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Intrathoracic fat-containing lesions may arise in the mediastinum, lungs, pleura, or chest wall. While CT can be helpful in the detection and diagnosis of these lesions, it can only do so if the lesions contain macroscopic fat. Furthermore, because CT cannot demonstrate microscopic or intravoxel fat, it can fail to identify and diagnose microscopic fat-containing lesions. MRI, employing spectral and chemical shift fat suppression techniques, can identify both macroscopic and microscopic fat, with resultant enhanced capability to diagnose these intrathoracic lesions non-invasively and without ionizing radiation. This paper aims to review the CT and MRI findings of fat-containing lesions of the chest and describes the fat-suppression techniques utilized in their assessment.

Objective To compare the diagnostic performance of contrast-enhanced radial T1-weighted gradient-echo 3-tesla (3T) magnetic resonance imaging (MRI) and computed tomography (CT) for the detection of visceral pleural surface invasion (VPSI). Visceral pleural invasion by non-small-cell lung cancer (NSCLC) can be classified into two types: PL1 (without VPSI), invasion of the elastic layer of the visceral pleura without reaching the visceral pleural surface, and PL2 (with VPSI), full invasion of the visceral pleura. Materials and methods Thirty-three patients with pathologically confirmed VPSI by NSCLC were retrospectively reviewed. Multidetector CT and contrast-enhanced 3T MRI with a free-breathing radial three-dimensional fat-suppressed volumetric interpolated breath-hold examination (VIBE) pulse sequence were compared in terms of the length of contact, angle of mass margin, and arch distance-to-maximum tumor diameter ratio. Supplemental evaluation of the tumor-pleura interface (smooth versus irregular) could only be performed with MRI (not discernible on CT). Results At the tumor-pleura interface, radial VIBE MRI revealed a smooth margin in 20 of 21 patients without VPSI and an irregular margin in 10 of 12 patients with VPSI, yielding an accuracy, sensitivity, specificity, positive predictive value, negative predictive value, and F-score for VPSI detection of 91%, 83%, 95%, 91%, 91%, and 87%, respectively. The McNemar test and receiver operating characteristics curve analysis revealed no significant differences between the diagnostic accuracies of CT and MRI for evaluating the contact length, angle of mass margin, or arch distance-to-maximum tumor diameter ratio as predictors of VPSI. Conclusion The diagnostic performance of contrast-enhanced radial T1-weighted gradient-echo 3T MRI and CT were equal in terms of the contact length, angle of mass margin, and arch distance-to-maximum tumor diameter ratio. The advantage of MRI is its clear depiction of the tumor-pleura interface margin, facilitating VPSI detection.

Ordering the appropriate diagnostic imaging for occupational lung disease requires a firm understanding of the relationship between occupational exposure and expected lower respiratory track manifestation. Where particular inorganic dust exposures typically lead to nodular and interstitial lung disease, other occupational exposures may lead to isolated small airway obstruction. Certain workplace exposures, like asbestos, increase the risk of malignancy, but also produce pulmonary findings that mimic malignancy. This publication aims to delineate the common and special considerations associated with occupational lung disease to assist the ordering physician in selecting the most appropriate imaging study, while still stressing the importance of a multidisciplinary approach. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

BACKGROUND: Thymic cysts can change in volume, CT attenuation, and MRI signal over time, raising possibility that spontaneous hemorrhage and resorption could contribute to these changes. A previous study showed some of their CT features to prompt misinterpretation as thymomas. We studied the pathological features of thymic cysts and correlated them with preoperative imaging findings. METHODS: The MGH Pathology archives were searched to identify thymic cyst resections between April 2000 and May 2020. Exclusion criteria included non-prevascular mediastinal localization, location within an enhancing mass (imaging), and/or presence of solid-cystic mass identified on gross examination. Cases without available imaging were also excluded. Various macroscopic/microscopic pathological parameters were evaluated and correlated with cyst imaging characteristics seen on CT or MRI performed closest to the time of surgery. RESULTS: Upon application of exclusion criteria, we identified 18 thymic cysts from the initial 84 mediastinal cystic specimens. The median age at resection was 60.5 with a range of 45–77 years. Most cysts were unilocular (11/18; 61%), with a gross maximum diameter ranging from 1.5 to 11.2 cm (mean ± SD: 4.2±2.7 cm). Microscopic review showed that most cysts had mixed patterns (8/16; 50%) of cuboidal, flat, squamous and/or pseudostratified epithelia. Common findings included hemosiderin deposition in the cyst wall (5/18; 28%), calcifications (6/18; 33%), chronic inflammation (6/18; 33%), hyalinosis (11/18; 61%), and significant fibrosis (12/18; 67%). Other findings included cyst walls with denuded epithelium (6/18; 33%); adjacent cholesterol clefts (3/18; 17%); and granulation tissue (2/18; 11%). The adjacent thymic tissue was involuted in 16/18 (89%) cysts, and showed fat necrosis in 11/18 (61%), microcystic Hassall’s corpuscles change in 4/18 (22%), lymphoid follicular hyperplasia in 3/18 (17%), and true thymic hyperplasia in 1/18 (6%). A total of 17/18 cysts were imaged by CT, and 4/18 imaged by MRI, including 3 imaged by CT. On CT, 6/17 (%) cysts demonstrated wall calcification, 11/17 (%) had attenuation values ≥20 HU, and mean/median wall thickness on CT [solely perceivable and measurable in 5/17 (%)] was 3 mm/3 mm ±1.5 (1 SD). Of the 4 cysts imaged by MRI, three were T1-isointense and the other T1-hypointense to muscle. CONCLUSIONS: Thymic cysts encompass a series of morphologically diverse lesions, which often show histological features suggestive of microbleeding, inflammation, and fibrosis, which may explain their variable CT and MRI appearance.

