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Principles behind Magnetic Resonance Imaging (MRI)
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
The equilibrium magnetization M0 is not time-varying (Figure 32.2a), and thus not detectable by Faraday induction. However, the equilibrium state can be temporarily disrupted by exposing the system to an electromagnetic field of resonance frequency, that is, a so-called radiofrequency (RF) pulse. A reorganization will gradually take place during the RF pulse, corresponding to a change in states of individual nuclei (i.e. c+ and c- become continuous functions of time), so that, collectively, the whole spin distribution is rotated away from the positive z-axis towards the xy-plane. Hence, the tip of will exhibit a nutational motion pattern (precession about the z-axis in combination with rotation towards the xy-plane) (Figure 32.2b).
Venous Return and Vascular Function
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The maintenance of a stable circulation requires an equilibrium between venous return and cardiac output. These two variables must be equal and cannot differ for more than a few heartbeats before a new equilibrium state is reached. The point of intersection of cardiac output and venous return curves is known as the equilibrium point (Figure 30.7). The normal curves intersect at a right atrial pressure of zero and a cardiac output or venous return equal to 5 L/min. Changes in either cardiac output or venous return will shift the equilibrium point and change the right atrial pressure.
Mathematical Modelling and Analysis of Fractional Epidemic Models Using Derivative with Exponential Kernel
Published in Devendra Kumar, Jagdev Singh, Fractional Calculus in Medical and Health Science, 2020
Kolade M. Owolabi, Abdon Atangana
By setting and , a simple calculation shows that the epidemic system seen in the previous section has a disease-free equilibrium state , which corresponds to the existence of population class of u only. We define the basic reproduction number as , where . If , we obtain a non-trivial state that corresponds to the existence of susceptible, infected and recovered individuals. This equilibrium state is denoted by
Neural Plasticity in the Ventral Tegmental Area, Aversive Motivation during Drug Withdrawal and Hallucinogenic Therapy
Published in Journal of Psychoactive Drugs, 2023
Hector Vargas-Perez, Taryn Elizabeth Grieder, Derek van der Kooy
Thus, an excessive demand for the homeostasis response endangers the balance of the affected system, which requires the participation of extra regulatory mechanisms. These extra regulatory mechanisms would modify the internal and external environment of the system, to induce and maintain a new equilibrium state of the organism, which has been labeled an allostatic state (Koob and Le Moal 2001). Thus, allostasis constitutes an emergency mechanism of regulation, lasting long-term, with the subject having a new (usually lower) set point. In the case of the consumption of substances of abuse, allostasis is reflected as a state in which the baseline loses its initial stability and becomes a descendant spiral, from the motivational point of view, producing a state of permanent dysphoria. The resulting dysphoric response can only be counteracted or minimized by the presence of a rewarding stimulus of great magnitude, such as the drug (Koob and Le Moal 2001)(Figure 1).
On biological availability dependent bone remodeling
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
Areti Papastavrou, Ina Schmidt, Paul Steinmann
The mechanical stimulus compares the weighted free energy with the attractor stimulus, consequently if these two values coincide, the mass source becomes zero and biological equlibrium is attained. The dimensionless scalar parameter m determines the stability of the resulting algorithm. Kaczmarczyk and Pearce specify that with m > 0 and n > 0 stability is given, see (Kaczmarczyk and Pearce 2011). Uniqueness and numerical stability is ensured if m > n, (Harrigan and Hamilton 1993), (Harrigan and Hamilton 1994). (Kuhl and Steinmann 2003) performed a detailed study of the parameters m and n. An increase in m respectively n results in a decrease in the relative density values over time. In addition, the time to a biological equilibrium state increases with increasing m.
Analysis of related factors of recurrence in horizontal semicircular canal benign paroxysmal positional vertigo: a pilot study
Published in Acta Oto-Laryngologica, 2020
Ling Ding, Tao Lin, Xuanchen Zhou, Jie Han, Anting Xu
The most important innovation of this study was we found the correlation between RD and the abnormal C-test, further discovered that the recurrence rate was determined by the abnormal CP and RD during the follow-up period in patients of HSC-BPPV. There were no widely accepted influencing factors for assessing patients in recurrence. We thought the recurrence may be related to vestibular disorder. The abnormal C-test was one of the possible interpretations of the vestibular disorder. Recovery process of vestibule dysfunction was a process in which the original equilibrium state was disrupted and new condition tends to neutralize the imbalance to rebalance of the activity [6]. Therefore, our study has confirmed that patients with CP represented an unstable state after the repositioning and would be more likely to recur. Just because of this, vestibule rehabilitation played a more important role which might be helpful to speed up the establishment of a new balance. The latest research recognized vestibular exercises improved the symptoms after repositioning treatments for BPPV and increased the overall efficacy of treatment with a lower rate of recurrence [20]. Other authors reported the principle of vestibule rehabilitation was by preventing the accumulation and dispersing otoconia debris in patients with recurrent BPPV [8].