Detection of ATP by "in line” 31P magnetic resonance spectroscopy during oxygenated hypothermic pulsatile perfusion of pigs' kidneys

Object: To demonstrate that adenosine triphosphate (ATP), which provides a valuable biomarker for kidney viability in the context of donation after cardiac death (DCD) transplantation, can be detected by means of 31P magnetic resonance spectroscopy (MRS) if kidneys are perfused with oxygenated hypothermic pulsatile perfusion (O2+HPP). Materials and methods: Porcine kidney perfusion was carried out using a home made, MR-compatible HPP-machine. Consequently, kidney perfusion could be performed continuously during magnetic resonance imaging and magnetic resonance spectroscopy recording. 31P MR spectroscopy consisted of 3-dimensional chemical shift imaging (CSI), which allowed for the detection of ATP level in line. 31P CSI was performed at 3tesla in 44min with a nominal voxel size of 6.1cc. Results: 31P CSI enabled the detection of renal ATP when pO2 was equal to 100kPa. With pO2 of 20kPa, only phosphomonoester, inorganic phosphate and nicotinamide adenine dinucleotide could be found. Semi-quantitative analysis showed that ATP level was 1.3mM in normal kidney perfused with pO2 of 100kPa. Conclusions: This combined technology may constitute a new advance in DCD organ diagnostics prior to transplantation, as it allows direct assessment of ATP concentration, which provides a reliable indicator for organ bioenergetics and viability. In this study, kidneys presenting no warm ischemia were tested in order to establish values in normal organs. The test could be easily integrated into the clinical environment and would not generate any additional delay into the transplantation clinical workflo

Noninvasive stress testing of myocardial perfusion defects: head-to-head comparison of thallium-201 SPECT to MRI perfusion

Background: To evaluate the diagnostic value of magnetic resonance imaging (MRI) of myocardial perfusion in the assessment of flow-limiting epicardial stenosis in a head-to-head comparison with abnormal thallium-201 (201TI) single photon emission tomography (SPECT) studies in patients with predominantly known coronary artery disease (CAD). Methods and Results: Twenty-one patients (mean age 65±10years) with reversible myocardial perfusion defects on 201TI-SPECT images during dipyridamole-stimulated hyperemia were recruited for study purpose. Within 5days of the 201TI-SPECT study, myocardial perfusion was studied again with MRI during dipyridamole stimulation and at rest. Overall, 201TI-SPECT identified 30 reversible regional perfusion defects. The sensitivity to detect hypoperfused segments was 70% (21/30) with the GRE-MRI perfusion analysis with 201TI-SPECT as reference. When patients were subgrouped according to the extent of regional reversible perfusion defects on 201TI-SPECT, mild- (SDS: 2-4), moderate- (SDS: 5-8), and severe- (SDS>8) perfusion defects were also identified by GRE-MRI perfusion analysis in 75% (6/8), in 56% (9/16) and 100% (6/6), respectively. Conclusions: GRE-MRI first-pass stress perfusion imaging may not identify up to 30% of mild-to-moderate perfusion defects in a group of preselected patients with predominantly known CAD and abnormal 201TI-SPECT studie

The effect of the elongation of the proximal aorta on the estimation of the aortic wall distensibility

The compliance of the proximal aortic wall is a major determinant of cardiac afterload. Aortic compliance is often estimated based on cross-sectional area changes over the pulse pressure, under the assumption of a negligible longitudinal stretch during the pulse. However, the proximal aorta is subjected to significant axial stretch during cardiac contraction. In the present study, we sought to evaluate the importance of axial stretch on compliance estimation by undertaking both an in silico and an in vivo approach. In the computational analysis, we developed a 3-D finite element model of the proximal aorta and investigated the discrepancy between the actual wall compliance to the value estimated after neglecting the longitudinal stretch of the aorta. A parameter sensitivity analysis was further conducted to show how increased material stiffness and increased aortic root motion might amplify the estimation errors (discrepancies between actual and estimated distensibility ranging from - 20 to - 62%). Axial and circumferential aortic deformation during ventricular contraction was also evaluated in vivo based on MR images of the aorta of 3 healthy young volunteers. The in vivo results were in good qualitative agreement with the computational analysis (underestimation errors ranging from - 26 to - 44%, with increased errors reflecting higher aortic root displacement). Both the in silico and in vivo findings suggest that neglecting the longitudinal strain during contraction might lead to severe underestimation of local aortic compliance, particularly in the case of women who tend to have higher aortic root motion or in subjects with stiff aortas

