A Radiation Dose Survey of Fluoroscopic 3D Imaging Modalities with an Anthropomorphic Pediatric Phantom
1Xiaowei Zhu, MS., 1Matthew Dirnbach, ARRT, and 2Marc Felice, MS.
1Radiology, The Children’s Hospital of Philadelphia, 2University of Pennsylvania
Philadelphia, Pennsylvania, 19104, United States
Measured CTDIvol of 3D Modalities in Comparison to that of Optimized CT Studies of a 5y Phantom
Purpose
Fluoroscopic x-ray units with 3D and CT-like imaging capabilities have recently been introduced. Due to
their portability (3D on a mobile C-arm) or convenience (C-arm in Interventional Radiology suites or
operating rooms), 3D imaging modalities have been adopted for some clinical studies in lieu of
conventional 2D imaging or CT. However, radiation dose reduction options on these 3D imaging
modalities are limited.
In our institution, flat panel cone-beam CT have been routinely used for treatments of vascular
anomalies, Temporomandibular Joint (TMJ) Disorder in Interventional Radiology Suites; 3D Rotation
Angiography are used for better visualization of vascular structures. A portable O-arm has been utilized
for orthopedic surgical procedures in the operating rooms.
This study compares the radiation doses of various 3D modalities. Guidelines are provided for
optimizing a balanced choice of radiation dose reduction with clinical imaging needs.
Methods
Rotational scans were performed on a 5-y old custom-designed anthropomorphic phantom. The
phantom has 5 pencil ionization chamber slots allowing measurements similar to that of standard CT
Dose Index (CTDI).
Utilizing the x-ray manufacturer’s suggested techniques, radiation doses were measured in the
phantom’s head, thorax, abdomen and pelvis. These techniques produced acceptable images for the
intended clinical applications.
The study included two IR 3D modalities (Philips Allura 3D-RA, installed in 2003, Siemens AXIOM Artis
Dyna CT, installed in2007), and one portable 3D C-arm (Medtrocnic O-arm, purchased in 2007) used in
operating rooms. The CTDI values were compared to our optimized routine CT scans on the same
pediatric phantom.
Siemens Artis Dyna CT
Head
TMJ
Sinus
Siemens
Sensation 64 CT
CTDIvol mGy
31.3
0.6
8.4
Philips Allura
3DRA
CTDIvol mGy
1.7
N/A
N/A
Medtronic
O-arm 3D
CTDIvol mGy
9.1
N/A
N/A
5sec Low
CTDIvol mGy
0.3
0.3
N/A
Chest
3.4
1.4
14
0.2
0.6
0.2
0.8
0.6
1.8
ABD
4.4
2.4
13.5
0.7
1.9
0.8
2.8
2.9
8.1
Pelvis
Measurement No.
4.4
1
2.2
2
12.8
3
0.7
4
1.9
4
0.8
4
2.8
4
2.9
4
8.1
4
Routine Protocols of:
5 sec Med
8sec Med
5sec Norm
8sec Norm
8sec Low
CTDIvol mGy CTDIvol mGy CTDIvol mGy CTDIvol mGy CTDIvol mGy
1.1
0.6
1.5
1.3
3.5
Only the optimized 5sec Low setting was used for TMJ
N/A
N/A
N/A
N/A
N/A
Table 1 Measured CTDIvol of 3D Modalities in Comparison with that of Optimized CT Studies
About Measurements:
1) Data for 1,2,3,4 were based on CHOP 5y old CIRS ATOM phantom measured with a Radical CT chamber
2) Measurements are taken at Center, 12', 3', 6', 9' clock locations with standard CTDI measurement approach
3) CTDIvol were calculated according to ACR standard method:1/3 (Center)+2/3 (Avarage of the Peripherals)
4) All exposure techniques used were based on CHOP specific clinical protocols for typical 5y old
5) All measurements applied practically achievable collimation both for clinical uses as well for CTDI measurements on each unit
6) Siemens Artis DYNA CT were with automatic filtration, Low 0.1μGy/f, 0.9 mmCu, Med. 0.17 μGy/f, 0.6 mmCu, Norm 0.36 μGy/f, 0.3 mmCu
7) Spins from non CT X-ray units are not of CT diagnostic quality. CTDIvol presented here are for dose comparison with routine CT scans at
CHOP.
8) Measurement 2, 3, have limited collimation, in both directions; 1,4 with collimation in z direction covering just measurement chamber
Results
The dose from 3D imaging modalities varied between vendors. In some cases, CTDI were higher than
routine CT scans due to the limitations on the available selections of dose, pulse rate, and collimation.
The standard techniques provided by the 3D modality manufacturers yield CTDI’s in the range of 5-29%
of conventional CT for head, 41-411% for thorax, 54-307% for abdomen, and 50-290% for pelvic studies.
Image qualities are generally inferior to conventional CT, but acceptable for the intended clinical tasks.
When using the Siemens Artis DynaCT for TMJ studies, radiation dose from manufacturer suggested
standard settings were significantly higher than that of optimized conventional TMJ CT scan. The
optimization processes for DynaCT TMJ study was reported on a separate poster. However, the Siemens
Artis Dyna CT reported in this study on Table 1 represented a progressive approach in working with
Siemens Medical to optimize our utilization of the 3D imaging tools in IR.
Figure 8. Phantom Images of O-arm
Figure 9. Phantom Images of O-arm
Conclusion
Based on these phantom studies, our institution has made progressive improvements in modifying 3D
imaging techniques to reduce radiation dose while maintaining the clinical integrity of the images.
Figure 1. The phantom family
Figure 2. The cross-section of a chest phantom
Figure 3. Dose measurement set-up
(with a head phantom)
References
Figure 4. A CT cross-sectional image of the chest phantom
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Figure 5. O-arm
Figure 6. Phantom Images of O-arm
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8. Phantom Images of O-arm
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Figure 7. Phantom Images of O-arm
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