Download Accuracy of linear measurement in Galileos cone beam CT under

University of Iowa
Iowa Research Online
Theses and Dissertations
Spring 2009
Accuracy of linear measurement in Galileos cone
beam CT under simulated clinical condition
Rumpa Ganguly
University of Iowa
Copyright 2009 Rumpa Ganguly
This thesis is available at Iowa Research Online: http://ir.uiowa.edu/etd/235
Recommended Citation
Ganguly, Rumpa. "Accuracy of linear measurement in Galileos cone beam CT under simulated clinical condition." MS (Master of
Science) thesis, University of Iowa, 2009.
http://ir.uiowa.edu/etd/235.
Follow this and additional works at: http://ir.uiowa.edu/etd
Part of the Other Dentistry Commons
ACCURACY OF LINEAR MEASUREMENT IN GALILEOS CONE BEAM CT
UNDER SIMULATED CLINICAL CONDITION
by
Rumpa Ganguly
A thesis submitted in partial fulfillment
of the requirements for the Master of
Science degree in Stomatology
in the Graduate College of
The University of Iowa
May 2009
Thesis Supervisor: Professor Axel Ruprecht
Copyright by
RUMPA GANGULY
2009
All Rights Reserved
Graduate College
The University of Iowa
Iowa City, Iowa
CERTIFICATE OF APPROVAL
_______________________
MASTER'S THESIS
_______________
This is to certify that the Master's thesis of
Rumpa Ganguly
has been approved by the Examining Committee
for the thesis requirement for the Master of Science
degree in Stomatology at the May 2009 graduation
Thesis Committee: ___________________________________
Axel Ruprecht, Thesis Supervisor
___________________________________
Steven Vincent
___________________________________
John Hellstein
___________________________________
Sherry Timmons
Fang Qian
To my adorable son, Adi
To my dear husband, Dev Shankar for his constant support and encouragement
To my loving parents, for their guidance and motivation throughout my life
ACKNOWLEDGMENTS
My heartfelt gratitude goes to Dr. Axel Ruprecht who not only served as my
thesis supervisor but also encouraged and guided me throughout my academic program
and residency. He and the other members of my thesis committee, Dr. Steven Vincent,
Dr. John Hellstein, Dr. Sherry Timmons and Dr. Fang Qian guided me through the
dissertation process through their valuable advice. I thank them all.
I extend my appreciation to Patrick Elbert, hospital mortician in the department of
Anatomy at The University of Iowa, who arranged for specimens for my research and
helped with preparing them for my research; to John Laffoon at Dows-Institute of dental
research for helping with the band saw for sectioning my specimens.
I would like to thank my colleague Dr. Nidhi Handoo, who assisted me a great
deal in setting up and dissection of the specimens for the project. I would also like to
thank my other colleagues of past and present, Shawneen, Tunde, Ek, Gayle, Rujuta and
Ali for their support.
My sincere thanks to my friends in Iowa City, Lopa, Soumya, Soma,
Arindam and Kajari, for all the good times we shared together and for being there
with me when I needed them.
I am deeply indebted to my parents and parents-in-law for their invaluable
support throughout my years of academic pursuits. I cannot thank my husband,
Dev, enough for his cooperation, understanding, love and support during my years
of training.
iii
TABLE OF CONTENTS
LIST OF TABLES ...................................................................................................v
LIST OF FIGURES ............................................................................................... vi
CHAPTER I
INTRODUCTION ........................................................................1
Aim .............................................................................................11
Hypotheses ..................................................................................11
CHAPTER II
MATERIALS AND METHODS ...............................................12
Imaging device ...........................................................................12
Linear distance measurement ....................................................12
CHAPTER III RESULTS ...................................................................................37
An overview of statistical methods ...........................................37
Data preparation .........................................................................38
Statistical analysis .....................................................................38
CHAPTER IV DISCUSSION.............................................................................46
CHAPTER V
CONCLUSION...........................................................................58
BIBLIOGRAPHY .................................................................................................59
iv
LIST OF TABLES
Table 1. Measurements obtained from six specimens ...........................................34
Table 2. Mean linear measurement values of bone height under each
condition ..................................................................................................41
Table 3. Mean difference between two measurements made by the same
observer ...................................................................................................45
v
LIST OF FIGURES
Figure 1. Imaging device – Galileos CBCT unit (Sirona Dental Systems Inc.,
Bensheim, Germany) ...........................................................................16
Figure 2. Imaging specimen in Galileos CBCT unit ...........................................17
Figure 3. CBCT image showing the plane of measurement on the left side of
specimen .............................................................................................18
Figure 4. CBCT image showing the plane of measurement on the left side of
specimen ..............................................................................................19
Figure 5. CBCT image showing the plane of measurement on the right side
of specimen ..........................................................................................20
Figure 6. CBCT image showing the plane of measurement on the right side
of specimen .........................................................................................21
Figure 7. CBCT image showing the plane of measurement on the left side of
specimen .............................................................................................22
Figure 8. CBCT image showing the plane of measurement on the right side
of specimen .........................................................................................22
Figure 9. CBCT image showing the plane of measurement on the right side
of specimen .........................................................................................23
Figure 10. CBCT image showing the plane of measurement on the right side
of specimen .........................................................................................24
Figure 11. CBCT image showing the plane of measurement on the right side
of specimen ..........................................................................................25
Figure 12. CBCT image showing the plane of measurement on the right side
of specimen .........................................................................................25
Figure 13. Specimen mounted on a base with the plane of dissection marked
consistent with the CBCT image ........................................................26
Figure 14. Band saw (Craftsman, Sears Roebuck & co) ......................................27
Figure 15. Tangent locator (Medical Instrument Shop, The University of
Iowa) ...................................................................................................28
vi
Figure 16. Digital vernier calipers (Mitutoyo, Japan) ...........................................29
Figure17. Combination square ..............................................................................30
Figure 18. Specimen set up for physical measurement..........................................31
Figure 19. Physical measurement between superior most and inferior most
points of the bone with calipers ...........................................................32
Figure 20. Physical measurement between superior most and inferior most
points of the bone with calipers ...........................................................33
Figure21. Graphical representation of mean values of bone height
(CBCT and Physical)
vii
44
1
CHAPTER I
INTRODUCTION
Radiography has been one of the frequently applied aids in human biometric
research when using images for measurement. It is essential to check for the accuracy of
reproduction with respect to enlargement and projection. Without this accuracy errors can
be incorporated into the measurement. Accuracy can be affected by the measurement
procedure itself due to errors in marking reference points or lines or whether the
measurement was obtained directly from the image or indirectly by addition or
subtraction of measurements obtained directly. One example of indirect measurement is
measuring the spacing of the teeth by using the difference between the arch perimeter and
sum of the tooth widths.
1
Measurement is a vital aspect of interpretation, either of
anatomical structures or pathological entities. It plays an important role in orthodontic
treatment and maxillofacial surgery especially when closely related to vital structures.
More recently, an increasing demand for dental implants for rehabilitation of edentulous
jaws has raised an interest in the available imaging techniques to perform an accurate
preoperative planning. It is essential to measure accurately the height of bone available
for implant placement to avoid compromising vital structures such as the inferior alveolar
nerve or maxillary sinus during placement of implants. Acquiring this information
requires some form of imaging, either two dimensional such as panoramic radiography or
three dimensional such as computed tomography depending on the case and experience
of the practitioner. 2
There are different types of imaging used in dentistry that have been used for
measurement of distances between anatomic structures, dimensions of anatomic or
2
pathologic entities and implant site assessment. These are intraoral radiographs, lateral
cephalometric radiographs, pantomographs, cross sectional imaging such as conventional
tomography, computed tomography, magnetic resonance imaging and more recently cone
beam computed tomography.
With intraoral radiographs, the implant site can be assessed in terms of the
trabecular bone pattern and relationship to adjoining anatomic structures. The advantage
of these radiographs are that they are inexpensive, readily available and well tolerated by
patients, and provide high resolution images of the implant site and low radiation dose to
the patient. 2
The disadvantages of intraoral radiographs are that they have nonreproducible
imaging geometry and produce distortions that are inherent to intraoral radiography.
5
The region visualized on an intraoral image is limited in size, sometimes not extending to
the inferior alveolar canal or maxillary sinus. Facial-lingual cross-sectional information
that is vital for implant site assessment is missing with intraoral radiographs. 6
Lateral cephalometric radiographs can be useful diagnostic aids for implant site
assessment.
7, 8, 9
These radiographs provide information regarding the midline region of
both the jaws with respect to the bone height, width and angulation. 2 However, because
of superimposition of structures of the right and left sides, measurements of bone height
and width in the symphyseal region may mask local bone defects.
6
The advantages are
low cost, easy acquisition and availability.
