Peter Koken

Helical cardiac cone beam reconstruction using retrospective ECG gating.

In modern computer tomography (CT) systems, the fast rotating gantry and the increased detector width enable 3D imaging of the heart. Cardiac volume CT has a high potential for non-invasive coronary angiography with high spatial resolution and short scan time. Due to the increased detector width, true cone beam reconstruction methods are needed instead of adapted 2D reconstruction schemes. In this paper, the extended cardiac reconstruction method is introduced. It integrates the idea of retrospectively gated cardiac reconstruction for helical data acquisition into a cone beam reconstruction framework. It leads to an efficient and flexible algorithmic scheme for the reconstruction of single- and multi-phase cardiac volume datasets. The method automatically adapts the number of cardiac cycles used for the reconstruction. The cone beam geometry is fully taken into account during the reconstruction process. Within this paper, results are presented on patient datasets which have been acquired using a 16-slice cone beam CT system.

Whole-heart coronary MR angiography with 2D self-navigated image reconstruction

Several self‐navigation techniques have been proposed to improve respiratory motion compensation in coronary MR angiography. In this work, we implemented a 2D self‐navigation method by using the startup profiles of a whole‐heart balanced Steady‐state free precession sequence, which are primarily used to catalyze the magnetization towards the steady‐state. To create 2D self‐navigation images (2DSN), we added phase encoding gradients to the startup profiles. With this approach we calculated foot–head and left–right motion and performed retrospective translational motion correction. The 2DSN images were reconstructed from 10 startup profiles acquired at the beginning of each shot. Nine healthy subjects were scanned, and the proposed method was compared to a 1D self‐navigation (1DSN) method with foot–head correction only. Foot–head correction was also performed with the diaphragmatic 1D pencil beam navigator (1Dnav) using a tracking factor of 0.6. 2DSN shows improved motion correction compared to 1DSN and 1Dnav for all coronary arteries and all subjects for the investigated diaphragmatic gating window of 10 mm. The visualized vessel length of the right coronary artery could be significantly improved with a multiple targeted 2D self‐navigation approach, compared to 2DSN method. Magn Reson Med, 2012.

Direct comparison of 3D spiral vs. Cartesian gradient-echo coronary magnetic resonance angiography

While 3D thin‐slab coronary magnetic resonance angiography (MRA) has traditionally been performed using a Cartesian acquisition scheme, spiral k‐space data acquisition offers several potential advantages. However, these strategies have not been directly compared in the same subjects using similar methodologies. Thus, in the present study a comparison was made between 3D coronary MRA using Cartesian segmented k‐space gradient‐echo and spiral k‐space data acquisition schemes. In both approaches the same spatial resolution was used and data were acquired during free breathing using navigator gating and prospective slice tracking. Magnetization preparation (T2 preparation and fat suppression) was applied to increase the contrast. For spiral imaging two different examinations were performed, using one or two spiral interleaves, during each R‐R interval. Spiral acquisitions were found to be superior to the Cartesian scheme with respect to the signal‐to‐noise ratio (SNR) and contrast‐to‐noise‐ratio (CNR) (both P < 0.001) and image quality. The single spiral per R‐R interval acquisition had the same total scan duration as the Cartesian acquisition, but the single spiral had the best image quality and a 2.6‐fold increase in SNR. The double‐interleaf spiral approach showed a 50% reduction in scanning time, a 1.8‐fold increase in SNR, and similar image quality when compared to the standard Cartesian approach. Spiral 3D coronary MRA appears to be preferable to the Cartesian scheme. The increase in SNR may be “traded” for either shorter scanning times using multiple consecutive spiral interleaves, or for enhanced spatial resolution. Magn Reson Med 46:789–794, 2001.

Automated assessment of whole-body adipose tissue depots from continuously moving bed MRI: A feasibility study

To present an automated algorithm for segmentation of visceral, subcutaneous, and total volumes of adipose tissue depots (VAT, SAT, TAT) from whole‐body MRI data sets and to investigate the VAT segmentation accuracy and the reproducibility of all depot assessments.

