Comparison Between Magnetic Resonance Imaging and Computed Tomography in the Detection and Volumetric Assessment of Lung Nodules: A Prospective Study

Rationale and Objectives

Computed tomography (CT) lung nodule assessment is routinely performed and appears very promising for lung cancer screening. However, the radiation exposure through time remains a concern. With the overall goal of an optimal management of indeterminate lung nodules, the objective of this prospective study was therefore to evaluate the potential of optimized ultra-short echo time (UTE) MRI for lung nodule detection and volumetric assessment.

Materials and Methods

Eight (54.9 ± 13.2 years) patients with at least 1 non-calcified nodule ≥4 mm were included. UTE under high-frequency non-invasive ventilation (UTE-HF-NIV) and in free-breathing at tidal volume (UTE-FB) were investigated along with volumetric interpolated breath-hold examination at full inspiration (VIBE-BH). Three experienced readers assessed the detection rate of nodules ≥4 mm and ≥6 mm, and reported their location, 2D-measurements and solid/subsolid nature. Volumes were measured by two experienced readers. Subsequently, two readers assessed the detection and volume measurements of lung nodules ≥4mm in gold-standard CT images with soft and lung kernel reconstructions. Volumetry was performed with lesion management software (Carestream, Rochester, New York, USA).

Results

UTE-HF-NIV provided the highest detection rate for nodules ≥4 mm (n = 66) and ≥6 mm (n = 32) (35 and 50%, respectively). No dependencies were found between nodule detection and their location in the lung with UTE-HF-NIV (p > 0.4), such a dependency was observed for two readers with VIBE-BH (p = 0.002 and 0.03). Dependencies between the nodule's detection and their size were noticed among readers and techniques (p < 0.02). When comparing nodule volume measurements, an excellent concordance was observed between CT and UTE-HF-NIV, with an overestimation of 13.2% by UTE-HF-NIV, <25%-threshold used for nodule's growth, conversely to VIBE-BH that overestimated the nodule volume by 28.8%.

Conclusion

UTE-HF-NIV is not ready to replace low-dose CT for lung nodule detection, but could be used for follow-up studies, alternating with CT, based on its volumetric accuracy.

Exploring a new method for quantitative sodium MRI in the human upper leg with a surface coil and symmetrically arranged reference phantoms

Background

The aim of this study is to validate and evaluate the reproducibility of a new setup for the quantification of the tissue sodium concentration (TSC) in the human upper leg muscles with sodium MRI at 3 Tesla. This setup is making use of an emit and receive single loop surface coil together with a set of square, symmetrically arranged reference phantoms. As a second aim, the performances of two MRI protocols for the TSC quantification in the upper leg muscles are compared: one using an ultra-short echo time (UTE) 3-dimensional radial sequence (UTE-protocol), and the other one using standard gradient echo sequence (GRE-protocol).

Methods

A validation test of the quantification of sodium concentration is performed in phantoms. The bias of the method is estimated and compared between both protocols. The reproducibility of TSC quantification is assessed in phantoms by the coefficient of variation (CV) and compared between both protocols. The reproducibility is also assessed in 11 health volunteers. Signal to noise ratio (SNR) maps are acquired in phantoms with both protocols in order to compare the resulting SNR.

Results

The apparatus and post processing were successfully implemented. The bias of the method was smaller than 10% in phantoms (excepted for Na concentration of 10 mmol/L when using the GRE protocol). The reproducibility of the method using symmetrically arranged phantoms was high in phantoms and humans (CV <5%). The GRE-protocol leads to a better SNR than the UTE-protocol in 2D images.

Conclusions

The use of symmetrically arranged reference phantoms lead to reproducible results in phantoms and humans. Sodium imaging in the human upper leg with a single loop surface coil should be performed with a standard 2-dimensional GRE protocol if an optimal SNR is needed. However, the quantification of the fast and slow decay time constants of the sodium signal, which plays a role in the TSC quantification, still has to be done with a UTE sequence. Moreover, the quantification of sodium concentration is more accurate with the UTE protocol for small sodium concentrations (<20 mmol).

Ultrashort echo time imaging of the lungs under high-frequency noninvasive ventilation: A new approach to lung imaging

Background

Although ultrashort echo time (UTE) sequences allow excellent assessment of lung parenchyma, image quality remains lower than that of computed tomography (CT).

Purpose

To investigate a high‐frequency noninvasive ventilation (HF‐NIV) technique allowing a stabilized inspiration and to compare image quality with current dedicated MR sequences.