Background Isoattenuating and hyperattenuating thymic cysts at CT are often misinterpreted as lymphadenopathy or thymic epithelial neoplasms. Purpose To evaluate the longitudinal change in thymic cyst appearance at CT and MRI. Materials and Methods All chest MRI studies showing thymic cysts between July 2008 and December 2019, identified from a retrospective search of a quality assurance database, were included in this study if initial CT depicted a thymic lesion, the patient was referred for follow-up MRI for characterization, and the baseline (ie, index) MRI indicated a cystic lesion. Follow-up CT scans and/or MRI scans were identified through July 2020. Thymic cyst characteristics, such as size, location, and morphologic features, as well as CT and MRI characteristics, were recorded. Change in size, attenuation, and T1-weighted MRI signal was assessed longitudinally. Descriptive statistics of longitudinal change were tabulated. Results A total of 244 chest MRI studies in 140 patients with 142 unique cysts and 392 CT examinations (636 total examinations and 645 thymic cysts-nine examinations with two cysts each) were evaluated. The median follow-up duration was 2.2 years. Thirty-three patients with 34 unique cysts (34 of 142 cysts [24%]) underwent imaging follow-up for more than 5 years. Thymic cysts followed up for more than 5 years were most commonly saccular (189 of 274 cysts [69% axially]) and retrosternal (14 of 34 cysts [41%]). Craniocaudal dimension was larger than transverse and anteroposterior dimensions in 223 of 274 cysts (81%). Mean thymic cyst attenuation was 25 HU (range, 15-100 HU). Five of 31 cysts (16%) exhibited wall calcification. The median cyst wall thickness was 2.0 mm (range, 0.9-3.0 mm). Most thymic cysts changed in volume (31 of 34 cysts [91%]), CT attenuation (15 of 35 cysts [43%]), and T1-weighted MRI signal (12 of 18 cysts [67%]) over time. None developed mural irregularity, nodularity, or septations. Conclusion Unilocular thymic cysts, defined at index MRI, never developed irregular wall thickening, mural nodularity, or septations that would raise concern for malignant transformation. However, these cysts showed mural calcification and change in size, CT attenuation, and MRI signal over more than 5 years of follow-up. © RSNA, 2021

AIM To assess the ability of artificial neural networks (ANNs) to predict the likelihood of malignancy of pure ground-glass opacities (GGOs), using observations from computed tomography (CT) and 2-[18F]-fluoro-2-deoxy- d- glucose (FDG) positron-emission tomography (PET) images and relevant clinical information. MATERIALS AND METHODS One hundred and twenty-five cases of pure GGOs described in a previous article were used to train and evaluate the performance of an ANN to predict the likelihood of malignancy in each of the GGOs. Eighty-five cases selected randomly were used for training the network and the remaining 40 cases for testing. The ANN was constructed from the image data and basic clinical information. The predictions of the ANN were compared with blinded expert estimates of the likelihood of malignancy. RESULTS The ANN showed excellent predictive value in estimating the likelihood of malignancy (AUC = 0.98±0.02). Employing the optimal cut-off point from the receiver operating characteristic (ROC) curve, the ANN correctly identified 11/11 malignant lesions (sensitivity 100%) and 27/29 benign lesions (specificity 93.1%). The expert readers found 23 lesions indeterminate and correctly identified 17 lesions as benign. CONCLUSION ANNs have potential to improve diagnostic certainty in the classification of pure GGOs, based upon their CT appearance, intensity of FDG uptake, and relevant clinical information, and may therefore, be useful to help direct clinical and imaging follow-up.

