TY  - JOUR
A1  - Kurz, Felix T.
A1  - Kampf, Thomas
A1  - Buschle, Lukas R.
A1  - Schlemmer, Heinz-Peter
A1  - Bendszus, Martin
A1  - Heiland, Sabine
A1  - Ziener, Christian H.
T1  - Generalized moment analysis of magnetic field correlations for accumulations of spherical and cylindrical magnetic perturbers
JF  - Frontiers in Physics
N2  - In biological tissue, an accumulation of similarly shaped objects with a susceptibility difference to the surrounding tissue generates a local distortion of the external magnetic field in magnetic resonance imaging. It induces stochastic field fluctuations that characteristically influence proton spin dephasing in the vicinity of these magnetic perturbers. The magnetic field correlation that is associated with such local magnetic field inhomogeneities can be expressed in the form of a dynamic frequency autocorrelation function that is related to the time evolution of the measured magnetization. Here, an eigenfunction expansion for two simple magnetic perturber shapes, that of spheres and cylinders, is considered for restricted spin diffusion in a simple model geometry. Then, the concept of generalized moment analysis, an approximation technique that is applied in the study of (non-)reactive processes that involve Brownian motion, allows deriving analytical expressions of the correlation function for different exponential decay forms. Results for the biexponential decay for both spherical and cylindrical magnetized objects are derived and compared with the frequently used (less accurate) monoexponential decay forms. They are in asymptotic agreement with the numerically exact value of the correlation function for long and short times.
KW  - magnetized sphere/cylinder
KW  - magnetic susceptibility
KW  - correlation function
KW  - diffusion
KW  - magnetic resonance imaging
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-190604
SN  - 2296-424X
VL  - 4
ER  - 
TY  - JOUR
A1  - Kurz, Felix T.
A1  - Kampf, Thomas
A1  - Buschle, Lukas R.
A1  - Schlemmer, Heinz-Peter
A1  - Heiland, Sabine
A1  - Bendszus, Martin
A1  - Ziener, Christian H.
T1  - Microstructural Analysis of Peripheral Lung Tissue through CPMG Inter-Echo Time R2 Dispersion
JF  - PLoS One
N2  - Since changes in lung microstructure are important indicators for (early stage) lung pathology, there is a need for quantifiable information of diagnostically challenging cases in a clinical setting, e.g. to evaluate early emphysematous changes in peripheral lung tissue. Considering alveoli as spherical air-spaces surrounded by a thin film of lung tissue allows deriving an expression for Carr-Purcell-Meiboom-Gill transverse relaxation rates R-2 with a dependence on inter-echo time, local air-tissue volume fraction, diffusion coefficient and alveolar diameter, within a weak field approximation. The model relaxation rate exhibits the same hyperbolic tangent dependency as seen in the Luz-Meiboom model and limiting cases agree with Brooks et al. and Jensen et al. In addition, the model is tested against experimental data for passively deflated rat lungs: the resulting mean alveolar radius of RA = 31.46 \(\pm\) 13.15 \(\mu\)m is very close to the literature value (similar to 34 \(\mu\)m). Also, modeled radii obtained from relaxometer measurements of ageing hydrogel foam (that mimics peripheral lung tissue) are in good agreement with those obtained from mu CT images of the same foam (mean relative error: 0.06 \(\pm\) 0.01). The model's ability to determine the alveolar radius and/or air volume fraction will be useful in quantifying peripheral lung microstructure.
KW  - transverse relaxation
KW  - number
KW  - HE-3 diffusion MRI
KW  - magnetic-resonance behavior
KW  - hyperpolarized HE-3
KW  - Bessle functions
KW  - self-diffusion
KW  - alveolar
KW  - field
KW  - morphometry
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-138345
VL  - 10
IS  - 11
ER  -