Personalized stent design for congenital heart defects using pulsatile blood flow simulations.

Stent size selection and placement are among the most challenging tasks in the treatment of pulmonary artery stenosis in congenital heart defects (CHD). Patient-specific 3D model from CT or MR improves the understanding of the patient's anatomy and information about the hemodynamics aid in patient risk assessment and treatment planning. This work presents a new approach for personalized stent design in pulmonary artery interventions combining personalized patient geometry and hemodynamic simulations. First, the stent position is initialized using a geometric approach. Second, the stent and artery expansion, including the foreshortening behavior of the stent is simulated. Two stent designs are considered, a regular stent and a Y-stent for bifurcations. Computational fluid dynamics (CFD) simulations of the blood flow in the initial and expanded artery models are performed using patient-specific boundary conditions in form of a pulsatile inflow waveform, 3-element Windkessel outflow conditions, and deformable vessel walls. The simulations have been applied to 16 patient cases with a large variability of anatomies. Finally, the simulations have been clinically validated using retrospective imaging from angiography and pressure measurements. The simulated pressure, volume flow and flow velocity values were on the same order of magnitude as the reference values obtained from clinical measurements, and the simulated stent placement showed a positive impact on the hemodynamic values. Simulation of geometric changes combined with CFD simulations offers the possibility to optimize stent type, size, and position by evaluating different configurations before the intervention, and eventually allow to test customized stent geometries and new deployment techniques in CHD.

Cardiac CT and MRI of cardiac malformations: How to interpret them?

A segmental sequential approach is widely used for the description of congenital heart disease abnormalities in routine reports of computed tomography and magnetic resonance imaging examinations. This consists of three stages as follows: (a) the anatomical description of each segment (viscero-atrial situs, the bulboventricular loop and the position of the great vessels); (b) the relationship between each segment at the atrioventricular and ventriculoarterial levels; and (c) related intra- and intersegmental abnormalities. This article describes the interpretation of computed tomography and magnetic resonance imaging examinations in patients with cardiac malformations using a structured plan.

Tetralogy of Fallot: Preoperative assessment with MR and CT imaging.

Tetralogy of Fallot has a broad anatomical spectrum. In mild forms of the condition the obstruction is only located in the right ventricular infundibulum, whereas in severe forms the pulmonary valve is atretic, the pulmonary arteries are absent and the lung is supplied by aorto-pulmonary collateral arteries. Surgical management differs from conventional surgery in the former situation, whereas in the latter it is complex and requires reconstruction of the pulmonary arteries (unifocalization) carried out in more than one stage and with a high morbidity rate. The key factors to establish before corrective surgery are the levels and degree of obstruction of the right ventricular outflow tract, the development of the pulmonary arteries and the presence of collateral arteries. The main role of magnetic resonance imaging along with that of computed tomography angiography are discussed and illustrated.

Imaging of postoperative tetralogy of Fallot repair.

Over the last years, the surgical techniques used to repair Tetralogy of Fallot as well as the cross-sectional cardiac imaging techniques have substantially improved. Now, the survival rate after surgical repair is more than 90% at 40 years old. A follow-up is needed and the imaging evaluation should be guided by the surgical techniques used. This article reviews the most common surgical procedures for a complete repair, the associated anatomic and hemodynamic complications and the role of cardiac imaging, mainly magnetic resonance imaging.

[Systemic learning planification for residents during the 6-month pediatric radiology training]. / Planification systémique de l'apprentissage des internes pendant un semestre de radiopédiatrie.

Diagnostic Radiology and Medical Imaging residents of French University Hospitals benefit from a wide array of learning tools. However, the professors' clinical workload, lack of sufficient proper formal training, lack of practical applicability of existing standards, and absence of rigorous assessment during the specialized training, reduce their very good quality formation to the level of accidental learning. This study originates from the need to apply a systemic planification of learning activities to the French residents' formal training curriculum, such as the one originally designed and applied within the Quebec educational system. This presentation also benefits from the recent introduction of the CanMEDS 2000 objectives by the Royal College of Physicians and Surgeons of Canada, in order to design an adapted version for the professional and academic activities of French radiologists. Needless to say this work will respect the outlined systematic planning of any learning activity: learning requirements, definition of learning objectives, selection of learning methods, assessment of the participants' achievement of these objectives, and evaluation of the learning activity itself.

