Optical coherence tomography of the ex vivo human and rat brain tissue samples is performed. The analysis of attenuation coefficient, coefficient based on effective refractive index, and their standard deviations was obtained from OCT measurements.
We summarize and discuss multifunctional medical instruments based on sapphire shaped crystals. Such instruments are able to combine several modalities, such as interstitial exposure to laser radiation, fluorescent diagnosis, as well as tissue resection, aspiration and cryodestruction. Sapphire instruments enable biocomopatability, withstand extremely low and high temperatures, along with operation in harsh environment. Sapphire fibers and waveguides also allows imaging of biological objects in THz range. In visible and infrared ranges, these instruments can be combined with optical fibers via small internal channels, which can be produced during sapphire crystal growth by means of the edge-defined film-fed growth (EFG) technique. This talk covers the resent developments and experimental investigations of sapphire needles, cryoapplicators, scalpels, and fibers.
In this paper, we study the examples of sapphire capillary needles for interstitial laser thermotherapy and photodynamic therapy. Such needles are fabricated by means of the Edge-defined Film-fed Growth (EFG) technology, so that they feature an as-grown optical quality. The optical fiber, which is used for delivering laser radiation to tissue, is placed inside the capillary channel in the needle's body. The channel is closed at the one side, therefore, the fiber is protected from the direct contact with biological tissue. The needle's tip form plays a significant role in the formation of the particular radiation pattern and the corresponding volume of treatment. Using a tissue phantom, we have experimentally studied the radiation distribution formed by sapphire needles with different tip angle. The results demonstrate rather smooth spatial distribution of light, confirming the high surface quality of the needles and the ability to control the amount of exposed tissue by changing the tip angle.
In this work, we present a brief overview of sapphire medical instruments. Sapphire demonstrates a unique combination of physical properties, such as high hardness and chemical inertness, biocompatibility and high thermal conductivity, high transparency in a wide spectral range that makes it suitable for various medical applications. We demonstrate the examples of scalpel, capillary needle for laser therapy, neuroprobe and applicator for cryosurgery. Each of them combines different modalities in one instrument. Among them are tissue resection, therapy via electromagnetic wave delivering, aspiration, diagnosis, and tissue freezing. Sapphire instruments can be accompanied with magnetic resonance imaging and allow multiple sterilization.
An intraoperative diagnosis of brain tumors is one of the most urgent and challenging problem of the modern neurosurgery. The most important measure of the effectiveness of treatment is the complete tumor resection. The existing methods of the intraoperative neurodiagnosis of tumors are plagued with limited sensitivity, especially for low-grade gliomas, and, furthermore, can remain rather expensive. The recently reported results of optical coherence tomography (OCT) application for finding differences between healthy and malignant tissues make it become one of the promising label-free diagnostic instruments. Nevertheless, the wide use of OCT in clinical practice is limited by the lack of complete study of its opportunities in neurosurgery, which leads to a huge scientific interest. Our research, aimed at the study of the ability of OCT for the intraoperative diagnosis of brain gliomas of different grades, has the goal to observe the differences between OCT signals obtained for ex vivo samples of various types of human brain glioma and intact brain tissue. We propose a 3D-feature based data analysis that demonstrates promising results in differentiation of tissue classes.
The problem of complete resection of human brain glioma during neurosurgery is still one of the most challenging, since the existed diagnostic methods are plagued with limited sensitivity and specificity; they remain laborious, time-consuming and/or rather expensive. The present work includes the ex vivo study of malignant brain gliomas featuring different grades (according to the World Health Organization) by means of two methods, i.e. optical coherence tomography (OCT) and terahertz pulsed spectroscopy (TPS). Both OCT and TPS studies were done just after the tissue resection and included gelatin embedding of the samples for conservation of water content. The further histological examination using hematoxylin and eosin (H&E) stained microscopy approved the diagnosis. The results demonstrate the potential of TPS to differentiate intact and malignant tissues and the potential of OCT to differentiate low- and high-grade gliomas as well as intact tissue and low-grade gliomas. Thus, combination of these modalities seems to be rather prospective for the further development of the advanced intraoperative diagnostic tools.
Intraoperative diagnosis of brain tumors remains a challenging problem of modern neurosurgery. A complete resection of tumor is the most important factor, determining an efficiency of its treatment, while an incomplete resection, caused by inaccurate detection of tumor margins, increases a probability of the tumor recurrence. The existing methods of the intraoperative neurodiagnosis of tumors are plagued with limited sensitivity and specificity; they remain laborious, time-consuming and/or rather expensive. Therefore, the development of novel methods for the intraoperative diagnosis of gliomas relying on modern instruments of medical imaging is a topical problem of medicine, physics, and engineering. In our research, we studied the ability of dual-modality imaging that combines such methods as optical coherence tomography (OCT) and terahertz (THz) pulsed spectroscopy, for intraoperative diagnosis of brain tumors with a strong emphasize on a human brain gliomas. We performed experimental studies of the frequency-dependent THz dielectric properties and OCT imaging of healthy (intact) and pathological brain tissues ex vivo in order to analyze the prospect for differentiation between tissue classes. The observed results highlight a potential of the considered instruments in the label-free intraoperative neurodiagnostics.
We have proposed a wavelet-domain de-noising technique for imaging of human brain malignant glioma by optical coherence tomography (OCT). It implies OCT image decomposition using the direct fast wavelet transform, thresholding of the obtained wavelet spectrum and further inverse fast wavelet transform for image reconstruction. By selecting both wavelet basis and thresholding procedure, we have found an optimal wavelet filter, which application improves differentiation of the considered brain tissue classes – i.e. malignant glioma and normal/intact tissue. Namely, it allows reducing the scattering noise in the OCT images and retaining signal decrement for each tissue class. Therefore, the observed results reveals the wavelet-domain de-noising as a prospective tool for improved characterization of biological tissue using the OCT.
We present the nanoparticle-enabled experimentally trained wavelet-domain denoising method for optical coherence tomography (OCT). It employs an experimental training algorithm based on imaging of a test-object, made of the colloidal suspension of the monodisperse nanoparticles and contains the microscale inclusions. The geometry and the scattering properties of the test-object are known a priori allowing us to set the criteria for the training algorithm. Using a wide set of the wavelet kernels and the wavelet-domain filtration approaches, the appropriate filter is constructed based on the test-object imaging. We apply the proposed approach and chose an efficient wavelet denoising procedure by considering the combinations of the decomposition basis from five wavelet families with eight types of the filtration threshold. We demonstrate applicability of the wavelet-filtering for the in vitro OCT image of human brain meningioma. The observed results prove high efficiency of the proposed OCT image denoising technique.
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