An investigation of temporal resolution parameters in cine‐mode four‐dimensional computed tomography acquisition

Yildirim D Mutaf,Debra H Brinkmann

doi:10.1120/jacmp.v9i4.2819

Abstract

The accuracy of four‐dimensional computed tomography (4DCT) imaging depends on temporal characteristics of the acquisition protocol—for example, the temporal spacing of the reconstructed images (also known as 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. It could lead to substantial inaccuracies in target delineation. The aim of the present study was to evaluate the interplay between parameters affecting temporal resolution and the accuracy of the resulting images.We acquired 4DCT images 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 10 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 images. Target delineation accuracy at end‐of‐inhalation phase was observed to be constant up to a threshold in the value of the 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 observable variations were noted with images from the end of exhalation when temporal spacing was varied. Target delineation accuracy was observed to be enhanced in acquisitions using faster gantry rotation speeds. An evaluation 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.PACS numbers: 87.53.Xd, 87.57.‐s, 87.57.Gg, 87.59.Fm

Highlights

173 Mutaf and Brinkmann: An investigation of temporal resolution parameters...motion into existing imaging modalities—for example, four-dimensional computed tomography (4DCT)(5–9)—the ability to identify the full excursion of critical anatomy improved substantially
To represent situations in which a subset of motion is considered, we evaluated the effect of temporal spacing on individual phase images
We studied the dependence of target delineation accuracy on the temporal resolution factors effecting 4DCT acquisitions

Summary

Introduction

173 Mutaf and Brinkmann: An investigation of temporal resolution parameters...motion into existing imaging modalities—for example, four-dimensional computed tomography (4DCT)(5–9)—the ability to identify the full excursion of critical anatomy improved substantially. 173 Mutaf and Brinkmann: An investigation of temporal resolution parameters. Despite simplicity of operation in principle, 4DCT imaging systems are prone to errors that could be propagated to undesirable dosimetric consequences. Potential sources for such errors include irregular breathing by patients,(10) inaccurate assessment of respiratory motion,(11,12) or inappropriate selection of acquisition parameters. The focus of the present study was on selection of the 4DCT acquisition parameters and subsequent evaluation of how the selected temporal parameters affect the accuracy of the final images. Conventional X-ray imaging parameters such as tube current, peak voltage, collimation size, and slice thickness were kept consistent while acquisition parameters that affect the temporal resolution were investigated:

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