Download Cone beam imaging: is this the ultimate imaging modality?

Review
Bernard Koong
Authors’ affiliations:
Bernard Koong, School of Dentistry, University of
Western Australia, Nedlands, WA, Australia
Corresponding author:
Bernard Koong
School of Dentistry
University of Western Australia
c/o 178 Cambridge Street, Suite 5
Wembley, WA 6014
Australia
Tel.: þ 618 6382 3888
Fax: þ 618 6382 3800
e-mail: [email protected]
Cone beam imaging: is this the ultimate
imaging modality?
Key words: application, beam hardening, caries, CBCT, computed tomography, cone beam, CT,
image quality, implant, interpretation, limitations, multislice, periapical, periodontal, radiation
dose, requirements, resolution, responsibilities, scatter, signal, soft tissue
Abstract: This review article provides an overview of cone beam (CB) imaging technology and its
role in orofacial imaging, including comparison with two-dimensional (2D) radiography and
multislice computed tomography (MCT). The radiation dose levels of CB systems are discussed,
with reference to those delivered by MCT and common dental 2D views. The large variation in
dose levels delivered by CB systems and the importance of using ultra low-dose CB units are
emphasized. Low-dose MCT protocols can be used. CB and MCT image quality are compared. CB
is an essential technique that all dental and orofacial clinicians must be familiar with. Where
ultra low-dose systems and protocols are used, CB imaging should be considered in day-to-day
clinical practice. However, CB imaging is not the technique of choice in many clinical scenarios.
Rather than replacing other modalities, CB imaging complements intraoral 2D radiography,
panoramic radiography, MCT and other techniques including magnetic resonance imaging,
ultrasound and nuclear medicine. MCT is a much more powerful and flexible modality and
presently remains the technique of choice over CB imaging in many clinical scenarios. All
radiologic examinations, including CB and MCT, should be comprehensively evaluated in
entirety. The responsibilities and the radiological skill levels of clinicians involved in imaging as
well as the associated ethical and medico-legal implications require consideration.
Defined in simple terms, multislice computed
tomography (MCT) uses finely collimated flat,
fan-shaped beams rotating around the patient in a
helical progression to acquire multiple image
slices. In contrast, cone beam (CB) units use a
divergent cone/pyramidal-shaped beam, obtaining multiple planar projections in a single rotation. These cone-shaped beams are similar to
those of X-ray units for two-dimensional (2D)
radiography. MCT data are acquired with patients in a supine position while many CB units
obtain data with patients standing or sitting. For
both MCT and CB, computers are used to reconstruct the volumetric images from the acquired
data, using a back-projection algorithm.
Radiation dose levels
Date:
Accepted 25 May 2010
To cite this article:
Koong B. Cone beam imaging: is this the ultimate imaging
modality?.
Clin. Oral Impl. Res. 21, 2010; 1201–1208.
doi: 10.1111/j.1600-0501.2010.01996.x
c 2010 John Wiley & Sons A/S
In 2007, the ICRP released new tissue weight
recommendations for calculating effective doses
(ICRP 2007). The key implication to orofacial
imaging is the inclusion of salivary glands (0.01),
which was not (ICRP 1990 recommendations)
specifically identified previously. This has resulted
in the overall increase in calculated effective doses
delivered during orofacial imaging, notably the
panoramic radiograph. It may remain necessary
to refer to the 1990 ICRP recommendations for
ease of comparison with earlier studies.
The reported effective doses delivered by orofacial CB units range widely; from 6–806 mSv (1990
tissue weights) and 27–1073 mSv (2007 tissue
weights) (Ludlow et al. 2003, 2006, 2008; Schulze
et al. 2004; Kumar et al. 2007; Ludlow & Ivanovic
2008; Scarfe & Farman 2008; White 2008; Okano
et al. 2009; Roberts et al. 2009; Suomalainen et al.
2009). Compared with MCT, there is relatively
limited control over CB protocols and the wide
range of CB doses delivered is largely unit specific.
Also of note is that some small field of view (FOV)
units deliver larger doses than some larger FOV
units. The difficulty in making a detailed comparison of the various units and published studies is
recognized (De Vos et al. 2009). This is due to a
variety of factors, including variation in device
properties, FOVs, detectors, frame rates and the
image quality required.
MCT examinations of the jaws have been
reported to deliver effective doses between 180–
2100 mSv (1990) and 474–1410 mSv (2007), with
significant variation in scanning protocols (Ngan
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Koong Cone beam imaging
et al. 2003; Loubele et al. 2005, 2008, 2009;
Ludlow & Ivanovic 2008; Suomalainen et al.
