Pulmonary MR imaging with ultra-short TEs: Utility for disease severity assessment of connective tissue disease patients

Pulmonary MRI with ultra-short TE using single- and dual-echo methods: comparison of capability for quantitative differentiation of non- or minimally invasive adenocarcinomas from other lung cancers with that of standard-dose thin-section CT

OBJECTIVE

The purpose of this study was thus to compare capabilities for quantitative differentiation of non- and minimally invasive adenocarcinomas from other of pulmonary MRIs with ultra-short TE (UTE) obtained with single- and dual-echo techniques (UTE-MRISingle and UTE-MRIDual) and thin-section CT for stage IA lung cancer patients.

METHODS

Ninety pathologically diagnosed stage IA lung cancer patients who underwent thin-section standard-dose CT, UTE-MRISingle, and UTE-MRIDual, surgical treatment and pathological examinations were included in this retrospective study. The largest dimension (Dlong), solid portion (solid Dlong), and consolidation/tumor (C/T) ratio of each nodule were assessed. Two-tailed Student's t-tests were performed to compare all indexes obtained with each method between non- and minimally invasive adenocarcinomas and other lung cancers. Receiver operating characteristic (ROC)-based positive tests were performed to determine all feasible threshold values for distinguishing non- or minimally invasive adenocarcinoma (MIA) from other lung cancers. Sensitivity, specificity, and accuracy were then compared by means of McNemar's test.

RESULTS

Each index showed significant differences between the two groups (p < 0.0001). Specificities and accuracies of solid Dlong for UTE-MRIDual2nd echo and CTMediastinal were significantly higher than those of solid Dlong for UTE-MRISingle and UTE-MRIDual1st echo and all C/T ratios except CTMediastinal (p < 0.05). Moreover, the specificities and accuracies of solid Dlong and C/T ratio were significantly higher than those of Dlong for each method (p < 0.05).

CONCLUSION

Pulmonary MRI with UTE is considered at least as valuable as thin-section CT for quantitative differentiation of non- and minimally invasive adenocarcinomas from other stage IA lung cancers.

CLINICAL RELEVANCE STATEMENT

Pulmonary MRI with UTE's capability for quantitative differentiation of non- and minimally invasive adenocarcinomas from other lung cancers in stage IA lung cancer patients is equal or superior to that of thin-section CT.

KEY POINTS

• Correlations were excellent for pathologically examined nodules with the largest dimensions (Dlong) and a solid component (solid Dlong) for all indexes (0.95 ≤ r ≤ 0.99, p < 0.0001). • Pathologically examined Dlong and solid Dlong obtained with all methods showed significant differences between non- and minimally invasive adenocarcinomas and other lung cancers (p < 0.0001). • Solid tumor components are most accurately measured by UTE-MRIDual2nd echo and CTMediastinal, whereas the ground-glass component is imaged by UTE-MRIDual1st echo and CTlung with high accuracy. UTE-MRIDual predicts tumor invasiveness with 100% sensitivity and 87.5% specificity at a C/T threshold of 0.5.

Hyperpolarized Gas Imaging in Lung Diseases: Functional and Artificial Intelligence Perspective

Pathophysiologic changes in lung diseases are often accompanied by changes in ventilation and gas exchange. Comprehensive evaluation of lung function cannot be obtained through chest X-ray and computed tomography. Proton-based lung MRI is particularly challenging due to low proton density within the lung tissue. In this review, we discuss an emerging technology--hyperpolarized gas MRI with inhaled 129Xe, which provides functional and microstructural information and has the potential as a clinical tool for detecting the early stage and progression of certain lung diseases. We review the hyperpolarized 129Xe MRI studies in patients with a range of pulmonary diseases, including chronic obstructive pulmonary disease, asthma, cystic fibrosis, pulmonary hypertension, radiation-induced lung injury and interstitial lung disease, and the applications of artificial intelligence were reviewed as well.

Lung Magnetic Resonance Imaging: Technical Advancements and Clinical Applications

ABSTRACT

Since lung magnetic resonance imaging (MRI) became clinically available, limited clinical utility has been suggested for applying MRI to lung diseases. Moreover, clinical applications of MRI for patients with lung diseases or thoracic oncology may vary from country to country due to clinical indications, type of health insurance, or number of MR units available. Because of this situation, members of the Fleischner Society and of the Japanese Society for Magnetic Resonance in Medicine have published new reports to provide appropriate clinical indications for lung MRI. This review article presents a brief history of lung MRI in terms of its technical aspects and major clinical indications, such as (1) what is currently available, (2) what is promising but requires further validation or evaluation, and (3) which developments warrant research-based evaluations in preclinical or patient studies. We hope this article will provide Investigative Radiology readers with further knowledge of the current status of lung MRI and will assist them with the application of appropriate protocols in routine clinical practice.

Segmentation-Based Analysis of T2- and T1-Weighted Dynamic Magnetic Resonance Images Provides Adequate Observer Agreement in the Evaluation of Interstitial Lung Disease

OBJECTIVE

The aim of the study is to quantify observer agreement in the magnetic resonance imaging (MRI) classification of inflammatory or fibrotic interstitial lung disease (ILD).

