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Biomedical subjects

K Kuroyanagi

Publications and source records attributed to K Kuroyanagi.

At least 19 recordsLinked to original sources
PubMed2000

Suitability of the general-purpose graphic printer as an image output device for digital dental x-ray images.

OBJECTIVES: The purpose of this study was to evaluate the suitability of the general-purpose graphic printer as an image output device for digital dental x-ray images. METHODS: The image quality as obtained by a thermal printer and by a dye sublimation printer was investigated. A grid pattern image was used to check parallelism and verticality of lines in each hard copy. A step-wedge image was printed with each printer, and the optical density, gradient, and root mean square granularity were compared. Depiction ability was also compared by using test images, including small signals. RESULTS: All of the lines were parallel and vertical on hard copies of both printers. The dye sublimation printer showed better results on optical density, gradient, root mean square granularity, and depiction ability. CONCLUSION: The dye sublimation printer produces images of the depiction ability comparable to the cathode ray tube display and seems suitable as an image output device for digital dental x-ray images.

Coloring Agents↗
PubMed2000

Evaluation of tuned-aperture computed tomography depth discrimination for image series acquired variously with linear horizontal, linear vertical, and conical beam projection arrays.

OBJECTIVE: To compare depth discrimination by using tuned-aperture computed tomography (TACT) variously with linear horizontal, linear vertical, combined linear horizontal and linear vertical, and conical beam projection arrays. STUDY DESIGN: The first test object was a metallic mesh angled at 30 degrees to the surface of a computed dental radiography size No. 1 x-ray sensor. The second test object was a dry human mandible. The sensor was mounted on an optical bench constructed to permit free and precise geometrical settings for the horizontal and vertical angulations of the x-ray beam. The extent of blurring of horizontal and vertical wires in each TACT reconstructed image slice was observed for each of the tested beam projection arrays. RESULTS: With a linear horizontal beam projection array, it was not possible to determine the depth of structures parallel to the horizontal dimension, such as the mandibular canal. With a linear vertical beam projection, it was not possible to determine the depth of structures parallel to the vertical dimension. A conical array of beam projections was best suited to the task of depth discrimination of objects in all planes. The best second alternative was a combination of linear vertical and linear horizontal projections. CONCLUSIONS: Beam projection geometry is important for the accurate depth discrimination of TACT reconstructed images. A conical beam projection array is ideal.

Dental Alloys↗
PubMed1999

Effect of number of projections on accuracy of depth discrimination using tuned-aperture computed tomography for 3-dimensional dentoalveolar imaging of low-contrast details.

OBJECTIVE: The purpose of this study was to test the hypothesis that the number of projections influences the accuracy of a simple depth discrimination task when tuned-aperture computed tomography is used. STUDY DESIGN: In each of 4 partially edentulous mandibles, 2 radiopaque steel spheres were attached to the facial and lingual surfaces and 1 ceramic sphere was place in the apical region of an open tooth socket. Errors in estimates of the depth of the apically positioned ceramic sphere relative to the 2 steel spheres were determined from 3-dimensional tuned-aperture computed tomography reconstructions. These data were compared with actual measurements produced independently by means of an optical micrometer. Multiple projections were produced from radially symmetric exposures bearing an angular disparity of 15 degrees. The number of symmetrically dispersed projections per tuned-aperture computed tomography reconstruction was varied systematically (2, 4, 8, 12, and 16 projections). The consequences of this variable, as well as specimen and observer effects, were evaluated in a balanced factorial experimental design. Depth estimates were performed by 10 trained observers. The depth reported was that corresponding to the tuned-aperture computed tomography slice perceived to yield the image of the ceramic sphere in sharpest focus. Resulting data were normalized by logarithmic transformation and analyzed statistically by analysis of variance. RESULTS: No statistically meaningful effects were found for the number of projections (P = .607) or for different observers (P = .093), but a significant specimen effect was demonstrated (P = .006). CONCLUSIONS: Factors other than high contrast limit the perception of image sharpness under these conditions. Depth may be estimated accurately from relatively small numbers of projections.

Analysis of Variance↗
PubMed1999

An electronic survey of opinions on the compatibility of current X-ray generators with intra-oral digital X-ray systems.

