ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
SQUID magnetometry is used to overcome the general problems of magnetoencephalography, which are the weakness of the magnetic fields generated by biological tissue (more so in brain tissue than in other tissues of interest, such as the heart) and the strength of the magnetic sources in the environment. SQUID magnetometry addresses these problems by allowing for the accurate detection of very low magnetic field strengths. It measures the quantum mechanical tunnelling current that passes through a link in a superconducting loop, this current being dependent on the magnetic flux through the loop. An individual SQUID magnetometer can be used to detect localized magnetic fields. An array of SQUIDs allows one to build a tomographic image of brain tissue in exactly the same way as other functional neuroimaging techniques do.
Restoration: Nanotechnology in Tissue Replacement and Prosthetics
Harry F. Tibbals in Medical Nanotechnology and Nanomedicine, 2017
The SQUID is the highest sensitivity magnetometer commercially available. Magnetic scanning systems approved for mapping neural activity are based on SQUID sensors. Although the first generation was bulky, it has been used successfully for brain and cardiac imaging. A second-generation design has been optimized with highly sophisticated software and good engineering to increase resolution and reduce the size and weight of the cooling and shielding systems. Applications include diagnostic imaging for neonatal brain assessment, liver susceptometry, and gastric ischemia, difficult to diagnose and serious conditions [231,232].
Motion Sensors in Osteoarthritis: Prospects and Issues
Daniel Tze Huei Lai, Rezaul Begg, Marimuthu Palaniswami in Healthcare Sensor Networks, 2016
Hybrid systems have been created that add an additional sensor, such as a magnetometer, to compensate for remaining deficiencies in the inertial sensors. A magnetometer is essentially an electronic compass, measuring heading (i.e., sensor direction in the horizontal plane) in relation to the earth’s magnetic field (which is not provided by the other two sensor types). However, magnetometers are not without their own drawbacks, which can be severe, mainly due to their sensitivity to other ferromagnetic influences in their surrounding environment (de Vries et al. 2009; Roetenberg, Baten, and Veltink 2007).
Patching for Amblyopia: A Novel Occlusion Dose Monitor for Glasses Wearers to Track Adherence
Published in Journal of Binocular Vision and Ocular Motility, 2022
Tessnim R. Ahmad, Meghan C. Martinez, Sameea Tahir, Omondi L. Nyong’o
The analysis algorithm uses the time sequence of magnetic field strength vectors to infer times of patch wear and the nature of patient activity such as head motion. When a patch is worn, its magnetic presence can be inferred from the two magnetometers, which provide a measure of the strength, direction, and curvature of the magnet’s highly non-uniform field. Although the field may be smaller than the Earth’s background field, the Earth’s field is uniform and therefore provides equal and canceling effects at each magnetometer. This allows us to clearly observe the presence or absence of a non-uniform magnetic field. Figure 3 illustrates the magnetic fields of the Earth versus patch magnet. Figure 4a,b demonstrate the magnetometer vectors. Using a mathematical model of the patch magnet’s field, the combined signals at the magnetometers can discriminate between the magnet and another source of a non-uniform field, such as headphones or mobile telephones. Further, the changing, individual signals of each magnetometer indicate if the glasses are in motion and their orientation within the Earth’s field.
Analysis, comparison and representation of occupational exposure to a static magnetic field in a 3-T MRI site
Published in International Journal of Occupational Safety and Ergonomics, 2022
Valentina Hartwig, Cristiano Biagini, Daniele De Marchi, Alessandra Flori, Chiara Gabellieri, Giorgio Virgili, Luca Fabiano Ferrante Vero, Luigi Landini, Nicola Vanello, Giulio Giovannetti
Exposure due to movements in the static magnetic field of an MRI site (GE_Signa_HD 3T at Fondazione Toscana G. Monasterio, Italy) was assessed through the measurement of magnetic flux density |B| using a 20-T Hallprobe Three-axis Hall Magnetometer THM1176 (Metrolab Instruments SA, Switzerland) in the area where the workers move during their daily work, according to the procedure described by Hartwig et al. [26]. Compared with the estimation of the magnetic field map obtained from isogauss plot lines (Figure 1), this procedure is more accurate [20]. Magnetic flux density was measured at two representative heights above the ground (on the y axis): y = 0 m, i.e., the MRI scanner isocenter quote corresponding to 1.15 m above the ground; and y = 0.45 m, corresponding to 1.6 m above the ground. For each y value, the probe of the magnetometer was placed on the xz plane (parallel to the ground plane), and moved in the x and z directions with a step of 0.10 m. The covered area was between the gantry and the door (starting from z = 0 at the gantry, up to z = 1.10 m), on the left and right sides of the patient bed. We measured the modulus of the magnetic flux density |B| at each point on a 0.10 m × 0.10 m grid. Then, we calculated the modulus of the magnetic flux density spatial gradient |dB/ds| with respect to the x and z axes using a home-made Matlab® version R2008b script.
Reliability and validity of smartphone applications to measure the spinal range of motion: A systematic review
Published in Expert Review of Medical Devices, 2021
Shibili Nuhmani, Moazzam Hussain Khan, Shaji J Kachanathu, Mohd Arshad Bari, Turki S Abualait, Qassim I Muaidi
Comparatively lower reliability and validity indices of smartphone applications for rotation ROM may be due to several factors. Static errors of smartphone sensors were three times higher in the transverse plane than in other cardinal planes [33]. Other factors include differences in smartphone sensors (magnetometers versus gravity-dependent gyroscopes) for ROM measurements in different planes. Magnetometers are preferable for the measurement of axial rotations in anti-gravity positions (e.g. sitting or standing). When compared to gyroscopes, magnetometers are more sensitive to signal distortion from environmental magnetic fields, which may reduce validity and reliability. The studies [27,30], which showed inadequate reliability and validity of smartphone applications, used magnetometer components for all measurements, as measurements were taken in the anti-gravity position. Similarly, Pourahmadi MR (25] also measured axial rotation in the supine position, using the gyroscope component of a smartphone sensor. This approach justified better reliability and validity of cervical rotation movements in their study compared with other studies [24,25]. A third influencing factor may have been the misalignment of the axis during measurement. This issue is more common in rotatory movements of the spine than other spinal movements, as there is a higher chance of secondary movements during rotation [34].
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