in-vitro study for determination of the degree of accuracy of CBCT in linear and volumetric measurements

1. I . S . S . N 0 0 7 0 - 9 4 8 4
w w w . e d a - e g y p t . o r g
EGYPTIAN
DENTAL JOURNAL
Vol. 57, 2917:2925, October, 2011
Determination of the Accuracy of Linear and
Volumetric Measurements on Cone Beam Computed
Tomography Images (In-vitro study)
ABSTRACT
Objectives: to determine the accuracy of the linear and volumetric measurements on
cone beam computed tomography images. Materials and methods: on four dry human jaws
impressions for single rooted teeth sockets were taken then their volumes were determined by
“water displacement technique” and compared with their volumes on CBCT scans. On each jaw
the linear distances between gutta percha pieces glued at certain positions were measured directly
by means of digital caliper, and on CBCT scans of these jaws and then compared. Results:
there was no statistically significant difference between direct and CBCT linear and volumetric
measurements, for CBCT linear measurements the average AME was 0.06mm and the average
error APE was 0.5%. While for CBCT volumetric measurements the average AME was 3.7 mm3
and the averageAPE was 4.9%. Conclusions: there is a positive correlation between (AME) and
distance length in CBCT linear measurements, whereas for CBCT volumetric measurements
there is an inverse correlation between (APE) and the volume size, CBCT linear measurements
are the most accurate at midline region and least accurate at canine region.
Keywords: Cone Beam CT, linear measurements, volumetric measurements.
Enas Antar*
; Mohamed Khalifa**
and Sahar Hosny***
* Instructor, Oral Radiology Dept., Faculty of Oral and Dental Medicine, Cairo University
** Lecturer, Oral Radiology Dept., Faculty of Oral and Dental Medicine, Cairo University
*** Associated Professor, Oral Radiology Dept., Faculty of Oral and Dental Medicine, Cairo University
INTRODUCTION
Nowadays accurate linear and volumetric
measurements have become essential in most of
the dental branches. As in implant dentistry, pre-
surgical dental implant planning requires accurate
evaluation of bone in terms of width, height and
quality (1)
. In diagnosis and treatment planning for
orthodontic patients it is necessary to calculate
spatial and angular relations between specific
landmarks (2)
, also In patients with periodontal
problems, linear measurements are needed to assess
the alveolar bone level and degree of alveolar
bone resorption, and in case of intra-bony defect,
volumetric measurement is needed to asses the size

2. (2918) Enas Antar, et al.E.D.J. Vol. 57, No. 4
of the defect and its response to the regenerative
procedures by monitoring the changes in its size
through out the follow up(3)
.
Manyradiographictechniqueshavebeenusedfor
assessment of linear and volumetric measurements
including plain radiography as periapical(4,5)
, pano-
ramic(6,7)
, and lateral cephalometric radiographs(8)
,
and cross-section imaging as conventional tomogra-
phy(9,10)
, computed tomography (11,12,13)
, and recently
cone beam computed tomography(14,15,16,17,18)
which
is a three dimensional imaging modality having low
dose of radiation, fast scan time, isotropic resolu-
tion of the images, variable field of view, and pos-
sibility of interaction with data using personal com-
puter(19,20)
. As cone beam CT is a relatively recent
three dimensional imaging modality so the accuracy
of linear and volumetric measurements taken from
its images need to be farther investigated for con-
firmation.
Materials and Methods
The study was conducted on four dry human
jaws–two mandibles and two maxillae– obtained
from Department of Anatomy-Faculty of Medicine-
Cairo University, thirty single rooted teeth sockets
were selected free from fenestrations or periapical
defects.
Samples preparation: The sockets were painted
internally with a thin layer of nail varnish, then small
gutta percha (GP) pieces (radiopaque marker) were
attached on the facial and lingual or palatal surfaces
of the dry specimens by means of glue. Each dry
jaw received 21 pieces of GP distributed at seven
selected areas. Three GP pieces were attached in
each area, two on the facial surface, one occlusaly
and one apically, both were on the same line and
perpendicular to the horizontal plane, and one on
the lingual or palatal surface opposing the occlusaly
placed buccal piece. The seven areas were selected
as one in the midline, and on each side one at the
canine region, one at the premolars region, and one
at the second molar region.
