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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 7  |  Issue : 2  |  Page : 58-63

Comparing the accuracy of linear measurements in different image views of Galileos cone-beam computed tomography unit


1 Department of Radiology, School of Dentistry, Dental Implants Research Center, Isfahan University of Medical Sciences, Isfahan, Iran
2 Department of Oral and Maxillofacial Radiology, Isfahan University of Medical Sciences, Isfahan, Iran
3 Faculty of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran
4 Department of Dental School, Isfahan University of Medical Sciences, Isfahan, Iran

Date of Web Publication19-May-2016

Correspondence Address:
Sajad Ghorbanizadeh
Department of Radiology, School of Dentistry, Dental Implants Research Center, Isfahan University of Medical Sciences, Hezarjerib Street, Isfahan
Iran
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DOI: 10.4103/0976-433X.182672

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  Abstract 

Objectives: The aim of this study was to compare the accuracy of linear measurements in axial, cross-sectional, and tangential cone-beam computed tomography. (CBCT) images in dry human skulls. Materials and Methods: Six dry human skulls were included in the study. Opaque markers were attached to the alveolar bone. Buccolingual and mesiodistal distances and height were measured in 5 different regions by a digital caliper. (Guanglu, Taizhou, China). Radiographic measurements were made in tangential, cross-sectional, and axial CBCT images. To determine the accuracy of linear measurements, the physical and radiographic measurements were compared. Intraclass correlation coefficient, Wilcoxon, one-sample t-test, and univariate analysis of variance were used to analyze the data. Results: The differences between physical and radiographic measurements were not clinically significant in any of the views. (P < 0.05). Conclusions: By opaque markers, the accuracy of measurements in Galileos CBCT machine is adequate in all CBCT image views.

Keywords: Cone-beam computed tomography, dental radiography, sensitivity and specificity, skull


How to cite this article:
Ghorbanizadeh S, Abdinian M, Faghihian R, Goroohi H. Comparing the accuracy of linear measurements in different image views of Galileos cone-beam computed tomography unit. SRM J Res Dent Sci 2016;7:58-63

How to cite this URL:
Ghorbanizadeh S, Abdinian M, Faghihian R, Goroohi H. Comparing the accuracy of linear measurements in different image views of Galileos cone-beam computed tomography unit. SRM J Res Dent Sci [serial online] 2016 [cited 2020 Oct 25];7:58-63. Available from: https://www.srmjrds.in/text.asp?2016/7/2/58/182672


  Introduction Top


Cone-beam computed tomography (CBCT) had found its niche in different fields of dental practice during recent years.[1],[2],[3],[4],[5] Nowadays, three-dimensional (3D) radiographs are widely used for diagnostic and therapeutic purposes in dentistry. Single-slice CT and multi-slice CT techniques were first introduced in this regard.[6],[7] The case against these two systems is that they expose patients to high radiation doses.[8],[9],[10] Among this, CBCTs were introduced to reduce radiation exposure, maintain the quality of the images, and reduce image processing time at reduced costs.[11],[12] Consequently, the use of this technique is dramatically increasing in implant dentistry,[2] maxillofacial surgery,[1],[13] orthodontics,[14] endodontics,[15], etc., Due to the high dependence of treatment approaches on the exact estimation of bone thickness and distance between anatomical landmarks, many clinicians prefer to use the linear measurement capability of CBCT. Previous studies have investigated the accuracy of linear measurements in CBCT images using NewTom 3G, Accuitomo, and other CBCT machines.[16],[17],[18],[19],[20] They convey the impression that the linear measurement capabilities of these units are reliable for the structures that are closely associated with dentomaxillofacial imaging. Mischkowski et al.[21] evaluated the geometric accuracy of scans obtained with Galileos CBCT device. They reported that the cone-beam device provides satisfactory information about linear distances.

It is demonstrated that radiographic units should be able to measure height, mesiodistal length, and buccolingual length for implant treatments.[22] Buccolingual and mesiodistal lengths and height of bone can each be measured in two views of CBCT image viewer: Axial and tangential, axial and cross-sectional, or tangential and cross-sectional. The measured distances in each pair views are not exactly similar. Therefore, it is important to determine whether the accuracy of measurements is significantly different in these views or not and to help the practitioners choose more accurate views if it is.

Although the newly introduced Galileos CBCT machine is reported to be one of the CBCT dental devices with the lowest effective dose,[23] its linear measurement accuracy has not been evaluated in different image views. The aim of this study was to compare the accuracy of linear measurements in different image views of Galileos CBCT unit by simulating clinical relevant distances in dry human skulls.