Fetal magnetic resonance imaging in the prenatal diagnosis of cerebellar hemorrhage.

We report the case of a fetus with a sonographic mid-gestation diagnosis of hyperechogenic cerebellum suspected to be of hemorrhagic origin on fetal brain magnetic resonance imaging (MRI). No etiological factors for fetal hemorrhage were found other than a maternal heterozygocity for factor V Leiden. Following termination of the pregnancy, autopsy confirmed the prenatal diagnosis of massive cerebellar hemorrhage without underlying vascular anomaly. As an additional tool to ultrasonography, fetal brain MRI can affirm the hemorrhagic origin of hyperechogenic cerebellar lesions, especially by showing a high signal on T1-weighted images.

Coarctation of the aorta: pre and postoperative evaluation with MRI and MR angiography; correlation with echocardiography and surgery.

AIMS: To compare MRI and MRA with Doppler-echocardiography (DE) in native and postoperative aortic coarctation, define the best MR protocol for its evaluation, compare MR with surgical findings in native coarctation. MATERIALS AND METHODS: 136 MR studies were performed in 121 patients divided in two groups: Group I, 55 preoperative; group II, 81 postoperative. In group I, all had DE and surgery was performed in 35 cases. In group II, DE was available for comparison in 71 cases. MR study comprised: spin-echo, cine, velocity-encoded cine (VEC) sequences and 3D contrast-enhanced MRA. RESULTS: In group I, diagnosis of coarctation was made by DE in 33 cases and suspicion of coarctation and/or aortic arch hypoplasia in 18 cases. Aortic arch was not well demonstrated in 3 cases and DE missed one case. There was a close correlation between VEC MRI and Doppler gradient estimates across the coarctation, between MRI aortic arch diameters and surgery but a poor correlation in isthmic measurements. In group II, DE detected a normal isthmic region in 31 out of 35 cases. Postoperative anomalies (recoarctation, aortic arch hypoplasia, kinking, pseudoaneurysm) were not demonstrated with DE in 50% of cases. CONCLUSIONS: MRI is superior to DE for pre and post-treatment evaluation of aortic coarctation. An optimal MR protocol is proposed. Internal measurement of the narrowing does not correspond to the external aspect of the surgical narrowing.

Lignin incorporation combined with electron-beam irradiation improves the surface water resistance of starch films.

We investigated the potential of an electron-beam post-treatment to tailor the properties of 70/30 and 80/20 wt. extruded starch-lignin films. The effect of a 400 kGy radiation on films differing essentially by the kind of lignins incorporated (lignosulfonates/alkali lignins) was assessed both at the macroscopic and the molecular levels. Changes in the polymer molecular structure were studied by IR spectroscopy, by thioacidolysis as well as by model compound experiments. Electron beam-irradiation at 400 kGy, a rather high dose for processing natural polymers, alters to some extent the mechanical resistance of the starch-based materials. However this treatment substantially reduces the hydrophilic surface properties of the films, while not harming their biodegradability. Involved in radical cross-coupling reactions, lignin phenolic compounds are likely to play a primary role in the formation of a hydrophobic condensed network. This study suggests that lower irradiation doses might yield biomaterials with improved usage properties.

[Noncompacted cardiomyopathy of the left ventricule]. / Cardiomyopathies par non compaction du ventricule gauche.

In response to a recent review on the role of MRI in the evaluation of cardiomyopathies, we wished, through a clinical example, to focus the attention on noncompacted cardiomyopathy of the left ventricule, an under-diagnosed entity at the border of pediatric and adult imaging, because of its congenital nature but of late presentation.

Capillary zone electrophoresis of coniferyl alcohol oxidation products.

