Klaus Kurt Gast

Diffusion-weighted MRI of the lung with hyperpolarized helium-3: a study of reproducibility.

To determine the reproducibility of several parameters of the ADC measurement by calculating the scan‐to‐scan intrasubject variability.

Chronic thromboembolic pulmonary hypertension — assessment by magnetic resonance imaging

Chronic thromboembolic pulmonary hypertension (CTEPH) is a severe disease that has been ignored for a long time. However, with the development of improved therapeutic modalities, cardiologists and thoracic surgeons have shown increasing interest in the diagnostic work-up of this entity. The diagnosis and management of chronic thromboembolic pulmonary hypertension require a multidisciplinary approach involving the specialties of pulmonary medicine, cardiology, radiology, anesthesiology and thoracic surgery. With this approach, pulmonary endarterectomy (PEA) can be performed with an acceptable mortality rate. This review article describes the developments in magnetic resonance (MR) imaging techniques for the diagnosis of chronic thromboembolic pulmonary hypertension. Techniques include contrast-enhanced MR angiography (ce-MRA), MR perfusion imaging, phase-contrast imaging of the great vessels, cine imaging of the heart and combined perfusion-ventilation MR imaging with hyperpolarized noble gases. It is anticipated that MR imaging will play a central role in the initial diagnosis and follow-up of patients with CTEPH.

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.

MRI in lung transplant recipients using hyperpolarized 3He: Comparison with CT

To elucidate the ability of 3He‐MRI to detect ventilation defects in lung transplant recipients, 3He‐MRI was compared to CT for concordance.

Functional Evaluation of Emphysema Using Diffusion-weighted 3helium-magnetic Resonance Imaging, High-resolution Computed Tomography, and Lung Function Tests

Purpose:To assess the emphysematous enlargement of distal airspaces and concomitant large and small airway disease using diffusion-weighted 3Helium-magnetic resonance imaging (MRI), high-resolution computed tomography (HRCT), and lung function tests (LFT). Methods:Seven patients were examined after single lung transplantation (LTx) and 1 before double LTx for various forms of emphysema. Five patients after double LTx served as controls. Patients were assessed by 3Helium-MRI (apparent diffusion coefficient [ADC]), HRCT (mean lung density [MLD], emphysema index [EI]), and LFT. Results:Transplanted lungs: mean ADC = 0.17 cm2/s, MLD = −848 H, EI = 22%. Emphysematous lungs: mean ADC = 0.33 cm2/s, MLD = −922 H; EI = 54%. Good correlations were found between ADC and MLD (r = 0.6), EI (r = 0.8), intrathoracic gas volume (r = 0.7), forced expiratory volume in 1 second (r = 0.7), and forced expiratory flows (r = 0.7). In contrast, HRCT only provided moderate correlations with LFT (EI: r = 0.5; MLD: r [le] 0.4). Conclusion:In this initial study, 3He-MRI yield good correlations with HRCT and agrees better than HRCT with the functional characterization of emphysema regarding hyperinflation, large and small airway disease as provided by LFT.

Assessment of lung microstructure with magnetic resonance imaging of hyperpolarized Helium-3☆

Magnetic resonance imaging of the apparent diffusion coefficient (ADC) of hyperpolarized Helium-3 is a new technique for probing pulmonary microstructure in vivo. The aim of this study was the assessment of potential sources of systematic errors of the ADC measurement. The influence of macroscopic motion was determined by measurements at two different delays after initiating the breath-hold, and before and after cardiac arrest. An intercentre comparison was performed in two age- and lung function-matched groups of lung-healthy volunteers at two research sites. Moreover, measurements of diffusion anisotropy were performed. We found no dependency of the ADC as a function of the delay after stop of inspiration. The influence of cardiac motion was less than 10%. In the intercentre comparison study, an excellent agreement between the two sites was found. First measurements of the diffusion tensor of intrapulmonary Helium-3 are shown.

