Magnetic Resonance Imaging for the Follow-up of Treated Thymic Epithelial Malignancies Purpose: The purpose of this article was to compare magnetic resonance imaging (MRI) depiction of thymic malignancy progression/recurrence with that of computed tomography (CT). Methods: We retrospectively reviewed all surgically treated thymic epithelial malignancy (TEM) patients between 2011 and 2018 who were followed-up with chest CT and MRI. We compared the detection of recurrence and metastatic disease between the CT and MRI scans in each of these patients. Results: Of 187 patients treated in our institution for TEM, 22 were followed-up with both CT and MRI. TNM stage at diagnosis was as follows: I (n=14), II (n=1), IIIa (n=4), IIIb (n=2), IVa (n=1), and IVb (n=0). Patients were followed-up for a mean of 6.2 years, range 0.7 to 17.7 years. The mean interval between CT and MRI was 5.4 (range, 1 to 15) months. Most patients had no recurrence (n=16), 4 had recurrence after R0 or R1 resection, 1 had stable disease, and 1 had progression of disease after R2 resection. CT and MRI performed equally in the identification of pleural spread (n=5), lymphadenopathy (n=4), and pulmonary metastases (n=1). Retrosternal recurrence (n=1) was identified by MRI despite sternotomy wire artifacts. MRI identified bone involvement and extension of disease into the thecal sac earlier and more readily. Three patients had an indeterminate mediastinal finding on CT that was correctly identified as a benign cyst or pericardial fluid collection by MRI. Conclusion: MRI is an alternative option to follow-up patients after treatment for TEM. However, for those with metallic sternotomy wires, we recommend alternating the follow-up with CT as well.

Errors in Interpretation of Magnetic Resonance Imaging for Thymic Lesions Purpose: The objectives of this study were to evaluate the magnetic resonance imaging (MRI) features of thymic lesions and to review those features that may result in diagnostic uncertainty or error. Materials and Methods: This multicenter retrospective study included patients with pathologically proven thymic epithelial neoplasms (TEN) and thymic cysts who underwent preoperative MRI. Clinical reports were evaluated for the radiologist’s first-choice diagnosis, if not already known before the MRI. MR images were reviewed by thoracic radiologists to identify cystic components on T2-weighted imaging (T2WI) as well as the presence of enhancement on postcontrast series. Results: Through a search of electronic medical records of 3 tertiary academic medical centers, we identified 41 TEN and 13 cysts. Of 35 evaluable clinical reports, 9 (26%) gave an incorrect diagnosis. Of these, 5 cases were misdiagnosed related to contrast enhancement, and 3 cases of cysts were misdiagnosed because of lack of fluid signal on T2WI. Upon rereview of images, of the 41 TENs, 4 (10%) did not show qualitative enhancement on the first postcontrast phase (although all enhanced eventually), and 4 cysts (31%) did not show fluid signal on T2WI. In addition, 4 cases of cysts (31%) showed mural or septal enhancement. Conclusions: Although atypical or misleading imaging features are uncommon in TEN and thymic cysts, they do occur and may lead to diagnostic error. We suggest that lesions with a T2 signal less than simple fluid and without enhancement on postcontrast images undergo follow-up imaging to confirm a benign diagnosis.

Extent of Intraprotocol and Intersite Variability of Thoracic Magnetic Resonance Acquisition Times at a Large Quaternary Institution: MR Technologist Insights as to Its Causes 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<0.001)—for example, mean, median, slowest, and fastest ATs for Thymus I− protocol (n=38) were 34, 32, 66, and 8 minutes, respectively. OPT site with fewest MR technologists and a single MR scanner had shortest mean AT across all protocols (35±15 min). Full Chest I− protocol had shortest AT across all sites (mean AT=33±13 min), compared with focused imaging protocols. All I−/I+ protocols had greater than expected AT, compared with the same protocol performed (I−). Surveyed MR technologists noted limited Thoracic MR training/experience, discomfort with thoracic anatomy and Thoracic MR performance, and AT-related benefit of effective communication with the radiologist with regard to lesion location. Conclusions: There was tremendous intraprotocol and intersite variability of Thoracic MR ATs. Increased technologist training, amplified experience, and a solid understanding of lesion location for focused examinations may all help reduce Thoracic MR AT.

