Risk-minimizing tube current and tube voltage modulation for CT: A simulation study

Area of Science:

• Medical Imaging
• Radiological Physics
• Radiation Dose Reduction

Background:

• Clinical CT imaging uses constant tube voltage, despite patient attenuation varying with position and anatomy.
• Optimal tube voltage generally increases with patient diameter but should be lower for iodine-enhanced scans.
• Current lowest clinical voltage (70 kV) is limited by tube current restrictions, hindering optimal contrast enhancement.

Purpose of the Study:

• To evaluate the additional effective dose reduction from combining tube voltage modulation with tube current modulation.
• To assess these benefits for both unenhanced and iodine-enhanced CT scans.

Main Methods:

• Monte Carlo simulations estimated effective dose per projection for various tube voltages using patient models.
• Optimized tube voltage and current curves were derived by minimizing dose-weighted noise (unenhanced) or maximizing contrast-to-noise ratio (iodine-enhanced).
• Simulated protocols (riskTCTVM) were compared against pure tube current modulation (riskTCM and mAsTCM) at equivalent noise or CNR.

Main Results:

• For unenhanced scans, combined modulation (riskTCTVM) offered <1% effective dose reduction compared to riskTCM.
• For iodine-enhanced scans at 70 kV, benefits ranged from <3% (thorax/abdomen) to 14% (shoulder).
• At 50 kV, benefits increased significantly (7% thorax to 28% shoulder), but required higher tube currents; dose reduction was notable for eccentric anatomies at 70 kV.

Conclusions:

• Tube voltage modulation provides negligible dose benefits for unenhanced CT.
• Significant dose reduction is achievable for iodine-enhanced scans with combined modulation, particularly if lower voltages (down to 50 kV) and sufficient power are available.
• Even at 70 kV, combined modulation offers substantial dose reduction for eccentric pelvic and shoulder anatomies.