Free-breathing Ultrashort Echo Time Research Articles

Detection of lung lesions in breath-hold VIBE and free-breathing Spiral VIBE MRI compared to CT

BackgroundDetection of pulmonary nodules in MRI requires fast imaging strategies without respiratory motion impairment, such as single-breath-hold Cartesian VIBE. As patients with pulmonary diseases have limited breath-hold capacities, this study investigates the clinical feasibility of non-Cartesian Spiral VIBE under free-breathing compared to CT as the gold standard.MethodsProspective analysis of 27 oncological patients examined in PET/CT and PET/MR. A novel motion-robust 3D ultrashort-echo-time (UTE) MR sequence was evaluated in comparison with CT and conventional breath-hold MR. CT scans were performed under breath-hold in end-expiratory and end-inspiratory position (CT ex, CT in). MR data was acquired with non-contrast-enhanced breath-hold Cartesian VIBE followed by a free-breathing 3D UTE Spiral VIBE. Impact of respiratory motion on pulmonary evaluation was investigated by two readers in Cartesian VIBE, followed by UTE Spiral VIBE and CT ex and the reference standard of CT in. Diagnostic accuracy was calculated, and visual image quality assessed.ResultsHigher detection rate and sensitivity of pulmonary nodules in free-breathing UTE Spiral VIBE in comparison with breath-hold Cartesian VIBE were found for lesions > 10 mm (UTE Spiral VIBE/VIBE/CT ex): 93%/54%/100%; Lesions 5–10 mm: 67%/25%/ 92%; Lesions < 5 mm: 11%/11%/78%. Lobe-based analysis revealed sensitivities and specificities of 64%/96%/41% and 96%/93%/100% for UTE Spiral VIBE/VIBE/CT ex.ConclusionFree-breathing UTE Spiral VIBE indicates higher sensitivity for detection of pulmonary nodules than breath-hold Cartesian VIBE and is a promising but time-consuming approach. However, sensitivity and specificity of inspiratory CT remain superior in comparison and should be preferred for detection of pulmonary lesions.

Magnetic resonance imaging with gradient sound respiration guide.

Respiratory motion management is crucial for high-resolution MRI of the heart, lung, liver and kidney. In this article, respiration guide using acoustic sound generated by pulsed gradient waveforms was introduced in the pulmonary ultrashort echo time (UTE) sequence and validated by comparing with retrospective respiratory gating techniques. The validated sound-guided respiration was implemented in non-contrast enhanced renal angiography. In the sound-guided respiration, breathe−in and–out instruction sounds were generated with sinusoidal gradient waveforms with two different frequencies (602 and 321 Hz). Performance of the sound-guided respiration was evaluated by measuring sharpness of the lung-liver interface with a 10–90% rise distance, w10-90, and compared with three respiratory motion managements in a free-breathing UTE scan: without respiratory gating (w/o gating), 0-dimensional k-space navigator (k-point navigator), and image-based self-gating (Img-SG). The sound-guided respiration was implemented in stack-of-stars balanced steady-state free precession with inversion recovery preparation for renal angiography. No subjects reported any discomfort or inconvenience with the sound-guided respiration in pulmonary or renal MRI scans. The lung-liver interface of the UTE images for sound-guided respiration (w10-90 = 6.99 ± 2.90 mm), k-point navigator (8.51 ± 2.71 mm), and Img-SG (7.01 ± 2.06 mm) was significantly sharper than that for w/o gating (17.13 ± 2.91 mm; p < 0.0001 for all of sound-guided respiration, k-point navigator and Img-SG). Sharpness of the lung-liver interface was comparable between sound-guided respiration and Img-SG (p = 0.99), but sound-guided respiration achieved better visualization of pulmonary vasculature. Renal angiography with the sound-guided respiration clearly delineated renal, segmental and interlobar arteries. In conclusion, the gradient sound guided respiration can facilitate a consistent diaphragm position in every breath and achieve performance of respiratory motion management comparable to image-based self-gating.

Quantification of MRI T2 Interstitial Lung Disease Signal-Intensity Volume in Idiopathic Pulmonary Fibrosis: A Pilot Study.

