Alterations of posterior pharyngeal wall movement during swallowing in postoperative tongue cancer patients: assessment with a videofluoroscopic swallowing study.

This study aimed to determine the association between the progressive contraction of the posterior pharyngeal wall and dysphagia in postoperative patients with tongue cancer. A videofluoroscopic swallowing study (VFSS) was performed in 34 patients after tongue cancer surgery. Images were analyzed using a two-dimensional video measurement software. Cases in which the processes on the posterior pharyngeal wall moved downward from the 2nd to 4th vertebral regions were defined as "normal type", other cases were defined as "abnormal type". Twenty-four patients showed normal movement of the posterior pharyngeal wall, whereas 10 patients showed the abnormal type. The results showed that there was a significant difference in dysphagia scores between the postoperative swallowing type and swallowing dysfunction score. This implies that dysphagia is related to the movement of the posterior pharyngeal wall after tongue cancer surgery. Furthermore, the extent of resection and stage were significantly different between the normal and abnormal groups in the posterior pharyngeal wall movement. There was also a significant difference between the two groups in terms of the following: whether the tongue base was included in the excision range (p < 0.01), whether neck dissection was performed (p < 0.01), or whether reconstruction was not performed (p < 0.01). VFSS results showed that posterior pharyngeal wall movement was altered after surgery in patients with tongue cancer who had severe dysphagia.

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.

Morphometric analysis of mandibular trabecular bone using cone beam computed tomography: an in vitro study.

PURPOSE: Recently, cone beam computed tomography (CBCT) was developed and applied to presurgical imaging for dental implant treatment. Because the values obtained from CBCT images are not absolute values, unlike the Hounsfield units obtained by medical CT, the relationship between the values of trabecular bone morphometry obtained in small-volume CBCT images and CT values obtained from multislice CT was evaluated in an in vitro study. MATERIALS AND METHODS: Small-volume CBCT and multislice CT were performed in the posterior mandible. Subsequently, morphometric analysis of the trabecular bone in CBCT images was performed using three-dimensional bone morphometry software, and the correlations between the trabecular bone volume per total tissue volume (BV/TV) obtained using CBCT images and CT values generated from multislice CT images were analyzed. RESULTS: BV/TV ranged from 3.1% to 42.7%, with a mean of 20.4% (SD: 11.4) when the setting was 0.5 for the threshold. The correlations between BV/TV using the threshold values ranged from 0.3 to 0.7, and CT values showed a high level of correlation (range: 0.83 to 0.93). CONCLUSIONS: The trabecular BV/TV was closely correlated with CT values obtained using multislice CT images. It was suggested that the trabecular BV/TV can be used to evaluate the density of mandibular cancellous bone in dental implant treatment.

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.

[Estimation of effective dose to salivary glands at examination of the oral and maxillofacial region].

The salivary glands and the oral mucosa were included in the determination of effective doses of radiography in the new ICRP (International Commission on Radiological Protection) recommendations. These changes will likely result in an upward reassessment of the effective dose during oral and maxillofacial radiographic examination. We measured the dose received by many organs and calculated the effective doses using the guidelines in ICRP Publications 103 and 60. For this study, we used intraoral radiography (incisor, canine, premolar, molar, maxillary, and mandibular areas) and panoramic radiography. The two levels of effective doses were compared. As a result, exposure during intraoral radiography ranged from 4 to 8 microSv and that during panoramic radiography ranged from 16 microSv in Publication 103. Effective doses in Publication 103 were higher than those in Publication 60. The dose was 1.6-4.5 times higher in intraoral radiography and 2.2 times higher in panoramic radiography. In conclusion, the salivary glands markedly influenced the value of the effective doses of radiography in this study.

[Comparison of absorbed and effective dose from two dental cone beam computed tomography scanners].

