title: Exposure time reduction of secondary radiographs used in digital subtraction radiography in detecting intrabony change.
abstract: OBJECTIVE
  Digital subtraction radiography (DSR) is a suitable technique for detecting incipient bone changes. However, in DSR, one or more follow-up radiographs must be taken. The aim of this study was to assess the possibility of reducing the exposure time for the radiographs that follow the initial one.
  
  
  METHODS
  Maxillary premolar and molar radiographic images of a dry skull were taken with a digital radiography system. The initial radiographs, without bone chips, were taken at 0.32 and 0.16 s. Then, five bone chips (weight range 7-15 mg) were placed on the maxillary molar buccal side of the dry skull. Secondary radiographs were taken at 0.32-, 0.16-, 0.08-, 0.04-, and 0.02-s exposure times. For each bone chip, radiographs were taken three times. The secondary and initial images were subtracted to yield subtraction images. Four observers were asked to evaluate bone change visibility in the subtraction images. The Friedman test was used for statistical analysis.
  
  
  RESULTS
  Significant differences were seen at each of the settings for the 0.32-s group (p= 1.24e-030) and 0.16-s group (p= 7.52e-009). By comparing the different groups, observer evaluations indicated that visibility changed when the secondary radiograph was taken at 1/8 of the exposure time of the initial radiograph. In both groups, the visibility of the 0.02-s subtraction image was significantly lower than that of the other subtraction images.
  
  
  CONCLUSIONS
  In DSR, the exposure time of the secondary radiograph can be reduced to 1/4 of the exposure time of the initial radiograph.
authors.affiliation: Division of Radiology, Department of Oral Diagnostic Sciences, Showa University School of Dentistry, 2-1-1 Kita-senzoku, Ohta-ku, Tokyo, 145-8515 Japan.
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Matsuda
authors.affiliation: Division of Radiology, Department of Oral Diagnostic Sciences, Showa University School of Dentistry, 2-1-1 Kita-senzoku, Ohta-ku, Tokyo, 145-8515 Japan.
authors.forename: Tsuneyasu
authors.initials: T
authors.lastname: Terauchi
authors.affiliation: Department of Biomedical Engineering, Tokyo City University, 1-28-1 Tamazutumi, Setagaya-ku, Tokyo, 158-8557 Japan.
authors.forename: Kota
authors.initials: K
authors.lastname: Murahira
authors.affiliation: Division of Radiology, Department of Oral Diagnostic Sciences, Showa University School of Dentistry, 2-1-1 Kita-senzoku, Ohta-ku, Tokyo, 145-8515 Japan.
authors.forename: Seema
authors.initials: S
authors.lastname: Patil
authors.affiliation: Division of Radiology, Department of Oral Diagnostic Sciences, Showa University School of Dentistry, 2-1-1 Kita-senzoku, Ohta-ku, Tokyo, 145-8515 Japan.
authors.forename: Vajendra
authors.initials: V
authors.lastname: Joshi
authors.affiliation: Division of Radiology, Department of Oral Diagnostic Sciences, Showa University School of Dentistry, 2-1-1 Kita-senzoku, Ohta-ku, Tokyo, 145-8515 Japan.
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Araki
authors.affiliation: Department of Biomedical Engineering, Tokyo City University, 1-28-1 Tamazutumi, Setagaya-ku, Tokyo, 158-8557 Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Taguchi
authors.affiliation: Division of Radiology, Department of Oral Diagnostic Sciences, Showa University School of Dentistry, 2-1-1 Kita-senzoku, Ohta-ku, Tokyo, 145-8515 Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Okano
keywords: Charge-coupled device (CCD); Digital subtraction radiography (DSR); Exposure time reduction; Intraoral radiography