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 anyplane

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 metricsnot 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 MiniCATversus 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, mid-forehead, 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 interfaceosteomeatal unitfrontal recessethmoid septacribiform platevidian canalforamen rotundumfrontal 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) Ave. mAs

DLP

(mGy*cm) ED (mSv)

Position Crosshair Thyroid Forehead Right Eye

Xoran Sinus 600 1st 2.8280 0.2346 1.5200 3.1660

Xoran Sinus 600 2nd 3.0820 0.2431 1.6660 3.3560

Xoran Sinus 600 3rd 2.8420 0.2325 1.6080 3.1900

Xoran Sinus 600 Ave. 2.9173 0.2367 1.5980 3.2373 48 97.0000 0.1700

Xoran Sinus 300 1.4300 0.1190 0.7766 1.6060 24 49.2000 0.0900

Xoran Sinus 150 0.7512 0.0731 0.4028 0.8321 12 24.6000 0.0400

RESULTS• Effective doses determined with the spiral CT at

current protocol of 84 mAs down to 20 mAs

Entrance Skin exposure (mGy) Ref mAs Avg mAs

CTDIvol

(mGy)

DLP

(mGy*

cm) ED (mSv)

Siemens mAs=84 p=0.8 7.7850 0.4057 7.0180 6.3140 84 67 9.70 130.00 0.4160

Siemens mAs=70 p=0.8 5.2390 0.3336 4.7730 5.9970 70 56 8.08 108.00 0.3456

Siemens mAs=70 p=0.6 6.1220 0.3515 5.2730 5.1186 70 55 7.90 109.00 0.3488

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

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 dose2. more efficient use of time and money3. 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