Radiofrequency ablation of right ventricular outflow tract tachycardia using a magnetic resonance 3D model for interactive catheter guidance.
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Adolescent↗
Biomedical subjects
R M Botnar
Publications and source records attributed to R M Botnar.
Analysis of residual coronary artery motion for breath hold and navigator approaches using real-time coronary MRI.
Coronary artery MRI methods utilize breath holds, or diaphragmatic navigators, to compensate for respiratory motion. To increase image quality and navigator (NAV) gating efficiency, slice tracking is used, with more sophisticated affine motion models recently introduced. This study assesses the extent of remaining coronary artery motion in free breathing NAV and single and multi breath hold coronary artery MRI. Additionally, the effect of the NAV gating window size was examined. To visualize and measure the respiratory induced motion, an image containing a coronary artery cross section was acquired at each heartbeat. The amount of residual coronary artery displacement was used as a direct measure for the performance of the respiratory motion correction method. Free breathing studies with motion compensation (slice tracking with 5 mm gating window) had a similar amount of residual motion (0.76+/-0.17 mm) as a single breath hold (0.52+/-0.20 mm) and were superior to multiple breath holds (1.22+/-0.60 mm). Affine NAV methods allowed for larger gating windows ( approximately 10 mm windows) with similar residual motion (0.74+/-0.17 mm). In this healthy adult cohort (N=10), free-breathing NAV methods offered respiratory motion suppression similar to a single breath hold.
Adolescent↗
Inversion prepared coronary MR angiography: direct visualization of coronary blood flow.
PURPOSE: Visualization of coronary blood flow by means of a slice-selective inversion pre-pulse in concert with bright-blood coronary MRA. MATERIALS AND METHODS: Coronary magnetic resonance angiography (MRA) of the right coronary artery (RCA) was performed in eight healthy adult subjects on a 1.5 Tesla MR system (Gyroscan ACS-NT, Philips Medical Systems, Best, NL) using a free-breathing navigator-gated and cardiac-triggered 3D steady-state free-precession (SSFP) sequence with radial k-space sampling. Imaging was performed with and without a slice-selective inversion pre-pulse, which was positioned along the main axis of the coronary artery but perpendicular to the imaging volume. Objective image quality parameters such as SNR, CNR, maximal visible vessel length, and vessel border definition were analyzed. RESULTS: In contrast to conventional bright-blood 3D coronary MRA, the selective inversion pre-pulse provided a direct measure of coronary blood flow. In addition, CNR between the RCA and right ventricular blood pool was increased and the vessels had a tendency towards better delineation. Blood SNR and CNR between right coronary blood and epicardial fat were comparable in both sequences. CONCLUSION: The combination of a free-breathing navigator-gated and cardiac-triggered 3D SSFP sequence with a slice-selective inversion pre-pulse allows for direct and directional visualization of coronary blood flow with the additional benefit of improved contrast between coronary and right ventricular blood pool.
Adult↗
[Technical aspects of MR coronary angiography].
Within the past several years, MR angiography (MRA) has experienced major technological improvements. Whereas the contrast enhanced MRA of non-coronary vessels has become established in routine clinical diagnostics, MR coronary angiography still represents technical challenges to the MR scientists and clinical investigators. To allow diagnostic quality MR coronary angiography, precise and reliable visualization of small tortuous vessels moving at fast speed is necessary. This article reviews the basic principles of MRA with special consideration to MR coronary artery imaging.
Contrast Media↗
Coronary magnetic resonance angiography for the detection of coronary stenoses.
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 > or = 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, and accuracy for patients with disease of the left main coronary artery or three-vessel disease were 100 percent (95 percent confidence interval, 97 to 100 percent), 85 percent (95 percent confidence interval, 78 to 92 percent), and 87 percent (95 percent confidence interval, 81 to 93 percent), respectively. The negative predictive values for any coronary artery disease and for left main artery or three-vessel disease were 81 percent (95 percent confidence interval, 73 to 89 percent) and 100 percent (95 percent confidence interval, 97 to 100 percent), respectively. CONCLUSIONS: Among patients referred for their first x-ray coronary angiogram, three-dimensional coronary magnetic resonance angiography allows for the accurate detection of coronary artery disease of the proximal and middle segments. This noninvasive approach reliably identifies (or rules out) left main coronary artery or three-vessel disease.
Adult↗
Superiority of prone position in free-breathing 3D coronary MRA in patients with coronary disease.
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.
Adult↗
Three-dimensional high-resolution fast spin-echo coronary magnetic resonance angiography.
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.
Adult↗
Temperature quantification using the proton frequency shift technique: In vitro and in vivo validation in an open 0.5 tesla interventional MR scanner during RF ablation.
