Investigation of cyano-bridged coordination nanoparticles Gd(3+)/[Fe(CN)6](3-)/D-mannitol as T1-weighted MRI contrast agents.

Cyano-bridged Gd(3+)/[Fe(CN)6](3-) coordination polymer nanoparticles of 3-4 nm stabilized with D-mannitol presenting a high r1 relaxivity value of 11.4 mM(-1) s(-1) were investigated in vivo as contrast agents (CA) for Magnetic Resonance Imaging (MRI). They allow an increase of the MR image contrast and can act as an efficient intravascular T1 CA with a relatively long blood-circulation lifetime (60 min) without specific toxicity.

Magnetic resonance imaging stereotactic target localization for deep brain stimulation in dystonic children.

OBJECT: The actual distortion present in a given series of magnetic resonance (MR) images is difficult to establish. The purpose of this study was to validate an MR imaging-based methodology for stereotactic targeting of the internal globus pallidus during electrode implantation in children in whom general anesthesia had been induced. METHODS: Twelve children (mean follow up 1 year) suffering from generalized dystonia were treated with deep brain stimulation by using a head frame and MR imaging. To analyze the influence of distortions at every step of the procedure, the geometrical characteristics of the frame were first controlled using the localizer as a phantom. Then pre- and postoperative coordinates of fixed anatomical landmarks and electrode positions, both determined with the head frame in place, were statistically compared. No significant difference was observed between theoretical and measured dimensions of the localizer (Student's t-test, ¿t¿ > 2.2 for 12 patients) in the x, y, and z directions. No significant differences were observed (Wilcoxon paired-sample test) between the following: 1) pre- and postoperative coordinates of the anterior commissure (AC) (deltax = 0.3+/-0.29 mm and deltay = 0.34+/-0.32 mm) and posterior commissure (PC) (deltax = 0.15+/-0.18 mm and deltay = 0.34+/-0.25 mm); 2) pre- and postoperative AC-PC distance (deltaL = 0.33+/-0.22 mm); and 3) preoperative target and final electrode position coordinates (deltax = 0.24+/-0.22 mm; deltay = 0.19+/-0.16 mm). CONCLUSIONS: In the authors' center, MR imaging distortions did not induce detectable errors during stereotactic surgery in dystonic children. Target localization and electrode implantation could be achieved using MR imaging alone after induction of general anesthesia. The remarkable postoperative improvement in these patients confirmed the accuracy of the procedure (Burke-Marsden-Fahn Dystonia Rating Scale score delta = -83.8%).

Assessment of stenosis severity using a novel method to estimate spatial and temporal variations of blood flow velocity in biplane coronarography.

The authors present a novel method to estimate absolute blood flow velocity in coronary arteries from biplane angiograms. Spatial and temporal velocity variations are derived giving simultaneously a direct geometric and an indirect functional index of stenosis severity, stenosis ratio and coronary flow reserve. No prior assumption concerning stenosis geometry is made. Deformable models are used to track a coronary artery segment dynamically in three dimensions. A densitometric map is obtained by summing densities across sections at every position along the previously calculated path and at every time of the cardiac cycle. An advection relationship between density and velocity is observed. The spatiotemporal velocity map is a solution of a nonlinear least-squares scheme. A simulation protocol based on simple geometric conformations and blood flow properties is used to assess numerical stability and immunity towards noise. Predicted results for temporal velocity variations are compared with the intracoronary Doppler recordings to test the model assumptions for basal state and hyperaemia examinations of the same patient. The stenosis ratio was accurate to within 3% for a simulated additive Gaussian noise with a standard deviation of 0.14. The limits of agreement between angiographic and Doppler velocities were -11.4 and 11.8 cm s-1 for a peak value of 23 cm s-1 (basal state) and -16.8 and 13.5 cm s-1 for a peak value of 52 cm s-1 (hyperaemia), corresponding to 18 and 3.5% errors on the average peak values and a 16% error on the coronary flow reserve. To summarize, the advection model derivation and its solution are presented. Simulated and experimental results corroborate the validity of the numerical schemes and support clinical applicability.

Effect of brine injection on water dynamics in postmortem muscle: study of T2 and diffusion coefficients by MR microscopy.

The dynamics of water in postmortem muscle were studied by magnetic resonance microscopy (MRM). Rabbit muscles were arterially injected with 3 and 5 M NaCl brine. T2 and diffusion mapping were performed during the onset of rigor mortis. A wide spread of T2 values and widely differing postmortem evolutions were observed for injected muscles, whereas T2 was spatially homogeneous for intact muscle. Also, highly variable spatial distribution of diffusion coefficients along (Dz) and across (Dx) the muscle fibers was observed and diffusion anisotropy Dz/Dx) was less marked in injected muscles. The results indicate heterogeneity of brine distribution far from the injection site soon after injection. The postmortem evolution of the parameters is discussed in terms of structural changes induced by brine injection. MRM provides insight into how water dynamics respond to different NaCl concentrations inside muscle.

