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Hiroshi Asakura

Publications and source records attributed to Hiroshi Asakura.

18 recordsLinked to original sources
PubMed2006

Improvement in banding artefacts in four-dimensional computed tomography for radiotherapy planning.

Respiratory-gated CT (RGCT) and four-dimensional CT (4DCT) scan techniques cover consecutive segments of the respiratory cycle. However, motion artefacts may occur in fast respiratory phases such as mid-inhalation and -exhalation. CT imaging involves the use of a number of x-ray tube positions for each couch position. We investigated the fundamental nature of motion artefacts using a constant-velocity moving phantom in motion in the CT plane or perpendicular to the CT plane, and in pigs to simulate a human model. Artefacts and movement distance were evaluated in a moving phantom and artificially ventilated pigs with a 256-multi-detector row CT (256MDCT). The phantom moved in the CT plane or perpendicular to the CT plane with a constant velocity. Backprojection used variable initial backprojection angles (IBAs). The phantom length for motion perpendicular to the CT plane was independent of IBA but was represented by phantom diameter plus the distance of movement per gantry rotation. In contrast, that for the motion in the CT plane was dependent on IBA, as represented by phantom diameter plus the distance of movement per rotation for IBA perpendicular to the phantom movement direction, and phantom diameter plus half the distance of movement per gantry rotation for other IBAs. Results for volumetric CT images with different IBAs showed the presence of banding artefacts. Similar findings were seen in artificially ventilated pigs. Motion artefacts are unavoidable in both conventional CT and 256MDCT. Banding artefacts will be improved if the same IBAs at each couch position are accounted for during image reconstruction. This improvement will be beneficial in respiratory gated and 4D radiation therapies.

Algorithms↗
PubMed2006

Respiratory correlated segment reconstruction algorithm towards four-dimensional radiation therapy using carbon ion beams.

PURPOSE: To enhance the precision of treatment planning for tumors which move under respiration, we developed a respiratory-correlated segment reconstruction method (RS) based on the Feldkamp--Davis--Kress algorithm (FDK) which provides high temporal resolution and a high signal-to-noise ratio. We compared full-scan (FS-FDK) and RS-FDK with regard to dose distribution in heavy ion treatment planning. MATERIALS AND METHODS: Data acquisition for RS-FDK is done using a respiratory sensing system in cine scan mode with a 256-multi-detector row CT (256-MDCT). To evaluate the accuracy of irradiation of moving tumors, dose distributions with each algorithm were compared in heavy ion treatment planning using beam parameters obtained with FS-FDK. RESULTS: Images obtained using RS-FDK did not show motion artifacts and visualized the edges of the liver and pulmonary vessels more clearly than those with FS-FDK. The iso-dose distributions for FS-FDK covered the target volume; in contrast, RS-FDK with the beam parameter of FS-FDK image provided an insufficient dose to the target and a considerable dose to normal tissues around it. CONCLUSIONS: The information provided by RS-FDK improves accuracy in the prescription of dose-to-target volume. Further, RS-FDK allows greater precision in the delivery of radiotherapy, including 4D radiation therapy.

Aged↗
PubMed2006

Enhancement of mice susceptibility to infection with Listeria monocytogenes by the treatment of morphine.

The effect of morphine on the susceptibility of BALB/c mice to diarrheagenic Escherichia coli, Shigella flexneri, Listeria monocytogenes, Salmonella Enteritidis, Yersinia enterocolitica, was examined via the intraperitoneal inoculation. Morphine treatment increased the susceptibility to S. Enteritidis and L. monocytogenes, resulting in bacteremia and central nervous system (CNS) invasion (for L. monocytogenes), while the infection with other bacteria did not show the systemic dissemination in the morphinetreated mice. Notably, L. monocytogenes infection caused 100% mortality with a mean survival time (MST) of 1.3 days in morphine-treated mice, but untreated mice did not die. The present data suggested that individuals using heroin or treated with morphine derivatives might be at high risk for listeriosis, especially those who are immunocompromised. Recent increasing consumption of morphine may propose the necessity for further epidemiological surveillance on infectious diseases.

Animals↗
PubMed2006

The sigma factor RpoN (sigma54) is involved in osmotolerance in Listeria monocytogenes.

Listeria monocytogenes is able to grow under conditions of high osmolarity. We constructed a deletion mutant of rpoN, encoding the alternative sigma factor RpoN, and analyzed its response to osmotic stress. In a minimal medium with 4% NaCl and 1 mM betaine, the mutant showed a similar growth to that of the parental strain, EGD. In the same medium with 4% NaCl and 1 M carnitine, the growth rate of the mutant was greatly reduced, when the optical density at 600 nm (OD600) at the starting point of growth, was 0.15. However, when growth of the culture was started at an OD600 of 0.025, the growth of the mutant was similar to that of EGD. The mutant's expression of two betaine transporter genes, betL and gbuB, and the carnitine transporter gene opuCA, was osmotically induced at a level similar to EGD, and its rate of carnitine uptake was similar to that of EGD. These results suggest that the growth defect from the rpoN mutant is caused not by the transcriptional regulation of opuCA or by a decrease in carnitine uptake, but possibly by larger amounts of carnitine being needed for growth of the mutant in minimal medium when NaCl is present.