OBJECTIVES: To assess opinions on the compatibility of current X-ray generators with intra-oral digital X-ray systems. METHODS: A questionnaire was posted in both English and in Japanese on oral and maxillofacial radiology electronic bulletin boards. The questionnaire was also mailed to selected researchers and manufacturers in oral and maxillofacial radiology. The replies were evaluated to determine opinion on the current and future status of digital intra-oral imaging with special reference to their compatibility with current X-ray generators. RESULTS: Seventy-one replies were received from 19 countries: 39% from Japan and Korea, 27% from North America, 25% from Europe and 8% from the rest of the world. Eighty per cent of respondents were from academia, 15% from industry and the remainder largely in private practice. Respondents' experience was equally divided between solid state, mainly charge-coupled devices (CCDs) and photostimulable phosphor (IP) technologies. Sixty-eight per cent considered that current X-ray generators are compatible with intra-oral digital systems and many believed this was due to their gray scale flexibility. Twenty-eight per cent believed that existing X-ray generators are inconsistent with low exposure times. Many of the replies suggested that in future pixel size would decrease and bit depth and receptor sensitivity increase. CONCLUSIONS: Most respondents are happy to use existing X-ray generators with digital X-ray systems. However, they also believe that increased sensitivity of receptors could lead to more stringent designs of X-ray generators to ensure more reliable outputs in the low exposure range.

Attitude of Health Personnel↗
PubMed1999

Dependency of dose response of five charge-coupled device-based digital intra-oral radiographic systems on tube voltage.

OBJECTIVE: To compare the dependency of dose response of five CCD-based digital intra-oral radiographic systems on tube voltage. METHODS: Characteristic curves for Sens-A-Ray (old and new generations; Regam Medical Systems, Sundsvall, Sweden), Computed Dental Radiography (Schick Technologies, Long Island City, NY, USA), CompuRay (Yoshida, Tokyo, Japan), and VIXA (Dentsply/Gendex, Des Plaines, IL, USA) were generated between 60 and 90 kVp at intervals of 10 kVp and corrected by subtraction of dark current. Their sensitivities were compared. RESULTS: The sensitivity of the old generation Sens-A-Ray decreased with increase in tube voltage whereas in the other systems it increased. CONCLUSION: In the newer systems using a rare earth intensifying screen as a scintillator, the sensitivity increases with increase in tube voltage, thus reducing the radiation dose to the patient.

Dose-Response Relationship, Radiation↗
PubMed1998

Distribution of scattered radiation during intraoral radiography with the patient in supine position.

OBJECTIVE: The purpose of this study was to investigate the spatial distribution of scattered radiation during intraoral radiography with the patient in a supine position to determine the exposure to an operator without a suitable barrier. STUDY DESIGN: A phantom was placed in the supine position on a dental chair with the occlusal plane perpendicular to the floor, and four intraoral periapical radiographic examinations in the anterior and posterior regions of the maxilla and mandible were performed. The scattered radiation was measured with an ionization chamber at distances ranging from 25 to 200 cm at 25 cm increments and at intervals of 45 degrees. Measurements were made at two different heights: level with the occlusal plane and 30 cm below it. The exposure was converted to an air-kerma/absorbed dose in air. RESULTS: The distribution of scattered radiation was symmetric during examinations of the anterior region. Circular iso-exposure curves of up to 0.5 microGy were observed at the level of the occlusal plane, and curves of up to 0.1 microGy were observed 30 cm below the plane. The lowest exposures were measured 30 cm below the occlusal plane and behind the chair. The distribution of scattered radiation was not symmetric during examinations of the posterior region. Iso-exposure curves of up to 0.25 microGy were observed at the level of the occlusal plane during exposure of the maxilla, and curves of up to 0.5 microGy were observed during exposure of the mandible. Circular iso-exposure curves of up to 0.1 microGy were observed 30 cm below the occlusal plane. Lower values for scattered radiation were observed 30 cm below the occlusal plane between 135 and 180 degrees behind the phantom. CONCLUSION: The spatial distribution of scattered radiation with the patient in a supine position was not the same in eight directions around the chair. Although the preferred position for the operator is behind a suitable barrier, the preferred position in the absence of a barrier is 200 cm behind the patient.

Dental Auxiliaries↗
PubMed1998

A sensitometric comparison of Kodak Ektavision and Fuji Super HR-S panoramic radiographic films.