In conventional tomography, the x-ray beam and receptor move in opposite
directions with respect to each other on opposite sides of the patient. A single plane in the
patient is well defined. This is called the focal plane. Structures outside this plane are
3
blurred. The use of a cephalostat, lasers or plastic positioning devices in conventional
tomography is recommended for data registration. Some means of relating the crosssectional image to the actual implant site in the oral cavity is necessary.
10, 11
This is
usually done by use of radiographic stents and radiopaque teeth contours. Broadly, there
are two types of tomographic movements, linear and multidirectional. The latter consists
of circular, spiral, elliptical and hypocycloidal paths of travel. Images from linear
tomography often appear streaked, whereas those from multidirectional movement
tomography are free of such streaks called parasite lines.
12
A constant magnification is
required to accurately perform any kind of measurements on radiographs. Linear
tomography provides non-uniform magnification as opposed to multidirectional
tomography which provides a constant magnification factor.
13
Deficient blurring of
structures outside the focal plane may lead to a reduction of image resolution making
visualization of structures difficult. 14 Such cases may lead to overestimation of distances.
The disadvantages also include limited availability of such imaging modalities and
increased time to acquire the images.
Pantomography is a special tomographic technique that produces a panoramic
radiograph of a curved surface. This is a curvilinear complex variant of conventional
tomography and is also based on the principle of the reciprocal movement of an x ray
source and an image receptor around a central point which moves during the image
acquisition; the movement and path of motion varies as specified by the manufacturer. 15
In most modern pantomographic units the center of rotation moves along a path defined
by the manufacturer (different for each unit) to try to compensate for the noncircular
shape of arch. The receptor moves within its carrier at a different rate corresponding to a
4
slice in the dental arch. Objects outside and inside the image layer are blurred.
Pantomographs provide a comprehensive view of the maxillofacial region, producing an
image of both dental arches in a single radiograph, and significantly reducing radiation
exposure to the patient in comparison to intraoral radiography.
2
The effective radiation
exposure is 35 µSv for a full mouth series with rectangular collimation and E speed films
or photostimulable phosphor plates. The effective radiation exposure with pantomographs
is 6-26 µSv. 15 In accordance with the ALARA principle exposure of patients to radiation
should be avoided unless the benefit from such exposure outweighs the risk from the
procedure.
Panoramic radiographs are useful for evaluating skeletal and dental pathosis,
making dimensional assessments, and determining relative angulations of teeth with
respect to other structures.2 In addition, pantomographs play an important role in
implantology by providing information about the vertical dimension of the bone available
for implant placement and the locations of certain anatomic structures in the orofacial
region.
However, dimensional measurements made on pantomographs can involve
considerable methodologic error. One major limiting factor of the pantomograph is its
inaccuracy in determining the dimensions of structures resulting in magnification and
distortion. A pantomographic image alone provides no information regarding the bone
thickness and may lead to errors in determining the bone width.
33
Superimposition of
structures can lead to poor image quality. The presence of metallic restorations, bone
screws etc. can cause metallic artifacts to appear on the image.
5
The inherent problems with 2D imaging led to the need for 3D imaging which can
overcome the issues of superimposition, blurring and magnification as these factors
compromise measurement accuracy to a large extent. Simultaneously, cross-sectional
information which is vital for preoperative planning for implant placement can be
available from 3D imaging.
Computed tomography which is a 3D imaging modality had long been in use in
medical radiology before its use in dental implant imaging. The first modern computed
tomography (CT) scanner developed by Godfrey Hounsfield in 1967 was first introduced
in clinics in 1971. The basic concept of CT includes measurement of attenuation of the xray beam through a subject at many positions around the subject and at a sufficient
number of angles. It is possible to determine attenuation differences of 0.5% which is
sufficient to distinguish between soft tissues. 34
The details in a CT image are a result of computer calculations that give the
weighted average of all tissues in a particular voxel (volume elements).
14
Patient
positioning and lack of movement are two critical factors necessary to obtain clear CT
images. Correct positioning is also important in the performance of applicable linear
measurements. 35 CT imaging has undergone technologic improvements over the years by
stages called “generations”. In late 1980s, the acquisition of CT images required 45 to 60
minutes,
36
whereas currently, the time has decreased significantly to approximately 5
seconds.
With modern multidetector CT imaging, multiple thin axial slices of data are
obtained through the area of interest and added together to form a data volume. Crosssectional and panoramic images are reconstructed from this data through the use of
6
software programs. The advantages of CT images are uniform magnification, high
contrast images with minimum blurring, simultaneous assessment of multiple implant
sites in a single study and multiplanar images. The disadvantages include a high cost, a
high radiation dose and metallic streak artifacts if metallic objects such as dental
restorations are present.
Several studies have been reported on the dimensional accuracy of various
systems for mandibular height and width, as well as for size and location of the
mandibular canal. The mandibular canal is not always well visualized radiographically, in
part because of a lack of the cortical outline in some jaws
could be easily seen by conventional tomography
37
10
In some studies, the canal
whereas in others CT gave better
results. 13, 37, 38
CT images provide high accuracy of measurement with no significant difference
between the measurement of actual landmarks or CT images.
39, 40, 41
However, the high
radiation dose, availability and cost limit the use of this modality in the maxillofacial
region for preoperative implant planning purposes.
Reports of dimensional accuracy also vary, particularly with respect to
measurement of the distance from the alveolar crest to the superior border of the inferior
alveolar canal. In one report, three forms of tomography (computed and both
hypocycloidal and spiral conventional tomography) all underestimated this distance by
less than 1 mm compared to a larger inaccuracy with standard panoramic imaging,
37
whereas another study concluded that CT was better than conventional tomography.
42
Linear tomography has been reported to significantly overestimate the distance between
the alveolar crest and the top of the canal. 13
7
A world-wide survey of CT use for implant imaging reported a tenfold variation
between lowest and highest absorbed doses from nine different makes of CT scanners
and the protocols being used.
lowering the mAs
44
43
Methods of dose reduction for implant imaging include
, changing the spiral CT pitch from 1:1 to 2:1
number of slices to the very minimum needed.
46
45
and reducing the
It is the responsibility of the both the
implant surgeon and the radiologist to work together to minimize the CT doses by
scanning only the concerned area and by choosing the lowest mAs and appropriate pitch
that will not significantly degrade the image quality. 2
Magnetic resonance imaging (MRI) is another advanced 3D imaging modality
which does not utilize ionizing radiation for the acquiring images. This is an advantage
over the other imaging modalities utilized for the purposes of preoperative planning.
However, MRI is good for imaging soft tissues but not bone, hence it is not
recommended for preoperative planning of implants.
Although CT provided cross-sectional information with high accuracy of
measurement yet it could not be used routinely for dental implant imaging due to high
radiation exposure and high cost leading to limited availability. There was need for a 3D
imaging modality which would overcome the issues of medical CT. A dedicated CT for
maxillofacial imaging called cone-beam computed tomography (CBCT) was introduced
in 1997 by NewTom 9000 in Italy. (Information received by personal communication
through email with chairman of NewTom, David Vozick on February 19, 2009). It was
introduced in literature in 1998-99. 47, 48 In the past decade the technology of cone beam
computed tomography (CBCT) has evolved which allows 3D visualization of the oral and
maxillofacial complex at a much smaller radiation dose than that produced by
8
conventional CT.49 CBCT was initially developed for angiography, but more recent
medical applications have included radiotherapy guidance and mammography. 50
CBCT allows 3D visualization of the oral and maxillofacial complex. This
imaging modality eliminates the shortcomings of 2D imaging, produces a smaller
radiation dose than that of conventional CT and enables clinicians to make more accurate
treatment planning decisions, which should lead to more successful surgical procedures.
49
The information obtained from CBCT can be used for evaluation of hard tissues for
dental implant placement or grafting, the temporomandibular joint complex, pathosis,
anatomic variations and trauma as well as for orthodontic treatment planning. 49 CBCT is
particularly helpful in presurgical planning for dental implant placement by localizing the
anatomy to be avoided during surgery.
49
It helps to measure the quantity and the quality
of the bone available for the placement of implants.
49
CBCT provides submillimeter
pixel resolution of projection images leading to high spatial resolution of the image.
CBCT is primarily used for investigating bone. Although CBCT is able to depict the
associated soft tissue in the region imaged, it is not able to distinguish between different
types of soft tissues.
CBCT was developed as an alternative to conventional CT to shorten the time of
image acquisition of the entire FOV (Field of View) with a comparatively less expensive
radiation detector. The lack of patient translational movement results in improved
sharpness of the image which is reduced in conventional CT imaging. The reduced time
of acquisition also reduces image distortion that may be caused by internal organ
movement. The main disadvantage, especially with larger FOVs, is a limitation in image
9
quality related to noise and contrast resolution because of detection of large amounts of
scattered radiation. 50
CBCT imaging produces images with submillimeter isotropic voxel resolution
ranging from as high as 0.4 mm to as low as 0.076 mm. This results in multiplanar
reconstructed images (axial, coronal and sagittal) with a level of spatial resolution
accurate enough for measurement in maxillofacial applications where precision in all
dimensions is important such as implant site assessment. 50
Depending on the type and model of CBCT device and the field of view (FOV)
selected, the effective radiation dose varies from 29 µSv (Galileos default) to 477 µSv
(CB MercuRay 12-in FOV) according to the published reports.
