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Debiao Li

Publications and source records attributed to Debiao Li.

53 records · Page 3Linked to original sources
PubMed2003

Real-time magnetic resonance imaging-guided coronary catheterization in swine.

BACKGROUND: We tested the hypothesis that real-time magnetic resonance imaging (MRI) can guide coronary artery catheterization in swine via a percutaneous femoral artery approach. METHODS AND RESULTS: In 12 pigs, we accessed femoral arteries percutaneously. We used 6- or 7-French coronary Judkins catheters filled with dilute 4% gadolinium (Gd) contrast agent and coaxially inserted 0.030-inch diameter active guidewires as endovascular devices. For catheter tracking, we used a 2-dimensional (2D) inversion recovery-prepared spoiled gradient echo sequence at a temporal resolution of 7 frames/s. For guidewire tracking, we used 2D steady-state free precession imaging at a temporal resolution of 9 frames/s. Coronary artery catheterization under MRI guidance was successful in 12/12 pigs. Successful coronary catheterization was verified by obtaining MR angiographic images after direct catheter-based injections of dilute Gd. CONCLUSIONS: Real-time MRI-guided catheterization of coronary arteries in swine is feasible via a percutaneous femoral artery approach. Selective coronary MR angiography can then be performed with dilute contrast agent injections.

Animals↗
PubMed2003

Coronary MR angiography: true FISP imaging improved by prolonging breath holds with preoxygenation in healthy volunteers.

In 15 healthy volunteers undergoing coronary magnetic resonance (MR) angiography, the breath-hold duration with and without preoxygenation was measured. The effect of preoxygenation on coronary artery imaging was also evaluated. A three-dimensional magnetization-prepared true fast imaging with steady-state precession sequence was employed for coronary MR angiography. All subjects showed an increase in comfortable breath-hold duration with preoxygenation. This extra imaging time allowed coronary artery imaging with increased spatial resolution.

Adult↗
PubMed2003

Reduction of transient signal oscillations in true-FISP using a linear flip angle series magnetization preparation.

An electrocardiogram (ECG)-triggered, magnetization-prepared, segmented, 3D true fast imaging with steady-state precession (true-FISP) sequence with fat saturation was recently proposed for coronary artery imaging. A magnetization preparation scheme consisting of an alpha/2 radiofrequency (RF) pulse followed by 20 constant flip angle dummy RF cycles was used to reduce signal oscillations in the approach to steady state. However, if large resonance offsets on the order of 70-100 Hz are present, significant magnetization oscillations will still occur during data acquisition, which will result in image ghosting and blurring. The goal of this work was to validate that a linear flip angle (LFA) series can be used during magnetization preparation to reduce these image artifacts. Computer simulations, phantom studies, and coronary artery imaging in healthy volunteers were performed to compare this magnetization preparation scheme with that of an alpha/2 pulse followed by constant flip angle dummy RF cycles. The results demonstrated substantial reduction in the apparent image artifacts when using linearly increasing flip angles during magnetization preparation.

Adult↗
PubMed2003

Artifact reduction in true-FISP imaging of the coronary arteries by adjusting imaging frequency.

The presence of resonance frequency offsets often causes artifacts in images acquired with true fast imaging with steady-state precession (true-FISP). One source of resonance offsets is a suboptimal setting of the synthesizer frequency. The goal of this work was to demonstrate that shifting the synthesizer frequency could minimize the off-resonance related image artifacts in true-FISP. A simple scouting method was developed to estimate the optimal synthesizer frequency for the volume of interest (VOI). To improve fat suppression, a similar scouting method was also developed to determine the optimal frequency offset for the fat saturation pulse. Coronary artery imaging was performed in healthy subjects using a 3D true-FISP sequence to validate the effectiveness of the frequency corrections. Substantial reduction in image artifacts and improvement in fat suppression were observed by using the water and fat frequencies estimated by the scouting scans. Frequency shifting is a useful and practical method for improving coronary artery imaging using true-FISP.

Adult↗
PubMed2003

Contrast-enhanced coronary artery imaging using 3D trueFISP.

An ECG-triggered, segmented, magnetization-prepared, 3D, trueFISP sequence was recently developed for coronary artery imaging. Fat saturation was achieved by a chemically selective fat saturation pulse, which is susceptible to field inhomogeneities. In addition, the blood-myocardial contrast was compromised because data were acquired during signal transience to steady state. The goals of this work were to investigate the potential benefits of T(1)-shortening agents in improving blood-myocardial contrast, and to develop a technique to make fat suppression robust to resonance offsets for coronary artery imaging using trueFISP. A magnetization-preparation scheme using saturation and inversion pulses was developed for simultaneous suppression of tissues over a wide range of T(1)'s, including myocardium and fat. An additional advantage of this method is that it is insensitive to heart rate variations. Computer simulations were used to design the magnetization preparation, and volunteer studies were performed to compare precontrast imaging to contrast-enhanced (CE) imaging. Results showed consistent fat suppression and a 78% increase in the blood-myocardial contrast-to-noise ratio (CNR) for postcontrast imaging over precontrast imaging. In conclusion, contrast agents are useful for trueFISP coronary artery imaging.