METHODS

Our study is a preliminary analysis of a larger prospective cohort. The MRI images of 18 patients with ILD (13 females; mean age, 65 years) were acquired in a 1.5 T scanner and included axial fat-saturated T2-weighted (T2-WI, n = 18) and coronal fat-saturated T1-weighted images before and 1, 3, 5, and 10 minutes after gadolinium administration (n = 16). The MRI studies were evaluated with 2 different methods: a qualitative evaluation (visual assessment and measurement of few regions of interest; evaluations were performed independently by 5 radiologists and 3 times by 1 radiologist) and a segmentation-based analysis with software extraction of signal intensity values (evaluations were performed independently by 2 radiologists and twice by 1 radiologist). Interstitial lung disease was classified as inflammatory or fibrotic, based on previously described imaging criteria.

RESULTS

Regarding the qualitative evaluation, intraobserver agreement was excellent (κ = 0.92, P < 0.05) for T2-WI and fair (κ = 0.29, P < 0.05) for T1 dynamic study, while interobserver agreement was moderate (κ = 0.56, P < 0.05) and poor (κ = 0.11, P = 0.18), respectively. In contrast, upon segmentation-based analysis, intraobserver and interobserver agreement were excellent for T2-WI (κ = 0.886, P < 0.001; κ = 1.00, P < 0.001; respectively); for T1-WI, intraobserver agreement was excellent (κ = 0.87, P < 0.05) and interobserver agreement was good (κ = 0.75, P < 0.05).

CONCLUSIONS

Segmentation-based MRI analysis is more reproducible than a qualitative evaluation with visual assessment and measurement of few regions of interest.

Lung T2 * mapping using 3D ultrashort TE with tight intervals δTE

PURPOSE

To develop 3D ultrashort-TE (UTE) sequences with tight TE intervals (δTE), allowing for accurateT 2 * $$ {\mathrm{T}}_2^{\ast } $$ mapping of lungs under free breathing.

METHODS

We have implemented a four-echo UTE sequence with δTE (< 0.5 ms). A Monte-Carlo simulation was performed to identify an optimal number of echoes that would result in a significant improvement in the accuracy of theT 2 * $$ {\mathrm{T}}_2^{\ast } $$ fit within an acceptable scan time. A validation study was conducted on a phantom with known shortT 2 * $$ {\mathrm{T}}_2^{\ast } $$ values (< 5 ms). The scanning protocol included a combination of a standard multi-echo UTE with six echoes (2.2-ms intervals) and a new four-echo UTE (TE < 2 ms) with tight TE intervals δTE. The human imaging was performed at 3 T on 6 adult volunteers.T 2 * $$ {\mathrm{T}}_2^{\ast } $$ mapping was performed with mono-exponential and bi-exponential models.

RESULTS

The simulation for the proposed 10-echo acquisition predicted over 2-fold improvement in the accuracy of estimating the shortT 2 * $$ {\mathrm{T}}_2^{\ast } $$ compared with the regular six-echo acquisition. In the phantom study, theT 2 * $$ {\mathrm{T}}_2^{\ast } $$ was measured up to three times more accurately compared with standard six-echo UTE. In human lungs,T 2 * $$ {\mathrm{T}}_2^{\ast } $$ maps were successfully obtained from 10 echoes, yielding average valuesT 2 * $$ {\mathrm{T}}_2^{\ast } $$  = 1.62 ± 0.48 ms for mono-exponential andT 2 s * $$ {\mathrm{T}}_{2s}^{\ast } $$  = 1.00 ± 0.53 ms for bi-exponential models.

CONCLUSION

A UTE sequence using δTE was implemented and validated on shortT 2 * $$ {\mathrm{T}}_2^{\ast } $$ phantoms. The sequence was successfully applied for lung imaging; the bi-exponential signal model fit for human lung imaging may provide valuable insights into the diseased human lungs.

Low-field 0.55 T MRI for assessment of pulmonary groundglass and fibrosis-like opacities: Inter-reader and inter-modality concordance

PURPOSE

To evaluate detection and characterization of groundglass and fibrosis-like opacities imaged by non-contrast 0.55 Tesla MRI, and versus clinically-acquired chest CT images, in a cohort of post-Covid patients.

MATERIALS AND METHODS

64 individuals (26 women, mean age 53 ± 14 years, range 19-85) with history of Covid-19 pneumonia were recruited through a survivorship registry, with 106 non-contrast low-field 0.55 T cardiopulmonary MRI exams acquired from 9/8/2020-9/28/2021. MRI exams were obtained at an average interval of 9.5 ± 4.5 months from initial symptom report (range 1-18 months). Of these, 20 participants with 22 MRI exams had corresponding clinically-acquired CT chest imaging obtained within 30 days of MRI (average interval 18 ± 9 days, range 0-30). MR and CT images were reviewed and scored by two thoracic radiologists, for presence and extent of lung opacity by quadrant, opacity distribution, and presence versus absence of fibrosis-like subpleural reticulation and subpleural lines. Scoring was performed for each of four lung quadrants: right upper and middle lobe, right lower lobe, left upper lobe and lingula, and left lower lobe. Agreement between readers and modalities was assessed with simple and linear weighted Cohen's kappa (k) coefficients.

