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Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy
YIJOM-2714; No of Pages 7
Int. J. Oral Maxillofac. Surg. 2013; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2013.06.005, available online at http://www.sciencedirect.com
Clinical Paper Orthognathic Surgery
Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy
B. F. Gaia, L. R. Pinheiro, O. S. Umetsubo, F. F. Costa, M. G. P. Cavalcanti School of Dentistry, University of Sa˜o Paulo, Sa˜o Paulo, Brazil
B. F. Gaia, L. R. Pinheiro, O. S. Umetsubo, F. F. Costa, M. G. P. Cavalcanti: Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy. Int. J. Oral Maxillofac. Surg. 2013; xxx: xxx–xxx. # 2013 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Abstract. The purpose of this study was to test the precision and accuracy of threedimensional (3D) linear measurements for Le Fort I osteotomy, obtained from multi-slice computed tomography (MSCT) and cone beam computed tomography (CBCT) scans. The study population consisted of 11 dried skulls submitted to 64row MSCT and CBCT scans. Three-dimensional reconstructed images (3D-CT) were generated, and linear measurements (n = 11) based on anatomical structures and landmarks of interest for Le Fort I osteotomy were performed independently by two oral and maxillofacial radiologists, twice each, using Vitrea software; this allows true 3D measurement on 3D-CT images. The results demonstrated no statistically significant differences between the inter-examiner and intra-examiner analyses, and physical and true 3D linear measurements using MSCT and CBCT images. Regarding examiner accuracy, no statistically significant differences were found for the comparisons among the physical and the MSCT and the CBCT linear measurements by either examiner. For examiners 1 and 2, the analysis intraexaminer correlation coefficient ranged from 0.87 to 0.96 and 0.82 to 0.98, respectively, using MSCT, and from 0.84 to 0.98 and 0.80 to 0.98, respectively, using CBCT, indicating almost perfect agreement for all analyses performed. 3D linear measurements obtained from MSCT and CBCT images were considered precise and accurate for Le Fort I osteotomy and thus accurate and helpful for Le Fort I osteotomy planning.
Currently available three-dimensional (3D) software has been developed specifically to assist in the diagnosis, treatment planning, and prediction of outcomes related to orthognathic surgery and to prevent perioperative complications such as haemorrhage, permanent neural disorders, and 0901-5027/000001+07 $36.00/0
unplanned fractures, especially for the Le Fort I osteotomy involving the pterygoid process.1–8 However a large number of parameters are involved that could influence the surgeon’s analysis and consequently compromise the surgical outcome, such as different computed tomography image
Key words: three-dimensional; computed tomography; orthognathic surgery. Accepted for publication 10 June 2013
acquisition (multi-slice computed tomography – MSCT, and cone beam computed tomography – CBCT), different reconstruction algorithms, and different forms of linear measurement method. The purpose of this study was to test the precision and accuracy of 3D linear
# 2013 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
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Gaia et al.
measurements for Le Fort I osteotomy obtained from MSCT and CBCT scans. Materials and methods Sample
The study population consisted of 11 intact human skulls (eight male and three female, aged 19–56 years), provided by the institution’s department of anatomy. Approval was granted by the institutional review committee/human specimens committee. There was no ethnic or gender preference when selecting the sample, and no history of bone disease was identified in the medical records.
Data collection
Before scanning the skulls, the mandibles were fixed to the skulls in central occlusion using tape. The skulls were placed in a plastic bucket with water for MSCT and in a bulk bag with water for CBCT, for beam attenuation and to mimic the soft tissues, in accordance with previously published methods.9–11 The skulls were then placed in the equipment to keep them in a position similar to that of the clinical situation for the MSCT and CBCT. The specimens were first submitted to a 64-row multi-slice CT procedure (Aquilion; Toshiba America Medical Systems Inc., Tustin, CA, USA). The boundaries of the imaging area were set superior to the vertex and extended inferiorly to below the mandible. High-resolution contiguous images were obtained following the acquisition image protocol (0.5 mm thick axial slices, 0.3 mm of reconstruction interval per 0.4 s of time, 512 512 matrix, 120 kVp and 300 mA, and 24.0 cm field of view), associated with a low frequency filter (bone filter). Subsequently, the skulls
were submitted to a CBCT scan (i-CAT Cone Beam 3D Dental Imaging System, Imaging Sciences International, Hatfield, PA, USA) at 0.25-mm voxel size for 40 s to acquire raw data. The field of view (FOV) was a 20-cm height and 16-cm diameter cylinder. The grey-scale range of the acquired images was 14 bits. After the original image was acquired, these data were recorded and stored in DICOM format (Digital Imaging Communication in Medicine) to avoid data loss. Multiplanar (MPR; axial, coronal, and sagittal) and 3D-CT reconstructed images using the bone protocol were obtained simultaneously, based on the original axial slices, and were generated in Vitrea version 3.8.1 software (Vital Images Inc., Plymouth, MN, USA) installed in a Dell 650 Precision independent workstation (Dell Computer Corp., Round Rock, TX, USA) running the Windows XP operational system (Microsoft, Redmond, WA, USA). Two oral and maxillofacial radiologists, with extensive experience in interpreting CT and knowledge of the software tools, were calibrated prior to study commencement. Linear measurements of the 3D coordinates used for this study were obtained using the anatomical structures described in Table 1. Most of the bone structures were selected expressly, instead of using the traditional craniometric points, since analysis of these structures is highly relevant in the planning of the Le Fort I osteotomy12–14 (Table 1). The examiners performed a total analysis of the volume using axial and MPR images, and pointed to the initial mark of the anatomical structure using an arrow. This first point was performed over the MPR and automatically transferred to the 3D reconstruction image. The examiners verified and confirmed the exact location
of the marked predefined structure point using rotation, translation, and transparency software tools. This point was considered the initial mark for true 3D linear measurements. Then, the volume was analysed again, and the second point was determined following the same steps described above (Figs 1 and 2). All measurements (n = 11) were performed for each of the scanned skulls and were made electronically by two oral and maxillofacial radiologists (twice each), independently, with a 7-day time interval between the repeated measurements to ensure intra-examiner and inter-examiner reliability. In all, 968 image measurements were made. The mean value for each measurement was obtained from all measurements performed on the 11 dry skulls. To obtain the physical data, a third examiner who had no knowledge of the imaging measurements, performed measurements of the same sets of landmarks directly on the dry skull, with a 7-day time interval between the repeated measurements. Linear dry skull measurements were obtained with a digital calliper (167 series; Mitutoyo Sul Americana Ltda, Suzano, SP, Brazil), the same device as used by Lopes et al.9 and Moreira et al.,10 with a 0.3 mm active point. Data analysis
Data analysis consisted of comparing dry skull measurements (gold standard) with 3D-MSCT and 3D-CBCT linear measurements obtained in true 3D measurement software. Precision was assessed based on the intra-examiner and inter-examiner measurements, and accuracy based on the difference between the measurements performed by the examiners and the corresponding physical measurements. The
Table 1. Description of the craniometric anatomical structures and respective linear measurements. Anatomical structures Length of maxilla (ANS–PNS) Length of lateral nasal walla (LNW) Length of the pterygoid processa (LPtg) Thickness of the junction between the pterygoid process and the tuberosity of the maxillaa (TPtg) Length of the lateral plate of the pterygoid processa (LLpPtg) Length of the medial plate of the pterygoid processa (LMpPtg) a
Description Distance between the anterior (ANS) and posterior nasal spine (PNS), determining the total length of the maxilla Distance from the piriform aperture (15 mm above the ANS) up to the anterior portion of the descending palatine artery canal, determining the length of the lateral nasal wall Distance representing the length of the bone fusion of the pterygoid process of the sphenoid bone to the tuberosity of the maxilla (lateral view) Distance between the lateral and medial point of the bone fusion of the pterygoid process to the tuberosity of the maxilla, representing the length of the bone fusion (axial view) Distance between a point in the pterygoid fossa (that was the shortest distance to the descending palatine artery canal) and the distal portion of the lateral pterygoid plate, representing the length of the lateral plate of the pterygoid process Distance between a point in the pterygoid fossa (that was the shortest distance to the descending palatine artery canal) and the distal portion of the medial pterygoid plate, representing the length of the medial plate of the pterygoid process
Measurements made on the right (R) and left (L) sides of the anatomical structure.
