Full-field speckle interferometry for non-contact photoacoustic tomography

Abstract

A full-field speckle interferometry method for non-contact and prospectively high speed Photoacoustic Tomography is introduced and evaluated as proof of concept. Thermoelastic pressure induced changes of the objects topography are acquired in a repetitive mode without any physical contact to the object. In order to obtain high acquisition speed, the object surface is illuminated by laser pulses and imaged onto a high speed camera chip. In a repetitive triple pulse mode, surface displacements can be acquired with nanometre sensitivity and an adjustable sampling rate of e.g. 20 MHz with a total acquisition time far below one second using kHz repetition rate lasers. Due to recurring interferometric referencing, the method is insensitive to thermal drift of the object due to previous pulses or other motion. The size of the investigated area and the spatial and temporal resolution of the detection are scalable. In this study, the approach is validated by measuring a silicone phantom and a porcine skin phantom with embedded silicone absorbers. The reconstruction of the absorbers is presented in 2D and 3D. The sensitivity of the measurement with respect to the photoacoustic detection is discussed. Potentially, Photoacoustic Imaging can be brought a step closer towards non-anaesthetized in vivo imaging and new medical applications not allowing acoustic contact, such as neurosurgical monitoring or burnt skin investigation.

A Problem of a Displacement Calculation of Tissue Surface in Non-Contact Photoacoustic Tomography

“…Also, it proves the numerical value of the error calculated by the formula (5). The error of the formula (1) is 71 % and for the formula (4) 18 %.…”

“…In the following, a brief introduction in a noncontact PAT setup by Medical Laser Center Lü-beck GmbH and the Institute of Biomedical Optics is given, a detailed description can be found in [5].…”

“…Therefore calculations of the displacement by the formula (1) may have a methodic error that is shown in [5].…”

Contact‐free endoscopic photoacoustic sensing using speckle analysis

“…It is also worth to discuss the main differences of the setup described in this work and the setup of Horstmann et al who established full‐field speckle interferometry for noncontact photoacoustic tomography . They show an interferometric system which measures the axial photoacoustic surface deformation with the phase shift of a probe laser.…”

Non-contact Photoacoustic Imaging Using A Commercial Heterodyne Interferometer

“…The second type, i.e., non-contact optical sensor, can detect PA signal remotely without any physical contact with the sample. It usually utilizes phase- or frequency-modulated light backscattered from sample surface to interferometrically detect ultrasound-induced surface vibration and can be remotely performed [31]–[39]. Exploratory studies have been focused on heterodyne interferometry [31], optical fiber-based interferometry [32], two-wave mixing interferometry [33], multi-beam Fabry-Perot interferometry [34], [35], low-coherence interferometry [36]–[38], full-field speckle interferometry [39], etc.…”