PubMed Health⌕ Search

Biomedical subjects

Eiji Yoshida

Publications and source records attributed to Eiji Yoshida.

15 recordsLinked to original sources
PubMed2006

Evaluation of static physics performance of the jPET-D4 by Monte Carlo simulations.

The jPET-D4 is the first PET scanner to introduce a unique four-layer depth-of-interaction (DOI) detector scheme in order to achieve high sensitivity and uniform high spatial resolution. This paper compares measurement and Monte Carlo simulation results of the static physics performance of this prototype research PET scanner. Measurement results include single and coincidence energy spectra, point and line source sensitivities, axial sensitivity profile (slice profile) and scatter fraction. We use GATE (Geant4 application for tomographic emission) as a Monte Carlo radiation transport model. Experimental results are reproduced well by the simulation model with reasonable assumptions on characteristic responses of the DOI detectors. In a previous study, the jPET-D4 was shown to provide a uniform spatial resolution as good as 3 mm (FHWM). In the present study, we demonstrate that a high sensitivity, 11.3 +/- 0.5%, is provided at the FOV centre. However, about three-fourths of this sensitivity is related to multiple-crystal events, for which some misidentification of the crystal cannot be avoided. Therefore, it is crucial to develop a more efficient way to identify the crystal of interaction and to reduce misidentification in order to make use of these high performance values simultaneously. We expect that effective sensitivity can be improved by replacing the GSO crystals with more absorptive crystals such as BGO and LSO. The results we describe here are essential to take full advantage of the next generation PET systems that have DOI recognition capability.

Algorithms↗
PubMed2006

Relationship between water status in dentin and interfacial morphology in all-in-one adhesives.

OBJECTIVES: All-in-one adhesive systems have been recently developed to simplify bonding procedures. The adhesives containing acidic resin monomers generate a relatively thin bonding zone between dentin and composite. This zone may be left acidic and permeable when polymerization is poor. In this study, the effect of water contained in dentin on the quality of the bonding interface was morphologically investigated for all-in-one adhesives. METHODS: Intact coronal dentin (hydrated dentin), desiccated coronal dentin (dehydrated dentin), caries-affected dentin (CAD) and resin composites were used for adherends to assess the effects of water contained in dentin on the ultra-structures of bonding interfaces created with two all-in-one adhesives and a resin composite. RESULTS: The bonding interfaces were observed under TEM without demineralization. Voids of various sizes were found at the bottom of the adhesive resin layers along the bonding interface of hydrated dentin, while dehydrated dentin, CAD and resin composites did not generate voids. The results showed that the voids were possibly formed by water that had penetrated from the underlying dentin. CONCLUSION: When the adherend contains little water, the formation of voids will not occur. It was verified that a phenomenon of void formation would not occur in a clinical situation in which caries-affected dentin is mainly subjected to adhesive practices.

Acids↗
PubMed2005

Transaxial system models for jPET-D4 image reconstruction.

A high-performance brain PET scanner, jPET-D4, which provides four-layer depth-of-interaction (DOI) information, is being developed to achieve not only high spatial resolution, but also high scanner sensitivity. One technical issue to be dealt with is the data dimensions which increase in proportion to the square of the number of DOI layers. It is, therefore, difficult to apply algebraic or statistical image reconstruction methods directly to DOI-PET, though they improve image quality through accurate system modelling. The process that requires the most computational time and storage space is the calculation of the huge number of system matrix elements. The DOI compression (DOIC) method, which we have previously proposed, reduces data dimensions by a factor of 1/5. In this paper, we propose a transaxial imaging system model optimized for jPET-D4 with the DOIC method. The proposed model assumes that detector response functions (DRFs) are uniform along line-of-responses (LORs). Then each element of the system matrix is calculated as the summed intersection lengths between a pixel and sub-LORs weighted by a value from the DRF look-up-table. 2D numerical simulation results showed that the proposed model cut the calculation time by a factor of several hundred while keeping image quality, compared with the accurate system model. A 3D image reconstruction with the on-the-fly calculation of the system matrix is within the practical limitations by incorporating the proposed model and the DOIC method with one-pass accelerated iterative methods.