Dynamic ventilation 3He-magnetic resonance imaging with lung motion correction: Gas flow distribution analysis

Gast KK, Puderbach MU, Rodriguez I, et al. Dynamic ventilation 3He-MRI with lung motion correction: gas flow distribution analysis. Invest Radiol 2002;37:126–134. rationale and objectives. Software was developed to correct for lung motion to improve the description of hyperpolarized 3He gas distribution in the lung. methods. Five volunteers were studied by dynamic ventilation 3He-MRI using an ultrafast FLASH 2D sequence with a temporal resolution of 128 milliseconds. Signal kinetics were evaluated in the trachea and seven parenchymal Regions of Interest. Reference ranges for healthy subjects were defined for motion-corrected and uncorrected images. results. Motion correction was successfully performed. Reference ranges were 0.11–1.21 seconds for tracheal transit time, 0–0.02 seconds for trachea-alveolar interval, 0.22–0.62 seconds for alveolar rise time and 0–76.6 arbitrary units for alveolar amplitude for motion corrected images, and 0–1.09 seconds, 0–0.11 seconds, 0.26–0.85 seconds, 46.4–99.8 arbitrary units for uncorrected images. conclusions. Evaluation of 3He-distribution in the lung using motion correction of dynamic 3He-ventilation imaging is feasible and gives more narrow reference ranges.

3He-MRI in follow-up of lung transplant recipients

The aim of this study was to evaluate the possible contribution of 3He-MRI to detect obliterative bronchiolitis (OB) in the follow-up of lung transplant recipients. Nine single- and double-lung transplanted patients were studied by an initial and a follow-up 3He-MRI study. Images were evaluated subjectively by estimation of ventilation defect area and quantitatively by individually adapted threshold segmentation and subsequent calculation of ventilated lung volume. Bronchiolitis obliterans syndrome (BOS) was diagnosed using pulmonary function tests. At 3He-MRI, OB was suspected if ventilated lung volume had decreased by 10% or more at the follow-up MRI study compared with the initial study. General accordance between pulmonary function testing and 3He-MRI was good, although subjective evaluation of 3He-MRI underestimated improvement in ventilation as obtained by pulmonary function tests. The 3He-MRI indicated OB in 6 cases. According to pulmonary function tests, BOS was diagnosed in 5 cases. All diagnoses of BOS were also detected by 3He-MRI. In 2 of these 5 cases, 3He-MRI indicated OB earlier than pulmonary function tests. The results support the hypothesis that 3He-MRI may be sensitive for early detection of OB and emphasize the need for larger prospective follow-up studies.

Distribution of ventilation in lung transplant recipients: evaluation by dynamic 3He-MRI with lung motion correction.

Rationale and objectives.The ability of motion corrected dynamic 3He-magnetic resonance imaging (MRI) to discriminate distributional patterns of inhaled hyperpolarized 3He between different groups of lung transplant recipients was evaluated. MethodsAn ultrafast low-angle shot 2D sequence (temporal resolution 128 ms) was used for ventilation 3He-MRI of 11 single and 6 double lung transplant recipients. After digital motion correction, signal kinetics were evaluated in a tracheal and 7 pulmonary regions of interest. Results from grafts and native lungs as well as from normal and rejected grafts were compared with each other and to reference values from healthy subjects. ResultsIn emphysema patients, median alveolar rise time, a parameter for increase of alveolar signal, was 0.28 seconds for the graft and 0.48 seconds for the native lung, in fibrosis patients its median was 0.46 seconds for the graft and 0.21 seconds for the native lung. In double lung recipients, alveolar rise time was 0.29 seconds in normal and clinically rejected grafts. ConclusionsDynamic ventilation 3He-MRI discriminated normal lung grafts from diseased native lungs in single lung recipients. Graft rejection in double lung recipients could not be discriminated.

3He‐MRI‐based vs. conventional determination of lung volumes in patients after unilateral lung transplantation: a new approach to regional spirometry

Background: To use 3Helium (3He)‐MRI in patients with unilateral lung grafts to assess the contributions of graft and native lung to total ventilated lung volume, and second to compare conventional measurements of intrapulmonary gas volume (spirometry, body plethysmography) with image‐based volumetry of ventilated lung parenchyma visualized by hyperpolarized 3He‐MRI.