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Objective: CT serves as gold standard for the evaluation of pulmonary nodules. However, CT exposes patients to ionizing radiation, a concern especially in screening scenarios with repeated examinations. Due to recent technological advances, MRI emerges as a potential alternative for lung imaging using 3D steady state free precession and ultra-short echo-time sequences. Therefore, in this study we assessed the performance of three state-of-the-art MRI sequences for the evaluation of pulmonary nodules., Methods: Lesions of variable sizes were simulated in porcine lungs placed in a dedicated chest phantom mimicking a human thorax, followed by CT and MRI examinations. Two blinded readers evaluated the acquired MR-images locating and measuring every suspect lesion. Using the CT-images as reference, logistic regression was performed to investigate the sensitivity of the tested MRI-sequences for the detection of pulmonary nodules., Results: For nodules with a diameter of 6 mm, all three sequences achieved high sensitivity values above 0.91. However, the sensitivity dropped for smaller nodules, yielding an average of 0.83 for lesions with 4 mm in diameter and less than 0.69 for lesions with 2 mm in diameter. The positive predictive values ranged between 0.91 and 0.96, indicating a low amount of false positive findings. Furthermore, the size measurements done on the MR-images were subject to a bias ranging from 0.83 mm to -1.77 mm with standard deviations ranging from 1.40 mm to 2.11 mm. There was no statistically significant difference between the three tested sequences., Conclusion: While showing promising sensitivity values for lesions larger than 4 mm, MRI appears to be not yet suited for lung cancer screening. Nonetheless, the three tested MRI sequences yielded high positive predictive values and accurate size measurements; therefore, MRI could potentially figure as imaging method of the chest in selected follow-up scenarios, e.g. of incidental findings subject to the Fleischner Criteria., Competing Interests: Thomas Benkert is employed by Siemens Healthcare GmbH. We confirm that this does not alter our adherence to PLOS ONE policies on sharing data and materials.

Objectives: To assess the image quality of 3 different ultralow-dose CT protocols on pulmonary nodule depiction in a ventilated ex vivo-system., Materials and Methods: Four porcine lungs were inflated inside a dedicated chest phantom and prepared with n = 195 artificial nodules (0.5-1 mL). The artificial chest wall was filled with water to simulate the absorption of a human chest. Images were acquired with a 2x192-row detector CT using low-dose (reference protocol with a tube voltage of 120 kV) and 3 different ULD protocols (respective effective doses: 1mSv and 0.1mSv). A different tube voltage was used for each ULD protocol: 70kV, 100kV with tin filter (100kV_Sn) and 150kV with tin filter (150kV_Sn). Nodule delineation was assessed by two observers (scores 1-5, 1 = unsure, 5 = high confidence)., Results: The diameter of the 195 detected artificial nodules ranged from 0.9-21.5 mm (mean 7.84 mm ± 5.31). The best ULD scores were achieved using 100kV_Sn and 70 kV ULD protocols (4.14 and 4.06 respectively). Both protocols were not significantly different (p = 0.244). The mean score of 3.78 in ULD 150kV_Sn was significantly lower compared to the 100kV_Sn ULD protocol (p = 0.008)., Conclusion: The results of this experiment, conducted in a realistic setting show the feasibility of ultralow-dose CT for the detection of pulmonary nodules.

Clinical/methodical Issue: Pulmonary infections are a common complication in immunosuppressed patients with a frequently fatal prognosis despite modern prophylactic therapy. An early and correct diagnosis is important for initiation of the appropriate therapy., Standard Radiological Methods: Chest radiography is the preferred initial imaging examination but is not accurate enough for the detection of pulmonary infections in immunosuppressed patients., Methodical Innovations: Pneumonia is caused by a broad spectrum of pathogens in immunocompromised patients. In addition to imaging, the clinical history and epidemiology also play an important role in the diagnostics., Performance: Using epidemiological and anamnestic information, computed tomography (CT) shows a significantly better sensitivity and specificity particularly for the diagnosis of atypical forms of pneumonia. Due to the exact imaging of the different infiltration patterns CT provides an increased sensitivity with respect to the etiological classification of pulmonary infections., Practical Recommendations: This article reviews in particular the radiological findings of commonly occurring pulmonary infections in immunosuppressed patients.

Objectives: To validate the anatomical accuracy, homogeneity and sensitivity of two-compartment modeled inversion recovery (TCIR) magnetic resonance imaging (MRI) in a multimodal animal experiment as a non-invasive alternative to standard functional imaging techniques., Methods: Seven pigs were studied on a 1.5 T whole-body MR scanner and SPECT/CT. The specimens were intubated and maintained in general anesthesia throughout the experiment. TCIR maps of the fractional pulmonary blood volume were compared to dynamic contrast enhanced MRI and SPECT/CT via a region of interest (ROI) based reader study. A comprehensive statistical analysis was performed on the coefficient of variation to evaluate homogeneity properties. Sensitivity was assessed by detecting gravitation dependent perfusion variation and delineation of pathological areas., Results: The fPBV-maps of all examined specimens indicate a superior homogeneity in the computed values (p<1.3×10(-4)). The sensitivity of the TCIR maps to a gravitation effect on the blood distribution was verified and a similar anteroposterior signal and count dependency was observed in DCE MRI and SPECT. Bland-Altman analysis showed no significant intra- or inter-observer difference within the ROI reader study (p>0.06)., Conclusion: Superior information content, significantly higher homogeneity and similar sensitivity of TCIR when compared to DCE and SPECT/CT demonstrated the feasibility of TCIR MRI as an alternative contrast agent-free, non-invasive functional lung imaging approach., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Purpose: To compare unenhanced lung ventilation-weighted (VW) and perfusion-weighted (QW) imaging based on Fourier decomposition (FD) magnetic resonance (MR) imaging with the clinical reference standard single photon emission computed tomography (SPECT)/computed tomography (CT) in an animal experiment., Materials and Methods: The study was approved by the local animal care committee. Lung ventilation and perfusion was assessed in seven anesthetized pigs by using a 1.5-T MR imager and SPECT/CT. For time-resolved FD MR imaging, sets of lung images were acquired by using an untriggered two-dimensional balanced steady-state free precession sequence (repetition time, 1.9 msec; echo time, 0.8 msec; acquisition time per image, 118 msec; acquisition rate, 3.33 images per second; flip angle, 75°; section thickness, 12 mm; matrix, 128 × 128). Breathing displacement was corrected with nonrigid image registration. Parenchymal signal intensity was analyzed pixelwise with FD to separate periodic changes of proton density induced by respiration and periodic changes of blood flow. Spectral lines representing respiratory and cardiac frequencies were integrated to calculate VW and QW images. Ventilation and perfusion SPECT was performed after inhalation of dispersed technetium 99m ((99m)Tc) and injection of (99m)Tc-labeled macroaggregated albumin. FD MR imaging and SPECT data were independently analyzed by two physicians in consensus. A regional statistical analysis of homogeneity and pathologic signal changes was performed., Results: Images acquired in healthy animals by using FD MR imaging and SPECT showed a homogeneous distribution of VW and QW imaging and pulmonary ventilation and perfusion, respectively. The gravitation-dependent signal distribution of ventilation and perfusion in all animals was similarly observed at FD MR imaging and SPECT. Incidental ventilation and perfusion defects were identically visualized by using both modalities., Conclusion: This animal experiment demonstrated qualitative agreement in the assessment of regional lung ventilation and perfusion between contrast media-free and radiation-free FD MR imaging and conventional SPECT/CT., (© RSNA, 2011.)