OBJECTIVES: The purpose of this study was to compare the combination of Ektavision film and Ektavision intensifying screen with the combination Super HR-S panoramic radiographic film and HR-4 intensifying screen with respect to sensitometric properties and the visualization of anatomic structures. METHODS: The density response and resolution of both panoramic radiographic film/intensifying screen combinations were evaluated through use of the generated characteristic curves and the modulation transfer function. The diagnostic clarity was evaluated by five oral and maxillofacial radiologists who used a rating scale to evaluate the image clarity of selected anatomic structures. RESULTS: The film speed and radiographic contrast, respectively, were 1.3 and 1.2 times higher for Ektavision than for Super HR-S. The image resolution with Ektavision was similar to that with Super HR-S. Ektavision was perceived to provide clearer images of the selected anatomic details than did Super HR-S. CONCLUSION: With respect to the clarity of anatomic structures, Ektavision film, with its higher speed and higher contrast, proved superior to Super HR-S film.

Absorptiometry, Photon↗
PubMed1998

Effects of projection geometry and number of projections on accuracy of depth discrimination with tuned-aperture computed tomography in dentistry.

OBJECTIVE: The purpose of this study was to determine the degree to which the number and angular disparity of component projections influence depth discrimination with tuned-aperture computed tomography. STUDY DESIGN: Groups of three tiny steel spheres served as fiducial references on and in four partially edentulous mandibles. Two spheres were attached to the facial and lingual surfaces of each mandible, and the third was fixed in the apical region of an open tooth socket. Errors in estimates of the depth of the apically positioned sphere relative to the other two spheres were determined from three-dimensional tuned-aperture computed tomography reconstructions. These data were compared with actual measurements produced independently with an optical micrometer. Multiple projections required by the tuned-aperture computed tomography reconstruction algorithm were produced from radially symmetric exposures bearing angular disparities of 5, 15, 30, and 45 degrees. The number of symmetrically dispersed projections per tuned-aperture computed tomography reconstruction likewise was varied systematically (2, 4, 8, 12, and 16 projections). These variables were manipulated through the use of a balanced factorial design. Depth estimates were performed by trained observers; the estimates were based on the determination of tuned-aperture computed tomography slices perceived as imaging the respective apical spheres in sharpest focus. Specimen and observer effects were also considered as independent variables. Resulting data were normalized by logarithmic transformation and analyzed statistically by analysis of variance. RESULTS: Significant differences (p < 0.005) were demonstrated for angular disparity and specimen effects, but the number of projections and the effect of the observer were not found to be statistically significant. CONCLUSIONS: In dentistry, angular disparities of 15 degrees or greater should be used when tuned-aperture computed tomography is being applied to diagnostic tasks requiring maximal depth discrimination accuracy.

Algorithms↗
PubMed1998

Intraoral radiographic storage phosphor image mean pixel values and signal-to-noise ratio: effects of calibration.

OBJECTIVE: The DIGORA intraoral radiographic storage phosphor system needs to be calibrated before images are made. Calibration involves inputting of the maximum exposure to be used. This investigation studied the effects of different maximum exposure calibration settings on the mean pixel value for selected regions of interest and the signal-to-noise ratio for images of a test phantom. STUDY DESIGN: A dental phantom containing a step wedge made of different thicknesses of homogeneously radiopaque bone-equivalent material was imaged at 70 kVp with exposures ranging from 12.8 to 105.2 microC.kg-1. Images were displayed through use of imaging software, and a region of interest was set for each bone-step. The mean pixel values and their standard deviations were measured. RESULTS: Except for very low exposures (< 10% of the calibrated maximum), there was a linear relationship between exposure and the pixel values within the regions of interest irrespective of the calibrated maximum exposure. Low exposures resulted in underexposed low-contrast images. Low calibrated maximum exposures (< 54.5 microC.kg-1) resulted in low-density images with poor signal-to-noise ratios. CONCLUSIONS: Because of the very wide image latitude of the DIGORA system, loss of image quality was not observed as a result of adjustments in the calibration setting over the range of exposure commonly used in dental practice. The highest accepted exposure was limited by prior calibration; hence, if diligence is applied, patient exposure can be minimized without detriment to image quality.

Calibration↗
PubMed1997

Evaluation of XD/A Plus and ST8G films for cephalometric radiography with Grenex G8 and BH-III screens.