RESULTS

Inter-reader concordance on CT for opacity presence, opacity extent, opacity distribution, and presence of subpleural lines and reticulation was 99%, 78%, 97%, 99%, and 94% (k 0.96, 0.86, 0.94, 0.97, 0.89), respectively. Inter-reader concordance on MR, among all 106 exams, for opacity presence, opacity extent, opacity distribution, and presence of subpleural lines and reticulation was 85%, 48%, 70%, 86%, and 76% (k 0.57, 0.32, 0.46, 0.47, 0.37), respectively. Inter-modality agreement between CT and MRI for opacity presence, opacity extent, opacity distribution, and presence subpleural lines and reticulation was 86%, 52%, 79%, 93%, and 76% (k 0.43, 0.63, 0.65, 0.80, 0.52).

CONCLUSION

Low-field 0.55 T non-contrast MRI demonstrates fair to moderate inter-reader concordance, and moderate to substantial inter-modality agreement with CT, for detection and characterization of groundglass and fibrosis-like opacities.

Three-dimensional ultrashort echo time magnetic resonance imaging in assessment of idiopathic pulmonary fibrosis, in comparison with high-resolution computed tomography

Background

We aimed to evaluate the image quality, feasibility, and diagnostic performance of three-dimensional ultrashort echo time magnetic resonance imaging (3D UTE-MRI) to assess idiopathic pulmonary fibrosis (IPF) compared with high-resolution computed tomography (HRCT) and half-Fourier single-shot turbo spin-echo (HASTE) MRI.

Methods

A total of 36 patients with IPF (34 men; mean age: 62±8 years, age range: 43 to 78 years) were prospectively included and underwent HRCT and chest MRI on the same day. Chest MRI was performed with a free-breathing 3D spiral UTE pulse sequence and HASTE sequence on a 1.5 T MRI. Two radiologists independently evaluated the image quality of the HRCT, HASTE, and 3D UTE-MRI. They assessed the representative imaging features of IPF, including honeycombing, reticulation, traction bronchiectasis, and ground-glass opacities. Image quality of the 3D UTE-MRI, HASTE, and HRCT were assessed using a 5-point visual scoring method. Kappa and weighted kappa analysis were used to measure intra- and inter-observer and inter-method agreements. Sensitivity (SE), specificity (SP), and accuracy (AC) were used to assess the performance of 3D UTE-MRI for detecting image features of IPF and monitoring the extent of pulmonary fibrosis. Linear regressions and Bland-Altman plots were generated to assess the correlation and agreement between the assessment of the extent of pulmonary fibrosis made by the 2 observers.

Results

The image quality of HRCT was higher than that of HASTE and UTE-MRI (HRCT vs. UTE-MRI vs. HASTE: 4.9±0.3 vs. 4.1±0.7 vs. 3.0±0.3; P<0.001). Interobserver agreement of HRCT, HASTE, and 3D UTE-MRI when assessing pulmonary fibrosis was substantial and excellent (HRCT: 0.727≤ κ ≤1, P<0.001; HASTE: 0.654≤ κ ≤1, P<0.001; 3D UTE-MRI: 0.719≤ κ ≤0.824, P<0.001). In addition, reticulation (SE: 97.1%; SP: 100%; AC: 97.2%; κ =0.654), honeycombing (SE: 83.3%; SP: 100%; AC: 86.1%; κ =0.625) patterns, and traction bronchiectasis (SE: 94.1%; SP: 100%; AC: 94.4%, κ =0.640) were also well-visualized on 3D UTE-MRI, which was significantly superior to HASTE. Compared with HRCT, the sensitivity of 3D UTE-MRI to detect signs of pulmonary fibrosis (n=35) was 97.2%. The interobserver agreement in elevation of the extent of pulmonary fibrosis with HRCT and 3D UTE-MRI was R²=0.84 (P<0.001) and R²=0.84 (P<0.001), respectively. The extent of pulmonary fibrosis assessed with 3D UTE-MRI [median =9, interquartile range (IQR): 6.25 to 10.00] was lower than that from HRCT (median =12, IQR: 9.25 to 13.00; U=320.00, P<0.001); however, they had a positive correlation (R=0.72, P<0.001).

Conclusions

As a radiation-free non-contrast enhanced imaging method, although the image quality of 3D UTE-MRI is inferior to that of HRCT, it has high reproducibility to identify the imaging features of IPF and evaluate the extent of pulmonary fibrosis.

ACR Appropriateness Criteria® Diffuse Lung Disease

Diffuse lung disease, frequently referred to as interstitial lung disease, encompasses numerous disorders affecting the lung parenchyma. The potential etiologies of diffuse lung disease are broad with several hundred established clinical syndromes and pathologies currently identified. Imaging plays a critical role in diagnosis and follow-up of many of these diseases, although multidisciplinary discussion is the current standard for diagnosis of several DLDs. This document aims to establish guidelines for evaluation of diffuse lung diseases for 1) initial imaging of suspected diffuse lung disease, 2) initial imaging of suspected acute exacerbation or acute deterioration in cases of confirmed diffuse lung disease, and 3) clinically indicated routine follow-up of confirmed diffuse lung disease without acute deterioration. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

