Sebastian Ley

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.

Value of contrast-enhanced MR angiography and helical CT angiography in chronic thromboembolic pulmonary hypertension.

The aim of this study was to evaluate the diagnostic value of contrast-enhanced MR angiography (ce MRA) and helical CT angiography (CTA) of the pulmonary arteries in the preoperative workup of patients with chronic thromboembolic pulmonary hypertension (CTEPH). The ce MRA and CTA studies of 32 patients were included in this retrospective evaluation. Image quality was scored by two independent blinded observers. Data sets were assessed for number of patent segmental, subsegmental arteries, and number of vascular segments with thrombotic wall thickening, intraluminal webs, and abnormal proximal to distal tapering. Image quality for MRA/CTA was scored excellent in 16 of 16, good in 11 of 14, moderate in 2 of 5, and poor in no examinations. The MRA/CTA showed 357 of 366 patent segmental and 627 of 834 patent subsegmental arteries. CTA was superior to MRA in visualization of thrombotic wall thickening (339 vs 164) and of intraluminal webs (257 vs 162). Abnormal proximal to distal tapering was better assessed by MRA than CTA (189 vs 16). In joint assessment of direct and indirect signs, MRA and CTA were equally effective (353 vs 355). MRA and CTA are equally effective in the detection of segmental occlusions of the pulmonary arteries in CTEPH. CTA is superior for the depiction of patent subsegmental arteries, of intraluminal webs, and for the direct demonstration of thrombotic wall thickening.

Assessment of pulmonary hypertension by CT and MR imaging

In the recent World Health Organization (WHO) classification the group of pulmonary arterial hypertension (PH) comprises the classic primary pulmonary hypertension and several conditions with definite or very high risk factors to develop pulmonary arterial hypertension. Therapeutic advances drive the need for a comprehensive pre-therapeutic evaluation for optimal treatment. Furthermore, follow-up examinations need to be performed to monitor changes in disease status and response to therapy. Up to now, the diagnostic imaging work-up of PH comprises mainly echocardiography, invasive right heart catheterization and ventilation/perfusion scintigraphy. Due to technical advances helical computed tomography (CT) and magnetic resonance imaging (MRI) became more important in the evaluation and for differential diagnosis of pulmonary arterial hypertension. Both modalities are reviewed and recommendations for clinical use are given.

Hybrid segmentation and exploration of the human lungs

Segmentation of the tracheo-bronchial tree of the lungs is notoriously difficult. This is due to the fact that the small size of some of the anatomical structures is subject to partial volume effects. Furthermore, the limited intensity contrast between the participating materials (air, blood, and tissue) increases the segmentation of difficulties. In this paper, we propose a hybrid segmentation method which is based on a pipeline of three segmentation stages to extract the lower airways down to the seventh generation of the bronchi. User interaction is limited to the specification of a seed point inside the easily detectable trachea at the upper end of the lower airways. Similarly, the complementary vascular tree of the lungs can be segmented. Furthermore, we modified our virtual endoscopy system to visualize the vascular and airway system of the lungs along with other features, such as lung tumors.

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.

Time-resolved echo-shared parallel MRA of the lung: observer preference study of image quality in comparison with non-echo-shared sequences

The aim of this study was to evaluate the image quality of time-resolved echo-shared parallel MRA of the lung. The pulmonary vasculature of nine patients (seven females, two males; median age: 44 years) with pulmonary disease was examined using a time-resolved MRA sequence combining echo sharing with parallel imaging (time-resolved echo-shared angiography technique, or TREAT). The sharpness of the vessel borders, conspicuousness of peripheral lung vessels, artifact level, and overall image quality of TREAT was assessed independently by four readers in a side-by-side comparison with non-echo-shared time-resolved parallel MRA data (pMRA) previously acquired in the same patients. Furthermore, the SNR of pulmonary arteries (PA) and veins (PV) achieved with both pulse sequences was compared. The mean voxel size of TREAT MRA was decreased by 24% compared with the non-echo-shared MRA. Regarding the sharpness of the vessel borders, conspicuousness of peripheral lung vessels, and overall image quality the TREAT sequence was rated superior in 75–76% of all cases. If the TREAT images were preferred over the pMRA images, the advantage was rated as major in 61-71% of all cases. The level of artifacts was not increased with the TREAT sequence. The mean interobserver agreement for all categories ranged between fair (artifact level) and good (overall image quality). The maximum SNR of TREAT did not differ from non-echo-shared parallel MRA (PA: TREAT: 273±45; pMRA: 280±71; PV: TREAT: 273±33; pMRA: 258±62). TREAT achieves a higher spatial resolution than non-echo-shared parallel MRA which is also perceived as an improved image quality.

