The Effects of Organ-based Tube Current Modulation on Radiation Dose and Image Quality in Computed Tomography Imaging
Date of Award
Master of Science (MS)
Schmidt, Taly G.
Stevens, Grant M.
The purpose of this thesis was to quantify dose and noise performance of organ-dose-based tube current modulation (ODM) through experimental studies with an anthropomorphic phantom and simulations with a voxelized phantom library. Tube current modulation is a dose reduction technique that modulates radiation dose in angular and/or slice directions based on patient attenuation. ODM technique proposed by GE Healthcare further reduces tube current for anterior source positions, without increasing current for posterior positions. Axial CT scans at 120 kV were performed on head and chest phantoms (Rando Alderson Research Laboratories, Stanford, CA) on an ODM-equipped scanner (Optima CT660, GE Healthcare, Chalfont St Giles, England). Dosimeters quantified dose to breast, lung, heart, spine, eye lens and brain regions (mobile MOSFET Dosimetry System, Best Medical, Ottawa, Canada) for ODM, AutomA (z-axis modulation), and SmartmA (angular and z-axis modulation) settings. Noise standard deviation was calculated in brain and chest regions of reconstructed images. To study a variety of patient sizes, Monte Carlo dose simulations, validated with experimental data, were performed on voxelized head and chest phantoms. Experimental studies on anthropomorphic chest and head phantoms demonstrated reduction in dose at all dosimeter locations with respect to SmartmA, with dose changes of -31.3% (breast), -20.7% (lung), -24.4% (heart), -5.9% (spine), -18.9% (eye), and -10.1% (brain). Simulation studies using voxelized phantoms indicated average dose changes of -33.4% (breast), -20.2% (lung), -18.6% (spine), -20.0% (eye) and -7.2% (brain). ODM reduced dose to the brain and lung tissues, however these tissues would experience up to 15.2% and 13.1% dose increase respectively at noise standard deviation equal to SmartmA. ODM reduced dose to the eye lens in 22 of 28 phantoms (-1.2% to -12.4%), had no change in dose for one phantom, and increased dose for four phantoms (0.7% to 2.3% ) with respect to SmartmA at equal noise standard deviation. All phantoms demonstrated breast dose reduction (-2.1% to -27.6%) at equal noise standard deviation. Experimental and simulation studies over a range of patient sizes indicate that ODM has the potential to reduce dose to radiosensitive organs by 5 - 38% with a limited increase in image noise.