State-of-the-art MR Imaging for Thoracic Diseases

Since thoracic MR imaging was first used in a clinical setting, it has been suggested that MR imaging has limited clinical utility for thoracic diseases, especially lung diseases, in comparison with x-ray CT and positron emission tomography (PET)/CT. However, in many countries and states and for specific indications, MR imaging has recently become practicable. In addition, recently developed pulmonary MR imaging with ultra-short TE (UTE) and zero TE (ZTE) has enhanced the utility of MR imaging for thoracic diseases in routine clinical practice. Furthermore, MR imaging has been introduced as being capable of assessing pulmonary function. It should be borne in mind, however, that these applications have so far been academically and clinically used only for healthy volunteers, but not for patients with various pulmonary diseases in Japan or other countries. In 2020, the Fleischner Society published a new report, which provides consensus expert opinions regarding appropriate clinical indications of pulmonary MR imaging for not only oncologic but also pulmonary diseases. This review article presents a brief history of MR imaging for thoracic diseases regarding its technical aspects and major clinical indications in Japan 1) in terms of what is currently available, 2) promising but requiring further validation or evaluation, and 3) developments warranting research investigations in preclinical or patient studies. State-of-the-art MR imaging can non-invasively visualize lung structural and functional abnormalities without ionizing radiation and thus provide an alternative to CT. MR imaging is considered as a tool for providing unique information. Moreover, prospective, randomized, and multi-center trials should be conducted to directly compare MR imaging with conventional methods to determine whether the former has equal or superior clinical relevance. The results of these trials together with continued improvements are expected to update or modify recommendations for the use of MRI in near future.

Lung magnetic resonance imaging in systemic sclerosis: a new promising approach to evaluate pulmonary involvement and progression

INTRODUCTION/OBJECTIVES

Interstitial lung disease (ILD) is frequent and highly disabling in systemic sclerosis (SSc). Magnetic resonance imaging (MRI) is not routinely used to evaluate the lung, due to poorer spatial resolution compared to high-resolution computed tomography (HRCT). We aimed to compare lung MRI signal with HRCT and evaluate the role of MRI in predicting ILD progression.

METHODS

Thirty SSc patients underwent lung MRI and HRCT. STIR and T1 mapping sequences were acquired before and after gadolinium injection. Patients were classified as normal (group 1 with normal HRCT and MRI), discordant (group 2 without ILD signs on HRCT but areas of hyperintensity on MRI), and abnormal (group 3 with ILD signs on HRCT and areas of hyperintensity on MRI). Patients were followed up for ILD progression.

RESULTS

Mean STIR and T1 values were different between the three groups (p < 0.0001). STIR values correlated with HRCT score (R = 0.79, p < 0.0001), lung ultrasound B-lines (R = 0.73, p < 0.0001), and %DLco (R = - 0.63, p = 0.0001). Nine events were recorded during a follow-up of 25 ± 20 months. Continuous STIR values were independently associated with events (HR 1.018; CI 1.005-1.031, p = 0.005). A STIR value >90 ms discriminated patients at a higher risk of worsening pulmonary involvement (HR 8.80; CI 1.81-42.74; p < 0.007).

CONCLUSIONS

Lung MRI can detect SSc-related ILD, with good correlations with other ILD markers. STIR values, independently of HRCT appearance, may predict worsening lung involvement. Lung MRI, although very preliminary, is a promising tool that in a near future could help selecting patients for an early treatment of SSc-related ILD and a more appropriate use of HRCT. Key points • Lung MRI has the potential to differentiate inflammation-predominant versus fibrosis-predominant lesions, but it is not currently used in routine clinical practice to assess SSc-related ILD. • Lung MRI STIR and T1 values are significantly different between patients with and without SSc-related ILD. STIR values, independently of HRCT appearance, are also able to predict worsening lung involvement over time. • These preliminary data suggest that, in a near future, MRI could support the choice for an early treatment of SSc-related ILD, as well as a more appropriate use of HRCT.

Expanding Applications of Pulmonary MRI in the Clinical Evaluation of Lung Disorders: Fleischner Society Position Paper

Pulmonary MRI provides structural and quantitative functional images of the lungs without ionizing radiation, but it has had limited clinical use due to low signal intensity from the lung parenchyma. The lack of radiation makes pulmonary MRI an ideal modality for pediatric examinations, pregnant women, and patients requiring serial and longitudinal follow-up. Fortunately, recent MRI techniques, including ultrashort echo time and zero echo time, are expanding clinical opportunities for pulmonary MRI. With the use of multicoil parallel acquisitions and acceleration methods, these techniques make pulmonary MRI practical for evaluating lung parenchymal and pulmonary vascular diseases. The purpose of this Fleischner Society position paper is to familiarize radiologists and other interested clinicians with these advances in pulmonary MRI and to stratify the Society recommendations for the clinical use of pulmonary MRI into three categories: (a) suggested for current clinical use, (b) promising but requiring further validation or regulatory approval, and (c) appropriate for research investigations. This position paper also provides recommendations for vendors and infrastructure, identifies methods for hypothesis-driven research, and suggests opportunities for prospective, randomized multicenter trials to investigate and validate lung MRI methods.

Magnetic resonance imaging of interstitial lung diseases: A state-of-the-art review

Magnetic resonance imaging (MRI) has been emerging as an imaging modality to assess interstitial lung diseases (ILD). An optimal chest MRI protocol for ILDs should include non-contrast breath-holding sequences, steady-state free-precession sequences, and contrast-enhanced sequences. One of the main MRI applications in ILDs is the differentiation between areas of active inflammation (i.e. reversible stage) and fibrosis. Alveolitis presents high signal intensity on T2-weighted sequences (WS) and early-enhancement on contrast-enhanced MR sequences, while fibrotic-predominant lesions present low signal and late-enhancement in these sequences, respectively. MRI can be useful in connective tissue diseases, idiopathic pulmonary fibrosis, and sarcoidosis. The aim of this state-of-the-art review was to perform a state-of-the-art review on the use of MRI in ILDs, and propose the optimal MRI protocols for imaging ILDs.

