potential of low dose cone beam computed...
TRANSCRIPT
Potential of low dose Cone Beam Computed Tomography and Multislice Computed
Tomography for zygomaticomaxillary fracture diagnosis – A blinded and randomized clinical
approach
Dose Reduction does not decrease the diagnostic acceptability of Cone Beam Computed
Tomography and Multislice Computed Tomography for the diagnosis of zygomaticomaxillary
fractures in a blinded and randomized approach.
Potential of low dose Cone Beam Computed Tomography and Multislice
Computed Tomography for zygomaticomaxillary fracture diagnosis
A blinded and randomized approach
Master Thesis
R. (Romke) Rozema, BSc
S2808323
Groningen, April 12, 2016
Medicine - Master’s Degree Program
Faculty of Medical Sciences, University of Groningen, Groningen, The Netherlands
Supervisor - B (Baucke) van Minnen, MD PhD - Consultant Oral and Maxillofacial Surgeon
Department of Oral and Maxillofacial Surgery, University Medical Center Groningen,
University of Groningen, Groningen, The Netherlands
R. Rozema, BSc1, R.N. Hartman, BSc1, M.H.J. Doff, DMD, PhD1, P.M.A. van Ooijen, MSc,
PhD, CPHIT2,3, H.E. Westerlaan, MD, PhD2,3, M.F. Boomsma, MD.4, B. van Minnen, MD.,
PhD1
Group member contribution
R. Rozema Lead organizer, study design creator, observer correspondent
R.N. Hartman Study design creator
M.H.J. Doff Statistical and data analysis support
P.M.A. van Ooijen Technical PACS and DICOM viewer support
H.E. Westerlaan Clinical support, finalizing image assessment, recruiting observers
M.F. Boomsma Clinical support, recruiting observers
B. van Minnen Study supervisor, study design creator, recruiting observers
1. Department of Oral and Maxillofacial Surgery, University Medical Center Groningen, University of
Groningen, Groningen, the Netherlands
2. Center for Medical Imaging - North East Netherlands (CMINEN), University Medical Center Groningen,
University of Groningen, Groningen, the Netherlands
3. Department of Radiology, University Medical Center Groningen, University of Groningen, Groningen, the
Netherlands
4. Department of Radiology, Isala Clinics, Zwolle, the Netherlands
PREFACE
This master thesis originates from a special interest in medical imaging. A radiology
department is constantly subjected to fast changing technology that provides new
opportunities to improve the clinical care. As for diagnostic devices, questions should always
be raised regarding the legitimate and correct use. This is especially the case for devices using
ionizing radiation. The focus of this study is the utilization of diagnostic devices in the field of
oral and maxillofacial surgery. One recent change is the increased use of Cone Beam
Computed Tomography. This shares similarities with the Multislice Computed Tomography,
which has also been well established in the radiology and emergency department. Both hold
advantages and drawbacks.
I have been educated in medical radiology and worked for 3 years as a diagnostic
radiographer. During this period I was concerned with the technical aspects and practical
decision making using diagnostic modalities. With this background I got in touch with
craniomaxillofacial trauma surgery, where Cone Beam Computed Tomography is especially
appreciated. However, it occurred to me that whenever I got concerned with a
craniomaxillofacial trauma patient at the emergency department, Multislice Computed
Tomography was the preferred modality. In view of these considerations I got interested in
the features and drawbacks of these imaging modalities.
I learned that Cone Beam Computed Tomography is appreciated because of the general lower
radiation dose. However, Multislice Computed Tomography is widely available in the
emergency department and the geometry enables to study any part of the human body. The
most significant drawback for both modalities are the radiation induced risks. This study
derived from the proposition that radiation dose should be reduced as low as reasonable
achievable. In this unique collaboration between the Department of Oral and Maxillofacial
Surgery and the Center of Medical Imaging North Eastern Netherlands of the University
Medical Center Groningen we were able to conduct the present study in a multidisciplinary
approach. The result is an experimental human cadaver study where the effect of radiation
dose reduction is studied for the diagnosis of midface fractures.
Romke Rozema
April 12, 2016
SAMENVATTING
DOEL: Het onderzoeken van de diagnostische waarde van dosis reduceerde Cone Beam
Computed Tomography (CBCT) en Multislice Computed Tomography (MSCT) voor de
diagnostiek van zygomaticomaxillaire fracturen.
MATERIAAL EN METHODE: Unilaterale zygomaticomaxillaire fracturen werden
aangebracht op vier van zes vers gevroren menselijke kadaver preparaten. Alle preparaten
werden gescand met twee CBCT en vier MSCT protocollen met systematisch gereduceerde
stralingsdosis. De vervaardigde beelden werden gerandomiseerd en geblindeerd beoordeeld
door 16 radiologen en 8 kaakchirurgen. De resultaten werden vergeleken met een gouden
standaard waarbij de aanwezigheid van een fractuur werd geverifieerd met een chirurgische
benadering van het zygomaticomaxillaire complex.
RESULTATEN: Bij gemiddeld 90,3 procent (n=130) werd een correcte diagnose van een
zygomaticomaxillaire fractuur gesteld. Bij 7,6 procent werd een incorrecte diagnose gesteld.
