Vantage 256

The clinical feasibility of LoSCAN was evaluated using matched DAS and LoSCAN images generated from channel data acquired from a collection of in vivo liver and fetal targets. All data were collected using a C5-2v curvilinear array on the Verasonics Vantage 256 research scanner (Verasonics, Inc., Kirkland, WA, USA) under Investigational Review Board (IRB) protocols approved by the Duke University Medical Center. Acquisitions were performed with a pulse-inversion imaging sequence using a 2.4-MHz transmit frequency, 60-mm focus, and F/2 focal geometry. Fundamental and harmonic images were formed by taking either the difference or sum of interleaved noninverted and inverted channel data and filtering across the appropriate bandwidth. LoSCAN was performed using coherence estimates averaged over the default 5 × 5 λ kernel size. Details of the in vivo data set used in this study are outlined in Table I.
Using adjacent regions of uniform speckle as reference, image quality metrics were measured from large vessels in the liver and hypoechoic organs inside and amniotic fluid around the fetus. For each set of matched images, comprising of fundamental and harmonic DAS and LoSCAN images, metrics were calculated using the same regions of interest (ROIs) selected based on the harmonic DAS image.

The USE acquisition system consisted of a Vantage 256 (Verasonics, Kirkland, WA, USA) ultrasound system with a L11–5V transducer and is shown in Fig. 1(right). The imaging and push frequencies were 7.8 MHz and the pulse duration was 128 μs. A thin layer of ultrasound gel was applied to the phantom surface. Special care was taken to ensure no bubbles were present. A shear wave was generated by the transducer at a focal point 4 mm below the surface and directly under the center of the transducer. Each push utilized 32 elements. After each measurement, the sample was removed and replaced to test repeatability. Five trials were completed for each phantom.

The 250-kHz spherically focused single-element transducer (H-115, Sonic Concepts, Bothell, WA) was placed at the bottom of a degassed water tank facing upwards and aligned to focus at each cell sample. The focal depth of the transducer was 45 mm. Cells or tumors were exposed to sine-wave ultrasound-bursts of 1000 cycles at a 30-Hz pulse repetition frequency (PRF) (duty cycle of 12%) for a total duration of 3 min. The peak negative pressure (PNP) generated in the region of interest was 500 kPa. MB oscillations in vitro were monitored by passive cavitation detection (PCD) using an unfocused and single-element transducer at a frequency of 2.25 MHz (V204-RM, Panametrics). The PCD transducer was aligned to the focus of the therapeutic 250-kHz transducer. MB distribution and destruction in tumors were monitored by real-time ultrasound imaging in contrast mode and PCD using a CL15-7 ultrasound transducer probe (128 elements, 0.18 mm pitch, Philips/ATL). Received radio frequency (RF) data were displayed and post processed by using a programmable ultrasound system Vantage 256 (Verasonics, Kirkland, WA).

A Verasonics Vantage 256 research platform (Verasonics, Bothell, WA, USA) was used to drive an L7–4 Linear array transducer with 128 elements, center frequency 5 MHz and 60% Bandwidth (L7–4, ATL Ultrasound, Bothell, WA, USA). A 3-plane wave spatial compounding acquisition imaging sequence, involving the transmission of 3 plane waves at angles θ_e (−10°, 0°, 10°) was implemented at a pulse repetition frequency of 10000 Hz. This particular acquisition sequence was chosen, because it has shown to meet the requirements for temporal resolution and imaging quality to perform PWI processing[25 (link)], while also it provides sufficiently large angles for vector Doppler imaging. The sequence was calibrated so that it satisfies the FDA safety guidelines prior to performing in vivo scans. The parameters involving ultrasound acquisitions are summarized in TABLE I.