54, 55, 56
These doses can
be compared to 5 times (Galileos) to 74 times (CB MercuRay) the dose of a single film
based panoramic radiograph or 3 to 48 days of background radiation. Patient positioning
modifications (tilting the chin) and use of additional personal protection (thyroid collar)
can cause significant reduction in dose by up to 40%.
55, 56
Maxillofacial imaging with
conventional CT exposed the patient to approximately 2000 µSv of radiation. Thus
CBCT significantly reduces the dose by a range of 98.5 to 76.2 %. 46, 57, 58
There are several disadvantages of CBCT. The cone beam projection geometry
results in irradiation of a large volume of tissue, resulting in large amount of scattered
radiation. This scattered radiation, recorded by the detector does not reflect the actual
attenuation of an object along the path of an x-ray beam. This is termed ‘noise’ and it is
proportional to the total mass of tissue irradiated by the primary beam. In addition there
may be added noise of the detector system and from variations in the homogeneity of the
incident beam. The increased divergence of the cone beam results in a pronounced ‘heel
10
effect’ leading to nonuniformity of the beam causing increased noise on images.
50
The
portions of the image at the edge of the imaging volume show peripheral noise due to the
cone beam effect. The beam, on encountering metal restorations in the mouth is
attenuated, producing information voids that result in streak artifacts in the images that
can obstruct the surrounding anatomy. Manufacturers attempt to remove noise and streak
artifacts during reconstruction of the raw data by using specific algorithms and filters.
There may also be patient motion artifact on the images which causes image degradation.
CBCT images also have poor soft tissue contrast. In addition to increasing noise in the
image, scattered radiation also reduces contrast of the CBCT system by adding
background signals that are not representative of the anatomy leading to inferior image
quality. 50
As with other imaging modalities, the question of accuracy of measurements
arose with CBCT. Accuracy of measurements with respect to distance is vital for
procedures such as implant surgery or other surgical procedures in close proximity to
vital structures such as the inferior alveolar canal or maxillary sinus as well as for
orthodontic treatment. Several studies have been carried out to determine the accuracy of
CBCT. However these have been done with dry skulls without the soft tissue component.
These studies have shown linear measurement to be accurate on CBCT images. 59, 60, 61, 62,
63, 64, 65
Although the previous studies have shown CBCT to be accurate, some of the
accuracy may be due to the increase in contrast when soft tissues are replaced by air, and
decreased scatter due to absence of soft tissues. It is important to determine if the
11
accuracy of measurement is maintained with soft tissues intact as this would simulate a
clinical situation more closely.
Aim
The aim of this study was to determine if the linear measurements made in
Galileos CBCT in the presence of soft tissue using cadaver heads are accurate.
Hypotheses
1. There is no significant difference in linear distance measurement between the
Galileos CBCT and Physical measurements on the right side in the presence of
soft tissue.
2. There is no significant difference in linear distance measurement between the
Galileos CBCT and Physical measurements on the left side in the presence of soft
tissue.
3. There is no significant difference in the overall linear distance measurement
between the Galileos CBCT and Physical measurements in the presence of soft
tissue.
12
CHAPTER II
MATERIALS AND METHODS
Imaging device
Three dimensional imaging data was acquired in a Galileos (Sirona Dental
Systems Inc., Bensheim, Germany). (Figure 1) The Galileos consists of an x-ray
generator and an image intensifier as detector aligned and mounted across from each
other on a U arm. The radiation source/detector unit completes a 200° rotation around the
patient’s head, acquiring 200 projected images 1° apart. During the examination, the
patient sits or stands in the rotation center. The position of the patient’s head in the image
field is determined either by a chin support or a craniostat. Tube voltage is fixed at 85 kV
and tube current/exposure time product is fixed at 42 mAs. The scan time is 14 seconds.
The x-ray detector component consists of a 9-inch (23 cm) image intensifier and a
charge-couple device camera. Each of the 200 captured projections is represented by a
1024 x 1024 pixel matrix, the pixels being defined by a 12-bit grayscale. The fixed field
of view size is 15 cm resulting in a scan volume of 15 x 15 x 15 cm. Reconstructed threedimensional data is saved together with the original two-dimensional projection views in
a proprietary data format file.
Linear distance measurement
The current study was based on 6 embalmed cadaver heads with intact soft tissue
provided by the Department of Anatomy and Cell biology of the College of Medicine,
The University of Iowa. The heads were sectioned such that the maxillary and
mandibular alveolar arches were preserved along with the surrounding soft tissues. These
13
specimens were resized by slicing off tissues superior and posterior to the
temporomandibular joints, such that only tissues surrounding the jaws were maintained.
The specimens were mounted on a base of dental stone in order to ensure that the vertical
orientation of the specimen was consistent for CBCT imaging and thereafter for
sectioning with band saw. Subsequently fiduciary markers made of gutta percha, were
placed on either side of the mandible along the buccal and lingual alveolar ridges such
that the buccal and lingual markers were in alignment. The selection of marker was based
on the radiopacity of the material and size of the marker such that they were more
radiopaque than the surrounding tissues and small enough to be not visible in more than
1-2 orthogonal slices. Three markers were placed on the buccal surface of the alveolar
bone such that they were aligned and contiguous. A marker was placed lingually such
that it was in alignment with the most anterior bead as visible to the naked eye. The
purpose of placing three markers buccally was to ensure that at least one of the markers
was in alignment with the lingual bead confirmed on imaging. This plane of alignment
would determine the plane of measurement for both CBCT and physical. The heads were
then imaged using the Galileos cone-beam computed tomography unit. (Figure 1) The
specimen was placed on a pedestal/stand in order to be placed within the unit for
scanning. The scan was performed at 85 kVp and 42 mAs. The total scan time for each
specimen was 14 seconds, the field of view (FOV) was 15 cm and 3D volume consisted
of 512 x 512 x 512 isotropic voxels (volume elements) each of 0.3 mm in size. Once the
images were reconstructed, the images were viewed to check for the alignment of the
beads on the orthoradial slices. The buccal bead that appeared to be best aligned with the
lingual bead on the orthoradial slice was selected and noted on the specimen. An
14
indelible ink marker was used on the specimen to indicate the proposed slicing plane
which connected the lingual bead with the buccal bead offering proper alignment.(Figure
13)
In the CBCT images, the cross-sectional image that showed the lingual and the
buccal marker in alignment and completely in focus was selected as the plane of
measurement. On this cross-sectional image, a horizontal tangent was drawn
electronically using the measurement tool in Sidexis touching the superiormost point on
the bone and another touching the inferiormost point of the bone. The vertical height was
measured between these two tangents using the measurement tool in Sidexis. (Figure 312)
The vertical distance was similarly measured between two tangents on the
contralateral side of the mandible. Three measurements were obtained for each side of the
mandible on three different days. All measurements were made by a single observer.
Similar procedure was followed for the remaining five specimens.
The specimens were dissected after imaging such that the maxilla with its
adjoining soft tissue was removed. The mandible with surrounding soft tissues was
retained. The specimens were then sliced along the plane marked previously using
indelible ink. A band saw (Craftsman, Sears Roebuck & co.) was used to make the
sections. (Figure 14) The specimens were kept in the same vertical orientation as in
CBCT using the base made for each specimen. An instrument designed in the medical
instrument shop (The University of Iowa) was used to make a tangent to determine the
highest and the lowest point. The purpose of using this instrument was to reproduce in the
specimen, the superiormost and inferiormost points of the bone as in the image. (Figure
15
15) These points were again marked with indelible ink. The distance between the two
points was measured using a pair of digital vernier calipers (Mitutoyo, Japan). (Figure
16) Measurement of the distance between the superiormost and inferiormost point of a
given section of bone at a particular site was taken as the mean of the measurements on
either side of the sectioned bone. This mean measurement was used as the physical
measurement of the height of bone for the particular site. Three measurements were made
at each site on three different days. In order to ensure that the measurement with vernier
calipers was absolutely in the vertical plane, a 6” combination square was used. (Figure
17) The measurement was made such that the reading on the caliper was facing away
from the measurer to avoid bias. (Figure 20)
The measurements of the height of bone obtained from CBCT images and caliper
measurements from six specimens were compared.