Radiographic Manifestations of Diffuse Pulmonary Alveolar Derecruitment Pulmonary alveolar derecruitment is a process of alveolar collapse that occurs in critically ill patients. While the entity and its physiological manifestations are described in the anesthesiology and critical care literature, the radiographic manifestations of alveolar derecruitment have not yet been thoroughly described. This phenomenon can have a similar appearance to pulmonary edema; however, patients often have severe intravascular volume depletion. As the treatment for these 2 entities is essentially contradictory, it is important to be familiar with alveolar derecruitment and consider it as a differential diagnosis when clinically appropriate.

Evaluation of Vascular Parameters in Patients With Pulmonary Thromboembolic Disease Using Dual-energy Computed Tomography Purpose: The purpose of this study was to evaluate patterns of vascular and lung parenchymal enhancement in patients with suspected chronic thromboembolic pulmonary hypertension (CTEPH) and in those with acute pulmonary embolism (PE) and compare those two groups. Materials and Methods: We retrospectively studied 186 thoracic DECT studies referred for evaluation of CTEPH or pulmonary hypertension. A total of 80 of these patients had a negative scan (control group), 13 had acute PE, and 53 had chronic thromboembolic disease (CTED)/CTEPH. Five different DECT-based parameters were evaluated that highlight patterns of vascular kinetics. Specifically, total DECT-based parenchymal attenuation in Hounsfield Unit (HU) (LungHU), percentage of perfused blood volume (PBV), peak enhancement of main pulmonary artery (PApeak in HU), maximum enhancement corresponding to 100 (PAmax), and the ratio of PApeak to LungHU were calculated. Results: Compared with patients with negative CT, patients with CTED/CTEPH tended to have lower LungHU (median: 27 vs. 38, P<0.001), lower PBV (median: 39 vs. 51, P=0.003), and higher PApeak/LungHU ratio (median: 17 vs. 13, P=0.003). Compared with patients with acute PE, patients with CTED/CTEPH tended to have lower LungHU (median: 27 vs. 39, P=0.006), lower PBV (median: 39 vs. 62, P=0.023), and higher PApeak/LungHU ratio (median: 17 vs. 11, P=0.023). No statistically significant differences were observed between patients with acute PE and those with negative CT. Conclusions: DECT-based vascular parameters offer the potential to differentiate patients with acute versus chronic PE. These various anatomic and functional vascular DECT-based parameters might be reflective of the state of the underlying vascular bed.

Pulmonary Vascular Morphology Associated With Gas Exchange in Systemic Sclerosis Without Lung Fibrosis Purpose: Gas exchange in systemic sclerosis (SSc) is known to be affected by fibrotic changes in the pulmonary parenchyma. However, SSc patients without detectable fibrosis can still have impaired gas transfer. We aim to investigate whether pulmonary vascular changes could partly explain a reduction in gas transfer of SSc patients without fibrosis. Materials and Methods: We selected 77 patients whose visual computed tomography (CT) scoring showed no fibrosis. Pulmonary vessels were detected automatically in CT images, and their local radii were calculated. The frequency of occurrence for each radius was calculated, and, from this radius histogram, 2 imaging biomarkers (α and β) were extracted, wherein α reflects the relative contribution of small vessels compared with large vessels, and β represents the vessel tree capacity. Correlations between imaging biomarkers and gas transfer [single-breath diffusion capacity for carbon monoxide corrected for hemoglobin concentration (DLCOc) %predicted] were evaluated with Spearman correlation. Multivariable stepwise linear regression was performed with DLCOc %predicted as the dependent variable and age, BMI, sPAP, FEV1 %predicted, TLC %predicted, FVC %predicted, α, β, voxel size, and CT-derived lung volume as independent variables. Results: Both α and β were significantly correlated with gas transfer (R=−0.29, P-value=0.011 and R=0.32, P-value=0.004, respectively). The multivariable stepwise linear regression analysis selected sPAP [coefficient=−0.78; 95% confidence interval (CI)=−1.07, −0.49; P-value<0.001], β (coefficient=8.6; 95% CI=4.07, 13.1; P-value<0.001), and FEV1% predicted (coefficient=0.3; 95% CI=0.12, 0.48; P-value=0.001) as significant independent predictors of DLCOc %predicted (R=0.71, P-value<0.001). Conclusions: In SSc patients without detectable pulmonary fibrosis, impaired gas exchange is associated with alterations in pulmonary vascular morphology.

