Potential for ultrasound transit time spectroscopy to improve axial resolution

An ultrasound wave reflected from two closely separated interfaces will suffer from phase-interference if the transit time difference is less than the propagating pulse length, thereby reducing axial resolution and image quality. The potential for pulse-echo ultrasound transit time spectroscopy (PE-UTTS) to identify signals otherwise indistinguishable due to phase-interference has recently been described. It is therefore hypothesised that PE-UTTS offers a means to improve axial resolution. In an experimental study of 1.0 mm incremental acrylic step-wedge samples immersed in water, PE-UTTS reliably identified all interfaces utilising a 1 MHz signal, whereas conventional A-scan analysis could not. Quantitative analysis was performed by calculating side-to-main lobe ratios; PE-UTTS analysis provided between 53.7% and 90.9% improvement over conventional A-scan analysis. PE-UTTS therefore offers the potential to improve ultrasound image axial resolution and fidelity, with particular benefit for scenarios where high tissue attenuation necessitates use of relatively low frequency transducers.