Artifact-free coronary magnetic resonance angiography and coronary vessel wall imaging in the presence of a new, metallic, coronary magnetic resonance imaging stent.

BACKGROUND: Coronary in-stent restenosis cannot be directly assessed by magnetic resonance angiography (MRA) because of the local signal void of currently used stainless steel stents. The aim of this study was to investigate the potential of a new, dedicated, coronary MR imaging (MRI) stent for artifact-free, coronary MRA and in-stent lumen and vessel wall visualization. METHODS AND RESULTS: Fifteen prototype stents were deployed in coronary arteries of 15 healthy swine and investigated with a double-oblique, navigator-gated, free-breathing, T2-prepared, 3D cartesian gradient-echo sequence; a T2-prepared, 3D spiral gradient-echo sequence; and a T2-prepared, 3D steady-state, free-precession coronary MRA sequence. Furthermore, black-blood vessel wall imaging by a dual-inversion-recovery, turbo spin-echo sequence was performed. Artifacts of the stented vessel segment and signal intensities of the coronary vessel lumen inside and outside the stent were assessed. With all investigated sequences, the vessel lumen and wall could be visualized without artifacts, including the stented vessel segment. No signal intensity alterations inside the stent when compared with the vessel lumen outside the stent were found. CONCLUSIONS: The new, coronary MRI stent allows for completely artifact-free coronary MRA and vessel wall imaging.

New metallic MR stents for artifact-free coronary MR angiography: feasibility study in a swine model.

RATIONALE AND OBJECTIVES: The objective of this study was to investigate the potential for artifact-free coronary magnetic resonance angiography (cMRA) in the presence of dedicated metallic MR stents in vitro and in a swine model. METHODS: All investigations were performed at 1.5 T, applying a standard cMRA gradient echo sequence with a T2 preparation pulse. Two prototypes of each hand-woven, mechanically woven, and lasered Aachen Resonance Coronary MR Stents made out of an MR-compatible metallic alloy and dilated to 2.5 mm and 4 mm were examined in a water bath. RESULTS: Artifact behavior was judged independently by 2 radiologists as showing "no artifacts" for all tested stent types. Signal-to-noise ratios inside and outside of the stents were measured yielding a Pearson correlation coefficient of 0.98 (y = 1.22 + 0.92x). Nineteen stents (8 hand woven, 3 mechanically woven, 8 lasered) were deployed in coronary arteries of 19 domestic pigs and were examined by cMRA. Artifact behavior of the stents was analyzed by measuring the signal-to-noise ratio at the stent positions and compared with signal-to-noise ratio measurements outside of the stents, yielding a Pearson correlation coefficient of 0.90 (y = -0.75 + 1.06x). CONCLUSIONS: All 3 prototypes of coronary MR stents allowed complete visualization of the stent lumen and consequently determination of stent patency by cMRA.

Coronary artery stents in multislice computed tomography: in vitro artifact evaluation.

RATIONALE AND OBJECTIVE: The aim of this study was to systematically compare the ability to assess the coronary artery lumen in the presence of coronary artery stents in multislice spiral CT (MSCT). METHODS: Ten different coronary artery stents were examined with 4- and 16-detector row MSCT scanners. For image reconstruction, a standard and a dedicated convolution kernel for coronary artery stent visualization were used. Images were analyzed regarding lumen visibility, intraluminal attenuation, and artifacts outside the stent lumen. Results were compared using repeated-measure analysis of variance. RESULTS: Depending on stent type, scanner hardware, and convolution kernel, artificial lumen narrowing ranged from 20% to 100%. The convolution kernel had the most significant influence on the visibility of the stent lumen. Artificial lumen narrowing and intraluminal attenuation changes decreased significantly using the dedicated convolution kernel. In general, most severe artifacts were caused by gold or gold-coated stents. CONCLUSIONS: Independent of the scanner hardware or dedicated convolution kernels, routine evaluation of most coronary artery stents is not yet feasible using MSCT.

