We present multimodal noncontact photoacoustic (PA) and optical coherence tomography (OCT) imaging. PA signals are acquired remotely on the surface of a specimen with a Mach-Zehnder interferometer. The interferometer is realized in a fiber-optic network using a fiber laser at 1550 nm as the source. In the same fiber-optic network, a spectral-domain OCT system is implemented. The OCT system utilizes a supercontinuum light source at 1310 nm and a spectrometer with an InGaAs line array detector. Light from the fiber laser and the OCT source is multiplexed into one fiber using a wavelength-division multiplexer; the same objective is used for both imaging modalities. Reflected light is spectrally demultiplexed and guided to the respective imaging systems. We demonstrate two-dimensional and three-dimensional imaging on a tissue-mimicking sample and a chicken skin phantom. The same fiber network and same optical components are used for PA and OCT imaging, and the obtained images are intrinsically coregistered.
In this paper we present multimodal non-contact photoacoustic and optical coherence tomography (OCT) imaging using a galvanometer scanner. Photoacoustic signals are acquired without contact on the surface of a specimen using an interferometric technique. The interferometer is realized in a fiber-optic network using a fiber laser at 1550 nm as source. In the same fiber-optic network a spectral-domain OCT system is realized, using a broadband light source at 1300 nm. Light from the fiber laser and the OCT source are multiplexed into the same fiber and the same objective is used for both imaging modalities. Fast non-contact photoacoustic and OCT imaging is demonstrated by scanning the detection spot utilizing a galvanometer scanner. Multimodal photoacoustic and OCT imaging is shown on agarose phantoms. As the same fiber network and optical components are used for non-contact photoacoustic and OCT imaging the obtained images are co-registered intrinsically.
In this paper we present multimodal non-contact photoacoustic and OCT imaging. Photoacoustic signals are acquired remotely on the surface of a specimen with a Mach-Zehnder interferometer. The interferometer is realized in a fiberoptic network using a fiber laser at 1550nm as source. In the same fiber-optic network a spectral-domain OCT system is realized. The OCT system utilizes a superluminescent diode at 1325nm as light source; imaging data are acquired using a spectrometer with an InGaAs line array. Light from the fiber laser and the superluminescent diode are multiplexed into one fiber and the same objective is used for both imaging modalities. Reflected light is demultiplexed and guided to the respective imaging systems. We demonstrate the photoacoustic and OCT imaging modalities on different phantom samples. Finally, we show multimodal imaging with both modalities simultaneously. The resulting photoacoustic and OCT images match perfectly.
We present a remote photoacoustic imaging system without the need of a physical contact to the specimen. The setup is based on a Mach-Zehnder interferometer using optical wave guide technology as usually used in telecommunication industries, thus guaranteeing long life times and relatively low costs. A detection beam is transmitted through an optical fiber to a lens system which focuses the beam to the surface of a specimen. The back reflected light is than collected by the same lens system and coupled into the same optical fiber. As the collected light intensity is less than 0.1% of the transmitted intensity in forward direction an optical amplifier is used for amplifying the collected light. After amplification the light is brought to interference with a reference beam for demodulation of the ultrasound signals. The modulated light intensity is converted into electrical signals by a self-built balanced photo detector. We present noncontact photoacoustic imaging of a tissue-mimicking phantom and on chicken skin.
We introduce a multichannel optical fiber based detector for photoacoustic imaging. By using in-house produced
photodetectors and relative low-cost components from telecommunication industries we were able to reduce the costs for
one channel significantly compared to previous setups. The estimated cost for one channel (without sampling device) is
below 800 €. The self-made balanced photodetector for 1550 nm achieves a gain of 100 dB, a -3dB bandwidth of 45
MHz and a maximum signal-to-noise-ratio of 48 dB. We present a four channel annular detector array based on optical
fiber Mach-Zehnder interferometers. Photoacoustic imaging is demonstrated by measuring photoacoustic signals of a
black polyethylene microsphere.
The recently introduced remote photoacoustic imaging technique allows measurement of photoacoustic signals on nonplanar
surfaces without the need for a water bath or coupling agent. Hereby, photoacoustically generated ultrasonic
displacements are detected without physical contact to the sample by utilizing laser interferometric techniques. In this
work we adapted different algorithms to allow reconstruction on non-planar surfaces and evaluate them on experimental
and simulated data. Experimental data were obtained using a remote photoacoustic setup based on two-wave mixing in a
photorefractive crystal. Ultrasonic displacements were acquired on flat and non-flat surfaces.
Three-dimensional reconstruction of simulated and real measurement data is shown with synthetic aperture focusing
technique, Fourier domain synthetic aperture focusing technique, and spectral-domain time reversal algorithms. For the
synthetic aperture focusing technique and the time reversal algorithm the surface morphology is taken into account. It is
demonstrated that artifacts can occur if the surface is not considered. For the experimental data the shape of the surface is
obtained from optical coherence tomography or by a priori knowledge.
In this paper we report on remote photoacoustic imaging using an interferometric technique. By utilizing a two-wave
mixing interferometer ultrasonic displacements are measured without any physical contact to the sample.
This technique allows measurement of the displacements also on rough surfaces. Mixing a plane reference beam
with the speckled beam originating from the sample surface is done in a Bi<sub>12</sub>SiO<sub>20</sub> photorefractive crystal.
After data acquisition the structure of the specimen is reconstructed using a Fourier-domain synthetic focusing
aperture technique. We show three-dimensional imaging on
tissue-mimicking phantoms and biological samples.
Furthermore, we show remote photoacoustic measurements on a human forearm in-vivo.
Photoacoustic Tomography is an emerging imaging technology mainly for medical and biological applications. A
sample is illuminated by a short laser pulse. Depending on the optical properties the electromagnetic radiation
is distributed and absorbed. Thereby local temperature increase generates thermal expansion and broadband
ultrasonic signals, also called photoacoustic signals. Unlike conventional ultrasound in photoacoustic imaging the
contrast depends on the optical properties of the sample which provides not only morphologic information but
also functional information. This way photoacoustic imaging combines the advantages of optical imaging (high
contrast) and ultrasonic imaging (high spatial resolution) and is particularly suited for medical applications like
mammography or skin cancer detection. Our group uses integrating line detectors instead of ultrasonic point
receivers. Line detectors integrate the pressure along one dimension whereby the 3D problem is reduced to a 2D
problem and enables a tomography setup that requires only a single axis of rotation. Implementations of line
detectors use optical interferometers, e.g. a Fabry-Perot interferometer or a Mach-Zehnder interferometer. We
use free-beam interferometers as well as fiber-based interferometers for collecting photoacoustic signals. The latter
are somewhat easier to handle because they require fewer optical components. Finally, the advantages of optical
detection methods over piezoelectric detection methods are the better frequency response and the resistance
against electrical interference from the environment. First measurements on phantoms and image reconstruction
using a time reversal method demonstrated the capability of integrating line detectors for collecting broadband
ultrasonic signals for photoacoustic tomography.