To understand the pathogenic processes for infectious bacteria, appropriate research tools are required for replicating and characterizing infections. Fluorescence and bioluminescence imaging have primarily been used to image infections in animal models, but optical scattering in tissue significantly limits imaging depth and resolution. Photoacoustic imaging, which has improved depth-to-resolution ratio compared to conventional optical imaging, could be useful for visualizing melA-expressing bacteria since melA is a bacterial tyrosinase homologue which produces melanin. Escherichia coli-expressing melA was visibly dark in liquid culture. When melA-expressing bacteria in tubes were imaged with a VisualSonics Vevo LAZR system, the signal-to-noise ratio of a 9×dilution sample was 55, suggesting that ∼20 bacteria cells could be detected with our system. Multispectral (680, 700, 750, 800, 850, and 900 nm) analysis of the photoacoustic signal allowed unmixing of melA-expressing bacteria from blood. To compare photoacoustic reporter gene melA (using Vevo system) with luminescent and fluorescent reporter gene Nano-lantern (using Bruker Xtreme In-Vivo system), tubes of bacteria expressing melA or Nano-lantern were submerged 10 mm in 1% Intralipid, spaced between <1 and 20 mm apart from each other, and imaged with the appropriate imaging modality. Photoacoustic imaging could resolve the two tubes of melA-expressing bacteria even when the tubes were less than 1 mm from each other, while bioluminescence and fluorescence imaging could not resolve the two tubes of Nano-lantern-expressing bacteria even when the tubes were spaced 10 mm from each other. After injecting 100-μL of melA-expressing bacteria in the back flank of a chicken embryo, photoacoustic imaging allowed visualization of melA-expressing bacteria up to 10-mm deep into the embryo. Photoacoustic signal from melA could also be separated from deoxy- and oxy-hemoglobin signal observed within the embryo and chorioallantoic membrane. Our results suggest that melA is a useful photoacoustic reporter gene for visualizing bacteria, and further work incorporating photoacoustic reporters into infectious bacterial strains is warranted.

A novel 3D photoacoustic imaging technique is experimentally demonstrated using a 64×64 element bias-sensitive crossed-electrode relaxor array. This technique allows for large 2D arrays to receive across all elements while using minimal channel counts. Hadamard-bias patterns are applied to column electrodes while signals are measured from row electrodes. Photoacoustic signals are measured from a crossed-wire phantom in an intralipid scattering medium. The Hadamard-bias-encoded imaging scheme showed a signal-to-noise (SNR) of 25.3 dB, while the single-column biasing strategy (or identity-matrix-bias pattern) showed a SNR of 8.8 dB.

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A combined photoacoustic-ultrasound (PAUS) tomography system is introduced using ring-array and novel aperture encoding schemes. The ultrasound subsystem is able to achieve diffraction limited half-wavelength isotropic in-plane spatial resolution unlike previous systems. S-sequence aperture encoding improves signal-to-noise ratio (SNR) for the ultrasound tomography (UST) subsystem. We measured an average resolution of [Formula: see text] for S-sequence UST and a resolution of [Formula: see text] for photoacoustic tomography. We were able to measure SNR improvement using S-sequence spatial encoding using tissue-mimicking phantoms, and we displayed a composite PAUS phantom image.

Recently, -norm based reconstruction approaches have been used with linear array systems to improve photoacoustic resolution and demonstrate undersampled imaging when there is sufficient sparsity in some domain. However, such approaches have yet to beat the half-wavelength resolution limit. In this paper, the ability to beat the half-wavelength diffraction limit is demonstrated using a 5 MHz ring array photoacoustic tomography system and -norm based reconstruction approaches. We used the array system to image wire targets at 2 3 depth in both intralipid scattering solution and water. The minimum observable separation was estimated as 70 10 , improving on the half-wavelength resolution limit of 145 . This improvement was demonstrated even when using a random projection transform to reduce data by 99 , enabling substantially faster reconstruction times. This is the first photoacoustic tomography approach capable of beating the half-wavelength resolution limit with a single laser shot.