Observer Performance for Detection of Pulmonary Nodules at Chest CT over a Large Range of Radiation Dose Levels.

Background There is a wide variation in radiation dose levels that can be used with chest CT in order to detect indeterminate pulmonary nodules. Purpose To compare the performance of lower-radiation-dose chest CT with that of routine dose in the detection of indeterminate pulmonary nodules 5 mm or greater. Materials and Methods In this retrospective study, CT projection data from 83 routine-dose chest CT examinations performed in 83 patients (120 kV, 70 quality reference mAs [QRM]) were collected between November 2013 and April 2014. Reference indeterminate pulmonary nodules were identified by two nonreader thoracic radiologists. By using validated noise insertion, five lower-dose data sets were reconstructed with filtered back projection (FBP) or iterative reconstruction (IR; 30 QRM with FBP, 10 QRM with IR, 5 QRM with FBP, 5 QRM with IR, and 2.5 QRM with IR). Three thoracic radiologists circled pulmonary nodules, rating confidence that the nodule was a 5-mm-or-greater indeterminate pulmonary nodule, and graded image quality. Analysis was performed on a per-nodule basis by using jackknife alternative free-response receiver operating characteristic figure of merit (FOM) and noninferiority limit of -0.10. Results There were 66 indeterminate pulmonary nodules (mean size, 8.6 mm ± 3.4 [standard deviation]; 21 part-solid nodules) in 42 patients (mean age, 51 years ± 17; 21 men and 21 women). Compared with the FOM for routine-dose CT (size-specific dose estimate, 6.5 mGy ± 1.8; FOM, 0.86 [95% confidence interval: 0.80, 0.91]), FOM was noninferior for all lower-dose configurations except for 2.5 QRM with IR. The sensitivity for subsolid nodules at 70 QRM was 60% (range, 48%-72%) and was significantly worse at a dose of 5 QRM and lower, whether or not IR was used (P < .05). Diagnostic image quality decreased with decreasing dose (P < .001) and was better with IR at 5 QRM (P < .05). Conclusion CT images reconstructed at dose levels down to 10 quality reference mAs (size-specific dose estimate, 0.9 mGy) had noninferior performance compared with routine dose in depicting pulmonary nodules. Iterative reconstruction improved subjective image quality but not performance at low dose levels. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by White and Kazerooni in this issue.

Prospective Pilot Evaluation of Radiologists and Computer-aided Pulmonary Nodule Detection on Ultra-low-Dose CT With Tin Filtration.

PURPOSE: The aim of this study was to evaluate the ability of computer-aided detection (CAD) and human readers to detect pulmonary nodules ≥5 mm using 100 kV ultra-low-dose computed tomography (ULDCT) utilizing a tin filter. MATERIALS AND METHODS: After informed consent, 55 patients prospectively underwent standard-dose chest CT (SDCT) using 120 kV followed by ULDCT using 100 kV/tin. Reference nodules ≥5 mm were identified by a thoracic radiologist using SDCT. Four thoracic radiologists marked detected nodules on SDCT and ULDCT examinations using a dedicated computer workstation. After a 6-month memory extinction, readers were shown the same ULDCT cases with all CAD markings as well as their original detections, and characterized CAD detections as true positive or false positive. RESULTS: Volume CT Dose index (CTDIvol) for SDCT and ULDCT were 5.3±2 and 0.4±0.2 mGy (P<0.0001), respectively. Forty-five reference nodules were detected in 30 patients. Reader sensitivity varied widely but similarly for SDCT (ranging from 45% to 87%) and ULDCT (45% to 83%). CAD sensitivity was 76% (34/45) for SDCT and 71% (32/45) for ULDCT. After CAD, reader sensitivity substantially improved by 19% and 18% for 2 readers, and remained nearly unchanged for the other 2 readers (0% and 2%), despite reader perception that many more nodules were identified with CAD. There was a mean of 2 false-positive CAD detections/case. CONCLUSIONS: ULDCT with 100 kV/tin reduced patient dose by over 90% without compromising pulmonary nodule detection sensitivity. CAD can substantially improve nodule detection sensitivity at ULDCT for some readers, maintaining interobserver performance.

Estimation of Observer Performance for Reduced Radiation Dose Levels in CT: Eliminating Reduced Dose Levels That Are Too Low Is the First Step.

