ORTHOPANTOMOGRAPH™ OP 3D
3D Constancy Check Procedure
216221 rev.4
0.805.5264
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Scope
This document instructs the 3D constancy check procedure, how values
are interpreted, and gives a short description of each measurement.
Following properties of 3D reconstructed volume are evaluated during
inspection:
- Image noise
- Grey value / Low contrast resolution
- Uniformity
- Artefacts
- High contrast spatial resolution
This document assumes KaVo Driver 19.3 (IAM 5.22.18241) or newer is
installed on the system. Always see latest driver information for possible
changes. For detailed description on csv table data output from the
automatic 3D QC check (not required for constancy check completion),
please refer to Appendix A.
The results of the periodical checks below should be recorded, and the
check images archived. To do this, it is recommended that a “Constancy
Test” “Patient” record is created under which the test images can be
recorded. Appendix B contains record sheet templates.
NOTICE! The reference levels may change with x-ray unit firmware /
driver updates. Upon such updates, new reference levels for measured
values for the unit should be established. Always refer to the limiting
values that are specified with current 3D QC test.
Appendix C contains reference tables for required tests in The State of
New Jersey.
Required tools:
- 3D QC Phantom (215966)
- 3D QC Phantom holder (included with the device)
Optional tools:
- Constancy test phantom and holder (3D Quality Tool Kit)
(215966)
1. Automatic 3D QC program:
-
Image noise
Grey values / Low contrast resolution
Field uniformity
High contrast resolution
Artefacts
Perform the “3D QC” program as described in the ORTHOPANTOMOGRAPH™
OP 3D User and Installation Manual.
Following measurements are checked automatically with the “3D QC”program:
-
Noise
Grey values / Low contrast resolution
Field uniformity
High contrast resolution
If 3D QC test result is “Passed” then above measurements are within
manufacturer specified limits.
Reference image of a passed 3D QC test and ROI measurements.
To check numerical results, open the resulting image in a 3D viewer. The
axial slice 140 of the volume contains measurement results and used
reference values. Record results to the sheet templates provided in
Appendix B.
The measurement results are automatically stored in a csv table. Path for
this file is typically C:\ProgramData\PaloDEx Group\IDX\Logs\. It is not
necessary, but the created .csv file can be copied to be archived as
constancy check results or imported to a spreadsheet program to closer
examine the measured values.
In case of failed QC result, this file can be attached for technical support
request. Appendix A has more information on interpreting this file.
Description for the measurements:
Image noise:
Noise is defined as standard deviation of the 3D measurement ROI
in the volume. Noise is determined from several materials in the
phantom:
- PMMA std. dev.
- PTFE std. dev.
- Air std. dev.
Grey values / Low contrast resolution:
Grey values of several materials in the reconstructed volume are
measured. There must be difference in grey values in different
materials to ensure adequate low contrast resolution and
consequently to make sure that good tissue/bone separation is
achieved in the 3D volume.
Following grey values are measured from the volume:
- PMMA average value
o Corresponds approximately to X-ray absorption of water
- PTFE average value
- Air average value
Field uniformity:
Field uniformity measurement calculates max difference in grey
values between centre and border regions of the PMMA material in
the phantom.
High contrast resolution:
High contrast resolution is measured, and the result presented as
MTF10 – value. MTF (Modulation Transfer Function) is a function of
spatial resolution which refers to the smallest line-pair the system
can resolve.
2. Artefacts
This check is carried out visually. Person with experience on interpreting
3D images should perform the check. Examine the axial slices of 3D QC
volume taken in the previous QC steps. Be aware of artefacts which do
not originate from the object or from the projection conditions. Please
note that there will be some circles drawn in the volume to indicate areas
used for 3D QC program result calculations.
Requirement for acceptance:
Absence of artefacts, except for those that may be expected due to
phantom or projection conditions.
If the requirement is fulfilled, confirm in the acceptance report by
checking “Artefact”.
Examples:
Acceptable, shadowing may appear around straight horizontal
material interfaces.
Not acceptable; discontinuity in circular shape due to geometry mismatch
between scans with different offset. In similar artefacts are observed,
redo 3D geometry calibrations before retrying 3D QC. If problem
persists, contact service.
3. High contrast spatial resolution (alternative method)
1. Place the Constancy test phantom and holder onto the 3D QC phantom
holder.
2. When running test for the first time on given unit, set the 3D imaging
program as follows:




Select the third molars from the dental chart
o This adjusts the ROI to middle of the phantom
o The FOV is set to 9 x 11
Set resolution to High
Set mA to 4.00 mA
Disable Scout mode
3. Record selected exposure parameters under constancy check sheet in
Appendix B “Selected reference values for the constancy check”. Use
these parameters in following periodical checks.
