A New Dynamic Complex Baseband Pulse Compression Method for Chirp-Coded Excitation in Medical Ultrasound Imaging

Phase aberration correction for ultrasound imaging guided extracorporeal shock wave therapy (ESWT): Feasibility study

Image guidance of extracorporeal shock wave therapy (ESWT) is important to enhance its efficacy while lowering pain in patients. Real-time ultrasound imaging is an appropriate modality for image guidance, but its image quality substantially reduces due to severe phase aberration from the different speed of sound between soft tissues and a gel pad, which is utilized to control a therapeutic focal point in ESWT. This paper presents a phase aberration correction method for improving image quality in the ultrasound imaging guided ESWT. To correct an error from phase aberration, a time delay based on a two-layer model with different speeds of sound is calculated for dynamic receive beamforming. For the phantom and in vivo studies, a rubber type gel pad (i.e., 1400 m/s) with a specific thickness (3 or 5-cm) was placed on the top of soft tissue and full scanline RF data were acquired. In the phantom study, with phase aberration correction, image quality was highly increased compared to image reconstructions with a fixed speed of sound (i.e., 1540 or 1400 m/s), i.e., 1.1 vs. 2.2 and 1.3 mm in -6dB lateral resolution and 0.64 vs. 0.61 and 0.56 in contrast-to-noise ratio (CNR), respectively. From an in vivo musculoskeletal (MSK) imaging, the phase aberration correction method provided a clearly improved depiction of muscle fibers in a rectus femoris region. These results indicate that the proposed method enables effective imaging guidance of ESWT by improving image quality of ultrasound imaging in real-time.

Clinical Applications of B-Flow Ultrasound: A Scoping Review of the Literature

Coded excitation ultrasound investigations have the potential to augment the resolution, increase the efficiency, and expand the possibilities of noninvasive diagnostic imaging. B-Flow ultrasound, a type of digitally encoded imaging, was developed more than 20 years ago with the aim to optimize the visualization of blood flow. It has been investigated for a plethora of applications so far. A scoping review regarding its clinical applications was conducted based on a systematic literature research. B-Flow has been investigated in various anatomic locations and pathologies. However, previous research is limited by small sample sizes, the rare occurrence of elaborate study designs, the reliance on subjective reports and qualitative data, as well as several potential biases. While results are in general promising, it should therefore still be considered an emerging technology. Nevertheless, the limitations can be addressed in future research and the potential to expand its applications make B-Flow an interesting candidate for further investigations.

Sensitivity Enhancement Using Chirp Transmission for an Ultrasound Arthroscopic Probe

Meniscal tear in the knee joint is a highly common injury that can require an ablation. However, the success rate of meniscectomy is highly impacted by difficulties in estimating the thin vascularization of the meniscus, which determines the healing capacities of the patient. Indeed, vascularization is estimated using arthroscopic cameras that lack of high sensitivity to blood flow. Here, we propose an ultrasound method for estimating the density of vascularization in the meniscus during surgery. This approach uses an arthroscopic probe driven by ultrafast sequences. To enhance the sensitivity of the method, we propose to use a chirp-coded excitation combined with a mismatched compression filter robust to the attenuation. This chirp approach was compared to a standard ultrafast emission and a Hadamard-coded emission using a flow phantom. The mismatched filter was also compared to a matched filter. Results show that, for a velocity of a few millimeters per second, the mismatched filter gives a 4.4-10.4-dB increase of the signal-to-noise ratio (SNR) compared to the Hadamard emission and a 3.1-6.6-dB increase compared to the matched filter. Such increases are obtained for a loss of axial resolution of 13% when comparing the point spread functions (PSFs) of the mismatched and matched filters. Hence, the mismatched filter allows increasing significantly the probe capacity to detect slow flows at the cost of a small loss in axial resolution. This preliminary study is the first step toward an ultrasensitive ultrasound arthroscopic probe able to assist the surgeon during meniscectomy.

Signal-to-noise ratio of diverging waves in multiscattering media: Effects of signal duration and divergence angle

In this paper, SNR maximization in coded diverging waves is studied, and experimental verification of the results is presented. Complementary Golay sequences and binary phase shift keying modulation are used to code the transmitted signal. The SNR in speckle and pin targets is maximized with respect to chip signal length. The maximum SNR is obtained in diverging wave transmission when the chip signal is as short a duration as the array permits. We determined the optimum diverging wave profile to confine the transmitted ultrasound energy in the imaging sector. The optimized profile also contributes to the SNR maximization. The SNR performances of the optimized coded diverging wave and conventional single-focused phased array imaging are compared on a single frame basis. The SNR of the optimized coded diverging wave is higher than that of the conventional single-focused phased array imaging at all depths and regions.