Direct linear measurements: Direct linear
measurements on the dry sample were obtained
using a digital caliper IOS-USA®
with an accuracy
of 0.01 mm. at each area three measurements were
taken including:
1) Bone height: as the distance between the
apical end of the occlusally placed GP piece and
the occlusal end of the apically placed GP piece on
the facial surface, 2) Bone thickness: as the distance
from occlusal end of occlusally placed buccal GP
piece to the occlusal end of the GP piece palataly
or lingually placed. 3) Bone width: as the distance
between the occlusal ends of two adjacent GP pieces
on the facial surface. Fig. (1)
Direct volumetric measurements: impressions
for the sockets were taken using [Speedex®
]
putty and light impression material by wash
impression technique. Fig. (2) Then volumes of
these impressions were calculated according to
the water displacement technique as following:
A 10 ml measuring cylinder with an accuracy of
0.1 ml was filled with water at room temperature
to a 6 ml mark. Then each socket impression was
Fig. (1) The digital caliper usage in determination of the bone
height (top), thickness (middle), width (bottom).

3. Determination of the Accuracy of Linear and Volumetric (2919)
immersed in the measuring cylinder and the volume
of the displaced water was determined using 0.1ml
measuring pipette (graded with 0.001 ml grades).
The volume of each tooth socket was measured
three times and the average volume was considered
the gold standard.
Sample scanning using CBCT: Each dry
specimen was scanned using i-CAT®
(Imaging
Sciences International, Hatfield, PA) scanner,
at (5mA) , (120 kV), with a single 360˚ rotation
and total scan time of (7 sec), and voxel size of
0.125 mm.
CBCT linear measurements were made on a
personal computer using distance icon on the tool
bar of i-Vision software, the image slices with the
radiopaque markers best visible were used for linear
measurements fig (3).
CBCT volumetric measurements: The CBCT
data set was then exported using the DICOM
(Digital Imaging and Communication in Medicine)
file format to a workstation for automated volume
measurement using separate software SimPlant®
(Materialise dental-Belgium) which allows
segmenting the teeth sockets on consecutive axial
slices as for segmentation a threshold for air was
selected then the region growing tool was applied
which allows selecting the largest connected volume
that contains all voxels with grey values lying inside
the defined threshold, then the selected socket
was displayed in a 3D form and its volume was
calculated using volume calculation function of the
software. These procedures were repeated for each
socket, and each socket in the sample was colour
coded to facilitate differentiation between them.
Statistical analysis: Estimation of the
measurements error between direct (gold standard)
measurements (A) and CBCT measurements (B)
was assessed according to the following equations:
• Absolute measurement error (AME) = [B – A]
• Absolute percentage error (APE) = [B–A] X100 %
A
The paired t test was used for statistical
analysis. Results were considered to be statistically
significant at P ≤ 0 .05. Reliability analysis tests
using Cronbach’s alpha and intra-class correlation
coefficient were used to determine the consistency
between the CBCT and direct measurements.
Higher values of Cronbach’s alpha (More than
0.7) denote acceptable consistency or agreement
between the methods. The significance level was
set at P ≤ 0.05. Statistical analysis was performed
with SPSS 16.0®
(Statistical Package for Scientific
Studies) for Windows.
Fig. (2) Impressions of the sockets for volume assessment of
these sockets.
