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“Dosimetry and optimisation of Cone Beam CT for dentomaxillofacial applications”
Safety and Efficacy of a New and Emerging Dental X-ray Modality
Cone Beam CT
Ruben PauwelsOral Imaging CenterFaculty of Medicine
• Introduction CBCT
• SEDENTEXCT project
• CBCT dosimetry
Effective dose (phantom)
Standardised dose index
• CBCT Optimisation
QC phantom development & analysis
• Work in progress
• Introduction CBCT
Cone Beam CT / Digital Volume Tomography
• Dentomaxillofacial • Radiotherapy• Cardiac imaging
Cone Beam CT / Digital Volume Tomography
• Dentomaxillofacial
Cone Beam CT / Digital Volume Tomography
• Dentomaxillofacial
Cone Beam CT / Digital Volume Tomography
Advantages• 3D (isotropic voxels)• Detail (voxel size 0.08-0.4mm)• Cost, size, ease of use, … • Applications• ‘Low dose’ (generally DE=20-100 µSv)• Viewing possibilities
Cone Beam CT / Digital Volume Tomography
• Dentomaxillofacial
Can CBCT replace traditional radiographic methods?
Can CBCT replace traditional radiographic methods?
• Excessive use: collective dose ↑• Used in primary care (by dentists)• Optimisation? ALARA?
Justification Optimisation (dose & image quality) Referral criteria Training
• Introduction CBCT
• SEDENTEXCT project
WP 0 Financial and administrative management
WP 1 Justification and Guideline development
WP 2 Dosimetry
WP 3 Optimisation
WP 4 Diagnostic accuracy
WP 5 Cost effectiveness
WP 6 Training and Valorisation
• Introduction CBCT
• SEDENTEXCT project
• CBCT dosimetry
WP 2: Dosimetry
Patient dosimetry
Protection of personnel
Standardised dose index
Phantom effective dose
In vivo dose
Mathematical models
• Introduction CBCT
• SEDENTEXCT project
• CBCT dosimetry
Effective dose (phantom)
Which organs are the major contributors to the effective dose for dental CBCT imaging?
Which acquisition parameters influence the effective dose, and in what way?
kV, mAs, filtration, …
FOV, ROI How can we use this info to reduce patient dose?
WP 2: Dosimetry
WP 2: Dosimetry• Thermoluminescent dosimeters (LiF:Mg,Ti)• Harshaw Reader 6600
WP 2: Dosimetry• Calibration: C → gU → Gy
WP 2: Dosimetry
• Alderson Radiation Therapy phantom• 147 organ TLDs, 10 background TLDs, 20 calibration TLDs • ICRP 103 tissue weighting factors
WP 2: DosimetryOrgan ICRP 60 ICRP 103
Gonads 0,2 0,08
Red bone marrow 0,12 0,12
Colon 0,12 0,12
Lung 0,12 0,12
Stomach 0,12 0,12
Bladder 0,05 0,04
Breast 0,05 0,12
Liver 0,05 0,04
Oesophagus 0,05 0,04
Thyroid 0,05 0,04
Skin 0,01 0,01
Bone surface 0,01 0,01
Brain 0 0,01
Salivary glands 0 0,01
Remainder 0,05 0,12
WP 2: Dosimetry
Scanora 3D
Galileos
Picasso Trio
ProMax 3D
Kodak 9000 3D
WP 2: DosimetryScanora 3D Upper jaw 100x75mm
Upper and lower jawLower jaw
Galileos Upper and lower jaw 150x150mm
Kodak 9000 3D Lower jaw (part) 50x37mm
Picasso Trio Lower jaw 120x70mm
ProMax 3D Lower jaw 80x80mm
WP 2: Dosimetry
WP 2: Dosimetry
WP 2: Dosimetry
WP 2: Dosimetry
WP 2: Dosimetry
WP 2: Dosimetry
WP 2: Dosimetry
WP 2: Dosimetry
OrganContribution (%)to effective dose
Red bone marrow 15
Thyroid 44
Skin 1,4
Bone surface 1,5
Brain 1,1
Salivary glands 36,9
Large dose range Thyroid & salivary glands are crucial FOV reduction should always be considered mAs should be selected in function of diagnostic
needs Thyroid shielding & avoidance
Ideal CBCT practice?→ FOV selection (single tooth, …, full head)→ Resolution (=mAs) selection→ Training!!!
WP 2: Dosimetry
• Introduction CBCT
• SEDENTEXCT project
• CBCT dosimetry
Effective dose (phantom)
Standardised dose index
Routine measurements → predict effective dose Conversion factors
(input: dose index + positioning) Existing methods (CTDI) Also include:
- patient (skin) entrance dose
- simulations
WP 2: Dosimetry
WP 2: Dosimetry
WP 2: Dosimetry
Typically available dosimeters
WP 2: Dosimetry
Central measurement?
Ionization chamber
WP 2: Dosimetry
Accuracy?