Non-contact phase coded excitation of ultrasonic Lamb wave for blind hole inspection

The combination of air-coupled ultrasonic testing (ACUT) and ultrasonic Lamb wave is featured with long-distance propagation and high sensitivity to discontinuities, which is a promising method for rapid and accurate inspection of plate-like materials and lightweighted structures. However, dispersive nature of Lamb wave, signal attenuation plus inevitable noises would lead to low signal-to-noise ratio (SNR). To address this problem, phase coded excitation and pulse compression technique are proposed in this paper to achieve higher SNR by over 10 dB in received signals. 13-bit and 1-carrier-period Barker code is employed as both main lobe peak and Peak Side-lobe Level (PSL) are relatively high. It is demonstrated that A0 mode Lamb wave has good localization ability for defects based on these SNR-enhanced signals. Furthermore, Damage Index (DI) and modified Reconstruction Algorithm for the Probabilistic Inspection of Damage (RAPID) are applied to realize ultrasonic imaging based defect evaluation. Results show that the imaging results agree well with the actual artificial defects in terms of size and shape. Lamb-wave-based air-coupled ultrasonic testing, combined with DI and ultrasonic imaging algorithm, could be a potential way in the NDT of lightweighted structures.

Research on Golay-coded excitation in real-time imaging of high frequency ultrasound biomicroscopy

High frequency ultrasonic imaging provides clinicians with high-resolution diagnostic images and more accurate measurement results. The technique is now widely used in ophthalmology, dermatology, and small animal imaging. However, since ultrasonic attenuation in tissue increases rapidly with increasing frequency, the depth of detection of high frequency ultrasound in tissue is limited to a few millimeters. In this paper, a novel method of using Golay-coded excitation as a replacement for conventional single-pulse excitation in high frequency ultrasound biomicroscopy was proposed, and real-time imaging was realized. While maintaining the transmission voltage and image resolution unchanged, the detection depth can be effectively improved. The ultrasonic transmission frequency is 30 MHz and the transmission voltage is ± 60 V p-p. In this study, 4-bit, 8-bit, and 16-bit coding sequences and decoding compression were used. To verify the effectiveness of the coding sequence in real-time imaging of ultrasound biomicroscopy, we designed a 10-μm diameter line target echo experiment, an ultrasound phantom experiment, and an in vitro porcine eye experiment. The experimental results show that the code/decode method of signal processing can not only maintain a resolution consistent with that of single-pulse transmission, but can also improve the detection depth and signal-to-noise ratio.

Orthogonal Chirp Coded Excitation in a Capacitive Micro-machined Ultrasonic Transducer Array for Ultrasound Imaging: A Feasibility Study

It has been reported that the frequency bandwidth of capacitive micro-machined ultrasonic transducers (CMUTs) is relatively broader than that of other ceramic-based conventional ultrasonic transducers. In this paper, a feasibility study for orthogonal chirp coded excitation to efficiently make use of the wide bandwidth characteristic of CMUT array is presented. The experimental result shows that the two orthogonal chirps mixed and simultaneously fired in CMUT array can be perfectly separated in decoding process of the received echo signal without sacrificing the frequency bandwidth each chirp. The experimental study also shows that frequency band-divided orthogonal chirps are successfully compressed to two short pulses having the -6 dB axial beam-width of 0.26- and 0.31-micro second for high frequency and low frequency chirp, respectively. B-mode image simulations are performed using Field II to estimate the improvement of image quality assuming that the orthogonal chirps designed for the experiments are used for simultaneous transmission multiple-zone focusing (STMF) technique. The simulation results show that the STMF technique used in CMUT array can improve the lateral resolution up to 77.1% and the contrast resolution up to 74.7%, respectively. It is shown that the penetration depth also increases by more than 3 cm.

Diverging wave compounding with spatio-temporal encoding using orthogonal Golay pairs for high frame rate imaging

Golay coded excitation for diverging wave compounding (DWC) has been demonstrated to increase the signal-to-noise ratio (SNR) and contrast for high frame rate cardiac imaging. However, the complementary codes need to be transmitted in two consecutive firings for decoding, which reduces the frame rate by 2 folds. This paper proposes an orthogonal Golay pairs coded (OGPs-coded) DWC sequence to overcome this problem, which implements spatio-temporal encoding for DWC. Two diverging waves (DWs) at different steering angles coded by an orthogonal Golay pair are transmitted simultaneously, thus compensating the frame rate reduction caused by transmissions of complementary codes. The two DWs can be separated based on the orthogonality of Golay pairs. To test the feasibility of the proposed sequence, we performed simulations of point targets and tissue phantoms in both static and moving states. Compared with non-coded DWC at the same frame rate, OGPs-coded DWC obtains comparable resolution, SNR gains of 7.5-10 dB and contrast gains of 3-5 dB. The OGPs-coded DWC sequence was also tested experimentally on a tissue-mimicking phantom. Compared with non-coded DWC, OGPs-coded DWC achieves improvements in the SNR (3-6 dB) and contrast (1-2 dB). Preliminary in vivo results show brighter myocardium and larger penetration depth with the proposed method. The proposed OGPs-coded DWC sequence has potential for high frame rate and high quality cardiac imaging.