Akitoshi Katsumata

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.

Positional changes of oropharyngeal structures due to gravity in the upright and supine positions

OBJECTIVES To compare the responses of oropharyngeal structures to gravity while sitting upright or lying down in a supine position. METHODS Seven subjects were evaluated by cone beam CT (CBCT) while in the upright position and by a four-row multidetector helical CT (MDCT) while in the supine position. All of the voxel sizes were adjusted to be 0.3x0.3x0.3 mm3 in the x-y-z axis. The posterior nasal spine, basion and fourth cervical bone were used as references to measure positional changes in the oropharyngeal structures between the upright and supine positions. The smallest areas in the oropharynx were also evaluated. RESULTS The soft palate, epiglottis and entrance of the oesophagus moved caudally with the positional change from supine to sitting upright, and moved posteriorly when the position changed from an upright to a supine position. The hyoid bone moved caudally but not posteriorly in response to the same positional changes. The width and length of the smallest area present in the oropharynx was larger in the upright position than in the supine position. CONCLUSIONS Gravity can produce movements in oropharyngeal structures in response to postural changes between sitting upright and lying in the supine position.

Reproducibility of maxillofacial anatomic landmarks on 3-dimensional computed tomographic images determined with the 95% confidence ellipse method.

OBJECTIVE To assess the plotting reproducibility of landmarks on 3-dimensional computed tomography (3D-CT) images through use of the 95% confidence ellipse in order to propose sufficiently stable coordinate systems for 3D-CT measurements. MATERIALS AND METHODS Six dentists plotted 19 landmarks twice on 3D-CT images. Scatterplots and the 95% ellipses were produced 3-dimensionally, and the areas of the ellipses were calculated for evaluating the reproducibility of landmarks. RESULTS The plotting reproducibility of each landmark showed characteristic features. Among five landmarks (the sella [S], nasion [N], basion [Ba], orbitale [Or], and true porion [Po]) that are frequently used as reference points on cephalograms, Ba showed the smallest areas for all three coordinate axes, indicating high reproducibility. The coronoid process (CP) and the tooth-related landmarks showed relatively high reproducibility. CONCLUSION Sufficiently stable coordinate axes could be proposed for different treatments and studies.

Use of sonographic elastography of the masseter muscles for optimizing massage pressure: a preliminary study

To examine the stiffness of the masseter muscle using sonographic elastography and to investigate its relationship with the most comfortable massage pressure in the healthy volunteers. In 16 healthy volunteers (10 men and 6 women), the Masseter Stiffness Index (MSI) was measured using EUB-7000 real-time tissue elastography. They underwent massages at three kinds of pressures using the Oral Rehabilitation Robot (WAO-1). A subjective evaluation regarding the comfort of each massage was recorded on the visual analogue scale. Elastography was also performed in two patients with temporomandibular joint dysfunction with the myofascial pain. The mean MSI of the right and left muscles in the healthy volunteers were 0.85 +/- 0.44 and 0.74 +/- 0.35 respectively. There was no significant difference between the right and left MSI in the healthy volunteers. The MSI was related to massage pressure at which the healthy men felt most comfortable. The two temporomandibular disorder patients had a large laterality in the MSI. The MSI was related to the most comfortable massage pressure in the healthy men. The MSI can be one index for determining the massage pressure.

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.

Masseter muscle sonographic features as indices for evaluating efficacy of massage treatment.

OBJECTIVE The aim of this study was to clarify the sonographic features of the masseter muscle as indices for judging the efficacy of massage treatment. STUDY DESIGN Fifteen patients with temporomandibular disorder (10 with unilateral and 5 with bilateral muscle pain) underwent massage treatment alternately on the bilateral masseter and temporal muscles with an oral rehabilitation robot. Sonography was performed before and after treatment, and the masseter thickness and existence of anechoic areas were evaluated. RESULTS The thickness on the symptomatic side in the unilateral group significantly decreased after treatment. Anechoic areas were shown in 20 muscles (66.7%) before treatment, and disappeared or were reduced in size in 17 muscles (85.0%) after treatment. The pretreatment thickness was significantly related to visual analog scale (VAS) scores regarding posttreatment muscle pain and massage impression. The existence of anechoic areas was relevant to VAS scores regarding muscle pain. CONCLUSION Masseter thickness and existence of anechoic areas might be related to the therapeutic efficacy regarding muscle pain.

