Comparison of Spiral and Axial CTDI Measurement Approaches

This technical report systematically compares the computed tomography dose index (CTDI) measurement approaches of axial and spiral CTDI under clinically relevant conditions. The objective is to evaluate the reproducibility of spiral CTDI and assess whether extended spiral CTDI concepts can serve as suitable alternatives to traditional axial CTDI for modern CT scanners. The study utilizes a standard PMMA CTDI body phantom and involves measurements taken with two clinical CT systems. Various spiral CTDI variants are defined to capture longitudinal scatter contributions, including eCTDI and oCTDI, which are expected to provide more accurate representations of CTDI. Results indicate that spiral CTDI measurements can yield values close to those of axial CTDI, particularly when axial protocols are unavailable. The findings suggest that spiral CTDI methods, especially eCTDI and oCTDI, may be practical substitutes for axial measurements, while xCTDI offers a comprehensive integration of the longitudinal dose profile but may be less practical for routine use.