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
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two initial observations of the examiners were considered as sample 1, and the two further observations as sample 2. For the inter-examiner agreement, only the first set of measurements was used. Intraexaminer, inter-examiner, and gold standard comparisons, as well the correlation between all individual measurements performed by examiners 1 and 2 using MSCT and CBCT and the gold standard, were conducted using the intra-class correlation coefficient (ICC), with a 95% confidence interval (95% CI). Results
Fig. 1. ANS–PNS linear measurement obtained from 3D-CBCT. (A) Axial, (B) sagittal, and (C) coronal views, showing the ANS point (yellow arrow), using multiplanar reconstruction. (D) 3D reconstructed image showing the ANS point marked (yellow arrow) to confirm the exact position, using software tools such as rotation, translation, and transparency.
Fig. 2. The same skull as in Fig. 1, showing the ANS–PNS linear measurement process. (A) Axial and (B) sagittal views, showing the PNS and ANS points (yellow arrow). (C) Coronal view showing the PNS point. (D) 3D reconstructed image demonstrating the true 3D measurement for the length of the maxilla (53.5 mm) based on the previously marked ANS–PNS points.
The results for the linear measurements are shown in Tables 2–5. Table 2 shows the means and standard deviations in millimetres of MSCT, CBCT, and physical measurements. The highest mean difference for each measurement was found for LMpPtg R: for both examiners using MSCT images, and for examiner 1 using CBCT. The highest mean differences found for examiner 2 were LPtg R (3.609 (SD)) and ANS–PNS (3.414 (SD)) using CBCT images (Table 2). The mean differences between the physical and the true 3D linear measurements using MSCT ranged from 0.05 to 0.68 mm for examiner 1, and from 0.12 to 0.92 mm for examiner 2. Regarding the CBCT images, the mean differences ranged from 0.03 to 0.54 mm for examiner 1 and from 0.02 to 0.64 mm for examiner 2 (Table 2). Table 3 shows that all measurements performed by examiners 1 and 2 using MSCT and CBCT presented excellent to good agreement (Table 3). The analysis inter-examiner correlation coefficient ranged from 0.85 to 0.98 for MSCT and from 0.80 to 0.99 for CBCT, indicating a moderate to almost perfect agreement between examiners (Table 4). The highest difference from the gold standard for each measurement was found for TPtg R using MSCT images and LLpPtg R using CBCT, although both results showed good agreement. The analysis intra-examiner correlation coefficient ranged from 0.87 to 0.96 and 0.82 to 0.98 for examiners 1 and 2, respectively, using MSCT, indicating almost perfect agreement. Using CBCT, the intra-class correlation coefficient ranged from 0.84 to 0.98 for examiner 1 and from 0.80 to 0.98 for examiner 2, indicating almost perfect agreement (Table 5). Discussion
The introduction of 3D tomography images for orthognathic planning and
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
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3.045 2.284 2.820 3.161 2.656 1.818 2.150 2.358 3.004 3.340 3.120 52.23 43.40 42.95 10.75 10.01 10.56 10.42 15.46 16.39 7.50 8.38 3.414 1.955 2.994 3.329 2.558 1.817 2.316 2.651 2.891 3.135 2.909 51.75 43.28 42.96 10.87 9.62 10.37 10.32 15.68 16.39 8.10 8.29 MSCT: multi-slice computed tomography; CBCT: cone beam computed tomography; SD: standard deviation; other abbreviations as per Table 1.
2.996 2.447 3.045 3.609 2.807 1.925 2.005 2.509 3.276 3.409 2.944 52.08 43.05 42.78 10.39 10.26 10.24 10.27 15.35 16.25 7.56 8.27 2.816 2.617 2.805 2.962 2.717 1.702 2.254 2.648 3.322 3.434 3.081 51.95 43.41 42.87 10.56 10.25 10.86 10.49 16.07 16.42 7.19 8.48 2.820 2.628 2.878 2.916 2.322 1.693 1.862 2.405 2.892 3.122 3.041 52.28 43.55 42.74 10.77 10.32 10.77 10.46 15.62 16.16 7.73 8.32 3.264 2.427 2.853 3.082 2.787 1.735 1.953 1.922 3.243 3.339 2.522 52.47 43.25 42.81 10.56 10.20 10.54 10.45 15.93 16.46 7.25 7.97 2.948 2.486 2.699 3.034 2.208 1.834 3.483 2.613 2.888 3.589 3.048 51.55 43.39 43.26 11.17 10.80 10.75 11.08 15.52 16.34 7.42 8.29 2.763 2.386 3.000 2.646 2.234 1.590 2.401 2.247 3.175 3.859 2.826 52.01 43.10 43.25 10.75 10.25 10.52 9.96 15.60 16.47 7.98 7.97
SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD
2.948 2.575 2.504 3.228 2.471 1.624 2.127 2.151 2.804 3.268 3.241 51.96 43.01 43.03 10.62 10.05 10.66 10.39 15.65 15.79 8.07 8.28 ANS–PNS LNW R LNW L LPtg R LPtg L TPtg R TPtg L LLpPtg R LLpPtg L LMpPtg R LMpPtg L
Physical measurements
Mean
Examiner 1: CBCT–second analysis Examiner 1: CBCT Examiner 2: MSCT–second analysis Examiner 2: MSCT Examiner 1: MSCT–second analysis Examiner 1: MSCT
Table 2. Comparison between MSCT and CBCT in comparison with physical measurements (means and standard deviations).
