Download Image Quality and Dose Comparison between

Image Quality and Dose Comparison
between Cone Beam and
Spiral CT for Sinus Evaluation
Taylor B, Ivanovic M, Jewells V,
McClintock B, Senor B
University of North Carolina
Hospitals
Chapel Hill, NC
DISCLOSURES
• The authors of this study have no disclosures
or conflicts of interest to report that may be
pertinent to this study.
OUTLINE
• Overview of CBCT
• Our study to evaluate dose and image quality
• How we were able to lower overall doses
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HISTORY OF CBCT
Adapted for clinical use in 1982.
First appeared on LINAC in 1999.
Dentomaxillofacial imaging in 2001.
C-arm CBCT (Interventional Radiology, Orbic, O-Arm).
HISTORY OF CBCT
• Why CBCT was able to develop?
– Advancements in flat panel detectors
– Improved computing power
– Low power requirements for x-ray tubes
• Inexpensive and Compact
• Deliver images with high isotropic spatial resolution
• Relatively low patient doses
DESIGN OF CBCT
• A: CBCT - entire volumetric dataset collected with single
rotation
• B: Conventional CT - requires z-direction translation
DESIGN OF CBCT
• Scanner rotates – generally hundreds of
distinct images
• Volumetric dataset can be reformatted in any
plane
PROS OF CBCT
•
•
•
•
Less expensive
Smaller
Whole organ coverage with one rotation
Isotropic sub-millimeter
spatial resolution
• Good for “bone” imaging
• Generally, lower dose
Almost 6x higher!
CONS OF CBCT
• Slower, motion artifacts
• Not good low contrast detectability due to:
• Increased scatter
• Lower temporal resolution
• No dose modulation
• Conventional dose metrics
not directly adapted
PURPOSE
• Assess overall image quality between the Xoran
MiniCAT CBCT and spiral CT at multiple dose levels
• Compare the radiation doses with the MiniCAT
versus the spiral CT
• Assess the accuracy vendor claims of reduced
radiation doses
Courtesy of www.xorantech.com
Courtesy of www.radsuitemedical.com
MATERIALS AND METHODS
• Radiation doses were measured for the Unfors PSD
Meter and an Anthropomorphic Skull Phantom
MATERIALS AND METHODS
• Detector leads were placed at the pterion, midforehead, right lens, and thyroid
MATERIALS AND METHODS
• Effective doses were subsequently compared with
vendor supplied literature for comparison
MATERIALS AND METHODS
• Two independent readers (Neuroradiologist and 4th
year Radiology resident) rated the overall image
quality by evaluating:
visibility of the bone-soft tissue interface
osteomeatal unit
frontal recess
ethmoid septa
cribiform plate
vidian canal
foramen rotundum
frontal recess
• excellent = 2, adequate =1, & poor = 0
MATERIALS AND METHODS
• Image quality was evaluated at the current protocol
for spiral CT (84 mAs) down to 20 mAs
RESULTS
• The MiniCAT system provides three imaging options
(150, 300, and 600)
– effective doses were supplied by the vendor
Entrance Skin exposure (mGy)
Position
Xoran Sinus 600 1st
Xoran Sinus 600 2nd
Xoran Sinus 600 3rd
Crosshair
Thyroid
Forehead
Right Eye
2.8280
3.0820
2.8420
0.2346
0.2431
0.2325
1.5200
1.6660
1.6080
3.1660
3.3560
3.1900
Xoran Sinus 600 Ave.
Xoran Sinus 300
Xoran Sinus 150
2.9173
1.4300
0.7512
0.2367
0.1190
0.0731
1.5980
0.7766
0.4028
3.2373
1.6060
0.8321
Ave. mAs
DLP
(mGy*cm)
ED (mSv)
48
24
12
97.0000
49.2000
24.6000
0.1700
0.0900
0.0400
RESULTS
• Effective doses determined with the spiral CT at
current protocol of 84 mAs down to 20 mAs
Siemens mAs=84 p=0.8
Siemens mAs=70 p=0.8
Entrance Skin exposure (mGy)
7.7850
0.4057
7.0180
6.3140
CTDIvol
Ref mAs Avg mAs (mGy)
84
67
9.70
DLP
(mGy*
cm)
ED (mSv)
130.00
0.4160
0.3336
0.3515
4.7730
5.2730
5.9970
5.1186
70
70
56
55
8.08
7.90
108.00
109.00
0.3456
Siemens mAs=70 p=0.6
5.2390
6.1220
Siemens mAs=60 p=0.8
4.4680
0.2845
4.0810
5.0960
60
47
6.83
92.00
0.2944
Siemens mAs=50 p=0.8
3.5620
0.2346
3.2840
5.0010
50
38
5.57
75.00
0.2400
Siemens mAs=40 p=0.8
3.0500
0.2024
2.7710
3.1850
40
32
4.67
63.00
0.2016
Siemens mAs=30 p=0.8
2.9740
0.1735
2.6520
2.4400
30
27
3.95
53.00
0.1696
Siemens mAs=20 p=1.0
1.8740
0.1304
1.4780
1.8850
20
20
2.87
40.00
0.1280
0.3488
RESULTS
• The MiniCAT produced significantly poorer image quality
secondary to streak artifact, noise, and lack of definition of
the osseous structures as compared spiral CT
Xoran MiniCAT – imaging at 600 protocol
Siemens spiral CT – kV 120, mAs 84
current UNCH Protocol for sinus imaging/surgical planning
RESULTS
• Image quality of spiral CT remained superior to MiniCAT at
parameters producing similar effective dose
• Scoring for the spiral CT vs CBCT was 6 vs 4
Xoran MiniCAT - 600
spiral CT – kV 120, mAs 30
RESULTS
• Image quality of spiral CT remained superior to MiniCAT at
parameters that produced a lower effective dose
Xoran MiniCAT - 600
spiral CT – kV 120, mAs 20
RESULTS/DISCUSSION
• Image quality with the spiral CT was superior for all
imaging parameters, even at lower doses
• While our currently employed spiral CT protocol
offers superior image quality, dose is also greater
RESULTS/DISCUSSION
• Some patients scanned on the MiniCAT system may
require a subsequent spiral CT for surgical navigation
• Why not just do ONE SCAN using appropriately
adjusted techniques:
1. reduce cumulative radiation dose
2. more efficient use of time and money
3. improved patient convenience
FURTHER DIRECTION
• Assessed reduced spiral CT techniques for
image quality in a subset of 11 patients
(84 mAs to 60 mAs)
• All lowered doses were adequate for surgical
guidance and Neuroradiology review
• Evaluating lowered techniques on a larger set
of patients
• Use of “Sapphire” and “Care kV” – 1/2013
CONCLUSION
• Overview of CBCT
• Know your doses
• Look for opportunity to evaluate your practice
and lower when you can