2009). While there are some equipment differences, the MCT doses delivered for jaw examinations are very much dependent on the imaging
protocols. It has been shown that appropriate
protocols can be used to significantly reduce
radiation dose levels with no significant compromise in image quality (Loubele et al. 2005). This
author’s experience supports these findings and
also that various low-dose MCT protocols can be
sufficient to produce diagnostic images for many
purposes in dentistry.
Reported effective dose levels associated with
panoramic radiographs also vary significantly,
with a range of 4.7–54 mSv (ICRP 1990) (Ludlow
et al. 2003; Ngan et al. 2003; Kobayashi et al.
2004; Gijbels et al. 2005; Gavala et al. 2009). A
full-mouth 2D intraoral series has been reported
to deliver effective dose levels between 34.9 and
388 mSv (ICRP 2007) (Ludlow et al. 2008; Aarup
et al. 2009).
When comparing the radiation dose levels
delivered by these modalities, the key points are:
CB radiation doses range widely, largely depending on the unit used,
some CB units deliver higher radiation dose
levels than MCT scans of the jaws, when
appropriate low-dose MCT protocols are used,
some CB units are able to deliver lower dose
levels than low-dose MCT scans for the same
volume,
small FOV CB units do not necessarily deliver doses that are lower than some larger FOV
CB units,
some CB units are capable of delivering doses
comparable to or even lower than the panoramic radiograph (some units) and some intraoral 2D series (number of projections,
technique and detector dependent),
comparing available data are difficult and this
technology continues to evolve quickly.
Fig. 1. Various cross-sectional (para-axial) cone beam images for implant planning. Note some variation in image quality,
noise, signal-to-noise ratio and beam hardening related to patient factors, and to a lesser extent, imaging protocols. The effect
of beam hardening is noted (vertical arrows). The mandibular canals are identified in the mandibular posterior sites (black
arrows). A prominent submandibular concavity is identified (horizontal arrow).
b
a
c
Image quality
d
CB units produce images with a voxel resolution
range of 0.076–0.4 mm (Scarfe & Farman 2008;
White 2008). However, the benefit of higher
resolution of CB compared with MCT can be
significantly reduced by other factors (Draenert
et al. 2007; Sanders et al. 2007; Watanabe et al.
2009).
For a similar volume, MCT scans are faster
than CB units, therefore reducing potential motion-related image degradation.
Patients are supine during MCT scans while
most of the presently used CB units image
patients in the standing or sitting position, potentially contributing to motion artefact.
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e
Fig. 2. Cross-sectional multislice computed tomography (MCT) images of various sites intended for implant placement.
Image quality can be further increased if higher dose protocols are used. In comparison with the cone beam images in Fig. 1,
note the higher signal-to-noise ratio. Also, beam hardening is not appreciable in these MCT images. There is also some
variation in image quality related to patient factors and imaging protocols. Image (a) demonstrates new bone formation in the
incisor socket (black arrow). Image (b) demonstrates a prominent sublingual concavity (white arrow) with only a cortex
separating the sublingual space and the neurovascular bundle (black arrows identify the mandibular canal and mental
foramen). The mandibular canals are also noted in images (c) and (d). Image E demonstrates bifurcation of a mandibular canal,
which merges further anteriorly (not seen in this image).
In CB imaging, a much larger cone-shaped
volume is irradiated during each planar basis
projection and large area detectors are used.
This leads to a much larger amount of Compton
scatter, which significantly increases image noise
and degradation compared with MCT images. In
addition, the lower energy photons of CB units
result in a much lower signal-to-noise ratio
c 2010 John Wiley & Sons A/S
Koong Cone beam imaging
compared with MCT. This results in relative
difficulty in examining the structures of interest
in CB images, as they do not ‘‘stand out’’ as
much from the increased ‘‘background noise’’,
compared with MCT. The appearance of less
variation between denser and less dense structures, a ‘‘flatter’’ image, is typical of CB images.
This needs to be considered when interpreting CB
images.
As a result of the low signal nature of CB
imaging, beam hardening can be a significant
disadvantage compared with MCT (Draenert et
al. 2007; Sanders et al. 2007). This is related to
the polychromatic nature of X-ray beams, with
the initial attenuation of low-energy photons and
the resultant increased mean energy of the beam.
This leads to the appearance of shadows and
bands associated with dense structures. Beam
hardening increases with patient head size and
denser structures, especially when these structures are in close proximity. In contrast, beam
hardening associated with dense non-metallic
objects is rarely of significance in MCT scans of
the head and neck region.
