Study of the acclimation stage and of the effect of the biodegradability on the performance of a microbial fuel cell

In this work, it has been studied the production of electricity and the oxidation of the pollutants contained in a synthetic wastewater fed with glucose and peptone of soybean as carbon sources, using a mediator-less microbial fuel cell (MFC). Special attention has been paid to the acclimation stage, in which it was found that with high hydraulic and solid retention times it is possible to obtain a very efficient process with a 90% COD removal and practically total conversion of COD into electricity (considering the typical stoichiometric yield of heterotrophic biomass). The influence of concentration sludge was studied working with three different amounts of suspended solids, from 120 to 14000 mg. The maximum power density increased exponentially with the concentration sludge from 2.1 mW m⁻² to 11 mW m⁻² at the highest concentration sludge. More over, the percentage of the influent COD used to produce electricity was higher than 100% when the highest sludge concentration was used. This was explained taking into account the endogenous metabolism of micro-organisms presented in the system.     

Ultrastructure of the median eminence of the rat

Summary The ependymal cells bordering the median eminence to the third ventricle are characterised by many microvillus-like projections and bulbous cell processes of the luminal plasma membrane. The latter contain many vesicles 500–1,000 Å in diameter. Cilia with 9+2 fibrillar pattern are seen occasionally. Adhesive devices in the from of zonula adhaerens and zonula occludens are found in the apical part of the intercellular junction. Unmyelinated nerve fibres with a mean diameter of 1 and containing many electron dense granules of 830–1,330 Å are often seen between the ependymal cells.Two types of glial cells are found in the median eminence. One is characterised by a nucleus with dense blods of chromatin and dense cytoplasm, and it is associated chiefly with the nerve fibres in the region of the hypothalamo-hypophysial tract. The other type of glial cell is characterised by fine, uniformly distributed chromatin in the nucleus and a relatively pale cytoplasm and branched processes which terminate perivascularly in the base of the median eminence.Myelinated nerve fibres are seen only in the region of the hypothalamo-hypophysial tract. Only a part of them contain electron dense granules 1,330–2,330 Å in diameter.Three types of unmyelinated nerve fibres can be distinguished in the median eminence according to the size of the electron dense granules they contain: 1. Nerve fibres containing granules 1,330–2,330 Å in diameter. They are seen primarily in the hypothalamo-hypophysial tract, but also in the zona externa; 2. those containing granules with a mean diameter of 1,330 Å; and 3. those containing granules with a mean diameter of 1,000 Å. The last two types are both encountered in the hypothalamo-hypophysial tract, the zona externa and the perivascular region of the base of the median eminence. Under high magnification, the membrane of the granules show evidence of a trilaminar structure and the content of the granules with a low electron density appeares to consist of small microvesicles or globular components. Besides granules, these nerve fibres contain vesicles mostly 420 Å in diameter whose relative number increases towards the perivascular nerve endings. 53 per cent of the inclusions in the hypothalamo-hypophysial tract are granules and 47 per cent vesicles, while the corresponding percentages for the zona externa are 40 and 60 and for the perivascular nerve endings 20 and 80.The mean width of the pericapillary space is 1 , but it varies greatly. It containes many collagen fibrils and fibroblasts. The capillary endothelium is frequently fenestrated and contains many vesicles of various sizes.Two types of granules-containing cells are found in the pars tuberalis depending on the size of the electron dense granules: 1. cells containing granules with a mean diameter of 1,330 Å: and 2. cells containing granules with a mean diameter of 2,000 Å. In addition, there are occasional follicular cavities filled with amorphous material, microvilli and cilia of 9+2 fibrillar pattern.Aided by a grant from the Sigrid Jusélius Stifteise.     

