E.J.R. van Beek

MRI of the lung (1/3): methods

AbstractProton magnetic resonance imaging (MRI) has recently emerged as a clinical tool to image the lungs. This paper outlines the current technical aspects of MRI pulse sequences, radiofrequency (RF) coils and MRI system requirements needed for imaging the pulmonary parenchyma and vasculature. Lung MRI techniques are presented as a “technical toolkit”, from which MR protocols will be composed in the subsequent papers for comprehensive imaging of lung disease and function (parts 2 and 3). This paper is pitched at MR scientists, technicians and radiologists who are interested in understanding and establishing lung MRI methods. Images from a 1.5 T scanner are used for illustration of the sequences and methods that are highlighted. Main Messages • Outline of the hardware and pulse sequence requirements for proton lung MRI• Overview of pulse sequences for lung parenchyma, vascular and functional imaging with protons• Demonstration of the pulse-sequence building blocks for clinical lung MRI protocols

MRI of the lung (2/3). Why … when … how?

AbstractBackgroundAmong the modalities for lung imaging, proton magnetic resonance imaging (MRI) has been the latest to be introduced into clinical practice. Its value to replace X-ray and computed tomography (CT) when radiation exposure or iodinated contrast material is contra-indicated is well acknowledged: i.e. for paediatric patients and pregnant women or for scientific use. One of the reasons why MRI of the lung is still rarely used, except in a few centres, is the lack of consistent protocols customised to clinical needs.MethodsThis article makes non-vendor-specific protocol suggestions for general use with state-of-the-art MRI scanners, based on the available literature and a consensus discussion within a panel of experts experienced in lung MRI.ResultsVarious sequences have been successfully tested within scientific or clinical environments. MRI of the lung with appropriate combinations of these sequences comprises morphological and functional imaging aspects in a single examination. It serves in difficult clinical problems encountered in daily routine, such as assessment of the mediastinum and chest wall, and even might challenge molecular imaging techniques in the near future.ConclusionThis article helps new users to implement appropriate protocols on their own MRI platforms. Main Messages • MRI of the lung can be readily performed on state-of-the-art 1.5-T MRI scanners.• Protocol suggestions based on the available literature facilitate its use for routine• MRI offers solutions for complicated thoracic masses with atelectasis and chest wall invasion.• MRI is an option for paediatrics and science when CT is contra-indicated

Pulmonary ventilation imaged by magnetic resonance: at the doorstep of clinical application

Over the past few years, magnetic resonance imaging (MRI) has emerged as an important instrument for functional ventilation imaging. The aim of this review is to summarize established clinical methods and emerging techniques for research and clinical arenas. Before the advent of MRI, chest radiography and computed tomography (CT) dominated morphological lung imaging, while functional ventilation imaging was accomplished with scintigraphy. Initially, MRI was not used for morphological lung imaging often, due to technical and physical limitations. However, recent developments have considerably improved anatomical MRI, as well as advanced new techniques in functional ventilation imaging, such as inhaled contrast aerosols, oxygen, hyperpolarized noble gases (Helium-3, Xenon-129), and fluorinated gases (sulphur-hexafluoride). Straightforward images demonstrating homogeneity of ventilation and determining ventilated lung volumes can be obtained. Furthermore, new image-derived functional parameters are measurable, such as airspace size, regional oxygen partial pressure, and analysis of ventilation distribution and ventilation/perfusion ratios. There are several advantages to using MRI: lack of radiation, high spatial and temporal resolution and a broad range of functional information. The MRI technique applied in patients with chronic obstructive pulmonary disease, emphysema, cystic fibrosis, asthma, and bronchiolitis obliterans, may yield a higher sensitivity in the detection of ventilation defects than ventilation scintigraphy, CT or standard pulmonary function tests. The next step will be to define the threshold between physiological variation and pathological defects. Using complementary strategies, radiologists will have the tools to characterize the impairment of lung function and to improve specificity.

Diagnostic value of CT for deep vein thrombosis: results of a systematic review and meta-analysis ☆

AIM To estimate the sensitivity and specificity of computed tomography (CT) for the diagnosis of deep vein thrombosis (DVT) in patients with suspected DVT and pulmonary embolus (PE). MATERIALS AND METHODS A search of the medical literature and citation lists was undertaken, and selected studies comparing CT to a reference standard in patients with suspected DVT or PE were retrieved. Data were analysed by random effects meta-analysis. RESULTS Thirteen articles were included in the meta-analysis. Most compared CT to ultrasound in patients with clinically suspected PE. The sensitivity ranged from 71-100%, while specificity ranged from 93-100%. The pooled estimate of sensitivity was 95.9% (95% CI 93 to 97.8%) and the pooled estimate of specificity was 95.2% (93.6 to 96.5%). However, pooled estimates should be interpreted with caution as these were subject to significant heterogeneity (p=0.025 and p<0.001, respectively). Most studies only appeared to report proximal DVT. Too few data were available to estimate sensitivity for distal DVT. CONCLUSIONS CT has a similar sensitivity and specificity to ultrasound in patients with suspected PE where investigation of suspected DVT is required. There is insufficient research to determine the diagnostic accuracy of CT in patients with suspected DVT alone.