Lung cancer is the leading cause of cancer-related deaths in both men and women. The major risk factor for lung cancer is personal tobacco smoking, particularly for small-cell lung cancer (SCLC) and squamous cell lung cancers, but other significant risk factors include exposure to secondhand smoke, environmental radon, occupational exposures, and air pollution. Education and socioeconomic status affect both incidence and outcomes. Non–small-cell lung cancer (NSCLC), including adenocarcinoma, squamous cell carcinoma, and large cell carcinoma, comprises about 85% of lung cancers. SCLC accounts for approximately 13% to 15% of cases. Prognosis is directly related to stage at presentation. NSCLC is staged using the eighth edition of the tumor-node-metastasis (TNM) criteria of the American Joint Committee on Cancer. For SCLC the eighth edition of TNM staging is recommended to be used in conjunction with the modified Veterans Administration Lung Study Group classification system distinguishing limited stage from extensive stage SCLC. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Objective To evaluate quantitative magnetic resonance imaging (MRI) parameters for differentiation of cysts from and solid masses in the anterior mediastinum. Materials and Methods The development dataset included 18 patients from two institutions with pathologically-proven cysts (n = 6) and solid masses (n = 12) in the anterior mediastinum. We measured the maximum diameter, normalized T1 and T2 signal intensity (nT1 and nT2), normalized apparent diffusion coefficient (nADC), and relative enhancement ratio (RER) of each lesion. RERs were obtained by non-rigid registration and subtraction of precontrast and postcontrast T1-weighted images. Differentiation criteria between cysts and solid masses were identified based on receiver operating characteristics analysis. For validation, two separate datasets were utilized: 15 patients with 8 cysts and 7 solid masses from another institution (validation dataset 1); and 11 patients with clinically diagnosed cysts stable for more than two years (validation dataset 2). Sensitivity and specificity were calculated from the validation datasets. Results nT2, nADC, and RER significantly differed between cysts and solid masses (p = 0.032, 0.013, and < 0.001, respectively). The following criteria differentiated cysts from solid masses: RER < 26.1%; nADC > 0.63; nT2 > 0.39. In validation dataset 1, the sensitivity of the RER, nADC, and nT2 criteria was 87.5%, 100%, and 75.0%, and the specificity was 100%, 40.0%, and 57.4%, respectively. In validation dataset 2, the sensitivity of the RER, nADC, and nT2 criteria was 90.9%, 90.9%, and 72.7%, respectively. Conclusion Quantitative MRI criteria using nT2, nADC, and particularly RER can assist differentiation of cysts from solid masses in the anterior mediastinum.

Aim To determine if pure ground-glass opacities (GGOs) and the subgroup of ground-glass nodules (GGNs) typically demonstrate higher 2-[18F]-fluoro-2-deoxy- d- glucose (18F-FDG) uptake at positron-emission tomography (PET) when benign than when malignant. Materials and methods Informed consent was waived for this institutional review board (IRB)-approved, Health Insurance Portability and Accountability Act (HIPAA) compliant, retrospective study. A review of all 1,864 combined PET/computed tomography (CT) examinations performed in 2011 on a single system to identify pure GGOs with mean diameter ≥1 cm yielded 166 GGOs. Two blinded subspecialty-trained thoracic radiologists independently assessed GGO size, morphology, attenuation, and location on CT. A blinded nuclear radiologist procured the SUVmax for each GGO. Final diagnosis of malignancy (n=21) was made based on histopathology or upon increased size and attenuation; a final diagnosis of benignity (n=106) was made if GGO resolved, was new within 3 months, evolved in a manner consistent with pulmonary fibrosis, or was stable for ≥60 months; 29 were indeterminate and were excluded, along with 10 cases with unreliable SUVmax measurements, yielding 127 GGOs, of which 68 were GGNs, in 76 patients. Results The SUVmax was significantly higher in benign than malignant GGOs (p=0.0017) and in the GGN subgroup (p=0.03). A threshold SUVmax >1.5 for GGOs, including GGNs, assured benignity in this cohort. Conclusion Benign GGOs and the benign GGN subgroup demonstrated significantly higher FDG uptake at PET than malignant GGOs/GGNs. Awareness of this finding may prevent misinterpretation of highly 18FDG-avid pure GGOs/GGNs as definitively malignant, which could lead to unnecessary thoracic surgery and its associated risks.

Thoracic MRI presents important and unique challenges. Decreased proton density in the lung in combination with respiratory and cardiac motion can degrade image quality and render poorly executed sequences uninterpretable. Despite these challenges, thoracic MRI has an important clinical role, both as a problem-solving tool and in an increasing array of clinical indications. Advances in scanner and sequence design have also helped to drive this development, presenting the radiologist with improved techniques for thoracic MRI. Given this evolving landscape, radiologists must be familiar with what thoracic MR has to offer. The first step in developing an effective thoracic MRI practice requires the creation of efficient and malleable protocols that can answer clinical questions. To do this, radiologists must have a working knowledge of the MR sequences that are used in the thorax, many of which have been adapted from use elsewhere in the body. These sequences can be broadly divided into three categories: traditional/anatomic, functional, and cine based. Traditional/anatomic sequences allow for the depiction of anatomy and pathologic processes with the ability for characterization of signal intensity and contrast enhancement. Functional sequences, including diffusion-weighted imaging, and high temporal resolution dynamic contrast enhancement, allow for the noninvasive measurement of tissue-specific parameters. Cine-based sequences can depict the motion of structures in the thorax, either with retrospective ECG gating or in real time. The purpose of this article is to review these categories, the building block sequences that comprise them, and identify basic questions that should be considered in thoracic MRI protocol design. Level of Evidence: 5 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2019;50:682-701.

OBJECTIVE. CT-based body composition analysis quantifies skeletal muscle and adipose tissue. However, acquisition parameters and quality can vary between CT images obtained for clinical care, which...