Radiological imaging as the basis for a simulation software of ventilation in the tracheo-bronchial tree

Abstract. The inhaled route is a promising new way for administering drugs to the human body. Flow and particle deposition in the human respiratory tract depends on the individuals anatomy as well as on the drug composition. A European Framework V Program supported project is currently developing a simulation tool for assessment of drug distribution and deposition. This tool relies heavily on the input of radiological data sets, which are obtained in humans. Both high temporal and spatial resolutions are required, and CT and MRI (including hyperpolarized helium-3 MRI) are applied. The radiological data are integrated into computation fluid dynamics software, which is capable of assessing air-flow profiles and compartmental behaviours. This is complemented by pharmacokinetic models, which should result in a simulation tool that will be of use for the theoretical design of new inhaled therapies. This article describes the special imaging requirements of each region of the respiratory tract and the feasibility of these sophisticated radiological techniques with a view of using these data in a simulation model of the lung.

Evaluation of changes in central airway dimensions, lung area and mean lung density at paired inspiratory/expiratory high-resolution computed tomography

Abstract.The aim of this study was to improve the understanding of interdependencies of dynamic changes in central airway dimensions, lung area and lung density on HRCT. The HRCT scans of 156 patients obtained at full inspiratory and expiratory position were evaluated retrospectively. Patients were divided into four groups according to lung function tests: normal subjects (n=47); obstructive (n=74); restrictive (n=19); or mixed ventilatory impairment (n=16). Mean lung density (MLD) was correlated with cross-sectional area of the lung (CSAL), cross-sectional area of the trachea (CSAT) and diameter of main-stem bronchi (DB). The CSAL was correlated with CSAT and DB. MLD correlated with CSAL in normal subjects (r=−0.66, p<0.0001) and patients with obstructive (r=−0.62, p<0.0001), restrictive (r=−0.83, p<0.0001) and mixed ventilatory impairment (r=−0.86, p<0.0001). The MLD correlated with CSAT in the control group (r=−0.50, p<0.0001) and in patients with obstructive lung impairment (r−0.27, p<0.05). In patients with normal lung function a correlation between MLD and DB was found (r=−0.52, p<0.0001). CSAL and CSAT correlated in the control group (r=0.67, p<0.0001) and in patients with obstructive lung disease (r=0.51, p<0.0001). The CSAL and DB correlated in the control group (r=0.42, p<0.0001) and in patients with obstructive lung disease (r=0.24, p<0.05). Correlations for patients with restrictive and mixed lung disease were constantly lower. Dependencies between central and peripheral airway dimensions and lung parenchyma are demonstrated by HRCT. Best correlations are observed in normal subjects and patients with obstructive lung disease. Based on these findings we postulate that the dependencies are the result of air-flow and pressure patterns.

Segmentation and virtual exploration of tracheobronchial trees

Abstract The tracheobronchial tree as part of the lung is part of one of the most important organs of the human body. Inhaled air is distributed to the alveolus where oxygen and carbon dioxide exchange between air and blood takes place. In this paper, we introduce the virtual endoscopy system VIVENDI to perform virtual inspections of tracheobronchial trees based on their segmentation and of the complementing blood vessels. It is based on a hybrid segmentation pipeline which enables the segmentation of vascular and tracheobronchial structures down to the seventh generation of the bronchi.

Diagnostik der pulmonalen Hypertonie

ZusammenfassungGenaue Anamnese, körperliche Untersuchung und Basisuntersuchungen wie EKG, Röntgenthorax und Lungenfunktion sowie die gezielte Fahndung nach Risikofaktoren führen zur Verdachtsdiagnose pulmonale Hypertonie. Der primäre Nachweis erfolgt mittels Dopplerechokardiographie. Wichtig ist die Bestimmung des klinischen Schweregrades entsprechend der WHO-Klassifikation und durch Belastungsuntersuchungen (6-min-Gehtest, Spiroergometrie). Behandelbare Grunderkrankungen wie Lungen-, Herz- und Leberkrankheiten, Kollagenosen und insbesondere chronische Lungenarterienembolien müssen identifiziert werden. Dies umfasst auch die moderne Bildgebung mittels CT und MRT. Bei bedeutsamer pulmonaler Hypertonie ist stets ein Rechtsherzkatheter, ggf. mit pharmakologischem Reversibilitätstest, erforderlich. Ist die Diagnose primär gestellt, wird die Kontaktaufnahme mit einem spezialisierten Zentrum dringend empfohlen.AbstractA meticulous history, physical examination, and basic exams including ECG, chest X-ray and pulmonary function tests as well as the targeted search for risk factors lead to the diagnosis of pulmonary hypertension. An elevated pulmonary arterial pressure is primarily detected by Doppler echocardiography. It is important to assess the clinical severity according to the WHO (modified NYHA) functional class and by exercise testing (6-min walking test, cardiopulmonary exercise test). An interdisciplinary approach is needed to identify treatable underlying conditions such as pulmonary, cardiac, liver, collagen vascular, and chronic thromboembolic disease. This includes modern imaging techniques such as CT and MRI. In cases of significant pulmonary arterial hypertension, right heart catheterisation including pharmacological reversibility testing is indispensable. Once the diagnosis has been established it is advisable to contact a centre specialising in pulmonary hypertension.