Principal component analysis of the relationship between the d-amino acid concentrations and the taste of the sake

We performed sensory evaluations on 141 bottles of sake and analyzed the relationship between the d-amino acid concentrations, and the taste of the sake using principal component analysis, which yielded seven principal components (PC1–7) that explained 100 % of the total variance in the data. PC1, which explains 33.6 % of the total variance, correlates most positively with strong taste and most negatively with balanced tastes. PC2, which explains 54.4 % of the total variance, correlates most positively with a sweet taste and most negatively with bitter and sour tastes. Sakes brewed with “Kimoto yeast starter” and “Yamahaimoto” had high scores for PC1 and PC2, and had strong taste in comparison with sakes brewed with “Sokujo-moto”. When present at concentrations below 50 μM, d-Ala did not affect the PC1 score, but all the sakes showed a high PC1 score, when the d-Ala was above 100 μM. Similar observations were found for the d-Asp and d-Glu concentrations with regard to PC1, and the threshold concentrations of d-Asp and d-Glu that affected the taste were 33.8 and 33.3 μM, respectively. Certain bacteria present in sake, especially lactic acid bacteria, produce d-Ala, d-Asp and d-Glu during storage, and these d-amino acids increased the PC1 score and produced a strong taste (Nojun). When d- and l-Ala were added to the sakes, the value for the umami taste in the sensory evaluation increased, with the effect of d-Ala being much stronger than that of l-Ala. The addition of 50–5,000 μM dl-Ala did not effect on the aroma of the sakes at all.     

Molecular analysis of the D-genome of the Triticeae

Summary The chromosome of three tetraploid Aegilops L. species containing the D-genome were analyzed by in situ hybridization with a repeated DNA sequence clone pAS1 isolated from Aegilops squarrosa and observed to be D-genome specific. This sequence is found on all seven D-genome chromosome pairs of A. squarrosa and hexaploid wheat. Two distinct D-genome patterns were observed in the tetraploid species. The D-genome of A. cylindrica was similar to hexaploid wheat. Seven pairs of chromosomes having large amounts and numerous sites of the sequence were observed. Five chromosome pairs with fewer and smaller sites of the repetitive sequence were observed in the D-genomes of A. crassa and A. ventricosa. In addition to these major repeated sequence differences, chromosomal modifications appear to have occurred between T. aestivum and A. cylindrica and between A. crassa and A. ventricosa resulting in changes with respect to location of the sequence between the respective species. D-genome divergence with respect to pAS1 sequence appears to have occurred at least in two forms, one characterized by the changes in amount of repetitive sequence and the second by changes in location of the sequence.     

Specificity of the lipase-specific foldases of gram-negative bacteria and the role of the membrane anchor

Folding of lipases that are secreted by Pseudomonads and other gram-negative bacteria via the type II secretion pathway is facilitated by dedicated chaperones, called lipase-specific foldases (Lifs). Lifs are membrane-anchored proteins with a large periplasmic domain. The functional interaction between the Lif and its cognate lipase is specific, since the Pseudomonas aeruginosa Lif was found not to substitute for Lifs from Burkholderia glumae or Acinetobacter calcoaceticus. However, the P. aeruginosa Lif was able to activate the lipase from the closely related species P. alcaligenes. Hybrid proteins constructed from parts of the P. aeruginosa and B. glumae Lifs revealed that the C-terminal 138 amino acids of the B. glumae Lif determine the specificity of the interaction with the cognate lipase. Furthermore, the periplasmic domain of the B. glumae Lif was functional when cloned in frame with a cleavable signal sequence, which demonstrates that the membrane anchor is not essential for Lif function in vivo. However, the recombinant Lif was released into the medium, indicating that the function of the membrane anchor is to prevent secretion of the Lif together with the lipase. Received: 12 November 1998 / Accepted: 19 February 1999     

Subcellular distribution of the PI effect in the pancreas of the guinea pig

Pancreas lobules incubated $\text{in vitro}$ actively incorporate (2-³H) myoinositol into the PI associated with a number of different membranes, $\text{i.e.}$, those of the rough- and smooth-surfaced microsomes, mitochondria, zymogen granules, as well as the plasmalemma. Stimulation of secretion with Acetylcholine + Eserine results in an increase of the incorporation (PI effect). This increase is approximately of the same order of magnitude (～ 4fold) in all the fractions. The results might be due either to a generalized breakdown of the PI associated with all the membranes under study, followed by resynthesis, or to a rapid intracellular redistribution of the PI molecules, synthetized in response to the stimulation.     

