Influence of laser pulse width to the photoacoustic temporal waveform and the image resolution with a solid state excitation laser

Irisawa, Kaku; Hirasawa, Takeshi; Hirota, Kaoru; Tsujita, Kazuhiro; Ishihara, Miya

doi:10.1117/12.907714

Cited by 13 publications

(13 citation statements)

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“…where λ = c/ f . Because broadband photoacoustic signals are sensed and filtered by a transducer with finite bandwidth, the λ term is primarily related to the acoustic frequency of the transducer [1], [40]. To evaluate (17) and obtain a spatial covariance, λ can be approximated as the wavelength corresponding to the center frequency of the transducer λ c .…”

Section: A Photoacoustic Spatial Coherencementioning

confidence: 99%

Photoacoustic Spatial Coherence Theory and Applications to Coherence-Based Image Contrast and Resolution

Graham

Bell

2020

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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The photoacoustic effect relies on optical transmission, which causes thermal expansion and generates acoustic signals. Coherence-based photoacoustic signal processing is often preferred over more traditional signal processing methods due to improved signal-to-noise ratios, imaging depth, and resolution in applications such as cell tracking, blood flow estimation, and imaging. However, these applications lack a theoretical spatial coherence model to support their implementation. In this article, the photoacoustic spatial coherence theory is derived to generate theoretical spatial coherence functions. These theoretical spatial coherence functions are compared with k-Wave simulated data and experimental data from point and circular targets (0.1-12 mm in diameter) with generally good agreement, particularly in the shorter spatial lag region. The derived theory was used to hypothesize and test previously unexplored principles for optimizing photoacoustic short-lag spatial coherence (SLSC) images, including the influence of the incident light profile on photoacoustic spatial coherence functions and associated SLSC image contrast and resolution. Results also confirm previous trends from experimental observations, including changes in SLSC image resolution and contrast as a function of the first M lags summed to create SLSC images. For example, small targets (e.g., <1-4 mm in diameter) can be imaged with larger M values to boost target contrast and resolution, and contrast can be further improved by reducing the illuminating beam to a size that is smaller than the target size. Overall, the presented theory provides a promising foundation to support a variety of coherence-based photoacoustic signal processing methods, and the associated theory-based simulation methods are more straightforward than the existing k-Wave simulation methods for SLSC images.

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Section: A Photoacoustic Spatial Coherencementioning

confidence: 99%

Photoacoustic Spatial Coherence Theory and Applications to Coherence-Based Image Contrast and Resolution

Graham

Bell

2020

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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“…Another method to reduce damage to the MMF is to reduce the "hot spots" in the spatial profile of the laser beam, which can be done using a beam homogenizer, which must be carefully aligned and designed to minimize diffraction effects [78], or by adjusting the laser's internal alignment [79]. Lastly, the coupled energy can be increased by reducing the peak energy per pulse by using a laser with a longer pulse width, which can range from a few ns to 10s of ns for PA signal generation [80].…”

Section: Design Of the Transurethral Illumination Source And Light Comentioning

confidence: 99%

Cylindrical illumination with angular coupling for whole-prostate photoacoustic tomography

Bungart¹,

Cao²,

Yang-Tran³

et al. 2019

Biomed. Opt. Express

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Current diagnosis of prostate cancer relies on histological analysis of tissue samples acquired by biopsy, which could benefit from real-time identification of suspicious lesions. Photoacoustic tomography has the potential to provide real-time targets for prostate biopsy guidance with chemical selectivity, but light delivered from the rectal cavity has been unable to penetrate to the anterior prostate. To overcome this barrier, a urethral device with cylindrical illumination is developed for whole-prostate imaging, and its performance as a function of angular light coupling is evaluated with a prostate-mimicking phantom.

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“…Exhaustive literature is already available on the use of OAM to image complex biological samples. 3,4 In most reports on OAM, 5,6 the excitation optical source is a laser delivering pulses of a typical duration of several nanoseconds, used in conjunction with a single-element ultrasound transducer (UT). The values of the pulse energy and duration provided by the source, and the acoustic bandwidth of the transducer, are of paramount importance for achieving high-quality OAM images in terms of signal-to-noise ratio (SNR) and axial resolution.…”

Section: Introductionmentioning

confidence: 99%

“…8,9 The number of reports demonstrating improvement in the axial resolution by manipulating the bandwidth of the acoustic waves is limited and typically restricted to situations where the bandwidth is enhanced by reducing the duration of the pulses from hundreds to several nanoseconds. 5,6 Using numerical simulations, it has been demonstrated that a 3-ps pulse duration laser is more efficient in generating high-frequency acoustic signals than a 3-ns pulse duration laser, however, no improvement in axial resolution was reported. 10 To our knowledge, enhancement in axial resolution by reducing the pulse duration below several nanoseconds has not been experimentally demonstrated yet.…”

Section: Introductionmentioning

confidence: 99%

Enhanced resolution optoacoustic microscopy using a picosecond high repetition rate Q-switched microchip laser

et al. 2022

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. Conventional optoacoustic microscopy (OAM) instruments have at their core a nanosecond pulse duration laser. If lasers with a shorter pulse duration are used, broader, higher frequency ultrasound waves are expected to be generated and as a result, the axial resolution of the instrument is improved. Here, we exploit the advantage offered by a picosecond duration pulse laser to enhance the axial resolution of an OAM instrument. In comparison to an instrument equipped with a 2-ns pulse duration laser, an improvement in the axial resolution of 50% is experimentally demonstrated by using excitation pulses of only 85 ps. To illustrate the capability of the instrument to generate high-quality optoacoustic images, en-face , in-vivo images of the brain of Xenopus laevis tadpole are presented with a lateral resolution of throughout the entire axial imaging range.

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Influence of laser pulse width to the photoacoustic temporal waveform and the image resolution with a solid state excitation laser

Cited by 13 publications

References 0 publications

Photoacoustic Spatial Coherence Theory and Applications to Coherence-Based Image Contrast and Resolution

Photoacoustic Spatial Coherence Theory and Applications to Coherence-Based Image Contrast and Resolution

Cylindrical illumination with angular coupling for whole-prostate photoacoustic tomography

Enhanced resolution optoacoustic microscopy using a picosecond high repetition rate Q-switched microchip laser

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