The purpose of this study is to identify the difference in nodule characteristics manifested on computed topography (CT) and X-ray images and to evaluate the ability of radiographic features to differentiate between benign and malignant nodules, when compared to the features extracted from CT. We collected 79 consecutive computed radiographic (CR) chest images with one or more CT-documented lung nodules. Upon viewing the CT slices, corresponding nodules were localized on CR images by an experienced chest radiologist. Of the 79 CT nodules (19 benign, 60 malignant), 61 (14 benign, 47 malignant) were considered to be definitely visible on the CR, and the rest were considered to be invisible or did not qualify for distinct feature assessment. Eleven nodule features each were visually extracted from CT and CR images. These features were used to characterize the nodule in terms of size, shape, lobulation, spiculation, density, etc. Correlation between the CT and CR features was calculated for the 61 definitely CR-visible nodules. Receiver operating characteristics (ROC) analysis was performed to evaluate the ability of these features in the task of differentiating between benign and malignant nodules. Results showed that CR and CT images agreed well in characterizing nodules in terms of shape, lobulation, spiculation and density features. We found that 40-50% of the cases had same CR and CT ratings and 41-51% of cases were rated by a difference of one between their ratings on CT and CR for shape (3-point scale), lobulation (4-point scale) and speculation (4-point scale) features. Ninety-two percent of the cases had same CT and CR ratings on the density feature. Size yielded a correlation coefficient of 0.84. In the task of differentiating between benign and malignant lung nodules, ROC analysis of individual features yielded an Az value ranging from 0.52 to 0.77 for the 14 CT features and from 0.52 to 0.75 for the CR features. In addition, we examined the characteristics of the 18 nodules that were excluded from feature analysis. On average, these 18 nodules were smaller in size (15.2 mm measured from CT) than the 61 CR-visible nodules (23.5 mm). We found that CR features agreed reasonably well with CT features and their ability to differentiate between benign and malignant nodules were similar to that of the CT features.
A novel method for the assessment and display of the distribution of
emphysema in low-dose helical CT scans has been developed. The
automated system segments the lung volume and estimates the degree of
emphysema as a function of slice position within the lung. Eighty
low-dose (120 kVp, 40 mA) high-resolution (2.5 mm slice thickness) CT
scans were randomly selected from our lung cancer screening
program. Three emphysema assessments were performed on each scan: the
traditional method of averaging the degree of emphysema on four
pre-selected CT slices, the total volumetric percentage of emphysema,
and a graphical display of emphysema burden as a function of slice
position based on a sliding window algorithm. The traditional
four-slice estimates showed a high correlation (0.98) with the total
volumetric percentages, yet provided limited spatial information. In
those cases with a higher overall percentage of emphysema, the
distribution within the lung as quantified by the new method was more
skewed than that of less severe cases or normals. Analysis and display
of the spatial distribution of emphysema allows for assessment of
emphysema burden within each lung zone, which may be useful for
quantitating the type of emphysema and the progression of disease over
time.
A study was performed to test whether automated computer analysis of
low-dose helical CT scans can accurately estimate the degree of
emphysema. We characterized the severity of emphysema on low-dose
high-resolution (2.5 mm slice thickness) CT scans into 4 categories
(normal, mild, moderate, and severe) as determined by a thoracic
radiologist. From our database we chose 80 cases (20 within each
category) for analysis. Our analysis system segments the lung
parenchyma from surrounding structures and computes an emphysema index
as the volumetric percentage of emphysema for the entire lung volume
using a dual thresholding technique. One-way analysis of variance was
used to assess the emphysema index. For those cases classified as
normal, the emphysema index was 11.74 ± 1.24 (mean ± sem), for mild it was 15.00 ± 1.31, for moderate it was 16.91 ± 1.72, and for severe it was 26.77 ± 1.73. The differences were statistically significant (p < 0.0001) and showed an increasing score with increasing severity of emphysema. Our system provides a useful index of the degree of emphysema present. Use of the system allows subjects undergoing lung cancer screening studies to have the extent of their emphysema quantified on a year-to-year basis.
Nodule growth is a key characteristic of malignancy. The measurement of nodule diameter on chest radiographs has been unsatisfactory due to insufficient accuracy and reproducibility. Additionally, the frequent use of high resolution CT scanners has increased the detection rate of very small nodules. On one hand, the small nodules present even greater diagnostic difficulties and, on the other hand, are more frequently benign, resulting in higher rates of unnecessary surgery. In this paper we present a 3-D algorithm to improve the consistency of nodule segmentation on multiple scans. The multi-criterion, multi-scan segmentation algorithm has been developed based on the fact that a typical small pulmonary nodule has distinct difference in density at the boundary and relatively compact shape, and that other tissues in the lung do not change in size over time. Our preliminary results with in-vivo nodules have shown the potential of applying this practical 3-D segmentation algorithm to clinical settings.
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