Stand-alone front-end system for high- frequency, high-frame-rate coded excitation ultrasonic imaging

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.

Broadband Linear High-Power Amplifier Based on the Parallel Amplification Architecture for Electromagnetic Ultrasonic Guided Wave

The linear power amplifier with high-output power in the broadband frequency is the critical component required by exciting the electromagnetic acoustic transducer (EMAT) to generate ultrasonic guided wave (UGW). The methods to realize the output of a high-power signal in the linear amplification mode and to expand the bandwidth at high-output power are seldom reported. To solve these problems, a power amplifier with differential structure is developed by using the parallel amplification architecture and the broadband feedback circuits. The proposed power amplifier uses a differential structure to suppress the even harmonic waves and remove the disruptions. Each branch of the differential structure consists of five linear power amplifier modules with output terminals connected in parallel to increase the output power. Also, the negative voltage feedback is used to extend the bandwidth of the power amplifier. The experimental results show that the −3 dB bandwidth of the amplifier is from 40 kHz to 2.5 MHz, and the transient output power is greater than 1 kW. The power amplifier can drive the EMATs to generate ultrasonic guided waves. Because of the high-output power and good linearity, the proposed power amplifier has excellent potential for EMAT UGW applications.

High frequency photoacoustic imaging for in vivo visualizing blood flow of zebrafish heart

A technique on high frame rate(28fps), high frequency co-registered ultrasound and photoacoustic imaging for visualizing zebrafish heart blood flow was demonstrated. This approach was achieved with a 40MHz light weight(0.38g) ring-type transducer, serving as the ultrasound transmitter and receiver, to allow an optic fiber, coupled with a 532nm laser, to be inserted into the hole. From the wire target study, axial resolutions of 38µm and 42µm were obtained for ultrasound and photoacoustic imaging, respectively. Carbon nanotubes were utilized as contrast agents to increase the flow signal level by 20dB in phantom studies, and zebrafish heart blood flow was successfully observed.

Pulse inversion chirp coded tissue harmonic imaging (PI-CTHI) of Zebrafish heart using high frame rate ultrasound biomicroscopy

This paper reports a pulse inversion chirp coded tissue harmonic imaging (PI-CTHI) method for visualizing small animal hearts that provides fine spatial resolution at a high frame rate without sacrificing the echo signal to noise ratio (eSNR). A 40 MHz lithium niobate (LiNbO(3)) single element transducer is employed to evaluate the performance of PI-CTHI by scanning tungsten wire targets, spherical anechoic voids, and zebrafish hearts. The wire phantom results show that PI-CTHI improves the eSNR by 4 dB from that of conventional pulse inversion tissue harmonic imaging (PI-THI), while still maintaining a spatial resolution of 88 and 110 μm in the axial and lateral directions, respectively. The range side lobe level of PI-CTHI is 11 dB lower than that of band-pass filtered CTHI (or F-CTHI). In the anechoic sphere phantom study, the contrast-to-noise ratio of PI-CTHI is found to be 2.7, indicating a 34% enhancement over conventional PI-THI. Due to such improved eSNR and contrast resolution, blood clots in zebrafish hearts can be readily visualized throughout heart regeneration after 20% of the ventricle is removed. Disappearance of the clots in the early stages of the regeneration has been observed for 7 days without sacrificing the fish.