RATIONALE AND OBJECTIVES: This study aims to estimate observer performance for a range of dose levels for common computed tomography (CT) examinations (detection of liver metastases or pulmonary nodules, and cause of neurologic deficit) to prioritize noninferior dose levels for further analysis. MATERIALS AND METHODS: Using CT data from 131 examinations (abdominal CT, 44; chest CT, 44; head CT, 43), CT images corresponding to 4%-100% of the routine clinical dose were reconstructed with filtered back projection or iterative reconstruction. Radiologists evaluated CT images, marking specified targets, providing confidence scores, and grading image quality. Noninferiority was assessed using reference standards, reader agreement rules, and jackknife alternative free-response receiver operating characteristic figures of merit. Reader agreement required that a majority of readers at lower dose identify target lesions seen by the majority of readers at routine dose. RESULTS: Reader agreement identified dose levels lower than 50% and 4% to have inadequate performance for detection of hepatic metastases and pulmonary nodules, respectively, but could not exclude any low dose levels for head CT. Estimated differences in jackknife alternative free-response receiver operating characteristic figures of merit between routine and lower dose configurations found that only the lowest dose configurations tested (ie, 30%, 4%, and 10% of routine dose levels for abdominal, chest, and head CT examinations, respectively) did not meet criteria for noninferiority. At lower doses, subjective image quality declined before observer performance. Iterative reconstruction was only beneficial when filtered back projection did not result in noninferior performance. CONCLUSION: Opportunity exists for substantial radiation dose reduction using existing CT technology for common diagnostic tasks.

Pulmonary nodule characterization, including computer analysis and quantitative features.

Pulmonary nodules are commonly detected in computed tomography (CT) chest screening of a high-risk population. The specific visual or quantitative features on CT or other modalities can be used to characterize the likelihood that a nodule is benign or malignant. Visual features on CT such as size, attenuation, location, morphology, edge characteristics, and other distinctive "signs" can be highly suggestive of a specific diagnosis and, in general, be used to determine the probability that a specific nodule is benign or malignant. Change in size, attenuation, and morphology on serial follow-up CT, or features on other modalities such as nuclear medicine studies or MRI, can also contribute to the characterization of lung nodules. Imaging analytics can objectively and reproducibly quantify nodule features on CT, nuclear medicine, and magnetic resonance imaging. Some quantitative techniques show great promise in helping to differentiate benign from malignant lesions or to stratify the risk of aggressive versus indolent neoplasm. In this article, we (1) summarize the visual characteristics, descriptors, and signs that may be helpful in management of nodules identified on screening CT, (2) discuss current quantitative and multimodality techniques that aid in the differentiation of nodules, and (3) highlight the power, pitfalls, and limitations of these various techniques.

5-year lung cancer screening experience: growth curves of 18 lung cancers compared to histologic type, CT attenuation, stage, survival, and size.

BACKGROUND: Although no study has prospectively documented the rate at which lung cancers grow, many have assumed exponential growth. The purpose of this study was to document the growth of lung cancers detected in high-risk participants receiving annual screening chest CT scans. METHODS: Eighteen lung cancers were evaluated by at least four serial CT scans (4 men, 14 women; age range, 53 to 79 years; mean age, 66 years). CT scans were retrospectively reviewed for appearance, size, and volume (volume [v] = pi/6[ab(2)]). Growth curves (x = time [in days]; y = volume [cubic millimeters]) were plotted and subcategorized by histology, CT scan attenuation, stage, survival, and initial size. RESULTS: Inclusion criteria favored smaller, less aggressive cancers. Growth curves varied, even when subcategorized by histology, CT scan attenuation, stage, survival, or initial size. Cancers associated with higher stages, mortality, or recurrence showed fairly steady growth or accelerated growth compared with earlier growth, although these growth patterns also were seen in lesser-stage lung cancers. Most lung cancers enlarged at fairly steady increments, but several demonstrated fairly flat growth curves, and others demonstrated periods of accelerated growth. CONCLUSIONS: This study is the first to plot individual lung cancer growth curves. Although parameters favored smaller, less aggressive cancers in women, it showed that lung cancers are not limited to exponential growth. Tumor size at one point or growth between two points did not appear to predict future growth. Studies and equations assuming exponential growth may potentially misrepresent an indeterminate nodule or the aggressiveness of a lung cancer.

Follicular bronchiolitis in surgical lung biopsies: clinical implications in 12 patients.