4. Open captured volume in the workstation using a 3D viewer. Use axial
view to find maximum number of distinguishable line pairs in the axial
slice.
Requirements:
The visually identifiable space resolution must be at least 1LP/mm.
Assessment:
The structure 12 (1.2 LP/mm) should be represented precisely as
dissociated lines.
NOTICE! The groups of lines 13 and 14 (1.3 and 1.4 LP/mm,
respectively) are generally easily identifiable.
Refer also to the image below for line pair identification (please note that
numerical index of the line groups do not appear in the image, they are
presented here for line group identification):
Following image shows visually accepted line pairs:
Reference image of a passed 3D high contrast spatial resolution test.
Appendix A. 3D QC measurement values and results in the 3D QC CSV table with Driver Update
version 19.3 or newer
File default location: C:\ProgramData\PaloDEx Group\IDX\Logs\
Naming: <year><month><day>T<time>-<serial number>-<phantom>-3D.csv
For example, 20190624T091258-KT1700009-QC2016-3D.csv
File structure:
Line
1
4
5
7
10
12
13
14
15
31
32
33
39
48
Contents
QC calculation date and time
Program ID number
Unit
FOV size
Exposure values
Unique image identifier
Index value for reconstruction type
Number of projections expected for current program
Actual number of valid projection images. Number smaller than on previous line may indicate problems in system.
Measurements from phantom upper areas
Measurements from phantom middle areas
Measurements from phantom lower areas
Listing of acceptance limits
Summary of measured acceptance values
Appendix B. Constancy check record and one-year monthly follow-up sheets
Operator:
System:
Serial numbers:
System:
Type of radiation emitter:
Number:
Selected reference values for the constancy check
(FOV, kV, mA):
Results of the check:
Series
Check item
Requirements
1
Image noise
Local variation of the pixel
3D QC phantom ROI
value around an average value measurements.
(according to manufacturer's
indications)
-
PMMA std.dev.
PTFE std.dev.
AIR std.dev.
2
Grey value / Low
contrast resolution
Grey values for different
materials in reconstructed
volume within limits.
3D QC phantom ROI
measurements.
-
PMMA average value
PTFE average value
AIR average value
3
Uniformity
Difference in voxel value of
similar thickness zones of a
sample within limits.
3D QC phantom ROI
measurements.
-
Uniformity
4
Artefacts
In accordance with DIN V
6868-161
Visual check of the phantom
5
High contrast spatial
resolution
≥ 1 Lp/mm for 10% contrast
(with sample in the center of
the scan)
Phantom test record, visual
assessment of the LP
phantom in software
Name of the
inspector
Signature
Check condition
Date
Result
Noise
Year:
Allowed deviation 20%
PMMA
AIR
PTFE
max
std.dev.
std.dev.
std.dev.
Grey values / low contrast
resolution
Allowed deviation 20%
AIR
PTFE
PMMA
average
average
average
value
value
value
Artefacts
January
February
March
April
May
June
July
August
September
October
November
December
Year:
Uniformity
<200
PMMA uniformity measurement values
Center
January
February
March
April
May
June
July
August
September
October
November
December
Left
Right
Anterior
Posterior
High contrast
spatial
resolution
>1 lp/mm
lp/mm
Appendix C. Manufacturer’s Recommendations for Alternate
Dental CBCT QA Program (for The State of New Jersey)
Table 3A
Computed Tomography QC Requirements
Item
1
2
3
Required Test
or Procedure
Equipment
Function
“Indicators,
Mechanical &
other Safety
Checks
Film Processing
QC Testing
CT Number for
Water
Frequency
Daily
Daily
Daily
Substitute Test or
Procedure
3D constancy check
procedure, code 216221
(part of separate QC
kit), Section 1:
Automatic 3D QC
program
None, not applicable
3D constancy check
procedure, code 216221
Section 1: Automatic 3D
QC program;
3D quality check
automatically performs
intensity check for
water equivalent
3D constancy check
procedure, code 216221
Section 1: Automatic 3D
QC program;
Quality check program
automatically performs
field uniformity check
4
Field Uniformity
Daily
5
Laser Film Printer
QC
Low Contrast
Resolution
Weekly
None, not applicable
Initial &
Annually
QC phantom
computerized SW test
has limits for signal and
noise values of PMMA,
PTFE and air. This
assures tissue
separation performance
specified by
manufacturer (low
contrast resolution).
6
7
High Contrast
Resolution
Initial &
Annually
Optionally, QA test can
be performed using
appropriate Low
Contrast phantom. Low
Contrast phantom is not
provided by
manufacturer.
