Non-linear Wave Propagation and Safety Standards for Diagnostic Ultrasound Devices

Spectral analysis enhanced net (SAE-Net) to classify breast lesions with BI-RADS category 4 or higher

Early ultrasound screening for breast cancer reduces mortality significantly. The main evaluation criterion for breast ultrasound screening is the Breast Imaging-Reporting and Data System (BI-RADS), which categorizes breast lesions into categories 0-6 based on ultrasound grayscale images. Due to the limitations of ultrasound grayscale imaging, lesions with categories 4 and 5 necessitate additional biopsy for the confirmation of benign or malignant status. In this paper, the SAE-Net was proposed to combine the tissue microstructure information with the morphological information, thus improving the identification of high-grade breast lesions. The SAE-Net consists of a grayscale image branch and a spectral pattern branch. The grayscale image branch used the classical deep learning backbone model to learn the image morphological features from grayscale images, while the spectral pattern branch is designed to learn the microstructure features from ultrasound radio frequency (RF) signals. Our experimental results show that the best SAE-Net model has an area under the receiver operating characteristic curve (AUROC) of 12% higher and a Youden index of 19% higher than the single backbone model. These results demonstrate the effectiveness of our method, which potentially optimizes biopsy exemption and diagnostic efficiency.

A new PLA-Tween composited drug-carrying C60-Fe3O4 multifunctional ultrasound contrast agent based on three kinds of lesions

A PLA-Tween composited drug-carrying C60-Fe₃O₄ microbubble was designed and prepared. Using Fe₃O₄ as a targeting factor and C60 as a drug carrier, warfarin (WF), netimixin (NET) and doxorubicin (DOX) respectively were loaded on a C60-Fe₃O₄ complex through π-π conjugate effect, and C60-Fe₃O₄-WF, C60-Fe₃O₄-NET and C60-Fe₃O₄-DOX targeted drug-loading complexes were obtained. The three drug-loading complexes were respectively combined into PLA and Tween membrane material, PLA-Tween composited C60-Fe₃O₄-DOX microbubbles, PLA-Tween composited C60-Fe₃O₄-NET microbubbles and PLA-Tween composited C60-Fe₃O₄-WF microbubbles were obtained, respectively. The average particle size of PLA-Tween composited drug-carrying C60-Fe₃O₄ microbubbles was 446.4 nm, the microbubble size was uniform, and the Zeta potential was -40.5 mV which showed a good stability. The loading rates of DOX, NET and WF in PLA-Tween composited drug-carrying C60-Fe₃O₄ microbubbles were 5.58%, 8.15% and 3.37%, respectively. PLA-Tween composited C60-Fe₃O₄-DOX microbubbles could inhibit the breast cancer MDA-MB-231 cells and normal mouse fibroblast 3T3 cells, the inhibition rates were respectively 53.4% and 18.6%, which significantly reduced the toxicity of free DOX drug on the normal cells (62.2%). PLA-Tween composited C60-Fe₃O₄-NET microbubbles had a inhibitory effect on the growth of Staphylococcus aureus and Escherichia coli, and the inhibitory effect on Escherichia coli was better. PLA-Tween composited C60-Fe₃O₄-WF microbubbles could inhibit the formation of thrombus, and PT, TT and APTT were significantly prolonged. PLA-Tween composited C60-Fe₃O₄ microbubbles had a developing effect on the kidney, bladder and abdominal aorta of rabbit. Under the action of external magnetic field, the ultrasonic imaging effect of composite microbubbles was significantly enhanced.

Spectral Shift Originating from Non-linear Ultrasonic Wave Propagation and Its Effect on Imaging Resolution

An amplitude-dependent downshift in the fundamental wave spectrum of a propagating ultrasonic pulse caused by non-linear wave propagation is described. The effects of non-linearity and the associated downshift on spatial resolution are also studied. The amounts of downshift and spatial resolution are extracted from the numerically simulated beam profile based on the KZK equation. Results for a 25-MHz transducer reveal that non-linear effects can lead to 58% additional downshift in the centre frequency of a pulse compared with a linear case with downshift caused only by attenuation. This additional downshift causes about 50% degradation in axial resolution. However, as the beam becomes narrower from the non-linear effects, the overall effect of non-linearity still leads to improved lateral resolution (≤26%). Therefore, as non-linearity increases with wave pressure, it is concluded that the increase in source pressure improves lateral resolution and degrades axial resolution.

Determination of the Ultrasonic Non-linearity Parameter B/A versus Frequency for Water

For tissue characterization, it is desirable to determine B/A using high-frequency transducers. Moreover, an accurate estimate of B/A at elevated frequencies (or at least the assumption of frequency independence of B/A) is required to evaluate the safety of high-frequency systems. However, common finite-amplitude approaches become increasingly inaccurate at high frequencies. In this article, a practical variation of the finite-amplitude method is proposed which combines experiments with numerical simulations of the Khokhlov-Zabolotskaya-Kuznetsov equation and can be used at elevated frequencies. The results at low frequencies show that the proposed approach is accurate with lower uncertainties compared with the finite-amplitude method because it avoids assumptions and approximations. The measured values of B/A versus frequency for water at 2.25-20 MHz show that there is no statistically significant variation in B/A values with frequency, and therefore the assumption of frequency independence of B/A is realistic.

100 MHz bandwidth planar laser-generated ultrasound source for hydrophone calibration

High-frequency calibration of hydrophones is becoming increasingly important, both for clinical and scientific applications of ultrasound, and user safety. At present, the calibrations available routinely to the user community extend to 60 MHz. However, hydrophones that can measure beyond this are available, and ultrasonic fields often contain energy at higher frequencies, e.g., generated through nonlinear propagation of high-amplitude ultrasound used for therapeutic applications, and the increasing use of higher frequencies in imaging. Therefore, there is a need for calibrations up to at least 100 MHz, to allow ultrasonic fields to be accurately characterized, and the risk of harmful bioeffects to be properly assessed. Currently, sets of focused piezoelectric transducers are used to meet the pressure amplitude and bandwidth requirements of Primary Standard calibration facilities. However, when the frequency is high enough such that the size of the ultrasound focus becomes less than the hydrophone element's diameter, the uncertainty due to spatial averaging becomes significant, and can be as high as 20% at 100 MHz. As an alternate to piezoelectric transducers, a laser-generated ultrasound calibration source was designed, fabricated, and characterized. The source consists of an optically absorbing carbon-polymer nanocomposite excited by a large-diameter 1064 nm laser pulse of 2.6 ns duration. Peak pressure amplitudes of several Mega-Pascal were readily achievable, and the signal contained measurable frequency components up to 100 MHz. The variation in the pressure amplitudes was less than 2% from its mean over a three-hour test period. The ultrasound beam was sufficiently broad that the uncertainties due to spatial averaging were negligible.