Análise Angular 3D em CT Multislice

Prévia do material em texto

3-D volume rendering maxillofacial analysis of angular
measurements by multislice CT
Patricia M. L. Lopes, DDS, PhD,a Carla R. Moreira, DDS, MS,b Andréia Perrella, DDS, MS,c
José L. Antunes, PhD,d and Marcelo G. P. Cavalcanti, DDS, PhD,e João Pessoa, Brazil, Bauru,
Brazil, and São Paulo, Brazil
CENTRO UNIVERSITÁRIO DE JOÃO PESSOA AND UNIVERSITY OF SÃO PAULO
Objective. This study was designed to determine the precision and accuracy of angular measurements using three-
dimensional computed tomography (3D-CT) volume rendering by computer systems.
Study design. The study population consisted of 28 dried skulls that were scanned with a 64-row multislice CT, and
3D-CT images were generated. Angular measurements, (n � 6) based upon conventional craniometric anatomical
landmarks (n � 9), were identified independently in 3D-CT images by 2 radiologists, twice each, and were then
performed by 3D-CT imaging. Subsequently, physical measurements were made by a third examiner using a Beyond
Crysta-C9168 series 900 device.
Results. The results demonstrated no statistically significant difference between interexaminer and intraexaminer
analysis. The mean difference between the physical and 3-D–based angular measurements was �1.18% and �0.89%,
respectively, for both examiners, demonstrating high accuracy.
Conclusion. Maxillofacial analysis of angular measurements using 3D-CT volume rendering by 64-row multislice CT is
established and can be used for orthodontic and dentofacial orthopedic applications. (Oral Surg Oral Med Oral
Pathol Oral Radiol Endod 2008;105:224-30)
With the improvement of three-dimensional (3-D) im-
aging technology, more accurate analysis of craniofa-
cial complex can be achieved. Several computer 3-D
methods have been developed to assist diagnosis, treat-
ment planning, and predict outcomes.1-7
Despite evolution in the orthodontic field, evalua-
tion of facial growth and dental relationship through
cephalometrics is still a difficult frontier to cross. In
this regard, 3-D analysis is essential for precisely
assessing craniofacial morphology. For orthodontic
purposes, software tools to facilitate accurate land-
mark identification for quantitative measurements
and the 3-D segmentation of regions of interest are
This research was supported by Foundation of Research of São Paulo
State (grants 2005/02157-8 to M. G. P. C.) and CAPES (PhD schol-
arships to A. P., C. R. M., and P. M. L. L.).
aProfessor, Department of Social Dentistry, College of Dentistry,
Centro Universitário de João Pessoa, João Pessoa, Brazil.
bStudent, Department of Stomatology, College of Dentistry, Univer-
sity of São Paulo, Bauru, Brazil.
cStudent, Department of Stomatology, College of Dentistry, Univer-
sity of São Paulo, São Paulo, Brazil.
dProfessor, Department of Social and Preventive Dentistry, College
of Dentistry, University of São Paulo, São Paulo, Brazil.
eProfessor, Department of Stomatology, College of Dentistry, Uni-
versity of São Paulo, São Paulo, Brazil.
Received for publication Jun 12, 2007; returned for revision Aug 24,
2007; accepted for publication Aug 28, 2007.
1079-2104/$ - see front matter
© 2008 Mosby, Inc. All rights reserved.
doi:10.1016/j.tripleo.2007.08.036
224
progressing.3-5,8 Three-dimensional analysis is es-
sential for precisely assessing craniofacial morphol-
ogy. Several 3-D techniques have been developed to
compensate for the drawbacks of two-dimensional
measurements.3
The accuracy of selected craniometric linear mea-
surements in a 3-D surface-shaded rendering tech-
nique from a single-slice computed tomographic
(CT) system has been reported.9 Recently, a three-
dimensional computed tomographic (3D-CT) vol-
ume-rendering protocol regarding several linear
craniometric measurements from multislice com-
puted tomography (MSCT) was evaluated for accu-
racy and precision of the system.10 There has, how-
ever, been no report regarding the validation of the
angular measurements using specific computer sys-
tem 3D-CT volume-rendering tools in association
with the newer generations of multislice CT
(MSCT).
The purpose of this research is to demonstrate the
precision and accuracy of angular measurements by
using 3-D volume-rendering imaging using 64-row
multislice CT for orthodontic applications.
MATERIAL AND METHODS
The study population consisted of 28 intact dry
skulls (5 females and 23 males), from 20 years old to
56 years old, provided by the Department of Anat-
omy, Federal University of Sao Paulo, of a medical
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Volume 105, Number 2 Lopes et al. 225
school, following approval by the Institutional Re-
view Committee/Human Specimens Committee
(School of Dentistry, University of Sao Paulo). No
history of bone disease was identified in the medical
records.