Brain↗
PubMed2005

[2D imaging simulations of a small animal PET scanner with DOI measurement: jPET-RD.].

We present a preliminary study on the design of a high sensitivity small animal DOI-PET scanner: jPET-RD (for Rodents with DOI detectors), which will contribute to molecular imaging. The 4-layer DOI block detector for the jPET-RD that consists of scintillation crystals (1.4 mm x 1.4 mm x 4.5 mm) and a flat panel position-sensitive photomultiplier tube (52 mm x 52 mm) was previously proposed. In this paper, we investigate imaging performance of the jPET-RD through numerical simulations. The scanner has a hexagonal geometry with a small diameter and a large axial aperture. Therefore DOI information is expected to improve resolution uniformity in the whole field of view (FOV). We simulate the scanner for various parameters of the number of DOI channels and the crystal length. Simulated data are reconstructed using the maximum likelihood expectation maximization with accurate system modeling. The trade-off results between background noise and spatial resolution show that only shortening the length of crystal does not improve the trade-off at all, and that 4-layer DOI information improves uniformity of spatial resolution in the whole FOV. Excellent performance of the jPET-RD can be expected based on the numerical simulation results.

Animals↗
PubMed2004

On-clock non-paralyzable count-loss model.

This paper proposes a new count-loss model that is applicable to radiation detection systems in the field of nuclear medicine. The proposed model, represented by n = (1 - exp(-tau(n)0))/tau(n)0: input rate, n: output rate,tau: system clock duration), gives higher count rates than the well-known standard nonparalyzable (non-extensible) model represented by n = n0/(1 + tau(n)0) does, being equally simple. This model assumes that a part of the data processing is performed on a fixed system clock, requiring a data buffering function (latch) to retain digital event information temporarily, and that input timing is random. The model's simple interpretation and expression also offers an advantage over various other advanced count-loss models proposed so far. This model was found to be a better fit to a data-acquisition system for a positron emission tomography scanner.

Algorithms↗
PubMed2004

Deproteinizing effects on resin-tooth bond structures.

This study investigated the effects of NaOCl on resin-tooth bonds to simulate the situations of long-term durability and caries invasion. Resin-tooth bonded specimens were produced with the use of two resin adhesives (Excite and One-Bond). Resin-tooth bonded beams (adhesive area; 0.9 mm2) were serially sectioned and the specimens were immersed in 10% NaOCl medium for 0 (control), 2, 4, and 6 h after being stored in water for 24 h. After immersion, microtensile bond tests were performed. SEM fractography was conducted to calculate each failure mode by image analysis. In addition, the adhesive interface was examined with the use of TEM. In the control specimens, enamel bond strengths had no difference between Excite (45.6 +/- 15.0) and One-Bond (56.9 +/- 12.9). On the other hand, dentin bond strengths had significant difference between Excite (80.6 +/- 21.2) and One-Bond (50.7 +/- 11.2). The bond strengths decreased with increased storage time for both systems with enamel and dentin bonds. The deteriorated mineralized dentin of beams resulted in bond-strength reduction for resin-enamel bonds. For dentin bonding, the adhesive interface was gradually dissolved from the outer to the center portion of the beam. The depletion of collagen fibrils within the demineralized dentin or hybrid layer deformation was found under SEM and TEM examinations. These morphological changes are responsible for bond strength reduction of resin-dentin bonds.

Dental Materials↗
PubMed2004

Voids formation along the bonding interface between a smeared dentin surface and all-in-one adhesives.

It has been reported that the adhesive resin layer of all-in-one adhesives is permeable and allows the formation of a water channel or water tree. The effects of a smear layer on the ultra-structure of bonding interface created with three all-in-one adhesives and a resin composite were evaluated in this study. Dentin surface was ground with of 180-, 600-, or 2000-grit SiC paper to produce different smear layer thickness. The bonding interfaces were observed under a transmission electron microscope without demineralization. Voids of various sizes and water channels were found at the bottom of the adhesive resin layer along the bonding interface of SiC 180-grit dentin, while SiC 2000-grit dentin did not produce any voids. The results showed that the voids were possibly related to water that had penetrated from the underlying dentin. A smear layer may have an adverse influence on the bonding performance of all-in-one adhesives to dentin.

