Showing papers by "Matthias Stuber published in 2002"

Three-Dimensional Black-Blood Cardiac Magnetic Resonance Coronary Vessel Wall Imaging Detects Positive Arterial Remodeling in Patients With Nonsignificant Coronary Artery Disease

Abstract: Background— Direct noninvasive visualization of the coronary vessel wall may enhance risk stratification by quantifying subclinical coronary atherosclerotic plaque burden. We sought to evaluate high-resolution black-blood 3D cardiovascular magnetic resonance (CMR) imaging for in vivo visualization of the proximal coronary artery vessel wall. Methods and Results— Twelve adult subjects, including 6 clinically healthy subjects and 6 patients with nonsignificant coronary artery disease (10% to 50% x-ray angiographic diameter reduction) were studied with the use of a commercial 1.5 Tesla CMR scanner. Free-breathing 3D coronary vessel wall imaging was performed along the major axis of the right coronary artery with isotropic spatial resolution (1.0×1.0×1.0 mm3) with the use of a black-blood spiral image acquisition. The proximal vessel wall thickness and luminal diameter were objectively determined with an automated edge detection tool. The 3D CMR vessel wall scans allowed for visualization of the contiguous pr...

Soap-Bubble visualization and quantitative analysis of 3D coronary magnetic resonance angiograms

Abstract: In order to compare coronary magnetic resonance angiography (MRA) data obtained with different scanning methodologies, adequate visualization and presentation of the coronary MRA data need to be ensured. Furthermore, an objective quantitative comparison between images acquired with different scanning methods is desirable. To address this need, a software tool ("Soap-Bubble") that facilitates visualization and quantitative comparison of 3D volume targeted coronary MRA data was developed. In the present implementation, the user interactively specifies a curved subvolume (enclosed in the 3D coronary MRA data set) that closely encompasses the coronary arterial segments. With a 3D Delaunay triangulation and a parallel projection, this enables the simultaneous display of multiple coronary segments in one 2D representation. For objective quantitative analysis, frequently explored quantitative parameters such as signal-to-noise ratio (SNR); contrast-to-noise ratio (CNR); and vessel length, sharpness, and diameter can be assessed. The present tool supports visualization and objective, quantitative comparisons of coronary MRA data obtained with different scanning methods. The first results obtained in healthy adults and in patients with coronary artery disease are presented.

Preliminary report on in vivo coronary MRA at 3 Tesla in humans

Abstract: Current limitations of coronary magnetic resonance angiography (MRA) include a suboptimal signal-to-noise ratio (SNR), which limits spatial resolution and the ability to visualize distal and branch vessel coronary segments. Improved SNR is expected at higher field strengths, which may provide improved spatial resolution. However, a number of potential adverse effects on image quality have been reported at higher field strengths. The limited availability of high-field systems equipped with cardiac-specific hardware and software has previously precluded successful in vivo human high-field coronary MRA data acquisition. In the present study we investigated the feasibility of human coronary MRA at 3.0T in vivo. The first results obtained in nine healthy adult subjects are presented. Magn Reson Med 48:425–429, 2002. © 2002 Wiley-Liss, Inc.

Coronary Magnetic Resonance Angiography in Adolescents and Young Adults With Kawasaki Disease

Abstract: Background— In patients with Kawasaki disease, serial evaluation of the distribution and size of coronary artery aneurysms (CAA) is necessary for risk stratification and therapeutic management. Although transthoracic echocardiography is often sufficient for this purpose initially, visualization of the coronary arteries becomes progressively more difficult as children grow. We sought to prospectively compare coronary magnetic resonance angiography (MRA) and x-ray coronary angiography findings in patients with CAA caused by Kawasaki disease. Methods and Results— Six subjects (age 10 to 25 years) with known CAA from Kawasaki disease underwent coronary MRA using a free-breathing T2-prepared 3D bright blood segmented k-space gradient echo sequence with navigator gating and tracking. All patients underwent x-ray coronary angiography within a median of 75 days (range, 1 to 359 days) of coronary MRA. There was complete agreement between MRA and x-ray angiography in the detection of CAA (n=11), coronary artery ste...