The high soft tissue contrast and tissue characterization properties of magnetic resonance imaging allow further characterization of indeterminate mediastinal lesions on chest radiography and computed tomography, increasing diagnostic specificity, preventing unnecessary intervention, and guiding intervention or surgery when needed. The combination of its higher soft tissue contrast and ability to image dynamically during free breathing, without ionizing radiation exposure, allows more thorough and readily appreciable assessment of a lesion's invasiveness and assessment of phrenic nerve involvement, with significant implications for prognostic clinical staging and surgical management.

Chronic dyspnea may result from a variety of disorders of cardiovascular, pulmonary, gastrointestinal, neuromuscular, systemic, and psychogenic etiology. This article discusses guidelines for the initial imaging of six variants for chronic dyspnea of noncardiovascular origin: (1) Chronic dyspnea of unclear etiology; (2) Chronic dyspnea with suspected chronic obstructive pulmonary disease; (3) Chronic dyspnea with suspected central airways disease; (4) Chronic dyspnea with suspected interstitial lung disease; (5) Chronic dyspnea with suspected disease of the pleura or chest wall; and (6) Chronic dyspnea with suspected diaphragm dysfunction. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Acute respiratory illness, defined as cough, sputum production, chest pain, and/or dyspnea (with or without fever), is a major public health issue, accounting for millions of doctor office and emergency department visits every year. While most cases are due to self-limited viral infections, a significant number of cases are due to more serious respiratory infections where delay in diagnosis can lead to morbidity and mortality. Imaging plays a key role in the initial diagnosis and management of acute respiratory illness. This study reviews the current literature concerning the appropriate role of imaging in the diagnosis and management of the immunocompetent adult patient initially presenting with acute respiratory illness. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

PURPOSE: To assess CT features of pulmonary fibrosis in patients with systemic lupus erythematosus (SLE) and to assess the presence of several distinctive patterns of fibrosis associated with connective tissue disease. MATERIALS AND METHODS: A cross-sectional retrospective analysis was performed. An institutional clinical database was queried for the years of 2005–2015 to identify CT examination reports of patients with SLE and fibrotic lung disease, which yielded 50 patients (median age, 49 years; age range, 22–71 years; 46 women). CT examination reports were scored by two subspecialty thoracic radiologists using a standard multilevel semiquantitative system. Readers noted the presence or absence of several recently described CT signs of variant patterns of fibrosis in connective tissue disease (the “anterior upper lobe,” “straight-edge,” and “exuberant honeycombing” signs), as well as two other morphologic characteristics (an “island-like” appearance of areas of well-defined fibrosis with angular margins surrounded by normal lung and confluent regions of lucent lung destruction). RESULTS: The most common CT patterns were characterized as either fibrotic nonspecific interstitial pneumonia (38%, 19 of 50) or variant fibrosis (44%, 22 of 50). CT signs of variant fibrosis were identified by both readers in up to 62% of patients, with good κ agreement (0.44–0.64); the island-like sign (62%) and anterior upper lobe sign (52%) were most commonly observed. Pulmonary function test results showed correlations with several imaging findings but did not show correlations with CT signs of variant fibrosis. CONCLUSION: When present, pulmonary fibrosis in SLE often has a distinctive appearance and may also manifest as several variant fibrotic patterns. Keywords: CT, Lung © RSNA, 2021 See also the commentary by White in this issue.

PURPOSE The purpose of this study was to describe Thoracic magnetic resonance (MR) acquisition time (AT) variability, associations, and technologist insights as to its causes at a large quaternary institution, by MR protocol and imaging site. MATERIALS AND METHODS A retrospective review of our 2017 QI database of 1.5 T MR imaging ATs for adults 19 years and above at the main hospital and outpatient (OPT) satellites was performed for all 5 Thoracic MR protocols. Summary statistics were calculated for ATs. Multivariable linear regression was adjusted for age, sex, body mass index, time of examination relative to shift change, technologist experience, and language interpreter. An anonymous REDCap survey of our MR technologists sought their assessment of reasons for AT variability and techniques that help reduce it. RESULTS A total of 174 adult OPT 1.5 T mediastinal, pleural, and lung MR examinations were analyzed, revealing high variability of median AT by protocol and site (P

The International Thymic Malignancy Interest Group (ITMIG) and the International Association for the Study of Lung Cancer (IASLC) formed the Thymic Domain of the Staging and Prognostic Factors Committee (TD-SPFC) to develop the first stage classification system for thymic epithelial tumors (TETs) which was published in the TNM Classification of Malignant Tumours issued by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC), now in 8th edition. This system was developed from evidence-based analysis of the large ITMIG database of TETs, in conjunction with expert opinion. Until its publication in December 2017, there had been no universally accepted, standard means of classifying these tumors, although Masaoka-Koga staging system had most closely approached this standard. This brief article will summarize this new stage classification system for TETs, highlighting its differences with Masaoka-Koga and relevant next goals.

