Supplementary "Video 1":http://www.nature.com/protocolexchange/system/uploads/2533/original/F1.mpg?1363372591.

Figure 5 shows a stack of representative cross-sectional photoacoustic reconstructions obtained in vivo from an adult rat imaged at 750 nm. The reconstructions were carried out using the 3D spatial phase-controlled algorithm method. Figures 5b–d show different 3D rendered structure at view angles. "Video 1":http://www.nature.com/protocolexchange/system/uploads/2533/original/F1.mpg?1363372591 shows a three dimensional rendering of the brain structure at a given time point. There is accurate congruence between features in the noninvasive photoacoustic images and the anatomical photographs of the rat. The brain structures, including the middle cerebral artery, right hemispheres, left hemispheres, left olfactory bulbs, and right olfactory bulbs, are clearly shown in the PAT images (Figs. 5b, c and d). Finally, such a stack of cross-sectional 2D images can be fed into a volumetric visualization toolbox(Amira) for direct 3D representation.

Figure 6 | 4-D PAT for monitoring ICG- pharmacokinetics in rat brain. Consecutive frames of a video showing ICG-based pharmacokinetics of drugs over a duration of 9 s.

Supplementary "Video 2":http://www.nature.com/protocolexchange/system/uploads/2534/original/F2.avi?1363372743.

ICG pharmacokinetics was also monitored within a rat brain in real time at 810 nm ( "Video 2":http://www.nature.com/protocolexchange/system/uploads/2534/original/F2.avi?1363372743). During the first 20 seconds the signal is constant while a sudden increase of the signal strength occurs right afterward due to the ICG injection, followed by a plateau in the photoacoustic signal strength. Also presented are five time frames of the 3D structures obtained from reconstructed representative 4D tomograms from t=16.650 s (left) and t= 26.640 s (right). Immediately after injection, indocyanine green(ICG) accumulation in the brain cortex is observed photoacoustically. The PA images of the ICG-dyed brain shows ICG accumulation enhanced the PA signal (green). After transient accumulation of ICG, the amount of drug reduces exponentially. A clear advantage of this in vivo approach is the opportunity of direct visualization of disease processes at the molecular scale and the quantification of changes to the relevant marker molecules in a non-invasive testing environment. In principle, any drugs with optical absorption contrast could be studied by 4-D photoacoustic tomography.

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Subject Areas

Biological techniques
Optics and photonics
Physics

Associated Publications

4-D photoacoustic tomography: the exploration of space and time in living tissue

Huabei Jiang, Liangzhong Xiang

Four dimensional (4D) photoacoustic tomography (PAT) has recently been developed to offer dynamic three-dimensional (3D) structural and functional imaging of living biological tissue with label-free, optical absorption contrast. 4D PAT integrates time resolution with three dimensional (3D) spatial resolution by using spherical arrays of ultrasonic detectors. The technique generates motion pictures of imaged tissue, enabling real time tracking of dynamic physiological and pathological processes at hundred micrometer-millisecond resolutions. Here we provide a detailed description of the 4D PAT imaging system setup, signal processing and data acquisition, system calibration, image reconstruction and animal handling. It currently takes ~300 ms for data acquisition by using a 10-Hz pulse -repetition rate laser system. The data acquisition time, however, can be significantly reduced by using a laser system with a higher pulse repetition rate.

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Associated Publications