Metal artefact (extreme attenuation) from restorations is more significant with MCT than CB
but the limitations of CB described, including
beam hardening (Draenert et al. 2007; Sanders et
al. 2007) tend to result in an overall similar
weakness in both techniques in relation to metallic objects.
The examples shown in Figs 1–6 demonstrate
some of the differences between CB and MCT
images.
The soft tissue contrast resolution of images
produced by current CB units used in dentistry is
poor (Watanabe et al. 2009). MCT scans produce
much better soft tissue contrast resolution (Watanabe et al. 2009), allowing an evaluation of
various soft tissue structures, soft tissue lesions
and soft tissue changes related to bony lesions.
This important diagnostic value can be further
enhanced with the use of IV contrast. This
advantage of MCTcan be of significant diagnostic
value (Figs 7–9). It should be noted that many
soft tissue lesions are best examined with magnetic resonance imaging (MRI).
The various limitations in CB image quality
described vary between different makes of CB
units.
Measurements made on images from MCTand
CB data have been shown to be similar and
sufficiently accurate to plan many common
dento-orofacial procedures (Klinge et al. 1989;
Hanazawa et al. 2004; Kobayashi et al. 2004;
Loubele et al. 2005; Marmulla et al. 2005;
Suomalainen et al. 2008; Kamburoglu et al.
2009; Nickenig et al. 2009). MCTand CB images
have been shown to be more accurate in identify-
c 2010 John Wiley & Sons A/S
Fig. 3. Cross-sectional (para-axial) cone beam images of two palatally positioned implants, not appreciated in twodimensional plain film imaging. While the relationship of the implant to the residual ridge is appreciated, note is made of
the associated artefact (white and black arrows), which contributes to difficulty in evaluating the immediately adjacent periimplant bone. The artefacts are worse when there are two or more adjacent implants.
CB sagittal image
MCT sagittal image
MCT coronal image
CB coronal image
Fig. 4. Coronal and sagittal multislice computed tomography (MCT) (reduced dose) and cone beam (CB) images of the same
case, demonstrating a periapical inflammatory lesion of the distal molar (black arrows) with reactive mucosal thickening at
the maxillary antral base. The significant reactive sclerosis of the adjacent bone is also evident. Note the ‘‘flatter’’ CB images
with less contrast between the root, adjacent bone and mucosal thickening compared with the MCT image. There is artefact
related to beam hardening of the CB image not seen in the MCT image (vertical white arrows). Metallic streak artefact is seen
in the MCT image (horizontal white arrow). Note the combined metal artefact and beam hardening in the CB image (right
angle arrow). The reduced image quality of this case compared with those in Fig. 1 is largely related to the large amount of
restorative therapy and head size.
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Koong Cone beam imaging
ing important structures (e.g. mandibular canal)
and allow for more accurate measurement compared with panoramic and intraoral 2D radiography (Klinge et al. 1989; Lindh et al. 1992;
Ylikontiola et al. 2002; Howe 2009; Kamburoglu
et al. 2009).
Application
The potential application of CB technology is
wide and the advantages of being able to evaluate
structures in three dimensional (3D) and high
resolution appears obvious. CB technology appears to have a role in almost all areas of dentistry, ranging from pain diagnosis, endodontics,
periodontics, implant planning, ectopic and impacted teeth, orthodontics to orofacial surgery
including image guided surgery, to name a few.
It is beyond the scope of this article to discuss
all the potential specific applications in detail.
However, note is made of the inability of CB in
evaluating caries when metallic or even radiodense restorations are present. In the absence of
restorations, studies evaluating the role of CB in
caries diagnosis appear promising but require
maturation, especially in vivo studies (van Daatselaar et al. 2004; Akdeniz et al. 2006; Kalathingal et al. 2007; Tsuchida et al. 2007; Haiter-Neto
et al. 2008). Also of note is that, overall, the
available literature suggests that CB and MCTare
superior to periapical 2D images in periapical
Fig. 5. Axial and sagittal cone beam images demonstrating the morphology of furcation and perio-endo defects. Obturation of
the mesiobuccal root does not extend apically. Note is made of the significant beam hardening in this study, related to
significant endodontic and restorative therapy as well as head size.
Fig. 6. Cross-sectional (para-axial) cone beam image demonstrating inflammatory focal
widened palatal periodontal ligament space causing pain. This was not identified in a
periapical radiograph.
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disease diagnosis and endodontics (Velvart et al.
