Free-breathing, zero-TE MR lung imaging

Gibiino, Fabio; Sacolick, Laura; Menini, Anne; Landini, Luigi; Wiesinger, Florian

doi:10.1007/s10334-014-0459-y

Cited by 63 publications

(59 citation statements)

References 32 publications

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“…Other potential applications of the ZTE sequence for PET/MR imaging would be lung visualization, to improve the estimation of parenchyma attenuation (29) and the detection of local coils.…”

Section: Discussionmentioning

confidence: 99%

Clinical Evaluation of Zero-Echo-Time MR Imaging for the Segmentation of the Skull

Delso¹,

et al. 2015

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MR-based attenuation correction is instrumental for integrated PET/ MR imaging. It is generally achieved by segmenting MR images into a set of tissue classes with known attenuation properties (e.g., air, lung, bone, fat, soft tissue). Bone identification with MR imaging is, however, quite challenging, because of the low proton density and fast decay time of bone tissue. The clinical evaluation of a novel, recently published method for zero-echo-time (ZTE)-based MR bone depiction and segmentation in the head is presented here. Methods: A new paradigm for MR imaging bone segmentation, based on proton density-weighted ZTE imaging, was disclosed earlier in 2014. In this study, we reviewed the bone maps obtained with this method on 15 clinical datasets acquired with a PET/CT/MR trimodality setup. The CT scans acquired for PET attenuation-correction purposes were used as reference for the evaluation. Quantitative measurements based on the Jaccard distance between ZTE and CT bone masks and qualitative scoring of anatomic accuracy by an experienced radiologist and nuclear medicine physician were performed. Results: The average Jaccard distance between ZTE and CT bone masks evaluated over the entire head was 52% ± 6% (range, 38%-63%). When only the cranium was considered, the distance was 39% ± 4% (range, 32%-49%). These results surpass previously reported attempts with dualecho ultrashort echo time, for which the Jaccard distance was in the 47%-79% range (parietal and nasal regions, respectively). Anatomically, the calvaria is consistently well segmented, with frequent but isolated voxel misclassifications. Air cavity walls and bone/fluid interfaces with high anatomic detail, such as the inner ear, remain a challenge. Conclusion: This is the first, to our knowledge, clinical evaluation of skull bone identification based on a ZTE sequence. The results suggest that proton density-weighted ZTE imaging is an efficient means of obtaining high-resolution maps of bone tissue with sufficient anatomic accuracy for, for example, PET attenuation correction.

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“…Other potential applications of the ZTE sequence for PET/MR imaging would be lung visualization, to improve the estimation of parenchyma attenuation (29) and the detection of local coils.…”

Section: Discussionmentioning

confidence: 99%

Clinical Evaluation of Zero-Echo-Time MR Imaging for the Segmentation of the Skull

Delso¹,

et al. 2015

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“…Patients were excluded on the basis of (11), ultrafast steady-state free precession (12), zero echo time (13), and three-dimensional (3D) gradientrecalled-echo (GRE) techniques (2,3). Recently, a free-breathing 3D radial ultrashort echo time (UTE) technique has been described for the evaluation of structural lung disease (14).…”

Section: Discussionmentioning

confidence: 99%

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

Burris¹,

Johnson²,

Larson³

et al. 2016

Radiology

132

106

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).q RSNA, 2015 Purpose: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. Materials and Methods: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. Results:Mean nodule diameter 6 standard deviation was 6.2 mm 6 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 (k = 0.90 for UTE imaging and k = 0.92 for dual-echo GRE imaging). Conclusion: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.q RSNA, 2015

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“…Zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences use specialized acquisition and reconstruction techniques to enable detection of ultrashort-T2 components in vivo. These sequences allow for direct visualization of tendons (

T_{2}^{*} \approx 1 ms

) (1–7), cortical bone (

T_{2}^{*} \approx 0.4 ms

) (8–16), and lung parenchyma (

T_{2}^{*} \approx 0.5 - 3 ms

) (17–22), as well as components in myelin (

T_{2}^{*} \approx 0.1 - 0.4 ms

(23–25)) and ligaments (26) (up to 80% fraction of

T_{2}^{*} \approx 1 ms

(27)).…”

Section: Introductionmentioning

confidence: 99%

Ultrashort echo time and zero echo time MRI at 7T

Larson

Han

Krug

et al. 2015

Magn Reson Mater Phy

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Object Zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences for MRI offer unique advantages of being able to detect signal from rapidly decaying short-T2 tissue components. In this paper, we applied 3D zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences at 7T to assess differences between these methods. Materials and Methods We matched the ZTE and UTE pulse sequences closely in terms of readout trajectories and image contrast. Our ZTE used the Water- and fat-suppressed solid-state proton projection imaging (WASPI) method to fill the center of k-space. Images from healthy volunteers obtained at 7T were compared qualitatively as well as with SNR and CNR measurements for various ultrashort, short, and long-T2 tissues. Results We measured nearly identical contrast-to-noise and signal-to-noise ratios (CNR/SNR) in similar scan times between the two approaches for ultrashort, short, and long-T2 components in the brain, knee and ankle. In our protocol, we observed gradient fidelity artifacts in UTE, and our chosen flip angle and readout also resulted as well as shading artifacts in ZTE due to inadvertent spatial selectivity. These can be corrected by advanced reconstruction methods or with different chosen protocol parameters. Conclusion The applied ZTE and UTE pulse sequences achieved similar contrast and SNR efficiency for volumetric imaging of ultrashort-T2 components. Several key differences are that ZTE is limited to volumetric imaging but has substantially reduced acoustic noise levels during the scan. Meanwhile, UTE has higher acoustic noise levels and greater sensitivity to gradient fidelity, but offers more flexibility in image contrast and volume selection.

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Free-breathing, zero-TE MR lung imaging

Abstract: Zero-TE appears to be an attractive pulse sequence for 3D isotropic lung imaging. Prospective and retrospective approaches provide high-quality, free-breathing MR lung imaging within reasonable scan time.

Cited by 63 publications

References 32 publications

Clinical Evaluation of Zero-Echo-Time MR Imaging for the Segmentation of the Skull

Clinical Evaluation of Zero-Echo-Time MR Imaging for the Segmentation of the Skull

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

Ultrashort echo time and zero echo time MRI at 7T

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