Adhesives↗
PubMed2004

In vitro testing of all-in-one adhesives as fissure sealants.

PURPOSE: To evaluate the clinical efficacy of all-in-one adhesives as fissure sealants. METHODS: Resin-enamel bonded specimens were fabricated between polished and ground enamel surfaces using two all-in-one adhesives (One-Up Bond F and Xeno CF Bond) and two resin sealants (Teethmate F-1 and Helioseal F). Specimen beams were prepared and microtensile bond tests were performed at a crosshead speed of 1 mm/minute. The bond strengths obtained were subjected to one-way ANOVA and Scheffe's F test (P < 0.05: n=12 for each group). To evaluate the etching effect of phosphoric acid and the all-in-one adhesives, the treated enamel surfaces (37% phosphoric acid, 40% phosphoric acid, or all-in-one adhesives) were examined by FE-SEM. RESULTS: The bond strengths of the two all-in-one adhesives tested to the polished enamel surface were significantly lower (P < 0.05) than to ground enamel. However, no significant differences (P > 0.05) were found between the polished and ground enamel surfaces for resin sealants using phosphoric acid. Under SEM examination, 37% or 40% phosphoric acid etched the enamel surface more than all-in-one adhesives.

Acid Etching, Dental↗
PubMed2003

Resin-enamel bonds made with self-etching primers on ground enamel.

Self-etching primer adhesives have recently been introduced to simplify bonding. However, the fundamental bonding mechanism of self-etching primers to enamel is not yet fully understood. This study aimed to investigate resin-enamel bonds of self-etching primer adhesives on ground enamel. Two self-etching primer adhesives (Clearfil Liner Bond 2 V and Clearfil SE Bond) were used in this study. A total-etch adhesive (One-Step) was used as a control. Resin-enamel beams were subjected to the microtensile bond test. Subsequently, the failure modes of all specimens were quantified using image analysis. Undemineralized and demineralized ultrathin sections of the resin-enamel bonded specimens were examined using transmission electron microscopy. The bond strengths of Clearfil SE Bond (39.8 +/- 11.9 MPa) and One-Step (46.2 +/- 12.7 MPa) were significantly greater than that of Clearfil Liner Bond 2V (30.4 +/- 6.2 MPa). Scanning electron microscopy of the fractured surfaces revealed the failure direction and weakest portion within each bond. Transmission electron microscopy showed a thin hybridized complex of resin in enamel produced by the self-etching primers without the usual micrometer-sized resin tags seen in resin-enamel bonds produced using the total-etch adhesive. The morphological features of the resin-enamel bonds produced by two self-etching primers tested were different from that created with the total-etch adhesive.

Adhesives↗
PubMed2003

[Basic investigation of data acquisition system for next generation PET scanner].

We are under development of a 3D PET scanner with depth of interaction (DOI) capable of high sensitivity and high resolution. In this paper, we estimated the data transfer rate of data acquisition system of this PET scanner by the simulation studies. A maximum data transfer rate of coincidence pair's event information is 10 Mcps and one coincidence event is a 64-bit data format. A data acquisition system, which fulfills the specification of this scanner, is considered for parallel collection with banks including several coincidence units. Simulator of parallel collection system composed of two stand-alone simulators and the server PC. Each stand-alone simulator is composed of data generation PC, data processing circuit, SCSI and data acquisition PC. As the result of simulation studies, the maximum data transfer rate of the stand-alone simulator was 12.0 MB/s, and the maximum data transfer rates at the server PC with one and two nodes were 11.0 and 21.8 MB/s, respectively. Data transfer rate was improved by parameter optimization of a message size and multi-processing of data acquisition software using RAM-DISK.

Computer Simulation↗
PubMed2002

Hydatid disease at the proximal end of the clavicle.