Bacterial Proteins↗
PubMed2006

Commissioning of a conformal irradiation system for heavy-ion radiotherapy using a layer-stacking method.

The commissioning of conformal radiotherapy system using heavy-ion beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC) is described in detail. The system at HIMAC was upgraded for a clinical trial using a new technique: large spot uniform scanning with conformal layer stacking. The system was developed to localize the irradiation dose to the target volume more effectively than with the old system. With the present passive irradiation method using a ridge filter, a scatterer, a pair of wobbler magnets, and a multileaf collimator, the width of the spread-out Bragg peak (SOBP) in the radiation field could not be changed. With dynamic control of the beam-modifying devices during irradiation, a more conformal radiotherapy could be achieved. In order to safely perform treatments with this conformal therapy, the moving devices should be watched during irradiation and the synchronousness among the devices should be verified. This system, which has to be safe for patient irradiations, was constructed and tested for safety and for the quality of the dose localization realized. Through these commissioning tests, we were successfully able to prepare the conformal technique using layer stacking for patients. Subsequent to commissioning the technique has been applied to patients in clinical trials.

Calibration↗
PubMed2005

Physical evaluation of multidetector-row computed tomography (MDCT) scan methods and conditions for improvement of carbon beam distribution.

To reduce errors in the carbon beam distribution between the treatment planning system and the actual situation, we evaluated the geometrical accuracy, volume accuracy, water-equivalent length (WEL), and treatment planning, and compared the results of evaluation of axial and helical scan methods with various scan parameters. The results indicated that both scan methods showed good geometrical accuracy for thin slice images, but for thick slice images it is easier to understand the phantom as a sphere from the helical as compared with the axial scan. Treatment planning with a thin slice thickness (ST) provided accurate dose distribution for both scan methods, and the dose distribution on the treatment planning system was almost the same as that in the actual situation. Not all institutes, however, can obtain thin slice CT images, and some have used thick slice CT images in planning. For the axial scan, such thick slice images induced differences in dose distribution between treatment planning and the actual situation. Helical scans with a small, reconstructed increment reduced these differences even with relatively thick CT images. To achieve a more accurate dose distribution, radiation therapy planning should be performed using a thin ST for both scan methods or the helical scan with a small, reconstructed increment. Although we reached this conclusion using a carbon beam, it also may be applicable to proton beam therapy.

Carbon↗
PubMed2005

Role of in vivo passage on the environmental adaptation of enterohemorrhagic Escherichia coli O157:H7: cross-induction of the viable but nonculturable state by osmotic and oxidative stresses.

In an enterohemorrhagic Escherichia coli (EHEC) O157:H7 outbreak caused by salted salmon roe that occurred in Japan, 1998, a food isolate (F2) was NaCl-resistant and a patient isolate (P5) was sensitive to NaCl. We show here that hydrogen peroxide, like NaCl, induced a significant loss of culturability in P5. The BacLight assay suggested that the EHEC O157:H7 entered a viable but nonculturable (VNC) state. We used the passage through mice in an attempt to model this transition in phenotype. Mouse-passaged isogenic variants of F2 became NaCl- and oxidation-sensitive, entered the nonculturable state in response to either of these stresses, and could be resuscitated by sodium pyruvate. Since the expression of RpoS in response to these stresses correlated with the isolates' culturabilities, we concluded that in vivo passage negatively modulated RpoS expression, and the subsequent stress exposure induced the VNC state in the EHEC O157:H7 isolates.

Acetates↗
PubMed2004

Tumour shapes and fully automated range compensation for heavy charged particle radiotherapy.

The idea of a computer-controlled range-compensating system for heavy charged particle radiotherapy, the multibar compensator, is proposed. By stacking multiple energy-absorbing layers along the beam, each of which has structure and behaviour similar to those of a multileaf collimator, variable range compensation will be achieved. The analysis of the conventional range compensators actually used for treatment concluded that the proposed system would not seriously degrade the treatment quality for the most cases, except for tumours in the head and neck region where 1 mm precision may be required. The system will even be able to coexist with the conventional range compensators to provide either method depending on clinical situations.

Automation↗
PubMed2004

Changes in Salmonella enterica serovar Oranienburg viability caused by NaCl-induced osmotic stress is related to DNA relaxation by the H-NS protein during host infection.