MRI of the lung (3/3)—current applications and future perspectives

AbstractBackgroundMRI of the lung is recommended in a number of clinical indications. Having a non-radiation alternative is particularly attractive in children and young subjects, or pregnant women.MethodsProvided there is sufficient expertise, magnetic resonance imaging (MRI) may be considered as the preferential modality in specific clinical conditions such as cystic fibrosis and acute pulmonary embolism, since additional functional information on respiratory mechanics and regional lung perfusion is provided. In other cases, such as tumours and pneumonia in children, lung MRI may be considered an alternative or adjunct to other modalities with at least similar diagnostic value.ResultsIn interstitial lung disease, the clinical utility of MRI remains to be proven, but it could provide additional information that will be beneficial in research, or at some stage in clinical practice. Customised protocols for chest imaging combine fast breath-hold acquisitions from a “buffet” of sequences. Having introduced details of imaging protocols in previous articles, the aim of this manuscript is to discuss the advantages and limitations of lung MRI in current clinical practice.ConclusionNew developments and future perspectives such as motion-compensated imaging with self-navigated sequences or fast Fourier decomposition MRI for non-contrast enhanced ventilation- and perfusion-weighted imaging of the lung are discussed. Main Messages • MRI evolves as a third lung imaging modality, combining morphological and functional information.• It may be considered first choice in cystic fibrosis and pulmonary embolism of young and pregnant patients.• In other cases (tumours, pneumonia in children), it is an alternative or adjunct to X-ray and CT.• In interstitial lung disease, it serves for research, but the clinical value remains to be proven.• New users are advised to make themselves familiar with the particular advantages and limitations.

Feasibility, safety and clinical utility of angiography in patients with suspected pulmonary embolism

The purpose of our study was to assess feasibility, safety and clinical utility of selective pulmonary angiography in patients with suspected pulmonary embolism and a nondiagnostic lung scan. The design was a prospective, descriptive study. The subjects were consecutive patients with clinically suspected pulmonary embolism and a nondiagnostic lung scintigram in whom pulmonary angiography was considered. Angiography was withheld in cases of manifest heart failure, renal failure, mean pulmonary artery pressure above 40 mmHg, or if there were compelling clinical reasons. All patients were followed-up for 6 months. The outcome measures were successful angiography, morbidity, mortality and recurrent pulmonary embolism in patients with normal angiogram in whom anticoagulants were withheld during 6 months of follow-up. Of 487 patients, 196 (40 %) had nondiagnostic lung scan findings. In 46 patients (23 %) pulmonary angiography was withheld. Pulmonary embolism was excluded in 105 patients (70 %), and proven in 40 (27 %) patients. In 5 (3 %) patients the angiogram was inadequate for interpretation. No fatal complications were encountered [95% confidence interval (CI) 0–2.4%]. Nonfatal complications occured in 3 patients (2%; 95% CI 0–3.4%). Pulmonary angiography is safe, rules out pulmonary embolism in two thirds of patients with a nondiagnostic lung scan and can be performed in almost 80% of these patients. It is safe to withhold long-term anticoagulants if a normal angiogram is obtained in this subgroup of patients with clinically suspected pulmonary embolism.

Hyperpolarised 3He MRI versus HRCT in COPD and normal volunteers: PHIL trial

The aim of the present study was to apply hyperpolarised (HP) 3He magnetic resonance imaging (MRI) to identify patients with chronic obstructive pulmonary disease (COPD) and α1-antitrypsin deficiency (α1-ATD) from healthy volunteers and compare HP 3He MRI findings with high-resolution computed tomography (HRCT) in a multicentre study. Quantitative measurements of HP 3He MRI (apparent diffusion coefficient (ADC)) and HRCT (mean lung density (MLD)) were correlated with pulmonary function tests. A prospective three centre study enrolled 122 subjects with COPD (either acquired or genetic) and age-matched never-smokers. All diagnostic studies were completed in 94 subjects (52 with COPD; 13 with α1-ATD; 29 healthy subjects; 63 males; and 31 females; median age 62 yrs). The consensus assessment of radiologists, blinded for other test results, estimated nonventilated lung volume (HP 3He MRI) and percentage diseased lung (HRCT). Quantitative evaluation of all data for each centre consisted of ADC (HP 3He MRI) and MLD measurements (HRCT), and correlation with forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) indicating airway obstruction, and the diffusing capacity of the lung for carbon monoxide (DL,CO) indicating alveolar destruction. Using lung function tests as a reference, regional analysis of HP 3He MRI and HRCT correctly categorised normal volunteers in 100% and 97%, COPD in 42% and 69% and α1-ATD in 69% and 85% of cases, respectively. Direct comparison of HP 3He MRI and CT revealed 23% of subjects with moderate/severe structural abnormalities had only mild ventilation defects. In comparison with lung function tests, ADC was more effective in separating COPD patients from healthy subjects than MLD (p<0.001 versus 0.038). ADC measurements showed better correlation with DL,CO than MLD (r = 0.59 versus 0.29). Hyperpolarised 3He MRI correctly categorised patients with COPD and normal volunteers. It offers additional functional information, without the use of ionising radiation whereas HRCT gives better morphological information. We showed the feasibility of a multicentre study using different magnetic resonance systems.