Before scanning, the mandibles were fixed to the
skulls in central occlusion by using tape. The axial slice
direction was assured by placing the skulls in the scan-
ner so that the Frankfurt plane was perpendicular to the
table and parallel to the sagittal plane. For imaging,
each skull was placed into a plastic bucket with water
to attenuate the radiation in a manner resembling that of
soft tissue. The scanning position was kept close to the
in vivo situation.
The specimens were scanned in 64-row multislice
CT (Aquilion, Toshiba-America Medical Systems Inc.,
Tustin, CA), beginning superior to the vertex and extend-
ing inferiorly to below the mandible. High-resolution
contiguous images were obtained with 0.5-mm thick
axial slices with 0.3 mm of reconstruction interval per
0.4 seconds of time, 512 � 512 matrix, and 120 kVp
and 300 mA, and a low frequency filter cutoff was used
in the reconstruction algorithm (bone filter). The field
of view was 24.0 cm. The original CT data were stored
on a CD-ROM to allow full retrospective review of any
data and image processing and transferred to an inde-
pendent workstation with Vitrea version 3.5 software
(Vital Images Inc., Plymouth, MN) to generate 3-D
volumetric images for visualization, manipulation, and
analysis.
Multiplanar (coronal and sagittal) and 3-D recon-
structed images using bone protocol were obtained simul-
taneously based on the original axial slices. In axial and in
the correspondent multiplanar reconstructed images, it
was possible to estimate certain landmark locations,
and these were automatically marked in the 3-D im-
ages.
Angular measurements of 3-D coordinates were ob-
tained using several unique and conventional cranio-
metric anatomic landmarks previously used by Caval-
canti and Vannier9 and by Cavalcanti et al.10 (Table I).
The computer graphics system allowed 3D-CT mea-
surements from different views by using rotation and
translation of the image rendered, and by using trans-
parency tools (Fig. 1). The craniometric points (n � 9;
Table I) were located and the correspondent angular
measurements (n � 6; Fig. 1 and Table II) were deter-
mined electronically by 2 examiners twice each, inde-
pendently, by using computer software tools. For each
skull, all points were located during 1 reading session,
and then the correspondent angular measurements were
obtained by computer tools. The time interval between
the repeated measurements for intraexaminer reliability
determination was 7 days for each examiner. The 28
skulls were scanned by the same MSCT scanner on the
same day. All measurements were made in an average
time of 20 minutes per skull.
In total, 672 image measurements were made. The
visualization, required adjustments, and analysis were
possible by using preestablished criteria for bone tissue
protocols. The parameters used were (1) the right side
was used to locate lateral points, (2) frontal and lateral
positions were standardized using program functions,
and (3) the same head position was utilized to deter-
mine the measurements in the 2 types of protocols
examined.10
To obtain the physical data, the mandibles were
positioned at the same occlusal relationship as they
were during image acquisition, and the set of landmark
measurements was performedonce by a third examiner.
A Beyond Crysta-C9168 series 900 device (Mitutoyo
Sul Americana Ltda, Suzano, SP, Brazil) was used for
3-D coordinates. This device was located at the Labo-
ratory for Reference in Measures for Coordinates (Mi-
tutoyo, Suzano, SP, Brazil). This equipment function is
based on a Cartesian 3-D system with 3 reading scales,
which allows the mapping of any point within the limits
of the equipment. The device had an active point that is
0.3-mm thick, to be equal to the thickness interval of CT
reconstruction. The data was imported to a personal com-
puter with Windows XP (Microsoft Corporation, Red-
mond, WA) operating system (Fig. 2, A, B). Geopak-
Win Version 2.4 R.8 Edition 10 (Mitutoyo, Neuss,
Germany) was used for making measurements. This
software collects all information from the coordinates
of each landmark and performs the correspondent cal-
culations to generate the results (angular measure-
ments). The device was calibration certified by Inmetro
(National Institute of Metrology, Rio de Janeiro, RJ,
Table I. Craniometric anatomical points
1. A Alveolare, deepest point of the maxillary alveolar bone
concavity
2. G Glabella, most anterior point of the skull in the sagittal
plane
3. Me Menton, most inferior and anterior point of the mental
region
4. N Nasion, medial point between the nasofrontal suture
and the nasal origin in midsagittal plane
5. Co Condylion, most posterior and superior point of the
mandibular condyle
6. ENA Anterior nasal spine, highest point on nasal spine
7. Go Gonion, most posterior and inferior point of the curve
between the body and ascending ramus of the
mandible
8. Pg Pogonion, most anterior point of the mental symphysis
9. B The deepest point of the mandibular alveolar concavity
Brazil). The direct measurements of the dry skulls were
n-alve
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226 Lopes et al. February 2008
considered as the gold standard for physical measure-
ments.
