Comparison of intensity-modulated continuous-wave lasers with a chirped modulation frequency to pulsed lasers for photoacoustic imaging applications

Petschke, Adam; Rivière, Patrick J. La

doi:10.1364/boe.1.001188

Cited by 29 publications

(35 citation statements)

References 43 publications

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“…30,31 The large increase of average temperature compared to pulsed-PA excitation can be problematic; however, the average temperature rise from low concentrations of absorbing molecules as we will show, is relatively small and unlikely to cause thermal damage. For media with dense absorbers, such as tissue, CW-PA imaging has been shown to be less sensitive than pulsed-PA imaging when the laser light intensity and pulse fluence are limited by the thermal damage threshold for tissue.…”

Section: Photoacoustic Systemmentioning

confidence: 74%

Noise-equivalent sensitivity of photoacoustics

2013

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The fundamental limitations of photoacoustic microscopy for detecting optically absorbing molecules are investigated both theoretically and experimentally. We experimentally demonstrate noise-equivalent detection sensitivities of 160,000 methylene blue molecules (270 zeptomol or 2.7×10-19 mol) and 86,000 oxygenated hemoglobin molecules (140 zeptomol) using narrowband continuous-wave photoacoustics. The ultimate sensitivity of photoacoustics is fundamentally limited by thermal noise, which can present in the acoustic detection system as well as in the medium itself. Under the optimized conditions described herein and using commercially available detectors, photoacoustic microscopy can detect as few as 100s of oxygenated hemoglobin molecules. Realizable improvements to the detector may enable single molecule detection of select molecules.

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Section: Photoacoustic Systemmentioning

confidence: 74%

Noise-equivalent sensitivity of photoacoustics

2013

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“…This gives a NEP of approximately 20 µPa/ √ H z. In contrast to UOT, where any temporal characteristics give the same CNR, in PAT a scheme with short pulses is more beneficial [19] due to the need to rise above the thermal noise floor. This means the pulse energy is set at the pulsed medical safety limit, and within the 250 ms single-shot duration three such pulses can be used at the rate corresponding to the allowed average power.…”

Section: Photo-acoustic Tomography (Pat)mentioning

confidence: 99%

Analysis of the potential for non-invasive imaging of oxygenation at heart depth, using ultrasound optical tomography (UOT) or photo-acoustic tomography (PAT)

Walther¹,

Rippe²,

Wang³

et al. 2017

Biomed. Opt. Express

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Despite the important medical implications, it is currently an open task to find optical non-invasive techniques that can image deep organs in humans. Addressing this, photo-acoustic tomography (PAT) has received a great deal of attention in the past decade, owing to favorable properties like high contrast and high spatial resolution. However, even with optimal components PAT cannot penetrate beyond a few centimeters, which still presents an important limitation of the technique. Here, we calculate the absorption contrast levels for PAT and for ultrasound optical tomography (UOT) and compare them to their relevant noise sources as a function of imaging depth. The results indicate that a new development in optical filters, based on rare-earth-ion crystals, can push the UOT technique significantly ahead of PAT. Such filters allow the contrastto-noise ratio for UOT to be up to three orders of magnitude better than for PAT at depths of a few cm into the tissue. It also translates into a significant increase of the image depth of UOT compared to PAT, enabling deep organs to be imaged in humans in real time. Furthermore, such spectral holeburning filters are not sensitive to speckle decorrelation from the tissue and can operate at nearly any angle of incident light, allowing good light collection. We theoretically demonstrate the improved performance in the medically important case of non-invasive optical imaging of the oxygenation level of the frontal part of the human myocardial tissue. Our results indicate that further studies on UOT are of interest and that the technique may have large impact on future directions of biomedical optics.

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“…CW lasers or diodes are cheaper and has smaller footprint and hence can aid in developing portable systems. When operating under the American National Standards Institute (ANSI)-prescribed safety limit, PA pressure generated with a sinusoidal excitation is about 6 orders of magnitude lower than that with pulsed excitation [19][20][21]. But for frequency domain imaging, the sensitivity can be enhanced using phase sensitive or lock-in detection.…”

Section: Funding Information National Eye Institute Grant/award Numbmentioning

confidence: 99%

A frequency‐domain non‐contact photoacoustic microscope based on an adaptive interferometer

George

Lloyd

Silverman

et al. 2018

Journal of Biophotonics

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A frequency-domain, non-contact approach to photoacoustic microscopy (PAM) that employs amplitude-modulated (0.1-1 MHz) laser for excitation (638-nm pump) in conjunction with a 2-wave mixing interferometer (532-nm probe) for non-contact detection of photoacoustic waves at the specimen surface is presented. A lock-in amplifier is employed to detect the photoacoustic signal. Illustrative images of tissue-mimicking phantoms, red-blood cells and retinal vasculature are presented. Single-frequency modulation of the pump beam directly provides an image that is equivalent to the 2-dimensional projection of the image volume. Targets located superficially produce phase modulations in the surface-reflected probe beam due to surface vibrations as well as direct intensity modulation in the backscattered probe light due to local changes in pressure and/or temperature. In comparison, the observed modulations in the probe beam due to targets located deeper in the specimen, for example, beyond the ballistic photon regime, predominantly consist of phase modulation.

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Comparison of intensity-modulated continuous-wave lasers with a chirped modulation frequency to pulsed lasers for photoacoustic imaging applications

Cited by 29 publications

References 43 publications

Noise-equivalent sensitivity of photoacoustics

Noise-equivalent sensitivity of photoacoustics

Analysis of the potential for non-invasive imaging of oxygenation at heart depth, using ultrasound optical tomography (UOT) or photo-acoustic tomography (PAT)

A frequency‐domain non‐contact photoacoustic microscope based on an adaptive interferometer

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