Examiner 2: CBCT
Examiner 2: CBCT–second analysis
Gold standard
Gaia et al. surgical simulation, associated with the rapidly emerging availability of this technology, has broadened the use and application of 3D imaging.15–19 The comparison between imaging and skull linear measurements is important to improve the surgical outcome. The results of our study show the great accuracy of real 3D linear measurements performed with specific software. The advantages and disadvantages of MSCT and CBCT have been published widely in the literature for several purposes, including analysis of diagnostic image quality, accuracy of pathological process diagnosis, and accuracy of linear and angular craniometric measurements.9– 11,20,21 There is evidence that both techniques are precise and accurate22; this is in agreement with our results, which showed accurate measurements for both acquisition and image modality. Several 3D techniques have been developed to compensate for the drawbacks of 2D measurements.23,24 Early recognition of possible anatomical differences can prevent intraoperative and postoperative complications, such as sensorial, neurological, or skeletal disturbances and bleeding, which may compromise a patient’s life.6,7,25,26 New software applications have been developed to enhance anatomical analysis pre-, intra-, and postoperatively in a single software platform, to minimize surgical complications and improve diagnosis and treatment planning and to obtain more predictable results after orthognathic surgery.4,5 Commercial software applications have similar tools that allow endocranial navigation, image rotation and translation, brightness and contrast adjustment, multiplanar and 3D reconstructions, and linear and angular measurement. However, a different reconstruction algorithm was developed to aid professionals in performing more accurate maxillofacial diagnoses and treatment planning; nonetheless, differences have been observed in both this reconstruction algorithm and the method of measurement used by these professionals. The reconstruction pattern (either surface or volumetric rendering) has been investigated previously,12,27 but the measurement evaluation patterns remain unclear. Different linear measurement methods are also available. This can affect the surgical planning and consequently compromise the surgical outcome. The methods used for linear and angular measurements differ significantly. Some software allows professionals to perform measurements over the reconstruction.
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
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Table 3. Intra-class correlation for each measurement performed by examiners 1 and 2 using MSCT and CBCT in comparison with physical measurements. Examiner 1: MSCT
Physical measurements ANS–PNS LNW R LNW L LPtg R LPtg L TPtg R TPtg L LLpPtg R LLpPtg L LMpPtg R LMpPtg L
Examiner 2: MSCT
Examiner 1: CBCT
Examiner 2: CBCT
ICC
(95% CI)
ICC
(95% CI)
ICC
(95% CI)
ICC
(95% CI)
0.97 0.89 0.98 0.96 0.93 0.94 0.94 0.90 0.95 0.90 0.97
(0.91–0.99) (0.63–0.97) (0.94–0.99) (0.86–0.99) (0.75–0.98) (0.80–0.98) (0.80–0.98) (0.65–0.97) (0.84–0.98) (0.66–0.97) (0.88–0.99)
0.95 0.89 0.96 0.98 0.74 0.97 0.80 0.96 0.97 0.98 0.96
(0.83–0.98) (0.63–0.97) (0.86–0.99) (0.92–0.99) (0.25–0.92) (0.88–0.99) (0.38–0.94) (0.87–0.99) (0.88–0.99) (0.93–0.99) (0.87–0.99)
0.98 0.96 0.97 0.97 0.95 0.96 0.97 0.96 0.98 0.98 0.98
(0.93–0.99) (0.88–0.99) (0.91–0.99) (0.90–0.99) (0.84–0.98) (0.87–0.99) (0.91–0.99) (0.86–0.99) (0.95–0.99) (0.92–0.99) (0.93–0.99)
0.93 0.96 0.94 0.93 0.97 0.95 0.95 0.96 0.94 0.97 0.95
(0.74–0.98) (0.85–0.99) (0.80–0.98) (0.77–0.98) (0.89–0.99) (0.82–0.98) (0.81–0.98) (0.84–0.98) (0.78–0.98) (0.89–0.99) (0.84–0.98)
MSCT: multi-slice computed tomography; CBCT: cone beam computed tomography; ICC: intra-class correlation coefficient; 95% CI, 95% confidence interval; other abbreviations as per Table 1.
Accordingly, this software allows 2D measurements over the 3D reconstruction, making it difficult to locate landmarks due to factors such as poor quality of the 3D reconstruction and the preclusion of multiplanar verification of the selected point. This can lead to a greater likelihood of errors in marking the points delimiting the anatomical structure. Other software, such as the Vitrea application used in the present study, determines the linear measurements based on predetermined points marked by multiplanar reconstruction (true 3D measurement). Marked points enable surgeons to determine the spatial location of the landmark exactly. This preciseness is required to perform linear measurements, by marking anatomical landmarks in different tomography slices (axial, coronal, and sagittal), and the software performs the measurements in high agreement with the gold standard (dry skull measurements), as found in the current research, thus enhancing the accuracy of the measurements. For professionals who are not used to handling image software, the proper way to recognize if the programme has
performed a true 3D measurement can be confirmed according to the following procedure: the operator must choose two different anatomical points on different CT slices (axial, coronal, or sagittal), and must then request and perform a linear measurement. If the programme calculates the linear measurement, it can then be said that this software enables a true 3D measurement. Albuquerque et al.11 used Vitrea software to determine the quantitative assessment of bone volume defects (oral clefts) using CT images to demarcate the limit of the bone defect, using MPR (true 3D measurements), as was done in the current study. They concluded that this method is a reliable and efficient technique to conduct volumetric assessments of bone defects of the cleft. All the measurements performed in our study showed a high accuracy between examiners and to the gold standard measurements. Intra- and inter-examiner analysis demonstrated no statistical difference for all anatomic structures, demonstrating that both MSCT and CBCT are precise. Based on the similarity of these results for linear measurements using a specific
Table 4. Inter-examiner analysis for MSCT and CBCT scans. Inter-examiner: MSCT ICC (95% CI) ANS–PNS LNW R LNW L LPtg R LPtg L TPtg R TPtg L LLpPtg R LLpPtg L LMpPtg R LMpPtg L
0.95 0.93 0.90 0.95 0.97 0.85 0.91 0.86 0.96 0.98 0.88
(0.85–0.99) (0.76–0.96) (0.80–0.98) (0.60–0.97) (0.91–0.99) (0.59–0.96) (0.71–0.97) (0.42–0.95) (0.85–0.99) (0.94–0.99) (0.58–0.96)
Inter-examiner: CBCT ICC (95% CI) 0.99 0.96 0.93 0.94 0.96 0.93 0.95 0.80 0.97 0.96 0.89
(0.96–0.99) (0.80–0.98) (0.74–0.98) (0.78–0.98) (0.79–0.98) (0.75–0.98) (0.76–0.98) (0.60–0.96) (0.89–0.99) (0.77–0.98) (0.60–0.96)
MSCT: multi-slice computed tomography; CBCT: cone beam computed tomography; ICC: intra-class correlation coefficient; 95% CI, 95% confidence interval; other abbreviations as per Table 1.
programme and different acquisition images (MSCT and CBCT), both types of image proved reliable in performing real 3D measurements for Le Fort I osteotomy planning. In agreement with our results, Lopes et al.,9 using the same software, found both the physical and 3D-based angular measurements by MSCT to be highly accurate. Moreira et al.10 found no statistically significant difference between physical and linear and angular measurements performed with CBCT and Vitrea software. Periago et al.28 compared the accuracy of linear measurements performed on 3DCBCT surface rendered images using Dolphin 3D (Dolphin Imaging, Chatsworth, CA, USA) with direct measurements on human skulls. They concluded that many linear measurements may be significantly different from anatomic dimensions statistically speaking, and considered some of them sufficiently accurate for craniofacial analyses, clinically speaking. In agreement with this finding, Berco et al.21 concluded that linear measurements made on CBCT, using the same software, enable clinically accurate and reliable 3D linear measurements, with an accuracy level limited in part to voxel size and method error. The wide-ranging linear measurements found in the publications of Periago et al.28 and Berco et al.21 could be explained by the fact that a different software programme, with a limited spatial interface, was used. In this regard, software that performs linear measurements over the 3D reconstructed images tends to show different results (statistically significant), since this measurement is considered a 2D measurement. Therefore, software that allows a true 3D linear measurement tends to show more accurate results, as found in our study.
