of a novel ultrasound imaging system which uses conformal transducer arrays. Current
challenges in ultrasound array technology, including 2D array processing, have motivated exploration
into new data acquisition and reconstruction techniques. Ultimately, these efforts encourage a broader
examination of the processes used to effectively validate new array configurations and image formation
procedures. Commercial software available today is capable of efficiently and accurately modeling
detailed operational aspects of customized arrays. Combining quality simulated data with prototyped
reconstruction techniques presents a valuable tool for testing novel schemes before committing more
costly resources. To investigate this practice, we modeled three 1D ultrasound arrays operating multistatically instead of by the conventional phased-array approach. They are: a simple linear array, a half-circle array with 180-degree coverage, and a full circular array for inward imaging. We present the process used to create unique array models in PZFlex, simulate operation and obtain data, and subsequently generate images by inputting data into a reconstruction algorithm in MATLAB. Further discussion describes the tested reconstruction algorithm and includes resulting images.
This paper presents a method setup for high-frequency ultrasound ranging based on stepped frequency-modulated
continuous waves (FMCW), potentially capable of producing a higher signal-to-noise ratio (SNR) compared to
traditional pulse-echo signaling. In current ultrasound systems, the use of higher frequencies (10-20 MHz) to
enhance resolution lowers signal quality due to frequency-dependent attenuation. The proposed ultrasound
signaling format, step-FMCW, is well-known in the radar community, and features lower peak power, wider
dynamic range, lower noise figure and simpler electronics in comparison to pulse-echo systems.
In pulse-echo ultrasound ranging, distances are calculated using the transmit times between a pulse and its
subsequent echoes. In step-FMCW ultrasonic ranging, the phase and magnitude differences at stepped frequencies are used to sample the frequency domain. Thus, by taking the inverse Fourier transform, a comprehensive range profile is recovered that has increased immunity to noise over conventional ranging methods. Step-FMCW and pulse-echo waveforms were created using custom-built hardware consisting of an arbitrary waveform generator and dual-channel super heterodyne receiver, providing high SNR and in turn, accuracy in detection.
This paper presents the use and evaluation of stepped frequency modulated continuous waves (FMCW) in a conformal
ultrasound array-based medical imaging system currently in development. Conventional medical ultrasound systems
featuring rigid transducer arrays are highly user-dependent and require manual rotation and translation to identify and
image landmarks. Conformal ultrasound arrays have a larger aperture that can follow the surface curvature of the body,
thereby enabling increased data capture without mechanical scanning. The complexity of image reconstruction in
conformal ultrasound necessitates the use of step-FMCW, since it directly captures the frequency space thereby enabling
image reconstruction techniques to operate directly on the data, greatly simplifying and allowing for real-time
performance. Further, FMCW is advantageous in general since it requires lower peak power and produces better
receiver noise characteristics than conventional pulse-echo signaling.
In the proposed stepped FMCW signaling, packets of acoustic waves at stepped frequencies are emitted from transducers
sequentially. Phase and magnitude information from each transmitter-receiver pair of the array are captured producing
the frequency space representation of the conventional A-scan data.
The results comprise of simulations and bistatic experimental data produced by the step-FMCW signaling method, and
obtained using a multistatic transducer array with a stationary metal target. In experimental verification using, the step-
FMCW signaling and processing method gave accurate target detection, thereby demonstrating its viability in a
conformal ultrasound array and imaging system.
In this paper, we present the image reconstruction algorithm developed for a conformal ultrasound
array imaging system operating in the step frequency-modulated continuous wave (FMCW) mode. The
image formation procedure is based on a key relationship that establishes the equivalence between
pulse-echo and step FMCW modalities, and thus permits conversion between the data types. Prior step
FMCW simulation work could then be merged with pulse-echo data collected experimentally to achieve
full-scale synthesis between laboratory data and a structured theoretical framework. We describe how
an experimentally acquired pulse-echo waveform was extracted and incorporated into a step FMCW
imaging simulation to increase image accuracy and improve visualization of physical effects. With
knowledge of the transducer element positions in a multistatic configuration, image reconstruction was
achieved by mapping the complex range profiles over to a target region. Included in this paper are
images reconstructed after waveform synthesis, which feature transducer elements uniformly spaced
around a circular aperture imaging several enclosed targets with different bandwidths.