Stability of voxel values from cone-beam computed tomography for dental use in evaluating bone mineral content.

OBJECTIVES: The objective of this study was to investigate the stability of voxel values from cone-beam CT (CBCT) using a flat panel detector in changing surrounding circumstances mimicking clinical situations. MATERIALS AND METHODS: Seven hydroxyapatite (HA) rods (0, 40, 80, 120, 160, 199, and 239 mg Ca/cm(3) ) were set in a 16 cm diameter water phantom and scanned with CBCT (FineCube) and also with multislice CT (MSCT) used as reference. The voxel values from CBCT were measured by the obtained images with OsiriX software (http://www.osirix-viewer.com), and compared with the CT numbers from MSCT. We examined the correlation between the voxel values and the HA contents, the variance of voxel values, and the influence of changing surrounding circumstances on the voxel values. RESULTS: The voxel values from CBCT were different from the CT numbers from MSCT, but there was a linear Pearson correlation between the voxel values and the HA contents. The voxel values were greatly influenced when the samples were scanned surrounded in air. However, the voxel values were not affected significantly in the existence of materials simulating oral hard tissues and/or a metal core post. CONCLUSIONS: There was a linear correlation between the voxel values of CBCT and the contents of HA rod samples. Our study indicated that it might be possible to evaluate bone mineral content(BMC) from the voxel values of CBCT for dental implant treatment.

Gumbel distribution-based technique enables quantitative comparison between streak metal artifacts of multidetector row CT and cone-beam CT: a phantom study.

Cone-beam computed tomography (CBCT), derived from multidetector row CT (MDCT), has a high spatial resolution and has recently been applied to various organs. One of the severe limitations common to CBCT and MDCT is metal artifacts. In particular, streak metal artifacts (SMAs) between multiple metal materials often hinder diagnosis. However, no studies have quantitatively compared the strength of SMAs in MDCT and CBCT. Nomura et al. reported an evaluation method specialized in SMAs of CBCT using the Gumbel distribution (GD), which can also be applied to SMAs of MDCT (Oral Surg Oral Med Oral Pathol Oral Radiol 131: 494-502, 2021, https://doi.org/10.1016/J.OOOO.2020.08.031 ). This study aimed to quantitatively compare SMAs occurring between titanium materials on MDCT and CBCT images using the GD-based method. The SMAs were investigated as follows: A hydroxyapatite block was sandwiched between two titanium rods to generate an SMA. They were placed in an acrylic phantom, simulating a human head, and scanned using an MDCT scanner and two CBCT scanners. The obtained images were analyzed using Gumbel plots and location parameters, and the SMA strength was calculated. The results showed that the SMAs on the MDCT images were significantly weaker than those on the CBCT images. In the CBCT scans, a smaller volume CT dose index value caused stronger SMAs. These results indicate that MDCT is more advantageous than CBCT in terms of SMA reduction when bone morphology between titanium materials must be evaluated. The characteristic should be considered in clinical cases.

Linear measurement accuracy of dental CT images obtained by 64-slice multidetector row CT: the effects of mandibular positioning and pitch factor at CT scanning.

PURPOSE: To evaluate whether the measurement accuracy of dental CT images is affected by the mandibular positioning and the pitch factor at CT scanning. MATERIALS AND METHODS: Three dry mandibles were scanned by 64-slice multidetector row CT (MDCT) and micro-CT. For MDCT scanning, 7 different mandibular positioning and 3 different pitch factors were applied. After reformatting dental CT images, the bone height was measured on these images. It was also measured on the corresponding micro-CT image, which was defined as the actual value. The difference of the measurement values between these 2 was defined as the measurement error. RESULTS: There was no significant difference in the measurement errors due to either the mandibular positioning or the pitch factor. CONCLUSION: The measurement accuracy of dental CT images obtained was not affected by either mandibular positioning or pitch factor at CT scanning.

Evaluation of streak metal artifacts in cone beam computed tomography by using the Gumbel distribution: a phantom study.

OBJECTIVE: The aim of this study was to confirm whether streak metal artifacts (SMAs) between titanium implants on cone beam computed tomography (CBCT) images could be evaluated by using the Gumbel distribution (GD). Moreover, the influence of different scan settings on SMAs was investigated. STUDY DESIGN: An iodine solution simulating dentin was placed between 2 titanium rods in an acrylic phantom. It was scanned by using CBCT at 2 settings with nearly equivalent exposure doses (90 kV, 7 mA; 78 kV, 10 mA). The images were analyzed, and the dependence of the voxel values in SMAs on GD was investigated with the coefficient of determination (r2). The location parameters, indicating the strength of the SMAs, were calculated for each scan setting and evaluated with the Mann-Whitney U test. Significance was established at p = .05. RESULTS: The SMAs on CBCT images depended on GD (r2 ≥ .959). The SMAs with the 78 kV, 10 mA settings were significantly smaller than those with the 90 kV, 7 mA settings (p < .01). CONCLUSIONS: SMAs on CBCT images could be evaluated by using methods based on GD. The strengths of metal artifacts varied with changes in scan settings, even at nearly equivalent exposure doses.

Reliability of voxel values from cone-beam computed tomography for dental use in evaluating bone mineral density.