Navigator-gated free-breathing three-dimensional balanced fast field echo (TrueFISP) coronary magnetic resonance angiography

Abstract: Rationale and objectives Recent developments of MR imaging equipment enabled high-quality steady state-free-precession (Balanced FFE, True-FISP) MR-imaging with a substantial 'T2 like' contrast, resulting in a high signal intensity of the blood-pool without the application of exogenous contrast agents. It is hypothesized that Balanced-FFE may be valuable for contrast enhancement in 3D free-breathing coronary MRA. Materials and methods Navigator-gated free-breathing cardiac triggered coronary MRA was performed in 10 healthy adult subjects and three patients with radiograph defined coronary artery disease using a segmented k-space 3D Balanced FFE imaging sequence. Results High contrast-to-noise ratio between the blood-pool and the myocardium (29 +/- 8) and long segment visualization of both coronary arteries could be obtained in about 5 minutes during free breathing using the present navigator-gated Balanced-FFE coronary MRA approach. First patient results demonstrated successful display of coronary artery stenoses. Conclusion Balanced FFE offers a potential alternative for endogenous contrast enhancement in navigator-gated free-breathing 3D coronary MRA. The obtained results together with the relatively short scanning time warrant further studies in larger patient collectives.

Selective three-dimensional visualization of the coronary arterial lumen using arterial spin tagging.

Abstract: Conventional coronary magnetic resonance angiography (MRA) techniques display the coronary blood-pool along with the surrounding structures, including the myocardium, the ventricular and atrial blood-pool, and the great vessels. This representation of the coronary lumen is not directly analogous to the information provided by x-ray coronary angiography, in which the coronary lumen displayed by iodinated contrast agent is seen. Analogous “luminographic” data may be obtained using MR arterial spin tagging (projection coronary MRA) techniques. Such an approach was implemented using a 2D selective “pencil” excitation for aortic spin tagging in concert with a 3D interleaved segmented spiral imaging sequence with free-breathing, and real-time navigator technology. This technique allows for selective 3D visualization of the coronary lumen blood-pool, while signal from the surrounding structures is suppressed. Magn Reson Med 47:322–329, 2002. © 2002 Wiley-Liss, Inc.

Renal arteries: navigator-gated balanced fast field-echo projection MR angiography with aortic spin labeling: initial experience.

Abstract: A cardiac-triggered free-breathing three-dimensional balanced fast field-echo projection magnetic resonance (MR) angiographic sequence with a two-dimensional pencil-beam aortic labeling pulse was developed for the renal arteries. For data acquisition during free breathing in eight healthy adults and seven consecutive patients with renal artery disease, real-time navigator technology was implemented. This technique allows high-spatial-resolution and high-contrast renal MR angiography and visualization of renal artery stenosis without exogenous contrast agent or breath hold. Initial promising results warrant larger clinical studies. © RSNA, 2002

Impact of navigator timing on free-breathing submillimeter 3D coronary magnetic resonance angiography.

Abstract: The purpose of this study was to investigate the impact of navigator timing on image quality in navigator-gated and real-time motion-corrected, free-breathing, three-dimensional (3D) coronary MR angiography (MRA) with submillimeter spatial image resolution. Both phantom and in vivo investigations were performed. 3D coronary MRA with real-time navigator technology was applied using variable navigator time delays (time delay between the navigator and imaging sequences) and varying spatial resolutions. Quantitative objective and subjective image quality parameters were assessed. For high-resolution imaging, reduced image quality was found as a function of increasing navigator time delay. Lower spatial resolution coronary MRA showed only minor sensitivity to navigator timing. These findings were consistent among volunteers and phantom experiments. In conclusion, for submillimeter navigator-gated and real-time motion-corrected 3D coronary MRA, shortening the time delay between the navigator and the imaging portion of the sequence becomes increasingly important for improved spatial resolution.

Coronary magnetic resonance angiography for assessment of the stent lumen: A phantom study

Abstract: Purpose: To evaluate the feasibility of visualizing the stent lumen using coronary magnetic resonance angiography in vitro. Material and methods: Nineteen different coronary stents were implanted in plastic tubes with an inner diameter of 3 mm. The tubes were positioned in a plastic container filled with gel and included in a closed flow circuit (constant flow 18 cm/sec). The magnetic resonance images were obtained with a dual inversion fast spin ‐echo sequence. For intraluminal stent imaging, subtraction images were calculated from scans with and without flow. Subsequently, intraluminal signal properties were objectively assessed and compared. Results: As a function of the stent type, various degrees of in-stent signal attenuation were observed. Tantalum stents demonstrated minimal intraluminal signal attenuation. For nitinol stents, the stent lumen could be identified, but the intraluminal signal was markedly reduced. Steel stents resulted in the most pronounced intraluminal signal voids. Conclusions: With the present technique, radiofrequency penetration into the stents is strongly influenced by the stent material. These findings may have important implications for future stent design and stent imaging strategies.

