Determination of stent stenosis: an in vivo experimental comparison of intravascular ultrasound and angiography with histology

Error estimation of geometrical data obtained by histomorphometry of oblique vessel sections: a computer model study

The errors of radius and wall thickness of a single vessel due to oblique sectioning in histomorphometry are expressed as a function of the circular shape factor (CSF) of the section's lumen, assuming cylindrical geometry and the absence of tissue deformation. Using computer model trees generated by constrained constructive optimization, mean errors are estimated for an ensemble of vessel segments. A geometrical exclusion criterion for segments cut too obliquely is defined on the basis of a CSF-cutoff value. It is shown that CSF-values ranging from 0.95 to 0.9 are reasonable choices for a cutoff and lead to mean errors of the same order of magnitude (9.6% [9.3%] to 15.4% [14.8%] for the radius [wall thickness]) as errors due to histological tissue processing.

Carbon-coated stents implanted in porcine iliac and renal arteries: histologic and histomorphometric study

PURPOSE

To test in a pig model the biocompatibility and effectiveness of carbon-coated renal and iliac artery stent systems during implantation procedures and at different follow-up periods.

MATERIALS AND METHODS

Twenty-two miniature pigs received carbon-coated balloon-expandable stainless-steel stents in their renal and iliac arteries. Animals were killed at 7, 30, or 180 days for evaluation of acute, subacute, and chronic biologic response to the implanted devices. Histologic, histomorphometric, and scanning electron microscopy (SEM) analyses were performed to assess inflammatory reaction, endothelialization process, and neointimal growth.

RESULTS

Forty-four iliac stents and 42 renal stents were successfully implanted. Mural thrombi were not observed by angiography or histologic examinations. Histologically, no significant inflammatory reaction was detected: the stents appeared covered by a thin monolayer of endothelial cells even at 7-day follow-up. The neointima showed homogeneous growth and moderate thickness at 30-day and 180-day explantations (0.09 mm +/- 0.06 and 0.15 mm +/- 0.13, respectively, for renal arteries; 0.12 mm +/- 0.04 and 0.21 mm +/- 0.12, respectively, for iliac arteries). Internal and external elastic laminae were intact in 82 of 86 cases (95%) of stent-implanted arteries. Histologic validations were obtained with SEM observations for each follow-up group.

CONCLUSIONS

This study showed good technical results of deployment of carbon-coated renal and iliac stents and very satisfactory biologic behavior in terms of tissue and hematologic compatibility. The devices do not induce thrombus formation.

Vascular stents as RF antennas for intravascular MR guidance and imaging

Stent deployment is used to improve the immediate and long-term results of vascular interventions in various vascular sites. X-ray angiography as an imaging modality is often limited in providing an accurate assessment with regard to vessel size, plaque calcification, or stent deployment. In this study, the potential of using the stent endoprothesis as a radiofrequency (RF) receive-only probe for MR guidance and lesion imaging was investigated. Three different principles were developed to visualize stents actively, the first employing the stent as a loop antenna, the second employing the stent in an electrical dipole configuration, and the third employing the stent in a hybrid configuration as a coaxial line antenna. The three configurations resulted in different signal characteristics. Based on two of these antenna configurations, stent deployment devices were built and evaluated in in vitro as well as in vivo sheep experiments. Active stent visualization allows real-time MR guidance through the vessel tree and monitoring of stent deployment. In addition, the stent antenna may become useful for high resolution imaging of the vessel wall. Magn Reson Med 42:738-745, 1999.

Brachytherapy for the prevention of stenosis in a canine hemodialysis graft model: preliminary observations

PURPOSE

To determine whether gamma brachytherapy can prevent in-stent stenosis in hemodialysis grafts.

MATERIALS AND METHODS

Six-millimeter polytetrafluoroethylene arteriovenous grafts were created bilaterally in six dogs. After 1 month, Wallstents spanning the venous anastomosis were placed to accelerate restenosis. Gamma irradiation (12 Gy) was delivered endoluminally to one of the two grafts by using an iridium 192 source; thus, each animal served as its own control. Fistulography was performed monthly for 10 months or until graft thrombosis, with measurement of stenosis at each time point. At the conclusion of the study period, the treated area was examined histologically, and a computer model was used to calculate the volume of intimal hyperplasia.

RESULTS

Delayed stent migration resulted in exclusion of one dog. In the remaining five dogs; maximum stenosis across all time intervals was less for the treated side (P < .04), and the volume of intimal hyperplasia was less for the treated side (P < .045). In one animal studied at 1 year, this trend reversed in terms of percentage stenosis but not total neointimal volume.

CONCLUSION

Brachytherapy with 192Ir (gamma) delivered at the time of stent placement reduces restenosis in this hemodialysis graft model, but, depending on the parameter evaluated (stenosis vs total volume of neointima), the benefit may wane or even reverse with time.

Metallic artifacts of coronary and iliac arteries stents in MR angiography and contrast-enhanced CT

Metallic artifacts of intravascular stents were assessed with MR angiography and contrast-enhanced spiral CT. Stainless steel showed less metal artifact than tantalum stent in CT. Metallic artifact in coronary and iliac arteries treated with tantalum stent was not remarkable in MR angiography. Contrast-enhanced CT might be preferable to assess patency of arteries treated with stainless steel stent. while MR angiography was useful in depicting intraluminal signal in tantalum stent.