Aortic stenosis, atherosclerosis, and skeletal bone: is there a common link with calcification and inflammation?

AIMS The pathophysiology of aortic stenosis shares many similarities with atherosclerosis and skeletal bone formation. Using non-invasive imaging, we compared aortic valve calcification and inflammation activity with that measured in atherosclerosis and bone. METHODS AND RESULTS Positron emission and computed tomography was performed using 18F-sodium fluoride (18F-NaF, calcification) and 18F-fluorodeoxyglucose (18F-FDG, inflammation) in 101 patients with calcific aortic valve disease (81 aortic stenosis and 20 aortic sclerosis). Calcium scores and positron emission tomography tracer activity (tissue-to-background ratio; TBR) were measured in the aortic valve, coronary arteries, thoracic aorta, and bone. Over 90% of the cohort had coexistent calcific atheroma, yet correlations between calcium scores were weak or absent (valve vs. aorta r(2) = 0.015, P = 0.222; valve vs. coronaries r(2) = 0.039, P = 0.049) as were associations between calcium scores and bone mineral density (BMD vs. valve r(2) = 0.000, P = 0.766; vs. aorta r(2) = 0.052, P = 0.025; vs. coronaries r(2) = 0.016, P = 0.210). 18F-NaF activity in the valve was 28% higher than in the aorta (TBR: 2.66 ± 0.84 vs. 2.11 ± 0.31, respectively, P < 0.001) and correlated more strongly with the severity of aortic stenosis (r(2) = 0.419, P < 0.001) than 18F-NaF activity outwith the valve (valve vs. aorta r(2) = 0.167, P < 0.001; valve vs. coronary arteries r(2) = 0.174, P < 0.001; valve vs. bone r(2) = 0.001, P = 0.806). In contrast, 18F-FDG activity was lower in the aortic valve than the aortic atheroma (TBR: 1.56 ± 0.21 vs. 1.81 ± 0.24, respectively, P < 0.001) and more closely associated with uptake outwith the valve (valve vs. aorta r(2) = 0.327, P < 0.001). CONCLUSION In patients with aortic stenosis, disease activity appears to be determined by local calcific processes within the valve that are distinct from atherosclerosis and skeletal bone metabolism.

Bone attenuation on routine chest CT correlates with bone mineral density on DXA in patients with COPD

Chronic obstructive pulmonary disease (COPD), although primarily a disease of the lungs, is associated with extrapulmonary effects such as muscle weakness and osteoporosis. Fractures owing to osteoporosis cause significant morbidity and mortality, particularly in patients with COPD. To prevent osteoporotic fractures, it is important to diagnose osteoporosis in an early stage and to start anti‐osteoporotic therapy in at‐risk patients. Because routine chest computed tomography (CT) is increasingly used to assess the extent of emphysema and airways disease in patients with COPD, we investigated whether simple attenuation measurement of the thoracic spine on routine chest CT may provide useful information on bone health in patients with COPD. Fifty‐eight patients with moderate to very severe COPD were included in our study. The average attenuation of thoracic vertebrae 4, 7, and 10 on chest CT was correlated with the lowest bone mineral density (BMD) of the hip and lumbar spine (L1 to L4) on dual‐energy X‐ray absorptiometry (DXA) in patients with COPD. The inter‐ and intra‐observer variabilities of the attenuation measurements were low as shown by Bland‐Altman plots. Pearsons correlation coefficient between the average attenuation of the three thoracic vertebrae and the lowest BMD of the hip and lumbar spine was high (r = 0.827, p < 0.001). A receiver‐operating characteristic (ROC) analysis of the area under the curve for osteoporosis was 0.969 (p < 0.001), corresponding to an attenuation threshold of 147 Hounsfield Units (HU). In conclusion, our data demonstrated that bone attenuation measured on routine chest CT correlated strongly with BMD assessed on DXA in patients with COPD. Routine chest CT may provide useful information on bone health in patients with COPD.

MR imaging of the lungs with hyperpolarized helium-3 gas transported by air

Hyperpolarized noble gas MRI shows promise in the functional imaging of the pulmonary air spaces. The production of hyperpolarized (HP) gas requires specialized laser optical pumping apparatus, which is not likely to be home built in the majority of clinical MRI radiology centres. There are two routes through which HP gas will be made available to hospitals for clinical use: either the apparatus will be installed locally at a considerable expense to the centre, or a central facility will produce the gas and then deliver it to remote MRI sites as and when required. In this study, the feasibility of transporting large quantities of HP gas for in vivo MR imaging from a remote production facility in Mainz, Germany, by airfreight to Sheffield, UK, was successfully demonstrated.