Wavefront Shaping and Its Application to Enhance Photoacoustic Imaging

Abstract

Abstract:Since its introduction to the field in mid-1990s, photoacoustic imaging has become a fast-developing biomedical imaging modality with many promising potentials. By converting absorbed diffused light energy into not-so-diffused ultrasonic waves, the reconstruction of the ultrasonic waves from the targeted area in photoacoustic imaging leads to a high-contrast sensing of optical absorption with ultrasonic resolution in deep tissue, overcoming the optical diffusion limit from the signal detection perspective. The generation of photoacoustic signals, however, is still throttled by the attenuation of photon flux due to the strong diffusion effect of light in tissue. Recently, optical wavefront shaping has demonstrated that multiply scattered light could be manipulated so as to refocus inside a complex medium, opening up new hope to tackle the fundamental limitation. In this paper, the principle and recent development of photoacoustic imaging and optical wavefront shaping are briefly introduced. Then we describe how photoacoustic signals can be used as a guide star for in-tissue optical focusing, and how such focusing can be exploited for further enhancing photoacoustic imaging in terms of sensitivity and penetration depth. Finally, the existing challenges and further directions towards in vivo applications are discussed.

Optimization of DMD-based independent amplitude and phase modulation: a spatial resolution and quantization

“…For instance, DMD patterns with lower spatial frequencies are used to correct aberrations by increasing the fringe period and decreasing the filtering aperture. Laser processing 14 , optoacoustic microscopy 19 or optical coherence tomography 54 require increased accuracy and high spatial resolution, which can be achieved by increasing the filtering aperture and decreasing the fringe period of binary hologram. In the case when the target wavefront poses a slow variation of amplitude and phase distributions, e.g., cells or intracellular organelles, quantization of modulated complex wave becomes important.…”

Perspective: Wavefront shaping techniques for controlling multiple light scattering in biological tissues: Toward in vivo applications

“…Such time-consuming drawback is mainly due to the inherent requirement of many (typically thousands or even tens of thousands) iterations for signal measurement, data transfer, algorithm computation, and phase pattern refreshing on the wavefront modulator. An improvement roadmap, mainly including the use of a faster wavefront modulator, onboard data acquisition, parallel processing, and more efficient optimization algorithm, has been detailed in the literature 61 and will not be reiterated here. For time-reversed wavefront shaping, the optical focusing optimization speed can already be completed within several milliseconds, 67,75,76 and the biggest obstacles toward in vivo are probably guidestar perturbation or modulation efficiency 83 and the complexity of the system.…”

“…II, wavefront shaping techniques for optical focusing at depths inside scattering media typically include two categories. These are pre-compensated wavefront shaping techniques 8,19,[58][59][60][61][62][63] to counteract the phase/intensity distortions induced by multiple scatterings and time-reversed wavefront shaping techniques 24,[64][65][66][67][68][69] to phase-conjugate scattered light back to the guidestar inside the scattering medium. Although the goals are identical, these two categories differ in both principle and implementation.…”

“…Thus, if one wants intense optical focusing, more independent elements on the SLM (large N) and/or a higher frequency ultrasound transducer (tighter focus, smaller M) is required. The former option, however, is restrained to a maximum pixel count of 1920 × 1080 with a commercial SLM, 8,60,61,71 and the latter is typically limited within 50 MHz, beyond which new challenges arise regarding transducer fabrication and acoustic attenuation in biological tissues. 92,93 Assuming a 50 MHz ultrasound transducer is employed, the acoustic focal region is typically ∼50 µm, containing ∼4 × 10 4 fully developed speckle grains at an optical wavelength of 532 nm.…”

Optimization of DMD-based independent amplitude and phase modulation: a spatial resolution and quantization

“…Each of the devices characterized by the type of modulation, among which they are distinguished: purely amplitude, pure-phase, and simultaneous amplitude-phase modulation, and each of modulators has its benefits and disadvantages [18][19][20] . The choice of the required device is determined by the peculiarities of the problem to be solved in a particular case.…”