Van de verschillende anatomische locaties werd de arcus zygomaticus gemiddeld het vaakst
correct gediagnosticeerd (91,0%). Betrokkenheid van de crista zygomaticus alveolaris werd
gemiddeld het minst vaak correct gediagnosticeerd (65,3%). Dosis reductie had geen invloed
op de mogelijkheid tot het beoordelen van de dislocatie, comminutie, orbitale inhoud, volume
rendering en de weke delen. Kaakchirurgen ervaarden de dosis gereduceerde protocollen
afdoende voor het plannen van de behandeling. De schatting van de effectieve dosis reikte van
122 µSv tot 28 µSv voor CBCT en 129.9 ± 9.2 µSv tot 51.0 ± 4.3 µSv voor MSCT.
CONCLUSIE: Dosis reductie lijkt geen duidelijke invloed te hebben op de diagnostische
waarde van CBCT en MSCT voor het diagnosticeren van zygomaticomaxillaire fracturen.
ABSTRACT
PURPOSE: To assess the diagnostic value of low dose Cone Beam Computed Tomography
(CBCT) and Multislice Computed Tomography (MSCT) for zygomaticomaxillary fracture
diagnosis.
MATERIAL AND METHODS: Unilateral zygomaticomaxillary fractures were inflicted on
four out of six fresh frozen human cadaver head specimen. All specimen were scanned using
two CBCT and four MSCT protocols where the radiation exposure was systematically
reduced. A blinded diagnostic routine was recreated where 16 radiologists and 8 oral and
maxillofacial surgeons performed 144 randomized image assessments. As a gold standard, the
presence of fractures of the zygomatic region was verified by an open operative approach.
RESULTS: Zygomaticomaxillary fractures were correctly diagnosed in 90.3% (n=130) of the
image assessments. The zygomatic arch was most often correctly diagnosed (91.0%). The
zygomatic alveolar crest showed the lowest degree of correct diagnosis (65.3%). No
significant decrease of correctly diagnosed fracture sites was found between the baseline and
low dose CBCT and MSCT protocols. Dose reduction did not significant decrease the ability
to assess dislocation, comminution, orbital volume, volume rendering and soft tissues. OMF
surgeons considered the low dose protocols sufficient for treatment planning. The effective
dose of MSCT (129.9 to 51.0 µSv) remained well in range of CBCT (122 to 28 µSv).
CONCLUSION: Dose reduction seems not to decrease the diagnostic value of CBCT and
MSCT protocols for the diagnosis of zygomaticomaxillary fractures.
1
TABLE OF CONTENTS
INTRODUCTION ...................................................................................................................... 2
MATERIAL AND METHODS ................................................................................................. 3
Research design ...................................................................................................................... 3
Research subjects .................................................................................................................... 3
Experimental design ............................................................................................................... 3
Image acquisition .................................................................................................................... 4
Gold standard .......................................................................................................................... 6
Image assessment ................................................................................................................... 6
Objective and subjective analysis ........................................................................................... 7
Statistical analysis ................................................................................................................... 8
RESULTS ................................................................................................................................... 9
Effective dose estimations ...................................................................................................... 9
Objective assessment results ................................................................................................ 10
Subjective assessment results ............................................................................................... 12
Effect of dose reduction ........................................................................................................ 12
DISCUSSION .......................................................................................................................... 15
CONCLUSION ........................................................................................................................ 20
ACKNOWLEDGEMENTS ..................................................................................................... 21
REFERENCES ......................................................................................................................... 22
ATTACHMENTS .................................................................................................................... 26
Image assessment form example for radiologists ................................................................ 26
Image assessment form example for OMF surgeons ........................................................... 27
2
INTRODUCTION
Cone-Beam Computed Tomography (CBCT) and Multislice Computed Tomography (MSCT)
are the imaging modalities of choice in midface trauma diagnostics and treatment planning
[1–4]. Both modalities are utilized to detect and characterize midfacial fractures [2, 5, 6]. The
zygomaticomaxillary buttress represents the most common site of facial fractures [7, 8].
Disruption of the zygomatic position can cause an aesthetic and functional deficit. It is
therefore mandatory that zygomatic bone injury is properly diagnosed and adequately
managed [9].
Both CBCT and MSCT offer a three dimensional dataset with sub-millimeter resolution
[2, 3]. CBCT utilizes a cone shaped x-ray beam where only one rotation is needed for data
acquisition. Current systems require acquisition either sitting or standing in a natural head
position. MSCT datasets, however, are acquired with a collimated fan beam over a multitude
of 360 degree scans. The patient is transported through the gantry in a recumbent position in
synchrony with continuous data acquisition. Therefore, MSCT offers the advantage of
multipurpose utilization that allows studying of any part of the human body.
Although CBCT is considered to produce a generally lower radiation dose, there are some
clinical considerations for the commonly use of MSCT to evaluate blunt facial trauma [1, 4,
10]. In the first place, there is limited availability of CBCT within the emergency department,
where some of the patients present initially. Second, some conditions force the patient in a
recumbent bedridden position. Acquisition in natural head position as done with CBCT is
therefore not possible. Third, one fifth of the maxillofacial traumas have concomitant injuries,
especially cerebral and cervical spine injuries [7]. Since MSCT is needed for these
indications, the head is scanned in one go from a necessary and practical point of view [11].
However, there is an increasing concern regarding the potential radiation induced risks due to
the exponentially increased use of MSCT and CBCT in medicine [1, 12]. Keeping the
radiation dose as low as reasonably achievable, remains the most important strategy for
decreasing this potential risk [13]. There is limited evidence regarding the effect of dose
reduction for craniomaxillofacial trauma. In one study, evidence for the potential of
substantial dose reduction for the diagnosis of midface fractures was successfully provided
[14]. However, no previous study conducted a randomized analysis where the observer was
blinded for the outcome of interest. The aim of this study was to assess the diagnostic value of
low dose CBCT and low dose MSCT for zygomaticomaxillary fractures using this approach.