Effects of the administration of cadmium and zinc on the concentration of zinc in the thymus of rats

The zinc content of thymus glands of male Wistar rats has been determined during five weeks of treatment with ZnCl₂ and CdCl₂, and compared with a group of control rats. THymus gland extracts were chromatographed on columns of Sephadex G-75 and the zinc content of the one hundred fractions obtained were determined by atomic absorption spectrophotometry. The rats treated with ZnCl₂ showed an increase in the thymus concentration of zinc bound to high and low molecular weight proteins. The rats treated with CdCl₂ showed an increase in zinc concentration, as opposed to the control group, during the first three weeks of treatment, and thereafter show a toxic effect of cadmium on the gland, with ulterior regression of the latter, and a decrease in the concentration of zinc.     

Characterisation of the membrane-extrinsic domain of the TatB component of the twin arginine protein translocase

The twin arginine protein transport (Tat) system transports folded proteins across cytoplasmic membranes of bacteria and thylakoid membranes of plants, and in Escherichia coli it comprises TatA, TatB and TatC components. In this study we show that the membrane extrinsic domain of TatB forms parallel contacts with at least one other TatB protein. Truncation of the C-terminal two thirds of TatB still allows complex formation with TatC, although protein transport is severely compromised. We were unable to isolate transport-inactive single codon substitution mutations in tatB suggesting that the precise amino acid sequence of TatB is not critical to its function.

Structured summary

TatAphysically interacts with TatA by two hybrid(View interaction)TatB and TatCbind by molecular sieving(View interaction)TatBphysically interacts with TatB by two hybrid (View Interaction 1, 2)     

The mechanism of the mycoinsecticide diluent on the efficacy of the oil formulation of insecticidal fungus

Adverse conditions, including low humidity, UV irradiation, and high temperature, appreciably affect the efficacy of mycoinsecticides. Oil formulation increased the virulence of Metarhizium anisopliae var. acridum (Ascomycota: Hypocreales) against locusts and grasshoppers by reducing the dependence on saturated water. A mycoinsecticide diluent (a water-in-oil emulsion) has been widely used to dilute the oil formulation of M. anisopliae in China. The aim of our study was to elucidate the mechanism by which the mycoinsecticide diluent improves the virulence of M. anisopliae. We investigated the effects of the mycoinsecticide diluent on the virulence, invasion speed, and viability of the conidia under various adverse conditions. The results demonstrated that the mycoinsecticide diluent significantly improved the virulence of conidia at low humidity (68, 75, and 84%). In particular, at an RH of 68%, the LT₅₀ for locusts treated with the emulsion was 5.4 days and was 31.6% lower than the value for locusts treated with an oil formulation. In addition, the concentration of the hyphal bodies found in the haemolymph of locusts treated with emulsion was about 27-fold higher than that in locusts treated with oil formulation four days after inoculation. This result was further confirmed by determining the concentration of M. anisopliae var. acridum DNA in locust haemolymph using quantitative PCR. The percentage germination of conidia in the emulsion was also significantly higher than that in oil at 68% RH. There was no significant difference in percentage germination between conidia treated with the emulsion and oil when exposed to irradiation with ultraviolet-B (UV-B) or high temperature. These results demonstrate that the mycoinsecticide diluent enhances the virulence of M. anisopliae formulated in oil at low humidity by providing adequate water for germination without interfering with the UV tolerance and thermotolerance of the conidia.     