Pulmonary Insufficiency: Advantage of Pulmonary Regurgitation Volume Versus Pulmonary Regurgitation Fraction in a Congenital Heart Disease Mixed Population Objective: The objective of this study was to compare the use of pulmonary regurgitation volume (PRV) or indexed PRV (PRVi) with that of pulmonary regurgitation fraction (PRF) in the assessment of patients with pulmonary regurgitation (PR) undergoing cardiac magnetic resonance (CMR) imaging. Materials and Methods: CMR of 176 patients with PR were retrospectively evaluated. Their right ventricular diastolic (end-diastolic volume index [EDVi]) and systolic (end-systolic volume index) volume indexes, stroke volume, and ejection fraction were obtained from cine CMR sequences, whereas phase-contrast flow sequences were analyzed to obtain PRV, PRVi, and PRF. Patients were divided into subgroups, according to underlying pathology and according to PR severity. Correlations between PRV or PRF and RV parameters were studied through Spearman ρ, both in the main group and subgroups. Follow-up examinations were analyzed, and correlations between PRV or PRF from the first CMR examination and volume data from the second were calculated. Results: Tetralogy of Fallot was the main setting of PR (98/179). Overall, EDVi strongly correlates with PRV (ρ=0.592, P<0.001) than with PRF (ρ=0.522, P<0.001), and end-systolic volume index strongly correlates with PRV (ρ=0.454, P<0.001) and PRF (ρ=0.406, P <0.001). As regards subgroup analysis, in moderate or severe PR patients, EDVi strongly correlates (P=0.043) with PRV (ρ=0.499, P<0.001) than with PRF (ρ=0.317, P<0.001). Follow-up EDVi correlates with PRV (ρ=0.450, P=0.031), but not with PRF. Conclusions: Especially when assessing moderate to severe PR, PRV and PRVi may be better indicators of right ventricular dysfunction than PRF. Moreover, PRV may be a predictor of worsening RV dilation.

Dual-Source Computed Tomography of the Chest in Blunt Thoracic Trauma: Reduced Aortic Motion Using a Novel Temporal Resolution Optimization Method Purpose: The purpose of this study was to evaluate the clinical utility of temporal resolution optimization (TR-Opt), a computed tomography (CT) postprocessing technique, in reducing aortic motion artifacts in blunt thoracic trauma patients. Materials and Methods: This was an IRB-approved study of 61 patients with blunt thoracic trauma carried out between February 18 and September 6, 2014; the patients had been imaged using a standardized dual-source high-pitch (DSHP) CT protocol. Image raw data were retrospectively postprocessed using the TR-Opt algorithm (DSHP-TR-Opt) and compared with conventional images (DSHP). Diagnostic ability to confidently identify and exclude potential injuries and qualitative aortic motion artifacts using a 5-point Likert scale (1=absence of motion artifacts; 5=severe motion artifact) was graded by 2 readers at multiple thoracic locations. Signal-to-noise and contrast-to-noise ratios were generated as quantitative indices of image quality. Results: Motion artifacts degrading interpretation and limiting diagnosis of aortic injuries were present in 45% (442/976) of the assessed regions on DSHP. TR-Opt algorithm eliminated motion artifacts in 85% of the motion-degraded areas (375/442), leaving persistent motion artifacts in only 15% (67/442). Motion artifacts were most improved at the interventricular septum (1±1 vs. 3±1), aortic valve (2±1 vs. 4±1.5), and ascending aorta (1±1 vs. 3±2, P<0.005). Mean aorta noise (NAo) was 41.7% higher in the DSHP-TR-Opt images (26.5 vs. 18.7 HU, P<0.0001). Conclusions: Temporal resolution optimized reconstruction is a raw data–based CT postprocessing technique that can be used to remove the majority of thoracic aortic motion artifacts that commonly degrade interpretation when imaging blunt thoracic trauma patients.