3
MATERIAL AND METHODS
Research design
A prospective experimental human cadaver study was designed to recreate a diagnostic
approach. Unilateral zygomaticomaxillary fractures were inflicted on four out of six obtained
human cadaver heads. All specimens were scanned using CBCT and MSCT. Dose reduction
was achieved by repeated acquisition with adjusted tube current parameters as an independent
variable. A group of 16 radiologist and 8 oral and maxillofacial (OMF) surgeons were asked
to assess fracture visibility and diagnostic value in a blinded objective image analysis. Six
unique CBCT and MSCT protocols were evaluated for all six human cadavers.
Research subjects
Six fresh frozen human cadaver heads were obtained and approved by the section anatomy of
the Department of Neurosciences of the University Medical Centre Groningen, Groningen,
the Netherlands. These cadavers have been donated for medical research and educational
purposes according to the legal and ethical framework of the Dutch uniform anatomical gift
act. Their age ranged from 60 to 96 years old. Thawing the cadaver specimens to room
temperature occurred 48 hours prior to experimentation. The specimens were isolated at the
craniovertebral junction keeping the intracranial contents intact.
Experimental design
An experiment was designed to systemically inflict unilateral zygomaticomaxillary fractures
on four out of six specimen. Simulating a blunt facial trauma recreates the injury mechanism
found as a major cause in midface trauma etiology [7]. Therefore, a guided fall method was
used as an impact model [15, 16]. This allows for a better control of motion of the impactor
and has the possibility of a local deformation of the midface [15]. The specimen were placed
horizontally on a solid wedge for stabilisation. The direction of impact was chosen as 40
degree angled from the mid sagittal section plane in order to obtain perpendicular impact on
the malar eminence. A cylindrical 2.0 kg impactor with flat impacting surface was used as a
free falling mass. A drop height estimation of 70 cm was calculated using biomechanical
fracture tolerance data where power of collision was measured in dynamic loads [16–18]. An
independent consultant OMF surgeon physically examined the zygomaticomaxillary complex
after impact for fracture presence. The drop height was raised with 10 cm consequently if no
fracture was found.
4
Figure 1 : The specimens were placed on a solid wedge for stabilisation. Zygomaticomaxillary fractures were
inflicted by a perpendicular impact of the malar eminence using a 2.0 kg impactor.
Image acquisition
Each specimen was scanned using two CBCT and four MSCT protocols. The field of view
(FOV) was standardized from the maxillary dentition up to the superior orbit rim of the
frontal sinus for both CBCT and MSCT. Scan parameter details are listed in table 1 and 2.
CBCT imaging was performed using the ProMax 3D Mid (Planmeca Oy, Helsinki, Finland).
The specimens were positioned on a fixed support in a natural head position. Alignment lasers
were used for horizontal and vertical centration. Each specimen was scanned using two 0,4
mm isotropic acquisition protocols, where one protocol was scanned in ultra-low dose (ULD)
mode. Projection data was gathered using a fixed tube voltage of 90 kV and tube current of
8,0 mA and 5,0 mA respectively in a partial arc scan geometry of 200 degree rotation. This
data was reconstructed into a single volumetric dataset using a Feldkamp-Davis-Kress (FDK)
filtered back projection algorithm.
MSCT imaging was performed using a third generation Siemens SOMATOM Force scanner
(Siemens Healthcare AG, Erlangen, Germany). The specimens were positioned supine and
centered such that the external auditory meatus was at the centre of the gantry. Based on the
lateral pre-scan topogram, we corrected the specimen position so that the hard palate was
parallel to the axial acquisition plane. Automatic exposure control (AEC) was used for
radiation dose optimization adapting tube current (CARE Dose4D, Siemens) and tube voltage
(CARE kV, Siemens). CARE Dose4D is a combined x-y-z automatic exposure control system
where the topogram localizer is used to determine attenuation characteristics at different
scanning positions. CARE kV is an automatic tube voltage optimization algorithm to optimize
radiation dose without increasing image noise. It is a recommendation regarding the optimal
combination of tube voltage and tube current taking the patient size, body habitus and clinical
question into account.
5
Quality reference mAs was used as the only variable to systemically reduce the radiation dose
for each MSCT acquisition protocol. We scanned each specimen with a quality reference mAs
of 50, 40, 30 and the lower limit of 20. The raw datasets were reconstructed into slice images
using two different types of image reconstruction algorithms also referred to as kernels. We
reconstructed a bone and soft tissue volume dataset using the Siemens Healthcare head
regular 59 (Hr59d) and head regular 32 (Hr32d) kernels. These kernels optimize high and low
contrast detectability respectively.
All CBCT and MSCT bone volumetric datasets were reconstructed into a 3D volume
rendering batch. This rendering technique conveys the axial acquisitioned two dimensional
data into a three dimensional volume of information providing the spatial relationship of the
osseous midface anatomy. The observer of this study was provided with a dynamic 360
degree rotational view round a fixed vertical axis. This volume rendering was batched using a
bone template. All images were exported in a Digital Imaging and Communications in
Medicine (DICOM) standard.
