Photoacoustic radar phase-filtered spatial resolution and co-registered ultrasound image enhancement for tumor detection.

Edem Dovlo,Wei Shi,Fei-Fei Liu,Andreas Mandelis,Bahman Lashkari

doi:10.1364/boe.6.001003

Abstract

Co-registered ultrasound (US) and frequency-domain photoacoustic radar (FD-PAR) imaging is reported for the first time in this paper. The merits of ultrasound and cross-correlation (radar) frequency-domain photoacoustic imaging are leveraged for accurate tumor detection. Commercial US imagers possess sophisticated, optimized software for rapid image acquisition that could dramatically speed-up PA imaging. The PAR image generated from the amplitude of the cross-correlation between detected and input signals was filtered by the standard deviation (SD) of the phase of the correlation signal, resulting in strong improvement of image spatial resolution, signal-to-noise ratio (SNR) and contrast. Application of phase-mediated image improvement is illustrated by imaging a cancer cell-injected mouse. A 14-15 dB SNR gain was recorded for the phase-filtered image compared to the amplitude and phase independently, while ~340 μm spatial resolution was seen for the phase PAR image compared to ~840 μm for the amplitude image.

Highlights

Over 585,000 cancer-related deaths are estimated in 2014 in the United States alone [1]
Co-registered ultrasound (US) and frequency-domain photoacoustic radar (FD-PAR) imaging is reported for the first time in this paper
The merits of ultrasound and cross-correlation frequencydomain photoacoustic imaging are leveraged for accurate tumor detection

Summary

Introduction

Over 585,000 cancer-related deaths are estimated in 2014 in the United States alone [1]. Photoacoustic (PA) imaging is an emerging non-ionizing, non-invasive imaging modality being investigated for early cancer diagnosis [3,4] It is based on the Photoacoustic (PA) effect – the generation of acoustic waves by the absorption of electromagnetic (EM) energy, which was first discovered by Alexander Graham Bell in 1880. In PA imaging, the pressure waves generated in the photoacoustic effect can be detected by conventional US array transducers that convert the mechanical acoustic waves to electrical signals, making them highly compatible with US imaging. Obtaining both US and PA images, and by extension their co-registration, is simplified since the same transducer is employed for both modalities. The concept of phase filtering [15], through which PA signal spatial resolution can be improved by filtering the amplitude with the more localized phase, is introduced to PAR imaging

PA radar imaging

Experimental set-up and imaging procedures

Results and discussion

Conclusions