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
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Table 5. Intra-examiner analysis for MSCT and CBCT scans. Examiner 1: MSCT
ANS–PNS LNW R LNW L LPtg R LPtg L TPtg R TPtg L LLpPtg R LLpPtg L LMpPtg R LMpPtg L
Examiner 2: MSCT
Examiner 1: CBCT
Examiner 2: CBCT
ICC
(95% CI)
ICC
(95% CI)
ICC
(95% CI)
ICC
(95% CI)
0.94 0.89 0.94 0.92 0.88 0.93 0.94 0.89 0.96 0.87 0.89
(0.86–0.99) (0.52–0.96) (0.78–0.98) (0.66–0.97) (0.54–0.96) (0.68–0.97) (0.84–0.98) (0.61–0.97) (0.81–0.98) (0.78–0.98) (0.72–0.98)
0.95 0.93 0.90 0.86 0.88 0.93 0.82 0.86 0.96 0.98 0.88
(0.66–0.97) (0.79–0.98) (0.77–0.98) (0.73–0.98) (0.71–0.97) (0.68–0.97) (0.77–0.98) (0.48–0.95) (0.84–0.98) (0.91–0.99) (0.75–0.98)
0.98 0.96 0.93 0.94 0.96 0.84 0.95 0.97 0.96 0.96 0.89
(0.94–0.99) (0.83–0.98) (0.81–0.98) (0.82–0.98) (0.85–0.99) (0.67–0.97) (0.75–0.97) (0.84–0.98) (0.75–0.98) (0.86–0.99) (0.71–0.97)
0.82 0.86 0.80 0.98 0.83 0.87 0.95 0.97 0.96 0.96 0.86
(0.54–0.96) (0.58–0.96) (0.63–0.97) (0.87–0.98) (0.50–0.95) (0.54–0.96) (0.77–0.98) (0.81–0.98) (0.77–0.98) (0.80–0.98) (0.50–0.95)
MSCT: multi-slice computed tomography; CBCT: cone beam computed tomography; ICC: intra-class correlation coefficient; 95% CI, 95% confidence interval; other abbreviations as per Table 1.
Lagrave`re et al.29 evaluated the accuracy of linear and angular measurements in 3D-CBCT images and found the mean measurement error to be less than 1 mm and 18 from the gold standard. These authors re-emphasized the possibility of using quantitative analyses for this kind of high quality image, and assumed this was a good result. However, we believe that 1 mm is a considerable distance when a posterior osteotomy of the maxilla is being performed, especially near the descending palatine artery. Determining the precise distance is very important for surgical planning, in order to prevent serious complications and thus decrease procedurerelated morbidity. The development of highly accurate 3D image software allowing the exact spatial location of the anatomical structures to be determined may be considered as producing effective results to prevent serious complications. The concept of image segmentation established on true Hounsfield units (HU) with MSCT and grey-scales in CBCT is not discussed in our paper because this does not influence our methods and results. Bryant et al.30 reported that segmentation on true HU and greyscales could influence the quality of the images in association with poorer object resolution and loss of fine detail, and have a great influence on the quality of 3D reconstruction. However the craniometric structures used in our paper were identified using MPR, eliminating or minimizing the interference on the results found. The 3D reconstructed images, which could be influenced by segmentation algorithms, were used in our study only to ensure that the anatomical structure was perfectly delimited, and did not influence the analysis of the anatomical structure. We studied Le Fort I osteotomy because the pterygoid bone presents important vascular structures (which can be the source
of major perioperative bleeding) and a higher incidence of unplanned fractures, and because there is difficulty in clearly identifying the bone structures in imaging modalities without reconstruction techniques. In conclusion, this study established that linear craniofacial measurements for Le Fort I osteotomy obtained with MSCT and CBCT are precise and accurate. The applicability of 3D reconstructed images using software that allows true 3D measurements was determined. A comparison of different 3D measurement techniques should be tested to compare the accuracy of the available software for image manipulation and orthognathic surgery planning. Funding
The authors would like to thank CAPES (Coordination of the Advancement of Higher Education, Brasilia, Brazil) for their financial support provided through a PhD grant (Bruno Gaia, Lucas Pinheiro, and Felipe Costa) and the CNPq (National Council for Development and Research, Brasilia, Brazil) for grants to Dr Marcelo Cavalcanti – Universal Research Project grant No. 472895/2009-5 and Research Productivity Scholarship grant No. 303847/2009-3. Competing interests
None declared. Ethical approval
Approval was granted by the Institutional Review Committee/Human Specimens Committee (0105.0.017.000-11). Acknowledgements. We acknowledge Claudio Mendes Pannuti, PhD, of the
Department of Periodontology, School of Dentistry, University of Sa˜o Paulo, for his review of the statistical analysis.
References 1. Cevidanes LH, Tucker S, Styner M, Kim H, Chapuis J, Reyes M, et al. Three-dimensional surgical simulation. Am J Orthod Dentofacial Orthop 2010;138:361–71. 2. Tucker S, Cevidanes LH, Styner M, Kim H, Reyes M, Proffit W, et al. Comparison of actual surgical outcomes and 3-dimensional surgical simulations. J Oral Maxillofac Surg 2010;68:2412–21. 3. Xia JJ, Gateno J, Teichgraeber JF. New clinical protocol to evaluate craniomaxillofacial deformity and plan surgical correction. J Oral Maxillofac Surg 2009;67:2093–106. 4. Swennen GR, Mollemans W, Schutyser F. Three-dimensional treatment planning of orthognathic surgery in the era of virtual imaging. J Oral Maxillofac Surg 2009;67:2080–92. 5. Popat H, Richmond S, Drage NA. New developments in: three-dimensional planning for orthognathic surgery. J Orthod 2010;37:62–71. 6. Pin˜eiro-Aguilar A, Somoza-Martı´n M, Gandara-Rey JM, Garcı´a-Garcı´a A. Blood loss in orthognathic surgery: a systematic review. J Oral Maxillofac Surg 2011;269:885–92. 7. Kim SG, Park SS. Incidence of complications and problems related to orthognathic surgery. J Oral Maxillofac Surg 2007;65:2438–44. 8. Quevedo LA, Ruiz JV, Quevedo CA. Using a clinical protocol for orthognathic surgery and assessing a 3-dimensional virtual approach: current therapy. J Oral Maxillofac Surg 2011;69:623–37. 9. Lopes PM, Moreira CR, Perrella A, Antunes JL, Cavalcanti MG. 3D volume rendering maxillofacial analysis of angular measurements by multislice CT. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008;105:224–30.