Reconstructing the phylogeny of the Sipuncula

Sipunculans are marine spiralian worms with possible close affinities to the Mollusca or Annelida. Currently 147 species, 17 genera, 6 families, 4 orders and 2 classes are recognized. In this paper we review sipunculan morphology, anatomy, paleontological data and historical affiliations. We have conducted cladistic analyses for two data sets to elucidate the phylogenetic relationships among sipunculan species. We first analyzed the relationships among the 45 species of Phascolosomatidea with representatives of the Sipunculidea as outgroups, using 35 morphological characters. The resulting consensus tree has low resolution and branch support is low for most branches. The second analysis was based on DNA sequence data from two nuclear ribosomal genes (18S rRNA and 28S rRNA) and one nuclear protein-coding gene, histone H3. Outgroups were chosen among representative spiralians. In a third analysis, the molecular data were combined with the morphological data. Data were analyzed using parsimony as the optimality criterion and branch support evaluated with jackknifing and Bremer support values. Branch support for outgroup relationships is low but the monophyly of the Sipuncula is well supported. Within Sipuncula, the monophyly of the two major groups, Phascolosomatidea and Sipunculidea is not confirmed. Of the currently recognized families, only Themistidae appears monophyletic. The Aspidosiphonidae, Phascolosomatidae and Golfingiidae would be monophyletic with some adjustments in their definition. The Sipunculidae is clearly polyphyletic, with Sipunculus nudus as the sister group to the remaining Sipuncula, Siphonosoma cumanense the sister group to a clade containing Siphonosoma vastumand the Phascolosomatidea, and Phascolopsis gouldi grouping within the Golfingiiformes, as suggested previously by some authors. Of the genera with multiple representatives, only Phascolosoma and Themiste are monophyletic as currently defined. We are aiming to expand our current dataset with more species in our molecular database and more detailed morphological studies.     

On the nucleoli of the dinoflagellate Prorocentrum

To date no nucleolus had been observed in Prorocentrum under the light microscope. The author failed to show the nucleoli of P. micans and P. cassubica with eosin in 70% alc or with methyl green-pyronin. But when these dinoflagellates were treated with an Ag-1 technique which had been improved for demonstrating NORs in unicellular organisms, nucleoli were stained dark brown or black, while all other parts showed no colour. When the materials were stained well, only the central part of the nucleolus was stained. Under the electron microscope, it was observed that all the silver grains were concentrated in the pars fibrosa of the nucleolus. P. cassubica had only one small oblate nucleolus attached to the nuclear envelope, with NOR usually in the shape of the letters O or C. P. micans had 1–7 nucleoli of various sizes and shapes with NORs in various complicated forms. The number of nucleoli bore a certain relationship to the living state of the dinoflagellate. One day after fresh medium was added, cells with 3 nucleoli were most common, and 28.5% of the individuals had 4–6 nucleoli. Cells having only one nucleolus accounted for 8.6%. 3 days after, cells with 2 nucleoli became dominant, and those with 4–6 decreased to 18.4%. After a month, cells with 1 nucleolus became most abundant, cells having 4 nucleoli decreased to 2.4%, and no cells had 5 or 6 nucleoli.     

