ABSTRACT
Most treatments of the optoacoustic inverse problem assume an idealized, nonattenuating, acoustic medium. However, because optoacoustic tomography (OAT) relies on broadband detection, and ultrasonic attenuation is frequency-dependent, an attenuating medium can produce distortion of the optoacoustic signal and thus blurring and artifacts in reconstructed images. In practice, optoacoustic-imaging experiments must employ transducers with finite temporal response characteristics. This chapter presents the first formulation of the optoacoustic imaging equation accounting for realistic frequency-dependent attenuation. It shows that in the temporal frequency domain, this yields a Helmholtz equation with complex wave number. The chapter obtains a very useful integral equation, relating the Fourier transform of the measured attenuated time signals to the ideal, unattenuated time signals. It explores the effects of frequency-dependent attenuation on image resolution and distortion. Obviously the corrected image is sharper than the uncorrected one, although the magnitude of the overshoot artifacts introduced by the bandpass filtering of the received signals is also higher.
