X-ray absorption and phase contrast imaging to study the interplay between plant roots and soil structure

Plant performance is, at least partly, linked to the location of roots with respect to soil structure features and the micro-environment surrounding roots. Measurements of root distributions from intact samples, using optical microscopy and field tracings have been partially successful but are imprecise and labour-intensive. Theoretically, X-ray computed micro-tomography represents an ideal solution for non-invasive imaging of plant roots and soil structure. However, before it becomes fast enough and affordable or easily accessible, there is still a need for a diagnostic tool to investigate root/soil interplay. Here, a method for detection of undisturbed plant roots and their immediate physical environment is presented. X-ray absorption and phase contrast imaging are combined to produce projection images of soil sections from which root distributions and soil structure can be analyzed. The clarity of roots on the X-ray film is sufficient to allow manual tracing on an acetate sheet fixed over the film. In its current version, the method suffers limitations mainly related to (i) the degree of subjectivity associated with manual tracing and (ii) the difficulty of separating live and dead roots. The method represents a simple and relatively inexpensive way to detect and quantify roots from intact samples and has scope for further improvements. In this paper, the main steps of the method, sampling, image acquisition and image processing are documented. The potential use of the method in an agronomic perspective is illustrated using surface and sub-surface soil samples from a controlled wheat trial. Quantitative characterization of root attributes, e.g. radius, length density, branching intensity and the complex interplay between roots and soil structure, is presented and discussed.

Parafoveal letter recognition at reduced contrast in normal aging and in patients with risk factors for AMD

Background Patients with early age-related maculopathy ( ARM) do not necessarily show obvious morphological signs or functional impairment. Many have good visual acuity, yet complain of decreased visual performance. The aim of this study was to investigate the aging effects on performance of parafoveal letter recognition at reduced contrast, and defects caused by early ARM and normal fellow eyes of patients with unilateral age-related macular degeneration (nfAMD). Methods Testing of the central visual field (8 radius) was performed by the Macular Mapping Test (MMT) using recognition of letters in 40 parafoveal target locations at four contrast levels (5, 10, 25 and 100%). Effects of aging were investigated in 64 healthy subjects aged 23 to 76 years (CTRL). In addition, 39 eyes (minimum visual acuity of 0.63; 20/30) from 39 patients with either no visible signs of ARM, while the fellow eye had advanced age-related macular degeneration (nfAMD; n=12), or early signs of ARM (eARM; n=27) were examined. Performance was expressed summarily as a ""field score"" (FS). Results Performance in the MMT begins to decline linearly with age in normal subjects from the age of 50 and 54 years on, at 5% and 10% contrast respectively. The differentiation between patients and CTRLs was enhanced if FS at 5% was analyzed along with FS at 10% contrast. In 8/12 patients from group nfAMD and in 18/27 from group eARM, the FS was statistically significantly lower than in the CTRL group in at least one of the lower contrast levels. Conclusion Using parafoveal test locations, a recognition task and diminished contrast increases the chance of early detection of functional defects due to eARM or nfAMD and can differentiate them from those due to aging alone.

Comparative study for the identification of myocardial ischemia by contrast ventriculography under the effect of isosorbide mononitrate and by perfusional myocardial scintigraphy in patients with ischemic heart disease

OBJECTIVE: To evaluate and compare the usefulness of cineventriculographies, before and after nitrate use, to technetium-99m sestamibi scintigraphy for the identification of myocardial ischemia. METHODS: Twenty-six patients were studied at basal conditions and 5 minutes after intravenous administration of isosorbide mononitrate (0.3mg/kg), to evaluate the performance and regional wall motion of the left ventricle (LV). The results were compared to those obtained with technetium-99m sestamibi scintigraphy. RESULTS: Before nitrate, contrast ventriculography identified 30 normal segments, 62 hypokinetic segments, 28 dyskinetic segments, and 14 akinetic segments. After drug administration, 99 segments were normal, 11 hypokinetic, 11 dyskinetic, and 13 akinetic. Myocardial scintigraphy revealed 110 ischemic segments and 18 fibrotic segments (p<0.005). After drug administration, the ventriculography showed increase in the velocity of circumferential fiber shortening (p=0.0142), the ejection fraction (p=0.0462), decrease in the end-systolic volume (p=0.0031) and no change in end-diastolic volume. CONCLUSION: Contrast ventriculography using nitrate proved to be similar to perfusional myocardial scintigraphy in the identification of myocardial ischemia.