Fig. (3) Implant screen for skull scan showing simulated
panoramic image of maxilla (top) and seven serial
trans-axial cross-sectional images (bottom), one of the
last showing height and thickness linear measurements
(in blue lines)

4. (2920) Enas Antar, et al.E.D.J. Vol. 57, No. 4
5. Height measurements
Measurement Min Max Mean SD
Direct
5.25
mm
15.74
mm
10.09
mm
2.92
mm
CBCT
5.25
mm
15.74
mm
10.07
mm
2.91
mm
AME
0.00
mm
0.23 mm
0.06
mm
0.038
mm
APE 0% 1.7% 0.5% 0.36%
6. Thickness linear measurements
Measurement Min Max Mean SD
Direct
4.19
mm
14.31
mm
8.30 mm
2.84
mm
CBCT
4.20
mm
14.32
mm
8.31 mm
2.85
mm
AME
0.00
mm
0.16 mm
0.045
mm
0.042
mm
APE 0% 1.6% 0.48% 0.43%
7. Width linear measurements
Measurement Min Max Mean SD
Direct
13.17
mm
23.95
mm
17.75
mm
3.09
mm
CBCT
13.17
mm
23.92
mm
17.76
mm
3.10
mm
AME
0.00
mm
0.33 mm 0.09 mm
0.08
mm
APE 0% 1.5% 0.48% 0.42%
8. All linear measurements
Measurement Min Max Mean SD
Direct 4.19 mm
23.95
mm
11.76
mm
4.95
mm
CBCT 4.20 mm
23.92
mm
11.77
mm
4.96
mm
AME 0.00 mm
0.33
mm
0.06
mm
0.054
mm
APE 0% 1.7% 0.5% 0.4%
Results
I. Linear Measurements
Table (1) The descriptive statistics for the whole
CBCT and direct linear measurements,
AME, and APE
1. Midline region linear measurements
Measurement Min Max Mean SD
Direct 4.19 mm
19.45
mm
12.12
mm
5.28
mm
CBCT 4.20 mm
19.40
mm
12.13
mm
5.27
mm
AME 0.00 mm
0.15
mm
0.04
mm
0.043
mm
APE 0% 1.05% 0.34% 0.31%
2. Canine region linear measurements
Measurement Min Max Mean SD
Direct 5.26 mm
21.33
mm
12.61
mm
5.91
mm
CBCT 5.26 mm
21.46
mm
12.62
mm
5.92
mm
AME 0.00 mm
0.31
mm
0.08
mm
0.084
mm
APE 0% 1.55%
0.60
%
0.43
%
3. Premolars region linear measurements
Measurement Min Max Mean SD
Direct 5.32 mm
23.95
mm
12.24
mm
4.66
mm
CBCT 5.35 mm
23.86
mm
12.21
mm
4.65
mm
AME 0.00 mm
0.16
mm
0.06
mm
0.04
mm
APE 0% 1.68% 0.54% 0.37%
4. Molars region linear measurements
Measurement Min Max Mean SD
Direct 5.64 mm
14.32
mm
9.41
mm
2.68
mm
CBCT 5.64 mm
14.31
mm
9.44
mm
2.68
mm
AME 0.00 mm
0.16
mm
0.05
mm
0.04
mm
APE 0% 1.68% 0.54% 0.37%

5. Determination of the Accuracy of Linear and Volumetric (2921)
II. Volumetric Measurements
Table (2) The descriptive statistics for the whole
CBCT and direct linear measurements,
AME, and APE
1. Maxillary volumetric measurements
Measurement Min Max Mean SD
Direct
60
mm3
271
mm3
141.79
mm3
74.06
mm3
CBCT
65
mm3
275
mm3
144.79
mm3
73.23
mm3
AME
2.5
mm3
10
mm3 5.8 mm3
2.4 mm3
APE 1.8% 10% 4.46% 2.4%
2. Mandibular volumetric measurements
Measurement Min Max Mean SD
Direct 42 mm3
140 mm3 71.80
mm3
29.21
mm3
CBCT
39.50
mm3
137.50
mm3
70.50
mm3
30.04
mm3
AME 0.5 mm3
6 mm3 3.4
mm3
1.52
mm3
APE 0.83% 9.6% 5.4% 2.8%
3. All volumetric measurements
Measurement Min Max Mean SD
Direct 42 mm3 271
mm3
105.6
mm3
65.1
mm3
CBCT
39.5
mm3
275
mm3
106.3
mm3
66.1
mm3
AME 0.5 mm3
10 mm3 3.7
mm3 2.3 mm3
APE 0.83% 10% 4.9% 2.6%
CBCT volumetric measurements showed
underestimation in 17 sockets ranged from (0.5mm3
to 10mm3
) and overestimation in 13 sockets ranged
from (1mm3
to 9mm3
).
Paired-t test results for comparison between
the volumetric measurements obtained by direct
and CBCT methods showed that there was no
statistically significant difference between the two
groups. Also, Cronbach’s alpha and intra-class
correlation coefficient values showed statistically
significant agreement between the CBCT and
direct volumetric measurements with a very good
reliability coefficient.
