Papers - KAWAZU Toshiyuki

Assessment of image quality in dental radiography, part 2 - Optimum exposure conditions for detection of small mass changes in 6 intraoral radiography systems Reviewed

K Yoshiura, T Kawazu, T Chikui, M Tatsumi, K Tokumori, T Tanaka, S Kanda

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY ORAL RADIOLOGY AND ENDODONTICS   87 ( 1 )   123 - 129   1999.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MOSBY-YEAR BOOK INC  

Objective, The purpose of this study was to compare 2 film systems and several digital intraoral systems with regard to visual image quality through use of a test phantom developed for this purpose.
Study design. The detectors used for digital imaging were as follows: Computed Dental Radiography (CDR), Digora, Dixel, and Sens-A-Ray without scintillator layer Two types of digital images were prepared for the observer performance test: one with original gray scales and another with contrast enhancement. Images with and without enhancement from the 4 systems were displayed to 7 observers. The change in the average number of perceptible holes was plotted against exposure, and modified perceptibility curves were created and compared with curves for the film systems. The exposure level at which the maximum number of holes was perceived was defined to be optimum. The optimum exposure levels were determined for each digital system and compared with that of the film systems. At the optimum exposure, the average maximum numbers of perceptible holes in each digital system with and without contrast enhancement were compared with the maximum numbers for the film systems. The minimum exposure levels were determined to be those at which the number of perceptible holes exceeded the number for film, and the possibility of exposure reduction was evaluated.
Results. All digital systems except the Digora system showed lower optimum exposures than E-speed film. In all digital images without enhancement, however, the maximum number of perceptible holes was significantly lower than that for the film systems at that exposure. With contrast enhancement, all digital systems except the Sens-A-Ray system showed visibility superior to that of the film systems. With the CDR, Digora, and Dixel systems, exposures could be further reduced by a considerable amount, with greater retention of information than was associated with film.
Conclusions. Our results strongly suggest that digital systems, if properly used, can exceed film systems in the detection of smalt mass changes.

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Assessment of image quality in dental radiography, part 1 - Phantom validity Reviewed

K Yoshiura, T Kawazu, T Chikui, M Tatsumi, K Tokumori, T Tanaka, S Kanda

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY ORAL RADIOLOGY AND ENDODONTICS   87 ( 1 )   115 - 122   1999.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MOSBY-YEAR BOOK INC  

Objective. The purpose of this study was to describe and validate an image-quality phantom to be used in dental radiography for comparison of film and digitally acquired images.
Study design. An aluminum block of 12 steps, with 7 holes in each step, was covered by acrylic blocks. This phantom was radiographed with Kodak Ultra-speed and Ektaspeed Plus films at 70, 65, and 60 kVp with the whole exposure range available. All together, 50 dental films were randomly sequenced and presented to 7 observers. The average number of perceptible holes from all steps was plotted against exposure for each tube voltage and film type, generating a modified perceptibility curve. The tentative optimum exposure revel was determined from perceptibility curves in each experimental condition and compared with that determined by means of the standard aluminum step-wedge and the preset time of the x-ray machine. The density range of this phantom at the optimum exposure was compared with that of clinical dental radiographs. Validity of the phantom was evaluated according to the optimum exposure level from the modified perceptibility curves and the overall density range. Finally, the average maximum numbers of perceptible holes at the tentative optimum exposure level were compared for each tube voltage and film type. The statistical test used was a 2-way factorial analysis of variance.
Results, The exposure at the perceptibility curve peak approximated that obtained by means of the standard aluminum step-wedge and the time preset by the manufacturer. The overall density range at the perceptibility curve peak covered the clinical density range for each tube voltage and film type. There were no statistically significant differences between firm types or among tube voltages.
Conclusions. The x-ray attenuation range for this phantom seemed to approximate clinical conditions. In addition, differences in image quality could be quantitatively evaluated by means of the number of the holes seen in the phantom.

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Consideration for Density Optimization and Dose Reduction of Digital Dental Imaging System Using Fuzzy C-Means Clustering

Tanaka Takemasa, Kawazu Toshiyuki, Kanda Shigenobu

International Journal of Biomedical Soft Computing and Human Sciences: the official journal of the Biomedical Fuzzy Systems Association   5 ( 1 )   33 - 38   1999

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Language：English   Publisher：Biomedical Fuzzy Systems Association  

Recently the digital dental imaging system (DDIS) has been developed and its use has spread widely. Although it has several advantages, the image quality is not better than that of conventional dental radiographs. Particularly, the density distributions of DDIS images are often insufficient and inadequate. Therefore, the authors considered the density optimization of DDIS images. For this aim, we applied a fuzzy c-means clustering algorithm because the pattern of DDIS images has an extensive variety. Using our method, the denstity distribution of most DDIS images can be improved appropriately. In addition, this method provides a dose reduction for the patients. Consequently, 38.3% of the absorbed dose was decreased.

