Redha Boubertakh

A subject-specific technique for respiratory motion correction in image-guided cardiac catheterisation procedures

We describe a system for respiratory motion correction of MRI-derived roadmaps for use in X-ray guided cardiac catheterisation procedures. The technique uses a subject-specific affine motion model that is quickly constructed from a short pre-procedure MRI scan. We test a dynamic MRI sequence that acquires a small number of high resolution slices, rather than a single low resolution volume. Additionally, we use prior knowledge of the nature of cardiac respiratory motion by constraining the model to use only the dominant modes of motion. During the procedure the motion of the diaphragm is tracked in X-ray fluoroscopy images, allowing the roadmap to be updated using the motion model. X-ray image acquisition is cardiac gated. Validation is performed on four volunteer datasets and three patient datasets. The accuracy of the model in 3D was within 5mm in 97.6% of volunteer validations. For the patients, 2D accuracy was improved from 5 to 13mm before applying the model to 2-4mm afterwards. For the dynamic MRI sequence comparison, the highest errors were found when using the low resolution volume sequence with an unconstrained model.

Automated analysis of atrial late gadolinium enhancement imaging that correlates with endocardial voltage and clinical outcomes: A 2-center study

Background For late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) assessment of atrial scar to guide management and targeting of ablation in atrial fibrillation (AF), an objective, reproducible method of identifying atrial scar is required. Objective To describe an automated method for operator-independent quantification of LGE that correlates with colocated endocardial voltage and clinical outcomes. Methods LGE CMR imaging was performed at 2 centers, before and 3 months after pulmonary vein isolation for paroxysmal AF (n = 50). A left atrial (LA) surface scar map was constructed by using automated software, expressing intensity as multiples of standard deviation (SD) above blood pool mean. Twenty-one patients underwent endocardial voltage mapping at the time of pulmonary vein isolation (11 were redo procedures). Scar maps and voltage maps were spatially registered to the same magnetic resonance angiography (MRA) segmentation. Results The LGE levels of 3, 4, and 5SDs above blood pool mean were associated with progressively lower bipolar voltages compared to the preceding enhancement level (0.85 ± 0.33, 0.50 ± 0.22, and 0.38 ± 0.28 mV; P = .002, P < .001, and P = .048, respectively). The proportion of atrial surface area classified as scar (ie, >3 SD above blood pool mean) on preablation scans was greater in patients with postablation AF recurrence than those without recurrence (6.6% ± 6.7% vs 3.5% ± 3.0%, P = .032). The LA volume >102 mL was associated with a significantly greater proportion of LA scar (6.4% ± 5.9% vs 3.4% ± 2.2%; P = .007). Conclusions LA scar quantified automatically by a simple objective method correlates with colocated endocardial voltage. Greater preablation scar is associated with LA dilatation and AF recurrence.

Lung Deflation and Cardiovascular Structure and Function in Chronic Obstructive Pulmonary Disease. A Randomized Controlled Trial

RATIONALE Patients with chronic obstructive pulmonary disease develop increased cardiovascular morbidity with structural alterations. OBJECTIVES To investigate through a double-blind, placebo-controlled, crossover study the effect of lung deflation on cardiovascular structure and function using cardiac magnetic resonance. METHODS Forty-five hyperinflated patients with chronic obstructive pulmonary disease were randomized (1:1) to 7 (maximum 14) days inhaled corticosteroid/long-acting β2-agonist fluticasone furoate/vilanterol 100/25 μg or placebo (7-day minimum washout). Primary outcome was change from baseline in right ventricular end-diastolic volume index versus placebo. MEASUREMENTS AND MAIN RESULTS There was a 5.8 ml/m(2) (95% confidence interval, 2.74-8.91; P < 0.001) increase in change from baseline right ventricular end-diastolic volume index and a 429 ml (P < 0.001) reduction in residual volume with fluticasone furoate/vilanterol versus placebo. Left ventricular end-diastolic and left atrial end-systolic volumes increased by 3.63 ml/m(2) (P = 0.002) and 2.33 ml/m(2) (P = 0.002). In post hoc analysis, right ventricular stroke volume increased by 4.87 ml/m(2) (P = 0.003); right ventricular ejection fraction was unchanged. Left ventricular adaptation was similar; left atrial ejection fraction improved by +3.17% (P < 0.001). Intrinsic myocardial function was unchanged. Pulmonary artery pulsatility increased in two of three locations (main +2.9%, P = 0.001; left +2.67%, P = 0.030). Fluticasone furoate/vilanterol safety profile was similar to placebo. CONCLUSIONS Pharmacologic treatment of chronic obstructive pulmonary disease has consistent beneficial and plausible effects on cardiac function and pulmonary vasculature that may contribute to favorable effects of inhaled therapies. Future studies should investigate the effect of prolonged lung deflation on intrinsic myocardial function. Clinical trial registered with www.clinicaltrials.gov (NCT 01691885).

Diagnostic Accuracy of Cardiac Magnetic Resonance Imaging in the Detection and Characterization of Left Atrial Catheter Ablation Lesions: A Multicenter Experience

MRI Detection of Left Atrial Ablation Lesions. Introduction: We tested the hypothesis that cardiovascular magnetic resonance (CMR) imaging can reliably distinguish the presence or absence of left atrial (LA) ablation lesions by blinded analysis of pre‐ and postablation imaging.