16
Figure1. Imaging device – Galileos CBCT unit (Sirona Dental Systems Inc., Bensheim, Germany)
17
Figure 2.Imaging specimen in Galileos CBCT unit
18
Figure 3.CBCT image showing the plane of measurement on the left side of specimen
19
Figure 4.CBCT image showing the plane of measurement on the left side of specimen
20
Figure 5.CBCT image showing the plane of measurement on the right side of specimen
21
Figure 6.CBCT image showing the plane of measurement on the right side of specimen
22
Figure 7.CBCT image showing the
plane of measurement on the left side of
specimen
Figure 8.CBCT image showing the
plane of measurement on the right side
of specimen
23
Figure 9.CBCT image showing the plane of measurement on the right side of specimen
24
Figure 10.CBCT image showing the plane of measurement on the right side of specimen
25
Figure 11.CBCT image showing
the plane of measurement on the
right side of specimen
Figure 12.CBCT image showing the
plane of measurement on the right
side of specimen
26
Figure 13.Specimen mounted on a base with the plane of dissection marked consistent with
the CBCT image
27
Figure 14.Band saw (Craftsman, Sears Roebuck & co)
28
Figure 15.Tangent locator (Medical Instrument Shop, The University of Iowa)
29
Figure 16.Digital vernier calipers (Mitutoyo, Japan)
30
Figure 17.Combination square
31
Combination square
Tongue
Superior most point of
measurement
Mandible
Soft tissue of chin
Inferior most point of
measurement
Base
Tangent locator
Figure 18.Specimen set up for physical measurement
32
Figure 19.Physical measurement between superior most and inferior most points of the bone with
calipers
33
Figure 20.Physical measurement between superior most and inferior most points of the bone with
calipers
34
Table 1. Measurements obtained from six specimens
Specimen
Case 1
Measurement Serial
Measurement Measurement
type
on Right side
on Left side
(mm)
(mm)
1
35.05
30.96
2
34.98
30.94
3
35.1
30.87
1
35.11
31.14
2
35.28
30.91
3
34.78
30.87
1
30.37
35.25
2
30.5
35.21
3
30.25
35.52
1
30.61
34.82
2
30.32
35.26
3
30.06
35.52
CBCT
Physical
Case 2
CBCT
Physical
number
35
Table1.continued
Case 3
CBCT
Physical
Case 4
CBCT
Physical
Case 5
CBCT
1
37.45
36.84
2
37.75
36.69
3
38.08
36.69
1
38.28
36.52
2
37.98
36.84
3
37.62
36.77
1
23.83
20.86
2
23.93
21.02
3
23.42
21.2
1
24.14
21.51
2
24.57
21.79
3
24.63
21.72
1
20.29
21.93
2
20.56
22.37
3
20.77
22.4
36
Table1.continued
Case 5
Case 6
Physical
CBCT
Physical
1
22.1
23.4
2
22.32
23.28
3
22.59
22.85
1
35.46
35.78
2
35.62
35.62
3
35.29
35.62
1
35.16
35.49
2
35.25
35.22
3
35.4
35.47
37
CHAPTER III
RESULTS
An overview of statistical methods
Descriptive statistics were calculated. A paired sample t-test was used to
determine whether there was a significant difference between the average values of the
same measurement made under two different conditions (CBCT vs. Physical). The same
test was also used to test for the difference between first and second or first and third or
second and third measurements made by the same observer.
In addition, the intraclass correlation was computed as a measure of agreement between
the first and second or first and third or second and third measurements which were made
by a single-observer.
The following is an approximate guide for interpreting an
agreement between two measurements that corresponds to an intraclass correlation
coefficient.
i)
0=No agreement
ii)
0.0 – 0.20=Poor agreement
iii)
0.21 – 0.40=Fair agreement
iv)
0.41 – 0.60=Moderate agreement
v)
0.61-0.8= Substantial agreement
vi)
0.81-0.99= Strong (or almost perfect) agreement
vii)
1.00= Perfect agreement
All tests had a 0.05 level of statistical significance. SAS for Windows (v9.1, SAS
Institute Inc, Cary, NC, USA) was used for the data analysis.
38
Data preparation
Six randomly selected cadaver heads were used in this study. Six paired (left and
right) measurements were made from each specimen using two methods, comprising 3
pairs of CBCT and 3 pairs of Physical. In order to assure the independence of samples
for performing the appropriate statistical analysis, for each method, the average of three
measurements at left or right side or the average of 6 measurements from the same
specimen was used for the data analysis.
Therefore, there were a total of 6 paired-
samples that were used for each method in this study.
Statistical analysis
Descriptive statistics are summarized in Table 2.
A. Testing a difference between CBCT and Physical at right side
In order to compare the two measurements made from the same head at right side
with the two methods, a new variable called “Diff_R” (Diff_R=CBCT_R –Physical_R)
was created.
A paired-sample t-test was used to determine whether the mean difference
measurement value of two measurements at right side was significantly equal to zero,
which would indicate no statistically significant difference between the two
measurements. The data revealed that overall there was no statistically significant
difference between CBCT and Physical at right side (p=0.2298). The mean difference
value is presented in Table 2.
B. Testing a difference between CBCT and Physical at left side
39
In order to compare the two measurements made from the same head at left side
with the two methods, a new variable called “Diff_L” (Diff_L=CBCT_L –Physical_L)
was created.
A paired-sample t-test was used to determine whether the mean difference
measurement value of two measurements at left side was significantly equal to zero,
which would indicate no statistically significant difference between the two
measurements.
The data revealed that overall there was no statistically significant
difference between CBCT and Physical at left side (p=0.3554). The mean difference
value is presented in Table 2.
C. Testing a overall difference between CBCT and Physical
In order to compare the overall two measurements made from the same head with
the two methods, a new variable called “DiffCP” (DiffCP=CBCT –Physical) was created.
A paired-sample t-test was used to determine whether the mean difference
measurement value of two measurements was significantly equal to zero, which would
indicate no statistically significant difference between the two measurements. The data
revealed that overall there was no statistically significant difference between CBCT and
Physical (p=0.2684). The mean difference value is presented in Table 2.
D. Reliability of measurement
Four measurements were made per specimen, two by calipers and two on CBCT
images for both sides of the specimen. A total of 24 measurements were thus obtained for
all 6 specimens. These measurements were repeated 3 times for each specimen. The
40
measurements were assigned variables M1, M2 and M3 for the first, second and third
measurements respectively.
In order to evaluate the reliability of duplicate measurements made by a single
observer, three new variables “Diff_M12” (Diff_M12=first measurement – second
measurement), “Diff_M13” (Diff_M13=first measurement – third measurement), and
“Diff_M23” (Diff_M23=second measurement – third measurement) were created.
A paired-samples t-test was used to determine if the mean difference between the
two measurements was equal to zero. The data revealed that there were no statistically
significant differences between first and second measurements (p=0.1237), between first
and third measurements (p=0.5608), and between second and third measurements
(p=0.5809).
The mean differences between each of those two measurements are
presented in Table 3.
In addition, intraclass correlation was computed as a measure of intra-observer
agreement between first and second or first and third or second and third measurements.
Data showed that intraclass coefficient was significantly different from zero (p<0.0001
for each instance), and intraclass coefficients of 0.9008, 0.9004 and 0.8950 for each
instance indicated strong agreement between the duplicated measurements made by a
single observer.