Characterization in vivo of muscle fiber types by magnetic resonance imaging.

Magnetic resonance imaging has been used to characterize muscle fiber types. Here, T1 and T2 values were determined in pure slow-twitch and fast-twitch rabbit muscles and in rabbit muscles with mixed fiber types. The muscles with high proportions of oxidative slow-twitch fibers had higher T2 values than the others. Echo time, orientation of muscle fibers in B0, and moving spins had no effect on relaxation parameters. The results are discussed in terms of slow myosin isoform content and oxidative metabolism.

Breast pathology in MRI. First results.

The authors present the first results of the assessment of MRI (0.35 T) with adapted surface reel in the exploration of mammary pathology in 90 cases. On a morphological level, MRI permits a new analysis of signs of dystrophy. As far as MRI is concerned, no specific sign of mammary neoplasia seems to exist. A classification is suggested, taking into account morphology and parameters of relaxation.

3D modeling in myocardial 201TL SPECT.

A method to model the left ventricular myocardium in thallium-201 Single Photon Emission Computed Tomography (SPECT) is presented. This method is based on the fitting of the morphological skeleton of the left ventricle to a truncated bullet. This automatic approach would provide a more reproducible visualization of the organ for clinical applications.

Experimental study of stochastic noise propagation in SPECT images reconstructed using the conjugate gradient algorithm.

Thanks to an experimental study based on simulated and physical phantoms, the propagation of the stochastic noise in slices reconstructed using the conjugate gradient algorithm has been analysed versus iterations. After a first increase corresponding to the reconstruction of the signal, the noise stabilises before increasing linearly with iterations. The level of the plateau as well as the slope of the subsequent linear increase depends on the noise in the projection data.

A comparative study of Powell's and Downhill Simplex algorithms for a fast multimodal surface matching in brain imaging.

Multimodal images registration can be very helpful for diagnostic applications. However, even if a lot of registration algorithms exist, only a few really work in clinical routines. We developed a method based on surface matching and compared two minimization algorithms: Powell's and Downhill Simplex. We studied the influence of some factors (chamfer map computation, number and order of parameters to determine, minimization criteria) on the final accuracy of the algorithm. Using this comparison, we improved some processing steps to allow a clinical use, and selected the simplex algorithm which presented the best results.

Magnetic resonance imaging and cerebral volumic evaluation: comparison of four post-processing techniques.

Four different MRI techniques of volumetric evaluation were applied in 10 healthy females and compared. The results have shown that not all techniques were interchangeable, but that the results of two groups of methods are not statistically different.

[The nuclear magnetic resonance in endocrinology. Spectroscopy and imaging, present and future]. / La résonance magnétique nucléaire en endocrinologie. Spectroscopie et imagerie, présent et avenir.

The first part, after a brief historical reminder, gives an oversimplified and non-rigorous approach to the Nuclear Magnetic Resonance (NMR) phenomenon; this "physical" introduction leads the clinician to know the essential about the spectral and imaging techniques in NMR, just to understand what is done... The second part of this paper shows some medical applications of these two aspects of NMR, with help of some examples, taken from the literature, according to what is concerned with endocrinology. Pure bio chemical applications (enzymology), or those concerning isolated (and perfused) organs, or living animals, and even human beings, are numerous and complementary, and there is no doubt that the applications of NMR technologies to medicine will know a promising future...

Relationship between discrimination tasks of the cantab and the corpus callosum morphology in Alzheimer's disease.

The relationship between performances on a simple discrimination task of the Attentional Set Shifting of the Cambridge Neuropsychological Test Auto mated Battery (CANTAB) and morphometry of the corpus callosum is examined in patients with Alzheimer's disease. Analysis showed patients with probable Alzheimer's disease are heterogeneous for the relationship between performances in the attentional test of the CANTAB and the anterior callosal atrophies. Interest in these results for clinical diagnosis of this mental disease is discussed.

In vivo quantitative NMR imaging of fruit tissues during growth using Spoiled Gradient Echo sequence.