Study Type

Prospective.

Population

Ten healthy volunteers.

Field Strength/Sequence

3D radial UTE sequence at 1.5T.

Assessment

UTE‐HF‐NIV sequence was compared with UTE‐free‐breathing (UTE‐FB), reconstructed at end expiration (UTE‐Exp) and average (UTE‐Avg), and breath‐hold VIBE sequences. The distance from lung apex to the dome of the right hemidiaphragm was measured. Visual assessment of the visibility and sharpness of normal anatomical structures was carried out. Dedicated software also quantitatively evaluated vessel–lung and right lung–liver interface sharpness. Apparent signal ratio (Sr) and contrast ratios (Cr) were quantitatively evaluated.

Statistical Tests

Wilcoxon signed rank test for visual scores, paired t‐test for continuous variables, significance at P < 0.05.

Results

The distance between apex and the right hemidiaphragmatic dome was significantly larger (P < 0.001) with UTE‐HF‐NIV compared with UTE‐FB and VIBE acquisitions. Vessel and airway visibility had identical median visual scores with all UTE methods. Median visual scores for sharpness of vessels and airways were significantly higher (P < 0.001) with HF‐NIV (vessels = 3; airways = 2) than in UTE‐FB (vessels = 2; airways = 1) and VIBE (vessels = 1; airways = 1). Software‐based vessel sharpness evaluation resulted in larger values in 8/10 volunteers with UTE‐HF‐NIV (67.3 ± 9.8) compared with UTE‐Avg (62.3 ± 12.6) but the average difference was not significant (P = 0.28). The sharpness of the lung–liver interface was significantly higher (P < 0.001) with HF‐NIV (17.3 ± 5.3) compared with UTE‐Avg (14.1 ± 3.9). Significantly higher values (P < 0.01) of Sr and Cr were observed with UTE‐HF‐NIV compared with UTE‐FB and VIBE.

Data Conclusion

HF‐NIV allowing acquisition at full inspiration significantly improves image quality for lung imaging. This could offer the option to alternate some follow‐up CT studies by using this technique.

Level of Evidence: 2

Technical Efficacy: Stage 1

J. Magn. Reson. Imaging 2019;50:1789–1797.

MR Volumetry of Lung Nodules: A Pilot Study

Introduction: Computed tomography (CT) is currently the reference modality for the detection and follow-up of pulmonary nodules. While 2D measurements are commonly used in clinical practice to assess growth, increasingly 3D volume measurements are being recommended. The goal of this pilot study was to evaluate preliminarily the capabilities of 3D MRI using ultra-short echo time for lung nodule volumetry, as it would provide a radiation-free modality for this task. Material and Methods: Artificial nodules were manufactured out of Agar and measured using an ultra-short echo time MRI sequence. CT data were also acquired as a reference. Image segmentation was carried out using an algorithm based on signal intensity thresholding (SIT). For comparison purposes, we also performed manual slice by slice segmentation. Volumes obtained with MRI and CT were compared. Finally, the volumetry of a lung nodule was evaluated in one human subject in comparison with CT. Results: Using the SIT technique, minimal bias was observed between CT and MRI across the entire range of volumes (2%) with limits of agreement below 14%. Comparison of manually segmented MRI and CT resulted in a larger bias (8%) and wider limits of agreement (-23% to 40%). In vivo, nodule volume differed of <16% between modalities with the SIT technique. Conclusion: This pilot study showed very good concordance between CT and UTE-MRI to quantify lung nodule volumes, in both a phantom and human setting. Our results enhance the potential of MRI to quantify pulmonary nodule volume with similar performance to CT.

Simultaneous Evaluation of Lung Anatomy and Ventilation Using 4D Respiratory-Motion-Resolved Ultrashort Echo Time Sparse MRI

BACKGROUND

Computed tomography (CT) and spirometry are the current standard methods for assessing lung anatomy and pulmonary ventilation, respectively. However, CT provides limited ventilation information and spirometry only provides global measures of lung ventilation. Thus, a method that can enable simultaneous examination of lung anatomy and ventilation is of clinical interest.

PURPOSE

To develop and test a 4D respiratory-resolved sparse lung MRI (XD-UTE: eXtra-Dimensional Ultrashort TE imaging) approach for simultaneous evaluation of lung anatomy and pulmonary ventilation.

STUDY TYPE

Prospective.

POPULATION

In all, 23 subjects (11 volunteers and 12 patients, mean age = 63.6 ± 8.4).