Table 2. Mean linear measurement values of bone height under each condition
Lower
Variable
Specimens
(N)
Mean
(mm)
Standard
deviation
Minimum
(mm)
Maximum
(mm)
Median
(mm)
Upper
95% CI 95% CI
for
for
mean
mean
(mm)
(mm)
CBCT_R
6
30.48
6.97
20.54
37.76
32.71
23.17
37.80
Physical_R
6
30.90
6.35
22.34
37.96
32.69
24.24
37.56
Diff_R
6
-0.42
0.75
-1.80
0.19
-0.11
-1.20
0.37
41
Table 2 continued
Variable
Specimens
(N)
Mean
Standard
Minimum
(mm)
deviation
(mm)
Maximum
(mm)
Median
(mm)
Lower
Upper
95% CI 95% CI
for
for
mean
mean
(mm)
(mm)
CBCT_L
6
30.32
7.03
21.03
36.74
33.13
22.94
37.70
Physical_L
6
30.52
6.58
21.67
36.71
33.09
23.62
37.42
*Diff_L
6
-0.20
0.48
-0.94
0.28
-0.01
-0.71
0.31
42
Table 2 continued
Lower
Variable
Specimens
(N)
CBCT
6
Mean
(mm)
30.40
Standard
deviation
6.81
Minimum
(mm)
Maximum
(mm)
Median
(mm)
Upper
95% CI 95% CI
for
for
mean
mean
(mm)
(mm)
21.39
37.25
32.92
23.26
37.55
Physical
6
30.71
6.27
22.76
37.34
32.89
24.13
37.29
*DiffCP
6
-0.31
0.61
-1.37
0.23
-0.06
-0.95
0.33
43
44
1 – Mean value right side
2 – Mean value left side
3 – Overall mean
Figure 21.Graphical representation of mean values of bone height (CBCT and
Physical)
Table 3. Mean difference between two measurements made by the same observer
Variable
Specimens
Mean Standard
deviation
Minimum Maximum
P-value*
(N)
(mm)
Diff_M12
24
-0.08
0.24
-0.44
0.30
-0.11
0.1237
Diff_M13
24
-0.05
0.40
-0.70
0.66
-0.02
0.5608
Diff_M23
24
0.03
0.26
-0.33
0.51
0.00
0.5809
(mm)
(mm)
45
*Paired sample t-test
(mm)
Median
46
CHAPTER IV
DISCUSSION
Radiological evaluation is necessary for information on quantity and quality of
bone available for implant placement and to localize the anatomical structures. There are
certain basic principles of radiography that should guide the clinician in selecting an
appropriate imaging technique and judging whether the resultant images are of required
diagnostic quality. First, there should be an adequate number and type of images to
provide the needed anatomic information. In implant imaging, this includes the quantity
and quality of bone as well as the location of anatomic structures, which generally require
multiple images at right angles to each other. Second, the selected imaging modality
should be precise and minimally distorted which is governed by ideal positioning of the
patient, imaging receptor and x-ray beam. Third, there must be a way of relating the
images with the patient’s anatomy such as with the use of a stent with radiopaque
markers for edentulous regions of the jaws. The exact location of the longitudinal and
cross-sectional views can thus be determined with respect to the edentulous region of the
jaw. Additionally, all images should be of adequate density and contrast and free of
artifacts that might interfere with interpretation of images. Finally, the risks and benefits
of an imaging technique should be weighed in that the radiation dose to the patient and
the financial cost of the imaging technique should be taken into consideration. The
ALARA (as low as reasonably achievable) principle should govern the selection of
imaging technique when more than one technique is suitable in a particular case. 2
Dental implant imaging should provide information about the implant site with
regards to the (1) presence of disease (2) location of anatomic structures to be avoided
47
during implant placement such as maxillary sinus, nasopalatine canal, inferior
alveolar canal, mental foramen, mental canal and submandibular salivary gland fossa (3)
osseous morphology such as knife edge ridges, developmental variations, postextraction
irregularities, enlarged marrow spaces, cortical irregularity and thickness and trabecular
bone density; and (4) amount of bone available for implant placement and orientation of
the alveolar bone. Lingually inclined bony contours which usually occur near the
posterior region of the mandible may lead to osseous undercuts which may lead to a poor
prognosis of an implant treatment plan. If the implant is not placed at a favorable angle
due to inadequate bone, then the functional loading of the implant may be adversely
affected. 2
Lekholm and Zarb3 developed a grading scheme for the quality of bone in the
proposed implant site in terms of relative proportion and density of cortical and
medullary bone. According to this scheme, the bone of the alveolar process is divided
into 4 classes: (1) almost the entire jawbone is composed of homogeneous compact bone,
(2) a thick layer of compact bone surrounds a core of dense trabecular bone, (3) a thin
layer of compact bone surrounds a core of dense trabecular bone of favorable strength,
and (4) a thin layer of compact bone surrounds a core of low density trabecular bone.
Cross-sectional imaging is required to apply this scheme for implant site assessment.
There is another system for bone quality classification proposed by Lindh et al
4
according to which the periapical radiographs grade the bone as dense, sparse or
alternating dense and sparse trabeculation. This method is less specific than the one
proposed by Lekholm and Zarb. 3
48
In pantomographs and other two-dimensional images, information such as the
width of the bone is lacking and even the apparent height of available bone measured
may not be accurate due to distortion caused by positioning errors and variable
magnification.
66, 67
The position of the object between the x ray source and the receptor
is responsible for the magnification seen on a pantomograph. In the sharply depicted
layer the image is free of distortion which means that the magnification factor is the same
for both vertical and horizontal planes.
16
Objects outside this layer will appear distorted
in the image because of the difference between the velocity of the receptor and the
velocity of the projection of the object on the receptor and because of the position of the
object in relation to the tube and receptor. The panoramic image is affected by both
magnification errors and displacement. Distortion, displacement, and magnification cause
changes in the dimensions in the image of depicted structures on radiographs compared
to those of the actual structures. 17 The magnification factor varies from one manufacturer
to another because of different projection geometries; this variation results in differences
in magnification and in the amounts of distortion and displacement of images of
structures relative to each other.
17
Non-uniform magnification with panoramic images
results in 15% to 220% enlargement of structures. 18, 19, 20 The major problem resulting in
errors is patient positioning 21, 22, 23, 24, 25, 26 which can result in geometric distortion of the
image. This distortion has a horizontal and a vertical component. The vertical distortion
is determined by the size of the x-ray focal spot and the distance between the patient’s
arch and the image receptor. The smaller the focal spot and the less the distance between
the patient’s arch and receptor, the less is the vertical distortion. The horizontal
dimensions are affected by the continuously moving rotation center of the beam, and
49
change significantly with the faciolingual positioning of the object and the length of the
effective projection radius. The horizontal magnification also varies from the anterior to
posterior regions as the width of the focal trough is narrower in the anterior region than
the posterior region. The vertical magnification factor varies less between different
faciolingual object positioning and moreover is a linear function.
27
Pantomographic
images reportedly produce 50% to 70% horizontal distortion and 10% to 32% vertical
distortion
28, 29, 30, 31
This distortion factor and the inconsistency in enlargement lead to
inaccurate determinations of implant lengths based on linear measurements from
pantomographic images.
18
To overcome this problem, the use of a surgical stent to
determine implant placement is suggested when making a panoramic image. Small
radiopaque markers placed over potential implant sites can be used to determine the
distortion factor by measuring the actual size of the markers and finding their difference
from the size as measured on the panoramic image. The true height of the residual
alveolar ridge at the prospective implant can be calculated by multiplying this distortion
factor with the distance measured radiographically from the crest of alveolar process to
the superior border of the inferior alveolar canal or floor of the maxillary sinus. 28 Direct
measurements on pantomographs cannot be used without mathematical correction for the
magnification factor. The x-ray beam is directed from below upwards approximately at
5° in the mandible and 15° in the maxilla such that the objects located to the lingual
aspect of the jaw are projected higher than facially positioned objects. This causes objects
to be projected at levels different from their true positions. Therefore, the lowest and
highest parts of rounded objects are not the parts that are reproduced on the image.
32
Furthermore, due to superimposition of the cervical spine over the anterior region of the
50
jaws and due to inherent blurring resulting from a narrow focal trough in the anterior
region, it is not possible to obtain diagnostically accurate information from this region on
a pantomograph.
Thus cross-sectional imaging is recommended to measure bone quantity in all
three dimensions and also accurately localize the anatomical structures such as the
inferior alveolar canal, maxillary sinus etc. Conventional tomography with complex
motions is a cost effective method with low radiation risk that is recommended for most
of the cases but provides slices limited in breadth. Conventional tomography is time
consuming and the image quality depends on the skill of the operator as the positioning
of the anatomical structure in relation to the image layer has to be accurate. Variation
from this position may lead to blurring due to superimposition of osseous and soft tissue
structures.
68
These variations lead to discrepancy of measurements both intraobserver
and interobserver.
Many factors must be evaluated when trying to decide which type of crosssectional imaging to use, including number of implant sites, degree of bone resorption or
history of bone grafting that may affect the precision needed, accuracy and reliability of
the imaging modality, convenience and cost and radiation dose. Both underestimating
and overestimating the amount of bone and the location of anatomic structures can affect
the success of implant placement. More complex implant cases, such as those involving
patients who have had facial trauma or surgery for malignancy or those who have
received ridge augmentation, may necessitate more complex imaging such as CT for
evaluation of the reconstructed bone before implant placement whereas conventional
tomography may be adequate for the majority of implant cases. CT is more appropriate
51
when multiple implants are considered as it provides slices through the entire region of
interest. Conventional CT provides cross-sectional views through the area of interest and
overcomes the issue of blurring associated with conventional tomography but this is
achieved at a higher cost and increased radiation to the patient.
The measurement error is generally required to be less than 1 mm on images
made for implant treatment.
69
In studies
67, 70
using cadaver mandibles, measurement
error was found to be less than 1 mm in 94% cases of CT, 39% cases of conventional
tomography, 53% cases of intraoral radiography and 17% cases of panoramic
radiography. CBCT is a new technology that provides cross-sectional images without
superimposition or blurring 47, 48 and reduces the risk of radiation significantly. 54, 71
CBCT provides 3D imaging dedicated to the maxillofacial region at low cost and
low dose of radiation. Imaging is accomplished by using a rotating gantry to which an xray source and detector are fixed. A divergent pyramidal or cone-shaped source of
ionizing radiation is directed through the middle of the area of interest onto the x-ray
detector on the opposite side.
50
The x-ray source and detector rotate around a rotation
fulcrum fixed within the center of the region of interest.
50
During the rotation, multiple
(from 150 to more than 600) sequential planar projection images of the field of view
(FOV) are acquired in a complete, or sometimes partial, arc.