Nondestructive studies of physiological processes in agronomic products require increasingly higher spatial and temporal resolutions. Nuclear Magnetic Resonance (NMR) imaging is a non-invasive technique providing physiological and morphological information on biological tissues. The aim of this study was to design a robust and accurate quantitative measurement method based on NMR imaging combined with contrast agent (CA) for mapping and quantifying water transport in growing cherry tomato fruits. A multiple flip-angle Spoiled Gradient Echo (SGE) imaging sequence was used to evaluate the intrinsic parameters maps M0 and T1 of the fruit tissues. Water transport and paths flow were monitored using Gd(3+)/[Fe(CN)6](3-)/D-mannitol nanoparticles as a tracer. This dynamic study was carried out using a compartmental modeling. The CA was preferentially accumulated in the surrounding tissues of columella and in the seed envelopes. The total quantities and the average volume flow of water estimated are: 198 mg, 1.76 mm(3)/h for the columella and 326 mg, 2.91 mm(3)/h for the seed envelopes. We demonstrate in this paper that the NMR imaging technique coupled with efficient and biocompatible CA in physiological medium has the potential to become a major tool in plant physiology research.

[Evaluation of glomerular filtration rate with magnetic resonance imaging]. / Évaluation du débit de filtration glomérulaire par imagerie par résonance magnétique.

Glomerular Filtration Rate (GFR) is one of the cardinal indices of renal function and is used clinically as the gold standard of renal dysfunction. In the past decade, many studies using dynamic contrast-enhanced MRI (DCE MRI) to measure GFR have been published. The MRI evaluation of GFR centers on visualizing the passage of contrast material (Gadolinium chelates) through the kidney. MRI appears as a promising tool but still relatively difficult to implement in the assessment of GFR. A high heterogeneity of protocols (e.g., in acquisition mode, dose of contrast, postprocessing techniques) is noted in the literature, reflecting the number of technical challenges that should first be solved in order to reach a consensus, and the reported accuracy and reproducibility are insufficient for justifying their use in clinical practice now. This paper presents and discusses the different steps that can be used to quantify the GFR by MRI.

[Characterization of the (Na+-K+)-ATPase from endometrial plasma membranes of immature mammals]. / Caractérisation de la (Na+-K+)-ATPase de la membrane plasmique des cellules de l'endomètre de mammifères immatures

The (Na+-K+)-ATPase in plasma membrane from Mammiferous endometrium is characterized by the Mg/ATP ratio equal to one, and by a distinct affinity for Na+ (1.3 mM) and K+ (2 mM). The activity is maximum for pH 7.4-7.5 in presence of Mg++ 2mM and ATP 2 mM, Na+ 140 mM and K+ 10 mM.

Early in vitro stimulation of endometrial (Na+-K+)-ATPase by estradiol.

Physiological concentrations of estradiol (2-10 nM) can approximately double the activity of the endometrical (Na+-K+)-ATPase in immature mammalians. This stimulation in vitro is optimum as early as 30 minutes after contact of uteri with the hormone and it is not inhibited by incubation with cycloheximide. Analogues of 17 beta estradiol have little effect on the enzyme activity, but another steroid hormone testosterone, is capable of a similar activating effect.

Optimal Measurement of Magnitude and Phase from MR Data

General expressions of magnitude- and phase-probability distributions of MRI signals are presented and discussed. From these expressions, maximum-likelihood estimators are derived that allow optimal measurement of true magnitude and true phase from a set of noisy samples. Bias and uncertainty of estimates are determined by Monte Carlo simulations. It is demonstrated that with 100 samples and for signal-to-noise ratios above 1, bias and uncertainty of ML estimates are approximately 1 and 3% for magnitude and 0.1 and 5% for phase, respectively.

Optimum tomographic reconstruction parameters for HMPAO brain SPET imaging: a practical approach based on subjective and objective indexes.

The purpose of this study was to define an optimal strategy for the tomographic reconstruction procedure in routine brain single-photon emission tomography (SPET) studies, including the number of projections, filter function and matrix size. A set of projection data with different count densities was obtained from a technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO) brain SPET acquisition from one volunteer. The projections were reconstructed with different filters and the quality of the reconstructed images was determined using both a subjective observer rating score and the Gilbert index. For each count density, the observers' choice corresponded to images with the lowest Gilbert index. The noise level in brain SPET sections was estimated and correlated with the fractal dimension. The results of this study indicate that although noise represents a fundamental component of brain SPET imaging, image quality also depends on the reconstructed spatial resolution. Image quality is satisfactorily described by fractal dimension. In addition the optimal filter function depends on the available count density. For high count levels, optimal reconstruction may be obtained by using a high-resolution matrix and a slightly smoother reconstruction filter. When count densities are low, best results are obtained by using a low-resolution matrix and a sharper filter. Finally, this study suggests that image quality is not influenced by the number of projections for equivalent count densities. These results were confirmed by 30 HMPAO brain SPET studies acquired in a routine clinical setting.