OBJECTIVES: Sensitometric properties, clinical image quality, and patient dose requirements are important considerations when selecting film for cephalometrics. Two recently released films, XD/A Plus and ST 8G green sensitive films, were studied. METHODS: The films were each combined with Grenex G8 (Fuji Medical) green-fluorescing matched and BH-III (Kasei Optonix) blue-fluorescing mismatched intensifying screens. The density response and resolution for each screen-film combination were evaluated by use of the characteristic curve and modulation transfer function. The kilovoltage settings providing clinically acceptable images were assessed individually by 12 observers. Clinically acceptable images for each combination were also compared, and the skin entrance doses in the temporomandibular joint region were determined. RESULTS: The average contrast at the most effective density range was found to be slightly higher for the BH-III group than for the G8 group. The modulation transfer function for the BH-III group was inferior to that for the G8 screens. There were no significant differences in diagnostically acceptable image quality among the four combinations; nevertheless the BH-III screen group required two to three times more exposure than the G8 screen group. CONCLUSIONS: XD/A Plus and ST8G films provide acceptable image detail for cephalometrics. To minimize the patient dose they should be used with green-emitting screens.

Analysis of Variance↗
PubMed1997

Sensitometric effects of varying the intensifying screens used with Agfa Dentus ST8G and RP6 panoramic radiographic films.

OBJECTIVES: To compare the sensitometric effects and information yield of varying the intensifying screens used with both Dentus ST8G and RP6 Agfa Gevaert, Dormagen, Germany panoramic radiographic films. MATERIAL AND METHODS: Four screen-film combinations were employed for each of the two film types. The screens used were blue fluorescing PX-III (Kasei Optonix, Tokyo, Japan) and Special (Siemens AG, Bensheim, Germany), as well as green fluorescing Lanex Regular (Eastman Kodak, Rochester, NY, USA) and Trimax T16 (3M, Mineapolis, Minnesota, USA). The density response for each screen-film combination was evaluated using the characteristic curves generated. Information yield, as determined by the radiographic detection of defects in an aluminium test object, was evaluated by nine observers. RESULTS: The characteristic curves for ST8G were different when green and blue fluorescing screens were used; however, those for RP6 varied little irrespective of the choice of intensifying screens. Observers were able to perceive defects at significantly lower radiation exposures for ST8G combined with green fluorescing screens compared with blue emitting screens. RP6 with all screen combinations provided similar image detail perceptibility at comparable exposures with ST8G with green-fluorescing screens. CONCLUSIONS: RP6 is suitable for use with either the spectrally matched blue emitting screens or green-emitting screens. ST8G radiographic film should always be matched to rare earth screens.

Analysis of Variance↗
PubMed1997

Radiation dosage reduction in general dental practice using digital intraoral radiographic systems.

This report describes the radiation dosage reduction possible in the general dental practice with two CCD (charge-coupled device)-based intraoral radiographic systems: the RVG-S (Trophy Radiologie, Vincennes, France) and the Sens-A-Ray (Regam Medical Systems, Sundsvall, Sweden). Radiation dosages (air-kerma; Gy) necessary for obtaining clinically acceptable images were measured at the cone tip using an ionization chamber type 660-1 (Nuclear Associates, Victoreen, Inc., Carle Place, New York, USA). When the RVG-S was used with an Oramatic 70 (Trophy Radiologie) X-ray generator, dosages at the cone tip ranged from 322 to 612 microGy. These corresponded to 40-60% of the dosages necessary when using Ektaspeed dental X-ray film (Eastman Kodak, Rochester, New York, USA) with a Heliodent 70 (Siemens, Erlangen, Germany) X-ray generator. At 60 kVp, the Sens-A-Ray reduced the dosage in the order of 30% compared with Ektaspeed dental X-ray film. Reduction in radiation dosage is one of the benefits of digital intraoral radiographic systems in general dental clinics. The RVG-S provides greater dose savings than does the Sens-A-Ray.

Evaluation Studies as Topic↗
PubMed1996

Optimum exposure ranges for computed dental radiography.

OBJECTIVE: Computed dental radiography (CDR; Schick Technologies Inc, Lond Island City, NY, USA) can be used with any dental X-ray generator. The optimum exposure at various tube voltage settings was studied. METHODS: Images were made of a dental QA jaw phantom and a standard aluminium stepwedge. Exposures were made between 50 and 90 kVp at 10 kVp intervals. Two contrast indices were calculated from the bone stepwedge pixel values: CI(1), the ratio between the highest and lowest pixel values, and CI(2), the difference between them. RESULTS: Contrast indices were greatest at low kVp. The gradual decrease in CI(1) with increased exposure demonstrated that the optimum exposure range was always relatively wide. Maximum CI(2) values were found at exposures of 27, 17, 15, 11 and 9microC kg-1 at 50, 60, 70, 80 and 90 kVp, respectively, at the centre of the optimum exposure range. Pixel values for each aluminium step increased both with increased exposure and with increased kVp. The longest contrast scale was obtained at 11.0, 9.6, 8.7, 7.2 and 7.0 microC kg-1 at 50, 60, 70, 80 and 90 kVp. The steepest slopes were obtained either with thin aluminium steps or at low kVp. CONCLUSIONS: CDR is a fast CCD-based system and is capable of operating at a wide range of kVp settings.

