Importance

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Abstract

Medical diagnostic apparatus and methods are disclosed. Ultrasound radiation pressure selectively modulates a target area within a body. One or more pulses of radiation containing temporally correlated groups of photons are generated. The photons are characterized by two or more different wavelengths that are selected to have specific interaction with a target chromophore. The two or more different wavelengths are also selected to have substantially similar scattering cross-sections and anisotropy parameters in the target and its surroundings. The pulses of radiation are injected into the body proximate the target area being modulated by the radiation pressure field. Photon groups at each of the different wavelengths that are backscattered from the target area are detected in temporal coincidence. Time-gated background-free amplification of the return signal is used to exclude photons which could not by virtue of their arrival time have interacted with the radiation-pressure-modulated target. Photon groups are selected with a modulation component at the modulation frequency of the radiation pressure modulation field, or at a harmonic of the modulation frequency. From the arrival rate of the detected temporally correlated photon pairs or multiplets, chemical information about the target area, such as an oxygenation or pH level can be inferred. Cardiac output may be computed from measurements of venous and/or arterial oxygenation using this technique.

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First Claim