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3D CT for Le Fort I osteotomy 10. Moreira CR, Sales MA, Lopes PM, Cavalcanti MG. Assessment of linear and angular measurements on three-dimensional conebeam computed tomographic images. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:430–6. 11. Albuquerque MA, Gaia BF, Cavalcanti MG. Oral cleft volumetric assessment by 3D multislice computed tomographic images. Int J Oral Maxillofac Surg 2011;40:1280–8. 12. O’Regan B, Bharadwaj G. Prospective study of the incidence of serious posterior maxillary haemorrhage during a tuberosity osteotomy in low level Le Fort I operations. Br J Oral Maxillofac Surg 2007;45:538–42. 13. Ueki K, Hashiba Y, Marukawa K, Okabe K, Alam S, Nakagawa K, et al. Assessment of pterygomaxillary separation in Le Fort I osteotomy in Class III patients. J Oral Maxillofac Surg 2009;67:833–9. 14. Ueki K, Hashiba Y, Marukawa K, Nakagawa K, Okabe K, Yamamoto E. Determining the anatomy of the descending palatine artery and pterygoid plates with computed tomography in Class III patients. J Craniomaxillofac Surg 2009;37:469–73. 15. Kang SH, Kim MK, Park SY, Lee JY, Park W, Lee SH. Early orthognathic surgery with three-dimensional image simulation during presurgical orthodontics in adults. J Craniofac Surg 2011;22:473–81. 16. Danforth RA, Dus I, Mah J. 3D volume imaging for dentistry: a new dimension. J Calif Dent Assoc 2003;31:817–23. 17. Kau CH, Richmond S, Palomo JM, Hans MG. Three-dimensional cone beam computerized tomography in orthodontics. J Orthod 2005;32:282–93. 18. Cevidanes LH, Styner MA, Proffit WR. Image analysis and superimposition of 3dimensional cone-beam computed tomogra-
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Address: Marcelo Cavalcanti Department of Radiology College of Dentistry University of Sa˜o Paulo Av. Prof. Lineu Prestes 2227 CEP 05508-900 Sa˜o Paulo SP Brazil Tel: +55 11 3091 7807; Fax: +55 11 3091 7899/7831 E-mails: [email protected], [email protected]
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
Int. J. Oral Maxillofac. Surg. 2013; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2013.06.005, available online at http://www.sciencedirect.com
Clinical Paper Orthognathic Surgery
Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy
B. F. Gaia, L. R. Pinheiro, O. S. Umetsubo, F. F. Costa, M. G. P. Cavalcanti School of Dentistry, University of Sa˜o Paulo, Sa˜o Paulo, Brazil
B. F. Gaia, L. R. Pinheiro, O. S. Umetsubo, F. F. Costa, M. G. P. Cavalcanti: Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy. Int. J. Oral Maxillofac. Surg. 2013; xxx: xxx–xxx. # 2013 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Abstract. The purpose of this study was to test the precision and accuracy of threedimensional (3D) linear measurements for Le Fort I osteotomy, obtained from multi-slice computed tomography (MSCT) and cone beam computed tomography (CBCT) scans. The study population consisted of 11 dried skulls submitted to 64row MSCT and CBCT scans. Three-dimensional reconstructed images (3D-CT) were generated, and linear measurements (n = 11) based on anatomical structures and landmarks of interest for Le Fort I osteotomy were performed independently by two oral and maxillofacial radiologists, twice each, using Vitrea software; this allows true 3D measurement on 3D-CT images. The results demonstrated no statistically significant differences between the inter-examiner and intra-examiner analyses, and physical and true 3D linear measurements using MSCT and CBCT images. Regarding examiner accuracy, no statistically significant differences were found for the comparisons among the physical and the MSCT and the CBCT linear measurements by either examiner. For examiners 1 and 2, the analysis intraexaminer correlation coefficient ranged from 0.87 to 0.96 and 0.82 to 0.98, respectively, using MSCT, and from 0.84 to 0.98 and 0.80 to 0.98, respectively, using CBCT, indicating almost perfect agreement for all analyses performed. 3D linear measurements obtained from MSCT and CBCT images were considered precise and accurate for Le Fort I osteotomy and thus accurate and helpful for Le Fort I osteotomy planning.
Currently available three-dimensional (3D) software has been developed specifically to assist in the diagnosis, treatment planning, and prediction of outcomes related to orthognathic surgery and to prevent perioperative complications such as haemorrhage, permanent neural disorders, and 0901-5027/000001+07 $36.00/0
unplanned fractures, especially for the Le Fort I osteotomy involving the pterygoid process.1–8 However a large number of parameters are involved that could influence the surgeon’s analysis and consequently compromise the surgical outcome, such as different computed tomography image
Key words: three-dimensional; computed tomography; orthognathic surgery. Accepted for publication 10 June 2013
acquisition (multi-slice computed tomography – MSCT, and cone beam computed tomography – CBCT), different reconstruction algorithms, and different forms of linear measurement method. The purpose of this study was to test the precision and accuracy of 3D linear
# 2013 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
YIJOM-2714; No of Pages 7
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Gaia et al.
measurements for Le Fort I osteotomy obtained from MSCT and CBCT scans. Materials and methods Sample
The study population consisted of 11 intact human skulls (eight male and three female, aged 19–56 years), provided by the institution’s department of anatomy. Approval was granted by the institutional review committee/human specimens committee. There was no ethnic or gender preference when selecting the sample, and no history of bone disease was identified in the medical records.
Data collection
Before scanning the skulls, the mandibles were fixed to the skulls in central occlusion using tape. The skulls were placed in a plastic bucket with water for MSCT and in a bulk bag with water for CBCT, for beam attenuation and to mimic the soft tissues, in accordance with previously published methods.9–11 The skulls were then placed in the equipment to keep them in a position similar to that of the clinical situation for the MSCT and CBCT. The specimens were first submitted to a 64-row multi-slice CT procedure (Aquilion; Toshiba America Medical Systems Inc., Tustin, CA, USA). The boundaries of the imaging area were set superior to the vertex and extended inferiorly to below the mandible. High-resolution contiguous images were obtained following the acquisition image protocol (0.5 mm thick axial slices, 0.3 mm of reconstruction interval per 0.4 s of time, 512 512 matrix, 120 kVp and 300 mA, and 24.0 cm field of view), associated with a low frequency filter (bone filter). Subsequently, the skulls
were submitted to a CBCT scan (i-CAT Cone Beam 3D Dental Imaging System, Imaging Sciences International, Hatfield, PA, USA) at 0.25-mm voxel size for 40 s to acquire raw data. The field of view (FOV) was a 20-cm height and 16-cm diameter cylinder. The grey-scale range of the acquired images was 14 bits. After the original image was acquired, these data were recorded and stored in DICOM format (Digital Imaging Communication in Medicine) to avoid data loss. Multiplanar (MPR; axial, coronal, and sagittal) and 3D-CT reconstructed images using the bone protocol were obtained simultaneously, based on the original axial slices, and were generated in Vitrea version 3.8.1 software (Vital Images Inc., Plymouth, MN, USA) installed in a Dell 650 Precision independent workstation (Dell Computer Corp., Round Rock, TX, USA) running the Windows XP operational system (Microsoft, Redmond, WA, USA). Two oral and maxillofacial radiologists, with extensive experience in interpreting CT and knowledge of the software tools, were calibrated prior to study commencement. Linear measurements of the 3D coordinates used for this study were obtained using the anatomical structures described in Table 1. Most of the bone structures were selected expressly, instead of using the traditional craniometric points, since analysis of these structures is highly relevant in the planning of the Le Fort I osteotomy12–14 (Table 1). The examiners performed a total analysis of the volume using axial and MPR images, and pointed to the initial mark of the anatomical structure using an arrow. This first point was performed over the MPR and automatically transferred to the 3D reconstruction image. The examiners verified and confirmed the exact location