Novel Imaging Approaches in Systemic Sclerosis-Associated Interstitial Lung Disease

PURPOSE OF THE REVIEW

Novel imaging approaches, such as quantitative computed tomography (CT), magnetic resonance imaging (MRI), and molecular imaging, are being applied to interstitial lung diseases to provide prognostic, functional, and molecular information. Here, we review such imaging approaches and their applicability to systemic sclerosis-associated interstitial lung disease (SSc-ILD).

RECENT FINDINGS

Quantitative CT can be used to quantify the radiographic response to SSc-ILD therapy. Due to advances in MRI sequence development, MRI can detect the presence of SSc-ILD with high accuracy. MRI can also be utilized to provide functional information as to SSc-ILD and paired with molecular probes to provide non-invasive molecular information. MRI and ultrasound have promising test characteristics for diagnosing ILD in SSc without the use of ionizing radiation. Novel imaging approaches can detect SSc-ILD without the use of ionizing radiation, provide non-invasive functional and molecular information, and quantify treatment response in SSc-ILD. These techniques hold promise for translation into clinical care and clinical trials.

Experimental and quantitative imaging techniques in interstitial lung disease

Interstitial lung diseases (ILDs) are a heterogeneous group of conditions, with a wide and complex variety of imaging features. Difficulty in monitoring, treating and exploring novel therapies for these conditions is in part due to the lack of robust, readily available biomarkers. Radiological studies are vital in the assessment and follow-up of ILD, but currently CT analysis in clinical practice is qualitative and therefore somewhat subjective. In this article, we report on the role of novel and quantitative imaging techniques across a range of imaging modalities in ILD and consider how they may be applied in the assessment and understanding of ILD. We critically appraised evidence found from searches of Ovid online, PubMed and the TRIP database for novel and quantitative imaging studies in ILD. Recent studies have explored the capability of texture-based lung parenchymal analysis in accurately quantifying several ILD features. Newer techniques are helping to overcome the challenges inherent to such approaches, in particular distinguishing peripheral reticulation of lung parenchyma from pleura and accurately identifying the complex density patterns that accompany honeycombing. Robust and validated texture-based analysis may remove the subjectivity that is inherent to qualitative reporting and allow greater objective measurements of change over time. In addition to lung parenchymal feature quantification, pulmonary vessel volume analysis on CT has demonstrated prognostic value in two retrospective analyses and may be a sign of vascular changes in ILD which, to date, have been difficult to quantify in the absence of overt pulmonary hypertension. Novel applications of existing imaging techniques, such as hyperpolarised gas MRI and positron emission tomography (PET), show promise in combining structural and functional information. Although structural imaging of lung tissue is inherently challenging in terms of conventional proton MRI techniques, inroads are being made with ultrashort echo time, and dynamic contrast-enhanced MRI may be used for lung perfusion assessment. In addition, inhaled hyperpolarised ¹²⁹Xenon gas MRI may provide multifunctional imaging metrics, including assessment of ventilation, intra-acinar gas diffusion and alveolar-capillary diffusion. PET has demonstrated high standard uptake values (SUVs) of ¹⁸F-fluorodeoxyglucose in fibrosed lung tissue, challenging the assumption that these are ‘burned out’ and metabolically inactive regions. Regions that appear structurally normal also appear to have higher SUV, warranting further exploration with future longitudinal studies to assess if this precedes future regions of macroscopic structural change. Given the subtleties involved in diagnosing, assessing and predicting future deterioration in many forms of ILD, multimodal quantitative lung structure-function imaging may provide the means of identifying novel, sensitive and clinically applicable imaging markers of disease. Such imaging metrics may provide mechanistic and phenotypic information that can help direct appropriate personalised therapy, can be used to predict outcomes and could potentially be more sensitive and specific than global pulmonary function testing. Quantitative assessment may objectively assess subtle change in character or extent of disease that can assist in efficacy of antifibrotic therapy or detecting early changes of potentially pneumotoxic drugs involved in early intervention studies.

The use of chest magnetic resonance imaging in interstitial lung disease: a systematic review

Thin-slices multi-detector computed tomography (MDCT) plays a key role in the differential diagnosis of interstitial lung disease (ILD). However, thin-slices MDCT has a limited ability to detect active inflammation, which is an important target of newly developed ILD drug therapy. Magnetic resonance imaging (MRI), thanks to its multi-parameter capability, provides better tissue characterisation than thin-slices MDCT.Our aim was to summarise the current status of MRI applications in ILD and to propose an ILD-MRI protocol. A systematic literature search was conducted for relevant studies on chest MRI in patients with ILD.We retrieved 1246 papers of which 55 original papers were selected for the review. We identified 24 studies comparing image quality of thin-slices MDCT and MRI using several MRI sequences. These studies described new MRI sequences to assess ILD parenchymal abnormalities, such as honeycombing, reticulation and ground-glass opacity. Thin-slices MDCT remains superior to MRI for morphological imaging. However, recent studies with ultra-short echo-time MRI showed image quality comparable to thin-slices MDCT. Several studies demonstrated the added value of chest MRI by using functional imaging, especially to detect and quantify inflammatory changes.We concluded that chest MRI could play a role in ILD patients to differentiate inflammatory and fibrotic changes and to assess efficacy of new ILD drugs.

