Volume estimation of low-contrast lesions with CT: a comparison of performances from a phantom study, simulations and theoretical analysis

Abstract

Measurements of lung nodule volume with multi-detector computed tomography (MDCT) have been shown to be more accurate and precise compared to conventional lower dimensional measurements. Quantifying the size of lesions is potentially more difficult when the object-tobackground contrast is low as with lesions in the liver. Physical phantom and simulation studies are often utilized to analyze the bias and variance of lesion size estimates because a ground truth or reference standard can be established. In addition, it may also be useful to derive theoretical bounds as another way of characterizing lesion sizing methods. The goal of this work was to study the performance of a MDCT system for a lesion volume estimation task with object-tobackground contrast less than 50 HU, and to understand the relation among performances obtained from phantom study, simulation and theoretical analysis. We performed both phantom and simulation studies, and analyzed the bias and variance of volume measurements estimated by a matched-filter-based estimator. We further corroborated results with a theoretical analysis to estimate the achievable performance bound, which was the Cramer-Rao's lower bound (CRLB) of minimum variance for the size estimates. Results showed that estimates of non-attached solid small lesion volumes with object-to-background contrast of 31-46 HU can be accurate and precise, with less than 10.8% in percent bias and 4.8% in standard deviation of percent error (SPE), in standard dose scans. These results are consistent with theoretical (CRLB), computational (simulation) and empirical phantom bounds. The difference between the bounds is rather small (for SPE less than 1.9%) indicating that the theoretical-and simulation-based performance bounds can be good surrogates for physical phantom studies.

Techniques for virtual lung nodule insertion: volumetric and morphometric comparison of projection-based and image-based methods for quantitative CT

“…The study used a series of synthetic nodules independently manufactured by Computerized Imaging Reference Systems (CIRS, Norfolk, VA.) of three sizes (8 mm, 9 mm and 10 mm), four morphologies (spherical, elliptical, lobular and spiculated) and with a single radiodensity of 100 HU (Li et al 2015). The nodules were physically inserted into the lung section of an anthropomorphic chest phantom (LUNGMAN, Kyoto Kagaku, Kyoto, Japan) (figure 1).…”

“…For example, Young et al evaluated the effects of dose reduction and reconstruction methods on lung nodule volumetry through simulations (Young et al 2015), and Li et al used simulations to evaluate volume estimation in low contrast conditions (Li et al 2015). Along this same line, it is possible to use computer simulations to fuse real patient CT data with simulated data, resulting in so-called ‘hybrid’ CT images.…”

Detectable change of lung nodule volume with CT in a phantom study with high and low signal to background contrast

“…The gelatin background was prepared as described in a previous study (11). The phantom was scanned using a 16-detector row Philips scanner with ten repeat acquisitions using 120 kVp, exposures (tube current x rotation time product) of 20, 100, and 200mAs (corresponding to CTDI vol of 1.3, 6.6, 13.2 mGy respectively), pitch of 1.2, slice collimation of 16x0.75mm, and was reconstructed with slice thicknesses of 0.75, 1.5, and 3.0mm using two reconstruction kernels (standard and smooth).…”

“…These effects, and the effect of the operator that uses the measurement tool, need to be understood and accounted for before volume can be fully characterized as a metric for estimating tumor burden in clinical practice. Several studies have been examining the aforementioned effects as summarized in a 2009 review by Gavrielides et al (1) and in subsequent studies (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18).…”

Comparison of One-Dimensional and Volumetric Computed Tomography Measurements of Injected-Water Phantoms

“…Since that time, volumetric measurements have been shown to offer an improvement over RECIST in both phantom [7][8][9][10][11][12] and clinical [13,14] studies. Moreover, whereas RECIST requires a minimum lesion size of 10 mm to be measurable, the advent of large-scale screening for small lung nodules [15], for which the lower bound in size is about 5 mm [16,17], underscores the necessity of developing techniques compatible with smaller nodules.…”