Resolution Photoacoustic Microscopy Research Articles

Parallel diffusion models promote high detail-fidelity photoacoustic microscopy in sparse sampling

Reconstructing sparsely sampled data is fundamental for achieving high spatiotemporal resolution photoacoustic microscopy (PAM) of microvascular morphology in vivo. Convolutional networks (CNN) and generative adversarial networks (GAN) have been introduced to high-speed PAM, but due to the use of upsampling in CNN-based networks to restore details and the instability in GAN training, they struggle to learn the entangled microvascular network structure and vascular texture features, resulting in only achieving low detail-fidelity imaging of microvascular. The diffusion models is richly sampled and can generate high-quality images, which is very helpful for the complex vascular features in PAM. Here, we propose an approach named parallel diffusion models (PDM) with parallel learning of Noise task and Image task, where the Noise task optimizes through variational lower bounds to generate microvascular structures that are visually realistic, and the Image task improves the fidelity of the generated microvascular details through image-based loss. With only 1.56% of fully sampled pixels from photoacoustic human oral data, PDM achieves an LPIPS of 0.199. Additionally, using PDM in high-speed 16x PAM prevents breathing artifacts and image distortion issues caused by low-speed sampling, reduces the standard deviation of the Row-wise Self-Correlation Coefficient, and maintains high image quality. It achieves high confidence in reconstructing detailed information from sparsely sampled data and will promote the application of reconstructed sparsely sampled data in realizing high spatiotemporal resolution PAM.

Fourier photoacoustic microscope improved resolution on single-pixel imaging.

A new single-pixel Fourier photoacoustic microscopy (PAM), to the best of our knowledge, is proposed to improve the resolution and region of interest (ROI) of an acquired image. In the previous structure of single-pixel Fourier PAM, called spatially invariant resolution PAM (SIR-PAM), the lateral resolution and ROI are limited by the digital micromirror device (DMD) pixel size and the number of pixels. This limitation is overcome here through illuminating fixed angle interfering plane waves, changing the fringe frequency via varying the frequency of the laser source. Given that the fringe sinusoidal patterns here can be produced by two mirrors, the DMD usage can be omitted. In this way, the fringe frequency can be changed in a wider spectrum, making it possible to capture a wider spectral bandwidth and thus a higher-resolution image. Also, the removal of the ROI limitation results in a high-resolution frequency-swept PAM structure. Monte Carlo simulations show 1.7 times improvement in lateral resolution compared to SIR-PAM based on the point-spread function and full-width-at-half-maximum.

High-speed simultaneous multiscale photoacoustic microscopy

.Photoacoustic microscopy (PAM) is a fast-growing biomedical imaging technique that provides high-resolution in vivo imaging beyond the optical diffusion limit. Depending on the scalable lateral resolution and achievable penetration depth, PAM can be classified into optical resolution PAM (OR-PAM) and acoustic resolution PAM (AR-PAM). The use of a microelectromechanical systems (MEMS) scanner has improved OR-PAM imaging speed significantly and is highly beneficial in the development of miniaturized handheld devices. The shallow penetration depth of OR-PAM limits the use of such devices for a wide range of clinical applications. We report the use of a high-speed MEMS scanner for both OR-PAM and AR-PAM. A high-speed, wide-area scanning integrated OR-AR-PAM system combining MEMS scanner and raster mechanical movement was developed. A lateral resolution of and penetration depth in vivo was achieved using OR-PAM at 586 nm, whereas a lateral resolution of and penetration depth of in vivo was achieved using AR-PAM at 532 nm.

ADMM based low-rank and sparse matrix recovery method for sparse photoacoustic microscopy

Photoacoustic microscopy (PAM) has evolved into a new promising medical imaging tool available for both in vivo surficial and deep-tissue imaging with a high spatial resolution. However, the long data acquisition time has made real-time imaging highly challenging. This paper presents an Alternating Direction Method of Multipliers (ADMM) based low-rank and sparse matrix recovery method for a sparse optical-scanning PAM system to realize fast PAM vascular imaging.For our system, an x-y galvanometer scanner is used to achieve compressive sampling, and the associated image recovery process is formulated as a matrix completion problem. The sparse scanning scheme might be easy to integrate with several other optical-resolution PAM modalities. Further, the sparse constraint (the total variation norm) and the low-rank constraint (nuclear norm) are combined for solving the optimization program under ADMM framework for matrix recovery in order to achieve better PAM image recovery even for images that are not well-approximated by their low-rank components.A prototype PAM system has been implemented and the recovery method has been validated. From both visual effects and quantitative parameters, such as PSNR, SSIM, Rerr and MSE, comparable image qualities with conventional full sampling optical resolution PAM could be acquired by just half of the data acquisition time. Besides, the ADMM based low-rank and sparse matrix recovery method could show better results than GoDec. The obtained results demonstrate the preclinical and clinical potential of sparse PAM system in investigating vascular diseases.

Simplified method for ultra high-resolution photoacoustic microscopy via transient absorption.

Photoacoustic microscopy (PAM) is a hybrid imaging modality that combines optical illumination with ultrasonic detection to achieve absorption contrast imaging of endogenous and exogenous chromophores. Optical resolution PAM achieves high lateral-resolution by tightly focusing the excitation light; however the axial resolution is still dependent upon the bandwidth of the ultrasonic transducer. As a result, PAM images have highly asymmetric voxels with submicron lateral resolution and axial resolution typically limited to tens of microns. We have previously reported on a resonant multiphoton approach to PAM called transient absorption ultrasonic microscopy (TAUM), which enables high axial resolution by frequency encoding the photoacoustic signal at the overlap of a pump and a probe beam. This approach enables photoacoustic imaging with subcellular resolution on par with other multiphoton microscopy techniques. Here, we report on an innovation that enables TAUM imaging with a much less sophisticated optical system than previously reported. If we allow the time delay between the pump and probe to collapse to zero, the pump and probe optical paths can be combined. An amplitude modulator in the single beam path is sufficient to encode the TAUM signal at the second harmonic of the modulation frequency. The resulting system is essentially a standard optical resolution PAM system that incorporates an amplitude modulator and utilizes a Fourier post processing algorithm to improve the axial resolution by approximately an order of magnitude. A prototype system based on this approach has been assembled and tested on fixed bovine erythrocytes.

Volumetric imaging of erythrocytes using label‐free multiphoton photoacoustic microscopy

Photoacoustic microscopy (PAM) is an imaging modality well suited to mapping vasculature and other strong absorbers in tissue. However, one of the primary drawbacks to PAM when used for high-resolution imaging is the relatively poor axial resolution due to the inverse dependence on the transducer bandwidth. While submicron lateral resolution PAM can be achieved by tightly focusing the excitation light, the axial resolution is fundamentally limited to 10s of microns for typical transducer frequencies. Here we present a multiphoton PAM technique called transient absorption ultrasonic microscopy (TAUM), which results in a completely optically resolved voxel with an experimentally measured axial resolution of 1.5 microns. This technique is demonstrated by imaging individual red blood cells in three dimensions in blood smear and ex vivo tissues. To the best of our knowledge, this is the first demonstration of fully resolved, volumetric photoacoustic imaging of erythrocytes.