Thermoacoustic Emission by Deeply Penetrating Microwave Radiation

Thermoacoustic emissions were induced in phantoms inside a microwave cavity by pulses from a 2450 MHz magnetron. These phantoms consisted o f graphite and lucite plates acting as interfaces in a small water tank and also of three components of tissue-simulatin g material. The acoustic emissions were received by an a irbacked 1-MHz resonant PZT5 transducer with two quarter-wave transformers for broadened bandwidth and increased e fficiency. The transducer's output was amplified by a very low noise amplifier and signal averaged by using a signal averager and microcomputer under CAMAC control. The results support the f easibility of thermoacoustic imaging of soft tissue by a transducer-ampli fieraveraging s ystem optimized for this application which might give information complementary to conventional imaging systems.