Aperture weighted cardiac reconstruction for cone-beam CT

Multi-row detectors together with fast rotating gantries made cardiac imaging possible for CT. Due to the cardiac motion, ECG gating has to be integrated into the reconstruction of the data measured on a low pitch helical trajectory. Since the first multi-row scanners were introduced, it has been shown that approximative true cone-beam reconstruction methods are most suitable for the task of retrospectively gated cardiac volume CT. In this paper, we present the aperture weighted cardiac reconstruction (AWCR), which is a three-dimensional reconstruction algorithm of the filtered back-projection type. It is capable of handling all illumination intervals of an object point, which occur as a consequence of a low pitch helical cone-beam acquisition. Therefore, this method is able to use as much redundant data as possible, resulting in an improvement of the image homogeneity, the signal to noise ratio and the temporal resolution. Different optimization techniques like the heart rate adaptive cardiac weighting or the automatic phase determination can be adopted to AWCR. The excellent image quality achieved by AWCR is presented for medical datasets acquired with both a 40-slice and a 64-slice cone-beam CT scanner.

Helical cardiac cone beam CT reconstruction with large area detectors: a simulation study

Retrospectively gated cardiac volume CT imaging has become feasible with the introduction of heart rate adaptive cardiac CT reconstruction algorithms. The development in detector technology and the rapid introduction of multi-row detectors has demanded reconstruction schemes which account for the cone geometry. With the extended cardiac reconstruction (ECR) framework, the idea of approximate helical cone beam CT has been extended to be used with retrospective gating, enabling heart rate adaptive cardiac cone beam reconstruction. In this contribution, the ECR technique is evaluated for systems with an increased number of detector rows, which leads to larger cone angles. A simulation study has been carried out based on a 4D cardiac phantom consisting of a thorax model and a dynamic heart insert. Images have been reconstructed for different detector set-ups. Reconstruction assessment functions have been calculated for the detector set-ups employing different rotation times, relative pitches and heart rates. With the increased volume coverage of large area detector systems, low-pitch scans become feasible without resulting in extensive scan times, inhibiting single breath hold acquisitions. ECR delivers promising image results when being applied to systems with larger cone angles.

The radon-split method for helical cone-beam CT and its application to nongated reconstruction

The mathematical analysis of exact filtered back-projection algorithms is strictly related to Radon inversion. We show how filter-lines can be defined for the helical trajectory, which serve for the extraction of contributions of particular kinds of Radon-planes. Due to the Fourier-slice theorem, Radon-planes with few intersections with the helix are associated with low-frequency contributions to transversal slices. This insight leads to different applications of the new method. The application presented here enables the incorporation of an arbitrary amount of redundant data in an approximate way. This means that the back-projection is not restricted to an n-Pi interval. A detailed mathematical analysis, in which we demonstrate how the defined filter-lines work, concludes this paper

Water/fat-resolved whole-heart Dixon coronary MRA: an initial comparison.

To improve coronary vessel visualization in whole‐heart coronary magnetic resonance angiography (CMRA), fat suppression is typically applied. However, recent studies have shown that cardiac fat can also have diagnostic value. To enhance CMRA image quality by improved fat suppression and to provide additionally fat‐only information highly resolved, dual‐echo Dixon CMRA approaches have been developed.

A new framework for interleaved scanning in cardiovascular MR: Application to image-based respiratory motion correction in coronary MR angiography.

To describe a new framework for interleaving scans and demonstrate its usefulness for image‐based respiratory motion correction in whole heart coronary MR angiography (CMRA).

A new framework for interleaved scanning in cardiovascular MR

To describe a new framework for interleaving scans and demonstrate its usefulness for image‐based respiratory motion correction in whole heart coronary MR angiography (CMRA).