Radiation-induced thermoacoustic imaging

The acoustic wave generated by sudden thermal stress is used to obtain information non-invasively on the composition and structure of the stressed body. One or more acoustic transducers are coupled with the surface of the body to intercept the acoustic wave and generate a corresponding electrical signal. The sudden thermal stress is induced by a pulse of radiation which deposits energy causing a rapid, but very small, rise of temperature. The radiation may be ionizing radiation, such as high energy electrons, photons (x-rays), neutrons, or other charged particles. The radiation may also be non-ionizing radiation, such as rf and microwave electromagnetic radiation and ultrasonic radiation. The electrical signal from the acoustic transducer is amplified and supplied to a digitizer, which provides a continuous stream of digital words corresponding to samples of the amplified signal. Because in most situations of practical interest the s/n ratio of a single pulse is much less than unity, it is necessary to signalaverage the signals from many successive pulses. This is accomplished with a minicomputer or data processor suitably interfaced with the digitizer. The resulting data can then be suitably displayed as an image on a crt display or plotted or numerically printed out