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Accurate noninvasive measurement of cell size and compartment shape anisotropy in yeast cells using double-pulsed field gradient MR.

ABSTRACT: The accurate characterization of pore morphology is of great interest in a wide range of scientific disciplines. Conventional single-pulsed field gradient (s-PFG) diffusion MR can yield compartmental size and shape only when compartments are coherently ordered using q-space approaches that necessitate strong gradients. However, double-PFG (d-PFG) methodology can provide novel microstructural information even when specimens are characterized by polydispersity in size and shape, and even when anisotropic compartments are randomly oriented. In this study, for the first time, we show that angular d-PFG experiments can be used to accurately measure cellular size and shape anisotropy of fixed yeast cells employing relatively weak gradients. The cell size, as measured by light microscopy, was found to be 5.32 ± 0.83 µm, whereas the results from noninvasive angular d-PFG experiments yielded a cell size of 5.46 ± 0.45 µm. Moreover, the low compartment shape anisotropy of the cells could be inferred from experiments conducted at long mixing times. Finally, similar experiments were conducted in a phantom comprising anisotropic compartments that were randomly oriented, showing that angular d-PFG MR provides novel information on compartment eccentricity that could not be accessed using conventional methods. Angular d-PFG methodology seems to be promising for the accurate estimation of compartment size and compartment shape anisotropy in heterogeneous systems in general, and biological cells and tissues in particular.

SUBMITTER: Shemesh N

PROVIDER: S-EPMC3203313 | biostudies-other | 2012 Feb

REPOSITORIES: biostudies-other

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Project description:One of the hallmarks of diffusion NMR and MRI is its ability to utilize restricted diffusion to probe compartments much smaller than the excited volume or the MRI voxel, respectively, and to extract microstructural information from them. Single-pulsed field gradient (s-PFG) MR methodologies have been employed with great success to probe microstructures in various disciplines, ranging from chemistry to neuroscience. However, s-PFG MR also suffers from inherent shortcomings, especially when specimens are characterized by orientation or size distributions: in such cases, the microstructural information available from s-PFG experiments is limited or lost. Double-pulsed field gradient (d-PFG) MR methodology, an extension of s-PFG MR, has attracted attention owing to recent theoretical studies predicting that it can overcome certain inherent limitations of s-PFG MR. In this review, we survey the microstructural features that can be obtained from conventional s-PFG methods in the different q regimes, and highlight its limitations. The experimental aspects of d-PFG methodology are then presented, together with an overview of its theoretical underpinnings and a general framework for relating the MR signal decay and material microstructure, affording new microstructural parameters. We then discuss recent studies that have validated the theory using phantoms in which the ground truth is well known a priori, a crucial step prior to the application of d-PFG methodology in neuronal tissue. The experimental findings are in excellent agreement with the theoretical predictions and reveal, inter alia, zero-crossings of the signal decay, robustness towards size distributions and angular dependences of the signal decay from which accurate microstructural parameters, such as compartment size and even shape, can be extracted. Finally, we show some initial findings in d-PFG MR imaging. This review lays the foundation for future studies, in which accurate and novel microstructural information could be extracted from complex biological specimens, eventually leading to new forms of contrast in MRI.

Project description:PURPOSE:To exploit the long 3.0T relaxation times and low flow velocity of lymphatic fluid to develop a noninvasive 3.0T lymphangiography sequence and evaluate its relevance in patients with lymphedema. MATERIALS AND METHODS:A 3.0T turbo-spin-echo (TSE) pulse train with long echo time (TEeffective ?=?600 msec; shot-duration?=?13.2 msec) and TSE-factor (TSE-factor?=?90) was developed and signal evolution simulated. The method was evaluated in healthy adults (n?=?11) and patients with unilateral breast cancer treatment-related lymphedema (BCRL; n?=?25), with a subgroup (n?=?5) of BCRL participants scanned before and after manual lymphatic drainage (MLD) therapy. Maximal lymphatic vessel cross-sectional area, signal-to-noise-ratio (SNR), and results from a five-point categorical scoring system were recorded. Nonparametric tests were applied to evaluate study parameter differences between controls and patients, as well as between affected and contralateral sides in patients (significance criteria: two-sided P < 0.05). RESULTS:Patient volunteers demonstrated larger lymphatic cross-sectional areas in the affected (arm?=?12.9?±?6.3?mm2 ; torso?=?17.2?±?15.6?mm2 ) vs. contralateral (arm?=?9.4?±?3.9?mm2 ; torso?=?9.1?±?4.6?mm2 ) side; this difference was significant both for the arm (P?=?0.014) and torso (P?=?0.025). Affected (arm: P?=?0.010; torso: P?=?0.016) but not contralateral (arm: P?=?0.42; torso: P?=?0.71) vessel areas were significantly elevated compared with control values. Lymphatic cross-sectional areas reduced following MLD on the affected side (pre-MLD: arm?=?8.8?±?1.8?mm2 ; torso?=?31.4?±?26.0?mm2 ; post-MLD: arm?=?6.6?±?1.8?mm2 ; torso?=?23.1?±?24.3?mm2 ). This change was significant in the torso (P?=?0.036). The categorical scoring was found to be less specific for detecting lateralizing disease compared to lymphatic-vessel areas. CONCLUSION:A 3.0T lymphangiography sequence is proposed, which allows for upper extremity lymph stasis to be detected in ?10 minutes without exogenous contrast agents. LEVEL OF EVIDENCE:1 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2017;46:1349-1360.

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Accurate noninvasive measurement of cell size and compartment shape anisotropy in yeast cells using double-pulsed field gradient MR.

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