An investigation of temporal resolution parameters in 4DCT acquisition

Abstract

The quality of 4DCT imaging depends on temporal characteristics of the acquisition protocol such as the temporal spacing of the reconstructed images (a.k.a. cine duration between images) and the gantry rotation speed. These parameters affect the temporal resolution of 4DCT images and a single default acquisition protocol, as commonly used in most clinics, may be suboptimal for a subset of respiratory motion characteristics and could lead to substantial inaccuracies in target delineation The aim of this study is to evaluate the interplay between parameters affecting temporal resolution and the integrity of resulting images. 4DCT images were acquired of cylindrical phantoms under repetitive motion induced by a translation platform. Acquisition settings varied with respect to temporal spacing, gantry rotation speed and motion period of the phantoms. Reconstructed images were sorted into ten phase bins and were compared to static phantom images acquired at corresponding positions of the respiration phase. Acquisitions with different temporal spacing did not play a significant role in the amount of motion observed in full cycle maximum intensity projection (MIP) images. End of inhalation phase image integrity was observed to be constant up to a threshold in the value of reconstruction interval, beyond which it varied arbitrarily. This threshold was found to be correlated with the number of phase bins and the motion period. No significant variations were observed with images from the end of exhalation when temporal spacing was varied. Image quality was observed to be enhanced in acquisitions utilizing faster gantry rotation speed. An optimization of the acquisition parameters needs to be performed depending on the period of the motion and limiting factors such as the availability of acquisition settings, x-ray tube workload, image storage and processing power.