We report a case of hydatid disease at the proximal end of the clavicle of a 47-year-old woman. In an open biopsy, laminated layers, characteristic of Echinococcus multilocularis larvae, were revealed by periodic acid-Schiff (PAS) staining. A marked foreign-body reaction was observed in the pathological findings. The patient was definitely diagnosed as having osseous hydatid disease. We performed resection of the infected part of the clavicle, and after the operation, she has been cured under medication with albendazole for 9 years, with no finding of recurrence in the clavicle.

Albendazole↗
PubMed2002

Dosimetry of fission neutrons in a 1-W reactor, UTR-KINKI.

The energy spectrum of fission neutrons in the biological irradiation field of the Kinki University reactor, UTR-KINKI, has been determined by a multi-foil activation analysis coupled with artificial neural network techniques and a Au-foil activation method. The mean neutron energy was estimated to be 1.26 +/- 0.05 MeV from the experimentally determined spectrum. Based on this energy value and other information, the neutron dose rate was estimated to be 19.7 +/- 1.4 cGy/hr. Since this dose rate agrees with that measured by a pair of ionizing chambers (21.4 cGy/hr), we conclude that the mean neutron energy could be estimated with reasonable accuracy in the irradiation field of UTR-KINKI.

Japan↗
PubMed2002

Contrast-enhanced 2D cine phase MR angiography for measurement of basilar artery blood flow in posterior circulation ischemia.

BACKGROUND AND PURPOSE: Dizziness is a symptom that develops with internal ear disturbances and with dysfunctions of the brain stem and cerebellum, in particular with blood flow disturbances of the brain stem and cerebellum (posterior circulation ischemia [PCI]). Patients with PCI often present with various neurologic signs and symptoms. To examine the usefulness of contrast-enhanced 2D cine phase MR angiography in the diagnosis of PCI, we examined quantitative blood flow of the basilar artery in patients with PCI who had primarily complained of dizziness. METHODS: We quantitatively measured the blood flow volume rate of the basilar artery by using a contrast-enhanced 2D cine phase MR angiographic technique in 21 patients diagnosed with PCI and in 16 age- and sex-matched control participants. RESULTS: Maximum and mean average flow velocities of the basilar artery in the PCI group were significantly lower than those of the control group (29.2 +/- 9.2 cm/s versus 38.5 +/- 8.2 cm/s [P <.005] and 18.0 +/- 5.6 cm/s versus 22.6 +/- 5.0 cm/s [P <.01], respectively). The flow volume rates of the basilar arteries were also significantly lower in the PCI group (103.3 +/- 37.3 mL/min versus 148.8 +/- 40.0 mL/min [P <.001]). CONCLUSION: The flow volume rate of the basilar artery in patients with PCI during intermittent ischemic attacks with dizziness was chronically reduced compared with that in the control participants. This suggests that flow volume rates may influence the development of the clinical signs and symptoms of PCI. We think that contrast-enhanced 2D cine phase MR angiography is a valuable method for the diagnosis of PCI.

Adult↗
PubMedDate not supplied

Effects of multiple adhesive coatings on dentin bonding.

Simple changes to bonding techniques can improve resin-dentin bond strengths. This study evaluated the effect of multiple consecutive coatings of adhesive resin on dentin by measuring both microtensile bond strength and nano-leakage following exposure to ammoniacal silver nitrate. Resin-dentin bonded specimens were prepared using two total-etch adhesives (OptiBond Solo Plus/Kerr or Single Bond/3M ESPE). During bonding, resin application and air evaporation were done 1, 2, 3, 4, 6 or 8 times on acid-etched, moist dentin surfaces. Mean microtensile bond strengths were evaluated by two-way ANOVA and Fisher's PLSD test (p<0.05; n=16 for each group). Additionally, nanoleakage of silver nitrate was evaluated by transmission electron microscopy (TEM). The results indicated that bond strengths increased with each coating up to four coats. Nanoleakage decreased with each coat, becoming very small after four or more coats. This adhesive application method can be easily applied to clinical practice, thereby improving the quality of resin-dentin bonds.

Bicuspid↗