BACKGROUND: Follicular bronchiolitis is a histopathologic finding that occurs in diverse clinical contexts. The current study was conducted to characterize clinico-radiologic features, and assess outcomes associated with follicular bronchiolitis. SUBJECTS AND METHODS: Twelve subjects with follicular bronchiolitis on lung biopsy were seen over a 9-year period, between 1996 and 2005. Medical records, biopsy and radiographic findings, and details of outcome at the time of last follow-up were recorded. RESULTS: The study population included 4 men and 8 women; the median age at diagnosis was 54 years (range, 33-81 years). Four patients had underlying systemic diseases that included: 2 with common variable immunodeficiency, 1 Sjögren's syndrome and 1 undifferentiated connective tissue disease. The diagnosis was obtained by surgical lung biopsy in all cases. Follicular bronchiolitis was the major histologic pattern in 9 patients; organizing pneumonia, nonspecific interstitial pneumonia and usual interstitial pneumonia was seen in 1 patient each with follicular bronchiolitis being an associated secondary histopathologic component. Computed tomographic findings included reticular opacities, small nodules and ground-glass opacities. Clinical course was characterized by relative stability with partial response to immunosuppressive agents. During a median follow-up period of 47 months, only one death occurred--out of 9 patients where the outcome information was available--and was unrelated to lung disease. CONCLUSIONS: The histologic lesion of follicular bronchiolitis may be seen as the predominant finding or a relatively minor feature in interstitial pneumonias. The clinical course and prognosis for most patients with follicular bronchiolitis is relatively good, and progressive lung disease is uncommon.

Effect of automated image registration on radiologist interpretation.

In this study, we present preliminary data on the effect of automated 3D image alignment on the time to arrive at a decision about an imaging finding, the agreement of multiple of multiple observers, the prevalence of comparison examinations, and technical success rates for the image alignment algorithm. We found that automated image alignment reduced the average time to make a decision by 25% for cases where the structures are rigid, and when the scanning protocol is similar. For cases where these are not true, there is little or no benefit. In our practice, 54% of cases had prior examinations that could be automatically aligned. The overall benefit seen in our department for highly similar exams might be 20% for neuro and 10% for body; the benefit seen in other practices is likely to vary based on scanning practices and prevalence of prior examinations.

Five-year lung cancer screening experience: CT appearance, growth rate, location, and histologic features of 61 lung cancers.

PURPOSE: To retrospectively evaluate the computed tomography (CT)-determined size, morphology, location, morphologic change, and growth rate of incidence and prevalence lung cancers detected in high-risk individuals who underwent annual chest CT screening for 5 years and to evaluate the histologic features and stages of these cancers. MATERIALS AND METHODS: The study was institutional review board approved and HIPAA compliant. Informed consent was waived. CT scans of 61 cancers (24 in men, 37 in women; age range, 53-79 years; mean, 65 years) were retrospectively reviewed for cancer size, morphology, and location. Forty-eight cancers were assessed for morphologic change and volume doubling time (VDT), which was calculated by using a modified Schwartz equation. Histologic sections were retrospectively reviewed. RESULTS: Mean tumor size was 16.4 mm (range, 5.5-52.5 mm). Most common CT morphologic features were as follows: for bronchioloalveolar carcinoma (BAC) (n = 9), ground-glass attenuation (n = 6, 67%) and smooth (n = 3, 33%), irregular (n = 3, 33%), or spiculated (n = 3, 33%) margin; for non-BAC adenocarcinomas (n = 25), semisolid (n = 11, 44%) or solid (n = 12, 48%) attenuation and irregular margin (n = 14, 56%); for squamous cell carcinoma (n = 14), solid attenuation (n = 12, 86%) and irregular margin (n = 10, 71%); for small cell or mixed small and large cell neuroendocrine carcinoma (n = 7), solid attenuation (n = 6, 86%) and irregular margin (n = 5, 71%); for non-small cell carcinoma not otherwise specified (n = 5), solid attenuation (n = 4, 80%) and irregular margin (n = 3, 60%); and for large cell carcinoma (n = 1), solid attenuation and spiculated shape (n = 1, 100%). Attenuation most often (in 12 of 21 cases) increased. Margins most often (in 16 of 20 cases) became more irregular or spiculated. Mean VDT was 518 days. Thirteen of 48 cancers had a VDT longer than 400 days; 11 of these 13 cancers were in women. CONCLUSION: Overdiagnosis, especially in women, may be a substantial concern in lung cancer screening.

Interstitial lung disease in primary Sjögren syndrome.