50
This procedure varies
from a conventional spiral CT, which uses a fan-shaped x-ray beam in a helical
progression to acquire individual image slices of the FOV and then stacks the slices to
obtain a 3D representation.
50
Each slice requires a separate scan and separate 2D
reconstruction. Because CBCT exposure incorporates the entire FOV, only one rotational
sequence of the gantry is necessary to acquire enough data for image reconstruction. 50
52
There are several commercially available CBCT units and although all of them provide
3D information, each manufacturer uses slightly different scanning parameters and
viewing software. Some of the CBCT units available commercially are Galileos 3D
(Sirona Dental Systems, Charlotte, N.C.), i-CAT (Imaging Sciences International,
Hatfield, PA), CB Mercuray (Hitachi Medical Systems America, Twinsburg, Ohio), New
Tom 3G and VG (AFP Imaging, Elmsford, N.Y.), ProMax 3D (TeraRecon, San Mateo,
Calif.), Scanora 3D (Soredex, Tuusula, Finland), 3D Accuitomo FPD XYZ Slice View
Tomograph (J. Morita USA, Irvine, Calif.). 49
The patient may sit, stand or be supine depending on the type of unit used. The
image detectors used in CBCT units are flat-panel
Couple Device (CCD) camera.
47, 48, 52
51
or image intensifier and Charge
The flat panel detectors or solid state receptors
absorb photons that are converted to an electric charge, which is measured by the
computer. One advantage of solid-state receptors is improved photon utilization; one
disadvantage is the high cost of production. Image intensifiers capture photons and
convert them to electrons that contact a fluorescent screen that emits light captured by a
charge-coupled device camera.
49
The image intensifiers with a CCD camera produce
increased noise from scatter radiation with a concomitant loss of contrast resolution. This
may lead to geometric distortions that must be addressed in the data processing software.
This disadvantage could reduce measurement accuracy of the CBCT units using this
configuration. 50The Galileos CBCT unit in this study has an image intensifier as detector
which could compromise the measurement accuracy but the results do not show any
significant variation of the linear measurements from the physical measures which was
considered as the gold standard.
53
The images acquired are in the Digital Imaging and Communications in Medicine
(DICOM) (National Electrical Manufacturers Association, Rosslyn, VA. and American
College of Radiology, Reston, VA) data format.
53
DICOM is a standard for handling,
storing, printing and transmitting information in medical imaging. During a single
rotation of the source and receptor, the receptor captures the entire volume of anatomy
within the FOV. The DICOM data is imported into the viewing software, allowing
visualization of the axial, coronal and sagittal reconstructed images as well as 3D volume
rendering. Third party software can serve as an adjunct in treatment planning. Examples
of such software are SimPlant (Materialise Dental NV, Leuven, Belgium) and Procera
Software 2.0 (Nobel Biocare USA, Yorba Linda, Calif.). These convert DICOM data into
files that provides information for presurgical planning.
Few studies have been carried out in the past evaluating the geometric accuracy of
the available CBCT units. Lascala and coworkers
59
used dry skulls and imaged them
with New Tom 9000 CBCT unit. Linear measurements made between anatomical sites
were compared with caliper measurements between the same points. The results showed
that the real measurements were always greater than the CBCT ones but these differences
were only significant for measurements of internal structures of the base of the skull.
Hence they concluded that although there were significant differences in measurements at
the base of skull but not for structures associated with maxillofacial imaging therefore it
is reliable for imaging this region.
Ludlow and coworkers 60 assessed dry skulls in ideal, shifted and rotated positions
and measured distances between anatomic points and reference wires. Images were
acquired using the New Tom 9000 CBCT scanner. Measurement accuracy was expressed
54
by average errors of less than 1.2% for two-dimensional measurement techniques and
less than 0.6% for three-dimensional measurement techniques. They concluded that both
two-dimensional and three-dimensional techniques provide acceptably accurate
measurement of mandibular anatomy which was not significantly influenced by variation
in skull positions during imaging.
Mischkowski and coworkers 61 compared measurements on images acquired with
a beta version of the Galileos CBCT unit with that of a conventional CT scanner
(Somatom sensation 6). Mean absolute error (AME) for linear distances for the CBCT
unit was 0.26 mm (+0.18 mm) and 0.18 mm (+0.17 mm) for the MDCT device. The
average absolute percentage error (APE) was 0.98% and 1.26% respectively. They
concluded that the Galileos CBCT unit provided satisfactory information about linear
distances and volumes. MDCT proved slightly more accurate but the difference is not
clinically relevant.
Stratemann and coworkers
62
worked with two different CBCT units: the New
Tom QR DVT 9000 and the Hitachi MercuRay. Measurements were made on human dry
skulls using both these units and compared to a gold standard of caliper measurements.
They concluded that both the CBCT systems provided highly accurate data with less than
1% relative error.
In another study, Periago and coworkers
63
used dry skulls and compared CBCT
(i-CAT) measurements with caliper measurements between anatomical landmarks. Mean
percentage measurement error for CBCT (2.31% + 2.11%) was significantly higher than
skull measurements (0.63% + 0.51%). They concluded that despite statistically
significant differences between linear measurements using cephalometric landmarks on
55
CBCT images and caliper measurements on skulls, most can be considered to be
clinically accurate for craniofacial analyses.
In the current study, specimens selected were human embalmed cadaver heads
with intact soft tissue around and within the jaws in its original anatomic relationship.
This is in contrast to previous studies which utilized dry skulls for evaluation of accuracy
of linear measurements between anatomical points on the skull. The measurements in
these studies were carried out between external points on the skull. This can be
significantly different from measurements made between points within the bone as the xray beam undergoes attenuation on passing through not only external soft tissue but also
the soft tissue within the bone. The image contrast is more when bone is imaged against
air as with a dry skull as opposed to imaging bone against soft tissue as in the case of live
patients. Imaging dry skulls may show high accuracy of measurement because the image
contrast is high which adds to the ease of delineating structures and boundaries of
structures. Having soft tissue surrounding the bone provides an additional source of
scatter radiation altering the image contrast which may compromise accurate localization
of points on images. Other than soft tissue attenuation, the accuracy of measurement
between different landmarks may be affected by a reduction in image quality due to
metallic artifacts and patient motion. Variation in scanning protocol such as voxel size
and number of projection images may also influence dimensional accuracy. This study
has incorporated the issue of soft tissue attenuation by using cadaver heads simulating
patient heads as closely as possible. The soft tissue around both the jaws was intact
during imaging as well as the tissue within the bone. Even though the CBCT images do
not distinguish between the different types of soft tissues, the soft tissue coverage as well
56
as the internal soft tissue may degrade the image quality. Other factors such as patient
motion which may degrade image quality and thus compromise measurement accuracy
were not applicable in this situation as these were not live samples. Some specimens used
in this study had metallic restorations and measurements were not significantly affected
in these samples as the associated artifacts were present away from the region of
measurements.
In the current study, the linear measurements made between the superior most
point and the inferior most point of the mandibular bone at a particular plane. This plane
of measurement was consistent with the CBCT and Physical measurements. The plane
was determined by placement of radiopaque fiduciary markers one each on the buccal
and lingual surfaces of the bone such that both these markers were visualized on a single
slice on the CBCT images. The selection of the marker was based on the radiopacity of
the material and size of the marker such that they were more radiopaque than the
surrounding tissues and small enough to be not visible in more than on 1-2 orthogonal
slices. The slice in which both the lingual and buccal markers appeared to be completely
in focus was selected for measurement.
The six specimens used in the current study were measured three times on both
right and left sides at the same spot by a single observer. The results showed no
statistically significant difference between the CBCT and Physical measurements on the
right side of the specimens (p=0.2298), on the left side (p=0.3554) and overall difference
between CBCT and Physical (p=0.2684).
The data revealed that there were no
statistically significant differences between first and second measurements (p=0.1237),
between first and third measurements (p=0.5608), and between second and third
57
measurements (p=0.5809) showing reproducibility of measurements. The mean physical
measurements were greater than the mean CBCT measurements both on the right and left
sides although the difference was not statistically significant. The overall mean of the
physical measurements (30.71) was higher than the overall mean of the CBCT
measurements (30.40) although the difference was not statistically significant. The results
from the current study are in agreement with similar studies carried out previously using
skulls without soft tissue components. The current study also shows that attenuation of xrays by soft tissue did not affect the accuracy of measurements of bone height on images
acquired in the Galileos CBCT unit.
The design of this study minimized the error associated with determining the
plane of measurement for both the CBCT and Physical measurements. Three markers
were placed on the buccal aspect of the bone and one on the lingual aspect. The buccal
marker that was completely in focus with the lingual marker in the same slice was
selected for determining the measurement plane. The same plane was selected for slicing
the specimen for determining the Physical measurement.
The drawback of the study was that the measurements were made by a single
observer which may introduce bias in the study even though the measurements were
made three times for the same location. The detector used in the Galileos CBCT unit is an
image intensifier which is known to introduce noise in the images which could be a
potential drawback; however, this did not adversely affect the accuracy of measurement
on the images in the current study.
