Showing papers by "Matthias Stuber published in 2001"

Coronary Magnetic Resonance Angiography for the Detection of Coronary Stenoses

Abstract: Background An accurate, noninvasive technique for the diagnosis of coronary disease would be an important advance. We investigated the accuracy of coronary magnetic resonance angiography among patients with suspected coronary disease in a prospective, multicenter study. Methods Coronary magnetic resonance angiography was performed during free breathing in 109 patients before elective x-ray coronary angiography, and the results of the two diagnostic procedures were compared. Results A total of 636 of 759 proximal and middle segments of coronary arteries (84 percent) were interpretable on magnetic resonance angiography. In these segments, 78 (83 percent) of 94 clinically significant lesions (those with a ≥50 percent reduction in diameter on x-ray angiography) were also detected by magnetic resonance angiography. Overall, coronary magnetic resonance angiography had an accuracy of 72 percent (95 percent confidence interval, 63 to 81 percent) in diagnosing coronary artery disease. The sensitivity, specificity,...

3D coronary vessel wall imaging utilizing a local inversion technique with spiral image acquisition

Abstract: Current 2D black blood coronary vessel wall imaging suffers from a relatively limited coverage of the coronary artery tree. Hence, a 3D approach facilitating more extensive coverage would be desirable. The straightforward combination of a 3D-acquisition technique together with a dual inversion prepulse can decrease the effectiveness of the black blood preparation. To minimize artifacts from insufficiently suppressed blood signal of the nearby blood pools, and to reduce residual respiratory motion artifacts from the chest wall, a novel local inversion technique was implemented. The combination of a nonselective inversion prepulse with a 2D selective local inversion prepulse allowed for suppression of unwanted signal outside a user-defined region of interest. Among 10 subjects evaluated using a 3D-spiral readout, the local inversion pulse effectively suppressed signal from ventricular blood, myocardium, and chest wall tissue in all cases. The coronary vessel wall could be visualized within the entire imaging volume.

Impact of bulk cardiac motion on right coronary MR angiography and vessel wall imaging.

Abstract: The purpose of this study was to investigate the impact of in-plane coronary artery motion on coronary magnetic resonance angiography (MRA) and coronary MR vessel wall imaging. Free-breathing, navigator-gated, 3D-segmented k-space turbo field echo ((TFE)/echo-planar imaging (EPI)) coronary MRA and 2D fast spin-echo coronary vessel wall imaging of the right coronary artery (RCA) were performed in 15 healthy adult subjects. Images were acquired at two different diastolic time periods in each subject: 1) during a subject-specific diastasis period (in-plane velocity <4 cm/second) identified from analysis of in-plane coronary artery motion, and 2) using a diastolic trigger delay based on a previously implemented heart-rate-dependent empirical formula. RCA vessel wall imaging was only feasible with subject-specific middiastolic acquisition, while the coronary wall could not be identified with the heart-rate-dependent formula. For coronary MRA, RCA border definition was improved by 13% (P < 0.001) with the use of subject-specific trigger delay (vs. heart-rate-dependent delay). Subject-specific middiastolic image acquisition improves 3D TFE/EPI coronary MRA, and is critical for RCA vessel wall imaging.

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

Abstract: 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. © 2001 Wiley-Liss, Inc.

Free-breathing black-blood coronary MR angiography: initial results.

Abstract: The authors developed a free-breathing black-blood coronary magnetic resonance (MR) angiographic technique with a potential for exclusive visualization of the coronary blood pool. Results with the MR angiographic technique were evaluated in eight healthy subjects and four patients with coronary disease identified at conventional angiography. This MR angiographic technique accurately depicted luminal disease in the patients and permitted visualization of extensive continuous segments of the native coronary tree in both the healthy subjects and the patients. Black-blood coronary MR angiography provides an alternative source of contrast enhancement.

Three‐dimensional high‐resolution fast spin‐echo coronary magnetic resonance angiography

Abstract: Due to SNR constraints, current "bright-blood" 3D coronary MRA approaches still suffer from limited spatial resolution when compared to conventional x-ray coronary angiography. Recent 2D fast spin-echo black-blood techniques maximize signal for coronary MRA at no loss in image spatial resolution. This suggests that the extension of black-blood coronary MRA with a 3D imaging technique would allow for a further signal increase, which may be traded for an improved spatial resolution. Therefore, a dual-inversion 3D fast spin-echo imaging sequence and real-time navigator technology were combined for high-resolution free-breathing black-blood coronary MRA. In-plane image resolution below 400 microm was obtained. Magn Reson Med 45:206-211, 2001.

