Remote photoacoustic sensing using speckle-analysis

Abstract

Laser surgery is a rising surgical technique, which offers several advantages compared to the traditional scalpel. However, laser surgery lacks a contact-free feedback system which offers high imaging contrast to identify the tissue type ablated and also a high penetration depth. Photoacoustic imaging has the potential to fill this gap. Since photoacoustic detection is commonly contact based, a new non-interferometric detection technique based on speckle-analysis for remote detection is presented in this work. Phantom and ex-vivo experiments are carried out in transmission and reflection-mode for proof of concept. In summary, the potential of the remote speckle sensing technique for photoacoustic detection is demonstrated. In future, this technique might be applied for usage as a remote feedback system for laser surgery, which could help to broaden the applications of lasers as smart surgical tools.

Contact‐free endoscopic photoacoustic sensing using speckle analysis

“…Lengenfelder et al already demonstrated the feasibility of remote photoacoustic sensing by speckle analysis . However, the detection system used in this work is not fiber based and thus not suitable for endoscopic applications.…”

“…This acoustic signal leads to mechanical deformation when reaching the sample surface generating a tilting with the angle α respective to the original undistorted surface. The speckle‐sensing technique allows the detection of α as explained in detail in . By CW‐illumination of a rough surface, a speckle pattern can be generated.…”

Towards non-contact photoacoustic imaging [review]

“…When a continuous-wave laser illuminates this region, these surface deformations modulate the speckle patterns of the backscattered beam. By characterizing these patterns, information about the surface deformations, and thus the acoustic pressure, can be extracted [ [144] , [145] , [146] , [147] , [148] ].…”

“…Through consecutive measurements, they were able to extract signals from porcine skin phantoms with a 90 μm lateral resolution over a 4 mm penetration depth range. Lengenfelder et al [ 144 ] performed experiments in both reflection and transmission modes for ex-vivo fat tissue imaging. To increase the SNR of the system, the optical exposure was 5-times higher than the ANSI MPE limits for biological tissues.…”

Combined Nd:YAG and Er:YAG lasers for real-time closed-loop tissue-specific laser osteotomy

“…In order to preserve the adjacent soft tissue, several approaches to such differentiation have been developed using the optical properties of the ablated tissues. These methods include optical coherence tomography (OCT) [12,13], Raman spectroscopy [14][15][16][17], autofluorescence spectroscopy [18,19], diffuse reflectance spectroscopy (DRS) [20][21][22][23], ablative optoacoustic techniques [24][25][26][27][28][29], random lasing [30], laser-induced breakdown spectroscopy (LIBS) [31][32][33][34][35][36][37][38][39][40][41][42], and combustion/pyrolysis light analysis [43,44]. However, many of these methods have not been tested in combination with an ablating laser; studies have focused on tissue differentiation only.…”