Purpose: Foreign body aspiration is difficult to diagnose because many aspirated foreign bodies are low density or radiolucent. Digital radiographs (DR) are poor at detecting radiolucent foreign bodies. Digital tomosynthesis (DTS) has been shown to be ideally suited for applications where DR is insensitive and the increased dose from computed tomography (CT) is not justified. Our objective was to determine if DTS can be a practical alternative to DR and CT in the diagnosis of foreign body aspiration.
Approach: A phantom approximating the densities of a pediatric chest was constructed. Radiolucent foreign bodies were placed in the airways. Seven pediatric radiologists assessed DTS and DR images with and without simulated breathing motion. Two rounds were performed with fixed exposure techniques and then automatic exposure control techniques. Interobserver agreement was evaluated using Fleiss’ kappa.
Results: DTS and DR images using fixed exposure techniques performed very poorly with accuracies of 42% to 60%. DTS with automatic exposure control techniques increased accuracy to 84% for a stationary phantom, but the accuracy dropped to 70% in a phantom with simulated motion. DTS outperformed DR, with DR accuracies of 60% and 63% for stationary simulations and motion, respectively. Interobserver agreement was poor with Fleiss’ kappa of 0.476.
Conclusion: DTS is superior to DR for radiolucent foreign body detection. However, the overall accuracy and interobserver agreement are likely too low for this modality to be clinically useful.
Plaque characterization may benefit from the increasing distinctiveness of the attenuating properties of different soft
plaque components at lower energies. Due to the relative slight increase in the CT number of the nonadipose soft plaque
at lower tube voltage settings vs. adipose plaque, a higher contrast between atheromous adipose and non-adipose plaque
may become visible with modern 64 slice systems. A contrast-detail (C-D) phantom with varying plaque composition as
the contrast generating method, was imaged on a commercial 64 slice MDCT system using 80, 120, and 140 kVp
settings. The same phantom was also imaged on a Cone Beam CT (CBCT) system with a lower tube voltage of 75 kVp.
The results of experiments from four different observers on three different plaque types (lipid, fiber, calcific) indicate
that CT attenuation within lipid cores and fibrous masses vary not only with the percentage of lipid or fiber present, but
also with the size of the cores. Furthermore, the C-D curve analysis for all three plaque types reveals that while the noise
constraints prevent visible differentiation of soft plaque at current conventional 64 slice MDCT settings, CBCT exhibits
superior visible contrast detectability than its conventional counterpart, with the latter having appreciably better
resolution limits and beneficial lower tube voltages. This low voltage CT technique has the potential to be useful in
composition based diagnosis of carotid vulnerable atherosclerotic plaque.
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