Localization of a misplaced coronary artery stent by magnetic resonance imaging

Accurate and continuous ultrasonography evaluation of small diameter vascular prostheses in vivo

There is a large clinical requirement for novel vascular grafts; however, the development of novel vascular grafts has not been extremely successful to date. The most successful method for the continuous evaluation of vascular grafts in vivo remains unclear. Therefore, an optimal successive, non-invasive imaging modality is necessary for the study of vascular transplantation. In the present study, a common rabbit model of carotid artery defect was utilized. The patency and hemodynamic characteristics of implanted grafts was examined following surgery by color Doppler ultrasound in three modes, including B-mode, color flow map and pulse-Doppler examination. The results revealed that ultrasound had sufficient spatial resolution to generate clear images of the carotid artery of rabbits with or without the implanted grafts. Color Doppler ultrasound may be applied to evaluate and differentiate the patent, stenosis and occlusion of carotid arteries in rabbits with different vascular grafts implanted. Furthermore, color Doppler ultrasound is an optimal imaging modality for continuous evaluation in vivo. It is also possible for some quantitative analyses to be performed, including measuring the diameter of vascular lumens and the flow velocity of the region of interest. The present study suggests vascular ultrasound as the optimum choice for continuous surveillance of vascular prostheses in vivo, which may provide valuable information about the grafts in order to greatly shorten the experimental period.

Clinical safety of magnetic resonanceimaging early after coronary artery stent placement

OBJECTIVES

Our aim was to examine the rate of adverse cardiac events in patients undergoing magnetic resonance imaging (MRI) <8 weeks after coronary stent placement.

BACKGROUND

The risk of coronary stent thrombosis from dislodgement due to MRI early after stent placement is not well defined. Manufacturers recommend postponing MRI studies until eight weeks after coronary stent placement.

METHODS

We analyzed the Mayo Clinic Rochester Percutaneous Coronary Intervention Database and examined records of 111 patients who underwent MRI <8 weeks after coronary stent placement treated with aspirin and a thienopyridine. Occurrence of death, myocardial infarction (MI), and repeat revascularization within 30 days of MRI were recorded.

RESULTS

Magnetic resonance imaging (1.5 tesla) was performed within a median of 18 days (range, 0 to 54 days) after coronary stent placement. Four noncardiac deaths occurred, and three patients had repeat revascularization procedures. Stent thrombosis did not occur (95% confidence interval, 0% to 3.3%).

CONCLUSIONS

Magnetic resonance imaging <8 weeks after coronary stent placement appears to be safe, and the risk of cardiac death or MI due to stent thrombosis is low. Postponing MRI does not appear to be necessary.

Safety of magnetic resonance imaging immediately following Palmaz stent implant: a report of three cases

Magnetic resonance imaging (MRI) can provide important information on patients with congenital heart defects. There is some reluctance to perform MRI acutely following intravascular stent implant, due to concerns of distortion or movement of the stent in the magnetic field. We report on three patients who underwent MRI evaluation less than 14 days following Palmaz stent implant in the pulmonary arteries and superior vena cava, with no acute adverse outcome or long-term problems.

Assessment of coronary artery patency after stent placement using magnetic resonance angiography

The ability to noninvasively assess the patency of coronary stents would represent a significant advance. We evaluated the safety and ability of two-dimensional coronary MR angiography in imaging stents and suggesting patency. Coronary MR angiography of 26 coronary stents (Palmaz-Schatz) was performed in 16 patients 39 to 73 years of age. Studies were performed between 2 and 4 months after stent placement. All patients were symptom free at the time of imaging. Coronary MR angiography was performed with a commercial 1.5-T MR imager using an electrocardiographically gated pulse sequence with breath-holding. Images were obtained in mid-diastole with and without fat suppression. Image artifacts caused by the metal in the stents were clearly visualized in all 26 stents (100% sensitivity for stent detection). Arterial flow signal was seen in the coronary artery or graft distal to the stent in 25 of 26 cases (96%). All patients, except for the one in which distal flow could not be seen, remained symptom free for >2 years. The distribution of stent locations was as follows: 10 in the right coronary artery (RCA), 10 in the left anterior descending coronary artery (LAD), 2 in the left circumflex coronary artery, and 4 in saphenous vein grafts (SVGs) to RCA. One patient had 2 RCA and 2 LAD stents, one had 3 RCA and 1 LAD stents, one had 3 SVG stents, and two had double RCA stents. Coronary MR angiography is safe for noninvasive imaging of coronary stents, and in the proper clinical setting, it can be used to help suggest patency.

Dynamic gadolinium DTPA-enhanced magnetic resonance of intravascular stents

RATIONALE AND OBJECTIVES

Magnetic resonance contrast enhancement depends on the timing of image acquisition. Human trials have demonstrated efficacy of renal artery stents on salvage of renal function. This study assessed the ability of dynamic gadolinium (Gd)-DTPA administration to demonstrate renal and iliac artery stent patency compared to conventional angiography as the gold standard.

METHODS

Seven subjects with eight stents referred for angiography underwent dynamic magnetic resonance studies, all with renal artery stenting. All were examined with conventional angiography and after dynamic Gd-DTPA infusion. Coronal magnetic resonance images were acquired using a GE Signa 1.5 T magnet (fast spoiled gradient echo; echo time = 4.2 ms; repetition time = 68-150 ms; flip angle = 75 degrees) 0 to 600 seconds after 0.1 mmol/Kg Gd-DTPA intravenous bolus injection during sequential breath-hold acquisitions 13 to 32 seconds each.

RESULTS

All eight stents were visualized with 100% accurate patency documentation.

CONCLUSIONS

Fast spoiled gradient echo magnetic resonance imaging with bolus Gd-DTPA administration can provide adequate time and spatial resolution to demonstrate arterial stent patency.

Contemporary stent designs: technical considerations, complications, role of intravascular ultrasound, and anticoagulation therapy

A number of studies have shown the benefits of stent placement over balloon angioplasty for the treatment of focal, native coronary artery, and saphenous vein graft disease. Although the number of stent designs available for clinical use has increased dramatically, the late clinical benefit of stenting over balloon angioplasty has yet to be shown in diffuse disease, complex bifurcation stenoses, or smaller (2.5-mm) vessels, each of which may require unique stent designs and adjunct therapies not currently available or extensively studied. The purposes of this review are to discuss the various stent designs currently available for clinical use, outline the known complications associated with these stents, assess the contribution of intravascular ultrasound, and describe current antiplatelet and antithrombotic therapy used after stent use.

Two-dimensional coronary MRA: limitations and artifacts

Our purpose was to assess image quality and interpretation problems of two-dimensional (2D) coronary MR angiograms. The coronary arteries of 27 subjects (12 normal volunteers and 15 patients) were evaluated with 2D coronary MR angiography (MRA). Coronary MRA was performed with a fat-suppressed electrocardiographically gated breath-hold gradient-echo sequence with k-space segmentation using a 1.5-T imager. Image quality throughout the study was occasionally degraded by: image ghosting (22%), ringing (19%), and/or blurring (22%) and incomplete fat-suppression (19%). Intermittent difficulties with breathholding were encountered in 44% of subjects. When limiting the analysis to those images with optimal image quality, interpretative difficulties were sometimes found: misregistration due to inconsistent breathholding (37%); difficulty in distinguishing veins from arteries (37%); obscured anatomy due to overlapping structures (26%); and poor visualization of portions of the left main coronary artery (59%). Two-dimensional coronary MRA studies have image quality and interpretive problems which need to be understood and addressed before routine clinical scanning is initiated.