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Diagnostic X-Ray Dosimetry
Published in James G. Kereiakes, Marvin Rosenstein, Handbook of Radiation Doses in Nuclear Medicine and Diagnostic X-Ray, 2019
James G. Kereiakes, Marvin Rosenstein
The phantoms consist basically of three regions of different composition and density: a skeletal region consisting of a homogeneous mixture of bone, marrow, and other organic constituents; a lung region; and the remainder of the phantom including the female breasts. A simulated diagnostic X-Ray examination table or wall cassette holder was included to provide a backscattering medium similar to that encountered in actual diagnostic procedures. The table can be positioned either at the front, rear, or side of the phantom. Its composition is tissue equivalent.
2D and 3D scintillation dosimetry for brachytherapy
Published in Sam Beddar, Luc Beaulieu, Scintillation Dosimetry, 2018
Dirk Flühs, Marion Eichmann, Assen Kirov
The following materials have been chosen for the scanner developed at TU Dortmund (Eichmann et al. 2009, 2012). RW3/RW1, which is a water-equivalent plastic for electrons/photons, has been used for all elements directly surrounding or contacting the applicator. All mechanical parts in the area surrounding the eye plaque (distance to plaque surface is greater than ) are made of anodized aluminum, because it is easier to machine than RW3 and ensures the stability of the guide components. Furthermore, aluminum, a low Z material, is chosen in order to minimize backscattering effects and Reece 2004]). Monte Carlo studies indicate no significant dose perturbation due to aluminum at distances of about from the eye plaque surface. At distances of more than from the eye plaque surface, the mechanical and stabilizing elements are made of stainless steel since the dose rate does not exceed of the dose rate at the eye plaque surface (for ). Thus, backscattering effects are negligible.
Theoretical Aspects of Radiation Dosimetry
Published in Gad Shani, Radiation Dosimetry, 2017
The effect of the thickness of tissue-equivalent material on the backscattering of low-energy x-rays has been studied by Lanzon and Sorell [32] by direct measurement for x-ray beams with first-half-value thicknesses in the range 0.5 mm to 0.8 mm Al and for filed sizes ranging from 15 mm in diameter to 70 mm square at 100 mm ssd. Measurements were made in a water phantom using a Nuclear Enterprises 2577 0.2-cm3 thimble ionization chamber with a 0.36-mm thick graphite cap. The x-ray generator was a Philips RT-100 superficial therapy machine. The ionization chamber was positioned with its center at the surface of the water phantom, and a lead disk of thickness 1.5 mm was mounted on the transport carriage. The surface ionization was measured as the lead disk traversed from its depth to the lower edge of the ionization chamber.
OCT Imaging in Infants
Published in Seminars in Ophthalmology, 2022
Sushma Jayanna, Subhadra Jalali, Tapas R Padhi, Komal Agarwal, Jay Chhablani
B scan has been one of the common tools to assess the thickness of choroid in infants. Though spectral domain OCT with sources centered at ∼840 nm wavelength are capable of imaging inner choroid, but fail to capture layers of outer choroid due to backscattering of rays at the RPE and inner choroid. Swept source OCT with 1050-nm wavelength rays helps in reducing these backscattering allowing deeper tissue penetration and visualization. With advent of HHOCT, measurement of choroid in neonates, term and preterm infants have been made possible, allowing us to assess the variation in normal thickness and in common pathological conditions like ROP. Pigmentation of RPE occurs early in second month whereas choroidal pigmentation develops later, around the eighth month. Decreased melanin content in preterm could enhance penetration help in acquiring images of deeper and outer layers of choroid. Choroid on OCT has been noted to be thinner in preterm babies compared to term babies. This could be either due to lack of completely developed RPE at preterm, which could lead to incomplete choroidal vascular development or due to global developmental delay of preterm infants or could be due to endothelial damage caused by the oxidative stress in preterm.44 Further thickness of nasal choroid is noted to be more than temporal part.94
Mathematical and computational modeling for the determination of optical parameters of breast cancer cell
Published in Electromagnetic Biology and Medicine, 2021
Shadeeb Hossain, Shamera Hossain
Multiphysics simulation that performs finite element analysis (FEA) delineates the results obtained through mathematical models and assist in interpreting the biophotonic properties of malignant and healthy cells. The inhomogeneous tissue attributes to light scattering and this quantitative optical property analysis provides pithy morphological information for malignant cell diagnosis (Bouma et al. 2000; Escobar et al. 2004; Mogensen et al. 2009; Nguyen et al. 2009; Sivak et al. 2000; Sridharan et al. 2015). Cancerous cells have stronger optical scattering than their healthier counterparts (Radosevich et al. 2013; Subramanian et al. 2009) and enhanced backscattering spectroscopy (EBS) helps to determine effectively the structural composition of the tissue sample. The scattering (S-parameter) explicates the propagation of electromagnetic waves through dielectric media. The distinction in dielectric properties of tissue is recapitulated in our previous study (Hossain 2020a, 2020b). The primary data from of Suroweic et al. and Sarkar et al. (2011) are used to derive the reflectance and other optical parameters for a sample malignant breast tissue.
Targetability of osteoid osteomas and bone metastases by MR-guided high intensity focused ultrasound (MRgHIFU)
Published in International Journal of Hyperthermia, 2018
Fabrice Bing, Jonathan Vappou, Michel de Mathelin, Afshin Gangi
Successful treatment of OOs requires complete destruction of the nidus, which means that sufficient energy has to penetrate the bone to ensure adequate ablation. Due to its high acoustic absorption, HIFU heats bone tissue with moderate acoustic power and facilitates thermal energy delivery to the nidus [40]; the lesion is then rapidly heated due to its small volume (mean 0.56 cm3 in our series) [21], enabling complete ablation. However, localized backscattering and reflection phenomena may injure adjacent soft-tissues, particularly if poorly perfused [40]. Moreover, OOs may be located next to a nerve, a nerve root (Figures 3 and 4), the spinal cord or an articulation, rendering the ablative procedure particularly hazardous in the absence of adjunctive thermo-protection.