2001; Huumonen et al. 2006; Simon et al. 2006;
Draenert et al. 2007; Lofthag-Hansen et al. 2007;
Mora et al. 2007; Nair & Nair 2007; Patel et al.
2007; Stavropoulos & Wenzel 2007; Low et al.
2008) as well as in the evaluation of periodontal
bone loss (Fuhrmann et al. 1995; Fuhrmann et al.
1997; Misch et al. 2006; Mol & Balasundaram
2008; Vandenberghe et al. 2008).
With regard to imaging for implant planning,
both MCT and CB have been shown to be
sufficiently accurate, being more accurate and
more reliable for morphologic evaluation than
common dental views (Klinge et al. 1989; Lindh
et al. 1992, 1997; Kobayashi et al. 2004; Hanazawa et al. 2004; Marmulla et al. 2005; de
Morais et al. 2007; Nickenig & Eitner 2007;
Loubele et al. 2008; Suomalainen et al. 2008;
Kamburoglu et al. 2009). The differences between CB and MCT discussed earlier should be
considered.
Overall, there is varying clinical and scientific
evidence supporting the benefits of using CB
technology. Further clinically based studies are
required to confirm the benefits of CB imaging,
especially the advantages of CB over plain 2D
radiography and how CB compares with MCT.
However, it is recognized that carrying out these
investigations with vigorous methodologies is not
simple, requiring considerable time. As a result of
the pace of evolution of imaging technology,
including CB and MCT, these studies are quite
frequently not ‘‘up to date’’ when finally published. With this in mind, the low dose of CB
Fig. 7. Axial multislice computed tomography (MCT) soft tissue window image demonstrating fluid collection in the submandibular space. This would likely not be appreciated in a
cone beam study. Vascular clips related to previous surgery are also evident.
c 2010 John Wiley & Sons A/S
Koong Cone beam imaging
produce diagnostic images remains critical. Associated costs, accessibility and other related factors
should also be considered.
MCT presently remains a more powerful and
flexible imaging modality than CB in orofacial
diagnosis. At this stage, it appears prudent to
continue evaluating complex cases and more
serious/significant pathoses with MCT rather
than with CB. The advantages of MCT, including
better signal-to-noise ratio and being able to
evaluate the soft tissues, can be critical in the
diagnosis and management of orofacial disease,
including dentoalveolar inflammatory disease.
Both CB and MCT units are able to export data
in the DICOM file format standard. This allows
both MCT and CB data to be viewed with a range
of third party software used for diagnostic and
treatment planning purposes, including creation
of 3D models and various applications related to
image-guided surgery.
Interpretation
Axial MCT bone window
Soft tissue window
MCT angiogram
Fig. 8. A large left mandibular arterio-venous malformation (AVM). The patient presented with loose left mandibular molars,
with no clinical evidence to suggest an AVM. The panoramic radiograph and multislice computed tomography (MCT) bone
window demonstrate radiological appearances compatible with a vascular lesion although these bony appearances can be
similar to those of more aggressive lesions. Internal soft tissue density is noted in the axial soft tissue window image. The
MCT angiogram confirmed the AVM (magnetic resonance imaging was also performed). Appropriate radiological tests and
interpretation allowed accurate identification, making it possible to avoid a surgical biopsy and the associated potentially
serious complications. Cone beam imaging alone would very likely have been insufficient to allow accurate identification of
this lesion presurgically. This case highlights the importance of the application of appropriate imaging technology, interpretive
skills and understanding of pathology.
The clinician obtaining the CB images is responsible for interpreting the volume data (Carter
et al. 2008; Scarfe & Farman 2008; Suomalainen
et al. 2008). The following points identify some
of the key requirements and responsibilities involved in radiologic interpretation of a CB study
of which the practitioner should be aware:
Appropriateness of CB imaging for a particular application.
Strengths and limitations of CB imaging
Effect of protocols on image quality
Other modalities, which may be more
suitable, e.g. MCT, MRI, ultrasound and
nuclear medicine
The entire data set must be evaluated.
To varying extents, most CB scans include
the paranasal sinuses, pharyngeal air spaces,
skull base, cervical spine and upper neck
The practitioner is responsible for the entire volume of information, not just for the
primary focus of the study (Carter et al.
