Program Information
Should We Utilize Tube Current Modulation in Head CT Exams? An Assessment of Image Quality and Direct Dosimetry with OSLDs
I Lipnharski*, C Carranza , N Quails , N Correa , D Rajderkar , L Rill , M Arreola , University of Florida, Gainesville, FL
Presentations
PO-BPC-Exhibit Hall-4 (Saturday, March 18, 2017) Room: Exhibit Hall
Purpose: Tube current modulation (TCM) in helical CT is not typically used for head exams due to the head’s cylindrical shape. Because it is difficult to determine whether TCM has the potential to reduce CT dose while maintaining image quality using phantoms, we approach this question using cadavers.
Methods: Five cadavers were scanned using a routine head CT protocol (120 kVp, 270 mA, 70.8mGy CTDIvol) followed by protocols with modulating tube current driven by noise-target levels of 2.5, 5, and 7.5 SD with and without iterative reconstruction (AIDR-3D), with mA limited between 10 and 270 mA. A neuroradiologist assessed 15 image quality features for diagnosing head scans on a three-point scale. Organ doses were measured in the cadaver with the smallest head with 21 OSL dosimeters placed on the surface and implanted into the brain, thyroid, salivary glands, and eye lens by a neurosurgeon. To address the issue of TCM utilization on mis-centered heads, the protocol with TCM of 5 SD was scanned with the cadaver shifted 4 cm anteriorly and posteriorly.
Results: Image quality was acceptable for protocols with 2.5 and 5 SD without AIDR. All other protocols received borderline acceptable scores and were considered too low dose for clinical use. The TCM protocol with 5 SD reduced the CTDIvol from 70.8 mGy to a mean of 61.6 mGy for the five cadavers, and average organ doses from 40.6 mGy to 33.3 mGy. When shifted 4 cm anteriorly and posteriorly, the maximum CTDIvol difference was 3.2 mGy and the maximum organ dose difference was 4.42 mGy to the eye lens.
Conclusion: Using TCM with a noise-target level of 5 SD and a carefully selected mA range allowed dose savings up to 18% while maintaining diagnostic image quality. Typical clinical mis-centering errors did not produce large organ dose differences.
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