Phase contrast micro-CT with adjustable in-slice spatial resolution at constant magnification.

Objective.To report on a micro computed tomography (micro-CT) system capable of x-ray phase contrast imaging and of increasing spatial resolution at constant magnification.Approach.The micro-CT system implements the edge illumination (EI) method, which relies on two absorbing masks with periodically spaced transmitting apertures in the beam path; these split the beam into an array of beamlets and provide sensitivity to the beamlets' directionality, i.e. refraction. In EI, spatial resolution depends on the width of the beamlets rather than on the source/detector point spread function (PSF), meaning that resolution can be increased by decreasing the mask apertures, without changing the source/detector PSF or the magnification.Main results.We have designed a dedicated mask featuring multiple bands with differently sized apertures and used this to demonstrate that resolution is a tuneable parameter in our system, by showing that increasingly small apertures deliver increasingly detailed images. Phase contrast images of a bar pattern-based resolution phantom and a biological sample (a mouse embryo) were obtained at multiple resolutions.Significance.The new micro-CT system could find application in areas where phase contrast is already known to provide superior image quality, while the added tuneable resolution functionality could enable more sophisticated analyses in these applications, e.g. by scanning samples at multiple scales.

Utility of knife-edge position tracking in cycloidal computed tomography.

Cycloidal computed tomography provides high-resolution images within relatively short scan times by combining beam modulation with dedicated under-sampling. However, implementing the technique relies on accurate knowledge of the sample's motion, particularly in the case of continuous scans, which is often unavailable due to hardware or software limitations. We have developed an easy-to-implement position tracking technique using a sharp edge, which can provide reliable information about the trajectory of the sample and thus improve the reconstruction process. Furthermore, this approach also enables the development of other innovative sampling schemes, which may otherwise be difficult to implement.

Cycloidal-spiral sampling for three-modal x-ray CT flyscans with two-dimensional phase sensitivity.

We present a flyscan compatible acquisition scheme for three-modal X-Ray Computed Tomography (CT) with two-dimensional phase sensitivity. Our approach is demonstrated using a "beam tracking" setup, through which a sample's attenuation, phase (refraction) and scattering properties can be measured from a single frame, providing three complementary contrast channels. Up to now, such setups required the sample to be stepped at each rotation angle to sample signals at an adequate rate, to prevent resolution losses, anisotropic resolution, and under-sampling artefacts. However, the need for stepping necessitated a step-and-shoot implementation, which is affected by motors' overheads and increases the total scan time. By contrast, our proposed scheme, by which continuous horizontal and vertical translations of the sample are integrated with its rotation (leading to a "cycloidal-spiral" trajectory), is fully compatible with continuous scanning (flyscans). This leads to greatly reduced scan times while largely preserving image quality and isotropic resolution.

Cycloidal CT with CNN-based sinogram completion and in-scan generation of training data.

In x-ray computed tomography (CT), the achievable image resolution is typically limited by several pre-fixed characteristics of the x-ray source and detector. Structuring the x-ray beam using a mask with alternating opaque and transmitting septa can overcome this limit. However, the use of a mask imposes an undersampling problem: to obtain complete datasets, significant lateral sample stepping is needed in addition to the sample rotation, resulting in high x-ray doses and long acquisition times. Cycloidal CT, an alternative scanning scheme by which the sample is rotated and translated simultaneously, can provide high aperture-driven resolution without sample stepping, resulting in a lower radiation dose and faster scans. However, cycloidal sinograms are incomplete and must be restored before tomographic images can be computed. In this work, we demonstrate that high-quality images can be reconstructed by applying the recently proposed Mixed Scale Dense (MS-D) convolutional neural network (CNN) to this task. We also propose a novel training approach by which training data are acquired as part of each scan, thus removing the need for large sets of pre-existing reference data, the acquisition of which is often not practicable or possible. We present results for both simulated datasets and real-world data, showing that the combination of cycloidal CT and machine learning-based data recovery can lead to accurate high-resolution images at a limited dose.

Technical Note: Practical implementation strategies of cycloidal computed tomography.