  Materials and Methods Top


This was an experimental study on partially edentulous human skulls.

Skull preparation

Six dry human skulls with no fracture were included in the study. The skulls were not identified by age, sex, or ethnicity. Five regions were selected on each jaw; one on anterior, two on premolar, and molar regions of the left and right sides of the jaw. To measure the distances, four points were determined using 1.5-mm rod-shaped size 40 Gutta-percha opaque markers. The first marker was glued to the buccal side of most coronal alveolar crest, the second marker was placed at the lingual side of most coronal alveolar crest, perpendicular to the first marker, the third marker was placed at the most apical region of buccal alveolar crest in the same direction of the first marker, and the fourth marker was placed next to the first marker, at the buccal side of alveolar crest [Figure 1]. Buccolingual and mesiodistal distances and height (referred to as aspect) in each region were measured using opaque markers [Table 1].
Figure 1: Panoramic view of a skull radiograph. Opaque Gutta-percha markers are observed in the image

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Table 1: Different physical and radiographic measured distances in molar, premolar and anterior regions

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Physical and radiographic measurement

The distances were measured twice by the first observer with 1-week interval and once by a second observer, using a digital caliper (Guanglu, Taizhou, China) [Figure 2]. Both observers were radiologists.
Figure 2: An example of measured distances; the arrow shows the measured distance between two ends of the markers

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Then, the skulls were prepared for radiographic assessment. The images were taken using Galileos Comfort 3D imaging system (Sirona Dental Systems Inc., Bensheim, Germany). To reconstruct the temporomandibular joint space, a 1.5 mm-thick baseplate wax was placed between the condylar process and the temporal fossa. After guiding the jaw into the centric occlusion, mandible was attached to maxilla by an adhesive tape. A polyvinyl pipe was placed into the foramen magnum and attached to a camera tripod (Zeiss Universal Tripod FT6302, Oberkochen, Germany). To provide standard radiographs, the skull was retained in the image field using the machine's occlusal bite block between teeth (in the way that the occlusal plane was perfectly horizontal; according to the manufacturer's instructions). To ensure the appropriate position of skulls, the system's light localizer, which displays the midsagittal line, was also used. Then, images were captured at 7 mA (42 mAs) and 85 kVp, with 14-s scan time and 204° rotation. Each scan produced 200 projections in a 15 cm × 15 cm × 15 cm field of view (FOV). A charge-coupled device detector, with 1024 × 1024 matrix and 0.15 mm voxel size, was used to detect the images. Images were saved in SVG file format and reconstructed using GALAXIS Viewer software version GAX5 [Figure 1] and [Figure 2]. Afterward, the radiographic distances were measured by mouse cursor, twice by the first observer with 2-week interval and once by the second observer. The distances were measured between two ends of markers. An example of measured distances is presented in [Figure 3] and [Figure 4].
Figure 3: Examples of measured distances in different views. (a) Axial slice showing mesiodistal length. (b) Cross-sectional slice showing buccolingual length

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Figure 4: Tangential (a) and cross-sectional (b) images of the same region in maxilla for measuring height. Note that both apical and coronal markers are apparent in tangential, but the coronal marker could not be displayed at the same time as the apical marker in cross-sectional view

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Statistical analysis

The statistical analyses were performed by SPSS software version 18.0. Intraclass correlation coefficient (ICC) was used to analyze intra- and inter-observer reliability of measurements (α = 0.05). Wilcoxon test was used to compare physical and radiographic values of different measurements (α = 0.05); less differences between physical and radiographic measurements show more accurate radiographic measurements. Post hoc Tukey test was performed to determine the significant differences. One-sample t-test was used to compare the differences with the accep[table 0].5-mm mean absolute error (α = 0.05). Univariate analysis of variance was performed by considering main effects, two-way effects and if possible, multi-way effects of (a) case number (skull), (b) measured region, (c) measured side, (d) jaw type (upper jaw or lower jaw), (e) measured aspect, and (f) radiographic view, to assess their influence on the accuracy of measurements.