TLD
WP 2: Dosimetry
Sensitivity?Calibration?
Film
WP 2: Dosimetry
FOV size and shapeUniform Distribution?(Practical) application for CBCT?
DAP
WP 2: Dosimetry→ Combine measurements→ Assesment of distribution (anthropomorph / homogeneous)
• Introduction CBCT
• SEDENTEXCT project
• CBCT dosimetry
Effective dose (phantom)
Standardised dose index
• CBCT Optimisation
Technical image quality assessment Image quality vs. Radiation dose! Diagnostical performance < technical parameters Optimising beyond available options Optimising on others levels: also in progress
Monte Carlo simulations (G.Zhang, Leuven)
Reconstruction (e.g. artefact reduction)
WP 3: Optimisation
What are the most relevant image quality parameters in dentomaxillofacial imaging, and how are they best measured using a test object?
How do CBCT devices relate to each other for these parameters?How do CBCT pixel values correlate to actual densities and CT
numbers (Hounsfield Units)? Are pixel values uniform throughout the reconstructed volume? Which are the most relevant acquisition parameters affecting the stability and linearity of pixel values?
Are CBCT datasets truly isotropic? How can metal artefacts be evaluated and which parameters
influence their appearance?
WP 3: Optimisation
WP 3: Optimisation
Development of QA tools
PMMAcylinder
Inserts
WP 3: Optimisation• Spatial resolution (XY and Z)• Point spread function• Line spread function• Contrast resolution • CT number• Artefact analysis• Geometric accuracy (XY and Z)• Homogeneity • Uniformity• Dose?
Scanora 3D
Galileos
Picasso TrioProMax 3D
Kodak 9000 3D
WP 3: Optimisation
3D Accuitomo
i-CAT SkyView
WP 3: Optimisation
• Spatial resolution (XY and Z)• Point spread function• Line spread function• Contrast resolution • CT number• Artefact analysis• Geometric accuracy (XY and Z)• Homogeneity • Uniformity• Dose?
WP 3: Optimisation
WP 3: Optimisation
WP 3: Optimisation
XY plane
Resolution < 3 lp/mm Artefacts Saturation XY plane
→ line pair pattern on PMMA background
WP 3: Optimisation
WP 3: Optimisation
• Spatial resolution (XY and Z)• Point spread function• Line spread function• Contrast resolution • CT number• Artefact analysis• Geometric accuracy (XY and Z)• Homogeneity • Uniformity• Dose?
WP 3: Optimisation
0.1 mm 0.25 mm
Steel wire in air
WP 3: Optimisation
WP 3: Optimisation
i-CAT HR
mm5,24,84,443,63,22,82,421,61,20,80,40
pixe
l val
ue
0,24
0,22
0,2
0,18
0,16
0,14
0,12
0,1
0,08
0,06
0,04
0,02
0
Cauchy distribution
WP 3: Optimisation3D Accuitomo
mm4,64,44,243,83,63,43,232,82,62,42,22
pixe
l val
ue
0,13
0,12
0,11
0,1
0,09
0,08
0,07
0,06
0,05
0,04
0,03
0,02
0,01
0
Galileos
mm5,65,24,84,443,63,22,82,421,61,20,80,40
pixe
l val
ue
0,4
0,36
0,32
0,28
0,24
0,2
0,16
0,12
0,08
0,04
0
i-CAT LR
mm6,45,64,843,22,41,60,80
pixe
l val
ue
0,26
0,24
0,22
0,2
0,18
0,16
0,14
0,12
0,1
0,08
0,06
0,04
0,02
0
WP 3: OptimisationKodak 9000 3D
mm65,65,24,84,443,63,22,82,421,61,20,80,40
pixe
l val
ue
0,064
0,056
0,048
0,04
0,032
0,024
0,016
0,008
0
Scanora 3D
mm65,65,24,84,443,63,22,82,421,61,20,80,40
pixe
l val
ue
0,13
0,12
0,11
0,1
0,09
0,08
0,07
0,06
0,05
0,04
0,03
0,02
0,01
0
SkyView LR
mm5,24,84,443,63,22,82,421,61,20,80,40
pixe
l val
ue
0,18
0,16
0,14
0,12
0,1
0,08
0,06
0,04
0,02
0
WP 3: Optimisation
Picasso Trio
mm65,65,24,84,443,63,22,82,421,61,20,80,40
pixe
l val
ue
0,3
0,28
0,26
0,24
0,22
0,2
0,18
0,16
0,14
0,12
0,1
0,08
0,06
0,04
0,02
0
SkyView HR
Histogram Cauchy
mm5,65,24,84,443,63,22,82,421,61,20,80,40
pixe
l val
ue
0,16
0,14
0,12
0,1
0,08
0,06
0,04
0,02
0
i-CAT HR
mm5,24,84,443,63,22,82,421,61,20,80,40
pixe
l val
ue
0,24
0,22
0,2
0,18
0,16
0,14
0,12
0,1
0,08
0,06
0,04
0,02
0
WP 3: Optimisation
WP 3: Optimisation
• Spatial resolution (XY and Z)• Point spread function• Line spread function• Contrast resolution • CT number• Artefact analysis• Geometric accuracy (XY and Z)• Homogeneity • Uniformity• Dose?