Interaction of the components of the prothrombinase complex

The interaction of components of the prothrombinase complex, i.e. bovine Factor X or Factor Xa. bovine Factor V or Factor Va, phospholipid, and Ca²⁺, in various combinations was studied primary by a gel filtration technique. In experiments, in which phospholipids ranging from those isolated from naturally occurring sources to those long chain (18 : 1) as well as short chain 6 : o and 7 : 0 fatty acids prepared by chemical and enzymatic synthesis were used, it was evident that a net negative surface charge on the lipid dispersions was one of the important requirements for interaction. Though the short chain fatty acid phospholipids interacted with the proteins of the prothrombinase complex, there was invariably a diminution in the activity of the enxyme complex. It was established that Factor V or Va did not bind Ca²⁺ and that the binding of either of these factors with phospholipids (with a net negative charge) was not dependent on Ca²⁺. However, the interaction of Factor X or Factor Xa with phospholipids with a negative charge required Ca²⁺. It was shown that Factor X could bind to the same type of lipid surface as that notes for Factor Xa. Of interest was the apparent difference in the phospholipid binding characteristics of the two variant forms of bovine plasma Factor X, i.e. X₁ and X₂, which might in part explain the differences in their specific activities. Of importance was the lack of demonstrable complex formation between Factors II, X and V in the absence of phospholipids and/or in the presence or absence of Ca²⁺. The significance of these results as they might apply to the configuration of the prothrombinase complex and its interaction with prothrombin plus the usefulness of the short chain fatty phospholipid in exploring these lipid-protein interactions are discussed.     

Studies of the chloride transport in the gastric mucosa of the frog

The unidirectional fluxes of Cl^- and Na⁺ across the frog gastric mucosa in vitro were investigated with radioactive isotopes, and related to the secretory and electrical properties of the normal, and metabolically inhibited, mucosa. The flux of Cl^- from nutrient to secretory surface of the mucosa was observed to rise sharply with increasing acid secretion, while the corresponding flux of Na⁺ did not change appreciably. Lowering [NaCl] in the secretory solution caused a proportional drop in the fluxes from secretory to nutrient surface, of both Cl^- and Na⁺. Under the same conditions, the flux of Cl^- from nutrient to secretory surface fell by nearly the same amount as did the flux of Cl^- in the opposite direction, while the flux of Na⁺ from nutrient to secretory surface remained essentially unchanged. Electrical and hydrodynamic causes for this observation could be excluded. Metabolic inhibitors, including cyanide, azide, DNP, and anaerobiosis depressed Cl^- flux in both directions distinctly below the corresponding values observed with the normal, non-secreting mucosa. At the same time, a decrease in electrical potential difference and conductance was observed under inhibition. The flux of Na⁺ was little changed by metabolic inhibition. The relationship between fluxes and conductance of Cl^- during metabolic inhibition differs markedly from that observed under normal conditions, and is consistent with the view that during metabolic inhibition most of the Cl^- moving across the mucosa does so as a free ion. From the above data it is concluded that Cl^- is normally transported across the mucosa in combination with a carrier, the supply of which is impaired under metabolic inhibition. According to the behavior of the Na⁺ flux, the passive permeability of the mucosa appeared to be little affected by the metabolic inhibition applied, but seemed to rise considerably after death of the mucosa, probably due to structural damage.     

Remarks on the chemical conditions on the surface of the primitive Earth and the probability of the evolution of life

The inner planets were formed from smaller objects that had no gases associated with them. These objects contained relatively small amounts of water and carbon in a form similar to that found in carbonaceous chondrites. The first forms of life must have originated during the time when the water reacted with the carbon (and also with nitrides, phosphides, etc.), while the hydrogen formed by this reaction was continuously lost from the gravitational field of the Earth. About 10⁴⁴ atoms of carbon reacted with water during less than 10¹⁷ s. The crucial question is whether some form of life will always develop under these conditions, or whether the origin of life is an improbable, perhaps an immensely improbable event. At present it is still impossible to answer this question.     

The dynamics of the yeast community of the Tagus river estuary: testing the hypothesis of the multiple origins of estuarine yeasts