Potential of hybrid 18F-fluorocholine PET/MRI for prostate cancer imaging

Purpose: To report the first results of hybrid 18F-fluorocholine PET/MRI imaging for the detection of prostate cancer. Methods: This analysis included 26 consecutive patients scheduled for prostate PET/MRI before radical prostatectomy. The examinations were performed on a hybrid whole-body PET/MRI scanner. The MR acquisitions which included T2-weighted, diffusion-weighted and dynamic contrast-enhanced sequences were followed during the same session by whole-body PET scans. Parametric maps were constructed to measure normalized T2-weighted intensity (nT2), apparent diffusion coefficient (ADC), volume transfer constant (K trans), extravascular extracellular volume fraction (v e) and standardized uptake values (SUV). With pathology as the gold standard, ROC curves were calculated using logistic regression for each parameter and for the best combination with and without PET to obtain a MR model versus a PETMR model. Results: Of the 26 patients initially selected, 3 were excluded due to absence of an endorectal coil (2 patients) or prosthesis artefacts (1 patient). In the whole prostate, the area under the curve (AUC) for SUVmax, ADC, nT2, K trans and v e were 0.762, 0.756, 0.685, 0.611 and 0.529 with a best threshold at 3.044 for SUVmax and 1.075×10−3mm2/s for ADC. The anatomical distinction between the transition zone and the peripheral zone showed the potential of the adjunctive use of PET. In the peripheral zone, the AUC of 0.893 for the PETMR model was significantly greater (p = 0.0402) than the AUC of 0.84 for the MR model only. In the whole prostate, no relevant correlation was observed between ADC and SUVmax. The SUVmax was not affected by the Gleason score. Conclusion: The performance of a hybrid whole-body 18F-fluorocholine PET/MRI scan in the same session combined with a prostatic MR examination did not interfere with the diagnostic accuracy of the MR sequences. The registration of the PET data and the T2 anatomical MR sequence data allowed precise localization of hypermetabolic foci in the prostate. While in the transition zone the adenomatous hyperplasia interfered with cancer detection by PET, the quantitative analysis tool performed well for cancer detection in the peripheral zone

Jean Briggs's Never in Anger as an Ethnography of Experience

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66542/2/10.1177_0308275X9301300406.pd

Molecular dynamics simulations of glassy polymers

We review recent results from computer simulation studies of polymer glasses, from chain dynamics around the glass transition temperature Tg to the mechanical behaviour below Tg. These results clearly show that modern computer simulations are able to address and give clear answers to some important issues in the field, in spite of the obvious limitations in terms of length and time scales. In the present review we discuss the cooling rate effects, and dynamic slowing down of different relaxation processes when approaching Tg for both model and chemistry-specific polymer glasses. The impact of geometric confinement on the glass transition is discussed in detail. We also show that computer simulations are very useful tools to study structure and mechanical response of glassy polymers. The influence of large deformations on mechanical behaviour of polymer glasses in general, and strain hardening effect in particular are reviewed. Finally, we suggest some directions for future research, which we believe will be soon within the capabilities of state of the art computer simulations, and correspond to problems of fundamental interest.Comment: To apear in "Soft Matter

Correction to: Consensus-based technical recommendations for clinical translation of renal diffusion-weighted MRI.

The article Consensus-based technical recommendations for clinical translation of renal diffusion-weighted MRI

Correction to: Consensus-based technical recommendations for clinical translation of renal diffusion-weighted MRI.

The article Consensus-based technical recommendations for clinical translation of renal diffusion-weighted MRI

Journal of Cardiovascular Magnetic Resonance BioMed Central Meeting abstract

Imaging at 3 T significantly improves myocardial tagging using spoiled gradient echo based sequences (GRE). At 1.5 T, tagging sequence with SSFP readout offers high contrast and robust quantification of contraction, similar t

Surfaces PDMS structurées et/ou décorées par des nanoparticules (vers des propriétés optiques et de mouillage modulables)

Le potentiel du polydiméthylsiloxane (PDMS), élastomère transparent et déformable réversiblement en temps réel, est mis en avant dans ce travail comme substrat fonctionnel dans le domaine de l optique et du mouillage. Dans une première partie, nous avons développé des surfaces de PDMS ridées à l aide d instabilités de flambage, de longueurs d onde ( ) et d amplitude (A) variables et contrôlées, puis nous avons organisé sélectivement des nano-objets sur cette texturation de surface avec afin d en moduler la physico-chimie. Dans une seconde partie, la génération, in situ, de nano-plots/nanoparticules d or et d argent à la surface de verre et de PDMS a été étudiée et caractérisée d un point de vue optique.The polydimethylsiloxane (PDMS), a transparent and stretchable elastomer, is put forward in this work as a functional substrate in the field of optics and wetting. In the first part, we have developed wrinkled PDMS surfaces via controlled buckling instabilities. We were able to tune both the wavelength ( ) and the amplitude (A) of the structuration on a large length scale. We have then selectively organized some nanoparticles the textured surfaces in order to modulate its physical-chemistry. In the second part, in situ generation of gold and silver nanoparticles/plots has been developed and studied both on glass PDMS surfaces and subsequently characterized optically.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF