We applied photoacoustics as a tissue tomography technique for the detection of blood concentrations, e.g., angiogenesis around tumors. We imaged blood vessels in highly scattering samples, using 532-nm light, to depths of ~1 cm . The samples were real tissue (chicken breast) or 10% dilutions of Intralipid-10%. The blood flowed through nylon capillaries. Polyvinylidene difluoride (PVdF) piezoelectric detectors were used in a surface-scanning mode. We demonstrate the sensitivity of the technique by photoacoustic detection of single red blood cells upon a glass plate. Lateral resolution is limited by the detector diameter (200 microm). The depth resolution is ~10 microm.

From the various mechanisms of photoacoustic (PA) signal generation, the one due to local thermal expansion in aqueous media is treated here in detail. This mechanism is also referred to as thermoelastic PA signal generation. A new physical explanation of the spherical PA profile is presented, from which the signals generated by other source geometries and temporal profiles can be deduced. The characteristic PA signal profiles are discussed for some fundamental and practical source geometries. Also the PA signal attenuation and deformation due to viscous and thermoelastic losses is discussed. The analytic result for the transient generated by a spherical Gaussian spatiotemporal PA source is presented. Experimental PA signals are shown for several geometries and source diameters.

By using red, green, and blue (RGB) light emitting diodes (LEDs) instead of cold cathode fluorescent lamps in edge lit LCD backlights brightness and color performance (gamut) of LCD displays can be improved considerably. However: the design of an RGB-LED backlight and electronic control need special attention: the colors of the separate LEDs need to be mixed well to obtain a good spatial color uniformity while a good balance between the red, green and blue levels has to be maintained to stabilize the white point. Additional features of an RGB-LED backlight solution are: dynamic white point control (tune color point of backlight to LCD and/or displayed material), large dimming range, long lifetime, ruggedness, and the absence of mercury.

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