From 80 linear measurements CBCT showed
underestimation in 29 measurements ranged
from (0.01 to 0.33mm) and overestimation in 42
measurements ranged from (0.01 to 0.31 mm).
Using paired t test analysis there was no
statistically significant difference between the
direct and CBCT linear measurements, Cronbach’s
alpha and intra-class correlation coefficient values
showed statistically significant agreement between
the CBCT and direct linear measurements with a
perfect reliability coefficient
Paired-t test results for comparison between
maxillary and mandibular CBCT linear
measurements (AME) and (APE) showed that there
was no statistically significant difference between
the two groups in both AME and APE
One Way Analysis of Variance (ANOVA) test
was used for comparison between theAME andAPE
for CBCT linear measurements at different regions
of the jaw, the significance level was set at P ≤ 0.05.
The results showed that there was no statistically
significant difference between the different regions
in both AME and APE
One Way Analysis of Variance (ANOVA) test
was used for comparison between the averages of
AME and APE for CBCT linear measurements in
different dimensions, the significance level was
set at P ≤ 0.05. The results showed that there was
no statistically significant difference between the
different dimensions in APE while for AME the
results showed that there was statistically significant
difference.
Pair-wise Multiple Comparison Procedures
(Holm-Sidak method) showed the presence of
statistically significant difference between width
and thickness AME; nevertheless no statistically
significant difference was found between AME of
height neither with width nor with thickness

6. (2922) Enas Antar, et al.E.D.J. Vol. 57, No. 4
(Mercury Computer Systems, Chelmsford, MA).
For assessment of accuracy of linear
measurements seven areas were selected on each
jaw including anterior, canine, premolar, and molar
regions. The GP pieces used were of small size to
avoid possible production of streaking artifacts in
CBCT images.
The CBCT linear measurements in this study
were proved to be accurate and highly reliable
although they were not constant in one direction
(overestimation or underestimation) but they
showed a higher tendency to overestimation.
Comparison between CBCT height, thickness and
width measurements using Pair-wise Multiple
Comparison Procedures (Holm-Sidak method)
showed the presence of a statistically significant
difference between width and thickness AME;
nevertheless no statistically significant difference
was found between AME of height neither with
width nor with thickness. However the results of
ANOVA test for comparison between the APE
at different dimensions showed no statistically
significant difference.
However this difference can be explained as
the linear distances that represent the width were
larger than the linear distances that represent the
height and thickness as the average real width
measurements was 17.75 mm, while those for
thickness and height respectively were 8.30 mm
and 10.9 mm respectively. This coincided with
(Mischkowski et al 2007) who stated that “there
is a positive correlation between AME and distance
length in CBCT-based measurements”.
The CBCT linear measurements accuracy of
this study was higher than CBCT linear measure-
ments accuracy of Kobayashi et al 2004 who had
examined the accuracy of linear measurements on
limited cone beam CT scans with 0.117 voxel reso-
lution the average AME for was 0.22 mm and the
average APE was 1.4% which are higher than those
Paired-t test results for comparison between
maxillary and mandibular CBCT volumetric
measurements (AME) and (APE) showed that there
was no statistically significant difference between
the two groups in APE, but there was statistically
significant difference between the two groups in
AME
Discussion
The sockets selected for assessment of accuracy
of CBCT volumetric measurements were single
rooted, free from periapical defects and fenestration
to facilitate impression taking with minimum
error and not to invite errors in automated volume
extraction, the sockets were painted internally to
block the minute openings of the cancellous bone
which both facilitated impression removal and
made delineation of the sockets walls in the CBCT
images thus facilitating and giving more accurate
automatic volume extraction. The impressions of
the sockets were taken using condensation silicon
rubber base impression material having a very
high degree of accuracy in the first hour before
polymerization shrinkage begins(21)
. The volumes
of sockets’ impressions were measured by water
displacement technique which was proved to be
accurate in determining the objects volume and it
had been used by Emirzeoglu et al 2005, Shiratori
et al 2005 and by Yang et al 2006 in determination
of different objects volumes.