Table 1 : Planmeca Promax 3D mid CBCT acquisition parameters for
the standard and ULD protocol
Tube voltage 90 kV
Tube current 8 mA
Tube current ULD 5 mA
Exposure time 13,6 s
Exposure time ULD 4,5 s
Grayscale depth 12 bit
Scan Time 18-26 s
FOV 200 x 100
Radiation source Pulsed
Rotation degree Single 200 degree rotation
Projections per rotation 300
Detector Type FPD
Voxel size (x,y,z) 0,4 mm3
Matrix 512 x 512
CBCT Cone Beam Computed Tomography
ULD Ultra Low Dose
FOV Field of View
FPD Flat Panel Detector
6
Gold standard
A gold standard was created in a consensus meeting between a head and neck radiologist and
an OMF surgeon with craniomaxillofacial trauma fellowship. Both were not included in the
image analysis procedure. The fracture site presence was recorded by the radiologist who had
access to all scanned MSCT and CBCT data. These findings were validated by the OMF
surgeon using a combined local transcutaneous and maxillary vestibular approach of the
specimen’s zygomaticomaxillary complex. Discrepancies were discussed and advocated.
Image assessment
The diagnostic quality of all six acquisition protocols was read in 114 image assessments by a
group of 24 observers. This group consisted of radiologists (n=16) and OMF surgeons (n=8)
from the University Medical Center Groningen (Groningen, NL), Isala clinics (Zwolle, NL),
Nij Smellinghe hospital (Drachten, NL), Tjongerschans hospital (Heereveen, NL) and
Sionsberg hospital (Dokkum, NL).
Table 2 : Siemens SOMATOM Force MSCT acquisition parameters
for the four different scan protocols. The quality reference mAs was
used to systemically reduce the radiation dose for four protocols.
Tube voltage CARE kV
Tube current CARE Dose4D
Quality reference mAs 50, 40, 30, 20
Average effective mAs 77, 52, 40, 29
ADMIRE Strength* 1
FOV 220.0 mm
Collimation 192 x 0,6 mm
Average scan length 118 mm
Slice thickness 0.6 mm
Position increment 0.4 mm
Grayscale depth 12 bit
Pitch 0.6
Rotation time 0.5 s
Exposure time 0.5 s
Scan time 3,4 s
Matrix 512 x 512
MSCT Multislice Computed Tomography
ADMIRE Advanced Modelled Iterative Reconstruction
FOV Field of View
7
Simulating a diagnostic routine, each specimen was presented as a fictive patient case with a
suspected zygomaticomaxillary fracture. The observer was blinded for the outcome of interest
and all scan parameters. Each observer performed this image assessment for all six patient
cases. One of the six acquisition protocols was random allocated for each patient case using a
research randomizer (www.randomizer.org). The order in which the patient cases were
assessed was also randomized for each observer. The use of a medical diagnostic display was
set as a condition for radiologist. These displays all met the acceptance and constancy tests
following the America Association of Physicists in Medicine (AAPM) Task Group 18 (TG18)
guidelines [19].
The DICOM datasets were provided on a mobile TeraRecon Aquarius iNtuition DICOM
Viewer (TeraRecon, Foster City, California, United States). This viewer application allowed
the features and functionalities a medical professional would use in the daily clinical care.
MSCT patient cases were provided with two datasets; a bone and soft tissue volume. Each
CBCT patient case was provided with the single reconstruction dataset. The volume rendering
batch was available for both acquisition modalities. The observer was allowed to adjust
window width and window level from a 2000/250 bone and 400/40 soft tissue preset. The
DICOM viewer interface loaded the volume datasets into orthogonal axial, sagittal and
coronal plane sections where free angle adjustment of a multi planar reconstruction was
possible.
Objective and subjective analysis
The image assessment was divided between an objective and subjective analysis. Each patient
case was provided in advance with the relevant personal particulars, mechanism of injury,
clinical presentation and the physical examination results. The objective analysis was
performed using a predefined selection of zygomaticomaxillary fracture associated anatomical
sites. First, the observer had to determine the presence of a suspected zygomaticomaxillary
fracture (yes/no/inconclusive). Subsequently, the analysis was subdivided into the
involvement of the frontozygomatic suture, lateral orbital wall, zygomatic arch, orbital floor,
zygomatic alveolar crest, anterior maxillary sinus wall, posterior maxillary sinus wall and the
zygomatic corpus (yes/no/inconclusive). The gold standard was used to verify if the outcome
for each of the observers was correct.
Each observer also performed a subjective analysis where the diagnostic acceptability for
each allocated scan protocol was assessed as a dichotomous outcome variable (yes/no). The
diagnostic acceptability covered the assessment of fracture dislocation, fracture comminution,
8
orbital volume, soft tissue and volume rendering assessment. In addition, each observer got a
profession related question. Radiologists assessed the sufficiency to diagnose and assess the
zygomaticomaxillary fracture and OMF surgeons the sufficiency to determine the treatment
plan and the potential surgical approach. The image assessment was standardized for each
patient case. Examples of these image assessment forms for both radiologists and OMF
surgeons are provided attachments.
Radiation dose assessment and comparison
Effective dose estimations were made for all CBCT and MSCT acquisition protocols.
Dosimetric comparison is a key component in balancing the clinical consideration for CBCT
and MSCT. The use of effective dose estimation allows stochastic effect quantification and
comparison between CBCT and MSCT. The effective dose estimation of the used CBCT
device was provided by a previous study where dose measurements were performed using
thermoluminescent dosimeters (TLD) in anthropomorphic Alderson Radiation Therapy
(ART) phantoms [20]. The MSCT dose estimations were calculated using volume weighted
CT dose index (CTDIvol) and Dose Length Products (DLP) provided by the scanner. These
represented the total absorbed radiation dose within the entire scan volume for each
acquisition protocol. Head conversion coefficients (mSv mGy-1 cm-1) quoted by the American
Association of Physicists in Medicine (AAPM) were used to convert DLP to effective dose
[21].