BACKGROUND: Primary Sjögren syndrome (pSS) has been associated with various histologic patterns of interstitial lung disease (ILD). METHODS: We retrospectively identified 18 patients with pSS and suspected ILD who underwent lung biopsies (14 surgical biopsies and 9 bronchoscopic biopsies) at our institution during a 13-year period from 1992 through 2004. Histopathologic findings were analyzed and correlated with radiologic features and outcome. RESULTS: Median age was 62 years (range, 34 to 78 years), and 15 patients (83%) were women. Most patients presented with dyspnea and cough. Chest radiographs demonstrated bilateral infiltrates, and high-resolution CT revealed abnormalities of various types including ground-glass, consolidation, reticular, and nodular opacities. The major histopathologic patterns included nonspecific interstitial pneumonia (NSIP) [five patients], organizing pneumonia (OP) [four patients], usual interstitial pneumonia (UIP) [three patients], lymphocytic interstitial pneumonia (three patients), primary pulmonary lymphoma (two patients), and diffuse interstitial amyloidosis (one patient). In four patients (three with OP and one with amyloidosis), the diagnosis was established on transbronchial biopsy results. Treatment commonly included prednisone with or without another immunosuppressive agent. During the follow-up period (median, 38 months), most patients improved or remained stable except three patients with UIP, one patient with NSIP, and one patient with amyloidosis. Seven patients (39%) died, including three deaths from acute exacerbation of interstitial pneumonia. CONCLUSIONS: A variety of histologic patterns can be seen in patients with pSS-associated ILD. Those with UIP tended to have progression of lung disease. Death from acute exacerbation of interstitial pneumonia may occur in patients with pSS-associated ILD.

Pulmonary cryptococcosis: CT findings in immunocompetent patients.

PURPOSE: To evaluate retrospectively the computed tomographic (CT) findings in immunocompetent patients with pulmonary cryptococcosis. MATERIALS AND METHODS: Institutional review board approval was obtained with a waiver of informed consent, and the study complied with requirements of the Health Insurance Portability and Accountability Act. Chest CT scans of 10 immunocompetent patients with clinically proved pulmonary cryptococcosis were retrospectively reviewed by four reviewers in consensus. Criterion for diagnosis of pulmonary cryptococcosis was (a) the histopathologic presence of the organism at lung biopsy or (b) a positive culture of a respiratory specimen or positive serum cryptococcal antigen test with clinical or radiographic evidence of active pulmonary infection. Patients included six women and four men ranging in age from 46 to 73 years (mean, 59 years). Scans were evaluated for nodules, masses, areas of ground-glass attenuation or of hazy increased attenuation, areas of consolidation, areas of cavitation, pleural effusions, linear opacities, septal thickening, lymphadenopathy, extent of parenchymal involvement, and distribution. RESULTS: The most common CT finding was pulmonary nodules (n = 9). Multiple nodules (n = 7) were more common than solitary nodules (n = 2). Nodules most commonly occupied less than 10% of the pulmonary parenchyma (n = 7), measured less than 10 mm in diameter (n = 7), and had middle and upper lung predominance (n = 6). The majority of the nodules were well defined with smooth margins (n = 7). Multiple nodules were usually bilaterally distributed (n = 5). Masses (n = 2), lymphadenopathy (n = 2), areas of consolidation (n = 2), areas of hazy increased attenuation (n = 1), pleural effusion (n = 1), and areas of cavitation (n = 1) were uncommon. CONCLUSION: CT most commonly demonstrated pulmonary nodules in immunocompetent patients with pulmonary cryptococcosis. The nodules were most often multiple, small, well defined, and smoothly marginated with middle and upper lung predominance.

Lung cancer screening experience: a retrospective review of PET in 22 non-small cell lung carcinomas detected on screening chest CT in a high-risk population.

OBJECTIVE: The objective of our study was to retrospectively review the PET results of non-small cell lung carcinomas detected on screening chest CT in a high-risk population. CONCLUSION: PET findings were negative in 32% of the cases of non-small cell carcinomas that were detected on screening CT in a high-risk patient population. These tumors were small, low-grade, or both. The most common histology was bronchioloalveolar cell carcinoma. The role of PET in evaluating screening-detected indeterminate nodules in a high-risk population may be more limited than in a general population.

Chest imaging in iatrogenic respiratory disease.

Iatrogenic respiratory disease is an important cause of patient morbidity and mortality. Clinical and radiologic findings are nonspecific and diagnosis can be difficult. Therefore, it is important for physicians to be familiar with the iatrogenic diseases for which their patients are at risk, as well as their common radiologic appearances. Causes of iatrogenic respiratory disease include drugs, transplantation, radiation, transfusion, or other miscellaneous therapies.