Adult↗
PubMed2003

Catheter-directed contrast-enhanced coronary MR angiography in swine using magnetization-prepared True-FISP.

Contrast-enhanced (CE) coronary magnetic resonance angiography (MRA) following intraarterial (IA) injection of contrast agent was compared using two sequences in swine: magnetization-prepared fast imaging with steady-state precession (True-FISP), and magnetization-prepared fast low-angle shot (FLASH). Thick-slice projection images were acquired with submillimeter in-plane spatial resolution (0.9 x 0.8 mm(2)). The magnetization-preparation scheme provided a clear delineation of the major coronary arteries with excellent background suppression. The True-FISP acquisition resulted in an increase in signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) by approximately a factor of 2 over FLASH (P < 0.05). Magnetization-prepared True-FISP is a promising technique for catheter-directed CE thick-slice projection coronary MRA.

Animals↗
PubMed2003

Use of internal coils for independent and direct MR imaging-guided endovascular device tracking.

PURPOSE: To test the hypotheses that a single internal guide wire coil (i) permits independent and direct depiction of guide wires and catheters and (ii) improves catheter-tracking accuracy and depiction compared to external receiver coils. MATERIALS AND METHODS: Standard 5-6-F angiographic catheters were filled with dilute 4% gadolinium chelate. A single 0.030-inch-diameter internal guide wire coil was placed inside the catheter. True fast imaging with steady-state precession was used to directly visualize the guide wire. Inversion recovery-prepared fast low-angle shot technique was used to track catheters over a thick slice. In phantom experiments, we compared catheter signal-to-noise ratios (SNRs) with the internal coil and a phased-array surface coil with use of the Wilcoxon signed-rank test. Tip-tracking accuracy was assessed with use of linear regression. In pigs (n = 7), catheters and guide wires were independently tracked in real time. RESULTS: In phantoms, catheter SNR with the internal coil (12.0) was significantly greater than that with the surface coil (4.0; P =.001). Tip-tracking accuracy was also improved with use of the internal coil (R(2) = 0.94 vs 0.50). In swine vasculature, catheters and guide wires could be directly and independently tracked at 1.7-2.0 frames per second. Catheters were clearly visualized with use of the internal coil, with a typical catheter background contrast-to-noise ratio of 6.6. Catheters were not visible with use of the external coil because of the small catheter size compared to the slice thickness. CONCLUSION: Internal guide wire coils permit independent and direct depiction of guide wires and catheters in vivo for MR imaging-guided endovascular interventions. They also improve catheter tracking accuracy and depiction compared to external coils.

Animals↗
PubMed2003

Two- and three-dimensional MR coronary angiography with intraarterial injections of contrast agent in dogs: a feasibility study.

Magnetic resonance (MR) images of coronary arteries were acquired with an inversion recovery-prepared technique after intraarterial injection of contrast material in five dogs. Real-time two-dimensional projection images were obtained with a temporal resolution of 3 frames per second. Three-dimensional electrocardiographically triggered high-spatial-resolution images were obtained with a fraction of the contrast agent required for intravenous injections. Background tissues were adequately suppressed in all images. On the basis of this experimental data, the optimal contrast agent concentration for two-dimensional real-time projection imaging was 6%. This preliminary work shows that contrast material-enhanced MR angiography with intraarterial injections is feasible with the proposed techniques.

Animals↗
PubMed2002

Minimizing contrast agent dose during intraarterial gadolinium-enhanced MR angiography: in vitro assessment.

PURPOSE: To minimize contrast agent dosage for intra-arterial (IA) contrast-enhanced magnetic resonance angiography (CE-MRA) by examining the effects of encoding order (elliptical vs. sequential) and injection duration (100% to 30% of the acquisition time). MATERIALS AND METHODS: Catheter-based IA gadolinium (Gd) injections were performed in an arterial flow phantom. Blood flow rates, injection rates, and injection durations were systematically varied. Signal-to-noise (SNR) measurements were obtained in the aorta, renal artery, and common iliac artery. RESULTS: No significant SNR losses were observed for any of the vessels with 75% injection duration, or for the aorta and iliac artery with 50% injection duration. Excellent images of all vessels were obtained at 50% injection duration. There was no significant SNR difference between encoding schemes. CONCLUSION: Contrast agent dosage can be substantially reduced without loss of SNR by limiting injection to part of the imaging acquisition time.