2008), e.g. implant planning
Fig. 9. Axial multislice computed tomography bone and soft tissue windows demonstrating a right pharyngeal squamous cell
carcinoma, unknown before imaging. The patient presented to an orofacial pain specialist with right maxillary pain. The
lesion is identified in the soft tissue window, demonstrating effacement of the right parapharyngeal fat planes extending
posteriorly. This would likely have not been identified in a cone beam examination and also emphasizes the importance of
radiologic interpretation.
imaging becomes a key factor. For many clinical
scenarios, the advantages of CB imaging seem
obvious if high-resolution CB 3D images for a
specific diagnostic purpose can be acquired while
c 2010 John Wiley & Sons A/S
delivering doses similar to or less than an equivalent plain 2D radiographic examination. However, this is only achievable with ultra low-dose
CB units. Also, the use of optimal protocols to
Knowledge of radiologic anatomy.
As depicted in multiplanar, volume and
other images reformatted from the volume
data. This differs from plain 2D radiographs
Awareness of anatomic variants
Knowledge of pathology, which may affect all
the structures included in the scan. Appreciation of the clinical significance of the various
disorders.
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Koong Cone beam imaging
Skill set to evaluate volumetric data.
The ability to perform morphologic analyses and plan surgical procedures is different to the skill set required to evaluate the
data set for disease
The algorithm used in evaluating volumetric data is different to that used to
interpret plain 2D radiographs
a
b
Fig. 10. Cone beam coronal images of two different cases. Features of the superior and inferior borders of the right maxillary
antral base lesion of Case A is compatible with a mucous retention cyst, while those of Case B are compatible with a radicular
cyst.
Understanding and an ability to identify radiologic features, which suggest the presence of
disease.
Many abnormalities do not present as obvious opacities or lucencies
Ability to identify the key radiologic characteristics of a lesion.
Knowledge to interpret the radiologic characteristics identified
Requires a thorough knowledge of the
radiologic characteristics of diseases affecting the orofacial structures
Fig. 11. Coronal cone beam image demonstrating paranasal sinus inflammatory disease, including air-fluid meniscus within
the left maxillary sinus and opacification of the ostio-meatal complexes.
Fig. 12. Cone beam sagittal image demonstrating cortical erosions of an infiltrative lesion such as lymphoma. The patient
presented to the dentist with facial swelling and discomfort and was concerned about dentoalveolar infection.
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Below are some examples of conditions, which
were identified during radiologic interpretation of
CB data. (Figs 10–17).
The responsibilities and the radiological skill
levels of clinicians involved in CB imaging as well
as the associated ethical and medico-legal implications require consideration (Carter et al. 2008;
Scarfe & Farman 2008). If the practitioner is not
able to comprehensively interpret CB datasets in
entirety or does not have suitable training, it
appears prudent that arrangements should be
made for appropriately skilled radiologists to perform this. Radiological reports should be provided
for CB scans (Carter et al. 2008).
Fig. 13. Axial cone beam image demonstrating left pharyngeal prominence suggesting a primary malignant lesion
or metastatic disease. This was proven to be lymph
node metastatic spread of a lateral tongue squamous cell
carcinoma.
c 2010 John Wiley & Sons A/S
Koong Cone beam imaging
Summary
Fig. 16. Axial cone beam image demonstrating two right
Vidian canals, a normal variant.
Fig. 14. Coronal cone beam images demonstrating radiologic
features of right sphenoidal sinus chronic inflammatory
disease.
Fig. 15. Cone beam coronal image demonstrating parotid
calcifications consistent with chronic sialadenitis related to
Sjogrens syndrome.
Fig. 17. Cone beam axial image demonstrating left mandibular condylar osteoradionecrosis, which can present with
aggressive appearances radiologically. A history of radiotherapy was obtained.
CB technology is certainly very much an integral
part of the imaging techniques for orofacial diagnosis. The many advantages over plain film are
obvious although further clinically based studies
remain necessary. With this in mind, the use of
ultra low-dose CB units capable of delivering dose
levels similar or only slightly higher than those
delivered during an equivalent plain 2D radiographic examination is important.
MCT is a much more powerful and flexible modality and presently remains the technique of choice
over CB imaging in several instances, especially
complex cases and in the evaluation of more serious
disease. Low-dose MCT protocols can be used.
CB imaging is an essential technique, which all
dental and orofacial clinicians must be familiar
with. CB imaging (using ultra low-dose units)
should be considered in day-to-day clinical practice to the same extent as intraoral 2D or panoramic radiographs. However, rather than replacing
other modalities, CB imaging complements plain
2D radiography, panoramic radiography, MCT
and other techniques including MRI, ultrasound
and nuclear medicine. CB imaging is not the
technique of choice in several clinical scenarios.
All radiologic examinations, including CB and
MCT, should be comprehensively evaluated in
entirety. The responsibilities and the radiological
skill levels of clinicians involved in imaging as
well as the associated ethical and medico-legal
implications require consideration.
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