58
CHAPTER V
CONCLUSION
Based on the statistical evaluation of the CBCT and Physical measurements it can
be concluded that the Galileos CBCT unit is reliable for evaluation of linear
measurements between anatomic structures within the mandible in the presence of soft
tissues. Based on the requirement that the measurement error be less than 1 mm on
images for preoperative implant site assessment, the Galileos CBCT is sufficiently
accurate for clinical use.
59
BIBLIOGRAPHY
1. Björk A, Solow B. Measurement on Radiographs. J Dent Res 1962.41(3)672683.
2. American Academy of Oral and Maxillofacial Radiology; edited by Tyndall
D.A., Brooks S.L. Selection criteria for dental implant site imaging : A position
paper of the American Academy of Oral and Maxillofacial Radiology. Oral
Surg Oral Med Oral Pathol Oral Radiol Endod 2000; 89:630-7.
3. Lekholm U, Zarb G.A. Patient selection and preparation. In: Branemark P-I,
Zarb GA, Albrektsson T, editors. Tissue-integrated prosthesis: Osseointegration
in clinical dentistry. Chicago: Quintessence; 1985.p. 199-209.
4. Lindh C, Peterson A, Rohlin M. Assessment of the trabecular pattern before
endosseous implant treatment. Diagnostic outcome of periapical radiography in
the mandible. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1996;
82:335-43.
5. Sewerin I.P. Errors in radiographic assessment of marginal bone height around
osseointegrated implants. Scand J Dent Res 1990; 98(5):428-33
6. BouSerhal C, Jacobs R, Quirynen M, Steenberghe D.V. Imaging Technique
Selection for the Preoperative Planning of Oral Implants: A Review of the
literature. Clinical Implant Dentistry and Related Research 2002; 4(3) 156-172.
7. Strid K.G. Radiographic procedures. In: Branemark PI, Zarb GA, Albrektsson
T, editors. Tissue-integrated prosthesis: Osseointegration in clinical dentistry.
Chicago: Quintessence; 1985.
8. Watson R.M., Davis D.M., Forman G.H., Coward T. Considerations in design
and fabrication of maxillary implant-supported prostheses. Int J Prosthodont
1991; 4: 232-9.
9. Babbush C.A. Evaluation and selection of the endosteal implant patient. In:
McKinney RV, editor. Endosteal dental implants. St Louis: Mosby Year Book;
1991. P. 63-74.
10. Stella J.P., Tharanon W. A precise radiographic method to determine the
location of the inferior alveolar canal in the posterior edentulous mandible:
implications for dental implants. Part 1: Technique. Int J Oral Maxillofac
Implants 1990; 5: 15-22.
11. Kassebaum D.K., Nummikoski P.V., Triplett RG, Langlais RP. Cross-sectional
radiography for implant site assessment. Oral Surg Oral Med Oral Pathol 1990;
70: 674-8.
60
12. Frederiksen N.L. Specialized radiographic techniques. In: White SC, Pharoah
MJ, Oral radiology, principles and interpretation. St Louis: Mosby Inc.,
2000:217–240.
13. Butterfield K.J., Dagenais M, Clokie C. Linear tomography's clinical accuracy
and validity for presurgical dental implant analysis. Oral Surg Oral Med Oral
Pathol Oral Radiol Endod 1997, 84:203–209.
14. Todd A.D., Gher M.E., Quintero G, Richardson A.C. Interpretation of linear
tomography and computed tomograms in the assessment of implant recipient
sites. J Periodontol 1993; 64:1243–1249.
15. Lurie A.G., Panoramic Imaging in White, S.C., Pharoah M.J., Oral Radiology
Principles and Interpretation, 6th edition, 2008, Mosby, Inc., 175-190.
16. McDavid W.D., Tronje G, Welander U. A method to maintain a constant
magnification factor throughout the exposure of rotational panoramic
radiographs.
17. Amir C, Asja C, Melita VP, Adnan C, Vjekoslav J, Muretic I, Croatia.
Evaluation of the precision of dimensional measurements of the mandible on
panoramic radiographs. Oral Surg Oral Med Oral Pathol Oral Radiol Endod
1998; 86:242-8.
18. SanGiacomo T.R. Topics in implantology III: Radiographic Treatment
Planning. RI Dent J 1990; 23:5-11.
19. Gratt B. Panoramic radiograph/oral radiography: principles and interpretation.
In: Goaz P, White S (eds), Oral Radiology: Principles and Interpretation. CV
Mosby Co., St. Louis, 1987.
20. Sanfors K, Welander U: Angle distortion in narrow beam rotation radiography.
Acta Radiologica Diagn 1974; 15: 570-576.
21. Glass B.J.: Successful panoramic radiography. Pub. No. N-406, Eastman Kodak
Co. Rochester, NY, 1991.
22. Schiff T, D’Ambrosio J, Glass B.J. et al. Common positioning and technical
errors in panoramic radiology. J Am Dent Assoc. 1986; 113:422-426.
23. Stramotas S, Geenty J.P., Petocz P and Darendeliler M.A. Accuracy of linear
and angular measurements on panoramic radiographs taken at various positions
in vitro. European Journal of Orthodontics 24 (2002) 43-52.
61
24. Laster W.S., Ludlow J.B., Bailey L.J., Hershey H.G. Accuracy of measurements
of mandibular anatomy and prediction of asymmetry in panoramic radiographic
images. Dentomaxillofac Radiol 2005; 34: 343-9.
25. Tronje G, Eliasson S, Julin P, Welander U. Image distortion in rotational
panoramic radiography. II Vertical distances. Acta Radiol Diagn (stockh). 1981;
22:449-55.
26. Catic A, Celebic A, Valentic-Peruzovic M, Catovic A, Jerolimov V, Muretic I.
Evaluation of the precision of dimensional measurements of the mandible on
panoramic radiographs. Oral Surg Oral Med Oral Pathol Oral Radiol Endo
1998; 86: 242-8.
27. Welander U, Tronje G, McDavid W.D. Theory of rotational panoramic
radiography. In: Langland OE, Langlais RP, McDavid W.D, DelBalso A.M,
editors. Panoramic radiology. 2nd ed. Philadelphia: Lea & Febiger; 1989. P.3840.
28. Hobo S, Ichida E, Garcia L.T: Osseointegration and Occlusal Rehabilitation.
Quintessence, Chicago, 1989.
29. Engelman M.J., Sorensen J.A., Moy P. Optimum placement of osseointegrated
implants. J Prosthet Cent 1988; 59:467-473.
30. Lund T, Manson-Hing L. A study of focal troughs of three panoramic dental xray machines: Part II. Image dimensions. Oral Surg 1975; 39:318-328.
31. Zinner I.D., Small S.A., Panno F.V.: Presurgical prosthetics and surgical
templates. Dent Clin North Am, 1989; 33:4-8.
32. Tronje G, Eliasson S, Julin P, Welander U. Image distortion in rotational
panoramic radiography. II. Vertical distances. Acta Radiol Diagn (Stockh) 1981;
22:449-55.
33. Miles D.A., Van Dis M.L.: Implant Radiology. Dent Clin North Am 1993; 37:
645-668.
34. Goldman L.W. Principles of CT and CT Technology. J Nucl Med Technol 2007;
35:115-128.
35. Williams M.Y., Mealey B.L., Hallmon W.W. The role of computerized
tomography in dental implantology. Int J Oral Maxillofac Surg 1992; 7:373380.
62
36. Rothman S.L., Chaftez N, Rhodes M.L., Schwarz M.S. CT in the preoperative
assessment of the mandible and maxilla for endosseous implant surgery. Work
in progress. Radiology 1988; 168: 171-175.
37. Lindh C. Radiography of the mandible prior to endosseous implant treatment.
Localization of the mandibular canal and assessment of the trabecular bone.
Swed Dent J 1996; Supp 112:1-45.
38. Gröndahl K, Ekestubbe A, Gröndahl H.G., Johnsson T. Reliability of
hypocycloidal tomography for the evaluation of the distance from the alveolar
crest to the mandibular canal. Dentomaxillofac Radiol 1991; 20:200-4.
39. Cavalcanti M.G., Haller J.W., Vannier M.W. Three-dimensional computed
tomography landmark measurement in craniofacial surgical planning:
experimental validation in vitro. J Oral Maxillofac Surg 1999; 57:690-4.
40. Lo LJ, Lin W.Y., Wong H.F., Lu K.T., Chen Y.R. Quantitative measurement on
three-dimensional computed tomography: an experimental validation using
phantom objects. Chang Gung Med J 2000; 23:354-9.
41. Cavalcanti M.G.P., Ruprecht A, Vannier M.W. 3D volume rendering using
multislice CT for dental implants. Dentomaxillofacial Radiology 2002; 31: 218
– 223.
