Myrna C.B. Godoy

Dual-Energy CT in Patients Suspected of Having Renal Masses: Can Virtual Nonenhanced Images Replace True Nonenhanced Images?

PURPOSE To qualitatively and quantitatively compare virtual nonenhanced (VNE) data sets derived from dual-energy (DE) computed tomography (CT) with true nonenhanced (TNE) data sets in the same patients and to calculate potential radiation dose reductions for a dual-phase renal multidetector CT compared with a standard triple-phase protocol. MATERIALS AND METHODS This prospective study was approved by the institutional review board; all patients provided written informed consent. Seventy one men (age range, 30-88 years) and 39 women (age range, 22-87 years) underwent preoperative DE CT that included unenhanced, DE nephrographic, and delayed phases. DE CT parameters were 80 and 140 kV, 96 mAs (effective). Collimation was 14 x 1.2 mm. CT numbers were measured in renal parenchyma and tumor, liver, aorta, and psoas muscle. Image noise was measured on TNE and VNE images. Exclusion of relevant anatomy with the 26-cm field of view detector was quantified with a five-point scale (0 = none, 4 = >75%). Image quality and noise (1 = none, 5 = severe) and acceptability for VNE and TNE images were rated. Effective radiation doses for DE CT and TNE images were calculated. Differences were tested with a Student t test for paired samples. RESULTS Mean CT numbers (+/- standard deviation) on TNE and VNE images, respectively, for renal parenchyma were 30.8 HU +/- 4.0 and 31.6 HU +/- 7.1, P = .29; liver, 55.8 HU +/- 8.6 and 57.8 HU +/- 10.1, P = .11; aorta, 42.1 HU +/- 4.1 and 43.0 HU +/- 8.8, P = .16; psoas, 47.3 HU +/- 5.6 and 48.1 HU +/- 9.3 HU, P = .38. No exclusion of the contralateral kidney was seen in 50 patients, less than 25% was seen in 43, 25%-50% was seen in 13, and 50%-75% was seen in four. Mean image noise was 1.71 +/- 0.71 for VNE and 1.22 +/- 0.45 for TNE (P < .001); image quality was 1.70 HU +/- 0.72 for VNE and 1.15 HU +/- 0.36 for TNE (P < .0001). In all but three patients radiologists accepted VNE images as replacement for TNE images. Mean effective dose for DE CT scans of the abdomen was 5.21 mSv +/- 1.86 and that for nonenhanced scans was 4.97 mSv +/- 1.43. Mean dose reduction by omitting the TNE scan was 35.05%. CONCLUSION In patients with renal masses, DE CT can provide high-quality VNE data sets, which are a reasonable approximation of TNE data sets. Integration of DE scanning into a renal mass protocol will lower radiation exposure by 35%.

Subsolid Pulmonary Nodules and the Spectrum of Peripheral Adenocarcinomas of the Lung: Recommended Interim Guidelines for Assessment and Management

Pulmonary nodule characterization is currently being redefined as new clinical, radiologic, and pathologic data are reported, necessitating a reevaluation of the clinical management, especially of subsolid nodules. These are now known to frequently, although not invariably, fall into the spectrum of peripheral adenocarcinomas of the lung. Strong correlation between the Noguchi histologic classification and computed tomographic (CT) appearances of these lesions, in particular, has been reported. Serial CT findings have further documented that stepwise progression of lesions with ground-glass opacity, manifested as an increase in size or the appearance and/or subsequent increase of solid components, does occur in a select subset of patients. As a consequence, recognition of the potential association between subsolid nodules and peripheral adenocarcinomas requires a review of current guidelines for the management of these lesions, further necessitated by a differential diagnosis that includes benign lesions such as focal inflammation, focal fibrosis, and organizing pneumonia. Specific issues that need to be addressed are the need for consensus regarding an appropriate CT classification, methods for precise measurement of subsolid nodules, including the extent of both ground-glass and solid components, as well as accurate assessment of the growth rates as means for predicting malignancy and prognosis. It is anticipated that interim guidelines may serve to standardize our current management of these lesions, pending further clarification of their natural history.

Overview and strategic management of subsolid pulmonary nodules.

A new classification of lung adenocarcinoma has been proposed recently—the International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society classification. Abundant information from recent lung cancer computed tomography (CT) screening programs has increased our understanding of the strong, although imperfect, correlation between histologic findings of lung adenocarcinoma and subsolid pulmonary nodules on CT, including both “pure” ground-glass nodules (GGNs) and “part-solid” GGNs. Moreover, serial CT imaging has demonstrated stepwise progression of these nodules in a subset of patients, characterized by increase in size and density of GGNs and development of a solid component. Given the higher incidence of malignancy and the considerably lower growth rate of subsolid nodules, dedicated standardized guidelines for management of these nodules have been proposed, including long-term (≥3 y) CT follow-up using a low-dose technique. Radiologists should be familiar with the new terminology of lung adenocarcinomas and strategic management of subsolid pulmonary nodules.