WP 3: Optimisation
PTFE cube PMMA
surrounding
ESF↓
LSF↓
MTF
Gumbel distribution
WP 3: Optimisation
i-CAT HR
mm1211109876543210
pixe
l val
ue
0,03
0,028
0,026
0,024
0,022
0,02
0,018
0,016
0,014
0,012
0,01
0,008
0,006
0,004
0,002
0
Gumbel distribution
WP 3: OptimisationGalileos
mm1211109876543210
pixe
l val
ue
0,072
0,064
0,056
0,048
0,04
0,032
0,024
0,016
0,008
0
i-CAT HR
mm1211109876543210
pixe
l val
ue
0,03
0,028
0,026
0,024
0,022
0,02
0,018
0,016
0,014
0,012
0,01
0,008
0,006
0,004
0,002
0
i-CAT LR
mm1211109876543210
pixe
l val
ue
0,06
0,056
0,052
0,048
0,044
0,04
0,036
0,032
0,028
0,024
0,02
0,016
0,012
0,008
0,004
0
Kodak 9000 3D
mm131211109876543210
pixe
l val
ue
0,028
0,026
0,024
0,022
0,02
0,018
0,016
0,014
0,012
0,01
0,008
0,006
0,004
0,002
0
WP 3: OptimisationScanora 3D
mm1211109876543210
pixe
l val
ue
0,026
0,024
0,022
0,02
0,018
0,016
0,014
0,012
0,01
0,008
0,006
0,004
0,002
0
SkyView HR
mm1211109876543210
pixe
l val
ue
0,1
0,09
0,08
0,07
0,06
0,05
0,04
0,03
0,02
0,01
0
SkyView LR
mm1211109876543210
pixe
l val
ue
0,09
0,08
0,07
0,06
0,05
0,04
0,03
0,02
0,01
0
Picasso Trio
mm1211109876543210
pixe
l val
ue
0,032
0,028
0,024
0,02
0,016
0,012
0,008
0,004
0
WP 3: Optimisation
WP 3: Optimisation
• Spatial resolution (XY and Z)• Point spread function• Line spread function• Contrast resolution • CT number• Artefact analysis• Geometric accuracy (XY and Z)• Homogeneity • Uniformity• Dose?
WP 3: Optimisation• Air• Aluminium• Hydroxyapatite (50, 100, 200)
WP 3: Optimisation
• Spatial resolution (XY and Z)• Point spread function• Line spread function• Contrast resolution • CT number• Artefact analysis• Geometric accuracy (XY and Z)• Homogeneity • Uniformity• Dose?
WP 3: Optimisation
CNR = MPV1-MPV2 (SD1+SD2)/2
WP 3: Optimisation
WP 3: Optimisation
WP 3: Optimisation
• Pixel value: relation HA 50,100,200?• Work in progress
WP 3: Optimisation
WP 3: Optimisation
WP 3: Optimisation
• Spatial resolution (XY and Z)• Point spread function• Line spread function• Contrast resolution • CT number• Artefact analysis• Geometric accuracy (XY and Z)• Homogeneity • Uniformity• Dose?
WP 3: Optimisation
Titanium rods
WP 3: Optimisation
WP 3: Optimisation
WP 3: OptimisationSmoothing + subtracting background
2 ROIs, ignore black streaks
WP 3: OptimisationMeasure along intervals, keep extreme values
Distribute (e.g. Gumbel) and evaluate parameters
ProMax 3D
84 kV 9 mA
ProMax 3D
84 kV 14 mA
WP 3: Optimisation
→ Inter-device variability→ Intra-device variability?
WP 3: Optimisation
• Spatial resolution (XY and Z)• Point spread function• Line spread function• Contrast resolution • CT number• Artefact analysis• Geometric accuracy (XY and Z)• Homogeneity • Uniformity• Dose?
WP 3: Optimisation
Cfr. spatial resolution
WP 3: Optimisation
• Spatial resolution (XY and Z)• Point spread function• Line spread function• Contrast resolution • CT number• Artefact analysis• Geometric accuracy (XY and Z)• Homogeneity • Uniformity• Dose?
WP 3: Optimisation
WP 3: Optimisation
Small FOV (truncation, …) Non-homogeneous slices
• Introduction CBCT
• SEDENTEXCT project
• CBCT dosimetry
Effective dose (phantom)
Standardised dose index
• CBCT Optimisation
QC phantom development & analysis
• Work in progress
Dose index Effective dose / organ dose analysis (+paediatric) QC phantom: second prototype Image analysis: artefacts, LSF, MTF Pixel homogeneity / uniformity Compare devices & evaluate differences