Photoacoustic computed tomography without accurate ultrasonic transducer responses

Abstract

Photoacoustic computed tomography (PACT) holds great promise for biomedical imaging. When the imaging system employs conventional piezoelectric ultrasonic transducers, the ideal photoacoustic (PA) signals are degraded by the transducers' acousto-electric impulse responses (EIRs) during the measurement process. If unaccounted for, this can degrade the accuracy of the reconstructed image. In principle, the effect of the EIRs on the measured PA signals can be ameliorated via deconvolution; images can be reconstructed subsequently by application of a reconstruction method that assumes an idealized EIR. Alternatively, the effect of the EIR can be incorporated into an imaging model and implicitly compensated for during reconstruction. In either case, the efficacy of the correction can be limited by errors in the assumed EIRs. In this work, a joint optimization approach to PACT image reconstruction is proposed for mitigating errors in reconstructed images that are caused by use of an inaccurate EIR. A variable projection method is employed to refine the measured EIR during the process of reconstructing the sought-after absorbed optical energy density. Computer-simulation and experimental studies are conducted to investigate the numerical properties of the method and demonstrate its value for mitigating image distortions and enhancing the visibility of fine structures.

Pushing the boundaries of optoacoustic microscopy by total impulse response characterization

“…In this way, the first complete optoacoustic microscopy TIR characterization has been also experimentally achieved. While TIR determination and correction methods have been considered for optoacoustic macroscopy 28,[41][42][43][44][45] , no such method has been so far developed for optoacoustic microscopy. We show herein that acquiring and using the TIR for correcting microscopy images brings essential performance improvements in the image quality and ability to resolve structures along depth.…”

“…As the optoacoustic PSF is defined laterally by the optical focus and, therefore, independent of acoustic properties, accurate correction would mainly affect the SNR and the axial projection of the data. The optoacoustic PSF constitutes in this regard the 3D spatial representation of signals from a point source incorporating (1) the optical impulse response describing the characteristics of optical excitation, (2) the spatial impulse response (SIR) capturing the spatiallydependent signal modification by the ultrasound detection, and (3) the spatially-invariant electric impulse response (EIR) embodying the signal digitization [28][29][30] . The convolution of these contributions is collectively termed the total impulse response (TIR), a 4D array (x, y, z, t) containing time-resolved optoacoustic impulse responses at all accessible positions.…”

Signal and Image Processing in Biomedical Photoacoustic Imaging: A Review

“…The SOAPs are produced by scanning an optical focus on an axially-translatable 250 nm gold layer. This TIR method includes the optical impulse response describing the characteristics of optical excitation, the spatial impulse response (SIR) capturing the spatiallydependent signal modification by the ultrasound detection, and the spatially-invariant electric impulse response (EIR) embodying the signal digitization [113][114][115]. Using a spatially dependent TIR-correction improved the SNR by >10 dB and the axial resolution by ~30%.…”

Image reconstruction for endoscopic photoacoustic tomography including effects of detector responses

“…Later, various methods for numerically compensating for the transducer effects in image reconstruction algorithms were explored. 12,[29][30][31][32][33][34][35][36][37][38] These methods are generally computationally burdensome because of their nature of iterative least-squares minimization. However, incorporating far-field approximation into the forward model can reduce the computational complexity.…”