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Magnetic Resonance Imaging
Published in Shoogo Ueno, Bioimaging, 2020
Imaging of diffusion phenomena using MRI has been carried out since the 1980s, mainly for self-diffusion of water molecules contained in living tissue [10]. Clinical applications began to be extensively demonstrated in the 1990s when rapid imaging techniques became available. These clinical studies showed a major advantage of diffusion MRI is in the diagnosis of acute cerebral infarction [11]. In the 1990s, active treatment of cerebral infarction began, and diffusion-weighted images that can depict the lesion in several hours after the onset were rapidly spread. In addition to acute cerebral infarction, diffusion-weighted images are known to show contrasts different from T1-weighted and T2-weighted images for tumors, and their usefulness has been established. Furthermore, in the tissue composed of fibrous cells such as the white matter of the brain, it has become possible to visualize the structure of the nerve fiber bundles in a three-dimensional manner by utilizing the property that the diffusion coefficient varies depending on the direction [12].
Diffusion Imaging and Tensor Physics for the Clinician
Published in Andrei I. Holodny, Functional Neuroimaging, 2019
The term “diffusion” is often used to describe the intermingling of one substance into another, driven by a concentration gradient. This process can be described mathematically with Fick’s law, in which the flux of molecules across a boundary is proportional to the concentration gradient across it. The constant of proportionality is the diffusion constant D, the same constant as in Einstein’s equation for the mean-squared displacement. It is the random motion of the molecules that allows this diffusive intermingling, so it is perhaps not surprising that the same constant appears in both equations. The term “self-diffusion” is used to describe water molecules spreading out among other water molecules. It is worth emphasizing that unlike tracer methods, diffusion MRI simply follows the movement of water molecules, without the need to introduce a foreign contrast agent.
Dose Coefficients
Published in Shaheen A. Dewji, Nolan E. Hertel, Advanced Radiation Protection Dosimetry, 2019
Nolan E. Hertel, Derek Jokisch
This section follows a pedestrian approach compared to the more detailed approach used by Schaeffer (1973). The reader interested in a more detailed discussion, including the accompanying derivations, is directed to that reference. The Boltzmann transport equation was formulated to calculate the coefficient of self-diffusion for a gas in which molecules are assumed to scatter as elastic spheres. This is equivalent to the transport of radiation, particularly neutral particle transport, with the exception that, for transport in a medium, particle–particle collisions are ignored due to their rarity compared to particle interactions with atoms in the medium through which they are transported.
Development and anti-Candida evaluation of the vaginal delivery system of amphotericin B nanosuspension-loaded thermogel
Published in Journal of Drug Targeting, 2018
Tianyuan Ci, Luo Yuan, Xiaoyan Bao, Yuting Hou, Hao Wu, Haifeng Sun, Dinglingge Cao, Xue Ke
During the gel erosion process, AmB was sustained released from P407/P188 Poloxamer hydrogel for ∼12 h (Figure 5(B)). And the releasing mechanisms were referring to both drug diffusion and polymer erosion, and predominated by polymer erosion. The release mechanisms were in accordance with the properties of both drug and hydrogel. That is, the drug AmB is water-insoluble and not easy to self-diffusion, and Poloxamer hydrogel is easily to erosion in water for its structure of micelle close packing and micelle entanglements [25,31]. And there is no significant difference between the two profiles of AmB NPs/thermogel and AmB NPs/thermogel (without egg lecithin), indicating the specific drug states, such as only AmB NPs or AmB/lecithin complex NPs, showed little effects on AmB release in this system.
Investigating protein–excipient interactions of a multivalent VHH therapeutic protein using NMR spectroscopy
Published in mAbs, 2022
Jainik Panchal, Bradley T. Falk, Valentyn Antochshuk, Mark A. McCoy
Interaction profiling was accomplished using a protein-enhanced diffusion-ordered spectroscopy (DOSY) experiment, Figure 4a. First, we collected translational self-diffusion data on the MV-VHH with 0% sucrose. The detection dimension of this data set is dominated by protein peaks, but an acetate signal was also identified at 1.9 ppm. From the MV-VHH diffusion data, a hydrodynamic radius, Rh, of 3.7 nm was calculated, whereas the aC and aD fragments had a hydrodynamic radius of 1.65 nm. These data indicate that the MV-VHH is in an extended conformation, which is consistent with the 2D 1H,13C sfHMQC fingerprinting studies in Figure 2, which found that the folded VHH domains are flexibly linked with minimal intramolecular interactions. The cartoon in Figure 4b is a PyMOL27 model of the MV-VHH protein that incorporates NMR Rh determination, with non-interacting domain positioning. The protein structure is a homology model, created using the SWISS-model,28 using the MV-VHH primary sequence. Rh was calculated with HullRad.29 The aC VHHs are shown in orange, and the aD VHH is shown in green. The VHHs are joined by a flexible 35-residue linker shown in gray. The gray sphere (radius 2.8 nm) represents the extent of the surface anticipated from a compactly folded, single domain 42 kDa protein. Note that while our model for the MV-VHH protein is not compact, it is not completely extended, with a minimum interdomain distance ~30 Å
Self-emulsifying drug delivery systems: a novel approach to deliver drugs
Published in Drug Delivery, 2022
These methods are utilized to investigate the dynamics and structure of microemulsions. Self-diffusion assessments utilizing several tracer approaches, most often radio labeling, provide information on the components' mobility and microenvironment. The magnetic gradient on the samples is used in the Fourier transform pulsed-gradient spin-echo (FT-PGSE) methods, which enables for the simultaneous and quick measurement of the self-diffusion coefficients of several components. The Stokes–Einstein equation may be used to compute the self-diffusion coefficient. T is the absolute temperature, η is the viscosity, K is the Boltzmann constant, and r is the radius of droplet.