Experimental study of z resolution in acousto-optical coherence tomography using random phase jumps on ultrasound and light

Abstract

Acousto-optical coherence tomography (AOCT) is a variant of acousto-optic imaging (also called ultrasound modulated optical tomography) that makes possible to get resolution along the ultrasound propagation axis z. We present here AOCT experimental results, and we study how the z resolution depends on time step between phase jumps T(φ), or on the correlation length Δz. By working at low resolution, we perform a quantitative comparison of the z measurements with the theoretical point spread function. We also present images recorded with different z resolution, and we qualitatively show how the image quality varies with T(φ), or Δz.

Ultrafast acousto-optic imaging with ultrasonic plane waves

“…The size of the inclusion can be calculated in both directions thanks to the same kind of fit as presented in Eq. (24). One finds then a vertical size of the inclusion of 2 mm, which is still relevant with the expected size, though a bit smaller.…”

“…where Σ di f f represents a Gaussian fit of the envelope, Σ incl a Gaussian fit of the inclusion and C is a fitted constant. This represents a good approximation of an absorbing inclusion in the middle of a diffused light pattern [24]. The size of the inclusion can be measured from the FWHM of Σ incl and has a value of 2.5 mm which is the expected value.…”

“…The distortion of the image is clearly appearing here since the scattered light envelope is almost flat though it is expected to be Gaussian-shaped as explained in Eq. (24) and visible on the green profile. The blue profile corresponds to the inclusions on the plane waves AO image using two probes and confirms that the two inclusions are well separated.…”