Imaging has played a pivotal role in the diagnosis of idiopathic pulmonary fibrosis (IPF). Recent reports suggest that T2 -weighted MRI could be sensitive to monitor signal-intensity modifications of the lung parenchyma, which may relate to the disease activity in IPF. However, there is a lack of automated tools to reproducibly quantify the extent of the disease, especially using MRI. To assess the feasibility of T2 interstitial lung disease signal-intensity volume quantification using a semiautomated method in IPF. Single center, retrospective. A total of 21 adult IPF patients and four control subjects without lung interstitial abnormalities. Both free-breathing ultrashort echo time (TE) lung MRI using the spiral volume interpolated breath hold examination (VIBE) sequence (3D-UTE) and T2 -BLADE at 1.5T. Semiautomated segmentation of the lung volume was done using 3D-UTE and registered to the T2 -BLADE images. The interstitial lung disease signal-intensity volume (ISIV) was quantified using a Gaussian mixture model clustering and then normalized to the lung volume to calculate T2 -ISIV. The composite physiological index (CPI) and forced vital capacity (FVC) were measured as known biomarkers of IPF severity. Measurements were performed independently by three readers and averaged. The reproducibility between measurements was also assessed. Reproducibility was assessed using the intraclass correlation coefficient (ICC) and Bland-Altman analysis. Correlations were assessed using Spearman test. Comparison of median was assessed using the Mann-Whitney test. The reproducibility of T2 -ISIV was high, with ICCs = 0.99. Using Bland-Altman analysis, the mean differences were found between -0.8 to 0.1. T2 -ISIV significantly correlated with CPI and FVC (rho = 0.48 and 0.50, respectively; P < 0.05). T2 -ISIV was significantly higher in IPF than in controls (P < 0.05). T2 -ISIV appears to be able to reproducibly assess the volumetric extent of abnormal interstitial lung signal-intensity modifications in patients with IPF, and correlate with disease severity. 4 TECHNICAL EFFICACY STAGE: 1.

A black-blood ultra-short echo time (UTE) sequence for 3D isotropic resolution imaging of the lungs.

Ultra-short echo time MRI is a promising alternative to chest CT for cystic fibrosis patients. Black-blood imaging in particular could help discern small-sized anomalies, such as mucoid plugging, which may otherwise be confused with neighboring blood vessels, particularly when contrast agent is not used. We, therefore, implemented and tested an ultra-short echo time sequence with black-blood preparation. Additionally, this sequence may also be used to generate bright-blood angiograms. Using this sequence, data was acquired during free breathing in 10 healthy volunteers to obtain respiratory-motion-resolved 3D volumes covering the entire thorax with an isotropic resolution of (1 mm)3 . The magnitude of signal suppression relative to a bright-blood reference acquisition was quantified and compared with that obtained with a turbo-spin echo (TSE) acquisition. Bright-blood angiograms were also generated by subtraction. Finally, an initial feasibility assessment was performed in 2 cystic fibrosis patients, and images were visually compared with contrast-enhanced images and with CT data. Black-blood preparation significantly decreased the average normalized signal intensity in the vessel lumen (-66%; P < 0.001). Similarly, blood signal was significantly lowered (-60%; P = 0.001) compared with the TSE acquisition. In patients, mucoid plugging could be emphasized in the black-blood datasets. An intercostal artery could also be visualized in the subtraction angiograms. Black-blood free-breathing ultra-short echo time imaging was successfully implemented and motion-resolved full volumetric coverage of the lungs with high spatial resolution was achieved, while obtaining an angiogram without contrast agent injection. Encouraging initial results in patients prompt further investigations in a larger cohort.

Morphologic Evaluation of Primary Non-Small Cell Lung Cancer by 3 Tesla MRI with Free-Breathing Ultrashort Echo Time and Radial T1-Weighted Gradient Echo Sequences: A Comparison with CT Analysis

Morphologic Evaluation of Primary Non-Small Cell Lung Cancer by 3 Tesla MRI with Free-Breathing Ultrashort Echo Time and Radial T1-Weighted Gradient Echo Sequences: A Comparison with CT Analysis

Free-breathing ultrashort echo time lung magnetic resonance imaging using stack-of-spirals acquisition: A feasibility study in oncology patients