Comparison of fat suppression strategies in 3D spiral coronary magnetic resonance angiography.

Abstract: Purpose In the present study, the impact of the two different fat suppression techniques was investigated for free breathing 3D spiral coronary magnetic resonance angiography (MRA). As the coronary arteries are embedded in epicardial fat and are adjacent to myocardial tissue, magnetization preparation such as T2-preparation and fat suppression is essential for coronary discrimination. Material and Methods Fat-signal suppression in three-dimensional (3D) thin- slab coronary MRA based on a spiral k-space data acquisition can either be achieved by signal pre-saturation using a spectrally selective inversion recovery pre-pulse or by spectral-spatial excitation. In the present study, the performance of the two different approaches was studied in healthy subjects. Results No significant objective or subjective difference was found between the two fat suppression approaches. Conclusion Spectral pre-saturation seems preferred for coronary MRA applications due to the ease of implementation and the shorter cardiac acquisition window. J. Magn. Reson. Imaging 2002;15:462–466. © 2002 Wiley-Liss, Inc.

High-resolution selective three-dimensional magnetic resonance coronary angiography with navigator-echo technique: segment-by-segment evaluation of coronary artery stenosis.

Abstract: Purpose To investigate the feasibility of high-resolution selective three-dimensional (3D) magnetic resonance coronary angiography (MRCA) in the evaluation of coronary artery stenoses. Materials and Methods In 12 patients with coronary artery stenoses, MRCA of the coronary artery groups, including the coronary segments with stenoses of 50% or greater based on conventional x-ray coronary angiography (CAG), was performed with double-oblique imaging planes by orienting the 3D slab along the major axis of each right coronary artery-left circumflex artery (RCA-LCX) group and each left main trunk-left anterior descending artery (LMT-LAD) group. Ten RCA-LCX and five LMT-LAD MR angiograms were obtained, and the results were compared with those of conventional x-ray angiography. Results Among 70 coronary artery segments expected to be covered, a total of 49 (70%) segments were fully demonstrated in diagnostic quality. The identification of segmental location of stenoses showed as high an accuracy as 96%. The retrospective analysis for stenosis of 50% or greater yielded the sensitivity, specificity, and accuracy of 80%, 85%, and 84%, respectively. Conclusion Selective 3D MRCA has the potential for segment-by-segment evaluation of major portions of the right and left coronary arteries with high accuracy. J. Magn. Reson. Imaging 2002;16:238–245. © 2002 Wiley-Liss, Inc.

Navigator-gated and real-time motion corrected free-breathing MR Imaging of myocardial late enhancement.

Abstract: Purpose: A new magnetic resonance imaging approach for detection of myocardial late enhancement during free-breathing was developed. Methods and Results: For suppression of respiratory motion artifacts, a prospective navigator technology including real-time motion correction and a local navigator restore was implemented. Subject specific inversion times were defined from images with incrementally increased inversion times acquired during a single dynamic scout navigator-gated and real-time motion corrected free-breathing scan. Subsequently, MR-imaging of myocardial late enhancement was performed with navigator-gated and real-time motion corrected adjacent short axis and long axis (two, three and four chamber) views. This alternative approach was investigated in 7 patients with history of myocardial infarction 12 min after i.v. administration of 0.2 mmol/kg body weight gadolinium-DTPA. Conclusion: With the presented navigator-gated and real-time motion corrected sequence for MR-imaging of myocardial late enhancement data can be completely acquired during free-breathing. Time constraints of a breath-hold technique are abolished and optimized patient specific inversion time is ensured.

Navigator‐gated free‐breathing 3D balanced FFE projection renal MRA: Comparison with contrast‐enhanced breath‐hold 3D MRA in a swine model

Abstract: A cardiac-triggered, free-breathing, 3D balanced FFE projection renal MR angiography (MRA) technique with a 2D pencil beam aortic labeling pulse for selective aortic spin tagging was developed. For respiratory motion artifact suppression during free breathing, a prospective real-time navigator was implemented for renal MRA. Images obtained with the new approach were compared with standard contrast-enhanced (CE) 3D breath-hold MRA in seven swine. Signal properties and vessel visualization were analyzed. With the presented technique, high-resolution, high-contrast renal projection MRA with superior vessel length visualization (including a greater visible number of distal branches of the renal arteries) compared to standard breath-hold CE-MRA was obtained. The present results warrant clinical studies in patients with renal artery disease. Magn Reson Med 48:739–743, 2002. © 2002 Wiley-Liss, Inc.