ACR Appropriateness Criteria® Chronic Dyspnea-Noncardiovascular Origin

Chronic dyspnea may result from a variety of disorders of cardiovascular, pulmonary, gastrointestinal, neuromuscular, systemic, and psychogenic etiology. This article discusses guidelines for the initial imaging of six variants for chronic dyspnea of noncardiovascular origin: (1) Chronic dyspnea of unclear etiology; (2) Chronic dyspnea with suspected chronic obstructive pulmonary disease; (3) Chronic dyspnea with suspected central airways disease; (4) Chronic dyspnea with suspected interstitial lung disease; (5) Chronic dyspnea with suspected disease of the pleura or chest wall; and (6) Chronic dyspnea with suspected diaphragm dysfunction. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Morphologic Characterization of Pulmonary Nodules With Ultrashort TE MRI at 3T

OBJECTIVE

Ultrashort TE (UTE) MRI has been shown to deliver high-resolution images comparable to CT images. Here we evaluate the potential of UTE-MRI for precise lung nodule characterization.

SUBJECTS AND METHODS

Fifty-one patients (mean [± SD] age, 68.7 ± 10.8 years) with 119 nodules or masses (mean size, 17.4 ± 16.3 mm; range, 4-88 mm) prospectively underwent CT (1-mm slice thickness) and UTE-MRI (TE, 192 μs; 1 mm³ resolution). Two radiologists assessed nodule dimensions and morphologic features (i.e., attenuation, margins, and internal lucencies), in consensus for CT and in a blinded fashion for UTE-MRI. Sensitivity, specificity, and kappa statistics were calculated in reference to CT.

RESULTS

Readers 1 and 2 underestimated the nodules' long axial diameter with UTEMRI by 1.2 ± 3.4 and 2.1 ± 4.2 mm, respectively (p < 0.001). The sensitivity and specificity of UTE-MRI for subsolid attenuation were 95.9% and 70.3%, respectively, for reader 1 and 97.1% and 71.4%, respectively, for reader 2 (κ = 0.71 and 0.68). With regard to margin characteristics, for lobulation, sensitivity was 70.6% and 54.9%, and specificity was 93.2% and 96.3% for readers 1 and 2, respectively; for spiculation, sensitivity was 61.5% and 48.0%, and specificity was 95.2% and 95.0%; and for pleural tags, sensitivity was 87.0% and 73.3%, and specificity was 93.8% and 95.0%. Finally, for internal lucencies, sensitivity was 72.7% and 61.3%, and specificity was 96.1% and 97.3% for readers 1 and 2, respectively (κ = 0.64-0.81 for reader 1 and 0.48-0.72 for reader 2). Interreader agreement for attenuation, margin characteristics, and lucencies was substantial to almost perfect with few exceptions (κ = 0.51-0.90).

CONCLUSION

UTE-MRI systematically underestimated dimension measurements by approximately 1-2 mm but otherwise showed high diagnostic properties and interreader agreement, yet unprecedented by MRI, for nodule morphologic assessment.

Pulmonary fibrosis: tissue characterization using late-enhanced MRI compared with unenhanced anatomic high-resolution CT

PURPOSE

We aimed to prospectively evaluate anatomic chest computed tomography (CT) with tissue characterization late gadolinium-enhanced magnetic resonance imaging (MRI) in the evaluation of pulmonary fibrosis (PF).

METHODS

Twenty patients with idiopathic pulmonary fibrosis (IPF) and twelve control patients underwent late-enhanced MRI and high-resolution CT. Tissue characterization of PF was depicted using a segmented inversion-recovery turbo low-angle shot MRI sequence. Pulmonary arterial blood pool nulling was achieved by nulling main pulmonary artery signal. Images were read in random order by a blinded reader for presence and extent of overall PF (reticulation and honeycombing) at five anatomic levels. Overall extent of IPF was estimated to the nearest 5% as well as an evaluation of the ratios of IPF made up of reticulation and honeycombing. Overall grade of severity was dependent on the extent of reticulation and honeycombing.

RESULTS

No control patient exhibited contrast enhancement on lung late-enhanced MRI. All IPF patients were identified with late-enhanced MRI. Mean signal intensity of the late-enhanced fibrotic lung was 31.8±10.6 vs. 10.5±1.6 for normal lung regions, P < 0.001, resulting in a percent elevation in signal intensity from PF of 204.8%±90.6 compared with the signal intensity of normal lung. The mean contrast-to-noise ratio was 22.8±10.7. Late-enhanced MRI correlated significantly with chest CT for the extent of PF (R=0.78, P = 0.001) but not for reticulation, honeycombing, or coarseness of reticulation or honeycombing.

CONCLUSION

Tissue characterization of IPF is possible using inversion recovery sequence thoracic MRI.

Connective tissue disease associated interstitial pneumonia: a challenge for both rheumatologists and pulmonologists

Interstitial lung disease (ILD) can be either idiopathic, the result of exposure or may be associated with extrapulmonary diseases. Among the latter, connective tissue diseases (CTDs) make up the largest part. The identification, follow-up and treatment of CTD-associated ILD (CTD-ILD) are a challenge for every physician as ILD can occur before, during and after the diagnosis of CTD. Early detection of pulmonary involvement is an essential task for the treating rheumatologist and recognition of the underlying CTD can pose a challenge for the treating pulmonologist. Multidisciplinary engagement towards the patient is therefore indispensable for optimal clinical care. (Sarcoidosis Vasc Diffuse Lung Dis 2017; 34: 326-335).