PURPOSE: Cycloidal computed tomography is a novel imaging concept which combines a highly structured x-ray beam, offset lateral under-sampling, and mathematical data recovery to obtain high-resolution images efficiently and flexibly, even with relatively large source focal spots and detector pixels. The method reduces scanning time and, potentially, delivered dose compared to other sampling schemes. This study aims to present and discuss several implementation strategies for cycloidal computed tomography (CT) in order to increase its ease of use and facilitate uptake within the imaging community. METHODS: The different implementation strategies presented are step-and-shoot, continuous unidirectional, continuous back-and-forth, and continuous pixel-wise scanning. In step-and-shoot scans the sample remains stationary while frames are acquired, whereas in all other cases the sample moves through the scanner continuously. The difference between the continuous approaches is the trajectory by which the sample moves within the field of view. RESULTS: All four implementation strategies are compatible with a standard table-top x-ray setup. With the experimental setup applied here, step-and-shoot acquisitions yield the best spatial resolution (around 30 µm), but are the most time-consuming (1.4 h). Continuous unidirectional and back-and-forth images have resolution between 30 and 40 µm, and are faster (35 min). Continuous pixel-wise images are equally time-efficient, although technical challenges caused a small loss in image quality with a resolution of about 50 µm. CONCLUSION: The authors show that cycloidal CT can be implemented in a variety of ways with high quality results. They believe this posits cycloidal CT as a powerful imaging alternative to more time-consuming and less flexible methods in the field.

Predicting the noise in hybrid (phase and attenuation) x-ray images acquired with the edge illumination technique.

PURPOSE: To analyze the noise performance of the edge illumination phase-based x-ray imaging technique when applying "single-shot" phase retrieval. The latter consists in applying a sample-specific low-pass filter to the raw data, leading to "hybrid" images in which phase and attenuation contrast are merged with each other. The second objective is to compare the hybrid images with attenuation-only images based on their respective signal-to-noise ratio (SNR). METHODS: Noise is propagated from the raw images into the retrieved hybrid images, yielding analytic expressions for the variances and noise power spectra of the latter. An expression for the relative SNR between hybrid and attenuation images is derived. A comparison with simulated data is performed. Experimental data are also shown and discussed in the context of the theory. RESULTS: The noise transfer into the retrieved hybrid images is strongly related to the setup and acquisition parameters, as well as the imaged sample itself. Consequently, the relative merit between hybrid and attenuation images also depends on these criteria. Generally, the hybrid approach tends to perform worse for highly attenuating samples, as the availability of phase contrast is outweighed by the loss of photons that is necessarily encountered in hybrid acquisitions. On the contrary, the hybrid approach can lead to a much better SNR for weakly attenuating samples, as here phase effects lead to much stronger contrast, outweighing the reduction in photon numbers. CONCLUSIONS: The analytic expressions inform the design of edge illumination setups that lead to minimum noise transfer into the retrieved hybrid images. We also anticipate our theory to guide the decision as to which imaging mode (hybrid or attenuation) to use in order to maximize SNR for a specific sample.

[Epidural non-Hodgkin's lymphoma presenting as a spinal cord compression]. / Lymphomes non hodgkiniens épiduraux révélés par une compression médullaire.

OBJECTIVE AND METHODS: epidural localization is a rare presenting sign of non Hodgkin's lymphoma. In this study, we describe the clinical, histological and immunohistochemical data in 13 cases (9 men and 4 women) of non-Hodgkin's lymphoma with epidural involvement. RESULTS: the median age was 63 years (range 36-76 years). Clinically, most patients complained of back pain (median duration, 3.4 months) followed by acute neurological deterioration. In 10 out of 13 tumors, a thoracic localization was observed and a decompressive laminectomy was performed in all cases. Histology and immunohistochemistry showed all tumors to be B-cell lymphomas which were classified as: lymphocytic lymphoma (3 cases), prolymphocytic lymphoma (1 case), follicular lymphoma (2 cases), diffuse large cell lymphoma (6 cases) and AIDS associated Burkitt lymphoma (1 case). Post-operative staging revealed bone and/or paravertebral involvement in 11 cases and disseminated disease in 5 cases. Median survival following complementary therapy, radiotherapy and chemotherapy in most cases, was 20 months. CONCLUSION: histological features of epidural lymphomas are similar to other extranodal lymphomas and their prognosis is better than other epidural neoplasms, especially when the tumor is localized.

[One heat-induced antigen retrieval step allows the sequential detection of two antigens on the same slide of tissue fixed and enclosed in paraffin]. / Un seul démasquage par la chaleur permet la détection successive de deux antigènes sur la même coupe de tissu fixé et inclus en paraffine.