Open magnetic resonance (MR) scanners allow MR-guided targeting of tumors, as well as temperature monitoring of radio frequency (RF) ablation. The proton frequency shift (PFS) technique, an accurate and fast imaging method for temperature quantification, was used to synthesize thermal maps after RF ablation in an open 0.5 T MR system under ex vivo and in vivo conditions. Calibration experiments with 1.5% agarose gel yielded a chemical shift factor of 0.011 +/- 0.001 ppm/ degrees C (r2 = 0.96). Three gradient echo (GRE) pulse sequences were tested for thermal mapping by comparison with fiberoptic thermometer (Luxtron Model 760) readings. Temperature uncertainty decreased from high to low bandwidths (BW): +/-5.9 degrees C at BW = 15.6 kHz, +/-1.4 degrees C at BW = 3.9 kHz, and +/-0.8 degrees C at BW = 2.5 kHz. In vitro experiments (N = 9) in the paraspinal muscle yielded a chemical shift factor of 0.008 +/- 0.001 ppm/ degrees C. Temperature uncertainty was determined as +/-2.7 degrees C (BW = 3.9 kHz, TE = 19.3 msec). The same experiments carried out in the paraspinal muscle (N = 9) of a fully anesthetized pig resulted in a temperature uncertainty of +/-4.3 degrees C (BW = 3.9 kHz, TE = 19.3 msec), which is higher than it is in vitro conditions (P < 0.15). Quantitative temperature monitoring of RF ablation is feasible in a 0.5 T open-configured MR scanner under ex vivo and in vivo conditions using the PFS technique.
Animals↗
The impact of navigator timing parameters and navigator spatial resolution on 3D coronary magnetic resonance angiography.
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.
Computer Systems↗
Impact of bulk cardiac motion on right coronary MR angiography and vessel wall imaging.
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.
Adult↗
Motion artifact reduction and vessel enhancement for free-breathing navigator-gated coronary MRA using 3D k-space reordering.
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.
Adult↗
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 (T(2) 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.
Adult↗
3D coronary vessel wall imaging utilizing a local inversion technique with spiral image acquisition.
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.
Adult↗
Scan reproducibility of magnetic resonance imaging assessment of aortic atherosclerosis burden.
Subclinical atherosclerosis precedes the onset of clinical disease by many years. Noninvasive magnetic resonance imaging (MRI) offers the opportunity to visualize and quantify atherosclerotic plaque. However, the reproducibility of MRI measurements of abdominal and thoracic aortic atherosclerosis has not been reported. Electrocardiogram-gated, T2-weighted, turbo spin echo MRI of the descending thoracic and abdominal aorta was performed on 16 subjects, comprising 10 subjects with multivessel coronary artery disease (CAD) and 6 subjects without angiographic CAD. Three identical MRIs were performed on each subject, with subject repositioning between the second and third scans. Aortic anatomic and plaque measurements were performed in a blinded fashion. Fourteen subjects (88%) had MRI evidence of atherosclerotic plaque on at least one image. Slice plaque burden, plaque area, and plaque perimeter were greater in the CAD group (52% vs. 9%, p = 0.002; 264 vs. 18 mm2, p = 0.009; 159 vs. 15 mm, p = 0.006, respectively). Measurements of total aortic lumen area, lumen circumference, plaque area, and plaque perimeter correlated highly among the three scans (all r = 0.96, all p < 0.001). Measurements of slice-specific aortic lumen area and lumen circumference also correlated highly (all r = 0.98, all p < 0.001). Correlations of slice-specific plaque area and plaque perimeter were significant (all p < 0.001) but less robust (r = 0.62-0.85). These data demonstrate that MRI is a reproducible technique for assessing aortic anatomy and total aortic atherosclerosis, but increased slice density should be considered if serial evaluation of slice-specific data is desired.
Aged↗
Free-breathing black-blood coronary MR angiography: initial results.
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.
Adult↗
In vivo magnetic resonance imaging of experimental thrombosis in a rabbit model.
The process of atherosclerotic plaque disruption has been difficult to monitor because of the lack of an animal model and the limited ability to directly visualize the plaque and overlying thrombus in vivo. Our aim was to validate in vivo magnetic resonance imaging (MRI) of the thrombus formation after pharmacological triggering of plaque disruption in the modified Constantinides animal model of plaque disruption. Atherosclerosis was induced in 9 New Zealand White male rabbits (3 kg) with aortic balloon endothelial injury followed by a high cholesterol (1%) diet for 8 weeks. After baseline (pretrigger) MRI, the rabbits underwent pharmacological triggering with Russell's viper venom and histamine, followed by another MRI 48 hours later. Contiguous cross-sectional T2-weighted fast spin echo images of the abdominal aorta were compared by histopathology. In all animals, aortic wall thickening was present on the pretrigger MRI. On MRIs performed 48 hours after triggering, a histologically confirmed intraluminal thrombus was visualized in 6 (67%) of the 9 animals. MRI data correlated with the histopathology regarding aortic wall thickness (R=0.77, P<0.0005), thrombus size (R=0.82, P<0.0001), thrombus length (R=0.86, P<0.005), and anatomic location (R=0.98, P<0.0001). In vivo, MRI reliably determines the presence, location, and size of the thrombus in this animal model of atherosclerosis and plaque disruption. The combination of in vivo MRI and the modified Constantinides animal model could be an important research tool for our understanding of the pathogenesis of acute coronary syndromes.
