No abstract

A dual-band method for ultrasound contrast agent detection is demonstrated in vivo in an animal experiment using pigs. The method is named Second -order UltRasound Field Imaging, abbreviated SURF Imaging. It relies on simultaneously transmitting two ultrasound pulses with a large separation in frequency. Here, a low-frequency pulse of 0.9 MHz is combined with a high-frequency pulse of 7.5 MHz. The low-frequency pulse is used to manipulate the properties of the contrast agent, and the high frequency pulse is used for high-resolution contrast detection and imaging. An annular array capable of transmitting the low- and high-frequency pulses simultaneously was constructed and fitted to a mechanically scanned probe used in a GE Vingmed System 5 ultrasound scanner. The scanner was modified and adapted for the dual-band transmit technique. In-house software was written for post-processing of recorded IQ-data. Contrast-processed B-mode images of pig kidneys after bolus injections of 1 mL of Sonovuer are presented. The images display contrast detection with contrast-to-tissue ratios ranging from 15-40 dB. The results demonstrate the potential of SURF Imaging as an ultrasound contrast detection technique for clinically high ultrasound frequencies. This may allow ultrasound contrast imaging to be available for a wide range of applications.

Objective Clinical assessments and laser Doppler perfusion measurements (LDPM) of skin microcirculation have limited value, as they fail to capture events regulated by local metabolic needs at a papillary capillary level. This study aimed to examine the ability of computer‐assisted video microscopy (CAVM) and diffuse reflectance spectroscopy (DRS) to assess skin nutritive perfusion—compared to LDPM. Methods Healthy volunteers (n = 10) were examined after (≈1 and ≈24 h) an incision (5 × 1 mm) on the forearm, at 0.1 mm (only with CAVM), 2−3 mm, and 30 mm from the trauma. Results No changes were detected by CAVM after ≈1 h. After ≈24 h, 0−1 mm from the trauma, both CAVM parameters were increased: functional capillary density (capillary crossings/mm, 11.8 ± 1.4 vs. 7.3 ± 1.2, p < .01) and capillary flow velocities (CFV, %capillaries with brisk flow, 10 ± 6.8 vs. 1 ± 1, p < .01). At a distance of 2−3 mm, only CFV was increased (6.2 ± 6.1 vs. 1 ± 1, p < .05). DRS and LDPM measurements increased 2−3 mm from the trauma line in relation to baseline after both ≈1 and ≈24 h, that is, with DRS (%microvascular oxygen saturation): 45.8 ± 7.4% (baseline), 70.0 ± 12.5% (≈1 h), and 73.1 ± 10.4% (≈24 h), p < .01 and with LDPM (a.u.): 7.2 ± 2.5 (baseline), 28.3 ± 18.7 (≈1 h), and 45.9 ± 16.3 (≈24 h), p < .01. Conclusions ≈24 h after skin trauma, an increased function of the nutritive papillary capillaries can be detected by CAVM.

Ultrasound exposure parameters that maximize drug release from liposomes were studied using two ultrasound transducers (300 kHz and 1 MHz). Variations in acoustic peak negative pressure (260 -2037 kPa), temporary average intensity (0.05 -6.08 W cm 2 ), mechanical index (MI) (0.4 -3.0), insonation time (0.5 -20 minutes), pulse repetition frequency (PRF) (100 -1000 Hz) and pulse length (0.05 -0.4 ms) were studied. Drug release was more efficient at 300 kHz compared to 1 MHz. A certain threshold in peak negative pressure had to be overcome to obtain drug release, and the pressure needed was lower at 300 kHz (0.72 MPa) than at 1 MHz (1. 39 MPa) which corresponds to MI values of 1.30 and 1.39 respectively. Above the threshold the release increased with increasing temporal average intensity, peak negative pressure, MI and duty cycle (i.e PRF and pulse length). The release was found to increase with exposure time, where the profile followed a first-order kinetics. The first-order rate constant for the release increased linearly with MI. This indicates that the release of the drug from liposomes was caused by mechanical rather than thermal effects. The results demonstrate that ultrasound has a potential in enhancing drug release from liposomes and can potentially improve cancer therapy.

In this article, acoustic propagation effects of dual-frequency wide-band excitation pulses in a focused ultrasound system are demonstrated in vitro. A designed and manufactured dual-frequency band annular array capable of transmitting 0.9/7.5 MHz center frequency wide-band pulses was used for this purpose. The dual-frequency band annular array, has been designed using a bi-layer piezo-electric stack. Water tank measurements demonstrate the function of the array by activating the low- and high-frequency layers individually and simultaneously. The results show that the array works as intended. Activating the low- and high-frequency layers individually, results in less than -50 dB signal level from the high- and low-frequency layers respectively. Activating both layers simultaneously, produce a well defined dual-frequency pulse. The presence of the low-frequency pulse leads to compression, expansion, and a time delay of the high-frequency pulse. There is a phase shift between the low- and high-frequency pulse as it propagates from the array to the focus. This makes the latter described effects also dependent on the array configuration. By varying the low-frequency pressure, a shift of up to 0.5 MHz in center frequency of a 8.0 MHz transmitted high-frequency pulse is observed at the array focus. The results demonstrate the high propagation complexity of dual-frequency pulses.