Capillary zone electrophoresis (CZE) was developed for the quantitative determination of dimers obtained by horseradish peroxidase-catalyzed oxidation of coniferyl alcohol. The influence of pH, electrolyte concentration, applied voltage, and temperature on CZE performance was investigated, resulting in an efficient and rapid separation. Coniferyl alcohol-derived dimers were directly analyzed from their reaction mixtures, without any extraction or derivatization step. In addition, these dimers were analyzed within 14 min, a substantially shorter time than is required for the HPLC method or the conventional capillary gas chromatography of their silylated derivatives. Standard deviations between injection replicates were in the 0.4-0.7% range for migration times and in the 1.8-5.1% range for relative normalized peak areas. The method could therefore be successfully applied to follow the peroxidase-catalyzed oxidation of coniferyl alcohol.

Strong decrease in lignin content without significant alteration of plant development is induced by simultaneous down-regulation of cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) in tobacco plants.

Different transgenic tobacco lines down-regulated for either one or two enzymes of the monolignol pathway were compared for their lignin content and composition, and developmental patterns. The comparison concerned CCR and CAD down-regulated lines (homozygous or heterozygous for the transgene) and the hybrids resulting from the crossing of transgenic lines individually altered for CCR or CAD activities. Surprisingly, the crosses containing only one allele of each antisense transgene, exhibit a dramatic reduction of lignin content similar to the CCR down-regulated parent but, in contrast to this transgenic line, display a normal phenotype and only slight alterations of the shape of the vessels. Qualitatively the lignin of the double transformant displays characteristics more like the wild type control than either of the other transgenics. In the transgenics with a low lignin content, the transformations induced other biochemical changes involving polysaccharides, phenolic components of the cell wall and also soluble phenolics. These results show that the ectopic expression of a specific transgene may have a different impact depending on the genetic background and suggest that the two transgenes present in the crosses may operate synergistically to reduce the lignin content. In addition, these data confirm that plants with a severe reduction in lignin content may undergo normal development at least in controlled conditions.

Soft-tissue venous malformations in adult patients: imaging and therapeutic issues.

Venous malformations are the most common vascular malformations. However, confusion with respect to terminology and imaging guidelines continues to result in improper diagnosis and treatment. An appropriate classification scheme for vascular anomalies is important to avoid the use of false generic terms. Adequate imaging in association with clinical findings is crucial to establishing the correct diagnosis. Doppler ultrasonography should be the initial imaging modality and demonstrates absence of flow or low-velocity venous flow. Computed tomography and magnetic resonance (MR) imaging are used primarily for pretreatment evaluation of lesion extension. These lesions are usually hypointense on T1-weighted MR images and markedly hyperintense on T2-weighted images with variable gadolinium enhancement. Direct phlebography helps confirm the diagnosis and exclude other soft-tissue tumors. Three distinct phlebographic patterns (cavitary, spongy, dysmorphic) have been identified. In most cases, conservative treatment is recommended. Sclerotherapy with or without surgery is useful in cases of functional impairment or significant aesthetic prejudice, even if recurrences are frequent. Direct phlebography is performed when a more detailed assessment of the vascular pattern is needed or as part of sclerotherapy. Use of the appropriate imaging technique is critical in establishing the diagnosis, evaluating extension, and planning appropriate treatment.

Repression of O-methyltransferase genes in transgenic tobacco affects lignin synthesis and plant growth.

Among the different enzymatic steps leading to lignin biosynthesis, two methylation reactions introduce the methyl groups borne by guaiacyl (G) and syringyl (S) units. Tobacco possesses a complex system of methylation comprising three classes of CCoAOMTs (caffeoyl-CoA-O-methyltransferases) and two classes of COMTs (caffeic acid OMTs). Antisense plants transformed with the CCoAOMT sequence alone or fused to COMT I sequence have been produced and compared to ASCOMT I plants in order to study the specific role of each OMT isoform in lignin biosynthesis, plant development and resistance to pathogens. Tobacco plants strongly inhibited in OMT activities have been selected and analyzed. Whereas antisense COMT I plants exhibited no visual phenotype, CCoAOMT repression was shown to strongly affect the development of both single and double transformants: a reduction of plant growth and the alteration of flower development were observed in the most inhibited plants. Lignin analysis performed by Klason and thioacidolysis methods, showed a decrease in the lignin quantity and changes in the lignin structure of ASCCoAOMT and ASCCoAOMT/ASCOMT I transgenics but not in ASCOMT I plants. Inhibition of COMT I in single as well as in double transformed tobacco was demonstrated to decrease S unit synthesis and to provoke the accumulation of 5-hydroxyguaiacyl lignin units. ASCCoAOMT/ASCOMT I tobacco was affected in lignin amount and composition, thus demonstrating additive effects of inhibition of both enzymes. The changes of lignin profiles and the phenotypical and molecular alterations observed in the different transgenic lines were particularly prominent at the later stages of plant development.