Statistical analysis
The Statistical Package for the Social Sciences (SPSS, version 20.0) was used for data
analysis. A chi-square test was performed to compare the proportions of correct diagnosed
fracture sites between the baseline CBCT and MSCT acquisition protocols. This comparison
was repeated with their corresponding low dose scan protocols for both CBCT and MSCT.
The proportions of correct diagnosed fracture sites were compared between radiologist and
OMF surgeons. The proportion of correct diagnosed fracture sites was compared between
radiologist and OMF surgeons using a chi-square test. The agreement within each profession
was calculated using Fleiss Kappa statistics. The significance level of α was set at 5%.
9
RESULTS
The consensus reading confirmed that zygomaticomaxillary fractures were sustained on all
four specimens in varying degree of severity (figure 2). All specimens had fractures at
multiple buttress relationships of the zygomaticomaxillary complex. Involvement of the
zygomatic alveolar crest was seen in one case. A fracture of the zygomatic corpus itself was
not seen in any of the cases. In one case, a fracture of the lateral orbital wall was combined
with an intact frontozygomatic suture. Based on the consensus reading the currently used
clinical acquisition protocols appeared sufficient to visualize fractures at all selected
anatomical sites of the midface (figure 2).
Figure 2 : The specimen sustained fractures a multiple buttress relationships of the zygomaticomaxillary
complex. Volume rendering reconstructions (A+C) are compared with the surgical dissection of the
zygomaticomaxillary complex (A+D) in a case were a fracture of the lateral orbital wall was combined
with an intact frontozygomatic suture.
Effective dose estimations
Effective dose estimations are summarized in figure 3. The CBCT effective dose ranged from
122 µSv to 28 µSv, resulting in a 77% dose reduction when using the ULD protocol [20]. The
average measured MSCT effective dose ranged from 129.9 ± 9.2 µSv (mean ± SD) to the
lower limit of 51.0 ± 4.3 µSv (mean ± SD).
10
A dose reduction of 61% for MSCT was achieved by reducing the quality reference mAs from
50 to 20. The dose of the baseline MSCT protocol remained well in range of CBCT. Dose
reduced MSCT protocols produced less effective dose than the baseline CBCT protocol. The
minimal dose was produced by the CBCT ULD protocol.
Objective assessment results
Over the total of 144 image assessments, 90.3% (n=130) of the zygomaticomaxillary fractures
were correctly diagnosed and 7.6% (n=11) were misdiagnosed. In another 2.1% (n=3) the
diagnosis was reported as inconclusive. All four specimens that had a fracture were diagnosed
correct by all 24 observers (100%). From the two specimens without a fracture, one was
diagnosed correctly by 23 observers (95.8%) and the last was diagnosed correct by 11
observers (45.8%).
The zygomatic arch fracture was most often diagnosed correctly (91.0%). In five of the six
specimens, the zygomatic arch fractures were diagnosed 100% correctly. It was noticeable
that whilst the remaining specimen did not have a fracture, 13 of the 24 observers suspected a
fracture of the zygomatic arch. In one specimen there was an exceptional low degree of
correct diagnosis of the orbital floor (8.3%), the anterior maxillary sinus wall (16.7%) and the
posterior maxillary sinus wall (8.3%). These fractures were initially missed in the consensus
reading but later confirmed by the surgical approach as minimal and non-dislocated (figure 5).
Figure 3 : Radiation Dose estimation of the two Cone Beam Computed Tomography and four
Multislice Computed Tomography (50-20) acquisition protocols.
0
25
50
75
100
125
150
MSCT - 50 MSCT - 40 MSCT - 30 MSCT - 20 CBCT CBCT ULD
Effe
ctiv
e D
ose
(µ
Sv)
11
The case where a lateral orbital wall fracture was combined with an intact frontozygomatic
suture was correctly diagnosed in 87.5% of the assessments. On average, the zygomatic
alveolar crest fractures showed the lowest degree of correct diagnosis (65.3%).
Figure 4 : Comparison of the baseline and low dose CBCT and MSCT scan protocols consecutively.
This right sided zygomaticomaxillary fracture included (1) zygomatic arch dislocation, (2) continuity loss
of the posterior maxillary sinus wall and (3) non-dislocated small defect of the anterior maxillary sinus
wall.
12
There was no significant difference between radiologists and OMF surgeons regarding the
proportions of correctly diagnosed fracture sites (X2=1.358, n=1152, p=0.507). The
agreement among the eight OMF surgeons was substantial, k=0.617 (95% CI, 0.594 to 0.639),
p=0.000. There was a moderate agreement among the sixteen radiologists, k=0.552 (95% CI,
0.505 to 0.599), p=0.000. Also, no significant difference was found between the baseline
CBCT and MSCT protocols (X2=1.805, n=384, p=0.406).
Subjective assessment results
On average, there was a high degree of conformity that the image quality was sufficient to
assess the fracture dislocation (95.5%), comminution (89.2%), the orbital volume (95.5%), the
provided 3D volume rendering (85.6%) and the soft tissues (91.8%). The soft tissue
reconstructions were only available on MSCT protocols. OMF surgeons considered the image
quality sufficient for treatment management in 95.7% of the image assessments on average.
There was no apparent decrease within the reducing the radiation dose. Radiologist
considered the image quality sufficient for fracture assessment in 83.3% of the image
assessment on overage. Although there was no decrease within the MSCT protocols, the
CBCT ULD protocol had a substantial reduced agreement (56.3%) when compared to the
standard CBCT protocol (82.4%). The observers mentioned that the ULD protocol contained
an unacceptable amount of beam hardening artefacts.