OBJECTIVES: The aim of this study was to investigate whether it was possible to evaluate bone mineral density (BMD) using voxel values from cone-beam CT (CBCT) for dental use. MATERIALS AND METHODS: A water phantom with an aluminum rod and sample tubes containing iodine solutions of various concentration was imaged by CBCT and multi-slice CT (MSCT). Voxel values and CT numbers, respectively, of the samples were measured and their correlation was investigated. In addition, based on the CT numbers of a hydroxyapatite (HA) reference phantom, a conversion formula from voxel value to BMD was obtained. RESULTS: There was a positive correlation between the voxel values of CBCT and the iodine concentration of the solutions, regardless of the X-ray dose or the mean energy, although the voxel values had a slight tendency to be saturated at higher iodine concentrations. An excellent correlation between the voxel values and CT numbers was also observed. A regression analysis showed that nonlinear (linear-quadratic model) regression was more appropriate than linear regression fitting for plotting these two values, although the latter might be usable for clinical applications. The conversion formula from the voxel value of CBCT to the equivalent BMD was as follows: y=-0.03669x(2)+3.602x-350.3 (x: voxel value, y: BMD mg/cm(3) HA). CONCLUSIONS: This study revealed that there was a high correlation between the voxel values of CBCT and the CT numbers of MSCT. Although this was an in vitro study with assumed ideal conditions for measuring voxel values, there was a clear possibility for estimating CT numbers and BMD using the voxel values from the CBCT images, but the relationship was not entirely linear and should be examined further.

Spatial resolution measurements by Radia diagnostic software with SEDENTEXCT image quality phantom in cone beam CT for dental use.

OBJECTIVES: We aimed to employ the Radia diagnostic software with the safety and efficacy of a new emerging dental X-ray modality (SEDENTEXCT) image quality (IQ) phantom in CT, and to evaluate its validity. METHODS: The SEDENTEXCT IQ phantom and Radia diagnostic software were employed. The phantom was scanned using one medical full-body CT and two dentomaxillofacial cone beam CTs. The obtained images were imported to the Radia software, and the spatial resolution outputs were evaluated. The oversampling method was employed using our original wire phantom as a reference. The resultant modulation transfer function (MTF) curves were compared. The null hypothesis was that MTF curves generated using both methods would be in agreement. One-way analysis of variance tests were applied to the f50 and f10 values from the MTF curves. The f10 values were subjectively confirmed by observing the line pair modules. RESULTS: The Radia software reported the MTF curves on the xy-plane of the CT scans, but could not return f50 and f10 values on the z-axis. The null hypothesis concerning the reported MTF curves on the xy-plane was rejected. There were significant differences between the results of the Radia software and our reference method, except for f10 values in CS9300. These findings were consistent with our line pair observations. CONCLUSIONS: We evaluated the validity of the Radia software with the SEDENTEXCT IQ phantom. The data provided were semi-automatic, albeit with problems and statistically different from our reference. We hope the manufacturer will overcome these limitations.

Diagnostic ability of limited volume cone beam computed tomography with small voxel size in identifying the superior and inferior walls of the mandibular canal.

BACKGROUND: The aim of this study was to evaluate the visibility of the superior and inferior walls of the mandibular canal separately using limited volume cone beam computed tomography (CBCT) with small voxel size. METHODS: CBCT cross-sectional images of 86 patients obtained by 3D Accuitomo FPD and reconstructed with a voxel size of 0.08 mm were used for the evaluation. A 30-mm range of the mandible just distal to the mental foramen was divided into three equal areas (areas 1, 2, and 3, from anterior to posterior). Each area contained 10 cross-sectional images. Two observers evaluated the visibility of the superior and inferior walls of the mandibular canal on each of the cross-sectional images in these three areas. The visibility ratio in each area was determined as the number of cross-sectional images with a visible wall divided by 10. RESULTS: In all areas, the visibility ratio of the superior wall was significantly lower than that of the inferior wall. As for variance among the three areas, the ratio was highest in the most posterior area (area 3) and tended to decrease gradually towards the mental foramen for both walls. Cases in which more than two thirds of the superior wall could be identified (visibility ratio of 0.7 or more) in areas 1, 2, and 3 were 44, 62, and 66%, respectively. CONCLUSIONS: The superior wall was significantly more poorly visualized than the inferior wall in all areas examined. The visibility of the superior wall on CBCT images was limited even when a limited volume device with small voxel size was used.

Location dependency of the spatial resolution of cone beam computed tomography for dental use.

OBJECTIVE: This study evaluates the spatial resolution of cone beam computed tomography for dental use (CBCT) via modulation transfer function (MTF) analyses. STUDY DESIGN: Two models of CBCT system, 3DX FPD8 and FineCube v.12, were used. MTF analysis was applied to each CBCT system using a thin tungsten wire technique. RESULTS: The MTF curves in the radial direction on the XY-plane were concordant regardless of position, whereas the curves in the azimuthal direction tended to decrease as the distance from the rotation center increased. In the Z-axis direction, the MTF curve of the medial level of the field of view was superior to that of any other level. CONCLUSION: The spatial resolution of CBCT systems depends on the location within the field of view. Because the spatial resolution was the highest in the medial level and rotation center position, an object should be placed at this position during a CBCT examination.

Visualization of the superior and inferior borders of the mandibular canal: a comparative study using digital panoramic radiographs and cross-sectional computed tomography images.

OBJECTIVE: To evaluate the visibility of the superior and inferior borders of mandibular canal using panoramic radiography (PR) and cross-sectional computed tomography (CT) images. STUDY DESIGN: Digital panoramic images and cross-sectional CT images of 100 patients were evaluated. The mandibular canal was divided into 4 areas of equal width (1-4), from anterior to posterior. The visibility of the superior and inferior borders was assessed using a 5-point visibility scoring system, with lower scores for worse visibility. RESULTS: For both modalities, the superior border showed significantly lower score than the inferior border in all areas. For the superior border, areas 1, 2, and 3 all showed significantly lower scores than area 4 for PR, whereas only area 1 showed a lower score than area 4 for CT. CONCLUSIONS: The visibility of the superior border was very poor on panoramic images. The use of cross-sectional CT images remarkably improved this poor visualization.