Abstract
BACKGROUND: Because the x-ray property of patient longitudinal axis in area detector computed tomography (ADCT) depends on a heel effect, radiation dose and beam quality are not uniform along the long axis of the patient. OBJECTIVE: This study aimed to measure the longitudinal beam properties and contrast uniformity of ADCT scanners in the 160-mm nonhelical volume-acquisition (NVA) mode and provide useful datasets for the radiation dose reduction in ADCT examinations. MATERIALS AND METHODS: Two different types of ADCT scanners were used in this study. To assess the heel effect in 256- and 320-row ADCT scanners, we measured dose profile, half-value layer, and iodine contrast uniformity along longitudinal beam direction. RESULTS: The maximum effective energy difference within a 160-mm x-ray beam is approximately 4 keV. Maximum radiation dose on the anode side of the x-ray tube showed approximately 40%-45% reduction compared with that on the isocenter position; the heel effect properties longitudinally differed throughout the x-ray beam, and the decrease in the radiation dose in 256- and 320-row ADCT scanners was observed on the patient table side and gantry side respectively. The CT numbers of iodinated solutions for 256-row ADCT scanner were independent of the heel effect; nevertheless, the CT numbers of 320-row ADCT scanner tended to increase on the patient table (cathode) side. CONCLUSION: This study reveals that the radiation dose on the anode side of the x-ray tube shows approximately 40%-45% reduction compared with that on the isocenter position, and the heel effect properties for 256- and 320-row ADCT scanners longitudinally differ throughout the x-ray beam. The x-ray tube for individual ADCT scanners is mounted in an opposite direction along the long axis of the patient.