| 1. |
- Lätt, Jimmy, et al.
(författare)
-
Accuracy of q-space related parameters in MRI: Simulations and phantom measurements
- 2007
-
Ingår i: IEEE Transactions on Medical Imaging. - 1558-254X. ; 26:11, s. 1437-1447
-
Tidskriftsartikel (refereegranskat)abstract
- The accuracy of q-space measurements was evaluated at a 3.0-T clinical magnetic resonance imaging (MRI) scanner, as compared with a 4.7-T nuclear magnetic resonance (NMR) spectrometer. Measurements were performed using a stimulated-echo pulse-sequence on n-decane as well as on polyethylene glycol (PEG) mixed with different concentrations of water, in order to obtain bi-exponential signal decay curves. The diffusion coefficients as well as the modelled diffusional kurtosis K-fit, were obtained from the signal decay curve, while the full-width at half-maximum (FWHM) and the diffusional kurtosis K were obtained from the displacement distribution. Simulations of restricted diffusion, under conditions similar to those obtainable with a clinical MRI scanner, were carried out assuming various degrees of violation of the short gradient pulse (SGP) condition and of the long diffusion time limit., The results indicated that an MRI system can not be used for quantification of structural sizes less than about 10 mu m by means of FWHM since the parameter underestimates the confinements due to violation of the SGP condition. However, FWHM can still be used as an important contrast parameter. The obtained kurtosis values were lower than expected from theory and the results showed that care must be taken when interpreting a kurtosis estimate deviating from zero.
|
|
| 2. |
- Malmborg, Carin, et al.
(författare)
-
Mapping the intracellular fraction of water by varying the gradient pulse length in q-space diffusion MRI
- 2006
-
Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1096-0856 .- 1090-7807. ; 180:2, s. 280-285
-
Tidskriftsartikel (refereegranskat)abstract
- Finite gradient pulse lengths are traditionally considered a nuisance in q-space diffusion NMR and MRI, since the simple Fourier relation between the acquired signal and the displacement probability is invalidated. Increasing the value of the pulse length leads to an apparently smaller value of the estimated compartment size. We propose that q-space data at different gradient pulse lengths, but with the same effective diffusion time, can be used to identify and quantify components with free or restricted diffusion from multi-exponential echo decay curves obtained on cellular systems. The method is demonstrated with experiments on excised human brain white matter and a series of model systems with well-defined free, restricted, and combined free and restricted diffusion behavior. Time-resolved diffusion MRI experiments are used to map the spatial distribution of the intracellular fraction in a yeast cell suspension during sedimentation, and observe the disappearance of this fraction after a heat treatment. (c) 2006 Elsevier Inc. All rights reserved.
|
|