Motion artifact reduction and vessel enhancement for free‐breathing navigator‐gated coronary MRA using 3D k‐space reordering

Abstract: Breathing-induced bulk motion of the myocardium during data acquisition may cause severe image artifacts in coronary magnetic resonance angiography (MRA). Current motion compensation strategies include breath-holding or free-breathing MR navigator gating and tracking techniques. Navigator-based techniques have been further refined by the applications of sophisticated 2D k-space reordering techniques. A further improvement in image quality and a reduction of relative scanning duration may be expected from a 3D k-space reordering scheme. Therefore, a 3D k-space reordered acquisition scheme including a 3D navigator gated and corrected segmented k-space gradient echo imaging sequence for coronary MRA was implemented. This new zonal motion-adapted acquisition and reordering technique (ZMART) was developed on the basis of a numerical simulation of the Bloch equations. The technique was implemented on a commercial 1.5T MR system, and first phantom and in vivo experiments were performed. Consistent with the results of the theoretical findings, the results obtained in the phantom studies demonstrate a significant reduction of motion artifacts when compared to conventional (non-k-space reordered) gating techniques. Preliminary in vivo findings also compare favorably with the phantom experiments and theoretical considerations. Magn Reson Med 45:645-652, 2001.

Methods and devices for combined ecg and ppu controlled magnetic resonance imaging

Abstract: This invention relates to medical imaging of parts of a patient in which imaging data acquisition is gated by a combination of electrocardiogram (ECG) and peripheral pulse (PPU) signals from the patient. ECG and PPU signals obtained from a patient in a medical imaging apparatus, provide one or more synchronization signals dependent on both the ECG and the PPU signals. The synchronization signals indicate occurrences of pre-determined phases of the cyclic movements of the heart only if the PPU signals also indicate that the determined heart phase is physiologically possible. The medical imaging apparatus is controlled by the synchronization signals to collect imaging data synchronized with cyclic movements of the heart from the patient in the examination zone and to reconstruct a medical image of a part of the patient from the collected imaging data. This invention is preferably applied to magnetic resonance imaging and to computed tomographic x-ray imaging.

Coronary Magnetic Resonance Angiography

Abstract: Coronary magnetic resonance angiography (MRA) is a powerful noninvasive technique with high soft-tissue contrast for the visualization of the coronary anatomy without X-ray exposure. Due to the small dimensions and tortuous nature of the coronary arteries, a high spatial resolution and sufficient volumetric coverage have to be obtained. However, this necessitates scanning times that are typically much longer than one cardiac cycle. By collecting image data during multiple RR intervals, one can successfully acquire coronary MR angiograms. However, constant cardiac contraction and relaxation, as well as respiratory motion, adversely affect image quality. Therefore, sophisticated motion-compensation strategies are needed. Furthermore, a high contrast between the coronary arteries and the surrounding tissue is mandatory. In the present article, challenges and solutions of coronary imaging are discussed, and results obtained in both healthy and diseased states are reviewed. This includes preliminary data obtained with state-of-the-art techniques such as steady-state free precession (SSFP), whole-heart imaging, intravascular contrast agents, coronary vessel wall imaging, and high-field imaging. Simultaneously, the utility of electron beam computed tomography (EBCT) and multidetector computed tomography (MDCT) for the visualization of the coronary arteries is discussed.

MR-venography using high resolution True-FISP.

Abstract: A new fast MR-venography approach using a high resolution True-FISP imaging sequence was investigated in 20 patients suffering from 23 deep vein thromboses Diagnosis was proven by x-ray venography, CT or ultrasound examination The presented technique allowed for clear thrombus visualization with a high contrast to the surrounding blood pool even in calf veins Acquisition time was less than 10 minutes for imaging the pelvis and the legs No contrast media was needed The presented high resolution True-FISP MR-venography is a promising non-invasive, fast MR-venography approach for detection of deep venous thrombosis

Superiority of prone position in free-breathing 3D coronary MRA in patients with coronary disease.

