Multi-Sensing Techniques with Ultrasound for Musculoskeletal Assessment: A Review.

The study of muscle contractions generated by the muscle-tendon unit (MTU) plays a critical role in medical diagnoses, monitoring, rehabilitation, and functional assessments, including the potential for movement prediction modeling used for prosthetic control. Over the last decade, the use of combined traditional techniques to quantify information about the muscle condition that is correlated to neuromuscular electrical activation and the generation of muscle force and vibration has grown. The purpose of this review is to guide the reader to relevant works in different applications of ultrasound imaging in combination with other techniques for the characterization of biological signals. Several research groups have been using multi-sensing systems to carry out specific studies in the health area. We can divide these studies into two categories: human-machine interface (HMI), in which sensors are used to capture critical information to control computerized prostheses and/or robotic actuators, and physiological study, where sensors are used to investigate a hypothesis and/or a clinical diagnosis. In addition, the relevance, challenges, and expectations for future work are discussed.

FPGA Implementation and Evaluation of an Approximate Hilbert Transform-Based Envelope Detector for Ultrasound Imaging Using the DSP Builder Development Tool.

In this paper, we present the FPGA implementation of an approximate Hilbert Transform-based envelope detector to compute the magnitude of the received ultrasound echo signals in real-time using a Model-based design flow. The proposed architecture exploits the negative odd-symmetry and interleaved zero-valued coefficients of a Hilbert Transform-based FIR filter to reduce hardware resource requirements and complexity. The hardware design is modeled using the DSP Builder development tool allowing the automatic generation of HDL algorithms directly from the Matlab/Simulink environment. The generated VHDL code was synthesized for an Intel Stratix IV FPGA and validated on a Terasic DE4-230 board. The accuracy and performance of the envelope detector are analyzed with real ultrasound phantom data for different filter orders, coefficient length and two filter design methods: Equiripple and Least-Squares. The normalized residual sum of squares (NRSS) and the normalized root mean square error (NRMSE) cost functions are used for comparison with the reference absolute value of the Matlab Hilbert function. The results demonstrate that the proposed method yields similar results to conventional envelope detection methods, while being simpler to implement and requiring lower computational cost.

Eigenspace generalized sidelobe canceller combined with SNR dependent coherence factor for plane wave imaging.

BACKGROUND: The eigenspace generalized sidelobe canceller (EGSC) beamformer combined with a signal-to-noise ratio (SNR) dependent coherence factor (CF) is suggested for coherent plane wave compounding (PW) imaging. Conventional CF based methods such as generalized CF and subarray CF can improve the image quality, however, they are not suitable for low SNR. On the other hand, the EGSC CF based approach can introduce improvements in image quality, however, in PW imaging is susceptible to suffer from degradation due to low SNR which leads to a poor image quality. To overcome this limitation, the SNR dependent CF method is suggested for application in such situations due to its ability to control the SNR levels. METHODS: The Field II and the Verasonics ultrasound imaging system with a L11-4v array transducer with a contrast resolution phantom were used to capture the plane wave sequences of simulation and experimental data, respectively. The performance evaluation using full width at half maximum (FWHM), contrast (CR and CNR) and the speckle statistics by using the signal to noise ratio (SNR) complemented by the Rayleigh distribution analysis was performed. In order to evaluate the performance of the [Formula: see text] (the SNR CF) beamformer, the comparison is done with particular importance to other CF-based approaches such as [Formula: see text] (the generalized CF) and, [Formula: see text] (the subarray CF) respectively. RESULTS: Taking DAS as reference, [Formula: see text] showed 30.3 and 39.5% of improvement for [Formula: see text] and [Formula: see text], respectively, when using experimental data. The proposed method also slightly outperforms the [Formula: see text] and [Formula: see text] methods for [Formula: see text], [Formula: see text], and speckle statistics assessment. CONCLUSION: The [Formula: see text] is, therefore, suitable for CPWC by improving the spatial resolution and contrast while preserving the speckle pattern.

Modeling and FPGA-based implementation of an efficient and simple envelope detector using a Hilbert Transform FIR filter for ultrasound imaging applications

Abstract Introduction Although the envelope detection is a widely used method in medical ultrasound (US) imaging to demodulate the amplitude of the received echo signal before any back-end processing, novel hardware-based approaches have been proposed for reducing its computational cost and complexity. In this paper, we present the modeling and FPGA implementation of an efficient envelope detector based on a Hilbert Transform (HT) approximation for US imaging applications. Method The proposed model exploits both the symmetry and the alternating zero-valued coefficients of a HT finite impulse response (FIR) filter to generate the in-phase and quadrature components that are necessary for the envelope computation. The hardware design was synthesized for a Stratix IV FPGA, by using the Simulink and the integrated DSP Builder toolbox, and implemented on a Terasic DE4-230 board. The accuracy of our algorithm was evaluated by the normalized root mean square error (NRMSE) cost function in comparison with the conventional method based on the absolute value of the discrete-time analytic signal via FFT. Results An excellent agreement was achieved between the theoretical simulations with the experimental result. The NRMSE was 0.42% and the overall FPGA utilization was less than 1.5%. Additionally, the proposed envelope detector is capable of generating envelope data at every FPGA clock cycle after 19 (0.48 µs) cycles of latency. Conclusion The presented results corroborate the simplicity, flexibility and efficiency of our model for generating US envelope data in real-time, while reducing the hardware cost by up to 75%.

Initial experiments of a 128-channel FPGA and PC-based ultrasound imaging system for teaching and research activities.

Although widely employed in medical diagnostic applications, most of the available commercial ultrasound (US) scanners do not always fit the needs of research users. Access to raw US data, portability, flexibility and advanced user control are essential features to explore alternative biomedical signal and imaging processing algorithms. In this paper, we present the initial results of a reconfigurable, cost-effective and modular 128-channel FPGA and PC-based US system, specifically designed for teaching and medical imaging research. The proposed system exploits the advantages of the MD2131 (Microchip Technology Inc.) beamformer source driver to generate arbitrary waveforms and the analog front-end AFE5805 (Texas Instruments Inc.) to obtain the maximum flexibility and wide data access to the various US data streams. Two applications involving plane wave excitation and delay-and-sum (DAS) beamforming are discussed. The results show that the open platform can help biomedical students and researchers to develop and evaluate different imaging strategies for medical US imaging and nondestructive testing (NDT) techniques, among other applications.

A programmable FPGA-based 8-channel arbitrary waveform generator for medical ultrasound research activities.

In modern ultrasound imaging systems, digital transmit beamformer module typically generates accurate control of the amplitude of individual elements in a multielement array probe, as well as of the time delays and phase between them, to enable the acoustic beam to be focused and/or steered electronically. However, these systems do not provide the ultrasound researchers access to transmit front-end module. This paper presents the development of a digital transmit beamformer system for generating simultaneous arbitrary waveforms, specifically designed for research purposes. The proposed architecture has 8 independent excitation channels and uses an FPGA (Field Programmable Gated Array) device for electronic steering and focusing of ultrasound beam. The system allows operation in pulse-echo mode, with pulse repetition rate of excitation from 62.5 Hz to 8 kHz, center frequency from 500 kHz to 20 MHz, excitation voltage over 100 Vpp, and individual control of amplitude apodization, phase angle and time delay trigger. Experimental results show that this technique is suitable for generating the excitation waveforms needed for medical ultrasound imaging researches.