Metallic renal artery MR imaging stent: artifact-free lumen visualization with projection and standard renal MR angiography.

A cardiac-triggered free-breathing three-dimensional (3D) balanced fast field-echo projection renal magnetic resonance (MR) angiographic sequence was investigated for in-stent lumen visualization of a dedicated metallic renal artery stent. Fourteen prototype stents were deployed in the renal arteries of six pigs (in two pigs, three stents were deployed). Projection renal MR angiography was compared with standard contrast material-enhanced 3D breath-hold MR angiography. Artifact-free in-stent lumen visualization was achieved with both projection MR angiography and contrast-enhanced MR angiography. These promising results warrant further studies for visualization of in-stent restenosis.

Artifact-free in-stent lumen visualization by standard magnetic resonance angiography using a new metallic magnetic resonance imaging stent.

BACKGROUND: Metallic stents cause susceptibility and radiofrequency artifacts on MR images, which, up to now, have not allowed for complete visualization of the stent lumen by MR angiography. The aim of this study was to investigate the potential of a new dedicated renal MRI stent for artifact-free in-stent lumen visualization in vitro and in a swine model. METHODS AND RESULTS: In vitro investigations were performed with prototypes of balloon-expandable Aachen Resonance Renal MRI Stents dilated to diameters of 3 to 6 mm and placed in an aqueous gadolinium solution (1:25). Phase-contrast and contrast-enhanced T1-weighted gradient echo images were acquired. Renal MRI stents (n=12) were deployed in the renal arteries of 6 pigs. Renal arteries were examined with phase-contrast angiography and with flow measurements before and after stent placement in the stented area, respectively. Additionally, a contrast-enhanced, T1-weighted, spoiled-gradient echo sequence after administration of 0.2 mmol gadolinium-DTPA/kg body weight was performed after stent placement. The visibility of artifacts was analyzed on in vitro and in vivo images by two investigators who knew the stent positions. Stent positions were determined visually (in vitro) or by x-ray angiography (animal experiments). No artifacts were detected independent of the applied imaging sequence and the stent orientation to the main magnetic field. CONCLUSION: The examined prototypes of fully MR-compatible MRI stents allow artifact-free visualization of the stent lumen with phase-contrast and contrast-enhanced T1-weighted angiography, as well as phase-contrast flow measurements in the stented area.

Magnetic resonance--guided coronary artery stent placement in a swine model.

BACKGROUND: Magnetic resonance (MR)--guided coronary artery stent placement is a challenging vascular intervention because of the small size of the coronary arteries combined with incessant motion during the respiratory and cardiac cycles. These obstacles necessitate higher temporal and higher spatial resolution real-time MR imaging techniques when compared with interventional peripheral MR angiography. METHODS AND RESULTS: A new, ultrafast, real-time MR imaging technique that combines steady-state free precession (SSFP) for high signal-to-noise ratio and radial k-space sampling (rSSFP) for motion artifact suppression was implemented on a 1.5-T clinical whole-body interventional MR scanner. The sliding window reconstruction technique yielded a frame rate of 15/s allowing for data acquisition during free breathing and without cardiac triggering. Eleven balloon-expandable stainless steel coronary stents were placed in both coronary arteries of 7 pigs (40 to 70 kg body weight) using a nitinol guidewire and passive device visualization. Position of the coronary stents was controlled by a navigator-gated free-breathing ECG-triggered three-dimensional SSFP coronary MRA sequence and confirmed visually on the ex vivo heart. The presented real-time MR imaging sequence reliably allowed for high-quality coronary MR fluoroscopy without motion artifacts in all pigs. Ten of 11 coronary stents were correctly placed under MR guidance. One stent dislodged proximally from the left main coronary artery because of too-small balloon size. Stent dislocation was correctly predicted during real-time MR imaging. CONCLUSION: The presented approach allows for real-time MR-guided coronary artery stent placement in a swine model.