of the marked predefined structure point using rotation, translation, and transparency software tools. This point was considered the initial mark for true 3D linear measurements. Then, the volume was analysed again, and the second point was determined following the same steps described above (Figs 1 and 2). All measurements (n = 11) were performed for each of the scanned skulls and were made electronically by two oral and maxillofacial radiologists (twice each), independently, with a 7-day time interval between the repeated measurements to ensure intra-examiner and inter-examiner reliability. In all, 968 image measurements were made. The mean value for each measurement was obtained from all measurements performed on the 11 dry skulls. To obtain the physical data, a third examiner who had no knowledge of the imaging measurements, performed measurements of the same sets of landmarks directly on the dry skull, with a 7-day time interval between the repeated measurements. Linear dry skull measurements were obtained with a digital calliper (167 series; Mitutoyo Sul Americana Ltda, Suzano, SP, Brazil), the same device as used by Lopes et al.9 and Moreira et al.,10 with a 0.3 mm active point. Data analysis
Data analysis consisted of comparing dry skull measurements (gold standard) with 3D-MSCT and 3D-CBCT linear measurements obtained in true 3D measurement software. Precision was assessed based on the intra-examiner and inter-examiner measurements, and accuracy based on the difference between the measurements performed by the examiners and the corresponding physical measurements. The
Table 1. Description of the craniometric anatomical structures and respective linear measurements. Anatomical structures Length of maxilla (ANS–PNS) Length of lateral nasal walla (LNW) Length of the pterygoid processa (LPtg) Thickness of the junction between the pterygoid process and the tuberosity of the maxillaa (TPtg) Length of the lateral plate of the pterygoid processa (LLpPtg) Length of the medial plate of the pterygoid processa (LMpPtg) a
Description Distance between the anterior (ANS) and posterior nasal spine (PNS), determining the total length of the maxilla Distance from the piriform aperture (15 mm above the ANS) up to the anterior portion of the descending palatine artery canal, determining the length of the lateral nasal wall Distance representing the length of the bone fusion of the pterygoid process of the sphenoid bone to the tuberosity of the maxilla (lateral view) Distance between the lateral and medial point of the bone fusion of the pterygoid process to the tuberosity of the maxilla, representing the length of the bone fusion (axial view) Distance between a point in the pterygoid fossa (that was the shortest distance to the descending palatine artery canal) and the distal portion of the lateral pterygoid plate, representing the length of the lateral plate of the pterygoid process Distance between a point in the pterygoid fossa (that was the shortest distance to the descending palatine artery canal) and the distal portion of the medial pterygoid plate, representing the length of the medial plate of the pterygoid process
Measurements made on the right (R) and left (L) sides of the anatomical structure.
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
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two initial observations of the examiners were considered as sample 1, and the two further observations as sample 2. For the inter-examiner agreement, only the first set of measurements was used. Intraexaminer, inter-examiner, and gold standard comparisons, as well the correlation between all individual measurements performed by examiners 1 and 2 using MSCT and CBCT and the gold standard, were conducted using the intra-class correlation coefficient (ICC), with a 95% confidence interval (95% CI). Results
Fig. 1. ANS–PNS linear measurement obtained from 3D-CBCT. (A) Axial, (B) sagittal, and (C) coronal views, showing the ANS point (yellow arrow), using multiplanar reconstruction. (D) 3D reconstructed image showing the ANS point marked (yellow arrow) to confirm the exact position, using software tools such as rotation, translation, and transparency.
Fig. 2. The same skull as in Fig. 1, showing the ANS–PNS linear measurement process. (A) Axial and (B) sagittal views, showing the PNS and ANS points (yellow arrow). (C) Coronal view showing the PNS point. (D) 3D reconstructed image demonstrating the true 3D measurement for the length of the maxilla (53.5 mm) based on the previously marked ANS–PNS points.
The results for the linear measurements are shown in Tables 2–5. Table 2 shows the means and standard deviations in millimetres of MSCT, CBCT, and physical measurements. The highest mean difference for each measurement was found for LMpPtg R: for both examiners using MSCT images, and for examiner 1 using CBCT. The highest mean differences found for examiner 2 were LPtg R (3.609 (SD)) and ANS–PNS (3.414 (SD)) using CBCT images (Table 2). The mean differences between the physical and the true 3D linear measurements using MSCT ranged from 0.05 to 0.68 mm for examiner 1, and from 0.12 to 0.92 mm for examiner 2. Regarding the CBCT images, the mean differences ranged from 0.03 to 0.54 mm for examiner 1 and from 0.02 to 0.64 mm for examiner 2 (Table 2). Table 3 shows that all measurements performed by examiners 1 and 2 using MSCT and CBCT presented excellent to good agreement (Table 3). The analysis inter-examiner correlation coefficient ranged from 0.85 to 0.98 for MSCT and from 0.80 to 0.99 for CBCT, indicating a moderate to almost perfect agreement between examiners (Table 4). The highest difference from the gold standard for each measurement was found for TPtg R using MSCT images and LLpPtg R using CBCT, although both results showed good agreement. The analysis intra-examiner correlation coefficient ranged from 0.87 to 0.96 and 0.82 to 0.98 for examiners 1 and 2, respectively, using MSCT, indicating almost perfect agreement. Using CBCT, the intra-class correlation coefficient ranged from 0.84 to 0.98 for examiner 1 and from 0.80 to 0.98 for examiner 2, indicating almost perfect agreement (Table 5). Discussion
The introduction of 3D tomography images for orthognathic planning and
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
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3.045 2.284 2.820 3.161 2.656 1.818 2.150 2.358 3.004 3.340 3.120 52.23 43.40 42.95 10.75 10.01 10.56 10.42 15.46 16.39 7.50 8.38 3.414 1.955 2.994 3.329 2.558 1.817 2.316 2.651 2.891 3.135 2.909 51.75 43.28 42.96 10.87 9.62 10.37 10.32 15.68 16.39 8.10 8.29 MSCT: multi-slice computed tomography; CBCT: cone beam computed tomography; SD: standard deviation; other abbreviations as per Table 1.
2.996 2.447 3.045 3.609 2.807 1.925 2.005 2.509 3.276 3.409 2.944 52.08 43.05 42.78 10.39 10.26 10.24 10.27 15.35 16.25 7.56 8.27 2.816 2.617 2.805 2.962 2.717 1.702 2.254 2.648 3.322 3.434 3.081 51.95 43.41 42.87 10.56 10.25 10.86 10.49 16.07 16.42 7.19 8.48 2.820 2.628 2.878 2.916 2.322 1.693 1.862 2.405 2.892 3.122 3.041 52.28 43.55 42.74 10.77 10.32 10.77 10.46 15.62 16.16 7.73 8.32 3.264 2.427 2.853 3.082 2.787 1.735 1.953 1.922 3.243 3.339 2.522 52.47 43.25 42.81 10.56 10.20 10.54 10.45 15.93 16.46 7.25 7.97 2.948 2.486 2.699 3.034 2.208 1.834 3.483 2.613 2.888 3.589 3.048 51.55 43.39 43.26 11.17 10.80 10.75 11.08 15.52 16.34 7.42 8.29 2.763 2.386 3.000 2.646 2.234 1.590 2.401 2.247 3.175 3.859 2.826 52.01 43.10 43.25 10.75 10.25 10.52 9.96 15.60 16.47 7.98 7.97
SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD
2.948 2.575 2.504 3.228 2.471 1.624 2.127 2.151 2.804 3.268 3.241 51.96 43.01 43.03 10.62 10.05 10.66 10.39 15.65 15.79 8.07 8.28 ANS–PNS LNW R LNW L LPtg R LPtg L TPtg R TPtg L LLpPtg R LLpPtg L LMpPtg R LMpPtg L
Physical measurements
Mean
Examiner 1: CBCT–second analysis Examiner 1: CBCT Examiner 2: MSCT–second analysis Examiner 2: MSCT Examiner 1: MSCT–second analysis Examiner 1: MSCT
Table 2. Comparison between MSCT and CBCT in comparison with physical measurements (means and standard deviations).
