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Computed Tomography Imaging in Radiotherapy
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Image quality also depends on the signal-to-noise ratio (SNR), which is increased by either increasing the signal or decreasing the noise. Using higher mAs or higher kVp leads to a better signal but increases the dose to the patient. In general, soft tissue contrast will be better at 120 kVp, but a higher voltage (135 kVp–140 kVp) may be used for a thick patient or for imaging regions containing a large quantity of bone (as in the pelvis). In paediatrics, the kVp and mAs should be kept as low as possible. The amount of noise in the image depends on the ability of the detector and its electronics to perform well at low dose. Commercial CT scanners use raw-data 3D reconstruction filters that reduce image artefacts due to the photon starvation* seen at the level of the shoulders or pelvis. In addition, reconstructed images can be processed by applying a denoising filter that removes the general noise present in the image within areas of uniform density. This may be combined with an edge enhancing filter that improves the visualisation of anatomical boundaries. These additional algorithmic 3D filters reduce noise, thus improving image quality at low dose, and can partially correct for artefacts. Artefact corrections will be further discussed in Section 32.4.2.
Review of the Human Brain and EEG Signals
Published in Teodiano Freire Bastos-Filho, Introduction to Non-Invasive EEG-Based Brain–Computer Interfaces for Assistive Technologies, 2020
Alessandro Botti Benevides, Alan Silva da Paz Floriano, Mario Sarcinelli-Filho, Teodiano Freire Bastos-Filho
The signal-to-noise ratio (SNR) is defined as the ratio of the average power in the signal to the average power in the noise [38]. As more epochs are used, the SNR of the time-locked event increases, allowing the observation of the ERP. In the ideal case, it is assumed that the measured EEG signals are made of a sequence of event-locked ERPs with invariable latency and shape, in addition to a noise, which can be approximated by a zero-mean Gaussian random process that is uncorrelated between trials and not time-locked to the event. The average power of the ERP signal is given by the expected value of its energy. When a signal is a stationary stochastic process, its power is defined to be the value of its correlation function at the origin. As the noise is supposed to be a stationary zero-mean Gaussian random process, its mean and variance do not vary with respect to time. Then, the correlation function at the origin is equal to its variance. The SNR of the EEG increases proportionally to the number of trials, and an excessive number of epochs will not result in significant changes in the ERP curve.
Exposure Indicators
Published in Christopher M. Hayre, William A. S. Cox, General Radiography, 2020
Detector quantum efficiency is the efficiency of a system to maintain signal to noise ratio. Increased signal to noise ratio increases the image quality. The exposure used is inversely proportional to the detector quantum efficiency; therefore, the higher the detector quantum efficiency, the lower the exposure for a given image quality. Additionally, detector quantum efficiency is considered by many as a standard of receptor performance encompassing detector efficiency, noise, and spatial resolution (Campeau and Fleitz, 2017: 155; Carter and Veale, 2014: 33; Williams et al., 2007: 378).
Acute physiological and functional effects of repetitive shocks on the hand–arm system: a pilot study on healthy subjects
Published in International Journal of Occupational Safety and Ergonomics, 2023
Jonathan Witte, Alexandra Corominas, Benjamin Ernst, Uwe Kaulbars, Robert Wendlandt, Hans Lindell, Elke Ochsmann
Surface electromyography (EMG) (Shimmer 2R; Shimmer Sensing, Ireland) was sampled at 512 Hz during the exposures on three muscles previously identified as potentially involved in absorbing shocks in the hand–arm system: triceps muscle, extensor digitorum muscle and flexor carpi ulnaris muscle [26]. EMG electrodes were aligned along the palpable muscle bellies in a bipolar configuration at approximately 25 mm distance. Manoeuvres for maximal voluntary isometric contractions (MVICs) against resistance as well as static force measurements with 50 N of push force against the handle were carried out, serving as references. The EMG data were matched with accelerometric data and postprocessed by bandpass filtering (lower frequency limit = 10 Hz, upper frequency limit = 250 Hz), rectification and integration using DIAdem version 2018. Activity integrals were defined as an EMG signal during the shock impact, i.e., between the zero crossing of the corresponding acceleration signal, and expressed as both % MVIC and % static load. To improve overall reliability, data collection was limited to measurements with a satisfying signal-to-noise ratio (SNR > 5), with the SNR defined as the quotient of average activity integral and the 5% smallest activity integrals.
Evaluation of a game-based hearing screening program for identifying hearing loss in primary school-aged children
Published in International Journal of Audiology, 2023
Patrick Bowers, Kelley Graydon, Gary Rance
The speech-in-noise game is designed to be sensitive to SPD. A target English language speech signal (an object’s name) is applied to both ears at a 0° azimuth to the head (using a head-related transfer function). Simultaneously, distractor speech signals (a story) using the same voice are applied to both ears using head-related transfer functions (at a ±90° azimuth to the head). The signal-to-noise ratio (SNR) is decreased by 2 dB for a correct response and increased by 2 dB for no response or 4 dB for an incorrect response. A correct response consists of the child tapping the correct object named by the talker. The result of this test is a speech reception threshold (in noise), which is the average SNR the child required for them to correctly identify 50% of the target words following a practice phase (Dillon et al. 2018).
Manganese-containing polydopamine nanoparticles as theranostic agents for magnetic resonance imaging and photothermal/chemodynamic combined ferroptosis therapy treating gastric cancer
Published in Drug Delivery, 2022
Zhian Chen, Zhenhao Li, Chuangji Li, Huilin Huang, Yingxin Ren, Zhenyuan Li, Yanfeng Hu, Weihong Guo
The morphology and elements mapping of NPs were characterized by transmission electron microscopy (TEM) (JEOL JEM-2100F TEM, Tokyo, Japan). The chemical state and composition were characterized by X-ray photoelectron spectroscopy (XPS) (ESCALAB250Xi, Thermo Fisher, Waltham, MA). Electron spin resonance (ESR, JEOL, Ltd., Tokyo, Japan) was used to measure the production of •OH. The Mn content in the PP@Mn NPs was determined by inductively coupled plasma mass spectrometry (ICP-MS) (Optima7300DV, PerkinElmer, Waltham, MA). A Shimadzu UV-2600 UV-vis spectrophotometer (Kyoto, Japan) was used to acquire ultraviolet (UV)–vis absorption spectra. The hydrodynamic diameter and zeta potentials were measured using a Zetasizer Nano ZS (Malvern, Worcestershire, UK) by dynamic light scattering (DLS). The powder X-ray diffraction (XRD) patterns were acquired on a PANalytical X’Pert PRO X-ray diffractometer. The photothermal capability was assessed used an 808 nm semiconductor lasers (Shanghai Xilong Optoelectronics Technology Co., Ltd., Shanghai, China). Relaxivity of different PP@Mn NPs concentrations (0, 125, 250, 500, and 1000 μg/mL) was placed in tube holders for measurements by a 3.0-T Philips Achieva clinical MRI scanner (Philips Healthcare, Best, The Netherlands). The signal-to-noise ratio (SNR) was defined as: SNR = SImean/SDnoise. Infrared (IR) thermal images were acquired using an IR thermal camera (FLIR E50, Wilsonville, OR).