Effect of dose reduction
The image assessments results per scan protocol are summarized in table 3. No significant
decrease of correctly diagnosed fracture sites was found between the baseline and low dose
CBCT and MSCT protocols. No significant decrease was found for the ability to assess
Figure 5 : Initial missed non-dislocated fracture of the infraorbital rim (A), and the posterior
maxillary sinus wall (B). These were confirmed during the surgical approach of the
zygomaticomaxillary complex.
13
Table 3 : Results of the image assessments for each acquisition protocol
Quality Reference mAs
MSCT protocol
CBCT protocol Sig.c
(p<0.05)
50 40 30 20 Reg. ULD
Objective analysisa
Fracture presence 87.5 95.8 87.5 91.7 87.5 91.7 NSd
Frontozygomatic suture 75.0 75.0 70.8 79.2 75.0 79.2 NSd,e
Lateral orbital wall 87.5 87.5 100 83.3 91.7 87.5 NSe
Zygomatic arch 95.8 91.7 87.5 91.7 87.5 91.7 NSe
Orbital floor 70.8 75.0 75.0 70.8 79.2 79.2 NSd
Zygomatic alveolar crest 62.5 62.5 66.7 75.0 62.5 62.5 NSd
Anterior maxillary sinus wall 79.2 79.2 79.2 79.2 87.5 87.5 NSe
Posterior maxillary sinus wall 70.8 79.2 66.7 79.2 70.8 79.2 NSd,e
Zygomatic corpus 75.0 83.3 79.2 70.8 62.5 87.5 NSd,e
Subjective analysisb
Dislocation 94.4 100 94.7 94.4 94.7 94.7 NSe
Comminution 83.3 100 73.7 94.4 89.5 94.7 NSe
Orbital Volume 88.9 100 89.5 100 94.7 100 NSe
Volume Rendering 100 94.4 78.9 94.4 68.4 78.9 NSe
Soft Tissue 94.4 94.4 84.2 94.4 - - NSe
Treatment management 85.7 100 100 100 100 100 NS
Fracture assessment 81.3 93.8 87.5 100 82.4 56.3 CBCT Sig.
a percentage correctly diagnosed fracture sites verified by the consensus reading.
b percentage sufficient considered image quality for the presented parameters.
c statistical difference between the baseline and low dose protocols for both CBCT and MSCT
d Pearson Chi-squared test
e Fisher’s exact test
CBCT Cone Beam Computed Tomography
MSCT Multislice Computed Tomography
ULD Ultra Low Dose
NS Not significant
14
dislocation, comminution and the orbital volume between the baseline and low dose CBCT
and MSCT protocols. Moreover, the effect of dose reduction did not significantly decrease the
considered sufficiency of volume rendering and MSCT soft tissue reconstructions. For OMF
surgeons, dose reduction did not significantly decrease the sufficiency to determine the
treatment pathway of the patient. However, for radiologists, the sufficiency to assess the
fracture did significantly decrease between the baseline and ULD CBCT protocol. This
decrease was not significant for MSCT.
15
DISCUSSION
As far as we know, this is the first study in which blinded randomized image assessments
were independently performed to assess the diagnostic value of low dose CBCT and MSCT
for the diagnosis of zygomaticomaxillary fractures. An increase of image noise affects the
interpretability of a suspected fracture. This study demonstrated that dose reduction did not
significantly decrease the objective fracture detectability of anatomical related sites of the
zygomaticomaxillary complex. These results are in agreement with a previous study where
low dose protocols were found sufficient for the diagnosis of both dislocated and non-
dislocated midface fractures [14].
Despite these findings, detectability percentages varied substantially among the assessed
anatomical sites. Zygomatic alveolar crest fractures were the least likely to be diagnosed
correctly (table 3). The zygomatic alveolar crest is located in the infrazygomatic region. In
anatomical terms this site is not clearly defined. It is clinically appreciated because the
cortical bone thickness provides anchory for the osteosynthesis screws during surgery [22].
We believe that the unclear anatomical demarcation of the crest resulted in a doubtful
determination of the involvement in the fracture. Also, a fracture of the zygomatic corpus was
found in a considerable part of the image assessments whilst none of the specimen sustained a
fracture in this region. A potential explanation is the position of the zygomaticofacial foramen
that transmits the zygomaticofacial nerve through the zygomatic corpus. The foramen could
lead to a deceptive conviction that a fracture line courses the zygomatic corpus. In one case,
the orbital floor, the anterior and posterior maxillary sinus wall had an exceptional low degree
of correct diagnosis. These fractures were minimal and non-dislocated (figure 5). These
findings suggest that the used scan protocols were not sufficient to visualize these fractures
properly. However, this was refuted during the consensus meeting. Although these finding
should not be nullified, misdiagnosis would have no clinical consequences as conservative
treatment is also preferred when diagnosing these fractures correctly. Nevertheless, the
detection variability among the anatomical sites do emphasize that careful reading of the
datasets and adequate anatomical proficiency is needed to properly assess a suspected midface
fracture.