The heat-induced antigen retrieval (HIAR) procedure allows the immunohistochemical detection of various antigens on paraffin-embedded sections. The re-use of slides negative for the detection of a first set of antigens may be an interesting alternative in case of a limited number of slides. After HIAR, a series of Bouin's liquid-fixed tonsil sections was stained for Epithelial Membrane Antigen (EMA) which labelled epithelial cells and plasma cells. A second immunostaining for CD20 (L26) was performed on the same slides divided in two sets. The HIAR was repeated in the first set but not in the second one. A similar staining of follicular B-cells was observed in the two sets. However background staining was enhanced by repetition of HIAR. Analogous results were obtained using anti-cytokeratin (KL1) instead of anti-EMA. This was confirmed on slides for which three or four cycles of HIAR were performed prior immunostaining. Our data suggest that the renewal of the HIAR procedure must be avoided since it was found stable for at least 1 year.

[Laënnec, re-inventor of the stethoscope?]. / Laënnec, ré-inventeur du stéthoscope?

According to our common medical culture, some facts are simply unquestionable, for instance Laënnec invented the stethoscope. But was he the first one? On a recent trip to Egypt we visited the temple of Kom Ombo, built prior to the roman period and renowned as a medical care center. Today, the tourist is fascinated by the magnificent hieroglyphics on the well-preserved walls testifying to significant advances in various fields of medicine including ophthalmology and gynecology. We were particularly interested by the basreliefs presenting vivid drawings of some of the first medical instruments. We easily identified curettes, scissors, a balance, forceps for dental extraction, and a surgical saw, but were captivated by two other instruments. The first one looked a lot like what Laënnec invented around 1820. The second one was amazingly similar to the instrument we use everyday, with a distal opening and flexible tubes (woven papyrus?) leading to proximal ear pieces. Our Egyptian guide was formal: the stethoscope was invented in Egypt. The scientific impact of our observations leaves something to be desired, but did make us think about the huge gap between the advancement of medical knowledge in ancient Egypt and Laënnec's (re)-invention. Exposed to a similar gap in history, what would our documents stored on CD and video tapes have to say to future touring doctors?

[Follow-up of 151 pregnant women exposed to antidepressant treatment (MAOI excluded) during organogenesis]. / Suivi de 151 grossesses exposées à un traitement antidépresseur (IMAO exclus) au cours de l'organogenèse.

The Pharmacovigilance and Poisons Center in Lyon undertook an analysis of their data on antidepressant (MAOI excluded) exposure during the first trimester of pregnancy. From 1986 to 1991, 151 prospective enquiries were collected of which 145 exposures occurred during the first trimester of pregnancy. The outcome of pregnancy was known for 114 of these cases. Voluntary or medical abortion was decided in 24 cases, spontaneous abortion occurred in 11 patients and fetal death, unrelated to drug exposure, was noted in one case. Delivery was reported in 78 cases including 69 (88.5%) normal infants, with obstetrical complications not related to the treatment in 7 of these cases. Neonatal complications were noted in 5 (6.4%) cases, including withdrawal symptoms possibly related to the treatment in 3 cases. Congenital abnormalities were identified in 4 cases (5.1%) with one case of major malformation (membranous ventricular septal defect). Such a study is not an exhaustive survey of antidepressant exposure during pregnancy, but a collection of inquiries received by our centre. Even though our study's ability to detect an overall increase in the risk of malformations is too low and limited the extent of our conclusion, our results are in agreement with the literature data as no important increased in major birth defect was observed.

Properties of spin labelled membranes of Fusarium oxysporum f. sp. lycopersici.

