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Biomedical Imaging Magnetic Resonance Imaging
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
In a technique that relies on an endogenous tracer, the magnetization of arterial blood spins is labeled by an inversion RF pulse, causing a signal reduction when the labeled blood enters the imaging location. This method is known as arterial spin labeling (ASL) which can produce quantitative or semi-quantitative maps of cerebral blood flow and other parameters (Alsop et al. 2015). ASL can be implemented in a number of ways depending on the type of the labeling pulse, the imaging sequence employed, the strategies to compensate for magnetization transfer effects, and other factors. Despite the variations, a consensus has been developed for consistent use of ASL techniques (Alsop et al. 2015).
Activity Images
Published in Hector J. Rabal, Roberto A. Braga, Dynamic Laser Speckle and Applications, 2018
One of fMRI techniques used to measure tissue perfusion in vivo is based on the use of an injected contrast agent that changes the magnetic susceptibility of blood and thereby the MR signal, which is repeatedly measured during passage of medicine. The other relies on arterial spin labeling (ASL), where arterial blood water is tagged using radiofrequency pulses that alter the magnetization of the blood before it enters into the tissue of interest. The amount of labeling is measured and compared to a control recording obtained without spin labeling. Both alternatives are expensive and the former is invasive.
A Functional BCI Model by the P2731 working group: Physiology
Published in Brain-Computer Interfaces, 2021
Ali Hossaini, Davide Valeriani, Chang S. Nam, Raffaele Ferrante, Mufti Mahmud
The primary modality within fMRI is BOLD (Blood Oxygen Level Dependent) MRI. As with light, oxyhemoglobin and deoxyhemoglobin and other components of tissue, respond differently to magnetic fields, and these changes can be tracked by radio pulses. fMRI exploits this trait to pinpoint changes in metabolism that accompany up-regulated neural activity. A complementary technique is arterial spin labeling (ASL) MRI which measures cerebral blood flow (CBF). However, ASL’s requirements, which include an injected contrast agent, have limited its use [55].