CBCT and MSCT both hold potential for diagnosing midfacial fractures [2, 5, 6]. Although it
has been stated that the image quality of CBCT is better [23], more recent studies provide
evidence that it is comparable to MSCT even though some variability exists among different
16
systems [10, 24]. The results of the present study also show that there was no significant
difference between the baseline CBCT and MSCT protocols for the proportion of correctly
diagnosed fracture sites. It is important to note that the way in which data acquisition is
performed varies between CBCT and MSCT. CBCT is dedicated to the oral and maxillofacial
region only and the patient is scanned in a natural head position [1]. When MSCT is used, the
patient is transported through the gantry in synchrony with continuous data acquisition. This
feature is especially appreciated when a craniomaxillofacial trauma patient is suspected of
concomitant injuries and forced in a recumbent position. 19.6 percent of the
craniomaxillofacial traumas are associated with cerebral and cervical spine injuries and for
these cases, the initial use of MSCT is justified from a necessary and patient safety
perspective.
Furthermore, MSCT is appreciated for the ability to detect associated soft tissue injury which,
in case of midface fractures, is utilized to assess the extraocular muscles [9, 25, 26]. In
addition, the ophthalmologic assessment may sometimes be difficult due to the severity of the
head injury, the extent of periorbital oedema, inadequate cooperation or altered consciousness
of the patient [9, 27]. However, dose reduction is not recommended for the evaluation of soft
tissues, as image noise and contrast resolution are closely related [13]. Therefore, the clinical
applicability of low dose protocols in this study could be convicted. However, in contrast to
what might be expected, the results of this study show no significant decrease for the ability to
assess soft tissues using low dose MSCT protocols. Since this was assessed subjectively,
more extensive research is needed to provide more conclusive evidence.
Radiation dose is a significant parameter within the clinical consideration of the used imaging
modality. Previous studies provided effective dose estimations for CBCT and MSCT. A meta-
analysis reported CBCT effective dose measurements ranging from 46 to 1073 µSv for large
FOVs, 9-560 µSv for medium FOVs and 5-652 µSv for small FOVs. Other studies reported
MSCT effective dose estimations of 474 to 1160 µSv [4], 534 to 860 µSv [28] and 0.1 to 3.6
mSv [14]. These results support the common believe that MSCT delivers a higher radiation
exposure than CBCT does [1, 4, 6]. However, our study provides evidence that the dose of the
used MSCT is well in range of CBCT. Moreover, the MSCT protocols of this study often
remain below the enumerated CBCT doses. Widmann et al. also successfully confirmed a
dose reduction below the levels of CBCT [29].
17
Nevertheless, the remarkable wide range of these dose estimations confine the generalizability
[30]. As the delivered radiation dose is the result of interplay between different elements,
optimization should be performed using an appropriate selection of scan parameters.
Therefore we would like to address the following four aspects of parameters that should be
taken into careful consideration.
First, a topogram of the complete scan range is a requisite. A careful determination of the scan
range allows limitation of exposure to the area of interest only. Also, the AEC uses the
topogram to improve consistency of the image quality and this curtails the radiation dose for
each individual patient [13]. In this study this was performed adjusting both tube current
(CARE Dose4D) and tube voltage (CAREkV). For CBCT, a distinction is needed between
small-, medium-, and large FOVs [20]. A significant reduction in effective dose is associated
with the use of small FOV sizes [30].
Second, the performance difference among scanners is associated with the radiation dose
given. Modern CBCT and MSCT scanners feature better detector performance, improved
beam shape filtering or reduced amount of overranging that allow radiation exposure
optimization better than former scanners do [13, 30]. This should be taken into account when
medical modalities are compared.
Third, the diagnostic task and the intrinsic contrast of the area of interest should be decisive
for the used scan parameters. Some studies propose the use of a full head MSCT protocol for
maxillofacial applications [4, 14]. The MSCT head protocol requisites low contrast
detectability because of the close range of intracranial tissue densities. This is greatly
influenced by the image noise and is less apparent with a higher radiation exposure. However,
MSCT protocols for craniomaxillofacial trauma are predominantly used to visualize the
osseous anatomy. This requires a lower radiation exposure than a full head protocol because
the image noise is reduced when a broad window width is combined with a bone algorithm
reconstruction.
Fourth, the reconstruction algorithm type applied to reconstruct raw MSCT projection data
has a unique role in radiation dose adjustments and the image quality. Currently, filtered back
projection (FBP) is the well-established reconstruction type for clinical MSCT protocols. The
recent availability of iterative reconstruction (IR) algorithms have the advantage in accurately
modelling the system geometry, incorporating physical effects such as beam spectrum, noise,
beam hardening effect, scatter and incomplete data sampling [13]. IR also offers the potential
for radiation dose reduction [14, 31].
18
In this study FBP was combined with a modelled-based IR (ADMIRE 1, Siemens) that
incorporates modelling, both in the raw projection data and in the image domains, such that a
different statistical weighting is applied according to the quality of the projection data [31].
With respect to constant image quality, this allowed the use of a reduced quality reference
mAs. Widmann at al. concluded that the use of IR could not improve the detection rate of
fractures due to the smoothing effects [14]. Despite the dose reduction potential of IR
algorithms, the clinical applicability of the computational time requirements should be taken
into consideration. This is especially in case of craniomaxillofacial trauma where a minimum
time to diagnosis is a prerequisite. In view of limited evidence, further research should focus
on the use of IR for craniomaxillofacial trauma.
When comparing radiologists and OMF surgeons, no significant difference was found for the
proportion of objective diagnosed fracture sites. The subjective image assessments show that,
according OMF surgeons, dose reduction did not significantly decrease the sufficiency for
treatment management. For radiologists, the subjective diagnostic sufficiency did not
significant decrease for dose reduced MSCT protocols. However, it is important to note that
this was significant for CBCT (table 3). The average agreement among OMF surgeons
(95.7%) was higher than radiologists (83.3%). These findings suggest that image
interpretation by OMF surgeons is performed from a different perspective than that of
radiologists. OMF surgeons predominantly focus on the determination of the treatment
pathway and the necessity of surgery. However, radiologists carry the responsibility for an
appropriate diagnosis and therefore assess the image quality from a more critical approach.
