SURF imaging: In vivo demonstration of an ultrasound contrast agent detection technique

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.

Radial modulation contrast imaging using a 20-mhz single-element intravascular ultrasound catheter

“…RM signal increased with LF amplitude, as previously reported by us and others [24], [26]–[28], [36] and decreased with depth. Our results indicate that driving MBs near resonance using a phase lag of 0 (or π ) produces a strictly positive (negative) envelope-subtracted RM image and corresponded to a peak in CTR RM (Figs.…”

“…4). This corresponds to an HF/LF ratio near 10, a recommended rule of thumb for radial modulation imaging [28], which allows snapshots of the LF-driven MB oscillation to be imaged with the HF pulse. Because of the geometry of the catheter element, the LF pressure decayed rapidly with distance.…”

“…RM imaging is particularly advantageous because unlike nonlinear approaches such as second-harmonic or subharmonic imaging, it decouples the MB size from the imaging frequency, which can thus be increased for improved spatial resolution required for applications such as IVUS. RM imaging systems have been implemented with a modified clinical scanner operating at lower frequencies (7.5/0.9 MHz combination) [28] and a high-frequency ultrasound scanner (VisualSonics 770- 20/3.7 MHz combination, VisualSonics Inc., Toronto, ON, Canada) [27]. RM imaging has been reported to achieve up to 40 dB of contrast-to-tissue ratio in a porcine kidney perfusion model [28] and could be well-suited for IVUS contrast imaging.…”

Dual-frequency transducer for nonlinear contrast agent imaging

“…The LF was chosen at 20 MHz, and the HF at 40 MHz. The same year, Masoy et al have designed a five-element annular array for SURF imaging using a LF element centered at 0.9 MHz for microbubble radial modulation while four HF elements were used at 7.5 MHz for imaging [5].…”

Intravascular ultrasound contrast imaging at 25 MHz using radial modulation: A promising approach for coronary vasa vasorum imaging

“…Radial modulation (RM) imaging [7][8][9][10][11][12] is a dual frequency technique in which a low frequency (LF), also called modulation frequency, is used to manipulate the microbubble size, while high frequency (HF) scattering variations in amplitude and/or phase are monitored. One implementation of RM imaging consists of synchronizing two successive HF pulses such that they reach the microbubble, in an expanded and a compressed state, respectively, as induced by the LF pressure wave [10].…”