While some cystic masses can be definitively diagnosed on CT, others remain indeterminate. Because of its intrinsic superior soft tissue resolution, MR is an important tool in the evaluation of select mediastinal masses that are incompletely characterized on CT. This review describes how non-vascular MR provides greater diagnostic precision in the evaluation of indeterminate cystic mediastinal masses on CT. It also emphasizes key MR pulse sequences for optimal evaluation of problematic mediastinal masses.

Objectives To compare image quality, visibility of anatomic landmarks, tubes and lines, and other clinically significant findings on portable (bedside) chest radiographs acquired with wireless direct radiography (DRw) and computed radiography (CR). Methods In a prospective IRB-approved and HIPAA-compliant study, portable DRw (DRX-1C mobile retrofit portable wireless direct radiography, CareStream Inc., Rochester, NY) and portable CR (AGFA CR (DXG) version; NIM2103, AGFA Healthcare, Ridgefield Park, NJ) images of the chest were acquired within 24-hours in 80 patients in the intensive care unit (ICU). Image pairs of 75 patients (37% female) with a mean age of 60.7±16 years were independently compared side-by-side by 7 experienced thoracic radiologists using a five-point scale. When tubes and lines were present, the radiologist also compared an edge-enhanced copy of the DRw image to the CR image. Results Most radiologists found significantly fewer artifacts on DRw images compared to CR images and all readers agreed that when present, these artifacts did not significantly preclude the ability to evaluate anatomic landmarks, tubes and lines, or clinically significant findings. None of the radiologists (0/7) reported superior visibility of anatomic structures on CR images compared to DRw images and some radiologists (3/7) found DRw images significantly better for visibility of anatomic landmarks such as the carina (p=0.01–0.001). Most radiologists (6/7) found DRw images to be better or clearly better than CR images for position of tubes and lines, and edge-enhanced DRw images to be especially helpful for evaluation of central venous catheters and esophageal tubes (p=0.027-0.001). None of the radiologists deemed CR images superior for visibility of clinically significant findings. Conclusions Critical care chest radiography with a portable DRw system can provide similar or superior information compared to a CR system regarding clinically significant findings and position of tubes and lines.

The purpose of this study was to compare submillisievert chest CT images reconstructed with filtered back projection (FBP), SafeCT, adaptive statistical iterative reconstruction (ASIR), and model-based iterative reconstruction (MBIR) with standard of care FBP images.Fifty patients (33 men and 17 women; mean age [± SD], 62 ± 10 years) undergoing routine chest CT gave written informed consent for acquisition of an additional submillisievert chest CT series with reduced tube current but identical scanning length as standard of care chest CT. Sinogram data of the submillisievert series were reconstructed with FBP, SafeCT, ASIR, and MBIR and compared with FBP images at standard-dose chest CT (n = 8 × 50 = 400 series). Two thoracic radiologists performed independent comparison for visualization of lesion margin, visibility of small structures, and diagnostic acceptability. Objective noise measurements and noise spectral density were obtained.Of 287 detected lesions, 162 were less than 1-cm noncalcified nodules. Lesion margins were well seen on all submillisievert reconstruction images except MBIR, on which they were poorly visualized. Likewise, only submillisievert MBIR images were suboptimal for visibility of normal structures, such as pulmonary vessels in the outer 2 cm of the lung, interlobular fissures, and subsegmental bronchial walls. MBIR had the lowest image noise compared with other techniques.FBP, SafeCT, ASIR, and MBIR can enable optimal lesion evaluation on chest CT acquired at a volume CT dose index of 2 mGy. However, all submillisievert reconstruction techniques were suboptimal for visualization of mediastinal structures. Submillisievert MBIR images were suboptimal for visibility of normal lung structures despite showing lower image noise.

Purpose To determine the impact of nonvascular thoracic magnetic resonance (MR) imaging on the clinical decision making and diagnostic certainty of thoracic surgeons. Materials and Methods Seven thoracic surgeons at Massachusetts General Hospital, an academic quaternary referral hospital, participated in this 2-year, prospective, institution review board-approved, HIPAA-compliant pre- and post-MR imaging survey study after completing a one-time demographic survey. Between July 16, 2013, and July 13, 2015, each time a thoracic surgeon ordered a nonvascular thoracic MR imaging study via radiology order entry, he or she was sent a link to the pre-test survey that ascertained the clinical rationale for MR imaging, the clinical management plan if MR imaging was not an option, and pre-test diagnostic certainty. Upon completion of the MR imaging report, the surgeon was sent a link to the post-test survey assessing if/how MR imaging changed clinical management, the surgeon's comfort with the clinical management plan, and post-test diagnostic certainty. Data were analyzed with Student t, Wilcoxon, and McNemar tests. Results A total of 99 pre- and post-test surveys were completed. Most MR imaging studies (64 of 99 [65%]) were requested because of indeterminate computed tomographic findings. The use of MR imaging significantly reduced the number of planned surgical interventions (P < .001), modified the surgical approach in 54% (14 of 26) of surgical cases, and increased surgeon comfort with the patient management plan in 95% (94 of 99) of cases. Increased diagnostic certainty as a result of MR imaging was highly significant (P < .0001). In 21% (21 of 99) of cases, definitive MR imaging results warranted no further follow-up or clinical care. Conclusion In appropriate cases, assessment with nonvascular thoracic MR imaging substantially affects the clinical decision making and diagnostic certainty of thoracic surgeons. (©) RSNA, 2016 Online supplemental material is available for this article. An earlier incorrect version of this article appeared online. This article was corrected on May 2, 2016.