Aorta, Abdominal↗
PubMed2002

Breath-hold three-dimensional true-FISP imaging of coronary arteries using asymmetric sampling.

PURPOSE: To evaluate the feasibility of using asymmetric sampling in a three-dimensional, magnetization-prepared, segmented true-FISP (fast imaging with steady-state precession) sequence in order to reduce the sensitivity to resonance offsets, while simultaneously improving imaging speed. MATERIALS AND METHODS: Asymmetric sampling reduces the repetition time, leading to reduced resonance offset effects and improved resolution in a fixed imaging time. However, it introduces additional phase terms due to blood flow, which can cause image artifacts. Computer simulations were performed to study the off-resonance and flow effects of asymmetric sampling in true-FISP. Coronary artery imaging was performed in healthy volunteers. RESULTS: Simulations and volunteer studies show that image artifacts due to flow-induced phase variations may be acceptable at low velocities. Volunteer studies demonstrate that relatively high-resolution coronary artery images can then be acquired within a single breath-hold with segmented three-dimensional true-FISP imaging using data asymmetry in the readout direction. CONCLUSION: Asymmetric sampling is a useful modification to true-FISP for reducing the off-resonance artifacts and improving imaging speed when the flow velocities are small.

Adult↗
PubMed2002

Three-dimensional true-FISP imaging of the coronary arteries: improved contrast with T2-preparation.

PURPOSE: To evaluate the effectiveness of a T2-magnetization preparation scheme for improving coronary artery imaging with true fast imaging with steady-state precession (True-FISP). MATERIALS AND METHODS: Simulations were performed to compare the blood-myocardium signal difference with no T2-preparation to that with various T2-preparation times (24, 40, and 60 msec) using an electrocardiogram (ECG)-triggered, segmented True-FISP acquisition. Seven volunteers were imaged to evaluate the effectiveness of T2-preparation for coronary artery delineation using True- FISP and to optimize the T2-preparation time. RESULTS: Simulations showed that T2-preparation improved the signal difference between blood and myocardium over that without T2-preparation. The optimal T2- preparation time was determined to be 40 msec. In volunteer studies, a T2- preparation time of 40 msec provided a significant improvement in contrast- to-noise ratio (CNR) between the coronary arteries and myocardium over that without T2-preparation. It also showed a significant improvement in visualizing the distal portions of the coronary arteries. CONCLUSION: T2-preparation improves coronary artery delineation with True-FISP.

Adult↗
PubMed2002

Passive catheter tracking using MRI: comparison of conventional and magnetization-prepared FLASH.

PURPOSE: To compare a magnetization-prepared gradient-echo (GRE) sequence with a conventional GRE sequence for visualizing contrast agent-filled catheters. MATERIALS AND METHODS: Passive visualization of endovascular catheters using MRI was compared between two imaging sequences: 1) inversion recovery (IR)-fast low angle shot (FLASH), and 2) conventional FLASH. Two-dimensional projection images of the catheters filled with 4% diluted contrast agent in a phantom and the aorta of swine were obtained with each sequence with a temporal resolution of two frames per second. We compared background suppression and catheter visibility using the catheter-to-background signal ratio and the ratings of two radiologists. RESULTS: In the phantom, IR-FLASH allowed for a 200% increase in catheter-to-background ratio (p < 0.01) and improved depiction of catheters over conventional FLASH. In swine, the IR-FLASH images showed a statistically significant improvement of 80% (p < 0.001) over conventional FLASH in all comparisons of the catheter-to-background signal ratio, and an improvement of 160% (p < 0.05) in comparison with the radiologists' observations. CONCLUSION: This study shows that IR-FLASH is a better technique for passive tracking of contrast agent-filled catheters than conventional FLASH.

Animals↗
PubMed2002

Coronary MRA with 3D undersampled projection reconstruction TrueFISP.

Undersampled projection reconstruction (PR) offers improved imaging efficiency allowing a relative tradeoff between signal-to-noise ratio (SNR) or streak artifact and the number of acquired k-space views rather than the tradeoff between resolution or aliasing artifact and the number of acquired k-space lines inherent to Fourier imaging techniques. TrueFISP (true fast imaging with steady state precession) is ideally suited for undersampled PR imaging because of its inherently high SNR. The purpose of this work was to investigate the feasibility of using undersampled three-dimensional (3D) PR TrueFISP for breathhold coronary artery imaging. Phantom studies and a preliminary in vivo comparison demonstrated the improved spatial resolution of PR over Fourier TrueFISP with the same imaging time. In a 24-heartbeat coronary imaging scheme, segmented 3D PR TrueFISP provided a 1.0 x 1.0 mm(2) isotropic in-plane voxel size while acquiring between 93 and 153 views per partition. Streak artifacts were present in some images but were not found to impede coronary artery delineation. In conclusion, 3D undersampled PR TrueFISP provides isotropic in-plane voxel size within a single breathhold and is a promising technique for coronary artery imaging.

