Propagation of limited diffraction beams in biological soft tissues

Recently, diffraction limited beams have received increased attention for use in imaging and material characterization. Properties of two particular types, Bessel beams and the X waves, in lossless media have been reported. In medical applications, however, the propagation media are highly attenuative. The authors investigate propagation of Bessel beams and X waves in attenuating media, like soft tissues. In both cases, field of infinite aperture (ideal beam) and field of finite aperture (practical beam) have been studied. Pulsed beams, which are of interest in pulse echo applications, have been included in the authors´ studies. Results show that Bessel beams do not spread laterally in attenuating media. In contrast, the X waves spread rapidly in such media. Lateral spreading of wideband X waves is linearly proportional to the depth and the attenuation coefficient. Spreading rate is lower for narrowband beams. It is concluded that while Bessel beam can be considered as limited diffraction beam in soft tissues, such assumption is not true for X waves, unless when narrowband signals are used