Ultrasonically modulated x-ray phase contrast and vibration potential imaging methods

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.