Reversed Halo Sign: High-Resolution CT Scan Findings in 79 Patients

BACKGROUND The purpose of this study was to evaluate the high-resolution CT (HRCT) scan findings of patients with the reversed halo sign (RHS) and to identify distinguishing features among the various causes. METHODS Two chest radiologists reviewed the HRCT scans of 79 patients with RHS and determined the CT scan findings by consensus. We studied the morphologic characteristics, number of lesions, and presence of features associated with RHS. RESULTS Forty-one patients presented with infectious diseases (paracoccidioidomycosis, TB, zygomycosis, invasive pulmonary aspergillosis, Pneumocystis jiroveci pneumonia, histoplasmosis, cryptococcosis), and 38 presented with noninfectious diseases (cryptogenic organizing pneumonia, pulmonary embolism, sarcoidosis, edema, lepidic predominant adenocarcinoma [formerly bronchiolo-alveolar carcinoma], granulomatosis with polyangiitis [Wegener]). The RHS walls were smooth in 58 patients (73.4%) and nodular in 21 patients (26.6%). Lesions were multiple in 40 patients (50.6%) and single in 39 patients (49.4%). CONCLUSION The presence of nodular walls or nodules inside the halo of the RHS is highly suggestive of granulomatous diseases.

Reversed Halo Sign on Computed Tomography: State-of-the-Art Review

The reversed halo sign (RHS) is a chest computed tomography (CT) pattern defined as a focal round area of ground-glass attenuation surrounded by a crescent or ring of consolidation. The RHS was first described as being relatively specific for cryptogenic organizing pneumonia but was later observed in several other infectious and noninfectious diseases. Although the presence of the RHS on CT may help narrow the range of diseases considered in differential diagnoses, final diagnoses should be based on correlation with the clinical scenario and the presence of additional disease-specific CT findings. However, frequently a biopsy may be needed to establish the diagnosis. Organizing pneumonia is the most frequent cause of the RHS. This is a distinct clinical and pathologic entity that can be cryptogenic or secondary to other known causes. Morphologic aspects of the halo, particularly the presence of small nodules in the wall or inside the lesion, usually indicate an active granulomatous disease (tuberculosis or sarcoidosis) rather than organizing pneumonia. Immunocompromised patients presenting with the RHS on CT examination should be considered to have an infection until further analyses prove otherwise. Pulmonary zygomycosis and invasive pulmonary aspergillosis are typically seen in patients with severe immunosuppression, most commonly secondary to hematological malignancies. Other causes of the RHS include noninvasive fungal infections such as paracoccidioidomycosis, histoplasmosis, and Pneumocystis jiroveci pneumonia. Furthermore, Wegener’s granulomatosis, radiofrequency ablation, and lymphomatoid granulomatosis may also lead to this finding. Based on a search of the PubMed and Scopus databases, we review the different diseases that can manifest with the RHS on CT.

Benefit of computer-aided detection analysis for the detection of subsolid and solid lung nodules on thin- and thick-section CT

OBJECTIVE The objective of our study was to evaluate the impact of computer-aided detection (CAD) on the identification of subsolid and solid lung nodules on thin- and thick-section CT. MATERIALS AND METHODS For 46 chest CT examinations with ground-glass opacity (GGO) nodules, CAD marks computed using thin data were evaluated in two phases. First, four chest radiologists reviewed thin sections (reader(thin)) for nodules and subsequently CAD marks (reader(thin) + CAD(thin)). After 4 months, the same cases were reviewed on thick sections (reader(thick)) and subsequently with CAD marks (reader(thick) + CAD(thick)). Sensitivities were evaluated. Additionally, reader(thick) sensitivity with assessment of CAD marks on thin sections was estimated (reader(thick) + CAD(thin)). RESULTS For 155 nodules (mean, 5.5 mm; range, 4.0-27.5 mm)-74 solid nodules, 22 part-solid (part-solid nodules), and 59 GGO nodules-CAD stand-alone sensitivity was 80%, 95%, and 71%, respectively, with three false-positives on average (0-12) per CT study. Reader(thin) + CAD(thin) sensitivities were higher than reader(thin) for solid nodules (82% vs 57%, p < 0.001), part-solid nodules (97% vs 81%, p = 0.0027), and GGO nodules (82% vs 69%, p < 0.001) for all readers (p < 0.001). Respective sensitivities for reader(thick), reader(thick) + CAD(thick), reader(thick) + CAD(thin) were 40%, 58% (p < 0.001), and 77% (p < 0.001) for solid nodules; 72%, 73% (p = 0.322), and 94% (p < 0.001) for part-solid nodules; and 53%, 58% (p = 0.008), and 79% (p < 0.001) for GGO nodules. For reader(thin), false-positives increased from 0.64 per case to 0.90 with CAD(thin) (p < 0.001) but not for reader(thick); false-positive rates were 1.17, 1.19, and 1.26 per case for reader(thick), reader(thick) + CAD(thick), and reader(thick) + CAD(thin), respectively. CONCLUSION Detection of GGO nodules and solid nodules is significantly improved with CAD. When interpretation is performed on thick sections, the benefit is greater when CAD marks are reviewed on thin rather than thick sections.