Development of Oral Rehabilitation Robot for Massage Therapy

It is well known that the massage therapy is useful for the rehabilitation of various diseases. Although various apparatus have been developed for the massage of the torso and limbs, a machine to perform precise massage therapy to maxillofacial region is not developed yet. Therefore, we developed a robot system that provides massage therapy to maxillofacial region. The name of our newly developed robot was WAO-1. WAO-1 has been designed to perform appropriate massage to the patients with dry mouth, etc. WAO-1 is composed by two 6-degree of freedom arms with plungers attached at the end-effectors. The massage is applied to the patient by controlling the force and position of the plunger (virtual compliance). As a preliminary step of the clinical application, a simulation therapy of robotic massage to stimulate salivary flow from parotid gland was performed. The dynamic force on patients head during the massage using WAO-1 was evaluated. The results suggested that WAO-1 could perform equivalent massage to human hand. We expect that WAO-1 will be useful to provide massage therapy to several patients with oral health problems. This will aim in reducing the therapy costs due to the need of human efforts when long-time therapies are needed.

Assessment of Three-dimensional X-ray Images: Reconstruction From Conventional Tomograms, Compact Computerized Tomography Images, and Multislice Helical Computerized Tomography Images

Three-dimensional X-ray images (3D images) were used for imaging diagnosis in the oral and maxillofacial region. These images could be fundamentally reconstructed from various tomograms, though clinical 3D images were mainly reconstructed from computerized tomography (CT) images. In this investigation, 3D images were reconstructed from conventional tomograms with a panoramic unit, compact CT images, and multislice helical CT images, and the usefulness of each system was subjectively assessed for dental implant treatment. Three hemilateral dried human mandibles were used and were examined by linear tomography with a panoramic unit, compact CT, and multislice helical CT, and 3D images were reconstructed by using the rendering software for each system. The 3D images were visually evaluated on a 5-point scale covering the alveolar ridge, buccal and lingual bone surface, mental foramen, and tooth sockets. As a result, 3D images reconstructed from conventional tomograms with the panoramic unit were assessed as fair to unsure, compact CT 3D images were assessed as unsure to good, and multislice helical CT 3D images were assessed as good to excellent. It was concluded that compact CT 3D images and multislice helical CT 3D images were useful in dental implant treatment.

Reproducibility of landmark identification in the jaw and teeth on 3-dimensional cone-beam computed tomography images.

OBJECTIVE To compare the reproducibility of landmark identification on three-dimensional (3D) cone-beam computed tomography (CBCT) images between procedures based on traditional cephalometric definitions (procedure 1) and those tentatively proposed for 3D images (procedure 2). MATERIALS AND METHODS A phantom with embedded dried human skull was scanned using CBCT. The acquired volume data were transferred to a personal computer, and 3D images were reconstructed. Eighteen dentists plotted nine landmarks related to the jaws and teeth four times: menton (Me), pogonion (Po), upper-1 (U1), lower-1 (L1), left upper-6 (U6), left lower-6 (L6), gonion (Go), condyle (Cd), and coronoid process (Cp). The plotting reliabilities of the two procedures were compared by calculating standard deviations (SDs) in three components (x, y, and z) of coordinates and volumes of 95% confidence ellipsoid. RESULTS All 27 SDs for procedure 2 were less than 1 mm, and only five of them exceeded 0.5 mm. The variations were significantly different between the two procedures, and the SDs of procedure 2 were smaller than those of procedure 1 in 21 components of coordinates. The ellipsoid volumes were also smaller for procedure 2 than procedure 1, although a significant difference was not found. CONCLUSIONS Definitions determined strictly on each three sectional images, such as for procedure 2, were required for sufficient reliability in identifying the landmark related to the jaws and teeth.