When the image quality is compared to MSCT, CBCT is more prone to additional artefacts,
such as aliasing, scatter and a general higher noise level [32]. This could explain why a
substantial share of the radiologists considered the CBCT ULD protocol insufficient (table 3).
Also, initial interpretation of CBCT datasets is usually not performed by a radiologist but by
the OMF surgeons itself. The OMF surgeon is therefore more proficient in CBCT imaging
interpretation. This is not the case for MSCT where the diagnostic findings of a radiologist are
used by the OMF surgeon to define the treatment for a patient.
This study has limitations. First, the post-mortem status of human cadaver specimen carry
process changes that affect the interpretability of the scans. The specimen suffer cerebral
atrophy and reduced attenuation between soft tissue structures [33]. Also, trauma patients may
have indirect predictive CT findings, such as sinus opacification and periorbital contusion,
that have discriminatory benefits for predicting midface fractures [34]. These findings are
19
absent in human cadavers. Nevertheless, we believe that as a surrogate model it is the most
accurate approach of a craniomaxillofacial trauma patient and moreover this prevents the
unjustifiable high radiation dose a living patient would receive upon repeated study
acquisitions. Another limitation is the paucity of fracture variability. In this study, a total of
six cases are used as representation of a midface trauma patient population. However,
clinicians are faced with a broad range of fracture patterns. Moreover, a craniomaxillofacial
trauma patient could also suffer fractures other than to the zygomaticomaxillary buttress, such
as Le Fort or naso-orbitoethmoid fractures that are not assessed in the present study.
Therefore, it is important to be circumspect about the direct applicability of low dose
protocols in a clinical environment.
20
CONCLUSION
In conclusion, in this human cadaver study we found that dose reduction did not decrease the
diagnostic value of CBCT and MSCT for the diagnosis of zygomaticomaxillary fractures.
Low dose protocols were also considered sufficient for treatment management according
OMF surgeons. This study emphasizes that CBCT and MSCT datasets of a suspected midface
fracture should be interpreted carefully and that anatomical proficiency is required for an
appropriate diagnosis. The results of this study show that the effective dose of MSCT is well
in range, or even lower than CBCT. In addition, a successful method was provided to inflict
zygomaticomaxillary fractures on human cadaver specimen in varying degree of severity.
Further research should focus on the potential of IR algorithms and the applicability of low
dose CBCT and MSCT protocols in a clinical environment.
21
ACKNOWLEDGEMENTS
We would like to thank Ronald Dob (Department of Radiology) and Arjan Dieters
(Department of Orthodontics) from the University Medical Center Groningen for their advice
and technical assistance during the use of the MSCT and CBCT devices respectively. Also,
we would like to thank Klaas van Linschoten and dr. Janniko Georgiadis from the Section
Anatomy, Department of Neuroscience, (University of Groningen, Groningen, the
Netherlands) for the accompaniment and support in the provision and use of the human
cadaver specimens in this study. Finally a special thanks for Steve Oosterhoff for his
persevering assistance in scanning these specimens in the late night hours.
22
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26
ATTACHMENTS
Image assessment form example for radiologists
Case history; 48 years old male bumped into a lamppost while walking the dog. Consulted the
general practitioner with right sided facial pain and periorbital oedema the next day.
Table 1*
Yes No Inconclusive
Is this patient diagnosed with a fracture?
* Table 2 and 3 only need to be completed when answered YES
Table 2 - Classify the fracture whether the following anatomical sites are involved
Yes No Inconclusive
Frontozygomatic suture / Lateral orbital rim
Lateral orbital wall
Zygomatic arch
Orbital floor
Zygomatic alveolar crest
Anterior maxillary sinus wall
Posterior maxillary sinus wall
Corpus zygomaticus (i.e. the body itself)
Table 3 - Is the image quality sufficient to assess the following parameters?
Yes No
Dislocation of the fracture
Comminution of the fracture
Orbital Volume
3D (volume rendering)
Soft Tissue (see soft tissue series for CT)
Table 4
Yes No
Is the image quality of this acquisition protocol sufficient to
diagnose and assess midfacial fractures according your
professional standard?
27
Image assessment form example for OMF surgeons
Case history; 48 years old male bumped into a lamppost while walking the dog. Consulted the
general practitioner with right sided facial pain and periorbital oedema the next day.
Table 1*
Yes No Inconclusive
Is this patient diagnosed with a fracture?
* Table 2 and 3 only need to be completed when answered YES
Table 2 - Classify the fracture whether the following anatomical sites are involved
Yes No Inconclusive
Frontozygomatic suture / Lateral orbital rim
Lateral orbital wall
Zygomatic arch
Orbital floor
Zygomatic alveolar crest
Anterior maxillary sinus wall
Posterior maxillary sinus wall
Corpus zygomaticus (i.e. the body itself)
Table 3 - Is the image quality sufficient to assess the following parameters?
Yes No
Dislocation of the fracture
Comminution of the fracture
Orbital Volume
3D (volume rendering)
Soft Tissue (see soft tissue series for CT)
Table 4
Yes No
Is the image quality of this acquisition protocol sufficient for
medical treatment planning and potential surgical management
according your professional opinion?