The NaCl sensitivity of Salmonella enterica serovar Oranienburg strains depends on their origin. We found previously that food- and patient-origin isolates in an outbreak were, respectively, NaCl-resistant and NaCl-sensitive, and the NaCl-resistant strain of food-origin isolates became NaCl-sensitive after passage of the strain through mice [FEMS Microbiol. Lett. 212 (2002) 87]. Here, we report that this phenotypic difference is mainly dependent on topological changes regulated by H-NS, a bacterial histone-like nucleoid protein that binds non-specifically to DNA. That is, this phenotypic difference was caused by changes in DNA topology during infection of the host. Based on these findings, we propose this mechanism has a key role in promoting the survival of Salmonella under osmotic stress.

Animals↗
PubMed2004

Behavior of endocrine-disrupting chemicals in leachate from MSW landfill sites in Japan.

Endocrine-disrupting chemicals (EDCs) in landfill leachates and the effluent from leachate treatment facilities have been analyzed by many researchers. However, seasonal and yearly variations and the influence of landfill age are still not clear. In this study, leachate was sampled on four occasions each, at different seasons, from two MSW landfills which receive different waste material. Then, the quantities of alkylphenols (APs), bisphenol A (BPA), phthalic acid esters (PAEs) and organotin compounds (OTs) in leachate were determined. By sampling leachate from landfill cells of different age, the long-term behavior of EDCs was studied. Furthermore, leachate was also sampled at different points in the process of a leachate treatment system, and then the behavior of EDCs in the facility was studied. The concentrations of APs were as low as in surface waters, and OTs were not detected (detection limit was 0.01 microg/l), while BPA and DEHP, which were the most abundant of the four substances measured as PAEs, were found in all the leachates that were measured. Concentrations of BPA and DEHP were almost constant regardless of season, except for a couple of low concentrations observed for BPA. The varying composition of landfilled waste did not influence BPA and DEHP in leachate. Concentration of BPA in raw leachate tends to decrease as the years go by, but the concentration of DEHP was observed to remain at a constant level. BPA was considerably degraded by aeration for leachates from the two landfills, except when the leachate temperature was low. Aeration, coagulation/sedimentation, and biological treatment could not remove DEHP.

Air↗
PubMed2004

Isolation of mini-Tn5Km2 insertion mutants of Salmonella enterica serovar Oranienburg sensitive to NaCl-induced osmotic stress.

We previously reported that the viability of Salmonella Oranienburg strains under NaCl stress was variable and depended on the strain's origin; food strains were resistant and patient strains sensitive to NaCl. Therefore, we mutagenized a food strain with a mini-Tn5Km2 transposon. Of 2,400 mutants screened, 15 NaCl-sensitive mutants were isolated, and 7 genes associated with NaCl-sensitivity were identified. The intact genes complemented their own food-strain mutants, but not patient-strain mutants, suggesting that the difference in NaCl-sensitivity between food and patient S. Oranienburg strains might not arise from a single gene mutation, but from change in multiple osmoregulatory mechanisms in Salmonella.

Base Sequence↗
PubMed2003

Distribution of the secondary type III secretion system locus found in enterohemorrhagic Escherichia coli O157:H7 isolates among Shiga toxin-producing E. coli strains.

The ability of the complete genome sequence of enterohemorrhagic Escherichia coli O157 led to the identification of a 17-kb chromosomal region which contained a type III secretion system gene cluster at min 64.5. This locus contains open reading frames whose amino acid sequences show high degrees of similarity with those of proteins that make up the type III secretion apparatus, which is encoded by the inv-spa-prg locus on a Salmonella SPI-1 pathogenicity island. This locus was designated ETT2 (E. coli type III secretion 2) and consisted of the epr, epa, and eiv genes. ETT2 was found in enteropathogenic E. coli strains and also in some non-O157 Shiga toxin-producing E. coli (STEC) strains, but most of them contained a truncated portion of ETT2. Most O157 isolates had a complete collection of toxin-encoding genes eae and hlyA and the ETT2 locus, while most O26 strains had toxin-encoding genes eae and hlyA genes but an incomplete ETT2 locus. Thus, an intact copy of ETT2 might mark a pathogenic distinction for particular STEC strains. Therefore, the presence of the ETT2 locus can be used for identification of truly pathogenic STEC strains and for molecular fingerprinting of the epidemic strains in humans and animals.

Animals↗
PubMed2002

Viable but nonculturable Salmonella species recovery and systemic infection in morphine-treated mice.

In vivo recovery and pathogenicity of Salmonella enterica serovar Oranienburg that became viable but nonculturable (VNC) in food were examined. VNC cells were completely eliminated in normal mice but caused systemic bacteremia and were subsequently lethal to morphine-treated mice. Therefore, morphine-treated mice might be a useful bioassay for VNC Salmonella species in implicated food items.