Study of Coronary Flow Reserve with Intravenous Use of Microbubbles (Contrast Echocardiography) and Adenosine: Protocol for Clinical Application in Patients Suspected of Having Coronary Heart Disease

OBJECTIVE: To test the feasibility, safety and accuracy of the adenosine protocol in the study of myocardial perfusion with microbubbles contrast echocardiography. METHODS: 81 pts (64 male, 60+11 years) were submitted to contrast echocardiography with PESDA (sonicated solution of albumin 20%-1ml, dextrose 5%-12ml and deca-fluorobutane gas-8ml) to study the myocardial perfusion at rest and after bolus injection of adenosine (6 to 18mg) and to coronary angiography within 1 month each other. For each patient 3 left ventricle perfusion beds were considered (total of 243 territories). 208 territories were analyzed and 35 territories were excluded. PESDA was continuously infused (1-2ml/min), titrated for best myocardial contrast. Triggered (1:1) second harmonic imaging was used. RESULTS: Coronary angiography showed 70 flow limiting (> 75%) lesions and 138 no flow limiting lesions. At rest an obvious myocardium contrast enhancement was seen in at least 1 segment of a territory in all patients. After adenosine injection an unquestionable further increase in myocardial contrast was observed in 136 territories (99%) related to no flow limiting lesions, lasting < 10 s, and a myocardial perfusion defect was detected in 68 territories (97%) related to flow limiting lesions. It was observed only 4 false results. There were no serious complications. CONCLUSION: Myocardial perfusion study with PESDA and adenosine protocol is a practical, safe and accurate method to analyze the coronary flow reserve.

Whole-heart coronary vein imaging: a comparison between non-contrast-agent- and contrast-agent-enhanced visualization of the coronary venous system.

The feasibility of three-dimensional (3D) whole-heart imaging of the coronary venous (CV) system was investigated. The hypothesis that coronary magnetic resonance venography (CMRV) can be improved by using an intravascular contrast agent (CA) was tested. A simplified model of the contrast in T(2)-prepared steady-state free precession (SSFP) imaging was applied to calculate optimal T(2)-preparation durations for the various deoxygenation levels expected in venous blood. Non-contrast-agent (nCA)- and CA-enhanced images were compared for the delineation of the coronary sinus (CS) and its main tributaries. A quantitative analysis of the resulting contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) in both approaches was performed. Precontrast visualization of the CV system was limited by the poor CNR between large portions of the venous blood and the surrounding tissue. Postcontrast, a significant increase in CNR between the venous blood and the myocardium (Myo) resulted in a clear delineation of the target vessels. The CNR improvement was 347% (P < 0.05) for the CS, 260% (P < 0.01) for the mid cardiac vein (MCV), and 430% (P < 0.05) for the great cardiac vein (GCV). The improvement in SNR was on average 155%, but was not statistically significant for the CS and the MCV. The signal of the Myo could be significantly reduced to about 25% (P < 0.001).

Micro-Structural Brain Alterations in Aviremic HIV+ Patients with Minor Neurocognitive Disorders: A Multi-Contrast Study at High Field.

OBJECTIVE: Mild neurocognitive disorders (MND) affect a subset of HIV+ patients under effective combination antiretroviral therapy (cART). In this study, we used an innovative multi-contrast magnetic resonance imaging (MRI) approach at high-field to assess the presence of micro-structural brain alterations in MND+ patients. METHODS: We enrolled 17 MND+ and 19 MND- patients with undetectable HIV-1 RNA and 19 healthy controls (HC). MRI acquisitions at 3T included: MP2RAGE for T1 relaxation times, Magnetization Transfer (MT), T2* and Susceptibility Weighted Imaging (SWI) to probe micro-structural integrity and iron deposition in the brain. Statistical analysis used permutation-based tests and correction for family-wise error rate. Multiple regression analysis was performed between MRI data and (i) neuropsychological results (ii) HIV infection characteristics. A linear discriminant analysis (LDA) based on MRI data was performed between MND+ and MND- patients and cross-validated with a leave-one-out test. RESULTS: Our data revealed loss of structural integrity and micro-oedema in MND+ compared to HC in the global white and cortical gray matter, as well as in the thalamus and basal ganglia. Multiple regression analysis showed a significant influence of sub-cortical nuclei alterations on the executive index of MND+ patients (p = 0.04 he and R(2) = 95.2). The LDA distinguished MND+ and MND- patients with a classification quality of 73% after cross-validation. CONCLUSION: Our study shows micro-structural brain tissue alterations in MND+ patients under effective therapy and suggests that multi-contrast MRI at high field is a powerful approach to discriminate between HIV+ patients on cART with and without mild neurocognitive deficits.