Real-time motion correction in navigator-gated free-breathing double-oblique submillimeter 3D right coronary artery magnetic resonance angiography.

Abstract: RATIONALE AND OBJECTIVES The purpose of this study was the investigation of the impact of real-time adaptive motion correction on image quality in navigator-gated, free-breathing, double-oblique three-dimensional (3D) submillimeter right coronary magnetic resonance angiography (MRA). MATERIALS AND METHODS Free-breathing 3D right coronary MRA with real-time navigator technology was performed in 10 healthy adult subjects with an in-plane spatial resolution of 700 x 700 microm. Identical double-oblique coronary MR-angiograms were performed with navigator gating alone and combined navigator gating and real-time adaptive motion correction. Quantitative objective parameters of contrast-to-noise ratio (CNR) and vessel sharpness and subjective image quality scores were compared. RESULTS Superior vessel sharpness, increased CNR, and superior image quality scores were found with combined navigator gating and real-time adaptive motion correction (vs. navigator gating alone; P < 0.01 for all comparisons). CONCLUSION Real-time adaptive motion correction objectively and subjectively improves image quality in 3D navigator-gated free-breathing double-oblique submillimeter right coronary MRA.

MR Coronary Angiography with the New Intravascular Contrast Agent B-22956/1: First Human Experience