Growth temperature-induced compositional changes in membranes of Fusarium oxysporum provided a test system for study of the relationship between physical properties and composition. Growth at 15 degrees C was characterized by a decrease in phospholipid content relative to sterol content, a shift in phospholipid composition from phosphatidylcholine to phosphatidylethanolamine and a marked enhancement in the amount of polyunsaturated fatty acids in the phospholipid and triglyceride classes. Uptake of a spin labelled analog of stearic acid during growth and subsequent solution of the probe in the membranes allowed estimation of viscosity and molecular order of the membranes of live cells and of isolated membrane preparations. Less than 1/20 of the intracellular label was accessible to sodium ascorbate while none was released by sodium dodecyl sulfate. All of the label in live cells was reduced by in vivo respiratory activity above 20 degrees C but this process could be reversed or avoided by added ferricyanide. A cholestane spin probe was also incorporated into the membranes. The probes were not reduced as readily in isolated membranes and hence fluidity of the membranes could be assessed over a wide temperature range. At low temperatures (-10 degrees C) a nonlethal, liquid-solid phase transition was indicated in isolated membrane lipids while at higher (lethal) temperatures (40-45 degrees C), discontinuities appeared in Arrhenius plots of rotational correlation time. Activation energies for isotropic rotation of the stearate probes in the membranes changed markedly in this temperature range and this effect correlated closely with loss of viability of conidial cells. Correlation times for stearate probes showed little variation with growth temperature nor were any breaks in Arrhenius plots of this parameter detected in the range 0-35 degrees C in whole cells or isolated membranes. The data indicated control of membrane physical properties within close tolerances throughout the physiological temperature range regardless of growth temperature. It was concluded that this homeostatic phenomenon was due to the counteractive effects of sterol/phospholipid ratio, phospholipid composition and fatty acid polyunsaturation since the condensing and fluidizing components of the isolated total membranes vary in a reciprocal manner.

Structural and functional responses of wheat mitochondrial membranes to growth at low temperatures.

The responses in membrane lipid composition, structure, and function of four cultivars of wheat (Triticum aestivum L.) to growth at low temperature have been investigated. Marked growth temperature-dependent alterations in the fatty acid composition and unsaturation of the mitochondrial phospholipids correlate with changes in respiratory activity in all the varieties. Parameters such as the respiratory control ratio and the phosphorylative efficiency decrease in cold-adapted seedlings. Three temperature-dependent structural transitions were identified in the mitochondria by the spin-labeling method. The structural transitions occur at lower temperatures in the cold-grown material. The shift in one transition appears to be quantitatively greater in the winter hardy varieties. Cold-induced changes in all of the other measured parameters were indistinguishable in hardy and nonhardy varieties. The results indicate major involvement of the phospholipid matrix in cold acclimation. A link between cold acclimation and winter survival may exist involving the structural and functional modifications in membrane structure which occur during acclimation.

Changes in Phospholipid Composition of a Winter Wheat Cultivar during Germination at 2 C and 24 C.

Evaluation of various solvent systems for lipid extraction of wheat Triticum aestivum L. cv. Rideau seeds showed that boiling 2-propanol followed by the Bligh-Dyer procedure was the most efficient method, with respect to lipid yield and ability to inactivate lipolytic enzymes. Ten phospholipids were identified in dry seeds; the major components being phosphatidylcholine, lysophosphatidylcholine, N-acyl lysophosphatidyl-ethanolamine, N-acylphosphatidylethanolamine, and phosphatidylethanolamine. After growth for 1 week (2 C) or 31 hours (24 C), the proportions of phosphatidylethanolamine + lysophosphatidic acid and phosphatidic acid increased, lysophosphatidylcholine decreased, and the remaining phospholipids showed little change. At 5 weeks (2 C) or 72 hours (24 C), the seedlings showed 5-fold increases in the proportion of phosphatidic acid largely at the expense of phosphatidylcholine, small decreases in N-acyl lysophosphatidylethanolamine and N-acylphosphatidylethanolamine, and significant increases in lysophosphatidylcholine. The changes in phosphatidic acid and phosphatidylcholine are interpreted as being partially due to increasing phospholipase D activity during germination. In general, the phospholipid composition was similar in morphologically equivalent seedlings grown at 2 C or 24 C. The increased membrane content in seedlings grown at 2 C does not reflect any preferential synthesis of individual phospholipids.

Effects of fatty acid concentration and positional specificity on maize triglyceride structure.

The effects of fatty acid concentration and positional specificity on maize triglyceride structure were evaluated from the stereospecific analyses of triglycerides from 12 genotypes. The fatty acids at each position were influenced by the fatty acid concentration in the total triglyceride except for the saturates in the 2 position. The fatty acid concentration had the greatest effect on the fatty acid composition of position 3. The existence of positional specificity was evident from the nonrandom distribution of the fatty acids among the three positions of the triglycerides. The concentration and positional specificity effects could be separated in selected genotypes and their crosses. This indicated different genetic controls for each effect.