Propagation of polarized light in birefringent turbid media: time-resolved simulations

A Monte Carlo model was used to analyze the propagation of polarized light in linearly birefringent turbid media, such as fibrous tissues. Linearly and circularly polarized light sources were used to demonstrate the change of polarizations in turbid media with different birefringent parameters. Videos of spatially distributed polarization states of light backscattered from or propagating in birefringent media are presented

High-resolution thermoacoustic tomography of biological tissue

A study of pulsed-microwave-induced thermoacoustic tomography in biological tissues is presented. A backprojection algorithm based on rigorous theory is used to reconstruct the cross-sectional image from the thermoacoustic measurement in a circular configuration that encloses the sample under study. The results demonstrate the possibility of application in detecting small tumors buried in biological tissues using microwave absorption contrast and ultrasound spatial resolution. Finally, the method is compared with laser-induced thermoacoustic tomography

Cavitation induced shear and circumferential stresses on blood vessel walls during photo-mediated ultrasound therapy

Photo-mediated ultrasound therapy (PUT) is a novel technique using combined laser and ultrasound to generate enhanced cavitation activity inside blood vessels. The stresses produced by oscillating bubbles during PUT are believed to be responsible for the induced bio-effects in blood vessels. However, the magnitudes of these stresses are unclear. In this study, a two-dimensional axisymmetric finite element method-based numerical model was developed to investigate the oscillating bubble-produced shear and circumferential stresses during PUT. The results showed that increased stresses on the vessel wall were produced during PUT as compared with ultrasound-alone. For a 50-nm radius bubble in a 50-μm radius blood vessel, the produced circumferential and shear stresses were in the range of 100 kPa–400 kPa and 10 Pa–100 Pa, respectively, during PUT with the ultrasound frequency of 1 MHz, ultrasound amplitude of 1400 kPa–1550 kPa, and laser fluence of 20 mJ/cm2, whereas the circumferential and shear stresses produced with ultrasound-alone were less than 2 kPa and 1 Pa, respectively, using the same ultrasound parameters. In addition, the produced stresses increased when the ultrasound pressure and laser fluence were increased but decreased when the ultrasound frequency and vessel size were increased. For bubbles with a radius larger than 100 nm, however, the stresses produced during PUT were similar to those produced during ultrasound-alone, indicating the effect of the laser was only significant for small bubbles

Functional photoacoustic tomography of animal brains

This research is primarily focused on laser-based non-invasive photoacoustic tomography of small animal brains. Photoacoustic tomography, a novel imaging modality, was applied to visualize the distribution of optical absorptions in small-animal brains through the skin and skull. This technique combines the high-contrast advantage of optical imaging with the high-resolution advantage of ultrasonic imaging. Based on the intrinsic optical contrast, this imaging system successfully visualized three-dimensional tissue structures in intact brains, including lesions and tumors in brain cerebral cortex. Physiological changes and functional activities in brains, including cerebral blood volume and blood oxygenation in addition to anatomical information, were also satisfactorily monitored. This technique successfully imaged the dynamic distributions of exogenous contrast agents in small-animal brains. Photoacoustic angiography in small-animal brains yielding high contrast and high spatial resolution was implemented noninvasively using intravenously injected absorbing dyes. In the appendix, the theory of Monte Carlo simulation of polarized light propagation in scattering media was briefly summarized

All-optical photoacoustic microscopy

AbstractThree-dimensional photoacoustic microscopy (PAM) has gained considerable attention within the biomedical imaging community during the past decade. Detecting laser-induced photoacoustic waves by optical sensing techniques facilitates the idea of all-optical PAM (AOPAM), which is of particular interest as it provides unique advantages for achieving high spatial resolution using miniaturized embodiments of the imaging system. The review presents the technology aspects of optical-sensing techniques for ultrasound detection, such as those based on optical resonators, as well as system developments of all-optical photoacoustic systems including PAM, photoacoustic endoscopy, and multi-modality microscopy. The progress of different AOPAM systems and their representative applications are summarized

High-resolution functional photoacoustic tomography

All-optical imaging has high contrast but poor spatial resolution beyond the ballistic and quasiballistic regimes. All-ultrasonic imaging has high spatial resolution but poor contrast for early stage tumors. Photoacoustic tomography combines the high optical contrast and the high ultrasonic resolution. Our work in this emerging area of research will be summarized in this invited talk. In this technology, a diffraction-based inverse-source problem is solved in the image reconstruction, for which our group developed the rigorous reconstruction theory. We developed a prototype and accomplished noninvasive transdermal and transcranial functional imaging of small-animal brains in vivo