The validity of 3D-CT measurements was assessed
in terms of their differences, both in degree and per-
centages, to corresponding physical measurements. The
precision of 3D-CT was assessed in terms of the in-
traexaminer and interexaminer measurement, both in
terms of angular degree and percentage. Both validity
and precision analysis followed the criteria of Bland
and Altman.11 This method is based on simple calcu-
lation of the difference between 2 compared measure-
ments, following the formulas below:
● for precision:
intraexaminer difference (in degrees) � measure-
ment 1 � measurement 2
intraexaminer difference (in percentage) � 100 �
(measurement 1 � measurement 2)/measurement 1
interexaminer difference � examiner 1 � examiner 2
interexaminer difference (in percentage) � 100 �
Fig. 1. Three-dimensional computed tomographic measureme
B, Lateral view of glabella-anterior nasal spine-pogonion
spine-menton (N.ANS.Me; 166.9°). D, Frontal view of nasio
gonion-menton (Co.Go.Me; 126.7°). F, Frontal view of nasio
Table II. Angular measurements
1. N.A.Pg
2. G.ENA.Pg
3. N.ENA.Me
4. N.Me.Go
5. Co.Go.Me
6. N.A.B
(examiner 1 � examiner 2)/examiner 1
● for validation:
validation in degrees � examiner � gold standard
validation (in percentage) � 100 � (examiner �
gold standard)/gold standard
Systematic errors of the intraexaminer and interex-
aminer analysis were assessed by the Wilcoxon test and
the Mann-Whitney U test, respectively. The compari-
son between MSCT and physical measurements was
made using a paired t test. Statistical analyses were
made using the SPSS version 8.0 software (SPSS Inc.,
Chicago, IL). A P value �.05 was accepted to indicate
statistical significance.
RESULTS
Mean degree values for each measurement obtained
by physical and 3D-CT methods are shown in Table III.
The highest mean differences in degrees and percentage
ranked (Table IV), are �0.03° and �0.07% (intraex-
aminer error), and 0.55° and 0.29% (interexaminer
error). For each measurement, the highest mean per-
centage difference was 1.31% (nasion-alveolare-pogo-
nion) for the interexaminer and 0.46% (nasion-menton-
gonion) for the intraexaminer assessment (Table IV).
The largest difference between the physical and 3-D–
based angular measurements (Table V) was �3.16%
(nasion-menton-gonion), and the lowest value was
�0.10% (nasion-alveolare-point B). No statistically
significant difference was observed for both the intraex-
Lateral view of nasion-alveolare-pogonion (N.A.Pg; 174.5°).
NS.Pg; 173.7°). C, Lateral view of nasion-anterior nasal
ton-gonion (N.Me.Go; 69.9°). E, Lateral view of condylion-
olare-point B (N.A.B; 171.7°).
nts. A,
(G.A
n-men
aminer (examiner 1, P � .111; examiner 2, P � .712)
physic
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Volume 105, Number 2 Lopes et al. 227
and the interexaminer (P � .567) assessment. A statis-
tically significant difference was observed for the mea-
surement nasion-menton-gonion, referring to the com-
parison between CT and physical measurements for
both examiners (examiner 1, P � .027; examiner 2, P
� .029). Differences related to the other measurements
were not statistically significant (P � .05). The mini-
mum P values observed in this study (Table VI) ranked
from .027 (nasion-menton-gonion) to .789 (glabella-
anterior nasal spine-pogonion).
DISCUSSION
Several authors have studied CT imaging for analy-
ses using craniometric points, establishing the precision
and accuracy of this method by using different CT
Fig. 2. A, The Beyond Crysta-C9168 device used to perform
Table III. Mean degrees of each measurement in gold
standard and in 3D-CT for both examiners
Measurement
Physical
measurements,°
3D-CT
Examiner 1,° Examiner 2,°
N.A.Pg 167.1 167.2 165.1
G.ENA.Pg 167.9 167.5 167.6
Co.Go.Me 123.2 121.9 122.9
N.Me.Go 72.9 70.6 70.6
N.A.B 165.8 165.6 163.5
N.ENA.Me 160.6 159.2 158.9
3D-CT, three-dimensional computed tomography.
technology with 3-D reconstructed images.9,10,12-14
Furthermore, it was established that CT generations,
data acquisition, and parameters such as slice thickness
and interval of the reconstruction can determine a high
3-D imaging resolution,15,16 which corroborate to qual-
itative patterns of our 3-D images, because the source
was 64-row multislice CT using 0.3-mm intervals of
reconstruction. Our results highlight favorable indica-
tions of precision and accuracy for the 3-D volume-
rendering angular measurements from 64-row MSCT.