To compare visualization of subtle normal and abnormal findings at computed tomography (CT) of the chest for diffuse lung disease with images reconstructed with filtered back projection and adaptive statistical iterative reconstruction (ASIR) techniques.In this HIPAA-compliant, institutional review board-approved study, 24 patients underwent 64-section multi-detector row CT of the chest for evaluation of diffuse lung disease. Scanning parameters included a pitch of 0.984:1 and 120 kVp in thin-section mode, with 2496 views per rotation compared with 984 views acquired for normal mode. The 0.625-mm-thick images were reconstructed with filtered back projection, ASIR, and ASIR high-definition (ASIR-HD) kernels. Two thoracic radiologists independently assessed the filtered back projection, ASIR, and ASIR-HD images for small anatomic details (interlobular septa, centrilobular region, and small bronchi and bronchioles), abnormal findings (reticulation, tiny nodules, altered attenuation, bronchiectasis), image quality (graded by using a six-point scale, where 1 = excellent image quality, and 5 = interpretation impossible), image noise, and artifacts. Data were tabulated for statistical testing.For visualization of normal and pathologic structures, CT image series reconstructed with ASIR-HD were rated substantially better than those reconstructed with filtered back projection and ASIR (P.001). ASIR-HD images were superior to filtered back projection images in 15 of 24 (62%) patients for visualization of normal structures and in 24 of 24 (100%) patients for pathologic findings. ASIR-HD was superior to ASIR in three of 24 (12%) images for normal anatomic findings and in seven of 24 (29%) images for pathologic evaluation. None of the images in the three groups were rated as unacceptable for noise (P.001).ASIR-HD reconstruction results in superior visualization of subtle and tiny anatomic structures and lesions in diffuse lung disease compared with ASIR and filtered back projection reconstructions.

Received July 21, 2015; accepted after revision September 4, 2015. and by aiding in the discernment of thymoma from lymphoma [2, 3]. Thymic MRI typically is prompted by an incidental finding noted in the thymic bed on chest CT. A prior chest CT examination enables focused MRI to best answer a defined clinical question. Although MRI is useful in the diagnosis of thymic lesions, it can be helpful only if it is performed and interpreted correctly and if certain pitfalls are avoided. The purpose of this article is to heighten the awareness of these pitfalls.

This is a cardiothoracic curriculum document for radiology residents meant to serve not only as a study guide for radiology residents but also as a teaching and curriculum reference for radiology educators and radiology residency program directors. This document represents a revision of a cardiothoracic radiology resident curriculum that was published 10 years ago in Academic Radiology. The sections that have been significantly revised, expanded, or added are (1) lung cancer screening, (2) lung cancer genomic profiling, (3) lung adenocarcinoma revised nomenclature, (4) lung biopsy technique, (5) nonvascular thoracic magnetic resonance, (6) updates to the idiopathic interstitial pneumonias, (7) cardiac computed tomography updates, (8) cardiac magnetic resonance updates, and (9) new and emerging techniques in cardiothoracic imaging. This curriculum was written and endorsed by the Education Committee of the Society of Thoracic Radiology. This curriculum operates in conjunction with the Accreditation Council for Graduate Medical Education (ACGME) milestones project that serves as a framework for semiannual evaluation of resident physicians as they progress through their training in an ACGME-accredited residency or fellowship programs. This cardiothoracic curriculum document is meant to serve not only as a more detailed guide for radiology trainees, educators, and program directors but also complementary to and guided by the ACGME milestones.

The high soft tissue contrast of MR imaging enables superior tissue characterization of mediastinal masses, adding diagnostic specificity and often changing and benefiting clinical management. MR imaging can better discern cystic from solid content and can detect microscopic fat, hemorrhage, and fibrous content within lesions. In many cases, mediastinal MR imaging may prevent unnecessary diagnostic intervention. In other cases, MR imaging may indicate the optimal site for biopsy or the correct compartment for resection. Awareness of the efficacy of MR imaging with regard to mediastinal mass characterization and judicious MR imaging utilization should further improve patient care.

To assess if diagnostic dual energy CT (DECT) of the chest can be achieved at submillisievert (sub-mSv) doses.Our IRB-approved prospective study included 20 patients who were scanned on dual-source multidector CT(MDCT). All patients gave written informed consent for acquisition of additional image series at reduced radiation dose on a dual-source MDCT (80/140 kV) within 10 s after the standard of care acquisition. Dose reduction was achieved by reducing the quality reference milliampere-second, with combined angular exposure control. Four readers, blinded to all clinical data, evaluated the image sets. Image noise, signal-to-noise and contrast-to-noise ratio were assessed. Volumetric CT dose index (CTDIThe mean age and body mass index of the patients were 71 years ± 9 and 24 kg mRoutine chest DECT can be performed at sub-mSv doses with good image quality and without loss of relevant diagnostic information. Advances in knowledge: (1) Contrast-enhanced DECT of the chest can be performed at sub-mSv doses, down to mean CTDI