Standard-, Reduced-, and No-Dose Thin-Section Radiologic Examinations: Comparison of Capability for Nodule Detection and Nodule Type Assessment in Patients Suspected of Having Pulmonary Nodules

Purpose To compare the capability of pulmonary thin-section magnetic resonance (MR) imaging with ultrashort echo time (UTE) with that of standard- and reduced-dose thin-section computed tomography (CT) in nodule detection and evaluation of nodule type. Materials and Methods The institutional review board approved this study, and written informed consent was obtained from each patient. Standard- and reduced-dose chest CT (60 and 250 mA) and MR imaging with UTE were used to examine 52 patients; 29 were men (mean age, 66.4 years ± 7.3 [standard deviation]; age range, 48-79 years) and 23 were women (mean age, 64.8 years ± 10.1; age range, 42-83 years). Probability of nodule presence was assessed for all methods with a five-point visual scoring system. All nodules were then classified as missed, ground-glass, part-solid, or solid nodules. To compare nodule detection capability of the three methods, consensus for performances was rated by using jackknife free-response receiver operating characteristic analysis, and κ analysis was used to compare intermethod agreement for nodule type classification. Results There was no significant difference (F = 0.70, P = .59) in figure of merit between methods (standard-dose CT, 0.86; reduced-dose CT, 0.84; MR imaging with UTE, 0.86). There was no significant difference in sensitivity between methods (standard-dose CT vs reduced-dose CT, P = .50; standard-dose CT vs MR imaging with UTE, P = .50; reduced-dose CT vs MR imaging with UTE, P >.99). Intermethod agreement was excellent (standard-dose CT vs reduced-dose CT, κ = 0.98, P < .001; standard-dose CT vs MR imaging with UTE, κ = 0.98, P < .001; reduced-dose CT vs MR imaging with UTE, κ = 0.99, P < .001). Conclusion Pulmonary thin-section MR imaging with UTE was useful in nodule detection and evaluation of nodule type, and it is considered at least as efficacious as standard- or reduced-dose thin-section CT. ^© RSNA, 2017 Online supplemental material is available for this article.

State-of-the-Art Imaging of the Lung for Connective Tissue Disease (CTD)

Involvement of the respiratory system is common in connective tissue diseases (CTDs), and the resultant lung injury can affect every part of the lung: the pleura, alveoli, interstitium, vasculature, lymphatic tissue, and large and/or small airways. Most of the parenchymal manifestations of CTD are similar to those found in interstitial lung diseases (ILDs), especially idiopathic interstitial pneumonias, and can be classified using the same system. Although there is some overlap, each CTD is associated with a characteristic pattern of pulmonary involvement. For this reason, thin-section CT as well as pulmonary function tests and serum markers are utilized for diagnosis, disease severity assessment, and therapeutic efficacy evaluation of ILD associated with CTD. In addition, newly developed pulmonary magnetic resonance imaging (MRI) procedures have been recommended as useful alternative imaging options for patients with CTD. This review article will (1) address radiological findings for chest radiography and conventional or thin-section CT currently used for six major types of CTD, rheumatoid arthritis, scleroderma (progressive systemic sclerosis), polymyositis/dermatomyositis, systemic lupus erythematosus, Sjögren syndrome and mixed connective tissue disease; (2) briefly deal with radiation dose reduction for thin-section CT examination; and (3) discuss clinically applicable or state-of-the-art MR imaging for CTD patients.

Pulmonary high-resolution ultrashort TE MR imaging: Comparison with thin-section standard- and low-dose computed tomography for the assessment of pulmonary parenchyma diseases

BACKGROUND

To determine the accuracy of pulmonary MR imaging with ultrashort echo time (UTE) for lung and mediastinum assessments using computed tomography (CT) as the reference standard, for various pulmonary parenchyma diseases.

METHODS

Eight-five consecutive patients (46 males: mean age, 69 years and 39 females: mean age, 69 years) with various pulmonary parenchyma diseases were examined with chest standard- and low-dose CTs and pulmonary MR imaging with UTE. This was followed by visual assessment using a 5-point system of the presence of nodules or masses, ground-glass opacity, micronodules, nodules, patchy shadow or consolidation, emphysema or bullae, bronchiectasis, reticular opacity, and honeycomb and traction bronchiectasis. Presence of aneurysms, pleural or pericardial effusions, pleural thickening or tumor, and lymph adenopathy was also evaluated using a 5-point system. To compare the capability of the methods for lung parenchyma and mediastinum evaluation, intermethod agreement was evaluated by means of kappa statistics and χ2 test. Receiver operating characteristic analyses were used to compare diagnostic performance of all methods.

RESULTS

Intermethod agreements between pulmonary MR imaging and standard-dose and low-dose CT were significant and either substantial or almost perfect (0.67 ≤ κ ≤ 0.98; P < 0.0001). Areas under the curve for emphysema or bullae, bronchiectasis or traction bronchiectasis and reticular opacity on standard-dose CT were significantly larger than those on low-dose CT (emphysema or bullae: P = 0.0002; reticular opacity: P < 0.0001) and pulmonary MR imaging (emphysema or bullae: P < 0.0001; bronchiectasis: P = 0.008; reticular opacity: P < 0.0001).

