New setup for hybrid photoacoustic and ultrasound imaging with optical ultrasound detection

Jun 13, 2013 by K. Maedefessel-Herrmann
New setup for hybrid photoacoustic and ultrasound imaging with optical ultrasound detection

Photoacoustic (PA) imaging is a method to visualize structures with optical contrast in biological tissue. Despite the strong optical scattering in tissue, high resolution images in the visible and near infrared spectral range can be obtained. The method is based on sound waves which are generated in regions of enhanced optical absorption. The absorption of diffusely propagating optical radiation leads to a temperature rise and thermoelastic expansion causing sound waves which can be detected at the tissue surface. The strength of photoacoustic techniques is the imaging of the vasculature and the ability to derive functional properties such as oxygen saturation from signals detected at different optical excitation wavelengths.

However, anatomic details without optical contrast cannot be imaged. Hybrid devices, combining PA with ultrasound (US) techniques are ideally suited to visualize the complementary optical and acoustic contrast in . Common implementations use commercial ultrasound devices, to which a pulsed laser source is added. Yet, these devices are rather optimized for US than for PA imaging. Austrian researchers from the Universities of Graz and Innsbruck now propose a new setup that provides perfectly co-registered photoacoustic (PA) and ultrasound (US) from a section within an extended object.

Focusing into a selected plane is achieved by concentrating the coming from the object with a concave cylindrical acoustical mirror onto an optical detector, which is a light beam in an . For the US image, part of an infrared laser pulse is used to excite an acoustic pulse by directing it onto an optically absorbing layer on the acoustic mirror surface. Another part of the same laser pulse is frequency/wavelength converted by nonlinear optical processes and used for PA excitation. Co-registered PA and US images are obtained after applying the inverse Radon transform to the data, which are gathered while rotating the object relative to the detector. Phantom experiments demonstrated a resolution of 1.1 mm between the sections of both imaging modalities and an inplane resolution of about 60 mm and 120 mm for the US and PA modes, respectively. The complementary contrast mechanisms of the two modalities could be shown by images of a zebrafish.

Generation of focused ultrasound pulses with high bandwidth and detection of acoustical signals from a selected slice are made possible by a single element, a concave cylindrical lens coated with a light absorbing metal layer. This makes the device a cost-effective alternative to large scale array tomographs in cases where the region of interest can be covered by a low number of section images and where an imaging time of several seconds per slice is tolerable.

Explore further: Nature's designs inspire research into new light-based technologies

More information: Nuster, R., et al; Optoacoustic Imaging and Spectroscopy for Biomedical Diagnosis, J. Biophotonics 6(6-7), 549-559 (2013); DOI 10.1002/jbio.201200223

add to favorites email to friend print save as pdf

Related Stories

Researchers' new recipe cooks up better tissue 'phantoms'

Nov 30, 2011

The precise blending of tiny particles and multicolor dyes transforms gelatin into a realistic surrogate for human tissue. These tissue mimics, known as "phantoms," provide an accurate proving ground for new photoacoustic ...

Improving ultrasound imaging

Mar 05, 2013

Ultrasound technology could soon experience a significant upgrade that would enable it to produce high-quality, high-resolution images, thanks to the development of a new key material by a team of researchers that includes ...

Optics: Statistics light the way

May 22, 2013

Millions of years of evolution have molded our eyes into highly sensitive optical detectors, surpassing even many man-made devices. Now, Leonid Krivitsky and his co-workers at the A*STAR Data Storage Institute ...

Recommended for you

New energy record set for multilayer-coated mirrors

Sep 12, 2014

Multilayer-coated mirrors, if used as focusing optics in the soft gamma-ray photon energy range, can enable and advance a range of scientific and technological applications that would benefit from the large ...

User comments : 0