New era of radiotherapy: An update in radiation-induced lung disease

Over the last few decades, advances in radiotherapy (RT) technology have improved delivery of radiation therapy dramatically. Advances in treatment planning with the development of image-guided radiotherapy and in techniques such as proton therapy, allows the radiation therapist to direct high doses of radiation to the tumour. These advancements result in improved local regional control while reducing potentially damaging dosage to surrounding normal tissues. It is important for radiologists to be aware of the radiological findings from these advances in order to differentiate expected radiation-induced lung injury (RILD) from recurrence, infection, and other lung diseases. In order to understand these changes and correlate them with imaging, the radiologist should have access to the radiation therapy treatment plans.

Reversed Halo Sign in Invasive Fungal Infections: Criteria for Differentiation From Organizing Pneumonia

BACKGROUND The purpose of this study was to identify CT scan findings that differentiate the reversed halo sign (RHS) caused by invasive fungal infection (IFI) from the RHS caused by organizing pneumonia (OP). METHODS We retrospectively reviewed CT scans of patients with RHS caused by IFI or OP. The study included 15 patients with proven or probable IFI (eight men and seven women) and 25 patients with biopsy-proven OP (13 women and 12 men). The CT images were reviewed individually by two chest radiologists who were blinded to the final diagnosis. RESULTS Reticulation inside the RHS was observed in 14 of the 15 patients with IFI (93%) and in no patient with OP. The maximal thickness of the consolidation rim was 2.04 ± 0.85 cm for IFI and 0.50 ± 0.22 cm for OP. Pleural effusion was noted in 11 of the 15 patients with IFI (73%) and in no patient with OP. Other parenchymal abnormalities, such as consolidation and ground-glass and linear opacities, were observed in both groups. The number of lesions showing the RHS did not differentiate IFI and OP. CONCLUSION The presence of reticulation inside the RHS, outer rim thickness > 1 cm, and associated pleural effusion strongly suggest the diagnosis of IFI rather than OP.

Basic principles and postprocessing techniques of dual-energy CT: illustrated by selected congenital abnormalities of the thorax.

Recent technologic advances in multidetector computed tomography have allowed the performance of simultaneous acquisition dual-energy computed tomography (DECT). The advantages of this new technique include simultaneous visualization of lower voltage tube images with improved iodine conspicuity and the performance of material specific imaging, which attempts to differentiate specific materials in the generated images. In this article, we review the concepts and physical principles of DECT using congenital thoracic abnormalities as a substrate for depicting the versatility of DECT.

Original ResearchChest InfectionsReversed Halo Sign in Invasive Fungal Infections: Criteria for Differentiation From Organizing Pneumonia

BACKGROUND The purpose of this study was to identify CT scan findings that differentiate the reversed halo sign (RHS) caused by invasive fungal infection (IFI) from the RHS caused by organizing pneumonia (OP). METHODS We retrospectively reviewed CT scans of patients with RHS caused by IFI or OP. The study included 15 patients with proven or probable IFI (eight men and seven women) and 25 patients with biopsy-proven OP (13 women and 12 men). The CT images were reviewed individually by two chest radiologists who were blinded to the final diagnosis. RESULTS Reticulation inside the RHS was observed in 14 of the 15 patients with IFI (93%) and in no patient with OP. The maximal thickness of the consolidation rim was 2.04 ± 0.85 cm for IFI and 0.50 ± 0.22 cm for OP. Pleural effusion was noted in 11 of the 15 patients with IFI (73%) and in no patient with OP. Other parenchymal abnormalities, such as consolidation and ground-glass and linear opacities, were observed in both groups. The number of lesions showing the RHS did not differentiate IFI and OP. CONCLUSION The presence of reticulation inside the RHS, outer rim thickness > 1 cm, and associated pleural effusion strongly suggest the diagnosis of IFI rather than OP.