Examiner 2: CBCT
Examiner 2: CBCT–second analysis
Gold standard
Gaia et al. surgical simulation, associated with the rapidly emerging availability of this technology, has broadened the use and application of 3D imaging.15–19 The comparison between imaging and skull linear measurements is important to improve the surgical outcome. The results of our study show the great accuracy of real 3D linear measurements performed with specific software. The advantages and disadvantages of MSCT and CBCT have been published widely in the literature for several purposes, including analysis of diagnostic image quality, accuracy of pathological process diagnosis, and accuracy of linear and angular craniometric measurements.9– 11,20,21 There is evidence that both techniques are precise and accurate22; this is in agreement with our results, which showed accurate measurements for both acquisition and image modality. Several 3D techniques have been developed to compensate for the drawbacks of 2D measurements.23,24 Early recognition of possible anatomical differences can prevent intraoperative and postoperative complications, such as sensorial, neurological, or skeletal disturbances and bleeding, which may compromise a patient’s life.6,7,25,26 New software applications have been developed to enhance anatomical analysis pre-, intra-, and postoperatively in a single software platform, to minimize surgical complications and improve diagnosis and treatment planning and to obtain more predictable results after orthognathic surgery.4,5 Commercial software applications have similar tools that allow endocranial navigation, image rotation and translation, brightness and contrast adjustment, multiplanar and 3D reconstructions, and linear and angular measurement. However, a different reconstruction algorithm was developed to aid professionals in performing more accurate maxillofacial diagnoses and treatment planning; nonetheless, differences have been observed in both this reconstruction algorithm and the method of measurement used by these professionals. The reconstruction pattern (either surface or volumetric rendering) has been investigated previously,12,27 but the measurement evaluation patterns remain unclear. Different linear measurement methods are also available. This can affect the surgical planning and consequently compromise the surgical outcome. The methods used for linear and angular measurements differ significantly. Some software allows professionals to perform measurements over the reconstruction.
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
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Table 3. Intra-class correlation for each measurement performed by examiners 1 and 2 using MSCT and CBCT in comparison with physical measurements. Examiner 1: MSCT
Physical measurements ANS–PNS LNW R LNW L LPtg R LPtg L TPtg R TPtg L LLpPtg R LLpPtg L LMpPtg R LMpPtg L
Examiner 2: MSCT
Examiner 1: CBCT
Examiner 2: CBCT
ICC
(95% CI)
ICC
(95% CI)
ICC
(95% CI)
ICC
(95% CI)
0.97 0.89 0.98 0.96 0.93 0.94 0.94 0.90 0.95 0.90 0.97
(0.91–0.99) (0.63–0.97) (0.94–0.99) (0.86–0.99) (0.75–0.98) (0.80–0.98) (0.80–0.98) (0.65–0.97) (0.84–0.98) (0.66–0.97) (0.88–0.99)
0.95 0.89 0.96 0.98 0.74 0.97 0.80 0.96 0.97 0.98 0.96
(0.83–0.98) (0.63–0.97) (0.86–0.99) (0.92–0.99) (0.25–0.92) (0.88–0.99) (0.38–0.94) (0.87–0.99) (0.88–0.99) (0.93–0.99) (0.87–0.99)
0.98 0.96 0.97 0.97 0.95 0.96 0.97 0.96 0.98 0.98 0.98
(0.93–0.99) (0.88–0.99) (0.91–0.99) (0.90–0.99) (0.84–0.98) (0.87–0.99) (0.91–0.99) (0.86–0.99) (0.95–0.99) (0.92–0.99) (0.93–0.99)
0.93 0.96 0.94 0.93 0.97 0.95 0.95 0.96 0.94 0.97 0.95
(0.74–0.98) (0.85–0.99) (0.80–0.98) (0.77–0.98) (0.89–0.99) (0.82–0.98) (0.81–0.98) (0.84–0.98) (0.78–0.98) (0.89–0.99) (0.84–0.98)
MSCT: multi-slice computed tomography; CBCT: cone beam computed tomography; ICC: intra-class correlation coefficient; 95% CI, 95% confidence interval; other abbreviations as per Table 1.
Accordingly, this software allows 2D measurements over the 3D reconstruction, making it difficult to locate landmarks due to factors such as poor quality of the 3D reconstruction and the preclusion of multiplanar verification of the selected point. This can lead to a greater likelihood of errors in marking the points delimiting the anatomical structure. Other software, such as the Vitrea application used in the present study, determines the linear measurements based on predetermined points marked by multiplanar reconstruction (true 3D measurement). Marked points enable surgeons to determine the spatial location of the landmark exactly. This preciseness is required to perform linear measurements, by marking anatomical landmarks in different tomography slices (axial, coronal, and sagittal), and the software performs the measurements in high agreement with the gold standard (dry skull measurements), as found in the current research, thus enhancing the accuracy of the measurements. For professionals who are not used to handling image software, the proper way to recognize if the programme has
performed a true 3D measurement can be confirmed according to the following procedure: the operator must choose two different anatomical points on different CT slices (axial, coronal, or sagittal), and must then request and perform a linear measurement. If the programme calculates the linear measurement, it can then be said that this software enables a true 3D measurement. Albuquerque et al.11 used Vitrea software to determine the quantitative assessment of bone volume defects (oral clefts) using CT images to demarcate the limit of the bone defect, using MPR (true 3D measurements), as was done in the current study. They concluded that this method is a reliable and efficient technique to conduct volumetric assessments of bone defects of the cleft. All the measurements performed in our study showed a high accuracy between examiners and to the gold standard measurements. Intra- and inter-examiner analysis demonstrated no statistical difference for all anatomic structures, demonstrating that both MSCT and CBCT are precise. Based on the similarity of these results for linear measurements using a specific
Table 4. Inter-examiner analysis for MSCT and CBCT scans. Inter-examiner: MSCT ICC (95% CI) ANS–PNS LNW R LNW L LPtg R LPtg L TPtg R TPtg L LLpPtg R LLpPtg L LMpPtg R LMpPtg L
0.95 0.93 0.90 0.95 0.97 0.85 0.91 0.86 0.96 0.98 0.88
(0.85–0.99) (0.76–0.96) (0.80–0.98) (0.60–0.97) (0.91–0.99) (0.59–0.96) (0.71–0.97) (0.42–0.95) (0.85–0.99) (0.94–0.99) (0.58–0.96)
Inter-examiner: CBCT ICC (95% CI) 0.99 0.96 0.93 0.94 0.96 0.93 0.95 0.80 0.97 0.96 0.89
(0.96–0.99) (0.80–0.98) (0.74–0.98) (0.78–0.98) (0.79–0.98) (0.75–0.98) (0.76–0.98) (0.60–0.96) (0.89–0.99) (0.77–0.98) (0.60–0.96)
MSCT: multi-slice computed tomography; CBCT: cone beam computed tomography; ICC: intra-class correlation coefficient; 95% CI, 95% confidence interval; other abbreviations as per Table 1.
