Conventional B-mode ultrasound imaging lacks soft tissue contrast to differentiate various tissue types. Emerging ultrasound imaging technologies have therefore focused on extracting tissue parameters important for tissue differentiation such as scatterer size, tissue elasticity, and micro-vasculatures. Among these technologies, shear wave elastography (SWE) is an approach that measures tissue viscoelastic parameters. Our group has proposed Temporal Enhanced Ultrasound (TeUS) that differentiates tissue types without requiring any external stimuli. Through analytical derivations and simulations, we previously showed that the source of tissue typing information in TeUS is physiological micro-vibrations resulting mainly from perfusion. We further demonstrated that TeUS is sensitive to the size and distributions of scatterers in the tissue, as well as its visco-elasticity. In this paper, we designed ultrasound phantoms to mimic tissue with two different elasticities and two scatterer sizes. A exible microtube was embedded in the phantoms to generate local micro-vibrations. We experimentally demonstrate the relationship between TeUS and SWE and their sensitivity to tissue elasticity and scatterer size. This work indicated that while shear wave measurements are sensitive to the phantoms viscoelasticity, they are not sensitive to ultrasound scatterer size. On the contrary, the TeUS amplitude depends on both scatterer size and tissue viscoelasticity. This work could potentially inform clinicians of choosing imaging modalities and interventions based on each cancer's unique traits and properties.
Three examples of cavity-enhanced measurements of refractive index and optical absorption are discussed. Using
microphotonic silicon-on-insulator ring-resonators we determine the concentration of cyclohexane and m-xylene at
detection levels of 300-3000 ppm. The gases are first absorbed into a siloxane polymer and its refractive index change is
detected by a characteristic wavelength shift of the cavity resonance. In a second device phase-shift cavity ring-down
spectroscopy is applied to simultaneously measure the optical absorption at two wavelengths of either a dye, nucleic
acids or a pharmaceutical component. Multiplexing the ring-down measurement permits dual wavelength absorption spectroscopy without the use of a dispersion element. Finally, a combination of resonance wavelength measurements and cavity ring-down spectroscopy is used to simultaneously determine the change in refractive index and the absorption induced by adsorption of ethylene diamine on a 300 μm silica sphere. A whispering gallery mode of the microsphere resonator is excited with intensity modulated light and the intensity and AM modulation phase of the Rayleigh backscattered light is measured.
A chemical sensor system consisting of a coated long period grating, which was spliced into a fiber loop cavity, has been
prepared and characterized. Designer coatings based on polydimethylsiloxane and nanostructured organically modified
silica (ORMOSIL) materials were prepared to provide enhanced sensitivity for a variety of key environmental pollutants.
Upon microextraction of the analyte into the polymer matrix, an increase in the refractive index of the coating resulted in
a change of the attenuation spectrum of the long period grating. The grating was interrogated using ring-down detection
as a means to amplify the optical loss and to gain stability against misalignment and laser power fluctuations. Chemical
differentiation of cyclohexane and xylenes was achieved and a detection limit of 300 ppm of xylenes vapour in air was
readily realized for PDMS coatings. Ormosil-type coatings were capable of detecting lead cations at concentrations
below 1 ppm in water.
When monitoring separation events in microfluidic devices, one frequently needs to detect small amounts of analyte in picolitre sized volumes with a time response of milliseconds. Fluorescence detection is typically the method of choice due to its very high sensitivity and fast response. However, since many analytes are not naturally fluorescent, labelling protocols may have to be introduced and thereby increase the complexity of the analysis. Here, we present an alternative method that is based on optical absorption, or more specifically on the ring-down time of an optical signal in a cavity or loop made of waveguide material. This optical decay constant changes as small liquid samples containing absorbing species are introduced into a fiber-optic loop. It is demonstrated that one can obtain the optical decay constant using a continuous wave laser beam that is intensity modulated and then coupled into an optical fiber loop. The inherent exponential decay in the fiber loop introduces a phase shift of the light emitted from the loop with respect to the pumping beam. By measuring this phase shift, one can readily determine the concentration of the analyte introduced between the two fiber ends and a model is established to describe the relationship. It is demonstrated that this technique, dubbed "phase-shift fiber-loop ring-down spectroscopy" (PS-FLRDS), is well suited as an absorption detector for any flow system in which the optical absorption path is limited by the instrument architecture.
The deperturbation analysis of ReN and nonadiabatic dissociation dynamics of BrCl and BrNO are reported. In the case of ReN, couplings between different electronic states changes apparent molecular properties such as rotational constants and excited state lifetimes. An experimental approach which enabled us to separated the contributions to the mixed states from specified energies and the spin-orbit branching ratio was measured as a function of the excitation energy. The correlation of the spin-orbit states of the photofragments was established. Such observations enabled us to establish nonadiabatic dissociation mechanisms. In both the spectroscopy and dissociation dynamics studies, the coupling between the nuclear and electronic degrees of freedom was investigated.