Regarding linear measurements, our previous study
in MSCT10 found 0.83% and 1.78% of error for bone
and soft tissue measurements, respectively, when com-
pared with the physical measurements. These results
demonstrated high accuracy of both 3D-CT protocols.
Following Swennen et al.,2 a reconstruction interval
of 0.75 mm is acceptable for 3-D cephalometry. Mul-
tislice computed tomography 3-D cephalometry was
considered highly accurate and reliable. Intraexaminer
measurement errors were low: 0.88, 0.76, and 0.84 mm
for horizontal, vertical, and transverse orthogonal mea-
surements, respectively. Interexaminer measurement
error was also low: 0.78, 0.86, and 1.26 mm for hori-
zontal, vertical, and transverse orthogonal measure-
ments, respectively. Squared correlation coefficients
showed high intraexaminer and interexaminer reliabil-
ity.2
Kusnoto et al.4 assessed the accuracy of angular
measurements in 3-D projections and found an average
absolute error of 3.5°. They observed that errors in
al measurements in a dried skull. B, Nasion point landmark.
linear measurements were lower than those of the an-
1.4
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228 Lopes et al. February 2008
gular measurements. In our research, using newest CT
multislice technology, there was high precision and
accuracy of angular measurements—we found �1.18%
of difference for accuracy and 0.29% of difference for
intraexaminer and interexaminer analyses.
Cavalcanti et al.,10 Ward and Jamison,12 and Jamison
and Ward13 considered small dimensional measure-
ments of up to 6 cm to be less reliable than larger
dimensional measures. Our results demonstrated agree-
Table IV. Intraexaminers and interexaminers mean dePrecision intraexaminer 1 P
Degree % De
Mean SD Mean SD Mean
N.A.Pg 0.50 0.68 0.30 0.41 �0.56
G.ENA.Pg �0.04 0.95 �0.03 0.56 �0.18
Co.Go.Me �0.47 0.71 �0.39 0.58 �0.33
N.Me.Go �0.30 0.56 �0.43 0.80 0.31
N.A.B 0.62 1.95 0.37 1.17 0.20
N.ENA.Me �0.39 0.65 �0.24 0.41 0.40
Total �0.01 1.10 �0.07 0.76 �0.03
Table V. Mean degree and percentage differences of c
dent physical measurements
Validation examiner 1
Degree %
Mean SD Mean
N.A.Pg 0.17 1.18 0.11
G.ENA.Pg �0.42 1.17 �0.26
Co.Go.Me �1.25 1.91 �1.00
N.Me.Go �2.34 1.58 �3.16
N.A.B �0.16 1.68 �0.10
N.ENA.Me �1.49 1.45 �0.92
Total �0.91 1.73 �0.89
3D-CT, three-dimensional computed tomography.
Table VI. Minimum P values for comparison between
3D-CT and physical measurements
Measurements P values
N.A.Pg .254
G.ENA.Pg .789
Co.Go.Me .343
N.Me.Go .027*
N.A.B .173
N.ENA.Me .336
3D-CT, three-dimensional computed tomography.
*Statistically significant.
†Two examiners performing 2 examinations each. P � .05 for
significance.
ment with these earlier reports, because the smallest
angular measurements of the study (Table III: nasion-
menton-gonion, mean 70.6°) showed the greatest dif-
ferences in the validation analysis, which represents the
lowest accuracy value (Table V).
