Hybrid iterative wavefront shaping for high-speed focusing through scattering media

A major limiting factor of optical imaging in biological applications is the diffusion of light by tissue, preventing focusing at depths greater than ~1 mm in the body. To overcome this issue, phase-based wavefront shaping alters the phase of sections of the incident wavefront to counteract aberrations in phase caused by scattering. This enables focusing through scattering media beyond the optical diffusion limit and increases signal compared to amplitude-based compensation. However, in previous studies, speed of optimization has typically been limited by the use of a liquid crystal spatial light modulator (SLM) for measurement and display. SLMs usually have refresh rates of less than 100 Hz and require much longer than the speckle correlation time of tissue in vivo, usually on the order of milliseconds, to determine the optimal wavefront. Here, we present a phase-based iterative wavefront shaping method based on an onaxis digital micromirror device (DMD) in conjunction with an electro-optic modulator (EOM) for measurement and a fast SLM for display. By combining phase modulation from an EOM with the modal selection of the DMD, we take advantage of DMDs higher refresh rate, approximately 23 kHz, for iterative phase measurement. The slower SLM requires one update for display following the rapid determination of the optimal wavefront via the DMD, allowing for high-speed wavefront shaping. Using this system, we are able to focus through scattering media using 64 modes in under 8 milliseconds, on the order of the speckle correlation time for tissue in vivo

Hybridized wavefront shaping for high-speed, high-efficiency focusing through dynamic diffusive media

One of the prime limiting factors of optical imaging in biological applications is the diffusion of light by tissue, which prevents focusing at depths greater than the optical diffusion limit (typically ∼1  mm). To overcome this challenge, wavefront shaping techniques that use a spatial light modulator (SLM) to correct the phase of the incident wavefront have recently been developed. These techniques are able to focus light through scattering media beyond the optical diffusion limit. However, the low speeds of typically used liquid crystal SLMs limit the focusing speed. Here, we present a method using a digital micromirror device (DMD) and an electro-optic modulator (EOM) to measure the scattering-induced aberrations, and using a liquid crystal SLM to apply the correction to the illuminating wavefront. By combining phase modulation from an EOM with the DMD’s ability to provide selective illumination, we exploit the DMD’s higher refresh rate for phase measurement. We achieved focusing through scattering media in less than 8 ms, which is sufficiently short for certain in vivo applications, as it is comparable to the speckle correlation time of living tissue

High-speed alignment optimization of digital optical phase conjugation systems based on autocovariance analysis in conjunction with orthonormal rectangular polynomials

Digital optical phase conjugation (DOPC) enables many optical applications by permitting focusing of light through scattering media. However, DOPC systems require precise alignment of all optical components, particularly of the spatial light modulator (SLM) and camera, in order to accurately record the wavefront and perform playback through the use of time-reversal symmetry. We present a digital compensation technique to optimize the alignment of the SLM in five degrees of freedom, permitting focusing through thick scattering media with a thickness of 5 mm and transport scattering coefficient of 2.5  mm  −  1 while simultaneously improving focal quality, as quantified by the peak-to-background ratio, by several orders of magnitude over an unoptimized alignment

British research in accounting and finance (2001–2007): the 2008 research assessment exercise

No abstract available

The validity of the test of memory malingering (TOMM) with deaf individuals.

OBJECTIVE: Administration of performance validity tests (PVT) during neuropsychological assessments is standard practice, with the Test of Memory Malingering (TOMM) being a commonly used measure. The TOMM has been well validated in hearing populations with various medical and psychiatric backgrounds. A major gap in the literature is the use of the TOMM amongst culturally Deaf individuals who use American Sign Language (ASL) as their first and preferred language. The purpose of this study was to explore the use of the TOMM with this population to determine if there may be differences related to the use of semantic knowledge and recall using signs rather than spoken phonemes. METHOD: This study recruited 30 culturally Deaf, community-dwelling adults, who self-reported that they were not involved in litigation ordisability claims. In addition to the TOMM, participants were screened for cognitive ability using non-verbal components of the Wechsler Abbreviated Scale of Intelligence, Second Edition (WASI-II) and the Mini Mental State Examination: ASL Version (MMSE:ASL). RESULTS: Nonverbal intelligence for this sample was within the average range of ability. No participants scored lower than the standard cut-off score for Trial 2 or the Retention Trial on the TOMM (≤44 raw score to indicate invalid responding). Trial 1 performances ranged from 44 to 50, Trial 2 performances ranged from 49 to 50, and Retention performances ranged from 49 to 50. CONCLUSION: These results support the use of the same standard cut-off scores established for hearing individuals in culturally Deaf individuals who use ASL

Amplitude-masked photoacoustic wavefront shaping: theory and application in flowmetry

Optical diffusion in scattering media prevents focusing beyond shallow depths, causing optical imaging and sensing to suffer from low optical intensities, resulting in low signal-to-noise ratios (SNR). Here, we demonstrate focusing using a fast binary-amplitude digital micromirror device to characterize the transmission modes of the scattering medium. We then identify and selectively illuminate the transmission modes which contribute constructively to the intensity at the optical focus. Applying this method to photoacoustic flowmetry, we increased the optical intensity at the focus six-fold, and showed that the corresponding increase in SNR allows particle flow to be measured

In Vitro Susceptibility of Canine Influenza A (H3N8) Virus to Nitazoxanide and Tizoxanide

Infection of dogs with canine influenza virus (CIV) is considered widespread throughout the United States following the first isolation of CIV in 2004. While vaccination against influenza A infection is a common and important practice for disease control, antiviral therapy can serve as a valuable adjunct in controlling the impact of the disease. In this study, we examined the antiviral activity of nitazoxanide (NTZ) and tizoxanide (TIZ) against three CIV isolates in vitro. NTZ and TIZ inhibited virus replication of all CIVs with 50% and 90% inhibitory concentrations ranging from 0.17 to 0.21 μM and from 0.60 to 0.76 μM, respectively. These results suggest that NTZ and TIZ are effective against CIV and may be useful for treatment of canine influenza in dogs but further investigation of the in vivo efficacy against CIV as well as the drug's potential for toxicity in dogs is needed

Focusing light through scattering media by polarization modulation based generalized digital optical phase conjugation

Optical scattering prevents light from being focused through thick biological tissue at depths greater than ∼1 mm. To break this optical diffusion limit, digital optical phase conjugation (DOPC) based wavefront shaping techniques are being actively developed. Previous DOPC systems employed spatial light modulators that modulated either the phase or the amplitude of the conjugate light field. Here, we achieve optical focusing through scattering media by using polarization modulation based generalized DOPC. First, we describe an algorithm to extract the polarization map from the measured scattered field. Then, we validate the algorithm through numerical simulations and find that the focusing contrast achieved by polarization modulation is similar to that achieved by phase modulation. Finally, we build a system using an inexpensive twisted nematic liquid crystal based spatial light modulator (SLM) and experimentally demonstrate light focusing through 3-mm thick chicken breast tissue. Since the polarization modulation based SLMs are widely used in displays and are having more and more pixel counts with the prevalence of 4 K displays, these SLMs are inexpensive and valuable devices for wavefront shaping