Yeasts are common inhabitants of different types of aquatic habitats, including marine and estuarine waters and rivers. Although numerous studies have surveyed yeast occurrence in these habitats, the identification of autochthonous populations has been problematic because several yeast species seem to be very versatile and therefore mere presence is not sufficient to establish an ecological association. In the present study we investigated the dynamics of the yeast community in the Tagus river estuary (Portugal) by combining a microbiological study involving isolation, quantification, and molecular identification of dominant yeast populations with the analysis of hydrological and hydrographical data. We set out to test the hypothesis of the multiple origins of estuarine yeast populations in a transect of the Tagus estuary and we postulate four possible sources: open sea, terrestrial, gastrointestinal and the estuary itself in the case of populations that have become resident. Candida parapsilosis and Pichia guilliermondii were correlated with Escherichia coli, which indicated an intestinal origin. Other cream-colored yeasts like Debaryomyces hansenii and Candida zeylanoides had similar dynamics, but no association with E. coli and quite distinct ecological preferences. They might represent a group of resident estuarine populations whose primary origin is diverse and can include marine, terrestrial, and gastrointestinal habitats. Another major yeast population was represented by Rhodotorula mucilaginosa. The cosmopolitan nature of that species and its moderate association with E. coli point to terrestrial sources as primary habitats.     

Rhythmic fluctuations in the synthetic activities of the nodulated root of the legume

Summary If a nodulated legume is decapitated immediately after a brief period of photosynthesis in C¹⁴O₂ a highly reproducible pattern of labelling is detected among the amino compounds of the root bleeding sap. The sequences of this pattern apparently reflect the consequences of the exchange of labelled carbohydrate with various morphological and metabolic compartments of the root. The progress of the exchange is greatly influenced by diurnal variations in root metabolism.An endogenous component is described for the rhythmic discharge of amino compounds into the bleeding sap. At 24°C the period of the rhythm is slightly greater than 24 hours.Plants with branched shoots are used to study environmental influences on the translocation of labelled assimilates from a shoot, and the utilisation of these materials in synthesis of organic compounds of nitrogen in the nodulated root. One half of the branched shoot is fed with C¹⁴O₂ and its unlabelled partner removed for collection of bleeding sap. A progressive enrichment of bleeding sap with radiocarbon occurs only if the plants are exposed to normal photoperiods and ambient temperatures. Similar plants retained in darkness in constant temperature exhibit a rapid decline in the specific activity of the amino fraction of the bleeding sap, suggesting that translocation from the pool of labelled carbohydrate in the shoot has failed to keep pace with root synthesis.     

Influence of the pycnocline on the vertical migration of chaetognaths in the northern Benguela

The vertical distribution and migration patterns of chaetognathswere studied at a sampling station off northern Namibia (18°00'S,10°30'E during a 48 h sampling cycle. The sampling areawas characterized by mixing of the Angola current with the northernmostwaters of the Benguela current in the surface region. The continuousflow of the Angola current during the study period gave riseto a thermocline and a halocline at a depth of 40 m. The samplingintervals used to study the behaviour of epipelagic chaetognathspecies under these conditions were 200–100, 100–60,60–40, 40–20 and 20–0 m. A total of 10 differentchaetognath species were captured. Sagitia enflata was the predominantspecies, with a mean density of 4400 individuals per 1000 m³in daytime hauls, accounting for 54.1% of all individuals collectedin the samples. Sagitia minima was the next most predominantspecies, with a mean density of 2400 individuals per 1000 m³in daytime hauls, accounting for 16.6% of the chaetognath communitysampled. Three maturity stages were considered in analysingpossible ontogenetic migrations. Nearly all the species wereaggregated above the pycnocline, and stages I and II of manyspecies carried out short migrations in the surface layers.The limited migration pattern, together with a staggered distributionof the different species and stages above the pycnocline, hasbeen interpreted as a space partitioning mechanism to preventintra- and interspecific competition.     