programme and different acquisition images (MSCT and CBCT), both types of image proved reliable in performing real 3D measurements for Le Fort I osteotomy planning. In agreement with our results, Lopes et al.,9 using the same software, found both the physical and 3D-based angular measurements by MSCT to be highly accurate. Moreira et al.10 found no statistically significant difference between physical and linear and angular measurements performed with CBCT and Vitrea software. Periago et al.28 compared the accuracy of linear measurements performed on 3DCBCT surface rendered images using Dolphin 3D (Dolphin Imaging, Chatsworth, CA, USA) with direct measurements on human skulls. They concluded that many linear measurements may be significantly different from anatomic dimensions statistically speaking, and considered some of them sufficiently accurate for craniofacial analyses, clinically speaking. In agreement with this finding, Berco et al.21 concluded that linear measurements made on CBCT, using the same software, enable clinically accurate and reliable 3D linear measurements, with an accuracy level limited in part to voxel size and method error. The wide-ranging linear measurements found in the publications of Periago et al.28 and Berco et al.21 could be explained by the fact that a different software programme, with a limited spatial interface, was used. In this regard, software that performs linear measurements over the 3D reconstructed images tends to show different results (statistically significant), since this measurement is considered a 2D measurement. Therefore, software that allows a true 3D linear measurement tends to show more accurate results, as found in our study.
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005
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Gaia et al.
Table 5. Intra-examiner analysis for MSCT and CBCT scans. Examiner 1: MSCT
ANS–PNS LNW R LNW L LPtg R LPtg L TPtg R TPtg L LLpPtg R LLpPtg L LMpPtg R LMpPtg L
Examiner 2: MSCT
Examiner 1: CBCT
Examiner 2: CBCT
ICC
(95% CI)
ICC
(95% CI)
ICC
(95% CI)
ICC
(95% CI)
0.94 0.89 0.94 0.92 0.88 0.93 0.94 0.89 0.96 0.87 0.89
(0.86–0.99) (0.52–0.96) (0.78–0.98) (0.66–0.97) (0.54–0.96) (0.68–0.97) (0.84–0.98) (0.61–0.97) (0.81–0.98) (0.78–0.98) (0.72–0.98)
0.95 0.93 0.90 0.86 0.88 0.93 0.82 0.86 0.96 0.98 0.88
(0.66–0.97) (0.79–0.98) (0.77–0.98) (0.73–0.98) (0.71–0.97) (0.68–0.97) (0.77–0.98) (0.48–0.95) (0.84–0.98) (0.91–0.99) (0.75–0.98)
0.98 0.96 0.93 0.94 0.96 0.84 0.95 0.97 0.96 0.96 0.89
(0.94–0.99) (0.83–0.98) (0.81–0.98) (0.82–0.98) (0.85–0.99) (0.67–0.97) (0.75–0.97) (0.84–0.98) (0.75–0.98) (0.86–0.99) (0.71–0.97)
0.82 0.86 0.80 0.98 0.83 0.87 0.95 0.97 0.96 0.96 0.86
(0.54–0.96) (0.58–0.96) (0.63–0.97) (0.87–0.98) (0.50–0.95) (0.54–0.96) (0.77–0.98) (0.81–0.98) (0.77–0.98) (0.80–0.98) (0.50–0.95)
MSCT: multi-slice computed tomography; CBCT: cone beam computed tomography; ICC: intra-class correlation coefficient; 95% CI, 95% confidence interval; other abbreviations as per Table 1.
Lagrave`re et al.29 evaluated the accuracy of linear and angular measurements in 3D-CBCT images and found the mean measurement error to be less than 1 mm and 18 from the gold standard. These authors re-emphasized the possibility of using quantitative analyses for this kind of high quality image, and assumed this was a good result. However, we believe that 1 mm is a considerable distance when a posterior osteotomy of the maxilla is being performed, especially near the descending palatine artery. Determining the precise distance is very important for surgical planning, in order to prevent serious complications and thus decrease procedurerelated morbidity. The development of highly accurate 3D image software allowing the exact spatial location of the anatomical structures to be determined may be considered as producing effective results to prevent serious complications. The concept of image segmentation established on true Hounsfield units (HU) with MSCT and grey-scales in CBCT is not discussed in our paper because this does not influence our methods and results. Bryant et al.30 reported that segmentation on true HU and greyscales could influence the quality of the images in association with poorer object resolution and loss of fine detail, and have a great influence on the quality of 3D reconstruction. However the craniometric structures used in our paper were identified using MPR, eliminating or minimizing the interference on the results found. The 3D reconstructed images, which could be influenced by segmentation algorithms, were used in our study only to ensure that the anatomical structure was perfectly delimited, and did not influence the analysis of the anatomical structure. We studied Le Fort I osteotomy because the pterygoid bone presents important vascular structures (which can be the source
of major perioperative bleeding) and a higher incidence of unplanned fractures, and because there is difficulty in clearly identifying the bone structures in imaging modalities without reconstruction techniques. In conclusion, this study established that linear craniofacial measurements for Le Fort I osteotomy obtained with MSCT and CBCT are precise and accurate. The applicability of 3D reconstructed images using software that allows true 3D measurements was determined. A comparison of different 3D measurement techniques should be tested to compare the accuracy of the available software for image manipulation and orthognathic surgery planning. Funding
The authors would like to thank CAPES (Coordination of the Advancement of Higher Education, Brasilia, Brazil) for their financial support provided through a PhD grant (Bruno Gaia, Lucas Pinheiro, and Felipe Costa) and the CNPq (National Council for Development and Research, Brasilia, Brazil) for grants to Dr Marcelo Cavalcanti – Universal Research Project grant No. 472895/2009-5 and Research Productivity Scholarship grant No. 303847/2009-3. Competing interests
None declared. Ethical approval
Approval was granted by the Institutional Review Committee/Human Specimens Committee (0105.0.017.000-11). Acknowledgements. We acknowledge Claudio Mendes Pannuti, PhD, of the
Department of Periodontology, School of Dentistry, University of Sa˜o Paulo, for his review of the statistical analysis.
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Address: Marcelo Cavalcanti Department of Radiology College of Dentistry University of Sa˜o Paulo Av. Prof. Lineu Prestes 2227 CEP 05508-900 Sa˜o Paulo SP Brazil Tel: +55 11 3091 7807; Fax: +55 11 3091 7899/7831 E-mails: [email protected], [email protected]
Please cite this article in press as: Gaia BF, et al. Validity of three-dimensional computed tomography measurements for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2013), http://dx.doi.org/10.1016/j.ijom.2013.06.005