FIELD STRENGTH/SEQUENCE

3T MR; a prototype 3D golden-angle radial UTE sequence, a Cartesian breath-hold volumetric-interpolated examination (BH-VIBE) sequence.

ASSESSMENT

All subjects were scanned using the 3D golden-angle radial UTE sequence during normal breathing. Ten subjects underwent an additional scan during alternating normal and deep breathing. Respiratory-motion-resolved sparse reconstruction was performed for all the acquired data to generate dynamic normal-breathing or deep-breathing image series. For comparison, BH-VIBE was performed in 12 subjects. Lung images were visually scored by three experienced chest radiologists and were analyzed by two observers who segmented the left and right lung to derive ventilation parameters in comparison with spirometry.

STATISTICAL TESTS

Nonparametric paired two-tailed Wilcoxon signed-rank test; intraclass correlation coefficient, Pearson correlation coefficient.

RESULTS

XD-UTE achieved significantly improved image quality compared both with Cartesian BH-VIBE and radial reconstruction without motion compensation (P < 0.05). The global ventilation parameters (a sum of the left and right lung measures) were in good correlation with spirometry in the same subjects (correlation coefficient = 0.724). There were excellent correlations between the results obtained by two observers (intraclass correlation coefficient ranged from 0.8855-0.9995).

DATA CONCLUSION

Simultaneous evaluation of lung anatomy and ventilation using XD-UTE is demonstrated, which have shown good potential for improved diagnosis and management of patients with heterogeneous lung diseases.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:411-422.

Chemical shift encoding (CSE) for sensitive fluorine-19 MRI of perfluorocarbons with complex spectra

PURPOSE

To implement a fluorine-19 (¹⁹ F) chemical shift encoding (CSE) approach for the sensitive imaging of molecules with multi-resonance spectra to remove their chemical shift displacement (CSD) artifacts, and to characterize its sensitivity versus established pulse sequences.

METHODS

The feasibility of CSE spoiled gradient echo (GRE) and balanced steady-state free precession (bSSFP) was first demonstrated in a phantom study. The dependence of the sensitivity of CSE-bSSFP on several pulse sequence parameters was then established, after which the occurrence of out-of-plane excitation was assessed for 2D and 3D techniques. Next, the sensitivity (in mm^-3 s^-0.5 ) of both CSE techniques was compared to bSSFP ultrashort echo time (bSSFP-UTE) imaging and multi-chemical-shift-selective turbo spin echo (MCSS-TSE) in a second phantom study. Finally, the sensitivity of the CSE-bSSFP, bSSFP-UTE, and MCSS-TSE pulse sequences was compared in a preliminary in vivo mouse study.

RESULTS

Both CSE approaches were successfully implemented and resulted in negligible residual CSD artifacts, while large-volume 3D acquisitions should be considered to reduce problems related to out-of-plane excitation. CSE-bSSFP was shown to have a higher sensitivity than the bSSFP-UTE and MCSS-TSE pulse sequences (15.8 ± 1.3 vs. 11.7 ± 1.0 vs. 13.3 ± 0.9 mm^-3 s^-0.5 , respectively, P < 0.001), whereas CSE-GRE technique had a lower sensitivity (4.8 ± 1.1 mm^-3 s^-0.5 ).

CONCLUSION

CSE ¹⁹ F MR imaging enables the unambiguous visualization of compounds with complex spectra, and provides high sensitivity both in vitro and in vivo. Magn Reson Med 79:2724-2730, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

A double echo ultra short echo time (UTE) acquisition for respiratory motion-suppressed high resolution imaging of the lung

PURPOSE

Magnetic resonance imaging is a promising alternative to computed tomography for lung imaging. However, organ motion and poor signal-to-noise ratio, arising from short T2*, impair image quality. To alleviate these issues, a new retrospective gating method was implemented and tested with an ultra-short echo time sequence.

METHODS

A 3D double-echo ultra-short echo time sequence was used to acquire data during free breathing in ten healthy adult subjects. A self-gating method was used to reconstruct respiratory motion suppressed expiratory and inspiratory images. These images were objectively compared to uncorrected data sets using quantitative end-points (pulmonary vessel sharpness, lung-liver interface definition, signal-to-noise ratio). The method was preliminarily tested in two cystic fibrosis patients who underwent computed tomography.