Abstract: We assessed the potential of the new intravascular contrast agent B-2295611 for application in MRCA. TI of blood and nzyocardium was measured for 24 volunteers receiving various doses on a Siemens Symphony scanner using a segmented IR TrueFlSP sequence Blood TI amounted to 35 and 55 ms at 5 and 30 min after 0 1 mmol/kg of B-22956/1, respectively Free-breathing IR 3 0 segmented GRE MR Coronary Angiographies were performed on 12 volunteers on a Philips Gyroscan scanner afier 0.075 mmollkg of B-2295M. SNR and CNR increased by 37 and 92%, respectively, over previously recorded baseline scans with T2 preparation. Introduction: The protein-binding gadolinium chelate B-22956i1 has shown strong promise for application as an intravascular contrast agent for Magnetic Resonance Coronary Angiography (MRCA) in animal imaging experiments [I]. This paper aims at determining the clinical potential of this agent by assessing extent and duration of TI-shortening in blood and myocardium as well as the visualization of the coronary artery tree in freebreathing MR Coronary Angiography of normal volunteers. Materials and Methods Contrast Agent: B-2295611 was administered as a 0.25 M solution in saline at a rate of 20mLimin. TI nzeasurements : Longitudinal relaxation times were measured for six dose groups of four volunteers each. Dose levels of 0.01, 0.02, 0.05, 0.1, 0.125 and 0.15 mmolikg were tested. Relaxation rate measurements were performed on a 1.5T Siemens scanner equipped with a gradient set of 40mTim strength and 200 T i d s slew rate using a 2D Inversion-Recovery segmented TrueFISP sequence with TR of 3.0ms and flip angle: 40" which had been previously validated on phantoms [2]. Blood TI values were measured in the descending aorta by twelve breath-hold acquisitions of 40 successive segments each with an echo train length=8 following the inversion pulse. Myocardium TI values were measured by acquiring three breath-hold acquisitions of 13 segments each having an echo train length=32. MR Coronary Angiography: Free breathing MR Coronary Angiography using a specially adapted [3] Inversion Recovery 3D navigator echo gated and corrected, segmented gradient recalled echo sequence was performed on twelve healthy male volunteers on a 1.5 T Philips Gyroscan ACS NT scanner between 5 and 45 min after administration of 0.075 mmolikg of B-2295611 at a rate of 20mLimin. Ten adjacent slices of 3mm each were acquired for a Field of View of 360mm and a 512 matrix. Acquisition volumes were targeted to cover either the territory of the RCA or the territory of the LAD including the proximal and median part of the LCX. Other acquisition parameters included TRITE: 7.512.lms; flip angle: 40'; inversion time: 180ms; imaging window: 70ms; and gating window : 5mm. Postcontrast scans were compared with precontrast scans taken with the same parameters but substituting the inversion pulse with a T2 preparation scheme [4] (TE: 50ms) for native contrast enhancement. Image analysis included determination of intraluminal SNR of coronaly arteries, vessel-muscle CNR, and visible length (VL) of coronary arteries. Results and Discussion TI nzeasurements: The T I values measured for blood and myocardium prior to as well as at 5, 15-20, and 25-30 min after administration of Qarious doses of B-22956/1 are shown in Table 1. The average value for blood amounted to 35ms at 5 min after a dose of 0.1 mmolikg, while TI of myocardium was more than fourfold at the same time point. Blood T, was as low as 55ms at 30 min after administration. Thus, B-2295611 shows unprecedented efficacy for blood T, shortening, both in terms of magnitude and duration of the effect. Up to 0.1 mmolikg the relaxation rate enhancement of blood scales almost linearly with the dose, reinforcing the notion that there are more than one binding site for this chelate on the HSA molecule. Thus, a positive dose-effect correlation will hold also at doses which are higher than that resulting in an equimolar concentration of 0-2295611 and HSA in plasma (roughly 0.05 mmol/kg). MR Coronaiy Angiography: Free-breathing MR Coronary Angiographies taken after administration of 0.075 mmolikg of B-2295611 showed strong improvement over native scans with T2 preparation over the whole observation period (up to 45 min after administration) both in terms of visually perceived image qualities (Fig.1) and of objective image quality parameters (Table 2). Images of MRCA taken at 30 min after administration clearly visualized the first branching point, the second branch (a. marginalis) and the full extent of the bifurcation after the crux. Table 1 In-vivo longitudinal relaxation times (ms) for blood (native Ti' 1450 ms) and myocardium (native T, 950 ms) after administration of various doses of B2295UI Dose of Blood TI Blood TI Blood TI 0.010 mmolikg 303 ms 375 ms 385 ms 0 020 mmolikg 168 ms 210 ms 235 ms 0.050 mmol1kg 75 ms 105 ms 113ms 0.100 mmolikg 35 ms 55 ms 55 ms 0.125 mmol1kg 30 ms 38 ms 45 ms 0 1 S O mmol1kg 30 ms 30 ins 30 ms B-2295611 5 min post 15-20 min post 25-30 rnin post Dose of Myocard. TI Myocard. TI Myocard.T1 B-22956/1 5 min post 15-20 min post 25-30 min post 0.010 mmolikg 515 ms 480 ms 480 ms 0.020 mmolikg 350 ms 350 ms 350 ms 0.050 mmolikg 233 ms 260 ms 268 ms 0.100 mmolikg 148 ms I60 ms 165 ms 0.125 mmolikg 120 ms 140 ms 190 ms Table 2 Obiective imaEe aualitv parameters for postcontrast and native scans, . . . . . values are average for 12 subjects i S E M Ta preparation B-22956i1 (5-15 min post) lntraluminal SNR 34.5 + 5.6 47.4 f 4 1 Vessel-muscle CNR 21.6 + 5.5 42.1 i-8 1 VL of coronary arteries (mm) 46 f 13 60 f 9 Fig 1 Reformatted multi-planar precontrast T2-prep images ofthe RCA (a) and the LAD/LCX (c); postcontrast rmages of the RCA at 30 min (b) and of the LAD/LCXat 5 nun (4 afler confrasf Conclusion: The high intravascular containment of B-2295611 resulting from its strong binding (hound fraction 94%) to HSA and its slow elimination from plasma (elimination half life 7h) allow for a prolonged imaging window with high intraluminal signal intensity and efficient suppression of myocardial muscle. Our results bode well for successful clinical application of contrast enhanced, free breathing high resolution MR Coronary Angiography.

Technical Principles of MRA

Abstract: In this chapter we discuss the basic principles underlying magnetic resonance angiography (MRA) and the specific boundary conditions that apply to the different vascular beds. Unlike X-ray angiography, MRA does not expose the patient to potentially harmful ionizing radiation nor does it require iodinated contrast. In addition, it has the potential to noninvasively visualize the vessel wall, atherosclerotic plaque, and thrombus, thereby providing new insights into the process and stage of atherosclerotic disease. MRA is primarily based on blood flow and can be divided into “bright blood” and “black blood” methods depending on whether blood appears “bright” or “black” on the MR images.