title: Relationship between density variability and imaging volume size in cone-beam computerized tomographic scanning of the maxillofacial region: an in vitro study.
abstract: OBJECTIVE
  In limited-volume cone-beam computerized tomography (CBCT) imaging, projection data discontinuity caused by maxillofacial hard tissue structures outside the reconstructed volume are reported to affect the density value of the hard and soft tissue structures within the volume. The intensity of this effect is purported to be related to the size of the imaging volume. The aim of this study was to characterize the effect of the size of the scanned volume on density values in vitro.
  
  
  METHODS
  Test objects were positioned in a custom phantom in the following 4 patterns: bimandible and vertebrae, bimandible, left mandible and vertebrae, and left mandible. We used a newly developed flat panel detector CBCT system (Alphard Vega; Asahi Roentgen, Kyoto, Japan) to acquire scans of the left molar region using cylindrical volumes of approximately 5, 10, 15, and 20 cm in diameter and height. The density values of the mandible and the adjacent soft tissue regions were analyzed.
  
  
  RESULTS
  Highest density variability was observed in the smallest-volume (5 cm) scans. Density variability increased when more objects were included outside the area being imaged. Fewer effects were noted in CBCT scans of larger (10, 15, and 20 cm) volumes.
  
  
  CONCLUSIONS
  Larger-volume CBCT scans may yield more consistent density values. Smaller CBCT volumes have the advantages of better image resolution and lower radiation doses. The optimization of the image characteristics is maximized by careful consideration of the purpose of the CBCT examination.
authors: Department of Oral Radiology, Asahi University School of Dentistry, Gifu, Japan. kawamata@dent.asahi-u.ac.jp
authors: Akitoshi
authors: A
authors: Katsumata
authors: Akiko
authors: A
authors: Hirukawa
authors: Shinji
authors: S
authors: Okumura
authors: Munetaka
authors: M
authors: Naitoh
authors: Masami
authors: M
authors: Fujishita
authors: Eiichiro
authors: E
authors: Ariji
authors: Robert P
authors: RP
authors: Langlais
mesh_terms: D000465:Algorithms; D015519:Bone Density; D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation*; D006801:Humans; D008334:Mandible / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted; D011861:Radiography, Dental / Q000379:methods*; D012984:Software