Elucidation of new structures in lignins of CAD- and COMT-deficient plants by NMR.

Studying lignin-biosynthetic-pathway mutants and transgenics provides insights into plant responses to perturbations of the lignification system, and enhances our understanding of normal lignification. When enzymes late in the pathway are downregulated, significant changes in the composition and structure of lignin may result. NMR spectroscopy provides powerful diagnostic tools for elucidating structures in the difficult lignin polymer, hinting at the chemical and biochemical changes that have occurred. COMT (caffeic acid O-methyl transferase) downregulation in poplar results in the incorporation of 5-hydroxyconiferyl alcohol into lignins via typical radical coupling reactions, but post-coupling quinone methide internal trapping reactions produce novel benzodioxane units in the lignin. CAD (cinnamyl alcohol dehydrogenase) downregulation results in the incorporation of the hydroxycinnamyl aldehyde monolignol precursors intimately into the polymer. Sinapyl aldehyde cross-couples 8-O-4 with both guaiacyl and syringyl units in the growing polymer, whereas coniferyl aldehyde cross-couples 8-O-4 only with syringyl units, reflecting simple chemical cross-coupling propensities. The incorporation of hydroxycinnamyl aldehyde and 5-hydroxyconiferyl alcohol monomers indicates that these monolignol intermediates are secreted to the cell wall for lignification. The recognition that novel units can incorporate into lignins portends significantly expanded opportunities for engineering the composition and consequent properties of lignin for improved utilization of valuable plant resources.

The phenolic fraction of maize bran: evidence for lignin-heteroxylan association.

Maize bran heteroxylan samples were extracted in various conditions of severity. Their ferulate and diferulate content was investigated by GC-MS of methyl ester-TMSi derivatives. When extracted by 0.5 M NaOH in mild conditions, the heteroxylan sample contained a low level of ferulic acid (0.032% by wt.) and the main diferulate surviving alkaline extraction was found to be the 8-8' diferulate. On peroxidase treatment, this sample nevertheless produced a firm and brittle gel without any change in the diferulate profile. Typical lignin structures, mainly comprising syringyl units interconnected through beta-O-4, beta-1 and beta-beta interunit bonds, were evidenced in the maize bran sample. More importantly, these lignin structures were found to be tightly associated with the alkali-extracted heteroxylans. Thioacidolysis revealed the occurrence of 0.1-0.5% (by wt.) lignin structures in heteroxylan fractions extracted in mild or severe conditions, before and after purification of the polysaccharides. The gelling potential of the heteroxylan fractions was not only dependent on their ferulate level, but also influenced by associated lignin structures. These results argue for the occurrence of covalent linkages between heteroxylan chains and lignin structures which could participate in the peroxidase-driven gelation of feruloylated polysaccharides. They demonstrate the role of low lignin levels in the organization of native or reconstructed polysaccharide networks.

Simultaneous down-regulation of caffeic/5-hydroxy ferulic acid-O-methyltransferase I and cinnamoyl-coenzyme A reductase in the progeny from a cross between tobacco lines homozygous for each transgene. Consequences for plant development and lignin synthesis.