Cryopreservation of the sperm of the Japanese bitterling

Sperm of the Japanese bitterling Tanakia limbata that had been cryopreserved with 5 or 10% methanol plus 95 or 90% foetal bovine serum (FBS) showed higher percentage and longer duration of motility than those that had been cryopreserved with 90% FBS and 10% DMSO, glycerol, N,N-dimethylacetamide or N, N-dimethylformamide. Foetal bovine serum, used as extender, had some cryoprotective effects when spermatozoa were cooled either with 10% methanol or without methanol. Spermatozoa, cooled to −40° C and then immersed in liquid nitrogen, had greater post-thaw motility than those cooled to −20, −60, or −80° C. The post-thaw percentage of motile spermatozoa increased significantly ( P < 0·001) with decreases in the freezing rate from 60 to 5°C min⁻¹. These results indicate that 10% methanol plus 90% foetal bovine serum is a suitable diluent for cryopreservation of bitterling spermatozoa and that samples should be cooled to -40°C at a low freezing rate for effective storage.     

FKBP12 Modulation of the Binding of the Skeletal Ryanodine Receptor onto the II-III Loop of the Dihydropyridine Receptor

In skeletal muscle, excitation-contraction coupling involves a functional interaction between the ryanodine receptor (RyR) and the dihydropyridine receptor (DHPR). The domain corresponding to Thr⁶⁷¹-Leu⁶⁹⁰ of the II-III loop of the skeletal DHPR α₁-subunit is able to regulate RyR properties and calcium release from sarcoplasmic reticulum, whereas the domain corresponding to Glu⁷²⁴-Pro⁷⁶⁰ antagonizes this effect. Two peptides, covering these sequences (peptide A_Sk and C_Sk, respectively) were immobilized on polystyrene beads. We demonstrate that peptide A_Sk binds to the skeletal isoform of RyR (RyR1) whereas peptide C_Sk does not. Using surface plasmon resonance detection, we show that 1) domain Thr⁶⁷¹-Leu⁶⁹⁰ is the only sequence of the II-III loop binding with RyR1 and 2) the interaction of peptide A_Sk with RyR1 is not modulated by Ca²⁺ (pCa 9-2) nor by Mg²⁺ (up to 10 mM). In contrast, this interaction is strongly potentiated by the immunophilin FKBP12 (EC₅₀ = 10 nM) and inhibited by both rapamycin (IC₅₀ = 5 nM) and FK506. Peptide A_Sk induces a 300% increase of the opening probability of the RyR1 incorporated in lipid bilayer. Removal of FKBP12 from RyR1 completely abolishes this effect of domain A_Sk on RyR1 channel behavior. These results demonstrate a direct interaction of the RyR1 with the discrete domain of skeletal DHPR α₁-subunit corresponding to Thr⁶⁷¹-Leu⁶⁹⁰ and show that the association of FKBP12 with RyR1 specifically modulates this interaction.     

Influence of the type of imaging on the delineation process during the treatment planning

AimThe aim of this study was to compare the intra- and interobserver contouring variability for structures with density of organ at risk in two types of tomography: kilovoltage computed tomography (KVCT) versus megavoltage computed tomography (MVCT). The intra- and interobserver differences were examined on both types of tomography for structures which simulate human tissue or organs.Materials and methodsSix structures with density of the liver, bone, trachea, lung, soft tissue and muscle were created and used. For the measurements, the special water phantom with all structures was designed. To evaluate interobserver variability, five observers delineated the structures in both types of computed tomography (CT).ResultsIntraobserver variability was in the range of 1–14% and was the largest for the liver. The observers segmented larger volumes on MVCT compared with KVCT for the trachea (79.56 ccm vs.74.91 ccm), lung (87.61 vs. 82.50), soft tissue (154.24 vs. 145.47) and muscle (164.01 vs. 157.89). For the liver (98.13 vs. 99.38) and bone (51.86 vs. 67.97), the volume on MVCT was smaller than KVCT. The statistically significant differences between observers were observed for structures with density of the liver, bone and soft tissue on KVCT and for the liver, lung and soft tissue on MVCT. For the structures with density of the trachea and muscles, there were no significant differences for both types of tomography.ConclusionsDuring the contouring process the interobserver and intraobserver contouring uncertainty was larger on MVCT, especially for structures with HU near 80, compared with KVCT.