DOI： 10.24466/ijbschs.5.1_33

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Computer-assisted Diagnostic System for Ultrasonography Using Fuzzy Reasoning : -Consideration of Defuzzification Procedure-

Tanaka Takemasa, Kawazu Toshiyuki, Kanda Shigenobu

Journal of Biomedical Fuzzy Systems Association   1 ( 1 )   1 - 6   1999

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Language：Japanese   Publisher：Biomedical Fuzzy Systems Association  

The authors have developed a computer-assisted diagnostic system for ultrasonograpny using fuzzy reasoning. In this system, we adopted the centroid method of defuzzification for fuzzy reasoning. There have been reported, however, several methods for defuzzidication. Although the computer-assisted diagnosis obtained from fuzzy reasoning might varies with different defuzzification methods, there were few literatures concerning this subject. Hence, the authors considered other defuzzidcation methods;centroid(Cent), bisector(Bis), middle of maximum(MOM), largest of maximum(LOM)and smallest of maximum(SOM)methods. Diagnostic accuracy, sensivity and specificity acquired from these defuzzifications were compared each other. Consequently, Cent, Bis and MOM are adequate procedures. On the other hand, diagnostic accuracy acquired by LOM or SOM is worse than other procedures. However, sensitivity of LOM and specificity of SOM are better than others. Therefore, these methods are useful when sensitivity or specificity is clinically important.

DOI： 10.24466/jbfsa.1.1_1_2

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Diagnostic accuracy of CT and US for cervical lymph node metastasis of oral cancer patients.

Yuasa Kenji, Kawazu Toshiyuki, Kanda Shigenobu

Journal of Japanese Society of Oral Oncology   10 ( 4 )   288 - 296   1998

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Language：Japanese   Publisher：Japanese Society of Oral Oncology  

Purpose: The purposes of this study were to show our protocol of diagnostic imaging using CT and ultrasonography and to evaluate the diagnostic accuracy for cervical lymph node metastasis in oral squamous cell carcinoma.<BR>Material and Methods: CT and/or ultrasonography of 147 patients were evaluated retrospectively. Lymph nodes were confirmed pathologically whether metastasis or non-metastasis. The detection ratio, enhanced pattern and short diameter of lymphadenopathy were analyzed on CT. Internal echoes such as hilus and parenchymal echoes, the short diameter, long diameter and the long to short diameter ratio (S/L ratio) were evaluated on ultrasonography.<BR>Results: Ten percent of lymphadenopathy, which was confirmed pathologically as metastasis, was not found on CT. Heterogeneous or rim-enhanced pattern was presented in 50.9% of metastasis and only 4.5% of non-metastasis cases on CT. Strong parenchymal echo pattern was shown in 56.9% of metastasis cases. On the other hand, 66.5% of non-metastasis cases showed a hilus but strong parenchymal echoes. Under the circumstances where lymph nodes had neither hilus nor strong parenchymal echoes, but were 10 mm or more in short diameter, 27.4% were shown in metastasis and only 3.0% in non-metastasis cases. Futhermore, under the circumstances where lymph nodes had neither hilus nor strong parenchymal echoes, but were 3.5 or more in S/L ratio, only 1.5% were shown in metastasis and 13.5% in non-metastasis cases.<BR>Conclusion: On basis of the results of this study, it was suggested that criteria for cervical metastasis using CT and ultrasonography in which"Questionable only on diagnostic imagings"be included. It was considered that this criteria is clinically useful.

DOI： 10.5843/jsot.10.288

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Imaging Diagnosis Between Benign Odontogenic Tumor And Cyst Using Neural Network

Kawazu Toshiyuki, Tanaka Takemasa, Kanda Shigenobu

Proceedings of the Annual Conference of Biomedical Fuzzy Systems Association   11   27 - 28   1998

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Language：Japanese   Publisher：Biomedical Fuzzy Systems Association  

Aim of this study is to consider the accuracy in differentiating between benign odontogenic tumor (ameloblastoma) and cyst (odontogenic keratocyst) on CT image using neural network. In order to determine the weights and the biases of our neural network system, 53 cases (29 ameloblastomas, and 24 odontogenic keratocysts) were used for the learning mode. Another 20 cases (6 ameloblastomas, and 14 odontogenic keratocysts) were evaluated for determining the accuracy in the test mode. The result showed that the diagnostic accuracy was 85 %. It was suggested that the neural network is useful for differentiating these lesions.