Abstract: Navigator-gated and corrected 3D coronary MR angiography (MRA) allows submillimeter image acquisition during free breathing. However, cranial diaphragmatic drift and relative phase shifts of chest-wall motion are limiting factors for image quality and scanning duration. We hypothesized that image acquisition in the prone position would minimize artifacts related to chest-wall motion and suppress diaphragmatic drift. Twelve patients with radiographically-confirmed coronary artery disease and six healthy adult volunteers were studied in both the prone and the supine position during free-breathing navigator-gated and corrected 3D coronary MRA. Image quality and the diaphragmatic positions were objectively compared. In the prone position, there was a 36% improvement in signal-to-noise ratio (SNR; 15.5 ± 2.7 vs. 11.4 ± 2.6; P < 0.01) and a 34% improvement in CNR (12.5 ± 3.3 vs. 9.3 ± 2.5, P < 0.01). The prone position also resulted in a 17% improvement in coronary vessel definition (P < 0.01). Cranial end-expiratory diaphragmatic drift occurred less frequently in the prone position (23% ± 17% vs. 40% ± 26% supine; P <0.05), and navigator efficiency was higher. Prone coronary MRA results in improved SNR and CNR with enhanced coronary vessel definition. Cranial end-expiratory diaphragmatic drift also was reduced, and navigator efficiency was enhanced. When feasible, prone imaging is recommended for free-breathing coronary MRA. J. Magn. Reson. Imaging 2001;13:185–191. © 2001 Wiley-Liss, Inc.

The impact of navigator timing parameters and navigator spatial resolution on 3D coronary magnetic resonance angiography

Abstract: The impact of navigator spatial resolution and navigator evaluation time on image quality in free-breathing navigator-gated 3D coronary magnetic resonance angiography (MRA), including real-time motion correction, was investigated in a moving phantom. Objective image quality parameters signal-to-noise ratio (SNR) and vessel sharpness were compared. It was found that for improved mage quality a short navigator evaluation time is of crucial importance. Navigator spatial resolution showed minimal influence on image quality. J. Magn. Reson. Imaging 2001;14:311–318. © 2001 Wiley-Liss, Inc.

Magnetic resonance coronary lumen and vessel wall imaging.

Abstract: Coronary magnetic resonance angiography (MRA) is a technique aimed at establishing a noninvasive test for the assessment of significant coronary stenoses. There are certain boundary conditions that have hampered the clinical success of coronary MRA and coronary vessel wall imaging. Recent advances in hardware and software allow for consistent visualization of the proximal and mid portions of the native coronary arteries. Current research focuses on the use of intravascular MR contrast agents and black blood coronary angiography. One common goal is to create a noninvasive test which might allow for screening for major proximal and mid coronary artery disease. These novel approaches will represent a major step forward in diagnostic cardiology.

New methods and algorithms for the accurate, real-time motion analysis of the left ventricle with MRI-tagging

Abstract: Despite its tremendous advantages, magnetic resonance tagging remains unserviceable in clinical conditions due to very tedious image pre-processing tasks. We present here a novel algorithm, fully automatic, real-time and extremely accurate, to perform the tagging pattern extraction. We then address the problem of motion computation and analysis using a novel kinetic deformation class. Very accurate registrations enable to perform automatic ventricle segmentation propagation and a highly sharp motion analysis of the walls. Our work mainly focuses on the CSPAMM protocol, which is briefly recalled. Experiments on acquisitions from 15 healthy volunteers are shown.

3D Coronary Vessel Wall Imaging with a Local Inversion Technique and Spiral Image Acquisition

Abstract: Introduction Coronary MRA has shown great potential for non-invasive assessment of the lumen of the coronary arteries (1), but it does not provide any information on the presence or magnitude of atherosclerotic plaque. It is also known that approximately 60-70% of acute coronary syndromes are caused by < 50% luminal diameter stenoses (2). Thus, a noninvasive approach for coronary plaque imaging would be desirable. Recently, MR coronary vessel wall and plaque imaging using dual inversion (Dual-IR) 2D fast spin echo techniques have been reported. It could be demonstrated that respiratory motion artifacts can be minimized by the use of breathholding or respiratory navigators and that both techniques allow for direct assessment of coronary wall thickness and the visualization of atherosclerotic plaque (3-6). However, for clinical use, 3D approaches would be more favorable as they allow for a more extensive coverage of the coronary artery tree and they offer the potential for higher spatial image resolution. The combination of a 3D-acquisition technique together with a Dual-IR pre-pulse can decrease the effectiveness of the Dual-IR preparation, thereby decreasing the black blood properties. We therefore implemented a 2D selective local inversion pre-pulse, which preserves the signal from the area of interest while minimizing unwanted signal from adjacent tissues and blood. We hypothesize that this approach allows for 3D black blood coronary vessel wall imaging.