Inhibition of specific lignin biosynthetic steps by antisense strategy has previously been shown to alter lignin content and/or structure. In this work, homozygous tobacco (Nicotiana tabacum) lines transformed with cinnamoyl-coenzyme A reductase (CCR) or caffeic acid/5-hydroxy ferulic acid-O-methyltransferase I (COMT I) antisense sequences have been crossed and enzyme activities, lignin synthesis, and cell wall structure of the progeny have been analyzed. In single transformed parents, CCR inhibition did not affect COMT I expression, whereas marked increases in CCR activity were observed in COMT I antisense plants, suggesting potential cross talk between some genes of the pathway. In the progeny, both CCR and COMT I activities were shown to be markedly decreased due to the simultaneous repression of the two genes. In these double transformants, the lignin profiles were dependent on the relative extent of down-regulation of each individual enzyme. For the siblings issued from a strongly repressed antisense CCR parent, the lignin patterns mimicked the patterns obtained in single transformants with a reduced CCR activity. In contrast, the specific lignin profile of COMT I repression could not be detected in double transformed siblings. By transmission electron microscopy some cell wall loosening was detected in the antisense CCR parent but not in the antisense COMT I parent. In double transformants, immunolabeling of non-condensed guaiacyl-syringyl units was weaker and revealed changes in epitope distribution that specifically affected vessels. Our results more widely highlight the impact of culture conditions on phenotypes and gene expression of transformed plants.

NMR evidence for benzodioxane structures resulting from incorporation of 5-hydroxyconiferyl alcohol into Lignins of O-methyltransferase-deficient poplars.

Benzodioxane structures are produced in lignins of transgenic poplar plants deficient in COMT, anO-methyltransferase required to produce lignin syringyl units. They result from incorporation of 5-hydroxyconiferyl alcohol into the monomer supply and confirm that phenols other than the three traditional monolignols can be integrated into plant lignins.

Polymeric proanthocyanidins are catabolized by human colonic microflora into low-molecular-weight phenolic acids.

Polymeric proanthocyanidins are common constituents of many foods and beverages. Their fate in the human body remains largely unknown. Their metabolism by human colonic microflora incubated in vitro in anoxic conditions has been investigated using nonlabeled and (14)C-labeled purified proanthocyanidin polymers. Polymers were almost totally degraded after 48 h of incubation. Phenylacetic, phenylpropionic and phenylvaleric acids, monohydroxylated mainly in the meta or para position, were identified as metabolites by gas chromatography coupled to mass spectrometry (GC-MS). Yields were similar to those previously reported for flavonoid monomers. These results provide the first evidence of degradation of dietary phenolic polymers into low-molecular-weight aromatic compounds. To understand the nutritional properties of proanthocyanidins, it is therefore essential to consider the biological properties of these metabolites.

Abiotic and enzymatic degradation of wheat straw cell wall: a biochemical and ultrastructural investigation.

The action of an abiotic lignin oxidant and a diffusible xylanase on wheat straw was studied and characterized at the levels of the molecular structures by chemical analysis and of the cell wall ultrastructure by transmission electron microscopy. While distinct chemical changes in the target polymers were observed when each system was used separately, a combination of the two types of catalysts did not significantly increase either lignin oxidation or hemicellulose hydrolysis. Microscopic observations however revealed that the supramolecular organization of the cell wall polymers was significantly altered. This suggests that the abiotic Mn-oxalate complex and the xylanase cooperate in modifying the cell wall architecture, without noticeably enhancing the degradation of the constitutive polymers.

Lignification in transgenic poplars with extremely reduced caffeic acid O-methyltransferase activity.

Transgenic poplars (Populus tremula x Populus alba) were obtained by introduction of a sense homologous transgene encoding caffeic acid O-methyltransferase (COMT) under the control either of the cauliflower mosaic virus double 35S promoter or of the eucalyptus cinnamyl alcohol dehydrogenase promoter. Although these constructs conferred a moderate overexpression of COMT in some lines, a transgenic line with the double 35S promoter was found where COMT activity in woody tissues was close to zero due to a gene-silencing phenomenon. For the first time in COMT down-regulated trees, this alteration substantially reduced lignin level in 6-month-old trees (17% decrease). Lignin structure was found to be strongly altered, with a two times higher content in condensed bonds, an almost complete lack of syringyl units, and the incorporation of 5-hydroxyguaiacyl units to the most remarkable extent reported so far. Consistent with the higher cellulose content and with the higher condensation degree of the lignin, the impact of the transformation on the kraft-pulping performances of the poplar trees positively affected the pulp yield (10% relative increase), but made lignins less amenable to industrial degradations.