On the origin of the MR image phase contrast: an in vivo MR microscopy study of the rat brain at 14.1 T.

Recent studies at high magnetic fields using the phase of gradient-echo MR images have shown the ability to unveil cortical substructure in the human brain. To investigate the contrast mechanisms in phase imaging, this study extends, for the first time, phase imaging to the rodent brain. Using a 14.1 T horizontal bore animal MRI scanner for in vivo micro-imaging, images with an in-plane resolution of 33 microm were acquired. Phase images revealed, often more clearly than the corresponding magnitude images, hippocampal fields, cortical layers (e.g. layer 4), cerebellar layers (molecular and granule cell layers) and small white matter structures present in the striatum and septal nucleus. The contrast of the phase images depended in part on the orientation of anatomical structures relative to the magnetic field, consistent with bulk susceptibility variations between tissues. This was found not only for vessels, but also for white matter structures, such as the anterior commissure, and cortical layers in the cerebellum. Such susceptibility changes could result from variable blood volume. However, when the deoxyhemoglobin content was reduced by increasing cerebral blood flow (CBF) with a carbogen breathing challenge, contrast between white and gray matter and cortical layers was not affected, suggesting that tissue cerebral blood volume (and therefore deoxyhemoglobin) is not a major source of the tissue phase contrast. We conclude that phase variations in gradient-echo images are likely due to susceptibility shifts of non-vascular origin.

Enhanced generation of specific tumor-reactive CTL in vitro by selected Melan-A/MART-1 immunodominant peptide analogues.

The Melan-A/MART-1 gene, which is expressed by normal melanocytes as well as by most fresh melanoma samples and melanoma cell lines, codes for Ags recognized by tumor-reactive CTL. HLA-A*0201-restricted Melan-A-specific CTL recognize primarily the Melan-A(27-35) (AAGIGILTV) and the Melan-A(26-35) (EAAGIGILTV) peptides. The sequences of these two peptides are not necessarily optimal as far as binding to HLA-A*0201 is concerned, since both lack one of the dominant anchor amino acid residues (leucine or methionine) at position 2. In this study we introduced single amino acid substitutions in either one of the two natural peptide sequences with the aim of improving peptide binding to HLA-A*0201 and/or recognition by specific CTL. Surprisingly, analogues of the Melan-A(27-35) peptide, which bound more efficiently than the natural nonapeptide to HLA-A*0201, were poorly recognized by tumor-reactive CTL. In contrast, among the Melan-A(26-35) peptide analogues tested, the peptide ELAGIGILTV was not only able to display stable binding to HLA-A2.1 but was also recognized more efficiently than the natural peptide by two short-term cultured tumor-infiltrated lymph node cell cultures as well as by five of five tumor-reactive CTL clones. Moreover, in vitro generation of tumor-reactive CTL by stimulation of PBMC from HLA-A*0201 melanoma patients with this particular peptide analogue was much more efficient than that observed with either one of the two natural peptides. These results suggest that the Melan-A(26-35) peptide analogue ELAGIGILTV may be more immunogenic than the natural peptides in HLA-A*0201 melanoma patients and should thus be considered as a candidate for future peptide-based vaccine trials.

Multicenter study of a new fully automated HBsAg screening assay with enhanced sensitivity for the detection of HBV mutants.