  Results Top


Because of unilateral severe bone resorption, the distances in the mandibular left premolar and molar regions in one skull and also mandibular right premolar and molar regions in another skull were not separately measured, reducing the whole measurements to 174. According to ICC values, inter observer correlations for radiographic measurement and physical measurements were both 0.996 (P < 0.001). Intraobserver correlation was 0.995 for radiographic measurements (P < 0.001) and 0.996 for physical measurements (P < 0.001). The mean difference between physical and radiographic measurements was 0.22 ± 0.61 mm. There was neither significant difference between cross-sectional and axial views for buccolingual aspect (P = 0.14), nor between axial and tangential views for mesiodistal aspect (P = 0.15); however, the difference between cross-sectional and tangential views for height was significant (P < 0.001). Data showed that measurements of height were more accurate in tangential view [Table 2]. No significant difference was observed between 0.5 mm absolute error and mean differences of physical and radiographic measurements [Table 3]. In addition, there was no significant difference between accuracy of measurements in upper jaw or lower jaw (P = 0.28). Univariate analysis of variance [Table 4] revealed that radiographic view, three-way effects, and other multi-way effects do not influence accuracy of measurements (P > 0.05). Tukey showed that the accuracy of measurements in skull number 3 was more than skull number 4 (P = 0.01). Furthermore, the accuracy of measurements of height was higher than the other two aspects (P < 0.001).
Table 2: Mean difference between physical measurements and radiographic measurements for buccolingual and mesiodistal aspects and height in different views

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Table 3: Comparison of mean differences with 0.5 mm absolute error: One-sample t-test

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Table 4: Assessment of difference between physical and radiographic measurements: Univariate analysis of variance model

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  Discussion Top


This study showed that the accuracy of measurements in different Galileos CBCT views is clinically acceptable. Although the accuracy of radiographic measurements was significantly lower than physical measurements in a number of distances, the average difference was <0.5 mm, which is considered not clinically significant.[24] To make sure that the measurements were accurate, two observers measured the distances. The intra- and inter-observer correlations were above 0.95 which shows that the measurements were precise. Larger FOVs, 15 cm × 15 cm × 15 cm in this study, result in higher scatter radiation, lower resolution, and more difficult determination of markers;[22] however, high ICC values suggest that the rod-shaped opaque markers would allow the observers to more easily and accurately measure the distance between two ends of the markers.[25]

The results of Kamburoglu and Kursun's study [26] support this interpretation, as they did not use markers for detecting internal resorption cavities, which led to lower ICC values.

In this study each aspect – buccolingual, mesiodistal, and height could be measured in two different CBCT image views; buccolingual length in cross-sectional and axial views, mesiodistal length in axial and tangential views, and height in cross-sectional and tangential views. It was sometimes observed that the opaque markers which were placed in the same direction (for measurements of height), could be detected simultaneously in one view (e.g., tangential view), so that the distance was easily measured. However, the same markers were not observed in the other view (e.g., cross-sectional view) [Figure 4], even with changing the image section in panorama view. For measuring the latter distance, the observer has to label the first marker, scroll through the slices back and forth to detect the second marker and then measure the distance between the label and the second marker; an “indirect” measurement. This complicates the measurement process and typically requires more time and effort and can be considered inappropriate. Moreover, making such a measurement may not be achieved in the absence of opaque markers which leads to insufficient accuracy; however, this study proved that, as long as opaque markers exist, the reduction in accuracy of measurement is not clinically significant.

In dental implant treatments, different angulations and inclinations are used, according to different anatomic considerations.[27] It is crucial that the CBCT software allows 3D sections in cross-sectional and tangential views. Galileos CBCT software prepares only two-dimensional image sections, which makes the practitioner use indirect measurements. If the CBCT software has the possibility of preparing images from desired 3D sections, indirect measurements will not be needed.

Ganguly et al.[28] evaluated the accuracy of bone height measurements on cadaver heads using Galileos CBCT unit. Although they included intra- and extra-oral soft tissues, the results of their study and this study were similar. These findings emphasize the insignificant effect of soft tissue on the accuracy of measurements.[28]

Kamburoglu and Kursun [26] also demonstrated that smaller defects are more difficult to be detected, representing lower accuracy. These findings may be distributed to the accuracy of linear measurements. The accuracy of linear measurements in larger distances exceeds smaller distances. In other words, measurement error occurs more frequently in smaller distances.[29]

The majority of previous studies have investigated the accuracy of linear measurements in larger distances, or in restricted aspects (usually one aspect),[16],[18],[20],[21],[25],[27],[28],[30] which might not specifically determine the accuracy for clinical use. Since radiographic units should be able to measure height, mesiodistal length, and buccolingual length for implant treatments,[22] all of these distances were included in this study.