Animals↗
PubMed2002

Passage in mice causes a change in the ability of Salmonella enterica serovar Oranienburg to survive NaCl osmotic stress: resuscitation from the viable but non-culturable state.

An outbreak caused by dried processed squids contaminated with Salmonella Oranienburg occurred in Japan in 1999. Isolates obtained from the causative food were resistant to NaCl osmotic stress, but isolates from the patients were sensitive to NaCl. Although strains from both sources were almost identical in their virulence in mice, a NaCl-resistant strain from food (Sa9911T) became NaCl-sensitive after passage in mice and a NaCl-sensitive strain from one patient (Sa99004) retained NaCl sensitivity after such passage. When dried squid was contaminated experimentally with both strains during processing, only Sa9911T was recovered directly from the final product. Nevertheless, the viability of the Sa99004 cells was over 90% found by fluorescent staining. We suggested that Sa99004 might become viable but non-culturable (VNC) by NaCl stress. This hypothesis was confirmed by resuscitation by efficient enrichment. We concluded that VNC S. Oranienburg would be potentially dangerous contaminants of NaCl-preserved foods and that measures to ensure their detection should be taken at the time of food inspection.

Animals↗
PubMed2002

[The serotype and Shiga toxin type of Shiga toxin-producing Escherichia coli from humans and various animals].

To clear the route of STEC (Shiga toxin-producing Escherichia coli) infection to humans, we examined the serotype. Shiga toxin genotype and eae gene of STEC strains from humans and various animals. The most predominant serotype originated from humans was O157:H7, followed by O26:H11, and other serotypes were O91:H21, O103:H2, O111:NM, O121:H19, etc. The eae gene was found in 79 of 93 strains from human origin. The serotypes of STEC from cattle were significant by similar to that of STEC from humans. The eae gene was found in 44 of 87 strains from cattle. Shiga toxin genotypes possessed O157 strains from humans and cattle, were divided into six groups, stx1, stx2, stx2c, stx1 + stx2, stx1 + stx2c and stx2 + stx2c. Moreover, frequency rates of Shiga toxin genotypes of O157 were also similar to both human and cattle origins. The serotypes of STEC from sheep were also a little similar to that of STEC from humans. Seven of 8 strains from deer possessed stx2d gene that the strains from humans seldom possessed, and none of the strains possessed eae gene. In STEC originated from swine, 15 of 25 strains were O139:H1 that Shiga toxin genotype was stx2e. It was thought that the sources of STEC infection to human are cattle and sheep, and deer and swine had little possibility to human STEC infection.

Animals↗
PubMed2002

Treatment planning for the layer-stacking irradiation system for three-dimensional conformal heavy-ion radiotherapy.

We have upgraded a heavy-ion radiotherapy treatment-planning system to adapt for the layer-stacking irradiation method, which is to conform a variable spread-out Bragg peak to a target volume by means of dynamic control of the conventional beam-modifying devices. The biophysical model, the beam-setup logic, and the dose-calculation algorithm implemented for the layer-stacking method are described and the expected clinical usability is discussed. The layer-stacking method was integrated in perfect accordance with the ongoing conventional treatments so that the established protocols, which are the clinically optimized dose fractionation schemes, will still be valid. On the other hand, a simulation study indicated a substantial improvement of dose distribution with the layer-stacking method though the significance may depend on the size, shape, and location of the tumor. The completed treatment system will provide an option for improved conformal radiotherapy without interfering with the conventional method and we expect a gradual expansion of the clinical cases applicable to the layer-stacking method.

Algorithms↗
PubMed2002

Long-term excretion of Shiga toxin-producing Escherichia coli (STEC) and experimental infection of a sheep with O157.

To investigate a long-term shedding of Shiga toxin (Stx)-producing Escherichia coli (STEC) from sheep, a fifteen-month study for STEC isolation from a sheep, which had yielded STEC before, was attempted. The sheep continued to shed STEC and 39 STEC were isolated. The number of STEC in the feces was estimated at 1.7 x 10(3) per gram. In addition, although Stx1-negative O157 and stx2-encoding bacteriophage were experimentally infected to the sheep, Stx-positive O157 or Stx2- producing bacterial cells were not detected. The genetical and biochemical characterization of those 39 STEC strains showed that all STEC strains produced Shiga toxin 1 (Stx1) and were divided into three classes (I to III). From phylogenetic analysis of their amino acid sequences, class-I STEC was classified as group 1 comprising mainly human STEC, and classes II/III were as group 2 comprising sheep STEC. Our results suggest that STEC easily colonized in sheep and that the sheep continued to shed STEC, showing that sheep might be an important reservoir for human STEC infection.

Animals↗