In a multicenter study a new, fully automated Roche Diagnostics Elecsys HBsAg II screening assay with improved sensitivity to HBsAg mutant detection was compared to well-established HBsAg tests: AxSYM HBsAg V2 (Abbott), Architect HBsAg (Abbott), Advia Centaur HBsAg (Bayer) Enzygnost HBsAg 5.0 (Dade-Behring), and Vitros Eci HBsAg (Ortho). A total of 16 seroconversion panels, samples of 60 HBsAg native mutants, and 31 HBsAg recombinant mutants, dilution series of NIBSC and PEI standards, 156 HBV positive samples comprising genotypes A to G, 686 preselected HBsAg positive samples from different stages of infection, 3,593 samples from daily routine, and 6,360 unselected blood donations were tested to evaluate the analytical and clinical sensitivity, the detection of mutants, and the specificity of the new assay. Elecsys HBsAg II showed a statistically significant better sensitivity in seroconversion panels to the compared tests. Fifty-seven out of 60 native mutants and all recombinant mutants were found positive. Among 156 HBV samples with different genotypes and 696 preselected HBsAg positive samples Elecsys HBsAg II achieved a sensitivity of 100%. The lower detection limit for NIBSC standard was calculated to be 0.025 IU/ml and for the PEI standards ad and ay it was <0.001 and <0.005 U/ml, respectively. Within 2,724 daily routine specimens and 6.360 unselected blood donations Elecsys HBsAg II showed a specificity of 99.97 and 99.88%, respectively. In conclusion the new Elecsys HBsAg II shows a high sensitivity for the detection of all stages of HBV infection and HBsAg mutants paired together with a high specificity in blood donors, daily routine samples, and potentially interfering sera.

Study of OSEM with different subsets in grating-based X-ray differential phase-contrast imaging.

Impressive developments in X-ray imaging are associated with X-ray phase contrast computed tomography based on grating interferometry, a technique that provides increased contrast compared with conventional absorption-based imaging. A new "single-step" method capable of separating phase information from other contributions has been recently proposed. This approach not only simplifies data-acquisition procedures, but, compared with the existing phase step approach, significantly reduces the dose delivered to a sample. However, the image reconstruction procedure is more demanding than for traditional methods and new algorithms have to be developed to take advantage of the "single-step" method. In the work discussed in this paper, a fast iterative image reconstruction method named OSEM (ordered subsets expectation maximization) was applied to experimental data to evaluate its performance and range of applicability. The OSEM algorithm with different subsets was also characterized by comparison of reconstruction image quality and convergence speed. Computer simulations and experimental results confirm the reliability of this new algorithm for phase-contrast computed tomography applications. Compared with the traditional filtered back projection algorithm, in particular in the presence of a noisy acquisition, it furnishes better images at a higher spatial resolution and with lower noise. We emphasize that the method is highly compatible with future X-ray phase contrast imaging clinical applications.

Development of a hepatocyte hollow fiber bioreactor for the study of contrast agents by magnetic resonance imaging

Thanks to the continuous progress made in recent years, medical imaging has become an important tool in the diagnosis of various pathologies. In particular, magnetic resonance imaging (MRI) permits to obtain images with a remarkably high resolution without the use of ionizing radiation and is consequently widely applied for a broad range of conditions in all parts of the body. Contrast agents are used in MRI to improve tissue discrimination. Different categories of contrast agents are clinically available, the most widely used being gadolinium chelates. One can distinguish between extracellular gadolinium chelates such as Gd-DTPA, and hepatobiliary gadolinium chelates such as Gd-BOPTA. The latter are able to enter hepatocytes from where they are partially excreted into the bile to an extent dependent on the contrast agent and animal species. Due to this property, hepatobiliary contrast agents are particularly interesting for the MRI of the liver. Actually, a change in signal intensity can result from a change in transport functions signaling the presence of impaired hepatocytes, e.g. in the case of focal (like cancer) or diffuse (like cirrhosis) liver diseases. Although the excretion mechanism into the bile is well known, the uptake mechanisms of hepatobiliary contrast agents into hepatocytes are still not completely understood and several hypotheses have been proposed. As a good knowledge of these transport mechanisms is required to allow an efficient diagnosis by MRI of the functional state of the liver, more fundamental research is needed and an efficient MRI compatible in vitro model would be an asset. So far, most data concerning these transport mechanisms have been obtained by MRI with in vivo models or by a method of detection other than MRI with cellular or sub-cellular models. Actually, no in vitro model is currently available for the study and quantification of contrast agents by MRI notably because high cellular densities are needed to allow detection, and no metallic devices can be used inside the magnet room, which is incompatible with most tissue or cell cultures that require controlled temperature and oxygenation. The aim of this thesis is thus to develop an MRI compatible in vitro cellular model to study the transport of hepatobiliary contrast agents, in particular Gd-BOPTA, into hepatocytes directly by MRI. A better understanding of this transport and especially of its modification in case of hepatic disorder could permit in a second step to extrapolate this knowledge to humans and to use the kinetics of hepatobiliary contrast agents as a tool for the diagnosis of hepatic diseases.