Arteries↗
PubMed2002

Catheter-directed gadolinium-enhanced MR angiography.

In the setting of MRI-guided endovascular interventions, catheter-directed Gd-enhanced MRA offers many of the same capabilities as conventional x-ray DSA. Local injections permit rapid depiction of blood vessels and help guide interventions. The primary benefit of IA injections is significant reduction of administered contrast-agent dose compared with conventional IV injections. Another major benefit is facilitated background suppression, including that of adjacent vascular beds. As MRI guidance methods improve, catheter-based Gd injections should gain expanded use in clinical practice.

Catheterization↗
PubMed2002

Validation of injection parameters for catheter-directed intraarterial gadolinium-enhanced MR angiography.

RATIONALE AND OBJECTIVES: Catheter-directed intraarterial (IA) injections of gadolinium contrast agents may be used during endovascular interventions with magnetic resonance (MR) imaging guidance. Injection protocols require further validation. Using a flow phantom and swine, the authors aimed to (a) measure the optimal arterial gadolinium concentration ([Gd]) required for MR angiography and (b) validate a proposed IA injection protocol for gadolinium-enhanced MR angiography. MATERIALS AND METHODS: For in vitro experiments, the authors placed a catheter in the aorta of an aorto-renal-iliac flow phantom. Injected [Gd], injection rates, and aortic blood flow rates were varied independently for 36 separate IA gadolinium injections. The authors performed 2D and 3D MR angiography with a fast spoiled gradient-recalled echo sequence. For subsequent in vivo experiments, they selectively placed catheters within the aorta, renal artery, or common iliac artery of three pigs. Injection rate and injected [Gd] were varied. The authors performed 32 separate IA gadolinium injections for 2D MR angiography. Signal-to-noise ratios (SNRs) were compared for the various combinations of injection rate and injected [Gd]. RESULTS: In vitro, an arterial [Gd] of 2%-4% produced an optimal SNR for 2D MR angiography, and 3%-5% was best for 3D MR angiography. In swine, an arterial [Gd] of 1%-4% produced an optimal SNR. In the phantom and swine experiments, SNR was maintained at higher injection rates by inversely varying the injected [Gd]. CONCLUSION: Dilute arterial [Gd] is required for optimal IA gadolinium-enhanced MR angiography. To maintain an optimal SNR, injection rates and injected [Gd] should be varied inversely. The postulated injection protocol was validated.

Animals↗
PubMed2002

Comparison of intraarterial and IV gadolinium-enhanced MR angiography with digital subtraction angiography for the detection of renal artery stenosis in pigs.

OBJECTIVE: Catheter-based intraarterial injections of gadolinium are useful during MR imaging-guided endovascular procedures to generate rapid vascular road maps. Using an animal model of renal artery stenosis, we tested the hypothesis that intraarterial gadolinium-enhanced MR angiography is as accurate as IV gadolinium-enhanced MR angiography and digital subtraction angiography (DSA). We also tested the hypothesis that intraarterial MR angiography uses less gadolinium than IV MR angiography. MATERIALS AND METHODS: We induced bilateral renal artery stenosis in five pigs. All pigs underwent comparative imaging with DSA, IV MR angiography, and aortic catheter-directed intraarterial MR angiography. For IV and intraarterial MR angiography, we used the same three-dimensional acquisition. We assessed differences in quantitative stenosis measurements among DSA, IV MR angiography, and intraarterial MR angiography using the Wilcoxon's signed rank test. RESULTS: Mean stenosis measurements (+/-SD) were as follows: DSA, 58% +/- 12%; IV MR angiography, 63% +/- 9.3%; and intraarterial MR angiography, 64% +/- 11%. There were no statistically significant differences in accuracy between DSA and IV MR angiography (p = 0.06), DSA and intraarterial MR angiography (p = 0.16), or IV and intraarterial MR angiography (p = 0.70). Intraarterial MR angiography used a mean gadolinium dose of 5.6 mL, compared with 9 mL for IV MR angiography. CONCLUSION: In swine, IV and intraarterial MR angiography have a similar accuracy for detecting renal artery stenosis. Intraarterial MR angiography uses smaller doses of injected gadolinium.

Angiography, Digital Subtraction↗