Nevertheless, there are no similar studies to further discuss the results.

There are a number of factors which can explain different results of this study and other studies on the accuracy of measurements of CBCT units. These factors include different methods for localizing measurement points,[30] different skulls, different CBCT units,[31] different distances,[29] different markers, and landmarks.[25]

The effect of indirect measurements – as described above, as well as predominant artifacts in CBCT imaging including noise, scatter, extinction artifact, beam hardening, exponential edge gradient effect, aliasing artifacts, and ring artifacts [32] may cause difficulties in detecting the exact situation of objects in a CBCT image. This leads to inaccurate measurements. Although it has been reported that CBCT artifacts are more seen in axial slices,[32] this study showed that the accuracy of measurements in different CBCT image views was not significantly different.

Distortion also can cause errors in linear measurements. The rotation of CBCT unit with wobble pattern is a probable source of distortion. Moreover, the anatomical distortion, a function of shape and orientation of the structures, can cause distortions as well.[30]

The negative impact of these factors is more obvious in different skulls and special parts of FOV.[31] Thus, the results of univariate ANOVA [Table 4] will be discussed in the following paragraphs.

The measurements made on skull number 3 were more accurate than skull number 4 since the morphology of skulls cannot be standardized.[31] Tsutsumi et al. showed that accuracy of measurements in different parts of FOV is not the same. The distances may be overestimated near the center or periphery of FOV, depending on the CBCT unit and the nature of markers.[31] In this study Gutta-percha markers and Galileos CBCT unit were used. Due to the probable effect of teeth region and jaw type (upper jaw or lower jaw), both mandible and maxilla were investigated in five areas. The results revealed that two-way effect of region-jaw type affects the accuracy of measurements because the measured distances were in different parts of FOV.[31]

The accuracy of measurements was not different between the upper jaw and lower jaw when comparing the same regions. For example, the accuracy of measurements in the right mandibular premolar and the right maxillary premolar regions are not significantly different. This is probably because maxilla and mandible are in similar parts of FOV when evaluating the same regions. In fact, main effect of jaw type was not considerable.

Height measurements, in this study, were more accurate than mesiodistal and buccolingual lengths (main effect of aspect) since the measurement error of horizontal measurements tends to exceed vertical measurements.[29]

The main effect of radiographic view was not considerable. It implies that mesiodistal and buccolingual lengths and height of bone can be measured in both displaying views; however, measurements in tangential view were more accurate than the cross-sectional view (P < 0.05). We suggest that this difference is because of indirect measuring. Since 3D sections were not available, the observer had to use indirect measurements in both tangential and cross-sectional views.

The main effect of the side was not considerable either. Ganguly et al.[28] obtained the same results. Since the skulls are placed in the center of FOV, the left side and right side of skull locate in symmetrical parts of FOV, resulting in the same accuracies.

As illustrated in [Table 4], anatomy of skull, the measured aspect, two-way effect of region-jaw, and that of jaw-aspect can affect the accuracy of measurements. It suggests that CBCT units should be enhanced by features-like a posteriori position adjustment,[33] which allow the practitioner to consider anatomical asymmetries and differences; however, distortion caused by anatomical asymmetry cannot always be distinguishable from radiographic distortion.[30] The manufacturer of Galileos CBCT machine claims that the accuracy of length measurements is ± 0.15 mm; however, the results of this study showed that this accuracy depends on numerous criteria and is not always in the above-mentioned range.

This study failed to incorporate the effect of a patient motion for determining the accuracy of measurements.


  Conclusion Top


We may suggest that future studies develop more clinically relevant conditions. We also suggest that a similar study be conducted by defining anatomical markers on the alveolar ridge without using opaque markers. We may suggest also conducting a study including soft tissue substitute, upon the manufacturer's advice, an aluminum cylinder. Moreover, it is reasonable that other CBCT machines be evaluated which allows detailed comparisons.

This study demonstrates that the accuracy of measurements in axial, tangential, and cross-sectional Galileos CBCT images varies for buccolingual length, mesiodistal length, or height of the alveolar bone [Table 2]; however, the reduction in accuracy is not clinically significant [Table 3]. The radiopaque markers might have had a dramatic role in making precise measurements. As a result, if we need precise measurement for example in implant surgery, it is suggested to use radiopaque markers at the end of favorite measured lines (mesiobuccal, distobuccal, or height).

Financial support and sponsorship

This study is financially supported and approved by Dental Faculty of Isfahan Medical University.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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