Akiko Hirukawa

Relationship between density variability and imaging volume size in cone-beam computerized tomographic scanning of the maxillofacial region: an in vitro study

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. STUDY DESIGN 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. CONCLUSION 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.

Evaluation of voxel values in mandibular cancellous bone: relationship between cone‐beam computed tomography and multislice helical computed tomography

OBJECTIVE Measurements of bone density in designed sites are important in presurgical imaging for dental implant treatment. However, the pixel or voxel values obtained from cone-beam computed tomography (CT) images are not absolute values. Hence, the relationship between voxel values obtained from cone-beam CT with a limited-volume exposure field and a flat panel detector and bone mineral densities (BMDs) obtained from multislice CT was evaluated in the mandible. MATERIAL AND METHODS A total of 16 (four males and 12 females) patients who had undergone imaging for mandibular dental implant treatment using cone-beam CT with Alphard VEGA and multislice CT were enrolled in this investigation. Cross-sectional images of cone-beam and multislice CT were reconstructed, and values of regions of interest (ROIs) in images were calculated. RESULTS A high-level correlation between voxel values of cone-beam CT and BMDs of multislice CT was observed (r=0.965). CONCLUSION It was suggested that voxel values of mandibular cancellous bone in cone-beam CT could be used to estimate bone density.

Prospective study to estimate mandibular cancellous bone density using large‐volume cone‐beam computed tomography

OBJECTIVE Because pixel or voxel values obtained from cone-beam computed tomography (CBCT) images are not absolute values, the bone density cannot be evaluated. Hence, the regression line between voxel values of CBCT and the bone mineral density (BMDs) of multislice CT (MSCT) was prospectively evaluated to investigate the mandibular cancellous bone density. Also, the usefulness of a reference bone block was evaluated on assessing a low mandibular bone density. MATERIALS AND METHODS A total of 15 (two males and 13 females) patients who had undergone postoperative imaging for mandibular dental implant treatment with a bone graft using CBCT and MSCT were enrolled in this investigation. Voxel values of region of interests in CBCT were transformed to BMDs using a regression line from a previous study, and differences between BMDs obtained using CBCT and MSCT were calculated. Also, the voxel values of CBCT at the selected sites, in which the bone density was measured between 100 and 300 mg/cm(3) of hydroxyapatite (HA) in MSCT, were assessed regarding whether they were higher or lower than the BMD of the reference bone block. RESULTS The mean overall difference was 38 mg/cm(3) of HA. Thirty-eight of the 45 sites (84%) were accurately assessed using the reference bone block. CONCLUSION The usefulness of a regression line for BMD estimation in CBCT was prospectively confirmed in mandibular cancellous bone. Also, the reference bone block was useful to assess the low bone density of mandibular cancellous bone on CBCT with a large volume.

Imaging artifact and exposure conditions in limited-volume cone-beam computed tomography: comparison between an image intensifier system and a flat panel detector

ObjectiveArtifacts due to halation from an image intensifier (I.I.) appear on limited-volume cone-beam computed tomography (CBCT). We evaluated the influence of exposure conditions on this artifact.MethodsA hydroxyapatite block was imaged using limited-volume CBCT with an I.I. system for various exposures and positions. For comparison, limited-volume CBCT with a newly developed flat panel detector was also performed. The artifact was measured using image analysis software.ResultsWith the I.I. system and a high exposure, a large artifact was observed, whereas with the flat panel detector, the artifact was small.ConclusionsOptimal exposure conditions for diagnosis may exist in limited-volume CBCT with an I.I. system.