Aluminum↗
PubMed1996

Technical report. Processing to achieve high-contrast images with computed dental radiography.

OBJECTIVES: To determine the effects of equalization on image contrast and signal-to-noise ratio (SNR) with Computed Dental Radiography (CDR). METHODS: Pixel value distributions were measured for various tissue thicknesses of a dental quality assurance jaw phantom and the average pixel values and SNR calculated. RESULTS: Equalization resulted in enhanced image contrast of underexposed images by effecting pixel value adjustment with little change in SNR. Overexposed images demonstrated minimal difference in contrast or SNR when equalization was applied. CONCLUSION: The equalize function of CDR is a convenient method to provide high-contrast images from underexposed images without detriment to the SNR. As it does not compensate for overexposure, the function will not lead to inappropriate overdosage of the patient.

Humans↗
PubMed1996

Technical note. Modulation transfer function analysis of a newly revised rotational panoramic machine.

OBJECTIVES: To determine the modulation transfer function (MTF) and noise equivalent passband (NE) values for a newly revised rotational panoramic X-ray machine, the PC-1000 (Panoramic Corp., Fort Wayne, Indiana, USA). METHODS: Images of a 10 microns test slit were taken at various locations along the X-ray beam projection path using a Lanex Regular/T-Mat G image receptor. Line spread functions were obtained at specific beam paths by scanning slit images with a microdensitometer. RESULTS: MTF values were highest around the central plane of the image layer, with a maximum near the centre of 0.25 at 4 cycles/mm. The NE values near the central plane of image layer were 1.4 cycles/mm. MTF and NE values in the anterior region were low, 0.2 and 1.2, respectively. The width of the image layer was narrower in the anterior and wider in the posterior segments. Rapid decreases in MTF and NE values were found on the X-ray tube side compared with the receptor side of the central plane. Using a spatial frequency of 0.25 MTF the shape of the image layer was coincident with that determined visually. CONCLUSION: On the basis of the MTF and NE values the image resolution produced by this machine is considered acceptable for panoramic dental radiography.

Mathematics↗
PubMed1996

Low-cost teleradiology for dentistry.

The performance of a low-cost teleradiology system was studied. The time needed for radiographic transmission between computers and the image integrity following transmission were measured. The image resolution was analyzed with a line-pair test chart. Images were transmitted through computers that had a video-processing board and a modem at both the transmission and receiving sites. Intraoral radiographs were captured with a black and white charge-coupled device camera. The time required for image transmission was less than 1 minute (46 to 56 seconds), an effective transmission speed of 1.73 kbyte/s (13.9 kbit/s). No changes were observed in pixel value distributions; hence, there was no loss of image detail. The maximal resolution of the system was 4 line-pairs/mm. The performance of the teleradiology system demonstrated its potential as an effective, low-cost telenetwork for dentistry.

Diagnosis, Computer-Assisted↗
PubMed1995

Sens-A-Ray characteristics with variations in beam quality.

This study examined the relationship between x-ray beam quality and image characteristics with the use of the Sens-A-Ray (Regam Medical Systems, Sundsvall, Sweden). To evaluate the x-ray response, properties of the image sensor, dark current and statistical noise, sensitivity, and contrast resolution were measured. Tube voltage, tube current, and exposure time were varied. Exposures were determined with the use of an ionization chamber. Pixel values beneath a lead strip were used to calculate dark current effects. Contrast was measured with pixel values from the images of a step-wedge. Dark current noise increased in proportion to exposure time. Although the sensitivity at each tube voltage was linear and proportional to the exposure, the gradient was inversely proportional to increased tube voltage. After subtraction of the dark current and statistical noise, the gradient of the sensitivity at low tube voltage remained steeper than at high tube voltages. Hence, sensitivity decreased with increased tube voltage. Sensitivity gradients at each different tube current were similar. Irrespective of exposure, contrast resolution between adjoining step-wedge steps > or = 9 mm were too small to distinguish at 50 kVp. The gray levels for each step below 12 mm in thickness were distinguishable with 90 kVp. Increased dark current noise consequent to long exposure times narrowed the available gray scale range. Lower tube voltage resulted in higher sensitivity with larger gradients than higher tube voltages.

Analog-Digital Conversion↗