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Inverse Problems in Radiative Transfer
Published in John R. Howell, M. Pinar Mengüç, Kyle Daun, Robert Siegel, Thermal Radiation Heat Transfer, 2020
John R. Howell, M. Pinar Mengüç, Kyle Daun, Robert Siegel
Diffuse optical tomography (Boas et al. 2001) uses near-infrared radiation to infer the optical properties of physiological tissues, which are highly scattering. This technique has been used for oncology, for example, since the absorption and scattering coefficients associated with healthy tissues and cancerous tumors are distinct. The ill-posedness introduced by scattering may be mitigated by modulating the incident light source (e.g., picosecond laser pulses) and then measuring the time-resolved intensity of the light exiting the medium at various locations along the boundary. Charette et al. (2008) summarize techniques for reconstructing the absorption and scattering coefficients using this approach.
Functional Optoacoustic Imaging
Published in Francesco S. Pavone, Shy Shoham, Handbook of Neurophotonics, 2020
The true multi-scale imaging capabilities of optoacoustics can be better appreciated when comparing its dynamic imaging performance with other neuroimaging modalities (Figure 6.8). While optical microscopy can provide micron-scale spatial resolution (Ntziachristos, 2010) along with proven sensitivity to fast calcium- or voltage-related signals, the imaging rate rendered with state-of-the-art volumetric microscopy methods lies in the 1 mm3/s range, which is insufficient for large-scale recording of brain activity at the whole mouse brain level. Moreover, photon scattering remains the fundamental physical limitation for those methods, and thus the imaged volume cannot be extended beyond several hundreds of microns in the depth direction, further impeding acquisition of dynamic information from large tissue volumes. Deep tissue optical imaging can be alternatively done by means of diffuse optical tomography techniques, which, however, suffer from severely impaired spatial resolution that degrades to about 5–10 mm at centimeter-scale depths (Eggebrecht et al., 2014), depending on the type of imaged tissue. On the opposite edge of the performance scale are functional magnetic resonance imaging (fMRI) (Bosshard et al., 2015) or functional ultrasound (fUS) (Mace et al., 2011). Some of these non-optical imaging methods are excellent in visualizing large tissue volumes, including the entire human brain (Moeller et al., 2010). Yet the contrast is mainly representative of tissue morphology, its mechanical properties, or hemodynamics. Despite significant efforts in the past decade, synthesis of specific contrast agents remains difficult for those modalities, limiting their applicability for direct visualization of fast neural activity.
Optical-CT Imaging
Published in George C. Kagadis, Nancy L. Ford, Dimitrios N. Karnabatidis, George K. Loudos, Handbook of Small Animal Imaging, 2018
Xueli Chen, Dongmei Chen, Fenglin Liu, Wenxiang Cong, Ge Wang, Jimin Liang
As a small-animal molecular imaging technology, optical imaging has been attracting increased attention and has been a rapidly developing biomedical imaging field because of its significant advantages in temporal resolution, imaging contrast and sensitivity, nonionizing radiation, and cost-effectiveness (Weissleder and Ntziachristos 2003; Ntziachristos et al. 2005; Tian et al. 2008). The goal of optical imaging is to depict noninvasive in vivo cellular and molecular processes sensitively and specifically, such as monitoring multiple molecular events, cell trafficking, and targeting (Bhaumik and Gambhir 2002; Contag and Bachmann 2002; Massoud and Gambhir 2003). However, optical imaging has been in a planar mode and largely a qualitative imaging tool, which limits its applications. To overcome the limitations, a tomographic counterpart such as optical tomography has been developed and has become a valuable tool in the biomedical imaging field, which integrates multiple optical acquisitions from optical imaging, geometrical structures from computed tomography (CT), and tissue’s optical properties to directly reconstruct the optical probe distribution inside a small living animal. Optical tomography (OT), also called hybrid optical-CT imaging, is capable of three-dimensional (3D) recovery of the location and concentration of the optical probe inside a small living animal (Arridge 1999; Ntziachristos et al. 2002; Gibson et al. 2005). Among the modalities of OT, two main categories can be addressed according to whether the optical probe receives an external excitation source. One category is called spontaneous optical tomography (SOT), in which the optical probes emit luminescent light in the absence of an external excitation source, such as bioluminescence tomography (BLT) and Cerenkov luminescence tomography (CLT) (Wang et al. 2003, 2004; Hu et al. 2010; Li et al. 2010). The other is called passive optical tomography (POT), in which the optical probes can only emit fluorescent light in case of an external excitation source, such as fluorescence-mediated tomography (FMT) and x-ray luminescence computed tomography (XRLT). This chapter aims to review the four typical kinds of OT modalities stated earlier, including the mechanism, the imaging principle, the mathematical model and related reconstruction algorithm, and the prototype system and its biomedical applications.
Deep learning based image reconstruction for sparse-view diffuse optical tomography
Published in Waves in Random and Complex Media, 2021
Mohammad Hosein Jalalimanesh, Mohammad Ali Ansari
Diffuse Optical Tomography (DOT) as a non-invasive optical imaging has been widely applied for oncological and neurovascular imaging [1–12]. DOT applies near-infrared (NIR) light (approximately 600–1000 nm) to probe the variation of spectroscopic properties such as absorption and scattering of biological tissue [6,13]. This method provides spatial distributions of intrinsic tissue optical properties or molecular contrast agents through diffusion model-based reconstruction algorithms using NIR measurements along or near the tissue boundary [13]. A typical DOT system includes an array of source optic fibers attached to the surface of the tissue and multiple detectors (or detection fibers) to receive the intensity of photons on the boundary of the tissue. Due to various cellular structures inside the tissue, the arriving photons are multiply scattered, and a significant part of them are absorbed by chromophores such as blood, water, melanin, bilirubin, and carotenoids [13,14]. Anisotropic scattering of photons inside biological tissue can result in (a) low penetration depth of NIR photons in the brain and joints [13] and (b) degradation of image quality [15].
Use of X-ray micro-computed tomography for the investigation of drying processes in porous media: A review
Published in Drying Technology, 2022
Robert Haide, Stephanie Fest-Santini, Maurizio Santini
Different imaging techniques can be applied to the task, the most prominent of which are tomographic methods such as 3D ultrasound imaging,[36] magnetic resonance imaging (MRI),[37,38] neutron imaging,[39] and, as the literature reviewed in this article suggests, X-ray computed tomography. In contrast to conventional 2D inspection techniques as e.g., reflected or transmitted light microscopy, some optical methods such as laser scanning confocal microscopy can be extended to yield nondestructive optical tomographic capabilities.[40]
Determination of experimental Cherenkov spectrum (200–1050 nm) of 18F and its implications on optical dosimetry: murine model
Published in Radiation Effects and Defects in Solids, 2022
Eugenio Torres-García, Hansel Torres-Velazquez, Luis E. Díaz-Sánchez, Liliana Aranda-Lara, Keila Isaac-Olivé
Optical tomography has an enormous challenge since, due to the close 99% contribution of diffuse radiation to a possible optical image, its quality is expected to be low and does not show reliable information on the geometry and dimensions of the source volume.