The Detectability of Iterative CT Reconstruction for Low-contrast Lesions in Hyperacute Cerebral Infarction: Assessment with Newly Developed Dedicated Head Phantoms

Abstract

SummaryIterative reconstruction techniques, such as adaptive statistical iterative reconstruction (ASiR), improve the contrast-to-noise ratio of computed tomography (CT) images; however, underlying anatomical structures may nevertheless hamper detectability of low-contrast areas in clinical situations, despite using such a technique. We therefore conducted a phantom study to investigate the efficacy of ASiR in improving the detectability of lowcontrast areas in the presence of brain anatomical structures. We developed dedicated head phantoms simulating hyperacute cerebral infarction and confirmed that their CT numbers were sufficiently reproducible and that observer performance in detecting low-contrast areas using these phantoms more closely resembled that in clinical situations than that using a simple phantom. The efficacy of ASiR in improving low-contrast detectability was evaluated via receiver operating characteristics analysis. The mean area under the curve (AUC) values at ASiR blend rates of 0%, 30%, 60%, and 100% were 0. 57, 0.57, 0.59, and 0.59 at 200 mA; 0.83, 0.84, 0.84, and 0.90 at 500 mA; and 0.79, 0.77, 0.76, and 0.79 at 800 mA, respectively. No significant differences were noted in AUC values among ASiR blend rates at any mA setting, suggesting that ASiR does not improve the detectability of subtle low-contrast lesions seen in hyperacute cerebral infarction in clinical situations.

Computed Tomography Using a Low Tube Voltage Technique for Acute Ischemic Stroke

“…We initially attempted to understand this characteristic using a commercially available phantom, but no phantom separates gray matter and white matter. Development and analysis results of a phantom expressing early ischemic change by changing the density of the substance have been reported [30], but the influence of differences in atomic number on CT value was not considered. Moreover, in Report 44 of the ICRU, the mass attenuation coefficients of gray matter and white matter were equal [31].…”