Abstract:
:For protons diffusing among a system of magnetic particles, the process by which initial phase coherence is lost depends substantially on particle size. In this article, evidence for three dephasing mechanisms is presented: an incremental process at small particle sizes (motional averaging regime), a discrete process at intermediate particle sizes (visit limited regime), and a continuous process at large particle sizes (static dephasing regime). While motional averaging regime and static dephasing regime are well known, the distinct dynamics in visit limited regime are often overlooked. Revisiting earlier analytic treatments for the dynamics in this regime, Monte Carlo simulations are performed to extract the details of dephasing and to test the concept of an inner zone of rapid dephasing herein named the full dephasing zone. It is shown that the emergence of a full dephasing zone marks the transition from motional averaging regime to visit limited regime since protons can be fully dephased in a single encounter. Moving from the visit limited regime to the static dephasing regime, a crossover between a purely discrete process and a purely continuous process occurs. Developing a simple model of the dephasing process, the average dephasing time is demonstrated to be relatively constant thus giving insight into the long lasting plateau in the relaxation rate.
journal_name
Magn Reson Medjournal_title
Magnetic resonance in medicineauthors
de Haan HWdoi
10.1002/mrm.22966subject
Has Abstractpub_date
2011-12-01 00:00:00pages
1748-58issue
6eissn
0740-3194issn
1522-2594journal_volume
66pub_type
杂志文章abstract::The regional cerebral blood flow (rCBF) values determined using continuous arterial spin labeling (CASL) are subject to several sources of variability, including natural physiologic variations, sensitivity to the input parameters, and the use of different quantification models. To date, a thorough analysis of the impa...
journal_title:Magnetic resonance in medicine
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