Anatomy, Cross-Sectional↗
Noninvasive coronary vessel wall and plaque imaging with magnetic resonance imaging.
BACKGROUND: Conventional x-ray angiography frequently underestimates the true burden of atherosclerosis. Although intravascular ultrasound allows for imaging of coronary plaque, this invasive technique is inappropriate for screening or serial examinations. We therefore sought to develop a noninvasive free-breathing MR technique for coronary vessel wall imaging. We hypothesized that such an approach would allow for in vivo imaging of coronary atherosclerosis. METHODS AND RESULTS: Ten subjects, including 5 healthy adult volunteers (aged 35+/-17 years, range 19 to 56 years) and 5 patients (aged 60+/-4 years, range 56 to 66 years) with x-ray-confirmed coronary artery disease (CAD), were studied with a T2-weighted, dual-inversion, fast spin-echo MR sequence. Multiple adjacent 5-mm cross-sectional images of the proximal right coronary artery were obtained with an in-plane resolution of 0.5x1.0 mm. A right hemidiaphragmatic navigator was used to facilitate free-breathing MR acquisition. Coronary vessel wall images were readily acquired in all subjects. Both coronary vessel wall thickness (1.5+/-0.2 versus 1.0+/-0.2 mm) and wall area (21.2+/-3.1 versus 13.7+/-4.2 mm(2)) were greater in patients with CAD (both P:<0.02 versus healthy adults). CONCLUSIONS: In vivo free-breathing coronary vessel wall and plaque imaging with MR has been successfully implemented in humans. Coronary wall thickness and wall area were significantly greater in patients with angiographic CAD. The presented technique may have potential applications in patients with known or suspected atherosclerotic CAD or for serial evaluation after pharmacological intervention.
Adipose Tissue↗
Free-breathing 3D coronary MRA: the impact of "isotropic" image resolution.
During conventional x-ray coronary angiography, multiple projections of the coronary arteries are acquired to define coronary anatomy precisely. Due to time constraints, coronary magnetic resonance angiography (MRA) usually provides only one or two views of the major coronary vessels. A coronary MRA approach that allowed for reconstruction of arbitrary isotropic orientations might therefore be desirable. The purpose of the study was to develop a three-dimensional (3D) coronary MRA technique with isotropic image resolution in a relatively short scanning time that allows for reconstruction of arbitrary views of the coronary arteries without constraints given by anisotropic voxel size. Eight healthy adult subjects were examined using a real-time navigator-gated and corrected free-breathing interleaved echoplanar (TFE-EPI) 3D-MRA sequence. Two 3D datasets were acquired for the left and right coronary systems in each subject, one with anisotropic (1.0 x 1.5 x 3.0 mm, 10 slices) and one with "near" isotropic (1.0 x 1.5 x 1.0 mm, 30 slices) image resolution. All other imaging parameters were maintained. In all cases, the entire left main (LM) and extensive portions of the left anterior descending (LAD) and the right coronary artery (RCA) were visualized. Objective assessment of coronary vessel sharpness was similar (41% +/- 5% vs. 42% +/- 5%; P = NS) between in-plane and through-plane views with "isotropic" voxel size but differed (32% +/- 7% vs. 23% +/- 4%; P < 0.001) with nonisotropic voxel size. In reconstructed views oriented in the through-plane direction, the vessel border was 86% more defined (P < 0.01) for isotropic compared with anisotropic images. A smaller (30%; P < 0.001) improvement was seen for in-plane reconstructions. Vessel diameter measurements were view independent (2.81 +/- 0.45 mm vs. 2.66 +/- 0.52 mm; P = NS) for isotropic, but differed (2.71 +/- 0.51 mm vs. 3.30 +/- 0.38 mm; P < 0.001) between anisotropic views. Average scanning time was 2:31 +/- 0:57 minutes for anisotropic and 7:11 +/- 3:02 minutes for isotropic image resolution (P < 0.001). We present a new approach for "near" isotropic 3D coronary artery imaging, which allows for reconstruction of arbitrary views of the coronary arteries. The good delineation of the coronary arteries in all views suggests that isotropic 3D coronary MRA might be a preferred technique for the assessment of coronary disease, although at the expense of prolonged scan times. Comparative studies with conventional x-ray angiography are needed to investigate the clinical utility of the isotropic strategy.
Adult↗