Cephalometric analysis with 3D-CT was used for
facial asymmetry by Maeda et al.17 and Katsumata
et al.18 These authors considered 3D-CT as an appli-
cable method that can substitute conventional tech-
niques. Park et al.3 proposed a new cephalometric
analysis with 3D-CT and showed the method used
for a patient with facial asymmetry. The CT images
were made with a single slice CT. The thickness of
the axial images was 3 mm, the table speed was 6
mm per second, and the 3-D image was reconstructed
with a 2-mm slice thickness. For this protocol, no
statistically significant differences were found. All
landmarks were reproducible, and there was no sig-
nificant intraexaminer error between the 2 sessions
(P � .01). There are some limitations when using
3D-CT as a diagnostic tool, as they found relatively
large errors in the vertical position (z-coordinate)
compared with the anteroposterior (y-coordinate)
and transverse (x-coordinate) positions. However,
these errors can be decreased if thin slices are used
nd percentual differences for each measurement
intraexaminer 2 Precision interexaminer
% Degree %
Mean SD Mean SD Mean SD
7 �0.35 0.85 2.17 2.10 1.31 1.28
6 �0.12 0.70 �0.15 1.23 �0.10 0.73
0 �0.27 1.15 �0.97 1.65 �0.82 1.39
9 0.46 1.79 �0.04 1.29 �0.07 1.86
9 0.12 0.98 2.06 2.55 1.26 1.57
8 0.24 1.01 0.21 1.65 0.14 1.05
3 0.01 1.15 0.55 2.13 0.29 1.55
ison of all measurements in 3D�CT to the correspon-
Validation examiner 2
Degree %
Mean SD Mean SD
0 �2.00 2.26 �1.21 1.36
1 �0.27 1.22 �0.16 0.72
4 �0.27 2.63 �0.19 2.14
6 �2.30 1.99 �3.09 2.68
2 �2.21 2.76 �1.36 1.71
9 �1.70 1.83 �1.07 1.16
5 �1.46 2.31 �1.18 1.98
gree a
recision
gree
SD
1.3
1.1
1.4
1.2
1.5
1.5
ompar
SD
0.7
0.7
1.5
2.0
1.0
0.8
1.6
during the reconstruction.3 In comparison, our re-
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Volume 105, Number 2 Lopes et al. 229
search used a CT multislice with 0.5-mm axial slice
thicknesses and 0.3 mm for interval of reconstruc-
tion, which allowed higher 3-D resolution. Conse-
quently, we found high precision and accuracy of
angular measurements, because the 3-D images were
obtained from volume-rendering technique software.
Newer 64-row MSCTs yield several technological
improvements over earlier systems, permitting greater
fidelity in anatomical structure. A volumetric image set
with isotropic properties can be obtained in multiple
acquisitions, with a 0.5-mm slice width. Multislice
computed tomography allows extended anatomic cov-
erage with thin slices, in a very short time. The near
future will include 256-row MSCT19 for craniofacial
applications. This technology will allow dramatic
shortening of the acquisition time.
The substitution of CT for cephalometric skull radi-
ography can become practical when high-quality 3-D
reconstructions of the skull can be obtained with suit-
able geometric accuracy, typically imprinted on hard-
copy in a life-size film format. However, the radiation
dose and the cost effectiveness are still the particular
points that limit this specific application, turning this
technique mainly toward surgical purposes. All modern
CT scanners possess some form of 3-D reconstruction
imaging capability, and manufacturers now offer a
wide range of products.20,21 The computer graphics
methods that serve as the basis for 3-D reconstruction
imaging have evolved rapidly, and dramatic improve-
ments in image quality, efficiency, versatility, ease of
use, and reduction in the cost of systems have been
realized.20,21 These intrinsically quantitative 3-D imag-
ing methods have enabled the development of objective
measurement protocols for the study of skull form and
volume change. It is important to point out that mea-
surements using 3-D technology can be widely applied
in many areas, especially involving surgical procedure,
forensics, and radiotherapy.
Regarding our research, 3D-CT images were used to
develop measurements that were then employed in pro-
cedures to aid in the displacement or reorientation of
the facial skeletal components, which were freed from
their normal attachments through orthodontic treatment
planning. The acceptance of these systems for orth-
odontic treatment and the dentofacial orthopedic field is
widespread. These imaging techniques are playing an
important role in the orthodontic field, representing
cutting-edge technology and improving diagnostic and
clinical treatment.
CONCLUSIONS
Angular measurements obtained from 64-row MSCT
3-D reconstructions are precise and accurate. The 3-D
volume-rendering technique can distinguish craniofa-
cial anatomy accurately in bone tissue protocols, add-
ing important sources for maxillofacial analyses and
applications.
We thank University Center of João Pessoa, Paraíba,
Brazil, for software upgrade support.
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Reprint requests:
Marcelo G. P. Cavalcanti, DDS, PhD
Department of Radiology
University of São Paulo, College of Dentistry
Av. Prof. Lineu Prestes, 2227
CEP 05508-900
São Paulo, SP, Brazil
mgpcaval@usp.br
http://www.madeforlife.toshiba.com/ct256/TMS082_CT_WP_256.pdf
http://www.madeforlife.toshiba.com/ct256/TMS082_CT_WP_256.pdf
mail to:mgpcaval@usp.br
	3-D volume rendering maxillofacial analysis of angular measurements by multislice CT
	MATERIAL AND METHODS
	RESULTS
	DISCUSSION
	CONCLUSIONS
	ACKNOWLEDGMENT
	REFERENCES