Towards prospective identification of optimal scan parameters for CT-guided interventions: a phantom study.

CT-guided interventions require balance between radiation dose and image quality. This study evaluates the impact of tube voltage and tube load on the contrast-to-noise ratio (CNR) across different patient sizes and target tissues. A modular multi-energy phantom with effective diameters of 20 cm and 35 cm was used. Bone, iodine-blood mixture, and pure blood targets were scanned axially at matched dose levels. Images were equally reconstructed. For analysis, CNR was the primary metric. Tube voltages of 80, 100, 120 and 140 kVp were applied with corresponding mAs adjustments to achieve dose levels between 1 and 10 mGy SSDE (Size Specific Dose Estimate). In the small phantom, low kVp settings yielded the highest CNR for high-contrast targets like iodine. For low-contrast imaging, higher kVp settings were more beneficial. In the large phantom, higher kVp consistently improved CNR across all materials. E.g. raising kVp from 80 to 120 raised the CNR from 6.5 to 8.6 for the iodine-blood setup. In conclusion, for optimal image quality in CT-guided interventions, scan protocols must adapt tube voltage and tube load dynamically to the target tissue and patient size. Finding the sweet spot between contrast loss and noise reduction for increasing tube voltages is key for intervention planning.