Combined chirp coded tissue harmonic and fundamental ultrasound imaging for intravascular ultrasound: 20–60MHz phantom and ex vivo results

Abstract

The application of chirp coded excitation to pulse inversion tissue harmonic imaging can increase signal to noise ratio. On the other hand, the elevation of range side lobe level, caused by leakages of the fundamental signal, has been problematic in mechanical scanners which are still the most prevalent in high frequency intravascular ultrasound imaging. Fundamental chirp coded excitation imaging can achieve range side lobe levels lower than –60 dB with Hanning window, but it yields higher side lobes level than pulse inversion chirp coded tissue harmonic imaging (PI-CTHI). Therefore, in this paper a combined pulse inversion chirp coded tissue harmonic and fundamental imaging mode (CPI-CTHI) is proposed to retain the advantages of both chirp coded harmonic and fundamental imaging modes by demonstrating 20–60 MHz phantom and ex vivo results. A simulation study shows that the range side lobe level of CPI-CTHI is 16 dB lower than PI-CTHI, assuming that the transducer translates incident positions by 50 μm when two beamlines of pulse inversion pair are acquired. CPI-CTHI is implemented for a proto-typed intravascular ultrasound scanner capable of combined data acquisition in real-time. A wire phantom study shows that CPI-CTHI has a 12 dB lower range side lobe level and a 7 dB higher echo signal to noise ratio than PI-CTHI, while the lateral resolution and side lobe level are 50 μm finer and –3 dB less than fundamental chirp coded excitation imaging respectively. Ex vivo scanning of a rabbit trachea demonstrates that CPI-CTHI is capable of visualizing blood vessels as small as 200 μm in diameter with 6 dB better tissue contrast than either PI-CTHI or fundamental chirp coded excitation imaging. These results clearly indicate that CPI-CTHI may enhance tissue contrast with less range side lobe level than PI-CTHI.

Targeted ultrasound contrast agents for ultrasound molecular imaging and therapy

“…However, performance of these imaging methods is degraded because the excitation frequency is much higher than the resonance frequency of the MBs, attenuation is higher, and far-wall artefacts are a big challenge to overcome [112][113][114][115][116]. Therefore, improved imaging methods have been extensively studied, such as improved harmonic imaging methods [117][118][119], chirp coded excitation alone [120,121] or combined with pulse inversion [122,123]. Among the non-linear components of the MB response the SH signal has drawn much attention lately, due to its MB specificity and artefact-free characteristics.…”

Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics

“…In this study, the SNR and penetration were improved by using coded excitation and increasing the total transmitted energy, but the available transducer bandwidth is still the biggest limitation for the superharmonic imaging. The commercial ultrasound probes do not have sufficient bandwidth; however the research on transducer and CMUT technology is focusing on increasing the transducer bandwidth and reception sensitivity [9]- [11], [15], [17], [18], [53], [54]. With the availability of very broad bandwidth (>150%) and dual frequency transducers, the superharmonic imaging can become a standard modality for high resolution imaging in the future.…”

“…Use of dual frequency transducers is another option for superharmonic imaging, where Guiroy et al developed a transducer for imaging of high-order nonlinear harmonics generated by microbubbles [11]. The capacitive micromachined ultrasound transducers (CMUTs) can easily achieve > 120% fractional bandwidths, but usually have poor performance in terms of the output distortion and power [12]- [15]. However, recent developments in CMUT research showed that it is possible to fabricate very wideband transducers with small harmonic distortions on transmit and high pressure levels [16]- [18], making CMUTs suitable for superharmonic imaging.…”

Supplementary Golay pair for range side lobe suppression in dual-frequency tissue harmonic imaging

“…The resultant second-order harmonic signal can be modeled by the square of the transmit waveform in Eq. (2) [15,16]:…”