Two-sided residual refocusing for an acoustic lens-based photoacoustic imaging system

Abstract

In photoacoustic (PA) cameras, an acoustic lens-based system can form a focused image of an object plane. A real-time C-scan PA image can be formed by simply time gating the transducer response. While most of the focusing action is performed by the lens, residual refocusing is needed to image multiple depths with high resolution simultaneously. However, a refocusing algorithm for a PA camera has not been studied so far in the literature. In this work, we reformulate this residual refocusing problem for a PA camera into a two-sided wave propagation from a planar sensor array. One part of the problem deals with forward wave propagation while the other deals with time reversal. We have chosen a fast Fourier transform (FFT) based wave propagation model for the refocusing to maintain the real-time nature of the system. We have conducted point spread function (PSF) measurement experiments at multiple depths and refocused the signal using the proposed method. The full width at half maximum (FWHM), peak value and signal to noise ratio (SNR) of the refocused PSF is analyzed to quantify the effect of refocusing. We believe that using a two-dimensional transducer array combined with the proposed refocusing can lead to real-time volumetric imaging using a PA camera.

Multiview spatial compounding using lens-based photoacoustic imaging system

“…Our proposed re-focusing algorithm provides an additional improvement to the PSF when it is combined with SC [17] . If it is applied alone after the PA camera data is acquired, the PSF gets equalized at all depths, approaching its best value at 2 F (see Fig.…”

“…In addition, we investigate the use of another technique we have developed that can be applied to each of the angular views of the PA camera before SC. The details of this technique, which we will refer to henceforth as residual refocusing, can be found in [17] . The additional blurring or defocusing of depth planes in front and behind the optimally focused plane that we mentioned earlier, can be reversed by this technique.…”

Approaching closed spherical, full-view detection for photoacoustic tomography

“…Other proposed solutions have included the use of acoustic reflectors to multiply the physical detectors, 18 – 22 acoustic backscatterers as virtual detectors, 23 and integrating line arrays. 24 Furthermore, substantial research has been conducted to improve reconstruction methods for limited-view cases.…”

Annular illumination photoacoustic probe for needle guidance in medical interventions

“…3,4 Moreover, relatively high blood absorption and hyper-vascularisation of tumors have shown to offer good contrast in PA imaging. 5,6 Most PA systems proposed so far use extracorporeal illumination approach where the light illumination and acoustic detection is done at the surface of the skin. A fundamental constraint of extracorporeal PA imaging is the limited imaging depth in absorbing tissue.…”