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fMRI and Nanotechnology
Published in Sarhan M. Musa, Nanoscale Spectroscopy with Applications, 2018
Aditi Deshpande, George C. Giakos
The BOLD response cannot discriminate between forward and backward mechanisms that take place. Both restraining and stimulating inputs to a neuron from other neurons contribute toward the BOLD response, which is a summation of all the inputs combined. Also, the magnitude of the BOLD signal is not a good indicator of its behavior. An intricate and difficult cognitive task might require high perfusion in the beginning and hence displays a strong BOLD signal (related to good performance by the patient), but the need of excess blood flow might decrease with time as the subject gets better at it. This is because the brain demands lesser perfusion to save energy and reduce wastage of excess of it by channeling the neurons more efficiently. Factors that can alter the hemodynamic response of the body can affect the BOLD response, such as age, medication, anxiety, and diseases (Figure 10.18).
The Multi-Aspect Measurement Approach: Rationale, Technologies, Tools, and Challenges for Systems Design
Published in Pamela Savage-Knepshield, John Martin, John Lockett, Laurel Allender, Designing Soldier Systems, 2018
Kelvin S. Oie, Stephen Gordon, Kaleb McDowell
Functional near-infrared spectroscopy (fNIRs) While the use of hemodynamics-based functional neuroimaging measurement modalities such as fMRI and positron emission tomography (PET) have been essential to the explosive growth observed in cognitive neuroscience, their deployment in operationally relevant environments is clearly infeasible. By contrast, fNIRs provides a non-invasive, minimally intrusive, relatively inexpensive, and portable method for hemodynamic imaging in real-world environments. fNIRs works by irradiating the scalp with near-infrared light in the range of 700–900 nm. Most biological tissues are relatively transparent to light in this range. However, oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) in the blood are not, and differentially absorb light in this functional range. Observed changes in the concentrations of oxy-Hb and deoxy-Hb can then be used to measure the hemodynamic response, providing an index of brain activity (Aslin and Mehler 2005, Izzetoglu et al. 2007).
Artifacts and Pitfalls of fMRI
Published in Ioannis Tsougos, Advanced MR Neuroimaging, 2018
The hemodynamic response also poses limitations in temporal resolution of the fMRI signals acquired. EPI images have an acquisition window of about 20–30 ms, which relative to the inertia and variability of the hemodynamic response is quite fast and adequate. Nevertheless, the problem arises when the signal is influenced by the underlying vasculature a voxel covers. That is, if a voxel happens to cover large vessel effects, the magnitude of the signal can be up to an order of magnitude larger than the capillary effects and the timing somewhat delayed for up to 4 sec. It follows that signal temporal dynamics varies, and it can generally be described by an increase of the fMRI signal, approximately 2 sec following neuronal activity as well as a plateau in the so-called “on” state for about 7–10 sec (Buxton et al., 2004).
Brain oxygenation during multiple sets of isometric and dynamic resistance exercise of equivalent workloads: Association with systemic haemodynamics
Published in Journal of Sports Sciences, 2022
Andreas Zafeiridis, Anastasios Kounoupis, Stavros Papadopoulos, Aggelos Koutlas, Afroditi K Boutou, Ilias Smilios, Konstantina Dipla
This is the first study to compare brain oxygenation responses between isometric and dynamic-RE of similar exercise characteristics. We hypothesized that changes in cerebral oxygenation and blood volume (tHb) would be higher during the dynamic-RE protocol than in isometric-RE of similar exercise characteristics, as previous studies showed higher CO and muscle activity during dynamic than isometric RE (Lewis et al., 1985; Vedsted et al., 2006). In contrast, we observed that the pattern of change in prefrontal NIRS parameters was consistently similar between the protocols, despite their marked differences in systemic haemodynamics (Figure 3). The fact that the type of contraction did not differentially affect the oxygenation and blood volume responses during isometric and dynamic-RE of similar exercise characteristics is a unique observation indirectly inferring to relatively similar changes in (i) brain response to maintain a predetermined force and (ii) cerebral haemodynamic response (oxygenation, perfusion). The comparable increases in O2Hb and tHb also imply that cerebral hyper-perfusion does not differ between the two RE-protocols. The lack of difference in cerebral oxygenation between the isometric and dynamic-RE in our study may be attributed to well-matched exercise characteristics. Thus, the type of contraction per se during RE does not appear as a contributing factor to cerebral oxygenation and blood volume responses when the exercise characteristics are well matched. Up to date, the one study that compared cerebral oxygenation between isometric- and dynamic-RE (Matsuura et al., 2011) used a single exercise set and did not match the protocols for either intensity, duration or workload; factors that may affect cerebral oxygenation/blood flow (Bhambhani et al., 2014; Korotkov et al., 2005).
Developments in the human machine interface technologies and their applications: a review
Published in Journal of Medical Engineering & Technology, 2021
Harpreet Pal Singh, Parlad Kumar
Few other types of metabolic neuroimaging techniques are also available for medical diagnosis by accessing the biosignals like functional magnetic resonance imaging (fMRI), positron emission tomography (PET) and functional near infra-red spectroscopy (fNIR) [133]. Functional magnetic resonance imaging is a type of MRI scanning technique that determines the hemodynamic response by detecting the changes in blood flow, thereby able to measure the brain metabolic activity. It is further used for the diagnostics and treatment of various brain disorders and other kinds of diseases that cannot be detected by any other MRI technique [134]. PET is a radiology procedure used to examine the body tissues at specific conditions. The major area of application in which PET is currently being used is neurology, cardiology and oncology. In the PET examination procedure, very little radioactive substance called radionuclide is injected into the patient’s blood that emits the positrons and subsequently emerged gamma rays are monitored using specialised apparatus [32,135]. In the fNIR technique, infra-red light is induced into the brain and subsequent changes of reflected light are examined to detect changes in various wavelengths. Based on scattering and absorption attributes, the shape of function maps of brain activities is developed [136]. But fNIR does not find extensive use by researchers because of its low temporal resolutions [137]. Near infra-red spectroscopy (NIRS) is used in critical care to monitor the oxygenation of the regional brain tissues [138]. Single-photon emission computed tomography (SPECT) is a nuclear tomographic imaging technique that follows the procedure of injecting a radioactive substance into the bloodstream of the patient and a specially designed gamma camera creates 3D images of the internal organs or the tissues to be examined [139].