3D constancy check
procedure, code
216221, Section 3: High
contrast spatial
resolution
Standard
Must work properly
None, not applicable
Pass QC phantom
computerized SW test,
applicable measurement
Minimum PMMA ROI value
(acceptance limits shown by
the SW)
Pass QC phantom
computerized SW test,
applicable measurements
Maximum PMMA Std. Dev
Maximum PTFE Std. Dev
Maximum AIR Std. Dev
(acceptance limits shown by
the SW)
None, not applicable
Option 1:
Pass QC phantom
computerized SW test
Option 2:
To be established by Medical
Physicist
Constancy test phantom MTF10
– value must be at least 1.0
8
Noise
Initial &
Annually
3D constancy check
procedure, code 216221
Section 1: Automatic 3D
QC program;
Quality check
automatically performs
noise check
9
Scan Localization
Light Accuracy
Initial &
Annually
Medical Physicist’s
QC Survey
Medical Physicist’s
Quality Assurance
Program Review
Initial &
Annually
Initial &
Annually
OP 3D User &
Installation Manual;
Patient positioning light
adjustment
Same as Alternate
Dental CBCT
Same as Alternate
Dental CBCT
10
11
(Visually identifiable spatial
resolution must be at least
1.2LP/mm)
Pass QC phantom
computerized SW test,
applicable measurements
Maximum PMMA Std. Dev
Maximum PTFE Std. Dev
Maximum AIR Std. Dev
(acceptance limits shown by
the SW)
Exact alignment to geometry
test phantom marks as per
procedure
NJAC 7:28-22.10
NJAC 7:28-22.4(a)7
Manufacturer’s Recommendations for Alternate Dental CBCT QA Program
Table 6
Medical Physicist’s Computed Tomography QC Survey
Item
1
2
3
Required Test or
Procedure
Scan Increment
Accuracy
Scan Localization Light
Accuracy
Patient Dose (Multiple
Scan Average Dose)
MSAD or Computed
Tomography
4
Dose Index-CTDI
Pre-Patient Collimation
Accuracy
5
Contrast Scale
6
CT Number for Water
Substitute Test or
Procedure
None – Not Applicable
Standard
OP 3D User & Installation
Manual; Patient positioning
light adjustment
OP 3D User & Installation
Manual; Imaging program
specifications
Exact alignment to geometry test
phantom marks as per procedure
OP 3D User & Installation
Manual; Collimator
adjustment
3D constancy check
procedure, code 216221,
Section 1: Automatic 3D QC
program
Pass computerized collimation test
and test as established by the
Medical Physicist
Pass QC phantom computerized
SW test, applicable measurement
Minimum PMMA ROI value
Minimum PTFE ROI value
Maximum AIR ROI value
(acceptance limits shown by the
SW)
3D constancy check
procedure, code 216221
Section 1: Automatic 3D QC
program;
3D quality check
automatically performs
Pass QC phantom computerized
SW test
Small FOV Minimum PMMA ROI ≥ 120
None – Not Applicable
As established by the Medical
Physicist
7
8
Slice Thickness
Field Uniformity
9
Low Contrast Resolution
10
11
12
13
14
High Contrast Resolution
Noise
Scan Protocol Review
Review of Facility and
Technologists QC Tests
Physicist Report and
Recommendations
intensity check for water
equivalent
None- Not Applicable
3D constancy check
procedure, code 216221
Section 1: Automatic 3D QC
program;
Quality check program
automatically performs field
uniformity check
QC phantom computerized
SW test has limits for signal
and noise values of PMMA,
PTFE and air. This assures
tissue separation
performance specified by
manufacturer (low contrast
resolution).
Optionally, QA test can be
performed using
appropriate Low Contrast
phantom. Low Contrast
phantom is not provided by
manufacturer.
3D constancy check
procedure, code 216221
(part of separate QC kit),
Section 3: High contrast
spatial resolution
None- Not Applicable
Pass QC phantom computerized
SW test, applicable measurements
Maximum PMMA Std. Dev
Maximum PTFE Std. Dev
Maximum AIR Std. Dev
(acceptance limits shown by the
SW)
Option 1:
Pass QC phantom computerized
SW test
Option 2:
To be established by Medical
Physicist
Constancy test phantom MTF10 –
value must be at least 1.0
3D constancy check
procedure, code 216221
Section 1: Automatic 3D QC
program;
Quality check program
automatically performs
noise check
Same as NJAC 22.10(a)
Same as NJAC 22.10(a)
(Visually identifiable spatial
resolution must be at least
1.2LP/mm)
Pass QC phantom computerized
SW test, applicable measurements
Maximum PMMA Std. Dev
Maximum PTFE Std. Dev
Maximum AIR Std. Dev
(acceptance limits shown by the
SW)
Same as NJAC 22.10(a)
Same as NJAC 22.10(a)
Same as NJAC 22.10(a)
Same as NJAC 22.10(a)