ObjectivesTo investigate the diagnostic accuracy of lung magnetic resonance imaging (MRI) with a free-breathing three-dimensional ultrashort echo time spoiled gradient echo sequence using a stack-of-spirals acquisition (spiral 3D UTE) for pulmonary nodule detection at 3 T in oncology patients. MethodsThe institutional review board approved this retrospective study. Between June and September of 2017, 32 oncology patients underwent both free-breathing spiral 3D UTE of the lungs and thin-section chest computed tomography (CT) for pulmonary metastasis workups. Semiquantitative analyses of the visible pulmonary vessels, bronchi, mediastinum, and overall image quality on spiral 3D UTE were assessed by two reviewers; CT was used as the reference standard. The probability of nodule presence also was assessed. ResultsThe mean acquisition duration of the spiral 3D UTE was 327 s (range, 300–465 s). The pulmonary vessels and bronchi were visible nearly consistently up to the sub-sub-segmental branch levels on spiral 3D UTE (96.9% [31/32] and 90.6% [29/32], respectively). >90% of the spiral 3D UTE images had an acceptable or good mediastinal evaluation; >80% had good or excellent overall image quality. Fifty nodules (6.1 ± 5.9 mm) were identified in 13 patients on CT; the overall nodule detection rate of spiral 3D UTE was 86% (43/50). All 20 nodules ≥ 5 mm in diameter were identified on spiral 3D UTE (100%). ConclusionsFree-breathing spiral 3D UTE had high sensitivity for the detection of pulmonary nodules, a reasonable scan duration, and acceptable image quality, which may make it a potential alternative to CT for oncology patients.

Free-breathing pediatric chest MRI: Performance of self-navigated golden-angle ordered conical ultrashort echo time acquisition.

To assess the feasibility and performance of conical k-space trajectory free-breathing ultrashort echo time (UTE) chest magnetic resonance imaging (MRI) versus four-dimensional (4D) flow and effects of 50% data subsampling and soft-gated motion correction. Thirty-two consecutive children who underwent both 4D flow and UTE ferumoxytol-enhanced chest MR (mean age: 5.4 years, range: 6 days to 15.7 years) in one 3T exam were recruited. From UTE k-space data, three image sets were reconstructed: 1) one with all data, 2) one using the first 50% of data, and 3) a final set with soft-gating motion correction, leveraging the signal magnitude immediately after each excitation. Two radiologists in blinded fashion independently scored image quality of anatomical landmarks on a 5-point scale. Ratings were compared using Wilcoxon rank-sum, Wilcoxon signed-ranks, and Kruskal-Wallis tests. Interobserver agreement was assessed with the intraclass correlation coefficient (ICC). For fully sampled UTE, mean scores for all structures were ≥4 (good-excellent). Full UTE surpassed 4D flow for lungs and airways (P < 0.001), with similar pulmonary artery (PA) quality (P = 0.62). 50% subsampling only slightly degraded all landmarks (P < 0.001), as did motion correction. Subsegmental PA visualization was possible in >93% scans for all techniques (P = 0.27). Interobserver agreement was excellent for combined scores (ICC = 0.83). High-quality free-breathing conical UTE chest MR is feasible, surpassing 4D flow for lungs and airways, with equivalent PA visualization. Data subsampling only mildly degraded images, favoring lesser scan times. Soft-gating motion correction overall did not improve image quality. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:200-209.

Detection of Small Pulmonary Nodules with Ultrashort Echo Time Sequences in Oncology Patients by Using a PET/MR System.

To investigate the utility of a free-breathing ultrashort echo time (UTE) sequence for the evaluation of small pulmonary nodules in oncology patients by using a hybrid positron emission tomography (PET)/magnetic resonance (MR) imaging system and to compare the nodule detection rate between UTE and a conventional three-dimensional gradient-recalled-echo (GRE) technique. In this HIPAA-compliant, institutional review board-approved prospective study, 82 pulmonary nodules were identified in eight patients with extrathoracic malignancies. Patients underwent free-breathing UTE and dual-echo three-dimensional GRE imaging of the lungs in a hybrid PET/MR imaging unit immediately after clinical PET/computed tomography (CT). CT was considered the reference standard for nodule detection. Two reviewers identified nodules and obtained measurements on MR images. The McNemar test was used to evaluate differences in nodule detection rate between MR techniques, and interrater agreement was assessed by using Bland-Altman plots. Mean nodule diameter ± standard deviation was 6.2 mm ± 2.7 (range, 3-17 mm). The detection rate was higher for UTE imaging than for dual-echo GRE imaging for nodules of at least 4 mm (82% vs 34%, respectively; P < .001), with the largest difference in detection noted in the 4-8-mm nodule group (79% vs 21%, P < .001). UTE imaging displayed a higher detection rate than dual-echo GRE imaging for nodules without fluorodeoxyglucose avidity (68% vs 22%, respectively; P < .001). Interrater reliability of nodule detection with MR imaging was high (κ = 0.90 for UTE imaging and κ = 0.92 for dual-echo GRE imaging). A free-breathing UTE sequence has high sensitivity for the detection of small pulmonary nodules (4-8 mm) and outperformed a three-dimensional dual-echo GRE technique for the detection of small, non-fluorodeoxyglucose-avid nodules.