OBJECTIVE: This research compared the field of view with the tissue absorbed dose and effective doses using the two dental cone beam computed tomography (CBCT) scanners. MATERIALS AND METHODS: Two CBCT devices, an Alphard VEGA and 3DX multi-image micro CT MCT-1, were used. Measurements were made using an Alderson RANDO phantom and thermoluminescence dosimeters (TLDs). The calculation of the effective dose was carried out according to ICRP Publication 60 and 103. RESULTS: The effective doses for Alphard VEGA D mode, I mode, P mode, and C mode were 86, 238, 413, and 323 µSv, respectively. The effective doses using 3DX for the maxillary incisor, maxillary molar, mandibular incisor, mandibular molar, TMJ, and mandibular molar scout images were 27, 30, 48, 60, 14, and 1 µSv, respectively. CONCLUSIONS: Both Alphard VEGA and 3DX values revealed salivary gland and oral mucosa doses much higher than those required for other tissues. It is necessary to select a small mode suitable in order to realize optimization.

[Absorbed dose and the effective dose of panoramic temporo mandibular joint radiography].

PURPOSE: This study measured the radiation doses absorbed by the patient during Panoramic temporo mandibular joint radiography (Panoramic TMJ), Schüllers method and Orbitoramus projection. The dose of the frontal view in Panoramic TMJ was compared to that with Orbitoramus projection and the lateral view in Panoramic TMJ was compared to that with Schüllers method. METHODS: We measured the doses received by various organs and calculated the effective doses using the guidelines of the International Commission on Radiological Protection in Publication 103. Organ absorbed doses were measured using an anthropomorphic phantom, loaded with thermoluminescent dosimeters (TLD), located at 160 sensitive sites. The dose shows the sum value of irradiation on both the right and left sides. In addition, we set a few different exposure field sizes. RESULT: The effective dose for a frontal view in Panoramic TMJ was 11 µSv, and that for the lateral view was 14 µSv. CONCLUSION: The lens of the Orbitoramus projection was 40 times higher than the frontal view in Panoramic TMJ. Although the effective dose of the lateral view in Panoramic TMJ was 3 times higher than that of the small exposure field (10×10 cm on film) in Schüller's method, it was the same as that of a mid-sized exposure field. When the exposure field in the inferior 1/3 was reduced during panoramic TMJ, the effective doses could be decreased. Therefore we recommend that the size of the exposure field in Panoramic TMJ be decreased.

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.

Effects of image artifacts on gray-value density in limited-volume cone-beam computerized tomography.

OBJECTIVE: An in vitro study was designed to investigate the influence of projection data discontinuity-related artifacts in limited-volume cone-beam computerized tomography (CBCT) imaging of the jaws. STUDY DESIGN: Test objects were positioned in 4 patterns in a water-filled phantom as follows: bimandible and vertebrae, bimandible, left mandible and vertebrae, and left mandible. The CT imaging of the left molar region was performed using image intensifier (II)- and flat panel detector (FPD)-based CBCT scanners. The CT value of the mandible and the adjacent soft tissue region were analyzed for density by means of an 8-bit grayscale. RESULTS: The effects of artifacts were scored as the difference in relative density between the lingual and buccal soft tissue. The intensity of artifacts increased when more objects were presented outside the area being imaged. Fewer artifacts were noted in images produced by the particular FPD CBCT used in this investigation. CONCLUSION: The CBCT system using an FPD resulted in fewer artifacts than the CBCT system using an II in this particular study.

Image artifact in dental cone-beam CT.

PURPOSE: The purpose of this study was to investigate the appearance and possible cause of an artifact seen in limited-volume cone-beam CT imaging. METHODS: A water-filled plastic cylinder was used as a phantom of the head. A test object was constructed as a bone-equivalent phantom to be imaged. The test object was variously positioned at the center of the phantom and near its margins. CT images of the test object were acquired using a 3DX Accuitomo system. RESULTS: In slice images with the test object positioned near the margin of the phantom, arch-shaped defects or deformities were observed on the side of the object. There was a negative correlation between the artifact and the CT value of the object. The artifact was larger in images scanned with a higher voltage. CONCLUSION: The probability that this artifact is caused by halation from the image intensifier (II) system is suggested.