The sockets’ volumes on the CBCT images were
measured by automatic volume extraction function
of Simplant®
software for rapid, ease, and accuracy
of the procedures when compared with manual
delineation of the socket outline on each socket
segment which is time consuming and inviting
humane error. The automated volume extraction
technique was used by Pinsky et al 2006 utilizing
software called Analyze®
(Analyze Direct Inc.,
MN), and by Mischkawski et al 2007 utilizing
software called Amira 3.1.1 visualization®

7. Determination of the Accuracy of Linear and Volumetric (2923)
between maxillary and mandibular CBCT linear
measurements accuracy, AL-Ekrish and Ekram
2011 found a statistically significant difference
between them in AME, with a higher AME for
maxillae than that for mandibles, while in the
current study no statistically significant difference
was observed between maxillary and mandibular
linear measurements but there was a slight higher
accuracy for mandibular measurements (as in
their study). AL-Ekrish and Ekram 2011 also
found no difference between the different sites in
CBCT linear measurements accuracy, whereas in
the present study although comparison between
different regions of the jaw in CBCT linear
measurements accuracy using One Way Analysis
of Variance (ANOVA) test showed no statistically
significant difference between the different regions
in both AME and APE, but regarding the average
values ofAME andAPE the highest accuracy was at
midline linear measurements, and the least accuracy
was at the canine region linear measurements, while
for premolars and molars regions the averages
AME were very close and the averages APE were
the same. All the regions showed no statistically
significant difference between CBCT and direct
measurements with Paired-t test, and statistically
significant agreement between CBCT and direct
measurements with reliability analysis.
In this study we also evaluated the accuracy of
CBCT volumetric measurements using a volume
measurement approach from those offered by
popular softwares used for computer-aided surgical
procedures.
CBCT volumetric measurements were proved to
be accurate and reliable, they were not consistent in
one direction (overestimation or underestimation)
as they showed underestimation in 17 sockets and
overestimation in 13 sockets, and the AME values
in both directions were very close. However the
mandibular CBCT volumetric measurements
showed a greater tendency for underestimation.
of our study this could be due to the presence of the
soft tissue on the cadavers’ mandibles which most
probably negatively influenced the image quality of
the scans, and in turn the measurements accuracy.
While by comparison with the results of Pinsky
et al 2006 it was revealed that they had a mean
width (diameter) error of 0.01mm and mean height
(depth) error of 0.03mm for the acrylic block– (both
were lower than the AME in this study)– while for
the human mandible the mean width (diameter) error
was 0.07 mm–(which was almost equal to that in
this study) – and the mean height (depth) error was
0.27 mm (which was much higher than the AME in
this study). This difference can be explained on the
basis of the dry mandible wide trabeculations and
various bone densities which lead to variations in
CBCT densities which could impact the results.
The averages AME and APE for CBCT linear
measurements in Mischkowski et al 2007 study
were 0.26mm and 0.98% which are greater than
those of this study Anyway the distances measured
in Mischkowski’s study were greater than the
distances in this study, and by using linear regression
analysis they concluded that there was a positive
correlation between AME and distance length in
CBCT-based measurements which is in agreement
with this study results.
AME in Berco et al 2009 study is almost similar
or very close to that in our study, while the APE of
their study was in range of 0–1.1% with an average
of 0.19% which is smaller than that in our study, this
difference exist because Berco et al 2009 disagreed
with our and Mischkowski et al 2007 conclusion
that there is a positive correlation between AME
and distance length in CBCT-based measurements.
In contrast to the current study and all the
previously mentioned studies; AL-Ekrish and
Ekram 2011 found that both MDCT and CBCT
were associated with clinically and statistically
significant measurement error. In comparison

8. (2924) Enas Antar, et al.E.D.J. Vol. 57, No. 4
• The CBCT linear measurements are the most
accurate at midline region and least accurate at
canine region.
• There is a positive correlation between (AME)
and distance length in CBCT-based linear
measurements
• CBCT is accurate and reliable for volumetric
measurements
• CBCT volumetric measurements are not con-
stant in one direction (overestimation or under-
estimation) but they have a higher tendency to
underestimation in small sized volumes
• There is an inverse correlation between (APE)
and the volume size in CBCT-based volumetric
measurements
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