RESULTS

Vessel sharpness in expiratory ultra-short echo time data sets with second echo motion detection was significantly higher (13% relative increase) than in uncorrected images while the opposite was observed in inspiratory images. The method was successfully applied in patients and some findings (e.g., hypointense areas) were similar to those from computed tomography.

CONCLUSION

Free breathing ultra-short echo time was successfully implemented, allowing flexible image reconstruction of two different respiratory states. Objective improvements in image quality were obtained with the new method and initial feasibility in a clinical setting was demonstrated. Magn Reson Med 79:2297-2305, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Chest-MRI under pulsatile flow ventilation: A new promising technique

Objectives

Magnetic resonance imaging (MRI) of the chest has long suffered from its sensitivity to respiratory and cardiac motion with an intrinsically low signal to noise ratio and a limited spatial resolution. The purpose of this study was to perform chest MRI under an adapted non invasive pulsatile flow ventilation system (high frequency percussive ventilation, HFPV^®) allowing breath hold durations 10 to 15 times longer than other existing systems.

Methods

One volunteer and one patient known for a thymic lesion underwent a chest MRI under ventilation percussion technique (VP-MR). Routinely used sequences were performed with and without the device during three sets of apnoea on inspiration.

Results

VP-MR was well tolerated in both cases. The mean duration of the thoracic stabilization was 10.5 min (range 8.5–12) and 5.8 min (range 5–6.2) for Volunteer 1 and Patient 1, respectively. An overall increased image quality was seen under VP-MR with a better delineation of the mediastinal lesion for Patient 1. Nodules discovered in Volunteer 1 were confirmed with low dose CT.

Conclusion

VP-MR was feasible and increased spatial resolution of chest MRI by allowing acquisition at full inspiration during thoracic stabilization approaching prolonged apnoea. This new technique could be of benefit to numerous thoracic disorders.

Current artefacts in cardiac and chest magnetic resonance imaging: tips and tricks

Currently MRI is extensively used for the evaluation of cardiovascular and thoracic disorders because of the well-established advantages that include use of non-ionizing radiation, good contrast and high spatial resolution. Despite the advantages of this technique, numerous categories of artefacts are frequently encountered. They may be related to the scanner hardware or software functionalities, environmental factors or the human body itself. In particular, some artefacts may be exacerbated with high-field-strength MR machines (e.g. 3 T). Cardiac imaging poses specific challenges with respect to breath-holding and cardiac motion. In addition, new cardiac MR-conditional devices may also be responsible for peculiar artefacts. The image quality may thus be impaired and give rise to a misdiagnosis. Knowledge of acquisition and reconstruction techniques is required to understand and recognize the nature of these artefacts. This article will focus on the origin and appearance of the most common artefacts encountered in cardiac and chest MRI along with possible correcting methods to avoid or reduce them.

Dielectric pads and low- B1+ adiabatic pulses: complementary techniques to optimize structural T1 w whole-brain MP2RAGE scans at 7 tesla

PURPOSE

To evaluate the combination of low-B1 (+) adiabatic pulses and high permittivity (εr ≈ 165) dielectric pads effectiveness to reproducibly improve the inversion efficiency for whole-brain MP2RAGE scans, at ultra-high field.

MATERIALS AND METHODS

Two low-B1 (+) adiabatic pulses, HS8 and TR-FOCI, were compared with the conventional HS1 adiabatic pulse in MP2RAGE acquisitions of four subjects at 7 Tesla. The uniform MP2RAGE images were qualitatively assessed for poor inversion artifacts by trained observers. Each subject was rescanned using dielectric pads. Eight further subjects underwent two MP2RAGE scan sessions using dielectric pads and the TR-FOCI adiabatic pulse.

RESULTS

The HS8 and TR-FOCI pulses improved inversion coverage in all subjects compared with the HS1 pulse. However, in subjects whose head lengths are large (≥136 mm) relative to the coil's z-coverage, the B1 (+) field over the cerebellum was insufficient to cause inversion. Dielectric pads increase the B1 (+) field, by ∼50%, over the cerebellum, which in conjunction with the TR-FOCI pulse, reproducibly improves the inversion efficiency over the whole brain for subjects with head lengths ≤155 mm. Minor residual inversion artifacts were present in three of eight subjects (head lengths ≥155 mm).

CONCLUSION

The complementary techniques of low-B1 (+) adiabatic RF pulses and high permittivity dielectric pads allow whole-brain structural T1 w images to be reliably acquired at ultra-high field. J. Magn. Reson. Imaging 2014;40:804-812. © 2013 Wiley Periodicals, Inc.