Hybrid medical imaging: scanning thermoacoustic tomography

Scanning thermoacoustic tomography based on microwave-induced thermoacoustic waves studied. Two-dimensional images of /spl sim/50 mm thick biological tissue samples were obtained. The thermoacoustic signals were also simulated theoretically. The image resolution was significantly improved compared with purely microwave imaging

Scanning thermoacoustic tomography in biological tissue

Microwave-induced thermoacoustic tomography was explored to image biological tissue. Short microwave pulses irradiated tissue to generate acoustic waves by thermoelastic expansion. The microwave-induced thermoacoustic waves were detected with a focused ultrasonic transducer. Each time-domain signal from the ultrasonic transducer represented a one-dimensional image along the acoustic axis of the ultrasonic transducer similar to an ultrasonic A-scan. Scanning the system perpendicularly to the acoustic axis of the ultrasonic transducer would generate multi-dimensional images. Two-dimensional tomographic images of biological tissue were obtained with 3-GHz microwaves. The axial and lateral resolutions were characterized. The time-domain piezo-electric signal from the ultrasonic transducer in response to the thermoacoustic signal was simulated theoretically, and the theoretical result agreed with the experimental result very well

Combining microwave and ultrasound: scanning thermoacoustic tomography

Scanning thermoacoustic tomography based on microwave-induced thermoacoustic waves was studied. Two-dimensional images of /spl sim/50-mm thick biological tissue samples were obtained experimentally. The thermoacoustic signals were also simulated theoretically. The image resolution was significantly improved compared with purely microwave imaging

Frequency-swept ultrasound-modulated optical tomography of scattering media

A novel frequency-swept ultrasound-modulated optical tomography technique was developed to image scattering media. A frequency-swept ultrasonic wave was used to modulate the laser light passing through a scattering medium. The modulated light was received by an optical detector and was heterodyned with a reference frequency sweep. The heterodyned signal was recorded in the time domain and was then analyzed in the frequency domain to yield a one-dimensional image along the ultrasonic axis. Multiple one-dimensional images obtained at various positions perpendicular to the ultrasonic axis were combined to yield a two-dimensional tomographic image of the medium

High-resolution functional photoacoustic tomography

All-optical imaging has high contrast but poor spatial resolution beyond the ballistic and quasiballistic regimes. All-ultrasonic imaging has high spatial resolution but poor contrast for early stage tumors. Photoacoustic tomography combines the high optical contrast and the high ultrasonic resolution. Our work in this emerging area of research will be summarized in this invited talk. In this technology, a diffraction-based inverse-source problem is solved in the image reconstruction, for which our group developed the rigorous reconstruction theory. We developed a prototype and accomplished noninvasive transdermal and transcranial functional imaging of small-animal brains in vivo