To determine the non-therapeutic thymectomy rate in a recent six-year consecutive thymectomy cohort, the etiology of these unnecessary thymectomies, and the differentiating CT features of thymoma, lymphoma, thymic hyperplasia, and thymic cysts.Electronic data base query of all thymectomies performed at the Massachusetts General Hospital from 2006 to 2012 yielded 160 thymectomy cases, 124 of which had available imaging. The non-therapeutic thymectomy rate (includes thymectomy for lymphoma and benign disease) was calculated. Preoperative clinical and CT imaging features were assessed by review of the in-house electronic medical record by 2 thoracic surgeons and 2 pathology-blinded radiologists, respectively.The non-therapeutic thymectomy rate of 43.8% (70/160) was largely secondary to concern for thymoma and was comprised of lymphoma (54.3%, 38/70), thymic bed cysts (24.3%, 17/70), thymic hyperplasia (17.1%, 12/70), and reactive or atrophic tissue (4.3%, 3/70). Among these four lesions, there were significant differences in location with respect to midline, morphology, circumscription, homogeneity of attenuation, fatty intercalation, coexistent lymphadenopathy, overt pericardial invasion, and mass effect (p0.001). True thymic cysts ranged in attenuation from -20 to 58Hounsfield units (HU), with a mean attenuation of 23HU.The high rate of unnecessary thymectomy was due to misinterpretation of thymic cysts, thymic hyperplasia, and lymphoma as thymoma on chest CT. This study demonstrates differentiating features between thymoma, lymphoma, thymic hyperplasia, and thymic cysts on chest CT which may help triage more patients away from thymectomy toward less invasive and non-invasive means of diagnosis and thereby lower the non-therapeutic thymectomy rate.

The aim of the study was to determine the current state of training, utilization, and perceived value of nonvascular thoracic magnetic resonance imaging (MRI).The URL link for this anonymous, IRB-approved survey was e-mailed to all Society of Thoracic Radiology members with available e-mail addresses (733), of whom 693 were qualified to respond as per the survey's instructions. Survey questions focused on MRI training, interpretation volume, perceived value of thoracic MRI, and barriers to its utilization. Study data were collected and managed using Research Electronic Data Capture (REDCap) electronic data capture tools and analyzed with χ tests.The survey response rate was 27% (190/693). Thirty-seven percent (67/180) of respondents reported that they interpreted and reported zero thoracic MRIs and 64% (116/182) interpreted or reported10 MRIs over the prior year. The perceived value of thoracic MRI was highest for chest wall and neurovascular involvement and evaluation of the mediastinum, particularly thymus, next highest for assessment of pleural or diaphragmatic lesions, and lowest for assessment of lung function with hyperpolarized gases. Seventy-three percent (121/166) of respondents felt it would be of value to increase utilization of thoracic MRI. Perceived obstacles to increasing thoracic MRI utilization included lack of: awareness of referring health care providers as to the value of thoracic MRI (59%, 98/166), radiologist proficiency or comfort with thoracic MRI (46%, 77/166), standardized protocols (38%, 64/166), technologist experience (38%, 63/166), and sufficient training during residency and/or fellowship (32%, 54/166). Twenty-five percent (41/166) of respondents reported insufficient thoracic MRI literature and limited CME courses and lectures in this field as an additional impediment.The majority of survey respondents reported limited experience in thoracic MRI interpretation, a recognition of thoracic MRI's value, and an interest in increasing its utilization. Improved education of radiologists, technologists, and referring clinicians would ameliorate the current state.

Rationale and Objectives. The purpose of the study was to determine the relationship between pulmonary artery (PA) size at computed tomography (CT) and PA pressures, to develop a noninvasive CT method of PA pressure measurement, and to determine a PA diameter that can enable differentiation of normal subjects from those with ptfimonary hypertension. Methods. PA vessel diameters in 55 candidates for lung and heart-lung transplantation were measured at CT and correlated with PA pressures with both linear and stepwise multiple regression. The multiple regression equations were then tested prospectively in 35 pretransplantation patients. Results. Combined main and left main PA cross-sectional area corrected for body surface area showed the best correlation with mean PA pressure ( r = .87). The multiple regression equations helped predict mean PA pressure within 5 mm Hg in 50% of patients with chronic lung disease and in only 8% of patients with pulmonary vascular disease. Conclusion. There was a very good correlation between main and left main PA size and mean PA pressure. At present, however, CT has not demonstrated sufficient accuracy to be used clinically.

There is increasing perception that thoracic magnetic resonance imaging (MRI) is underutilized. Various obstacles to implementation and utilization of thoracic MRI can be overcome with continuous updating, improvement, and standardization of thoracic MRI protocols, close collaboration with MRI technologists, continued education of MRI technologists, radiologists, and referring health care providers, and incorporation of MRI training into thoracic imaging fellowship programs. The purpose of this article is to share the author's experience in developing a successful nonvascular thoracic MRI practice, discuss the fundamentals of nonvascular thoracic MRI, and provide a "how-to" manual for its performance.

