Cherenkov and Scintillation Imaging Dosimetry
Arash Darafsheh in Radiation Therapy Dosimetry: A Practical Handbook, 2021
Scintillation is a luminescence process – molecular excitation caused by absorption of ionizing radiation results in emission of light during material electronic relaxation. Numerous studies have shown that under appropriate conditions, scintillation signal can be directly proportional to dose [9]. Plastic scintillators used for dosimetry purposes are often composed of a bulk medium and organic fluorophores, where light production is enabled through fluorescence resonance energy transfer between these two components, with the medium being the conduit for radiation interaction and electron liberation, and the fluorophore being the electron/energy acceptor. A secondary fluorophore (a material that will absorb light at the lower end of the visible light spectrum) is sometimes added to shift the emission spectra to higher wavelengths [10]. Specifically, scintillators emit light when the excited organic fluorophore de-excites via a fluorescence, phosphorescence, or some alternate delayed fluorescence pathway [11].
Routine and Special Techniques in Toxicologic Pathology
Pritam S. Sahota, James A. Popp, Jerry F. Hardisty, Chirukandath Gopinath, Page R. Bouchard in Toxicologic Pathology, 2018
The term “fluorescence” refers to the property of some substances (fluorophores) to absorb light of a certain wavelength called excitation light and simultaneously reemit it at a longer wavelength referred to as emission light. The difference in wavelength between excitation and emission is known as Stokes’ shift and is fundamental to fluorescence labeling (Lichtman and Conchello 2005). Some substances (e.g., vitamin A and porphyrins) fluoresce naturally under ultraviolet excitation, which is primary or autofluorescence. Structures within tissues can also be made to fluoresce by the addition of a fluorochrome, termed secondary fluorescence. Each fluorochrome will fluoresce under light within a range of wavelengths, but optimal fluorescence occurs at a particular wavelength called the excitation peak. Fluorochrome labeling can identify cells, subcellular components, and other materials with a high degree of specificity and a high degree of sensitivity since only an extremely small number of fluorescent molecules are needed for detection by the human eye or digital sensor.
Biocompatibility and Biomaterials
Sirshendu De, Anirban Roy in Hemodialysis Membranes, 2017
The fluorescent microscope is a class of optical microscope but it uses the principle of fluorescence and phosphorescence instead of relying only on reflection and adsorption. The specimen is illuminated by a light of known wavelength and the fluorophores absorb the light, emitting a light of different wavelength. The most conventional way to prepare a fluorescent sample is by using a fluorescent stain, or if the sample itself has fluorescent properties, that is, autofluorescence. Typical components of a fluorescent microscope are a light source (xenon lamp or mercury lamp), an excitation filter, a dichroic mirror, and an emission filter (Figure 3.3a). The filters and dichroic are chosen one at a time in order to match the spectral excitation and emission characteristics of the fluorophore. If there are multicolored fluorophores present in the sample, then multiple images of the single specimen (each of a specific color) are combined to generate the collective image of the specimen. A typical fluorescence microscope is illustrated in Figure 3.3b, and a representative fluorescent image if NIH3T3 cells are presented in Figure 3.3c. The nucleus is stained with DAPI (a blue-colored dye).
A mechanistic review on the dissolution phase behavior and supersaturation stabilization of amorphous solid dispersions
Published in Drug Development and Industrial Pharmacy, 2021
P. Ashwathy, Akshaya T. Anto, M. S. Sudheesh
A variety of methods have been used to analyze phase behavior during LLPS. NMR spectroscopy has been used as a method to determine LLPS by characterizing the broad peak obtained due to molecular proximity during nanoaggregate formation [28]. The peak intensity is mainly determined by the concentration of drug in the dispersed molecular phase. When the colloidal phase is generated during LLPS, peak intensity remains constant on further increase in drug concentration. UV extinction coefficient method is an easy method to observe LLPS [32,40]. The wavelength at which the drug molecule shows no absorbance is selected. A sudden change in the extinction coefficient represents light scattering due to phase separation. LLPS has also been studied using steady-state fluorescence spectroscopy, by monitoring change in fluorescent intensity and wavelength maxima of an environment-sensitive fluorophore when it partitions into a colloidal rich phase during LLPS [29,40,48]. Fluorescence lifetime is an intrinsic property of a fluorophore, which has also been used to study LLPS [48]. It is the time during which a fluorophore remains in an excited state before returning to the ground state by emitting photons. The advantage of fluorescence lifetime is that it is largely independent of the method of measurement (e.g. wavelength of excitation and duration of exposure) and on the intensity and concentration of the fluorophore (under certain constraints).
Use of fluorescein sodium to obtain histological diagnosis of primary Central nervous system lymphoma ghost tumour despite disappearance on intraoperative magnetic resonance imaging: technical note and review of the literature
Published in British Journal of Neurosurgery, 2020
Jia Xu Lim, Daniel Loh, Leanne Tan, Lester Lee
Fluorescein guided surgery (FGS) was first used for intraoperative detection of malignant tumours in the brain in 1948. FS is a fluorophore that fluoresces strongly when exposed to light with a wavelength of 560 nm.24 It accumulates in areas of the brain where there is tumour related blood brain barrier breakdown.25,26 This same process also accounts for gadolinium enhancement on MRI27 and it allows FS usage for real time identification of lesional tissue and tumour margins. FS has primarily been used in glioma surgery where it has been shown to improve gross total resection when used in low doses (3–10 mg/kg) with specialized filters,28–31 or at a higher dose (20 mg/kg) under white light.32–35 In a multi-centre prospective phase II trial (FLUOGLIO) on fluorescein-guided high-grade glioma resection, the sensitivity and specificity of fluorescein in identifying tumor tissue were 80.8% and 79.1% respectively.36
Phenotypic analysis of extracellular vesicles: a review on the applications of fluorescence
Published in Journal of Extracellular Vesicles, 2020
Maria S. Panagopoulou, Alastair W. Wark, David J S Birch, Christopher D. Gregory
Fluorescence provides information about a range of processes, such as the interaction of fluorophores with the solvent or rotational freedom and molecular distances [21]. Here we discuss in detail the potential of fluorescence in the detection and nanometrology of EVs. However, there are also limitations in the use of fluorescence-based techniques for the analysis of biological material that are mainly attributed to interference from an intrinsic fluorescence background signal, the need for labelling, as well as photobleaching and quenching by oxygen. Interestingly, many of these drawbacks are ameliorated by the development of stable fluorophores such as quantum dots (QDs) to minimize photobleaching, as well as the use of far-red dyes to improve tissue penetration and eliminate autofluorescence interference. Indeed, in the case of Stimulated Emission Depletion microscopy (STED) microscopy, photobleaching has been put to good effect in providing the very principle upon which the technique is founded [20,22].
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