Mesoscopic relaxation time of dynamic image correlation spectroscopy by ProQuest


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									J. Biomedical Science and Engineering, 2010, 3, 625-632                                                                 JBiSE
doi:10.4236/jbise.2010.36085 Published Online June 2010 (

Mesoscopic relaxation time of dynamic image correlation
Kyongok Kang

Forschungszentrum Juelich, Weiche Materie (Soft Matter), Juelich, Germany.

Received 16 February 2010; revised 20 March 2010; accepted 28 March 2010.

ABSTRACT                                                           relaxation time [2]. These assumptions are feasible for a
                                                                   typical diffusion coefficient for water in soft tissues, and
Dynamical images contain useful information of how
                                                                   its relevant mean-squared displacement is reported as
the objects behave in time and space. When the sys-
                                                                   typical value of 30-60 μm size within about 125 ms re-
tem is in biological fluids, the motion of the object is
                                                                   covery time [2]. Depending on the biomedical system,
much over-damped; the relaxation time is the char-
acteristics in a diffusive time scale. We have found               for instance, gray and white matter in the brain, heart, and
dynamical states of melting and forming of small                   kidney are in a relatively slow relaxation process (relaxa-
nematic domains (10—30 μm) that are exhibited in                   tion time as about 1/s) within tissue and blood stream, as
the suspensions of fd-viruses under applied AC elec-               compared to other systems as liver and spleen [2]. Thus
tric field amplitude at low frequency. Dynamic image               as far as the contrast agent is efficiently fast enough, then
correlation function is used for extracting the mes-               the slow process of water permeability can be negligible
oscopic relaxation times of the dynamical states, which            in terms of the exchange rates between different com-
can be employed as an application to other dynamic                 partments for early detection of malignant tumor cells.
imaging process of biologically relevant soft con-                 Thus for an intermediate and slow time process, the
densed matter and biomedical systems.                              single exponent time constant is convenient to character-
                                                                   ize most biological relevant experimental parameters.
Keywords: Relaxation Time; Image Correlation                          When the time-evolutionary information is engaged
Spectroscopy; Dynamical states                                     with a local space, it is somewhat complicated to distin-
                                                                   guish between the time, and space-variable. For the sys-
1. INTRODUCTION                                                    tem that contains self-mimicking sizes or shapes of ob-
                                                                   jects (or images), but with different temporal events, it is
Dynamic contrast-enhanced MRI (magnetic resonance                  extremely useful to predict what will happen after a cer-
imaging) is widely used for early detection of breast              tain time steps of events. Relatively large-time scale,
tumors, where the kinetics of signal variation are moni-           such as astronomical or geographical-time, and macro-
tored after an injection of a paramagnetic contrast me-            scopic length are less relevant to predict “probable” events
dium to distinguish between benign and malignant breast            in mesoscopic time scale. Most physiochemical envi-
lesions [1]. The studies of microvasculature and micro-            ronments, i.e., medical, biochemical and biophysical
circulation are useful in the sense that the solid tumor           issues are more engaged with a shorter-time interval. In
objects can disturb the regional blood flow, and influ-            the latter case, the system of interested objects is gov-
ences the lack of linkage in a basement membrane. It is            erned by thermodynamics and hydrodynamics, commonly
still a challenge to generalize the estimation of a regional       in between the microscopic and macroscopic approach.
blood flow and capillary permeability as volume fraction           As far as in time-correlation aspect, this mesos-copic time
of the intravascular flow in breast tumors [1]. According          scale can be influenced by globally metastable but par-
to the authors in [1], the important criterions of reliable        tially (or locally) in non-equilibrium states. Thus time-
signal contrast (or relaxation times) are dependent on             correlation is still a challenge in mesoscopic length and
two assumptions; one is a negligible relaxavity of pro-            time scale and in the speculation, nevertheless which is
tons in different tissue compartment, and the other is             ambient in most soft matters. The demanding task of
much faster diffusion of water within a tissue and the             predicting “forward” temporal events relies on the com-
exchange rate between them. The relaxation of bulk                 plexity of dynamical entities (or inhomogenieties) them-
magnetization can be found and described by a single               selves that evolve in the physiological situations (or en-

Published Online June 2010 in SciRes.
626                           K. Kang et
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