Diffuse reflectance spectroscopy relies upon the spectral responsivity of the photon remission to the medium’s property for application. Practically, it is imperative to assess the conditions at which the photon remission becomes illy responsive or unresponsive to the change of an otherwise sensible property of the medium. Such limiting cases may be particularly relevant to single-fiber reflectance (SfR) for minimally invasive sensing and center-illuminatedcentral- acquired (CIC-A) geometry for non-contact sensing. The steady-state photon remission of SfR in the absence of absorption, for example, was shown by Monte Carlo (MC) to be insensitive to the scattering changes as the fiberdiameter scaled dimensionless reduced-scattering reaches μ'darea >10. Similar limiting patterns are observed with steady-state CIC-A known to be scalable over steady-state SfR. To gain insights on the conditions of saturation in CIC-A as projectable to SfR, we revise a model of the steady-state photon remission of CIC-A geometry demonstrated in (Sun & Piao, 2022, App. Opt.), which predicts the onset of saturation as the dimensionless reduced scattering increases. The model-projected saturation-level and the corner-condition of the saturation, both being absorptiondependent, are examined against MC simulations. Experiments in non-contact CIC-A geometry were conducted. Diffuse reflectance was collected from two co-centric areas that differ by ~10 times in diameter when responding to the same centered illumination. The limiting-pattern indicative model was applicable to the diffuse reflectance from aqueous samples of the scattering increased to near-saturation followed by absorption increasing. The scattering-saturation may be useful for simplifications such as implementing differential pathlength factor towards real-time assessment of absorption.
A semi-empirical model initiated in 2009 has facilitated clinical investigations of steady-state single-fiber reflectance spectroscopy (SfRS). We demonstrate an integration model for steady-state SfRS. Our model treats the single-fiber diffuse reflectance as the integration of a lever-set spatially resolved diffuse reflectance associated with a light incidence at the center of the fiber over the entire fiber facet. The integration over the collection area with a diameter ݀dfib reproduces the steady-state features of SfRS over the dimensionless reduced scattering μsdfib= [10-2, 103], absorption coefficient μa=[0.001, 1.0] mm-1 and an anisotropy factor ݃g= 0.9 for the Henyey-Greenstein scattering phase function.
Alternating magnetic field (AMF) configurable at a range of frequencies is a critical need for optimization of magnetic nanoparticle based hyperthermia, and for their application in targeted drug delivery. Currently, most commercial AMF devices including induction heaters operate at one factory-fixed frequency, thereby limiting customized frequency configuration required for triggered drug release at mild hyperthermia (40-42°C) and ablations (>55°C). Most AMF devices run as an inductor-capacitor resonance network that could allow AMF frequencies to be changed by changing the capacitor bank or the coil looped with it. When developing AMF inhouse, the most expensive component is usually the RF power amplifier, and arguably the most critical step of building a strong AMF field is impedance-matched coupling of RF power to the coolant-cooled AMF coil. AMF devices running at 10KA/m strength are quite common, but generating AMF at that level of field strength using RF power less than 1KW has remained challenging. We practiced a few techniques for building 10KA/m AMFs at different frequencies, by utilizing a 0.5KW 80-800KHz RF power amplifier. Among the techniques indispensable to the functioning of these AMFs, a simple cost-effective technique was the tapping methods for discretely or continuously adjusting the position of an RF-input-tap on a single-layer or the outer-layer of a multi-layer AMF coil for maximum power coupling into the AMF coil. These in-house techniques when combined facilitated 10KA/m AMF at frequencies of 88.8 KHz and higher as allowed by the inventory of capacitors using 0.5KW RF power, for testing heating of 10-15nm size magnetic particles and on-going evaluation of drug-release by low-level temperature-sensitive liposomes loaded with 15nm magnetic nanoparticles.
In vivo single-fiber reflectance spectroscopy (SfRS) was performed on an orthotopic AY-27 rat bladder
urothelial cell carcinoma model to explore potential spectroscopic features revealing neoplastic changes. AY-27
bladder tumor cells were intravesically instilled in four rats and allowed to implant and grow for one week, with
two additional rats as the control. A total of 107 SfRS measurements were taken from 27 sites on two control
bladders and 80 from four AY-27 treated bladders. The spectral profiles obtained from AY-27 treated bladders
revealed various levels of a methemoglobin (MetHb) characteristic spectral feature around 635nm. A multisegment
spectral analysis method estimated concentrations of five chromophore compositions including
oxyhemoglobin, deoxyhemoglobin, MetHb, lipid and water. The total hemoglobin concentration ([HbT]), the
MetHb proportion in the total hemoglobin and the lipid volume content showed possible correlations. The 80
measurements from the AY-27 treated bladders could separate to three sub-sets according to the MetHb
proportion. Specifically, 72 were in subset 1 with low proportion (5.3%<[MetHb]<7%), 6 in subset 2 with
moderate proportion (7%<[MetHb]<30%), and 2 in subset 3 with significant proportion (>30%). When grouped
according to [MetHB], the [HbT] increased from 368 μM of subset 1 to 488 μM of subset 2 to 541 μM of subset
3, in comparison to the 285 μM of the control. The increased total hemoglobin and the elevation of MetHb
proportion may signify angiogenesis and degradation in hemoglobin oxygen-transport. Additionally, the lipid
volume content decreased from 2.58% in the control to <0.2% in the tumor groups, indicating disruption of subepithelium
tissue architecture.
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