42. Klinge B, Peterson A, Maly P. Location of the mandibular canal: comparison of
macroscopic findings, conventional radiography and computed tomography. Int
J of Oral and Maxillofac Implants 1989; 4:327-32.
43. Ekestubbe A, Gröndahl K, Gröndahl H.G. The use of tomography for dental
implant planning. Dentomaxillofac Radiol 1997; 26: 206-13.
44. Ekestubbe A, Gröndahl K, Ekholm S, Johansson P.E., Gröndahl H.G. Low-dose
tomographic techniques for dental implant planning. Int J Oral Maxillofac
Implants 1996; 11:650-9.
45. Preda L, Di Maggio E.M., Dore R, La Fianza A, Solcia M, Schifino M.R., et al.
Use of spiral computed tomography for multiplanar dental reconstruction.
Dentomaxillofac Radiol 1997; 26: 327-31.
46. Dula K, Mini R, Lambrecht J.T., van der Stelt P.F., Schneeberger P, Clemens G
et al. Hypothetical mortality risk associated with spiral computed tomography of
the maxilla and mandible. Eur J Oral Sci 1996; 104: 503-10.
47. Mozzo P, Procacci C, Tacconi A, Martini P.T., Andreis I.A. A new volumetric
CT machine for dental imaging based on the cone-beam technique: preliminary
results. Eur Radiol 1998;8:1558-1564.
63
48. Arai Y, Tammisalo E, Iwai K, Hashimoto K, Shinoda K. Development of a
compact computed tomographic apparatus for dental use. Dentomaxillofac
Radiol 1999; 28: 245-248.
49. Howerton W.B., Mora M.A. Advancements in digital imaging. What is new and
on the horizon? JADA 2008;139;20s-24s.
50. Scarfe W.C., Farman A.G.. What is Cone-Beam CT and How Does it Work ?
Dent Clin N Am 52 (2008) 707-730.
51. Baba R, Ueda K, Okabe M. Using a flat-panel detector in high resolution cone
beam CT for dental imaging. Dentomaxillofac Radiol 2004; 33; 285-290.
52. Sarment D.P., Sukovic P, Clinthorne N. Accuracy of implant placement with a
stereolythographic surgical guide. Int J Oral Maxillofac Implants 2003; 18:571577.
53. Digital Imaging and Communications in Medicine. DICOM. Rosslyn, Va.:
NEMA. http://medical.nema.org/ Accessed April 16, 2008.
54. Ludlow J.B., Davies-Ludlow L.E., Brooks S.L. Dosimetry of two extraoral
direct digital imaging devices: NewTom cone beam CT and Orthophos Plus DS
panoramic unit, Dentomaxillofac Radiol 32 (2003), pp. 229–234.
55. Ludlow J.B., Davies-Ludlow L.E., Brooks S.L. et al., Dosimetry of 3 CBCT
devices for oral and maxillofacial radiology: CB Mercuray, NewTom 3G and iCAT. Dentomaxillofac Radiol. 35 (2006), pp. 219–226.
56. Ludlow J.B., Davies-Ludlow L.E., Mol A. Dosimetry of recently introduced
CBCT units for oral and maxillofacial radiology, Proceedings of the16th
International Congress of Dentomaxillofacial Radiology, Beijing, China (26–30
June, 2007), p. 97.
57. Schulze D, Heiland M, Thurmann H et al., Radiation exposure during midfacial
imaging using 4- and 16-slice computed tomography, cone beam computed
tomography systems and conventional radiography. Dentomaxillofac Radiol 33
(2004), pp. 83–86.
58. Scaf G, Lurie A.G., Mosier KM et al., Dosimetry and cost of imaging
osseointegrated implants with film-based and computed tomography. Oral Surg
Oral Med Oral Pathol Oral Radiol Endod 83 (1997), pp. 41–48.
59. Lascala C.A., Panella J, Marques M.M. Analysis of accuracy of linear
measurements obtained by cone beam computed tomography (CBCTNewTom). Dentomaxillofac Radiol (2004),33, 291-294.
64
60. Ludlow J.B., Laster W.S., See M, Bailey L.T.J., Hershey H.G. Accuracy of
measurements of mandibular anatomy in cone beam computed tomography
images. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007; 103: 53442.
61. Mischkowski R.A, Pulsfort R, Ritter L, Neugebauer J, Brochhagen H.G., Keeve
E, Zöller JE. Geometric accuracy of a newly developed cone-beam device for
maxillofacial imaging. Oral Surg Oral Med Oral Pathol Oral Radiol Endod
2007; 104:551-9.
62. Stratemann S.A., Huang J.C., Maki K, Miller A.J., Hatcher D.C. Comparison of
cone beam computed tomography imaging with physical measures.
Dentomaxillofac Radiol (2008),37, 80-93.
63. Periago D.R., Scarfe W.C., Moshiri M, Scheetz J.P., Silveira A.M., Farman
A.G. Linear Accuracy and Reliability of Cone Beam CT Derived 3Dimensional Images Constructed Using an Orthodontic Volumetric Rendering
Program. Angle Orthodontist, 2008; 78;3; 387-395.
64. Veyre-Goulet S, Fortin T, Thierry A. Accuracy of Linear Measurement
Provided by Cone Beam Computed Tomography to Assess Bone Quantity in the
Posterior Maxilla: A Human Cadaver Study. Clinical Implant Dentistry and
Related Research, 2008; 10(4): 226-30.
65. Lagrav re M.O., Carey J, Toogood R.W., Major P.W. Three-dimensional
accuracy of measurements made with software on cone-beam computed
tomography images. Am J Orthod Dentofacial Orthop 2008; 134: 112-16.
66. Bou Serhal C, Jacobs R, Flygare L, Quirynen M, Van Steenberghe D.
Perioperative validation of localisation of the mental foramen. Clin Oral
Implants Res 2002; 31:39–43.
67. Petrikowski C.G., Pharoah M.J., Schmitt A. A presurgical radiographic
assessment for implants. J Prosthet Dent 1989; 61:59–64.
68. Bou Serhal C, Van Steenberghe D, Quirynen M, Jacobs R. Localisation of the
mandibular canal using conventional spiral tomography: a human cadaver
study. Clin Oral Implants Res 2001; 12:230–236.
69. Wyatt C.C., Pharoah M.J. Imaging techniques and Image interpretation for
dental implant treatment. Int J Prosthodont 1998; 11: 442-452.
70. Bolin A, Eliasson S, von Beetzen M, Jansson L. Radiographic evaluation of
mandibular posterior implant sites: Correlation between panoramic and
tomographic determinations. Clin Oral implants Res 1996;7: 354-359.
65
71. Hashimoto K, Arai Y, Iwai K, Araki M, Kawashima S, Terakado M. A
comparison of a new limited cone beam computed tomography machine for
dental use with a multidetector row helical CT machine. Oral Surg Oral Med
Oral Pathol Oral Radiol Endod 2003; 95:371-377.
72. Habets L.L., Bezuur J.N., van Ooij C.P., Hansson T.L. The orthopantomogram,
an aid in diagnosis of temporomandibular joint problems. I. The factor of
vertical magnification. J Oral Rehabil 1987; 14: 475-80.
73. Kjellberg H, Ekestubbe A, Kiliaridis S, Thilander B. Condylar height on
panoramic radiographs. A methodologic study with a clinical application. Acta
Radiol Scand 1994; 52:43-50.
74. Turp J.C., Vach W, Harbich K, Alt K.W., Strub J.R. Determining mandibular
condyle and ramus height with the help of an Orthopantomogram- a valid
method? J Oral Rehabil 1996; 23:395-400.
75. Xie Q, Soikkonen K, Wolf J, Mattila K, Gong M, Ainamo A. Effect of head
positioning in panoramic radiography on vertical measurements: an in vitro
study. Dentomaxillofac Radiol 1996; 25:61-6.
76. Mckee I.W., Glover K.E., Williamson P.C., Lam E.W., Heo G, Major P.W. The
effect of vertical and horizontal head positioning in panoramic radiography on
mesiodistal tooth angulations. Angle Orthod 2001; 71: 442-51.
77. Stramotas S, Geenty J.P., Petocz P, Darendeliler M.A., Accuracy of linear and
angular measurements on panoramic radiographs taken at various positions in
vitro. Eur J Orthod 2002; 24:43-52.
78. Yosue T, Brooks S.L.: The appearance of mental foramina on panoramic and
periapical radiograph. Oral Surg Oral Med Oral Pathol Oral Radiol 1989;
68:488-492.
79. Quirynen M, Lamoral Y, Dedeyser C, Peene P, van Steenburghe D, Bonte J, et
al. CT scan standard reconstruction technique for reliable jaw bone volume
determination. Int J Oral Maxillofac Implants 1990; 5:384-9.
80. Ten Bruggenkate C.M., van der Linden L.W., Oosterbeek H.S. Parallelism of
implants visualized on the orthopantomogram. Int J Oral Maxillofac Surg 1989;
18:213-5.