DOI： 10.24466/pacbfsa.11.0_27

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Consideration for Density Optimization and Dose Reduction of Digital Dental Imaging System Using Fuzzy C-Means Clustering

Tanaka Takemasa, Kawazu Toshiyuki, Kanda Shigenobu

Proceedings of the Annual Conference of Biomedical Fuzzy Systems Association   11   29 - 30   1998

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Language：Japanese   Publisher：Biomedical Fuzzy Systems Association  

Recently the digital dental imaging system (DDIS) has been developed and spread widely. The density distribution of DDIS images, however, are insufficient or inadequate. Therefore, the authors considered the density optimization of DDIS images, and applied the fuzzy reasoning and fuzzy c-means clustering algorithm for this purpose. According to our method, density distribution of most DDIS images could be improved appropriately. Moreover, this method could be applied to the dose reduction of the patients. Consequently, it was suggested that the absorbed dose could be decreased 38.3%.

DOI： 10.24466/pacbfsa.11.0_29

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Density Optimization for Digital Dental Imaging System Using Fuzzy Reasoning and C-Means Clustering

Tanaka Takemasa, Kawazu Toshiyuki, Kanda Shigenobu

Proceedings of the Annual Conference of Biomedical Fuzzy Systems Association   10   75 - 76   1997

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Language：Japanese   Publisher：Biomedical Fuzzy Systems Association  

The digital dental imaging system (DDIS) has been developed and spread widely in recent years. The images of DDIS, however, aren't always so good, because of insufficient density distribution. Therefore, it seems that DDIS requires density optimization in an appropriate way. The authors applied the fuzzy reasoning and fuzzy c-means clustering algorithm for this purpose. According to our method, density distribution of most DDIS images could be improved better than the conventional histogram equalization method.

DOI： 10.24466/pacbfsa.10.0_75

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Morphologic analysis of odontogenic cysts with computed tomography Reviewed

Kazunori Yoshiura, Yoshinori Higuchi, Kazuyuki Araki, Masanori Shinohara, Toshiyuki Kawazu, Kenji Yuasa, Osamu Tabata, Shigenobu Kanda

Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics   83 ( 6 )   712 - 718   1997

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Mosby Inc.  

Purpose. The purpose of this study was to analyze the effects of lesion site and epithelial keratinization on the morphologic characteristics of odontogenic cysts and clarify determinate factors for cyst morphology. Material and methods. Computed tomographic images of 92 odontogenic cysts were analyzed: 31 primordial, 31 dentigerous and 30 radicular. Thirty-four cysts were located in the maxilla (6 primordial, 10 dentigerous, and 18 radicular) and 58 in the mandible (25 primordial, 21 dentigerous, and 12 radicular). Histologically, 31 cysts showed epithelial keratinization (18 primordial and 13 dentigerous). No keratinization was seen in radicular cysts. The morphologic features of cysts were assessed by measuring long length parallel to dental arch and short length vertical to it and calculating the long/short ratio. In addition, the computed tomography pattern of the cyst was classified into unilocular, lobulated, and multilocular patterns. Appearance of the sclerotic rim and surrounding cortex were classified into three and four patterns respectively to evaluate the developmental features of the cyst. Results. As a whole, the long length of the primordial cysts was statistically larger than the other two cyst groups and resulted in a larger long/short ratio. Statistical differences of CT pattern were also seen among cyst groups. There was no preference in any cyst group for the appearance of the sclerotic rim and cortex. There were statistical differences between maxilla and mandible in short axis and long/short ratio. The maxillary cysts generally showed round shapes irrespective of their histologic characteristics. A multilocular pattern was more frequent in the keratinized group of mandibular primordial cysts. In dentigerous cysts, a multilocular pattern was seen only in the keratinized group and the long/short ratio was statistically larger
cyst shape was elliptical along the long axis. Conclusion. Our results demonstrated morphologic differences of odontogenic cysts caused by lesion site and keratinization. The dentigerous cyst with predominant keratinization should be included in the primordial cyst (odontogenic keratocyst) group.

DOI： 10.1016/S1079-2104(97)90325-5

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