Endoluminal surgery for the treatment of early stage colorectal cancer is typically based on electrocautery tools which imply restrictions on precision and the risk of harm through collateral thermal damage to the healthy tissue. As a potential alternative to mitigate these drawbacks we present laser machining of pig intestine by means of picosecond laser pulses. The high intensities of an ultrafast laser enable nonlinear absorption processes and a predominantly nonthermal ablation regime.
Laser ablation results of square cavities with comparable thickness to early stage colorectal cancers are presented for a wavelength of 1030 nm using an industrial picosecond laser. The corresponding histology sections exhibit only minimal collateral damage to the surrounding tissue. The depth of the ablation can be controlled precisely by means of the pulse energy. Overall, the application of ultrafast lasers to ablate pig intestine enables significantly improved precision and reduced thermal damage to the surrounding tissue compared to conventional techniques.
Near-infrared spectroscopy (NIRS) is a popular sensing technique to measure tissue oxygenation noninvasively. However, the region of interest (ROI) is often beneath a superficial layer, which affects its accuracy. By applying focused ultrasound in the ROI, acousto-optic (AO) techniques can potentially minimize the effect of physiological changes in the superficial layer. Using absorption perturbation experiments in both transmission and reflection modes, we investigated the spatial sensitivity distributions and mean penetration depths of an AO system based on a digital correlator and two popular NIRS systems based on i. intensity measurements using a single source and detector configuration, and ii. spatially resolved spectroscopy. Our results show that for both transmission and reflection modes, the peak relative sensitivities of the two NIRS systems are near to the superficial regions, whereas those of the AO technique are near to the ROIs. In the reflection mode, when the ROI is deeper than 14 mm, the AO technique has a higher absolute mean sensitivity than the two NIRS techniques. As the focused ultrasound is moved deeper into the turbid medium, the mean penetration depth increases accordingly. The focused ultrasound can shift the peak relative sensitivity of the AO measurement toward its focused region.
Optical systems based on near infrared spectroscopy probe biological tissue oxygenation of a relatively large region.
The acousto-optic (AO) method can tag photons by focused ultrasound in a region of interest within the tissue for
potential localized oxygenation sensing. This study aimed to compare the regional sensitivity between the optical and
AO sensing techniques. The regional sensitivity was defined as the amount of change observed in the measured signal in
response to a small localized change in the optical absorption. In both reflection and transmission configurations, optical
systems based on a single source and detector have been shown to be more sensitive to the absorption variation in the
superficial region. The results demonstrate that the AO sensitivity region depends on the location of the ultrasound focal
region as well as the distribution of the optical fluence. In the transmission mode, the optimal AO sensitivity region has
been found to be in the ultrasound focal region. In the reflection mode, however, the optimal sensitivity region of AO
does not always coincide with the location of the ultrasound focal region. Instead, the AO measurement is also sensitive
to the local absorption change in regions between the ultrasound focal region and the optical probes. In general, the AO
method can probe deeper into the phantom as compared to the optical measurements.
The use of ultrasonic tagging of multiple scattered photons within turbid media for tomographic imaging is typically
performed using optical detection in transmission mode. This study aimed to optimize the detection of the acousto-optic
(AO) signal in cylindrical geometry, with a view to using the technique to measure blood oxygenation in the internal
jugular vein of infants in the future. In our experiments, homogeneous phantoms of multiple transport scattering
coefficients were constructed for the described geometry mimicking the infant neck. The optical source was
systematically repositioned at different angles relative to the optical detector and the resulting AO signal was measured.
The experimental results were also compared to focused ultrasound AO Monte Carlo (MC) simulation results. It was
found that the optimal modulation depth and noise variance were highly dependent on the overlap region between the
optical path length of the optical source-detector pair and the ultrasound focal zone. Therefore the optimal positions for
both the optical and ultrasound probes could be estimated from both experimental and simulation results for a given
geometry.
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