Application of Artificial Intelligence–based Image Optimization for Computed Tomography Angiography of the Aorta With Low Tube Voltage and Reduced Contrast Medium Volume Purpose: The purpose of this study was to evaluate the impact of artificial intelligence (AI)-based noise reduction algorithm on aorta computed tomography angiography (CTA) image quality (IQ) at 80 kVp tube voltage and 40 mL contrast medium (CM). Materials and Methods: After obtaining institutional review board approval and 8 written informed consents, 60 patients (35 men, 25 women; age range: 18 to 85 y) referred for aorta CTA examination were assigned to 2 groups at random. Group A underwent an 80 kVp protocol with 40 mL CM (320 mg I/mL). Group A reconstructed with iterative reconstruction was named as group A1 and further AI-based noise reduction was named as group A2. Group B was scanned with standard 120 kVp, 80 mL CM, and iterative reconstruction algorithm. The quantitative assessment of IQ included aorta CT attenuation, noise, signal-to-noise ratio, and contrast-to-noise ratio. A 5-point scale (5—excellent, 1—poor) was used by 2 radiologists independently for qualitative IQ analysis. Results: The image noise significantly decreased while signal-to-noise ratio and contrast-to-noise ratio significantly increased in the order of group A1, B, and A2 (all P<0.05). Compared with group B, the subjective IQ score of group A1 was significantly lower (P<0.05), while that of group A2 had no significant difference (P>0.05). The effective dose and CM volume of group A were reduced by 79.18% and 50%, respectively, than that of group B. Conclusions: The AI-based noise reduction could improve the IQ of aorta CTA with low kV and reduced CM, which achieved the potential of radiation dose and contrast media reduction compared with conventional aorta CTA protocol.

Retrospective Comparative Analysis of Computed Tomography Findings of Acute and Chronic Aortic Dissections and Intramural Hematomas Purpose: The objective of this study was to assess the reliability of ancillary imaging findings in distinguishing acute from chronic aortic dissection (AD) and intramural hematoma (IMH) using computed tomography angiography (CTA). Materials and Methods: Two radiologists specializing in cardiothoracic and vascular imaging reviewed paired CTAs of patients with AD or IMH who underwent CTA in the acute (within 24 h of presentation) and chronic settings. The radiologists were blinded to the temporal order of the CTAs. Minimum and maximum flap thicknesses and presence or absence of pleural effusion, pericardial effusion, mediastinal hematoma or fat standing, and mediastinal lymphadenopathy were recorded. Results: Patients included 25 male individuals and 13 female individuals with a mean age of 59 years (range: 34 to 87 y). The group included 29 AD and 9 IMH cases. The median interval between the paired CTs was 542 days (range: 100 to 2533 d). Respectively, the mean minimum flap thicknesses in the acute and chronic AD were 1.3 and 1.4 mm (P=0.3), and the mean maximum flap thicknesses were 2.7 and 2.9 mm (P=0.29). The incidences of ancillary findings in acute and chronic AD and IMH were as follows: pleural effusion (55% vs. 37%, P=0.143), pericardial effusion (8% vs. 11%, P=1.0), lymphadenopathy (47% vs. 47%, P=1.0), and periaortic fat stranding (87% vs. 76%, P=0.344). Conclusions: Ancillary CT imaging findings traditionally ascribed to acute AD and IMH are also often found in the chronic setting and are not reliable indicators of acuity. Flap thickness in AD may not be a reliable imaging indicator of acuity of AD.