Program Information
The Effects of Various CT Tube Current Modulation (TCM) Schemes On Dose. Do You Really Know What Your TCM Scheme Is Doing?
K Singhrao*, M Bostani , A Hardy , C Cagnon , M McNitt-Gray , UCLA School of Medicine, Los Angeles, CA
Presentations
TU-H-207A-6 (Tuesday, August 2, 2016) 4:30 PM - 6:00 PM Room: 207A
Purpose: To compare the effects of various tube current modulation (TCM) schemes – including attenuation-based, “organ-based” and combined schemes - on both the resulting tube current values as well as dose savings.
Methods: An anthropomorphic adult thorax phantom was scanned using a Multidetector row CT scanner that offered both attenuation-based and “organ-based” TCM schemes that could be used separately or in combination (Definition AS64, Siemens Healthcare). A small ion chamber was attached to a medial location on the surface of the chest phantom to provide a reference value which served as proxy for organ dose. Scans were performed under each possible TCM configuration (fixed mA, attenuation-based only, organ-based only and combined organ and attenuation based) using the same nominal parameters (e.g. Quality Reference mAs). The actual TCM scheme was extracted from the raw projection data of each scan to illustrate the actual mA variations. The scanner CTDIvol and ion chamber readings were recorded for each scan and comparisons were made across TCM schemes.
Results: Each of the TCM schemes showed substantially different mA patterns. All TCM schemes showed some reduction in CTDIvol compared to a fixed mA scan with the same nominal settings; however the values ranged from a decrease of 2% (organ based only) to 18% (attenuation based only). The dose reduction to the surface dose point varied from a decrease of 34% (organ based only) to an increase of 15% (attenuation based only) compared to the fixed mA scan. Examining the actual TCM schemes from the raw data files allows us to understand the effects of each scheme.
Conclusion: Phantom scans allowed us to compare the effects of different TCM schemes on both CTDIvol values as well as point doses. Future work will focus on organ doses from each scheme using validated Monte Carlo techniques.
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