UK Biobank’s cardiovascular magnetic resonance protocol

BackgroundUK Biobank’s ambitious aim is to perform cardiovascular magnetic resonance (CMR) in 100,000 people previously recruited into this prospective cohort study of half a million 40-69 year-olds.Methods/designWe describe the CMR protocol applied in UK Biobank’s pilot phase, which will be extended into the main phase with three centres using the same equipment and protocols. The CMR protocol includes white blood CMR (sagittal anatomy, coronary and transverse anatomy), cine CMR (long axis cines, short axis cines of the ventricles, coronal LVOT cine), strain CMR (tagging), flow CMR (aortic valve flow) and parametric CMR (native T1 map).DiscussionThis report will serve as a reference to researchers intending to use the UK Biobank resource or to replicate the UK Biobank cardiovascular magnetic resonance protocol in different settings.

Model-based respiratory motion correction using 3-D echocardiography

In this paper we investigate the use of 3-D echocardiography (echo) data for respiratory motion correction of MRI-derived roadmaps in image-guided interventions. By a combination of system calibration and tracking the MRI and echo coordinate systems are aligned. 3-D echo images at different respiratory positions are registered to an end-exhale 3-D echo image using a registration algorithm that uses a similarity measure based on local orientation and phase differences. We first assess the use of the echo-echo registration alone to perform motion-correction in the MRI coordinate system. Next, we investigate combining the echo-echo similarity measure with a MRI-derived motion model. Using experiments with cardiac MRI and 3-D echo data acquired from 2 volunteers, we demonstrate that significantly faster and more robust performance can be obtained using the motion model.

Robust registration between cardiac MRI images and atlas for segmentation propagation

We propose a new framework to propagate the labels in a heart atlas to the cardiac MRI images for ventricle segmentations based on image registrations. The method employs the anatomical information from the atlas as priors to constrain the initialisation between the atlas and the MRI images using region based registrations. After the initialisation which minimises the possibility of local misalignments, a fluid registration is applied to fine-tune the labelling in the atlas to the detail in the MRI images. The heart shape from the atlas does not have to be representative of that of the segmented MRI images in terms of morphological variations of the heart in this framework. In the experiments, a cadaver heart atlas and a normal heart atlas were used to register to in-vivo data for ventricle segmentation propagations. The results have shown that the segmentations based on the proposed method are visually acceptable, accurate (surface distance against manual segmentations is 1.0 ± 1.0 mm in healthy volunteer data, and 1.6 ± 1.8 mm in patient data), and reproducible (0.7 ± 1.0 mm) for in-vivo cardiac MRI images. The experiments also show that the new initialisation method can correct the local misalignments and help to avoid producing unrealistic deformations in the nonrigid registrations with 21% quantitative improvement of the segmentation accuracy.

Update of the European Association of Cardiovascular Imaging (EACVI) Core Syllabus for the European Cardiovascular Magnetic Resonance Certification Exam

An updated version of the European Association of Cardiovascular Imaging (EACVI) Core Syllabus for the European Cardiovascular Magnetic Resonance (CMR) Certification Exam is now available online. The syllabus lists key elements of knowledge in CMR. It represents a framework for the development of training curricula and provides expected knowledge-based learning outcomes to the CMR trainees, in particular those intending to demonstrate CMR knowledge in the European CMR exam, a core requirement in the CMR certification process.

A technique for respiratory motion correction in image guided cardiac catheterisation procedures

This paper presents a technique for compensating for respiratory motion and deformation in an augmented reality system for cardiac catheterisation procedures. The technique uses a subject-specific affine model of cardiac motion which is quickly constructed from a pre-procedure magnetic resonance imaging (MRI) scan. Respiratory phase information is acquired during the procedure by tracking the motion of the diaphragm in real-time X-ray images. This information is used as input to the model which uses it to predict the position of structures of interest during respiration. 3-D validation is performed on 4 volunteers and 4 patients using a leave-one-out test on manually identified anatomical landmarks in the MRI scan, and 2-D validation is performed by using the model to predict the respiratory motion of structures of the heart which contain catheters that are visible in X-ray images. The technique is shown to reduce 3-D registration errors due to respiratory motion from up to 15mm down to less than 5mm, which is within clinical requirements for many procedures. 2-D validation showed that accuracy improved from 14mm to 2mm. In addition, we use the model to analyse the effects of different types of breathing on the motion and deformation of the heart, specifically increasing the breathing rate and depth of breathing. Our findings suggest that the accuracy of the model is reduced if the subject breathes in a different way during model construction and application. However, models formed during deep breathing may be accurate enough to be applied to other types of breathing.

Dynamic three-dimensional undersampled data reconstruction employing temporal registration

Dynamic 3D imaging is needed for many applications such as imaging of the heart, joints, and abdomen. For these, the contrast and resolution that magnetic resonance imaging (MRI) offers are desirable. Unfortunately, the long acquisition time of MRI limits its application. Several techniques have been proposed to shorten the scan time by undersampling the k‐space. To recover the missing data they make assumptions about the objects motion, restricting it in space, spatial frequency, temporal frequency, or a combination of space and temporal frequency. These assumptions limit the applicability of each technique. In this work we propose a reconstruction technique based on a weaker complementary assumption that restricts the motion in time. The technique exploits the redundancy of information in the object domain by predicting time frames from frames where there is little motion. The proposed method is well suited for several applications, in particular for cardiac imaging, considering that the heart remains relatively still during an important fraction of the cardiac cycle, or joint imaging where the motion can easily be controlled. This paper presents the new technique and the results of applying it to knee and cardiac imaging. The results show that the new technique can effectively reconstruct dynamic images acquired with an undersampling factor of 5. The resulting images suffer from little temporal and spatial blurring, significantly better than a sliding window reconstruction. An important attraction of the technique is that it combines reconstruction and registration, thus providing not only the 3D images but also its motion quantification. The method can be adapted to non‐Cartesian k‐space trajectories and nonuniform undersampling patterns. Magn Reson Med, 2005.