Investigation of lung nodule detectability in low‐dose 320‐slice computed tomography

Abstract

Low-dose imaging protocols in chest CT are important in the screening and surveillance of suspicious and indeterminate lung nodules. Techniques that maintain nodule detectability yet permit dose reduction, particularly for large body habitus, were investigated. The objective of this study was to determine the extent to which radiation dose can be minimized while maintaining diagnostic performance through knowledgeable selection of reconstruction techniques. A 320-slice volumetric CT scanner ͑Aquilion ONE™, Toshiba Medical Systems͒ was used to scan an anthropomorphic phantom at doses ranging from ϳ0.1 mGy up to that typical of low-dose CT ͑LDCT, ϳ5 mGy͒ and diagnostic CT ͑ϳ10 mGy͒. Radiation dose was measured via Farmer chamber and MOSFET dosimetry. The phantom presented simulated nodules of varying size and contrast within a heterogeneous background, and chest thickness was varied through addition of tissue-equivalent bolus about the chest. Detectability of a small solid lung nodule ͑3.2 mm diameter, Ϫ37 HU, typically the smallest nodule of clinical significance in screening and surveillance͒ was evaluated as a function of dose, patient size, reconstruction filter, and slice thickness by means of nine-alternative forcedchoice ͑9AFC͒ observer tests to quantify nodule detectability. For a given reconstruction filter, nodule detectability decreased sharply below a threshold dose level due to increased image noise, especially for large body size. However, nodule detectability could be maintained at lower doses through knowledgeable selection of ͑smoother͒ reconstruction filters. For large body habitus, optimal filter selection reduced the dose required for nodule detection by up to a factor of ϳ3 ͑from ϳ3.3 mGy for sharp filters to ϳ1.0 mGy for the optimal filter͒. The results indicate that radiation dose can be reduced below the current low-dose ͑5 mGy͒ and ultralow-dose ͑1 mGy͒ levels with knowledgeable selection of reconstruction parameters. Image noise, not spatial resolution, was found to be the limiting factor in detection of small lung nodules. Therefore, the use of smoother reconstruction filters may permit lower-dose protocols without trade-off in diagnostic performance.

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“…A 320-slice columetric CT scanner (320-slice Aquilion ONE; Toshiba Medical Systems, Otawara, Tokyo) was used to scan the esophageal metal clips for 20 s (8)(9)(10). Images were collected on a clinical multidetector CT scanner.…”

Diagnostic Performance of a Prototype Dual-Energy Chest Imaging System

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A simple approach to measure computed tomography (CT) modulation transfer function (MTF) and noise‐power spectrum (NPS) using the American College of Radiology (ACR) accreditation phantom

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