A Laser-Driven Plasma X-ray Source (LPXS) can provide intense, hard X-rays in femtosecond pulses emitted from a micrometer-size spot on a recirculating liquid-metal target. Unlike X-ray tubes based on electron beams, which are subject to constraints of the electron optics and space-charge effects, there is no fundamental limit to the amount of laser power that can be concentrated into the micrometer focus. With the increasing availability of industrial picosecond and femtosecond laser systems it now is practical to offer high average X-ray flux, combined with far higher brilliance and far shorter pulses than possible with X-ray tubes. Because the laser target in an LPXS is a liquid-metal, each laser shot encounters a fresh surface. Metal vapor and droplets are collected and recirculated to the target metal pump for maintenance-free operation. Hard X-rays are generated at tens of keV photon energies consisting of continuum radiation and, depending on the target material composition, of Ga-K, Bi-K or In-K emission lines.
The optoacoustic effect is almost invariably produced by intensity modulated radiation, typically from a pulsed or an amplitude modulated continuous source. Given the form of the wave equation that describes the production of sound from absorption of light, it is clear that steady sources of radiation that move in space in an absorbing medium can also generate acoustic waves. Here the properties of a point source of radiation that rotates in a plane at a constant angular frequency are discussed. The source is shown to generate a spiral wave pattern that contains both compressions and rarefactions.
The in-line x-ray phase-contrast imaging method relies on changes in index of refraction within a body to
produce image contrast. In soft tissue, index of refraction variations arise from density changes so that phase
contrast imaging provides a map of density gradients within a body. An intense, short pulse laser beam that is
differentially absorbed by an object within a body will produce a thermal wave with an associated density change
that propagates outwardly from the interface between the object and the body. Experiments are described where
a pulsed Nd:YLF laser is synchronized to an image intensifier to record the effects of the energy deposited by a
pulsed laser.
The ultrasonic vibration potential refers to the voltage generated when ultrasound traverses a colloidal or ionic
fluid. The theory of imaging based on the vibration potential is reviewed, and an expression given that can be
used to determine the signal from arbitrary objects. The experimental apparatus consists of a pair of parallel
plates connected to the irradiated body, a low noise preamplifier, a radio frequency lock-in amplifier, translation
stages for the ultrasonic transducer that generates the ultrasound, and a computer for data storage and image
formation. Experiments are reported where bursts of ultrasound are directed onto colloidal silica objects placed
within inert bodies.
The ultrasonic vibraton potential refers to the production of a voltage that varies in time when ultrasound passes through a colloidal or ionic solution. The vibration potential can be used as an imaging method for soft tissue by recording its phase, time of arrival, and magnitude relative to the launching of a burst of ultrasound. A theory of the effect can be found from Maxwell's equations. Experimental results demonstrating the imaging method are shown for bodies with simple geometries.
We show that the radiation pressure exerted by a beam of ultrasound can be used for contrast enhancement in high resolution x-ray imaging of tissue. Interfacial features of objects are highlighted as a result of both the displacement introduced by the ultrasound and the inherent sensitivity of x-ray phase contrast imaging to density variations. The potential of the method is demonstrated by imaging various tumor phantoms and tumors from mice. The directionality of the acoustic radiation force and its localization in space permits the imaging of ultrasound-selected tissue volumes. In a related effort we report progress on development of an imaging technique using and electrokinetic effect known as the ultrasonic vibration potential. The ultrasonic vibration potential refers to the voltage generated when ultrasound traverses a colloidal or ionic fluid. The theory of imaging based on the vibration potential is reviewed, and an expression given that describes the signal from an arbitrary object. The experimental apparatus consists of a pair of parallel plates connected to the irradiated body, a low noise preamplifier, a radio frequency lock-in amplifier, translation stages for the ultrasonic transducer that generates the ultrasound, and a computer for data storage and image formation. Experiments are reported where bursts of ultrasound are directed onto colloidal silica objects placed within inert bodies.
Recording of an ultrasonic vibration potential when a burst of ultrasound traverses a body containing a colloidal object can be used as the basis for an imaging method. The fundamentals of the theory of signal production and experimental demonstration of the imaging method are given. In a second imaging method, the use of ultrasound to modify x-ray phase contrast images where the ultrasound acts as a kind of "phase contrast" agent used to translate objects in space is demonstrated.
The ultrasonic vibration potential refers to the generation of a potential when ultrasound traverses a colloidal or ionic solution. The vibration potential can be used for imaging of tissue by sending a burst of ultrasound into a body and recording the vibration potential on the surface of the body with a pair of electrodes attached to a preamplifier and signal processing electronics. The theory of imaging in one-dimension is based on an integral of the ultrasound burst over the colloid distribution in space. A complete theory gives the current from the vibration potential as an integral of the product of the pressure with the component of the gradient of the colloid distribution in space in the direction of propagation of the ultrasound.
The transient grating method acts as a monitor of the evolution of thermal energy following optical excitation of an absorbing molecule. The signals produced by a photodynamic therapy agent are shown to be strongly dependent on presence of oxygen in solution indicating transfer of energy from a triplet state of the dye to form excited 1Δg oxygen. Analysis of the data shows that the efficiency of excited oxygen production can be determined by a recording of the diffracted light intensity versus time.
An ultrasonic vibration potential is generated when an acoustic wave propagates in an ionic or colloidal suspension. Measurement of the potential as an ultrasonic wave propagates in a body offers the possibility of a method of imaging. The resolution of the method ultimately is limited by the wavelength of the ultrasound; the contrast of the technique will depend on inertial quantities and the relative zeta potentials of the irradiated regions. The prospects for tissue imaging using the ultrasonic vibration potential are discussed.
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