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

Deepu George, Harriet Lloyd, Ronald H Silverman, Parag V Chitnis, Deepu George, Harriet Lloyd, Ronald H Silverman, Parag V Chitnis

Abstract

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.

Keywords: interferometry; microscopy; photoacoustic imaging; photorefractive crystal.

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figures

FIGURE 1
FIGURE 1
Schematic of the PRC-based PAM system
FIGURE 2
FIGURE 2
Signal from the lock-in amplifier as a function of surface displacement (A) and calculated equivalent pressure (B)
FIGURE 3
FIGURE 3
(A) Photoacoustic image of chrome target; (B) PA image of an edge of thick chrome line
FIGURE 4
FIGURE 4
Photoacoustic image of human hair embedded in multiple layers of hippocampus tissue
FIGURE 5
FIGURE 5
(A) PA image of blood smear showing RBC; (B) corresponding bright field image
FIGURE 6
FIGURE 6
(A) PAM image of ex vivo retinal samples. (B) Photograph of the sample
FIGURE 7
FIGURE 7
(A) Signal detected by the lock-in as a function of frequency for an absorber at the surface. (B) Signal for an absorber at depth 1 mm . Dashed lines show the signal without the reference beam

Source: PubMed

Sponsorer och medarbetare

Medicinska tillstånd

Läkemedelsinterventioner

3
Prenumerera