Ultra-high-resolution 3D imaging of atherosclerosis in mice with synchrotron differential phase contrast: a proof of concept study.

The goal of this study was to investigate the performance of 3D synchrotron differential phase contrast (DPC) imaging for the visualization of both macroscopic and microscopic aspects of atherosclerosis in the mouse vasculature ex vivo. The hearts and aortas of 2 atherosclerotic and 2 wild-type control mice were scanned with DPC imaging with an isotropic resolution of 15 μm. The coronary artery vessel walls were segmented in the DPC datasets to assess their thickness, and histological staining was performed at the level of atherosclerotic plaques. The DPC imaging allowed for the visualization of complex structures such as the coronary arteries and their branches, the thin fibrous cap of atherosclerotic plaques as well as the chordae tendineae. The coronary vessel wall thickness ranged from 37.4 ± 5.6 μm in proximal coronary arteries to 13.6 ± 3.3 μm in distal branches. No consistent differences in coronary vessel wall thickness were detected between the wild-type and atherosclerotic hearts in this proof-of-concept study, although the standard deviation in the atherosclerotic mice was higher in most segments, consistent with the observation of occasional focal vessel wall thickening. Overall, DPC imaging of the cardiovascular system of the mice allowed for a simultaneous detailed 3D morphological assessment of both large structures and microscopic details.

Building legitimacy by criticising the pharmaceutical industry: a qualitative study among prescribers and local opinion leaders.

PRINCIPLES: The literature has described opinion leaders not only as marketing tools of the pharmaceutical industry, but also as educators promoting good clinical practice. This qualitative study addresses the distinction between the opinion-leader-as-marketing-tool and the opinion-leader-as-educator, as it is revealed in the discourses of physicians and experts, focusing on the prescription of antidepressants. We explore the relational dynamic between physicians, opinion leaders and the pharmaceutical industry in an area of French-speaking Switzerland. METHODS: Qualitative content analysis of 24 semistructured interviews with physicians and local experts in psychopharmacology, complemented by direct observation of educational events led by the experts, which were all sponsored by various pharmaceutical companies. RESULTS: Both physicians and experts were critical of the pharmaceutical industry and its use of opinion leaders. Local experts, in contrast, were perceived by the physicians as critical of the industry and, therefore, as a legitimate source of information. Local experts did not consider themselves opinion leaders and argued that they remained intellectually independent from the industry. Field observations confirmed that local experts criticised the industry at continuing medical education events. CONCLUSIONS: Local experts were vocal critics of the industry, which nevertheless sponsor their continuing education. This critical attitude enhanced their credibility in the eyes of the prescribing physicians. We discuss how the experts, despite their critical attitude, might still be beneficial to the industry's interests.

The impact of an enhanced recovery pathway on nursing workload: A retrospective cohort study.

BACKGROUND & AIMS: The importance of nursing for surgical patients has been frequently underestimated. The success of enhanced recovery programs after surgery (ERAS) depends on preferably complete fulfilment of the protocol and nurses are an important part of it. Due to the additional nursing action required, such protocols are suspected to increase the nursing workload. The aim of the present study was to observe and measure objectively nursing workload before, during and after systematic implementation of a comprehensive enhanced recovery pathway in colorectal surgery. METHODS: The program ERAS was introduced systematically in our tertiary academic centre 2011, since then our experience is based on more than 1500 ERAS patients. Nursing workload was prospectively assessed for all patients on a routine basis by means of a standardized and validated point system (PRN). In a retrospective cohort study, we compared nursing workload based on prospective data before, during and after ERAS implementation and correlated nursing workload to the compliance with the ERAS protocol. RESULTS: The study cohort included 50 patients before ERAS implementation (2010) and 69 (2011) and 148 (2012) consecutive patients after implementation; the baseline characteristics of the 3 groups were similar. Mean PRN values were 61.2 ± 19.7 per day in 2010 and decreased to 52.3 ± 13.7 (P = 0.005) and 51.6 ± 18.6 (P < 0.002) in 2011 and 2012, respectively. Increasing compliance with the ERAS protocol was significantly correlated to decreasing nursing workload (ρ = -0.42; P < 0.001). CONCLUSIONS: Nursing workload is - against a common belief - decreased by systematic implementation of enhance recovery protocol. The higher the compliance with the pathway, the lower the burden for the nurses!