To determine whether there is a sex difference in the appearance of the normal thymus in 20-30-year-old men and women.This retrospective study was approved by the institutional review board and was compliant with HIPAA. The requirement for informed consent was waived. Images and medical records of 238 consecutive subjects without known thymic disease (175 men, 63 women) who underwent chest computed tomography with intravenous contrast material in 2008 were reviewed. Average thymic region of interest (ROI), subjective assessment of thymic attenuation by using a scale of grades 0-3, thymic anteroposterior measurement, and mean maximal thymic lobe thickness were recorded by two independent thoracic radiologists, blinded to subject age and sex. Thymic morphologic characteristics were assessed in consensus. The two-sided Wilcoxon rank-sum test, Student t test, test for linear regression, analysis of covariance, two-way factorial analysis of variance, and continuity-adjusted χ(2) test were used for statistical analysis.There was a significant sex difference in thymic attenuation as measured objectively by using mean thymic ROI measurement (P.0001) and subjectively by using a scale of grades 0-3 (P.0001), which held true when corrected for age (P.0001). A sex difference was also found in regard to the rate of decrease in mean thymic attenuation with age, with men's thymuses exhibiting a significant decrease in attenuation during the decade, unlike women (P = .0479). There was no significant sex difference in mean maximal thymic lobe thickness (P = .8697). A quadrilateral, as opposed to triangular, configuration of the thymus was more common in women than men (P = .0034).There is a significant sex difference in normal thymic appearance in 20-30-year-old men and women. The thymus of 20-30-year-old women typically exhibits higher attenuation and more commonly exhibits a quadrilateral configuration.

AJR 2016; 206:W98 0361–803X/16/2066–W98 © American Roentgen Ray Society Reply to “Quantitative MRI of the Thymus: Chemical-Shift Ratio, Signal Intensity Index, and Apparent Diffusion Coefficient Value” My coauthors and I are grateful to Dr. Karabulut for his interest in our Structured Review article titled “Pitfalls in the Imaging and Interpretation of Benign Thymic Lesions: How Thymic MRI Can Help” [1] and his excellent comments. We agree with most of the comments and would like to add the following. First, Dr. Karabulut is correct that the initially electronically published article very unfortunately had a mistyped equation for the calculation of the chemical-shift ratio (CSR), with the denominators exchanged. This error was rapidly discovered and corrected within a few days, so the CSR equation is now correctly displayed as follows

A previously healthy 21-year-old woman presented with syncope and arrhythmia. A computed tomographic coronary angiogram was solely remarkable for an anterior mediastinal mass. Mediastinal magnetic resonance imaging of the reported mass revealed mildly prominent thymic tissue for age, with no suppression on out-of-phase chemical shift magnetic resonance imaging. Thymoma and lymphoma could not be excluded. After diagnosis and stabilization of her arrhythmia, the patient underwent median sternotomy and radical thymectomy, with pathology revealing normal thymus. This case suggests that nonsuppression of mildly prominent, homogenous thymic soft tissue in young women may not be sufficient to warrant diagnostic intervention and instead may warrant close follow-up.

W15 Limiting MRI to the area of interest to shorten image acquisition time is essential. A long image acquisition makes successful breath-holding difficult, with resultant motion artifact significantly compromising image evaluation. Hyperventilating the patient before each breath-hold can be helpful. Oxygen administration has been shown to be even more helpful in extending breath-hold capability [1]. Inand out-of-phase fast gradient-echo imaging is a rapid T1-weighted sequence that has been shown to be useful in distinguishing normal thymus and thymic hyperplasia from thymic neoplasms and lymphoma [2] and can serve as the T1-weighted unenhanced sequence for this examination. T2-weighted imaging of the mediastinum can be accomplished with double inversion recovery fast spin-echo imaging, a cardiac-gated black-blood fast spin-echo technique that requires approximately a 20to 25-second breath-hold per slice. Breath-hold duration will vary with the TR, which is dictated by the patient’s heart rate—bradycardia lengthens the TR and requisite breath-hold and tachycardia shorten the TR and breath-hold. Alternatively or in addition, rapid T2-weighted images can be obtained with nongated 2D axial balanced gradient-echo imaging, a sequence that requires an 8to 15-second breath-hold for the entire scan. Please note that these breathhold times and those that follow are estimates that can vary depending on scanning parameters, lesion size or required breadth of coverage, and whether or not cardiac gating is used. The T2-weighted coronal ultrafast spin-echo MRI of the Thymus

To our knowledge, no previous direct associations have been made between generalized myositis ossificans and pharmacological therapy. We report a case of generalized periarticular myositis ossificans associated with the use of curare and diazepam. The previously reported associations of myositis ossificans with tetanus and burns may be misleading. It is possible that it is not the disease process itself (e.g., tetanus, severe burn) that precipitates heterotopic ossification, but the treatment of these ailments. These observations suggest the importance of early mobilization and restrained use of immobilizing drugs. Further investigation is warranted with regard to the predisposing factors of generalized myositis ossificans and to its prevention.