CONCLUSION

Pulmonary MR imaging with UTE is useful for lung and mediastinum assessment and evaluation of radiological findings for patients with various pulmonary parenchyma diseases.

T2 mapping of CT remodelling patterns in interstitial lung disease

OBJECTIVES

To evaluate lung T2 mapping for quantitative characterization and differentiation of ground-glass opacity (GGO), reticulation (RE) and honeycombing (HC) in usual interstitial pneumonia (UIP) and non-specific interstitial pneumonia (NSIP).

METHODS

Twelve patients with stable UIP or NSIP underwent thin-section multislice CT and 1.5-T MRI of the lung. A total of 188 regions were classified at CT into normal (n = 29) and pathological areas, including GGO (n = 48), RE (n = 60) and HC (n = 51) predominant lesions. Entire lung T2 maps based on multi-echo single shot TSE sequence (TE: 20, 40, 79, 140, 179 ms) were generated from each subject with breath-holds at end-expiration and ECG-triggering.

RESULTS

The median T2 relaxation of GGO was 67 ms (range 60-72 ms). RE predominant lesions had a median relaxation of 74 ms (range 69-79 ms), while for HC pattern this was 79 ms (range 74-89 ms). The median T2 relaxation for normal lung areas was 41 ms (ranged 38-49 ms), and showed significant difference to pathological areas (p < 0.001). A statistical difference was found between the T2 relaxation of GGO, RE and HC (p < 0.05).

CONCLUSIONS

The proposed method provides quantitative information for pattern differentiation, potentially allowing for monitoring of progression and response to treatment, in interstitial lung disease.

KEY POINTS

• Multi-echo single shot TSE sequence allows for entire lung T2 mapping. • Lung remodelling patterns in ILD show different T2 relaxation. • Quantitative T2 mapping may provide information for monitoring of ILD.

Multistage three-dimensional UTE lung imaging by image-based self-gating

PURPOSE

To combine image-based self-gating (img-SG) with ultrashort echo time (UTE) three-dimensional (3D) acquisition for multistage lung imaging during free breathing.

METHODS

Three k-space ordering schemes (modified spiral pattern, quasirandom numbers and multidimensional Golden Angle) providing uniform coverage of k-space were investigated for providing low-resolution sliding-window images for image-based respiratory self-gating. The performance of the proposed techniques were compared with the conventional spiral pattern and standard DC-based self-gated methods in volunteers during free breathing.

RESULTS

Navigator-like respiratory signals were successfully extracted from the sliding-window data by monitoring the lung-liver interface displacement. A temporal resolution of 588 ms was adequate to retrieve gating signals from the lung-liver interface. Images reconstructed with the img-SG technique showed significantly better sharpness and apparent diaphragm excursion than any of the DC-SG methods. Direct comparison of the three implemented ordering schemes did not demonstrate any clear superiority of one with respect to the others.

CONCLUSION

Image-based respiratory self gating in UTE 3D lung images allows successful retrospective respiratory gating, also enabling reconstruction of intermediate respiratory stages.

Connective Tissue Disease-related Thoracic Disease

Pulmonary involvement is a frequent manifestation of connective tissue disease (CTD)-related thoracic disease. It is important to characterize the underlying pattern when pulmonary involvement occurs in a patient with CTD, and to exclude other causes. A systematic approach, evaluating each compartment of the lung (airway, interstitium, pleura, pulmonary vasculature) may be helpful. In complex cases, a multidisciplinary approach should be considered, potentially including the pulmonologist, rheumatologist, radiologist, pathologist, and sometimes the infectious disease specialist or oncologist. New techniques, such as quantitative computed tomography and MRI, are expected to be helpful for evaluation and management of CTD-associated thoracic disease.

Non invasive assessment of lung disease in ataxia telangiectasia by high-field magnetic resonance imaging

PURPOSE

A sensitive imaging technique that assesses ataxia telangiectasia (AT) lung disease without ionizing radiation is highly desirable. We designed a study to evaluate lung changes using magnetic resonance imaging (MRI), and to investigate the relationships among severity and extent of pulmonary abnormalities and clinical, microbiological and functional data in children and young adults with AT.

METHODS

Fifteen AT patients (age, 11.3 years; range, 6-31) underwent 3.0-T MRI, spirometry, and deep throat or sputum culture. Images were scored using a modified Helbich score.

RESULTS

Although only 8 patients (53 %) had recurrent/chronic respiratory symptoms, MRI identified lung abnormalities in all. Bronchiectasis, peribronchial thickening, mucous plugging, and collapse/consolidation were present in 60 %, 87 %, 67 %, and 13 % of cases, respectively, with no difference between subjects with or without respiratory symptoms. No difference in changes of specific scores was found between the two groups, but the total MRI score was higher in patients with respiratory symptoms (6.5 versus 5, respectively; p = 0.02). Total or specific MRI scores were not associated with patients' age. Of all scores, only mucous plugging subscore appeared significantly related to FEV1 (r = 0.7, p = 0.04) and FEF25-75% (r = 0.9, p = 0.001). MRI scores from patients with positive (n = 5) or negative (n = 10) sputum culture were not significantly different.

CONCLUSIONS

MRI is valuable in the assessment of extent and severity of pulmonary changes in children and adults with AT. It represents an helpful tool for the longitudinal evaluation of patients and may be also used as an outcome surrogate to track the effects of medications.