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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 • • • • 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